A combustion oscillation experiment fueling a mixture of hydrogen and natural gas was performed. The results showed oscillating frequencies of around 350 Hz in the case of the town gas only, whereas oscillating frequencies of around 200 and 400 Hz were observed in the hydrogen-containing fuel case. We hypothesized that the oscillating frequencies shift may occur by changing the temperature-distribution inside the tube, which was caused by different combustion conditions with the fuel mixture. As a result, the possible oscillating frequencies of not only around 350 Hz but also around 200 and 400 Hz were obtained. Although three types of possible oscillating frequencies were obtained in our previous study, more detailed temperature distributions should be considered to clarify the effect of the changing fuel mixture composition. In this paper, representative one-dimensional temperature distributions were formed by the combination of measured and calculated temperature distributions in the combustion tube for the corresponding fuel mixture. To include the detailed temperature distributions, the acoustic network model was divided into enough small elements to express the temperature distributions, where each element was connected by the transfer matrix. Then, the possible oscillating frequencies were calculated, taking account of the influence of the temperature distributions.

<title>Abstract</title>In this paper, we propose a novel method for predicting acute clinical deterioration triggered by hypotension, ventricular fibrillation, and an undiagnosed multiple disease condition using biological signals, such as heart rate, RR interval, and blood pressure. Efforts trying to predict such acute clinical deterioration events have received much attention from researchers lately, but most of them are targeted to a single symptom. The distinctive feature of the proposed method is that the occurrence of the event is manifested as a probability by applying a recurrent probabilistic neural network, which is embedded with a hidden Markov model and a Gaussian mixture model. Additionally, its machine learning scheme allows it to learn from the sample data and apply it to a wide range of symptoms. The performance of the proposed method was tested using a dataset provided by Physionet and the University of Tokyo Hospital. The results show that the proposed method has a prediction accuracy of 92.5% for patients with acute hypotension and can predict the occurrence of ventricular fibrillation 5 min before it occurs with an accuracy of 82.5%. In addition, a multiple disease condition can be predicted 7 min before they occur, with an accuracy of over 90%.

ディーゼル機関のモデルベースト燃焼制御器では，冷却損失を考慮した圧縮ポリトロープ指数の予測にこれまで実験式を用いてきた．著者らは，実験数を軽減するため，新たに物理モデルを開発し，制御器に実装した．実機にて過渡運転性能を評価したところ，実験値と比較して，モデルの予測誤差は0．３１％と評価された．

In this study, a multiple-input multiple-output feedforward controller for use with multiple-point fuel injection systems is applied to a diesel engine using an original control-oriented model. The target-tracking performance of this multiple-input multiple-output feedforward controller was then tested in terms of how well the controller adjusts the fuel delivery ratios to the pilot injection, pre-injection, main fuel injection, and the main fuel injection timing, and controls the in-cylinder peak pressure and its timing. Control experiments are conducted at different engine outputs and speeds while changing the targets of the in-cylinder peak pressure and its timing. The controller is able to track the varying targets within an acceptable error included in the original model. The calculation time, which is almost double that of a single-input single-output controller, is sufficiently fast to derive the applicable inputs.

<title>Abstract</title>This paper proposes a novel unconstrained monitoring system that measures heart and respiratory rates and evaluates autonomic nervous activity based on heart rate variability. The proposed system measures the aortic pulse waves (APWs) of a patient via an APW sensor that comprises a single microphone integrated into a mattress. Vital signs (i.e., heart rate, respiratory rate) and autonomic nervous activity were analyzed using the measured APWs. In an experiment with supine and seated participants, vital signs calculated by the proposed system were compared with vital signs measured with commercial devices, and we obtained the correlations of <italic>r</italic> &gt; 0.8 for the heart rates, <italic>r</italic> &gt; 0.7 for the respiratory rates, and <italic>r</italic> &gt; 0.8 for the heart rate variability indices. These results indicate that the proposed system can produce accurate vital sign measurements. In addition, we performed the experiment of image stimulus presentation and explored the relationships between the self-reported psychological states evoked by the stimulus and the measured vital signs. The results indicated that vital signs reflect psychological states. In conclusion, the proposed system demonstrated its ability to monitor health conditions by actions as simple as sitting or lying on the APW sensor.

The present study aims to propose a framework for the installation of distributed energy equipment, including cogeneration systems, photovoltaics, and storage batteries as well as emergency power generators, to enhance business continuity in a disaster-base hospital. Two types of simulation tools were developed: a planning tool and a verification tool. First, as a planning tool, a multi-objective optimization simulation with two objective functions was developed to determine the required amount of energy equipment. The first function was used to calculate the expected value of the ratio of electric power shortage to energy demand after disasters using an energy resilience risk index, and the second was used to calculate the total cost using an economic indicator. The optimal solutions formed the Pareto solution group. Next, the obtained solutions were verified to determine whether the energy demand in a disaster-base hospital would be satisfied by the energy supply of the installed distributed power generation equipment in case of disaster. For this purpose, an energy system simulator was developed as a verification tool. This simulator consisted of models of every piece of distributed energy generation equipment. Electric power generated by the gas engine generators of the cogeneration system, diesel engine emergency generators, and storage batteries is supplied to medical equipment as well as general equipment such as lighting and elevators. The installation of storage batteries to suppress fluctuations in the electricity supply was contemplated through the use of photovoltaics. The balance between the energy demand and supply was evaluated based on the frequencies of the alternating currents in the simulator. Finally, several case studies for different types of hospitals were examined.

本稿ではMAP作成の手間を自動化し, かつ環境変化に対するロバスト性を有する制御系設計法として, フィードバック誤差学習を用いたモデルベースト制御を提案する. また, 制御器の学習機構として小脳演算モデルコントローラを用いることで計算負荷を低減することができる. そして, 本手法の有効性を実機試験にて検証する.

We developed a feed-forward controller for a conventional diesel combustion engine with triple fuel injection and experimentally evaluated its performance. A combustion model that discretizes an engine cycle into a number of representative points to achieve a light calculation load is embedded into the controller
this model predicts the in-cylinder gas-pressure-peak timing with information about the operating condition obtained from the engine control unit. The controller calculates the optimal main-fuel-injection timing to control the in-cylinder gas-pressure peak using the prediction result as a controller with a single input and output. The controller’s performance was evaluated by experiments using a four-cylinder diesel engine under changing the target value of the in-cylinder gas-pressure-peak timing during a target-following test and the performance was also evaluated under changing the exhaust gas recirculation ratio at the constant target value of the in-cylinder gas-pressure-peak timing for the disturbance-response test. It was found that the controller could calculate the optimal main-injection timing over a cycle and maintain the targeted in-cylinder gas-pressure-peak timing even when the target value or exhaust gas recirculation changed. The combustion model was also shown to be fast enough at predicting diesel combustion for onboard control.

A free-standing (FS) rack is a type of a spent nuclear fuel rack, which is just placed on a floor of a pool. For this characteristic, seismic loads can be reduced by fluid force and friction force, but a collision between a rack and another rack or a wall must be avoided. Therefore, it is necessary for designing an FS rack to figure out how it moves under seismic excitation. In this research, a dynamic model of an FS rack is developed considering seismic inertial force, friction force, and fluid force. This model consists of two submodels: a translation model, which simulates planar translational and rotational motion, and a rocking model, which simulates nonslide rocking motion. First, simulations with sinusoidal inertial force were conducted, changing values of a friction coefficient. Next, to validate this dynamic model, a miniature experiment was conducted. Finally, the model is applied to a real-size FS rack and actually observed seismic acceleration. It is found that translational movement of a rack varies depending on the value of friction coefficient in the simulation with sinusoidal and actual acceleration. Also, simulation results are similar to the experimental results in the aspects of translational and rocking motion provided friction coefficient is selected properly. Through this research, the knowledge is acquired that friction force plays a significant role in a motion of FS rack so that estimating and controlling a friction coefficient is important in designing an FS rack.

Natural gas is relatively clean, and its demand is currently increasing. In most cases, gas fields are located at the bottom of the sea. Therefore, floating production, storage, and offloading (FPSO) systems are now attracting considerable attention. This paper is related to the dynamical design of a FPSO system; in particular, it focuses on the free surface elevation induced by the waves in a horizontal cylindrical and axisymmetric liquid vessel with end caps. In this study, the theory of the wave height and resonant frequency in a horizontal cylinder subjected to pitching via external excitation is developed. Then, a theory taking into account the effect of perforated plates is introduced. A special discussion is made with regard to the number and location of the perforated plates and the effect of a partial opening in a perforated plate on the damping. Finally, the experimental data of resonant wave heights up to the third mode are shown in comparison to the theoretically derived results.

After the 2011 Great East Japan Earthquake, a business continuity planning, i.e., BCP, in a disaster case is attracting attentions in Japan. However, when a customer, i.e. a building owner actually would like to introduce energy generation devices such as a cogeneration equipment, there is no guideline to decide suitable device capacity based on the evaluation of economic efficiency and BCP as well as energy saving performance. This study proposes a method to optimize a plan for installing cogeneration equipment considering BCP under disaster risks simultaneously. We develop a simulation tool to decide an optimized planning of energy-generation equipment configuration. With this simulation tool, we performed case studies for different business cases such as a hospital and a hotel. The simulation results showed that the optimized installing plan can be an over-specification of equipment configuration under the assumption of disaster risks, which is never chosen under conventional definition. Then, we examined the economic performance of an energy generation equipment configuration by calculating a net present value from the viewpoint of BCP. This examination can give judgments of investment-return possibility and suitable subsidy price.

This paper proposes a scheme, called the disaster-risk-weighted damage inequality, for a customer to perform introductory planning for a distributed generation system considering business continuity planning in a disaster case. To calculate this inequality, the relevant disaster risks are surveyed and system operating simulations for target buildings such as a hotel, a hospital, a large-scale office, and a collective housing building are performed by solving a mixed integer linear programming problem under the assumption that a cogeneration system is installed as a distributed generation system. Next, we determined the probabilities of a disaster occurrence and business interruption due to a disaster, the initial cost of the equipment, the running cost, and the reduction in running cost due to a cogeneration system installation. The cogeneration system was found to effectively reduce the running cost. Finally, the suggested inequality is calculated and determined whether it is satisfied. The result Showed that cogeneration system installation very effectively reduces the running cost for a hotel, a hospital, and a large-scale office, compared to the tolerable amount of loss that is preliminarily determined by a customer. (C) 2016 Elsevier Ltd. All rights reserved.

Spent nuclear fuel is settled in racks and stored in spent fuel pool. A free standing rack (FS rack) is a type of a spent fuel rack, which is not fixed to walls unlike conventional ones. For this characteristic, movement of an FS rack during an earthquake can be reduced by fluid force and friction force. However, collision between a rack and another rack or a wall must be avoided. Therefore, it is necessary for designing an FS rack to figure out how it moves under seismic excitation. In this research, a dynamic model of FS racks is constructed considering seismic inertial force, friction force and fluid force. This model consists of two sub-models: translation model, which simulates planar translational and rotational motion
and rocking model, which simulates rocking motion. Moreover, we developed two kinds of rocking model: slide-rocking considered model, which considers the equations of both slide-rocking motion and non-slide-rocking motion
and non-slide-rocking model, which considers only the equation of non-slide-rocking motion. Then, simulations with sinusoidal inertial force input were conducted, changing values of friction coefficient. To validate this dynamic model, a miniature experiment was conducted. It is found that the non-slide-rocking model simulates movement of an FS rack well and better than the slide-rocking considered model in the aspect of translational and rocking movement. However, planar rotational movement is not simulated well with either model. Through this research, the knowledge is acquired that friction force plays a significant role in motion of an FS rack so that estimating and controlling friction coefficient is important in designing an FS rack.

Hydrogen as one of energy sources is attracting attentions because of CO2 free combustion that can deaccelerate global warming. Recently, hydrogen enriched combustion technology for gas turbine combustors is developing, in which hydrogen is added to natural gas. However, hydrogen-rich combustion has different combustion characteristics from conventional natural gas combustion. In particular, such variety of combustion characteristics may lead to combustion oscillation, which may cause fatigue breaking of structural elements due to resonance with components. Combustion oscillation is mainly induced by thermo-acoustics interaction. Therefore, it is necessary to investigate characteristics of hydrogen-enriched combustion sufficiently. To understand combustion characteristics of enriched hydrogen mixture, combustion experiments were performed for various ratios of hydrogen in the fuel mixture. In this study, a mock-up combustor of a micro gas turbine combustor is used, where a radial swirler is installed to mix fuel and air and stabilize the flame. To grasp the characteristics of combustion oscillation, pressure fluctuation was detected by a pressure sensor installed at the bottom of the combustor. It is found that larger hydrogen ratio in the fuel mixture extends the range of large pressure fluctuation region expressed by the root-mean-square value. Succeedingly, more detail oscillation characteristics were examined by FFT analysis. In the case of natural gas 100%, the oscillation of around 350 Hz was detected. On the other hand, in the case of the hydrogen-contained fuel mixture, two kinds of oscillating frequencies around 200 and 400 Hz were detected. To examine the cause of the difference among these three oscillating frequencies, a simplified stepped tube model with closed- and open-end is considered. For further investigation, acoustic boundary conditions were measured by acoustic impedance method. Moreover, to obtain the representative flame positions and temperature in the combustor, CFD calculations were performed, and the measured acoustic impedance was combined with the CFD results. Then, parametric studies with various thermo-pressure interaction index were performed to obtain the effect of thermo-pressure interaction index on natural frequencies and gains using the Nyquist plot. As a result, it was found that the self-excited oscillation limit is sensitive to the value of thermo-pressure interaction index.

Spent nuclear fuel is settled in racks and stored in spent fuel pool. A free standing rack (FS rack) is a type of a spent fuel rack, which is not fixed to walls unlike conventional ones. For this characteristic, movement of an FS rack during an earthquake can be reduced by fluid force and friction force. However, collision between a rack and another rack or a wall must be avoided. Therefore, it is necessary for designing an FS rack to figure out how it moves under seismic excitation. In this research, a dynamic model of FS racks is constructed considering seismic inertial force, friction force and fluid force. This model consists of two sub-models: translation model, which simulates planar translational and rotational motion
and rocking model, which simulates rocking motion. Moreover, we developed two kinds of rocking model: slide-rocking considered model, which considers the equations of both slide-rocking motion and non-slide-rocking motion
and non-slide-rocking model, which considers only the equation of non-slide-rocking motion. Then, simulations with sinusoidal inertial force input were conducted, changing values of friction coefficient. To validate this dynamic model, a miniature experiment was conducted. It is found that the non-slide-rocking model simulates movement of an FS rack well and better than the slide-rocking considered model in the aspect of translational and rocking movement. However, planar rotational movement is not simulated well with either model. Through this research, the knowledge is acquired that friction force plays a significant role in motion of an FS rack so that estimating and controlling friction coefficient is important in designing an FS rack.

&lt;p&gt;HCCI combustion is effective for improving thermal efficiency of a gas engine, but it has problems such as control of the ignition and combustion. To solve the problem, availabilities of dedicated EGR technique are considered to control its ignition and combustion. Dedicated EGR involves reforming fuel into H&lt;sub&gt;2&lt;/sub&gt; or CO by running a single or more cylinder with rich mixture and supplying the exhaust gas directly into other cylinders. In this study, the effect of dedicated EGR on methane HCCI combustion was investigated by experiments. As a result, when equivalence ratio of rich SI combustion or EGR ratios increase, the ignition timing of HCCI advances and combustion becomes steep. The advanced ignition timing is caused by an increase of H&lt;sub&gt;2&lt;/sub&gt; mole fraction in the intake gas. In addition, the possibility of controlling the ignition timing, which is strongly concerned with the thermal efficiency of a HCCI engine, by dedicated EGR was discussed. It was shown that the ignition timing linearly depends on H&lt;sub&gt;2&lt;/sub&gt; mole fraction in the intake gas.&lt;/p&gt;

This study aims to tailor the bearing stiffness for enhancing the load-carrying capacity of foil thrust bearings. New architectures for the bump foil are introduced with structural stiffness tailored in the radial and circumferential directions to ensure a converging gas film under high axial loads while maintaining a reasonable bearing compliance to accommodate thermal as well as mechanical distortions. The structural stiffness of the bearing is calculated with an analytical method previously introduced by the authors, and the flow in the gas film is modeled with 2-D compressible Reynolds equation. The Couette Approximation technique is used to calculate the temperature distribution in the gas film and the small perturbations method is used to calculate its dynamic force coefficients. Enhanced load capacity could be obtained with the introduced bump foil designs.

In this paper, a simplified prediction model for aiming to design an engine control system of Homogeneous Charge Compression Ignition (HCCI) engine has been developed. Developed HCCI engine model is for rebreathing concept and employs the discretized cycle concept to realize fast calculation speed. The ignition timings are predicted by Livengood-Wu integration combined with a function of ignition delay and the combustion durations are predicted from supplied fuel mass quantity. Maximum pressure and its phase are compared to experiments. In addition, for designing an HCCI engine, the models to predict appropriate operation conditions are considered.

In the present study, the static and dynamic characteristics of Generation II bump-type foil thrust bearings are investigated. For the static characteristics, a 2D compressible Reynolds equation containing effects of centrifugal forces is derived to model the fluid flow in the thin gas film. The compliance of the bearing is calculated using analytical structural stiffness model. The fluid flow equation is coupled to the structural stiffness model and the coupled fluid-structure interaction problem is solved iteratively to obtain the steady-state characteristics of the bearing. For the dynamic characteristics, small perturbations method is used to obtain the linearized equations for the pressure components of dynamic force coefficients. The effects of rotation speed, ramp height, nominal film thickness, friction coefficients at bump foil interfaces, and bump foil stiffness on the static and dynamic characteristics of Generation II foil thrust bearings are thoroughly analyzed.

Free standing rack designed for storing spent fuel at nuclear power station has an advantage to earthquake excitations because both fluid force and friction force can reduce the movement of a rack. However, there are various motions of FS rack such as parallel, rotational and rocking which should be taken into consideration when it is subjected to earthquake excitations. Therefore, the motion of FS rack must be precisely figured out in order to apply FS rack design concept. In this research, to investigate the motion of FS rack, 2-dimensional dynamic model considering pressure loss of gap flow was constructed. In addition, an experiment with a 1/16 scale model was conducted to validate the dynamic model. From numerical results based on the proposed dynamic model, some important features for the design of FS rack were found. Finally, case studies by real size free standing rack under the excitation of actually observed earthquake wave like The Great East Japan earthquake and The Niigata-ken Chuetsu-Oki earthquake were conducted based on the proposed method of calculation.

This study aims to analyze the flow characteristics and the thermal features of foil thrust bearing. The flow in the gas film is modeled with 2D compressible Reynolds equation including effects of centrifugal forces in the gas film. The Couette Approximation is adopted for the analysis of temperature distribution in the gas film, and the small perturbations method is used to calculate its dynamic force coefficients. The results show that the Couette Approximation can be used to calculate the temperature distribution in foil thrust bearing with reasonable accuracy and the analysis of the fluid flow reveals that most of the side-leakage occurs in the low-temperature converging region removing less than 5% of the heat generated in the gas film. Furthermore, with the proper control of cooling flow rate through the bump foils, more than 70% of the heat generated in the gas film can be removed.

A new structural stiffness model for the compliant structure in foil gas bearings is introduced in the first part of this work. The model investigates the possibility that the flat segment between bumps, in bump foil strip, may deflect laterally and separate from the rigid bearing surface, and it also considers the interaction between bumps in the bump foil strip, the friction between the bump foil, and the surrounding structure. The validity of the analytical solution was verified through direct comparison with previous numerical and analytical models. In the second part of this work, the introduced bump foil model is used to investigate the static characteristics of generation II gas foil thrust bearing. The numerical simulations of the coupled fluid-structure interactions revealed that the foil thrust bearings share many features with their rigid bearing counterpart and the results showed clearly that the load carrying capacity of foil thrust bearings increases nonlinearly with the rotation speed and is expected to reach an asymptote as the rotation speed exceeds a certain value. The effects of ramp height and interface friction (i.e., friction at bump foil/rigid bearing interface and bump foil/top foil interface) on the static characteristics of generation II foil thrust bearings are investigated.

Natural gas is relatively clean and its demand is increasing these days. In most of the case, gas fields are located at the bottom of the sea. Therefore, floating production, storage and offloading (FPSO) system is now attracting big attention. This paper is related to dynamical design of FPSO system, specially focused on the free surface elevation in the horizontal cylindrical and axisymmetric liquid vessel with end caps induced by the wave. In this study, the theory on the wave height and resonant frequency in a horizontal cylinder subjected to longitudinal external excitation is developed. Then, the theory capable of taking account of the effect of punching plates is described. Finally, experimental data of resonant wave height up to 3rd mode are shown in comparison with theoretically derived results.

Pressure pulsations excited by a centrifugal turbomachinery such as compressor, fan or pump at the blade passing frequency may cause severe noise and vibrations in piping system. Therefore, the practical evaluation method of pressure pulsations is strongly recommended. In particular, the maximum pressure amplitude under the resonant conditions should be appropriately evaluated. In this study, a one-dimensional excitation source model for a compressor or pump is introduced based on the equation of motion, so as to incorporate the non-linear damping proportional to velocity squared in the total piping system including the compressor or pump. The damping characteristics of the compressor or pump are investigated by using the semi-empirical model. It is shown that the resistance coefficient of the compressor or pump depends on the Reynolds number that is defined using the equivalent velocity of the pulsating flow. The frequency response of the pressure amplitude and the pressure distribution in the piping system can be evaluated by introducing the equivalent resistance of the compressor or pump and that of piping system. In particular, the relation of the maximum pressure amplitude in piping system to the location of the excitation source under resonant conditions can be evaluated. Finally, the reduction of the pressure pulsations by use of an orifice plate is discussed in terms of the pulsation energy loss. (C) 2013 Elsevier Ltd. All rights reserved.

The interaction between the cylinder motion and the wake is a complex feedback phenomenon in which the symmetry relationship between the wake and the cylinder motion plays a key role. Depending on the frequency of oscillation the symmetry relationship between the unforced von Karman wake and the imposed forced oscillations can induce a series of bifurcations. This detailed bifurcation behavior is the subject of study in the present work. 2D and 3D simulations are carried out for a Reynolds number Re=1000. As the inline cylinder forcing amplitude is increased, the wake undergoes a series of bifurcations and associated changes in the flow structure. Although the 2D analysis is clearly non-physical, it leads to a 'simpler' and more tractable model.
Detailed comparison of the 2D and 3D POD modes provides insight into the forced wake dynamics. The 3D spatial mode shapes are significantly similar to those from 2D simulations. The relative modal energy distribution captures well the wake flow complexity. The first mode contains over 90% of the flow energy in the 2D simulations. This ratio drops significantly in the 3D case to around 45%. Clearly 3D effects are very important when it comes to energy distribution between the modes. However, the predominance of the first mode seems high enough to maintain the 2D -like dynamics.
The wake flow is found to undergo two main transitions with increased forcing. The first is periodic shedding to chaotic shedding. The second is chaotic shedding to half -frequency shedding caused by a period -doubling bifurcation. The 2D simulations correctly predict these bifurcations including the type and the number of bifurcations. The results suggest that the forced wake dynamics are primarily dominated by twodimensional rather than 3D dynamics. However, 3D effects are important in determining the exact parameter values where bifurcations occur. A previously developed low order analytical model, based on 2D simulations, is also used to predict the wake bifurcation behavior. The relevance of the low order model has interesting implications for VIV control.

In nuclear power plants, fluid structure interactions (FSI) occurring in component systems can cause excessive forces or stresses to the structures resulting in mechanical damages that may eventually threaten the structural integrity. FSI in the guidelines includes flow-induced vibration, water hammer, and pipewhip. It can also include movement, deformation, or fracture of equipthents by tsunami etc. They can be issues of design and maintenance. Authors cannot find complete guidelines to correspond to the FSI phenomena which can be important in the design and maintenance of nuclear power plants. Based on the background, International Atomic Energy Agency (IAEA) has drafted guidelines on FSI. This paper summarizes general description of FSI as well as design and maintenance against FSI.

Natural gas is relatively clean and its demand is increasing these days. In most of the case, gas fields are located at the bottom of the sea. Therefore, Floating Production, Storage and Offloading (FPSO) system is now attracting big attention. This paper is related to dynamical design of FPSO system, specially focused on the free surface elevation in the horizontal cylindrical and axisymmetric liquid vessel with end caps induced by the wave. In this study, the theory on the wave height and resonant frequency in a horizontal cylinder subjected to longitudinal external excitation is developed. Then, the theory capable of taking account of the effect of punching plates is described. Finally, experimental data of resonant wave height up to 3rd mode are shown in comparison with theoretically derived results.

In this study, applicability of the gas fuel generated from wood biomass by thermal chemical processes to an homogenous charge compression ignition engine is investigated in experiment. In particular, the availability of inhomogeneity of both fuel concentration and temperature is evaluated to control the combustion against the variation of fuel composition. Inhomogeneity of premixture is varied by changing the ratio of fuel injected to two points, one far from the intake valve and another near the intake valve. In this system, both local fuel concentration and local temperature of premixture vary
the lower fuel concentration point has higher initial temperature. Two test fuels with difference in H2 concentration are used. The influence of the inhomogeneity on both ignition timing and combustion duration was found. Higher inhomogeneity retards ignition timing for its lower temperature and prolong combustion duration for its distributed combustion in the cylinder. Furthermore, the effect of inhomogeneity and the acceptable inhomogeneity depended on fuel composition. Higher H2 content fuel can use higher inhomogeneity and receive much favors for decreasing maximum in-cylinder gas pressure rising rate.

This paper deals with a synchronous vibration instability that occurred in a two-stage overhung centrifugal compressor supported by magnetic bearings. The authors encountered an unbalance vibration that increased spirally in a polar plot at/near the first bending critical speed. The concentration of iron loss and thermal bending due to heat have been identified as the causes of the phenomenon, because the vibration stopped increasing when unbalance force rejection control (UFRC) was applied. In this paper, prior to an in-depth discussion of experiments on the above phenomenon, the compressor and magnetic bearing system are described. To provide a theoretical perspective, a model of the thermally induced vibration is presented and the stability is discussed. In the experiments, to exceed the first bending critical speed stably, balancing of the rotor under UFRC was carried out and rapid acceleration/deceleration was applied to the variable-speed drive system. The vibration behaviors around the critical speed were measured and the results verified the theoretical model. To evaluate the stability limit of the thermal bending, a method of measuring the model parameter that determines the stability is proposed and the measured data are compared with calculated results. Finally, methods for improving the stability are discussed. (C) 2012 Elsevier Ltd. All rights reserved.

A numerical model for 3D thermohydrodynamic analysis of bump-type foil bearings with a sparse mesh across the air film is described. The model accounts for heat convection into cooling air, thermal expansion of the bearing components, and material property variations due to temperature rise. Deflection of the compliant foil strip, described as a link-spring structure, is coupled to the solution of the generalized Reynolds equation and the energy equation to account for the effect of foil deformation on the film thickness. The variation in bump stiffness with the thermal growth of bumps is also considered in the model. The unique airflow in foil bearings created by the top foil detachment in the subambient region is analyzed for use in modifying the thermal boundary condition. The Lobatto point quadrature algorithm is used to represent the model on a sparse mesh and thereby reduce the computational effort. The calculated bearing temperatures are in remarkable agreement with both the published test data with the use of cooling air and that without the use of cooling air. The change of bearing radial clearance due to thermal growth of the bearing components was found to significantly affect the bearing load and to be a likely cause of the obvious drop in load capacity with a rise in ambient temperature. [DOI: 10.1115/1.4007728]

In this paper, a gas engine system capable of stable operation at any mix ratio of city gas 13A and biogas was developed. The gas engine system consists of a spark-ignition gas engine, an additional electric throttle valve for fuel and our own control algorithm. The engine is a 3-cylinder 1.6-l engine that was originally used for co-generation, and the fuel throttle valve was added to respond to different fuel compositions. The control algorithm was also designed to adjust the fuel and air ratio to attain a higher generation efficiency and lower NOx emission with different mix ratios of city gas 13A, biogas and load. Before developing the controller, the effect of the mix ratio on generation efficiency and NOx emission was investigated under various load conditions. The following summarizes the experimental results: a control algorithm using the Wobbe index for mixed fuels was formulated
this index determines the target fuel-to-air ratio. Next, operation tests were performed under varying fuel mix ratios and loads by applying the control algorithm to the gas engine. The target engine rotational speed and exhaust O2 concentration was realized in 5s when the biogas fraction varied from 20% to 40% and from 70% to 40%. When the load was also varied from 9.4kW to 0.5kW and from 0.5kW to 9.4kW at a constant rate, the rotational speed and exhaust O2 concentration achieved the target values in 20s. Under both transient operation conditions, the engine system met the NOx emission requirement, and the results indicate that the simple hardware modification to a conventional gas engine and our original control algorithm are capable of achieving stable engine operation at any mix ratio of city gas 13A and biogas. © 2012 Elsevier Ltd.

Two types of the automatic HCCI engine control systems to use biomass gas were developed. One is to use inhomogeneity of pre-mixture, and another one is to use city gas 13A to control ignition and combustion. Ion current measurement system was applied to detect the combustion behavior for the variation of biomass gas and was also used for the closed loop control systems. From these systems, it was clarified that the maximum timing of the ion current and the rate of heat release have correspondence regardless of fuel compositions and inhomogeneity of mixture. In both control systems, setting the maximum timing of ion current to a constant value is enough to achieve higher thermal efficiency. Both systems succeeded to operate the engine for varying compositions of biomass gas, although the combustion system using city gas 13A shows better applicability than the inhomogeneity of mixture control system. © 2013 The Japan Society of Mechanical Engineers.

To utilize photovoltaic power generation (PV), the compensation for power fluctuation is necessary since the fluctuation has a bad influence on electric power system. Therefore, micro grid using several kinds of distributed generation is considered to be a good solution. For this reason, studies on batteries have been done in particular, due to the high output responsiveness. However, the power generation cost of batteries is higher than other distributed generation such as gas engines, which have not been studied enough from the viewpoint of distributed generation to compensate for renewable energy. In this paper, the feasibility of gas engines to compensate for the PV fluctuation is investigated from the point of view of exhaust gas NOx and power cost by simulation. As a result, the amount of NOx increases as the output of the gas engine fluctuates, but this increase on NOx hardly has a problem in micro grid. As for power cost, it can be decreased by combining battery and a few kinds of gas engines efficiently. In conclusion, it can be said that gas engines are able to play an important role in micro grid as distributed generation. © 2013 The Japan Society of Mechanical Engineers.

In order to increase the capacity of renewable energy in power systems, it is necessary to reduce power fluctuations. In this paper, the potential of gas engines (GEs) is evaluated by means of dynamic simulation in hybrid power systems consist of GEs and photovoltaic cells (PV) supply power to a large grid. First, basic characteristics of gas engines were investigated for load changes. The small gas engine, its maximum output is 9.9kW, shows quicker response of output and lower generating efficiency than the gas engine of 350kW output. The load response of both engines is influenced by the amplitude and the frequency of the output demand, and not by the bias load. Next, the simulations were implemented using the real power profile of PV. As a result of simulations, 9.9 kW GE is very useful to compensate PV power fluctuation because of its quick response for the load change. The efficient system to use GEs to achieve both the suppression of the PV's power fluctuation and the higher efficiency of the system is also discussed. By combining a larger scale GE with small scale GEs, the system to control preferentially the small GEs shows higher system efficiency at the same output response condition. © 2013 The Japan Society of Mechanical Engineers.

The composition of the biomass producer gas varies for the resource of biomass and the gasification method. In order to establish the operation guideline for dual fuel engines with a traditional injection system to use such gas fuels, the effects of the gas composition, pilot injection quantity and EGR on engine performance and emissions were investigated in experiments. The various mock biomass producer gases consisting of H2, CH4, CO, N2 and CO2 were supplied by mass flow controllers to a direct-injection diesel engine with a jerk type fuel injection pump. JIS 2 type diesel was also used for pilot fuel. It is clarified that the laminar burning velocity is useful index to estimate the operating range regardless of the gas composition, although the suitable equivalence ratio to ensure the stable operation varies according to the gas composition. The laminar burning velocity of over 40 cm/s at the TDC condition is a qualification to keep stable engine operation. At lower loads, EGR improves combustion and leads to the higher thermal efficiency, although it decreases the thermal efficiency because of its lower degree of constant volume at medium loads. In addition, the effect of EGR is small for the fuel with lower hydrogen content.

Internal combustion engines are required to use various fuels. A conventional MAP based engine control system is not suitable for achieving stable operation and high thermal efficient operation for various fuels. Authors have been developing the engine control algorithm to realize fuel flexibility by employing experimental rules and a closed 1oop control using in-cylinder gas pressure. In this study, in order to improve fuel flexibility of engine control algorithm and to confirm the experimental rules, availability of calculation results with elementary reactions for the algorithm is investigated. Availability of instant crank shaft torque for a feedback sensor is also investigated. The result shows that the modified engine control system employing laminar burning velocities calculated from elementary reactions and the torque feedback 1oop can maintain stable operations when fuel lower heating value varies during engine operation. © 2013 The Japan Society of Mechanical Engineers.

When constructing the one-dimensional systemic artery tree, the Windkessel model based on parameters describing the total resistance and compliance is generally applied as outflow boundary conditions. However, the Windkessel model does not include wave propagation effects, and moreover, it is not obvious how the parameters should be estimated Hence, the main purpose of this study is to develop an outflow boundary condition based on the underlying physiology of the arterioles, enabling the prediction of blood flow and pressure in the systemic arteries including the arterioles. The obtained numerical results show the followings. Firstly, we verified that applying the structured tree model as an outflow boundary condition can reproduce the essential characteristics of the arterial pulse better than applying the Windkessel model. Secondly, by analyzing the pulse wave velocity in aorta, we found a correlation between pulse wave velocity and the degree of arteriosclerosis which correspond to the clinical observation.

Axial self-excited vibration may be induced in a balance piston by fluid with a tangential velocity component that flows into the piston orifices. To avoid such vibration, knowledge of the dynamic characteristics of axial self-excited vibration induced by swirling leakage flow is required at the design stage.
In this research, the effect of axial rotation and swirl strength on the added fluid force coefficients is clarified by modeling the piston orifice as the combination of rotational and stationary disks, and deriving the unsteady fluid force generated by swirling leakage flow between the disks.
As a result, reduction of the relative velocity in the circumferential direction is shown to destabilize the oscillatory system. In particular; the effect of swirl strength on the fluid force coefficient is found to be larger in the case of the divergent channel than in the case of the parallel flow path.

This investigation presents a thermohydrodynamic (THD) analysis for bump-type foil bearings. Two basic equations, the generalized Reynolds equation and the energy equation, are simultaneously solved for the air pressure and generated heat due to the viscous shearing action in the air film. The compliant foil strip is described as a link-spring structure. The calculated foil deflection is coupled into the solution of the two basic equations to account for its effect on the film thickness. This model accounts for heat convection in the air film region and the material property variations of the lubricant air due to the temperature rise, heat convection with the cooling air, heat conduction between the solid components, heat transfer at the surface of the solid components, and thermal expansion of the bearing components as well as change in the bump foil elasticity. The airflow within the air film is a distinctive characteristic of bump-type foil bearings (BTFBs) compared to normal oil bearings because the top foil detaches at sub-ambient regions. The unique airflow is also taken into consideration in this model to modify the thermal boundary condition of the air film.
Data from a published experimental investigation is used to validate the mathematical model. The predicted bearing temperatures, as well as the bearing load, agree well with the experimental data. The effects of ambient temperature on BTFB performance are discussed with the THD model. With increased ambient temperature, the influence of the bearing clearance changes, because the thermal growth of the bearing components is more significant than the decrease of the foil elasticity. Therefore, the thermal expansion coefficients of the bearing components should be considered during bearing design. The temperature profile within the foil bearing is predicted and compared with published tested temperature values. The calculated temperature correlates well with the experimental data at most of the positions. The deviation between the two values at the bearing-load position is demonstrated to be less than 10.3%.

An evaluation method for estimating the damping of loosely supported single U-bend tube used in a steam generator colliding with a support plate is proposed. First, we performed experimental modal analysis and obtained natural frequencies, modes and damping without collision by Impulse Modal Test and then analysed natural frequencies, modes and damping with collision employing FEM analysis taking account of the collision force. In modelling the characteristics of the collision force, we applied Bijlaard's model for the spring constant and assumed hysteresis. After that, we performed experiments for measuring the damping ratio by changing the gap size and the support plate position. Comparison between calculated and experimental results is made which shows good agreement. Experimentally observed fact showing damping coefficient increases with the initial amplitude is well explained by theoretical model.

Autoignition and combustion characteristics of biomass gas and city gas 13 A mixed fuels in a HCCI engine were investigated. A mock biomass gases consisting of H 2, CH 4, CO, N 2 and CO 2 were used assuming woody pyrolysis gases. Using a modified gas engine with high compression ratio pistons and an inlet air heating system, experiments were carried out. Influences of mixing ratio of two fuels on heat release and indicated thermal efficiency were investigated. Higher city gas 13 A content make maximum value of rate of heat release lower at a constant equivalence ratio and a constant IMEP. The mixed fuel obtains higher indicated thermal efficiency and lower cyclic variation than biomass gas or city gas 13A only. Effects of H 2 and CO contents of biomass gas were also investigated. It is clarified that H2 has a big influence on rate of heat release but CO does not. © 2012 The Japan Society of Mechanical Engineers.

This study aimed to invent handy method that can estimate the level of sitting people's sleepiness from RR interval(Time duration between two consecutive R waves of the ECG)in order to proposenew system for preventing car accidents caused by sleepiness. In the study, to estimate sleepiness level from RR interval, relationship of them was investigated by a series of experiment. RR interval was calculated from the pulse wave measured with a finger sensor. Sleepiness level was measured with Visual Analogue Scale (VAS), one of the typical subjective rate scales. The measured sleepiness level was named sleepiness score.
As a result of investigating relationship of RR interval and sleepiness score, clear correlation between them was found. Finally, sleepiness-estimate function was first determined by applying least-square method to the scatter diagram of RR interval and sleepiness score. Then, usability of this function was verified from the results of a series of experiments showing the possibility to universally estimate sleepiness from RR interval.

Systems capable of monitoring the biological condition of a driver and issuing warnings during instances of drowsiness have recently been studied. Moreover, many researchers have reported that biological signals, such as brain waves, pulsation waves, and heart rate, are different between people who have and have not consumed alcohol. Currently, we are developing a noninvasive system to detect individuals driving under the influence of alcohol by measuring biological signals. We used the frequency time series analysis to attempt to distinguish between normal and intoxicated states of a person as the basis of the sensing system.

In this study, the authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. Before developing a control algorithm, combustion experiments with various component fuels assumed to have the components of real biomass gases, such as fermentation and pyrolysis gases, were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio can be expressed by a first-order linear function regardless of fuel composition. Indicated thermal efficiency can also be expressed by combustion duration and volumetric efficiency when the coefficient of variation of indicated mean effective pressure is lower than 5% and pumping loss decreases against volumetric efficiency linearly, and the relationship between combustion duration and MBT can also be expressed by a first-order function. By using these relationships, a gas engine control algorithm, which can define the target values of the equivalence ratio of a premixture and ignition timing that realize a high thermal efficiency for fuel compositions automatically by analyzing in-cylinder gas pressure data in real time, is developed in order to use gaseous fuels produced from biomass resources effectively. Thus, a biomass gas fuel engine system is developed by applying the algorithm to an automobile gasoline engine, hardware modifications of which are only the fuel supply system and flywheel. The engine system is connected to a gasification plant using wood chips and an operation test is carried out. As a result, the engine system can set an optimum premixture condition and an ignition timing, which realizes a stable and high-thermal-efficiency operation automatically.

Bump-type foil bearings have demonstrated excellent performance in service experiences in recent 30 years. Due to their special structures, the performance prediction models must couple the air pressure with the elastic deflection of the compliant foil structure. The solution of air pressure has been well settled in the hydrodynamic lubrication theory, while the deflection of foils now still cannot be accurately solved due to the mechanical complexity of the corrugated bump structure. A theoretical model, link-spring model, was developed to predict the structure characteristics of foil strips in a previous work. Effects of four factors, i.e., the elasticity of the bump foil, the interaction forces between bumps, the friction forces at contact surfaces, and the local deflection in the top foil, had been taken into consideration. In this investigation, based on the link-spring model, a perturbation approach is used to determine the dynamic characteristics of bump-type foil bearings. The calculations have been performed with different meshes. And the accordant results show that the calculation is independent on the mesh. The effects on the dynamic coefficients of the friction forces and radial clearance are also evaluated using the perturbation method.

A complete analytical model of bump-type foil bearings taking into consideration the effects of four factors, i.e., the elasticity of bump foil, the interaction forces between bumps, the friction forces at the contact surfaces, and the local deflection of top foil, is presented in this investigation. Each bump is simplified to two rigid links and a horizontally spaced spring, the stiffness of which is determined from Castigliano&apos;s theorem. The interaction forces and the friction forces are coupled with the flexibility of bumps through the horizontal elementary spring. The local deflection of the top foil is described using a finite-element shell model and added to the film thickness to predict the air pressure with Reynolds&apos; equation. The bump deflections of a strip with ten bumps calculated using the presented model under different load distributions are consistent with the published results. Moreover, the predicted bearing load and film thickness obtained from a foil bearing with a bump circumferential extend of 360 deg also agree very well with the experimental data, especially for predictions with a proper selection of radial clearance (preload of foil structure) and friction coefficients. In addition, the radial clearance and friction force variations in the foil bearing are noted to significantly change the performance of the foil bearing. The predictions demonstrate that the radial clearance of the foil bearing has an optimum value for the maximum load capacity. [DOI: 10.1115/1.4001169]

In this study, the authors aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. Before developing a control algorithm, combustion experiments with various components fuels assuming component of real biomass gases like as fermentation gas and pyrolysis gas were carried out. It was clarified that the relationship between dimensionless combustion duration and equivalence ratio is expressed in first order liner function regardless of fuel components. Indicated thermal efficiency can be also expressed by combustion duration and volumetric efficiency under the condition that COV of IMEP was lower than 5% and pumping loss decreased against volumetric efficiency linearly, and the relationship between . combustion duration and MBT can also be expressed in first order function. By using these relationships, a gas engine control algorithm, which can define target values of equivalence ratio of premixture and ignition timing realizing high thermal efficiency for fuel compositions automatically analyzing in-cylinder gas pressure data in real time, is developed in order to use gaseous fuels produced from biomass resources effectively. Thus, biomass fueled gas engine system is developed by applying the algorithm to the automobile gasoline engine, hardware modification of which were only fuel supply system and flywheel. The engine system was connected to a gasification plant using wood chip and operation test was carried out. As a result, the engine system could set optimum premixture condition and ignition timing, which realized stable and high thermal efficiency operation automatically.

The characteristics of the pressure pulsations in a drum connected to a piping system excited by a centrifugal compressor or a blower operated at blade-passing frequencies were investigated. In this study, the equivalent resistance of a compressor and that of a piping system were introduced and linked to the three dimensional calculation model, so that the non-linear damping proportional to velocity squared in the system is properly incorporated. The experiment was performed in order to validate the proposed simulation model.
As a result, the three dimensional pressure response in the drum as well as the pipe can be well evaluated by this model. Furthermore, the effect of the acoustic dynamic absorber on the pressure pulsations in the pipe and drum is evaluated. When the resonant frequency of the pipe coincides with that of the drum, two peaks appear in the frequency response curve around the resonant frequency of the pipe, because the drum acts as an acoustic dynamic absorber. It is shown that the maximum pressure amplitude in the drum is obtained when the resonant frequency of the pipe is slightly shifted from the resonant frequency of the drum under the small damping conditions. The effect of the damping in the drum and the mode shape of the drum on the maximum pressure amplitude in the drum is discussed in detail.

In recent years, arteriosclerotic cardiovascular disease becomes a serious problem in the developed countries. The degree of the arteriosclerosis should be examined routinely and invasively, and the measurement of pulse wave is considered as an effective estimation method. Nowadays, pulse wave is widely used in clinical practice as a noninvasive method of examining circulatory kinetics, but the mechanism in the process of the systolic wave generated at heart and propagating to the peripheral artery remains to be elucidated. In this research, to investigate the effect of bifurcation on pulse wave propagation, numerical simulations by a dynamic model of arteries and in vitro experiments were conducted. A one-dimensional model of arteries is coupled by partial differential equations describing mass and momentum conservation with the tube law that relates the local cross-sectional area to the local radial pressure difference. In the case of a bifurcated artery model, the governing equations were solved by introducing the momentum caused by the reactive force at bifurcation into the equation of momentum conservation. The momentum by the reactive force at bifurcation was supposed to be proportional to the momentum flowing into the bifurcation, and the proportionality coefficient was derived from experiments. Then, the proposed one-dimensional model was validated by a comparison to experimental data. In the experimental setup, elastic tubes with different values of Young's modulus were tested to simulate human arteries. From the numerical and experimental results, it turns out that the characteristic waveforms of the pressure and velocity obtained from experiments are also captured by the numerical calculations.

A theoretical analysis is presented to investigate the nonlinear dynamic behavior, i.e., the stability and unbalance response of bump-type foil bearings. The link-spring model, presented and validated in a previous study, is used to describe the foil structure of bump-type foil bearings in this research. The orbit of the shaft is simulated from the iteration calculation of the motion equation at each time step, which is coupled to the Reynolds' equation and the foil structure model. Parametric studies on the mumber of bumps, the size of bumps, the thickness of the foils and the material of the foils are presented using the bearing load prediction and the nonlinear orbit simulations. The static loads of the foil bearing with various parameters are predicted to find out some guidelines for the design of foil bearings. The critical speeds of the rotor with a certain bearing load are also calculated. The analysis on unbalance response is presented by depicting journal trajectories as a function of mass unbalance. And the FFT analysis of the computed results is performed to show the variation of amplitudes in frequency domain.

A theoretical analysis model is presented to investigate the nonlinear dynamic behavior of bump-type foil bearings, i.e., the instability and unbalance response. In the developed model, the foil structure of bump-type foil bearings was simulated using the link-spring model, which was presented and validated in a previous study. During the calculation, the Reynolds equation and the foil structure model were coupled though the pressure and film thickness. An iteration solution method with the equation of shaft motion was applied for the shaft orbit. Parametric studies of design parameters, such as the bump number, the length ratio of the segment between two bumps and a bump, the foil thickness, the bump height, and the Young's Modulus, were presented upon the analysis of static performance and the instability of bump-type foil bearings. It is noted that more bumps or lager length ratio lead to larger load capacity. But the bearing load capacity does not change with different bump heights. Moreover, the threshold speed of instability decreases significantly with the rise of the bump number, especially when the number of bumps is low. However, it almost does not affect by other four parameters.

Aiming to understand applicable component of biomass gas to HCCI engines, combustion characteristics were investigated experimentally for mock biomass gas with varying fuel components. Mock biomass gases consisted of H_2, CH_4, CO, N_2 and CO_2 were used assuming wood pyrolysis gases. Using modified gas engine with air inlet heaters and high compression ratio pistons, experiments were carried out. Auto-ignition timing is temperature domain regardless of fuel component, ignition temperature is about 1000K as same as hydrocarbon fuels. Combustion speed following auto-ignition is influenced largely on H_2 and CO_2 content, it is clarified that combustion speed is proportional to H_2 and CO_2 ratio of fuel. Meanwhile CO of fuels does not effect on combustion speed. H_2 and CO_2 ratio of fuel is also largely concerned with knock, and it is one of index of minimum IMEP that knock yield. About Exhaust emissions, THC and CO is higher level because of lower cyclic maximum temperature for inert component of fuel, in another hand, NO_x is near zero regardless of fuel components and operation conditions.

Biomass, a renewable and carbon-neutral energy source, is widely recognized as an alternative to fossil fuels. But, because of the supply instability, it is hard to use Biomass as a single fuel in Engine. In this study, the combustion characteristics of a HCCI Engine using Mixture of City gas 13A and Biomass gas are investigated. As a result, it is noted that the ignition timing advances and the combustion duration becomes longer, when the ratio of 13A decrease and/or the intake gas temperature becomes higher. Moreover, it is suggested that the effect of H_2 on the ignition timing is more significant than other combustible components.

Axial vibration characteristics of centrifugal turbopumps are extremely complex. In the balance piston system, the axial vibration due to flow passing through the balance orifice occurs in some cases. Normally, the swirl flow may suppress the axial self-excited vibrations. But the mechanism is unclear. Therefore, in this study, we manufactured an experimental apparatus including a partial model of the balance piston in the centrifugal turbopump, and the effects of swirl flow on the vibration performance of the balance piston in the centrifugal turbopump are investigated. As a result, it is noted that the peak value on displacement from FFT at 120Hz decreases as the swirl flow increases.

To realize stable operation of microgrids, gas engines require to compensate load changes from demands and variation of other renewable energy devices. Then, prehension of load following capability is important in gas engines. In addition, when biomass gas is supplied to gas engines, effect of fuel component variation on dynamic characteristics must be investigated, because components of biomass gas depend on operating condition of gasification or raw material. This study proposed a dynamic simulation model of gas engine and estimated transient response to load changes. Load changes were sinusoidal wave, and bias value, amplitude and frequency of them were varied. As a result, the frequency has more influence on transient response than the bias value and the amplitude. When biomass gas is supplied to gas engines, transient response is worce than city gas over the frequency of 0.1 Hz.

The feature of sleep pattern is determined by the rhythm of body temperature. In this study, a method was conceived for capturing changes in the peripheral circulatory system during the process of lowering of core body temperature via finger plethysmogram. Recorded signals were then analyzed by chaos analysis. By analyzing the variations in the time series of the gradients of the largest Lyapunov exponent and the power value (the square of the finger plethysmogram amplitude), and by observing the conditions of the subject, the phenomenon that predicts the subject's transition to Stage 1 sleep during wakefulness was detected.

The applications of foil air bearings have been extended for use in a wide range of turbomachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature. This study presents a thermohydrodynamic (THD) analysis of multiwound foil bearing, in which the Reynolds' equation is solved with gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds equation, the foil elastic deflection equation, and the energy equation until convergence is achieved. A three-dimensional temperature prediction of air film is presented, and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution.

Foil Air bearings offer many advantages enabling high performance oil-free turbomachinery practicable, i.e. design simplicity, high speed and temperature capability, low power loss and environmental friendship. Experimental and analytical investigations have been performed extensively in recent decades, especially for bump-type foil bearing. However, by now, the low load capacity and deficient damping limit their wide applications in rotor systems.
This paper presents an elasto-aerodynamic model for the static performance of bump-type foil bearings by taking the interacting forces between bumps, the friction forces at contact surfaces, and the local deflection of top foil into account. A finite element model is developed to describe the foil elasticity, while the compressible Reynolds&apos; equation is solved for the air pressure distribution. An iterative procedure is carried out between the above two equations until the convergence is achieved. Published experimental data are used to validate the numerical model. The predicted static load and film thickness of the bump-type foil bearing using this model are very closed to the experimental data.

A two-axis, recuperated cycle micro-gas turbine (MGT) system for biomass gas is developed. The rated specifications of the MGT are as follows, pressure ratio of 2.7, turbine inlet temperature of 1120K, and output power of 5kW. The system consists of three components: the MGT power-generating system, control system and mock biomass gas supply system. The original two-stage combustor and H infinity system controller used in this system are discriminative. Since the gaseous fuel converted from biomass has a low heat quantity, the combustor is designed to achieve both high combustion efficiency and low NOx emission for lower calorific fuel. In the combustor, a stable tubular flame combustion of city gas in the first stage supplies burned gas, which has enthalpy and activated radicals, to the second stage and enables stable ignition and combustion of biomass gas and air premixture. In addition, because the gas composition of biomass gas is also affected by the sources, the gasification method, and the gasifying condition, the system controller is required to absorb fuel fluctuation while meeting the demanded output. Hence, the H infinity algorithm is employed as a system controller because of its robustness against disturbances from the unpredictable fuel component fluctuation. Using this MGT system, an operation test was earned out with mock biomass gases. The rotational speed of the power turbine could be kept almost constant with both mock fermentation gas and pyrolysis gas as the second-stage fuel, and NOx emission was 50ppm when load was increased to a rated power of 5kW. When the second-stage fuel composition changed from 100% methane to 50% methane and 50% CO(2) at a certain speed, the power turbine speed could also be kept constant. The H infinity controller is compared with the 2-DOF PID controller for secondary fuel concerning the response to varying load. The former shows slightly better performance than the 2-DOF PID controller.

Bump-type foil bearings have demonstrated excellent performance in service experiences in recent 30 years. Due to their special structures, the performance prediction models must couple the air pressure with the elastic deflection of the compliant foil structure. The solution of air pressure has been well settled in the hydrodynamic lubrication theory, while the deflection of foils now still cannot be accurately solved due to the mechanical complexity of the corrugated bump structure. A theoretical model, link-spring model, was developed to predict the structure characteristics of foil strips in a previous work. Effects of four factors, i.e., the elasticity of the bump foil, the interaction forces between bumps, the friction forces at contact surfaces, and the local deflection in the top foil, had been taken into consideration. In this investigation, based on the link-spring model, a perturbation approach is used to determine the dynamic characteristics of bump-type foil bearings. The calculations have been performed with different meshes. And the accordant results show that the calculation is independent on the mesh. The effects on the dynamic coefficients of the friction forces and radial clearance are also evaluated using the perturbation method.

The field experiences of gas foil bearings (GFBs) from the 1960s prove that GFBs offer several advantages over traditional oil bearings and rolling element bearings. They have the potential to be applied in a wide spectrum of turbomachinery. Bump-type foil bearings, which are considered as the best structure for GFBs, can be simply described as a hydrodynamic bearing utilizing the ambient air as the lubricant and a smooth shell supported by a corrugated bump foil as the bearing surface. However, the performance predictions of bump-type foil bearings are difficult due to mechanical complexity of the support elastic structure, especially for the effects of four factors, elasticity of bump foil, interaction forces between bumps, friction forces at contact surfaces, and local deflection of top foil. In this investigation, an analytical model of bump-type foil bearings considering the effects of all above factors is presented. In this model, each bump of the bump strip is simplified to two rigid links and a horizontally spaced spring, whose stiffness is determined from Castigliano&apos; theorem. Then, interaction forces and friction forces can be coupled with the bump flexibility though the horizontal elementary spring. The local deflection of top foil is described using a Finite Element model and added to the film thickness for the pressure prediction with the Reynolds&apos; equation.
The bump deflections of a strip with ten bumps under different load distributions are calculated with the presented model and the predictions show consistency with published results. Moreover, the predicted bearing load and film thickness of a full bump-type foil bearing using this model are very close to the experimental data. Also, radial clearance and friction force variations in the foil bearing are noted to change the stiffness of bump significantly. And the predictions from the calculation with a proper selection of radial clearance and friction coefficients show extremely good agreement with the experimental data.
The assumption of minimum reachable film thickness is based on experimental data to determine the load capacity of bearing. The results demonstrate that the radial clearance of foil bearing has an optimum value for the maximum load capacity.

The purpose of the present study is to improve the on-street exhaust noise measurement technique for regulating vehicles that emit unacceptably large exhaust noise. The method under development uses racing operation of engines with a wide-open throttle on a standing vehicle. In contrast, the engine operation condition considered in the conventional on-street measurement technique considers operation at 75% of rated power followed by the throttle valve being released to its original position. The current regulation considers the maximum noise level during this engine operation condition. Accordingly, the engine is not loaded during testing. This loading condition provides unsatisfactory correlation between the exhaust noise level measured by the on-street method and the ISO vehicle acceleration noise under the wide-open throttle condition. The present paper reports the advantages of the proposed method as well as some important factors in the proper application of the newly proposed method. In the present study, we perform noise measurement along highways, a vehicle experiment in an anechoic chassis dynamometer, and computer simulations. The results revealed that the proposed on-street measurement method can be used to approximately determine the exhaust noise level during full acceleration for most vehicle types. In addition, the sensitivities of the measured noise levels for the testing conditions were clarified. The second item in this study is efficient engine speed measurement using exhaust sound signal only without electric wire harnessing. A survey of the measurement systems proposed by three different companies revealed that the measurement principles of two of these systems have potential application to on-street exhaust measurement.
The last item investigated herein is better indices of exhaust noise evaluation. Loudness defined by ISO was found to be much better than the conventional dB(A) scale in terms of correlation with subjective evaluation results.

Dynamic performance of multiwound foil bearings with the effects of foil local deflection is investigated. The foils, separated and supported by projections on the ir surface are treated as thin plates. Deflections of the foils are solved with a finite element model. The air pressure is calculated with the Reynolds' equation by treating the lubricant as an isothermal idea gas. The effects of foils are simulated with the deflection of top foil added to the film thickness. A finite difference computer program is developed to solve the Reynolds equation and the elastic deflection equation, simultaneously. Perturbation method is used to determine the dynamic coefficients. The effects of foil deflection is discussed by comparing the dynamic coefficients of a foil bearing and a rigid bearing. Experimental data from a test rig supported by two multiwound foil bearings are used to validate this numerical solution.

Biomass resources are one of the attractive alternative fuels. It is effective to use such fuel in distributed power generation system with gas engine because it disperses. However, its calorific value is low, and the gas composition is affected by the source material, gasification method and gasifying conditions, causing it to change momentarily during engine operation. The gas engine must be stable and capable of high-thermal-efficiency operation under such fluctuations. The objective of this study is to develop a small gas engine system for biomass gaseous fuel. In this study, the effect of fuel composition on combustion was clarified by an engine experiment with low-calorific-value gaseous fuel. Diluted fuel exhibited longer combustion duration and lower thermal efficiency, but not necessarily a lower calorific value. It was also confirmed that spark timing control against fuel composition fluctuation was effective for maintaining high thermal efficiency even at a fixed speed engine. Fuels containing H2 also have lower calorific values, but they allow stable engine operation and higher thermal efficiency with respect to a shorter combustion duration.

In this study, to establish the methodology for controlling the rotational speed of two shaft axial micro gas turbine generator system, modeling strategy of static and dynamic characteristics of the system based on nonlinear model is proposed. This model is constructed based on the combination of measured data and correction factors and does not rely on compressor and turbine map, which yields better prediction results with higher accuracy. To investigate the stability and robustness of the system, H infinity algorithm is employed as a system controller. The difference on controller performance designed based on the dynamical modeling of the target system and the measured data is discussed.

Biomass is expected to be a renewable energy that can replace fossil fuels and it is considered of value to use biomass to generate electricity by a HCCI engine. However the combustion characteristics of a HCCI engine fueled by biomass gas is not investigated yet. Therefore, the requirement of biomass gas composition that can appropriately achieve the HCCI combustion is experimentally clarified. As a result, it is confirmed that the ratio of H_2 to CO_2 concentration represents the combustion characteristic of a HCCI engine. And also, the fact that the ratio of H_2 to CO_2 can be an indicator of the operating range without causing the knock is shown.

The micro gas turbine (MGT) system for the biomass gas has been constructed. This system consists of MGT power generation system, mock biomass gas supply system and control system. The features technologies in this system are two-stage combustor and H infinity system controller. The combustor achieves both higher combustion efficiency and lower NOx emission, in which a stable tubular flame combustion of the first stage supplies burned gas to the second stage and causes stable ignition and combustion of biomass gas and air pre-mixture. H infinity algorithm is employed as a system controller for its robustness for disturbances like as unpredictable fuel component fluctuation. By using this MGT system, operation test was carried out with mock biomass gas. Rotational speed of the power turbine could be kept constant with both fermentation gas and pyrolysis gas, and NOx emission was low. The speed could be also kept constant, even when the fuel composition or load changed.

Auto-ignition and combustion characteristics of biomass gas were investigated experimentally. Mock biomass gas consisted of H2, CH4, CO, N2 and CO2, was used assuming a wood pyrolysis gas. A test engine was a 3-cylinder 1.6 L gas engine modifying compression ratio from 9.5 to 24 and equipping the intake air heating system. Experiments were carried out by varying equivalence ratio and fuel composition. The engine could realize auto-ignition and combustion at higher thermal efficiency with mock biomass gas, IMEP was 0.28 MPa and indicated thermal efficiency was 37% at 600 rpm. The knock did not cause at higher equivalence ratio over 0.4, because the fuel had much dilution components, which made combustion speed slower like as EGR. Higher hydrogen content caused the combustion speed to be high, but it did not influence on the ignition timing. On the contrary, the high carbon monoxide content retarded ignition timing, but it did not influence on the combustion speed. Auto-ignition temperature of biomass gas was from 1 000 K to 1 050 K as same as hydrocarbon fuels.

In order to use biomass resources efficiently, a small-size gas engine in a small-distributed generation system is one of the effective methods. However, existing gas engines for energy generation are too big to use in small-distributed generation systems and very expensive. So, diverting automotive engines is sensible solution because of their low cost. On the other hand, the composition of biomass gas generated from gasification plants is affected not only by the source and the gasification method but also by the gasification condition. Therefore, we aimed to develop a low cost and small size biomass gas engine by diverting an automotive engine with original control system. The intake system of the automotive gasoline engine was changed to two throttles in order to control both fuel and air flow rate respectively. The control system was constructed by assuming to use various fuels whose composition can fluctuate. Operational test was carried out by using real biomass gas from the gasification plant. As results, engine speed and air fuel ratio were stably controlled and the engine output achieved 19 kW.

Systems capable of monitoring the biological condition of a driver and issuing warnings during instances of drowsiness have recently been studied. Moreover, many researchers have reported that biosignals, such as brain waves, pulsation waves, and heart beat are different between people who have and have not consumed alcohol. Currently, we are developing a noninvasive system to detect individuals driving under the influence of alcohol by measuring biosignals. In this paper, a new algorithm to distinguish between the normal and intoxicated state of a person is proposed as the basic theory of the sensing system.

The feature of sleep pattern is determined by the circadian rhythm that is typified by the rhythm of body temperature and homeostasis. In this study a method was conceived for capturing changes in the peripheral circulatory system during the process of lowering of core body temperature via finger plethysmogram. Recorded signals were then analyzed by chaos analysis. By analyzing the variations in the time series of the gradients of the largest Lyapunov exponent and the power value (the square of the finger plethysmogram amplitude), and by observing the conditions of the subject, the phenomenon that predicts the subject's transition to Stage 1 sleep during wakefulness was detected. These predictive signals for falling asleep can be found when the amplitude of the power gradient was in transition, and when the largest Lyapunov exponent's gradient and the power gradient have an inverse phase with 180 degrees.

For the purpose of quantifying and indicating the degree of fatigue as a result of sifting in an automobile seat for long periods of time, a method was developed by using a baseline oscillation and the amplitude of a finger plethysmogram. Between a finger plethysmogram and the degree of fatigue, there is about one hundred times difference in a fluctuation cycle. So, an idea was proposed to convert a finger plethysmogram into a gradient of comprehensive change to make fluctuation cycle scales easily comparable. The gradients of the square of the finger plethysmogram amplitude were converted into absolute values. Then, we drew a fatigue curve based on the results calculated at 18-second integrated values of the time series signals. This curve and the muscle fatigue curve from subjective judgment were in general accord. By using a finger plethysmogram featuring high sensitivity to the fatigue progress, differences in various subjects and seat performances could be found on this fatigue curve using only a 30-minute fatigue test. This new method has made it possible to greatly shorten the measurement time necessary to predict fatigue level by sensory evaluation.

The applications of foil air bearings, which are recognized to be the best choice for oil free applications, have been extended for use in a wide range of turbo-miachineries with high speed and high temperature. Lubricant temperature becomes an important factor in the performance of foil air bearings, especially at high rotational speeds and high loads or at high ambient temperature ([1]). However, most of the published foil air bearing models were based on the isothermal assumption. This study presents a thermohydrodynamic analysis (THD) of Multi Wound Foil Bearing (MWFB), in which the Reynolds&apos; equation is solved with the gas viscosity as a function of temperature that is obtained from the energy equation. Lobatto point quadrature, which was proposed by Elrod and Brewe ([10]) and introduced into compressible calculation by Moraru and Keith ([15]), is utilized to accelerate the iteration process with a sparse mesh across film thickness. A finite element model of the foil is used to describe the foil elasticity. An iterative procedure is performed between the Reynolds&apos; equation, the foil elastic deformation equation and the energy equation, until the convergence is achieved. A three-dimensional temperature prediction of air film is presented and a comparison of THD to isothermal results is made to emphasize the importance of thermal effects. Finally, published experimental data are used to validate this numerical solution.

To establish the practical evaluation method of the pressure pulsations excited by a centrifugal compressor or fan at blade passing frequency, a one-dimensional excitation source model for a compressor was proposed based on the equation of motion. The damping characteristics of the compressor were investigated experimentally and as a result, the resistance coefficient of the compressor depends on the Reynolds number defined by the equivalent velocity of the pulsating flow is introduced. It is also shown that the relation of the maximum pressure amplitude in piping systems to the location of the excitation source under resonant conditions can be evaluated by introducing the equivalent resistance of the compressor and that of piping systems.

Pressure pulsations excited by a centrifugal compressor or fan at blade passing frequency may cause severe noise and vibrations in piping systems. Therefore, the practical evaluation method of pressure pulsations is strongly required. In this study, a one-dimensional excitation source model for a compressor was proposed based on the equation of motion. An experiment was performed for the validation of this model. As a result, the relation of the maximum pressure amplitude in piping systems to the location of the excitation source under resonant conditions can be evaluated by introducing the equivalent resistance of the compressor and that of piping systems. The role of the system resistance to the response of pressure pulsations is discussed in detail.

Multi wound foil bearings (MWFB), as a kind of foil bearings with simple structures, are supposed to be one of the best candidates of supporting component for turbo-machineries because of their design simplicity, reduced weight and size, high speed and temperature capability, and easy maintenance. In this study, a theoretical model of MWFB taking account of the effect of the foil deformation is developed to predict its static performance. Reynolds' equation is solved using Finite Difference Method (FDM) to yield air pressure distribution, while the elastic deformation equation is solved by Finite Element Method (FEM) to predict the deformation of the foil. Then, the above two equations are coupled by several iterations until the convergence criterion is reached. Based on the calculations, static characteristics of MWFB such as film thickness, load capacity and torque are presented. Finally, an experimental apparatus is built up to measure the load of MWFB at different operation condition, which are used to validate numerical calculation results.

To investigate the mechanism and the usage of the information of pulse wave propagation and reflection in human arteries are the objects of this study. In this study, an experimental apparatus simulating human circulatory system by using silicon tubes to examine the pulse wave propagation and reflection with and without branches has been developed. We examined the effect of eight parameters, such as flow rate, tube diameter, tube thickness etc., affecting waveform, PWV (Pulse Wave Velocity) and PV loop (Pressure-Velocity Loop). Numerical analyses were also carried out, and the relation between PV Loop and local impedance was discussed. Finally, the effect of eight parameters on the P W and PV loop were clarified. It was also found that, the PV Loop includes much information on the tube characteristics, impedance, boundary condition, tube connection and reflection condition. Therefore, the PV loop method might be promising to be used in health diagnosis systems. In addition, we found that the effects of bifurcation angle on wave propagation and reflection were so little that they can be neglected in wave calculation models.

Biomass resources are drawing more and more attention as alternative fuel for combating the energy crisis and for atmospheric environment protection. The small gas engine in a distributed power generation system is an efficient system to use, because the biomass resource is stored in large area and its energy density is low. The heat quantity of gas fuel converted from biomass is low, and the gas composition is affected by the source type, the gasification method, and the gasifying condition. Therefore, the gas engine must be modified and operated stably with high thermal efficiency in view of these fuel fluctuations. In this study, we aim to develop a small gas engine system for biomass gas by modifying the control system of a conventional spark ignition engine. The engine control system for the biomass gas that was developed analyzed the fuel type in real time by measuring the in-cylinder gas pressure. With this control system, stable automatic engine operation was successfully achieved under different fuel composition percentages of methane and the mock biomass gas.

In this study, ignition and combustion characteristic of biomass gas in a HCCI engine was investigated experimentally. 1.6L gas engine for 13A fuel was remodeled to 24.6 compression ratio and rigged up an air heater for HCCI combustion. Fuel was assumed biomass gas consisted of CH_4, H_2, CO, CO_2 and N_2. In experiments, fuel composition was changed H_2 or CO of this biomass gas. As results, a HCCI engine moved in indicated thermal efficiency 37%. Higher H_2 composition made ignition timing of a HCCI engine advanced and lower CO composition made it delayed.

Biomass resources are effective energy sources against global warming. In order to utilize biomass resources effectively, the automotive engine as a small-distributed generation system is one of the effective methods. In this study, a small size engine fueled by biomass gas based on automotive engine has been realized. Operating experiment fueled by low calorie gas simulating biomass gas gave knowledge about combustion characteristics and requirement for stable operation. 26% thermal efficiency was accomplished under appropriate conditions. An engine plant fueled by real biomass gas supplied from gasifying plant generated 19kW at its maximum. Then, auto control program was applied to the system. The control of air-fuel ratio and ignition timings realized stable rotational speed and power generation.

In this investigation, a complete analytical model of the bump-type foil bearing considering the effects of four factors, the elasticity of bump foil, the friction forces at contact surfaces and the interacting forces between bumps, the local deflection of top foil and the assembly preload, is presented. In this model, the bump foil is simplified to a two rigid links and one horizontally spaced spring structure. Because the spring is parallel with the frictional forces and the interaction forces, it is easy to take into account the effects of the forces inside foil structure. The local deflection of top foil is described using a Finite Element model and added to the film thickness for the pressure prediction with Reynolds' equation. An assembly deflection of both top foil and bump foil is used to simulate the preload. The static load and film thickness of a bump-type foil bearing are predicted using this model and the results are very closed to the experimental data.

In this study, combustion field in a combustor designed for small size gas turbine fueled by low calorific gas was visualized by OF-PLIF method. To investigate the effect of mixing, air fuel ratio and combustion length, rectangular combustor is used. In addition, to verify the fact that flameless combustion is realized in our homemade small size combustor, cylindrical transparent combustor with the same size is used. Visualized pictures explain previously obtained data well.

In order to study aerodynamic characteristics of a carriage arm equipped on hard disk drives, water tunnel tests with ten times enlarged models of an actual arm were conducted based on Reynolds number similitude, which allows the time scale of the phenomena about 1,300 times slower than that compared with the phenomena under actual operation condition in the air. In the tests, flow visualization around the arm model. with fluorescent dye injection and laser-light sheet technique was carried out. Fluid dynamic drag, lift and torque on the model were also measured. The effects of the oncoming flow velocity and profile, the installation angle and position of the arm and the configuration of the trailing edge of the arm on the power spectral density of the fluid dynamic force were investigated. As a result, predominant spectrum peak, the Strouhal number of which is about 0.24, is found in the power spectral density of dynamic lift force on the arm. The flow visualization confirmed that the dynamic lift with the spectral peak originates from the alternating vortex shedding from the trailing edge of the arm. The peak rapidly decreases as the installation angle increases while the velocity profile of oncoming flow and the position of the arm in the gap direction have little effect on the peak component. Furthermore, it was demonstrated that the dynamic lift can be reduced by modification of trailing edge shape of the arm.

This study aims to develop a small size gas engine system with biomass gas by modifying the control system of a conventional spark ignition engine. In this paper, combustion characteristics of typical biomass gas assuming the wood chip pyrolysis gas, whose lower heating value was about 1/6 of the city gas in Japan, were investigated. Engine control system for biomass gas was also examined. It was confirmed that simulated biomass gas could achieve high thermal efficiency and stable combustion for wide range equivalence ratio without knocking and at low emissions. Automatic engine operation with real time in-cylinder gas pressure analysis was also tried under fuel composition change. Copyright © 2007 SAE International.

Biomass is one of the attractive alternative fuels, which exists dispersively. Small size gas engine power generation with gasification biomass gas is one of the efficient methods. However, since its calorific value is lower and its composition can be affected by gasifying conditions, it is difficult to stabilize and achieve high thermal efficiency engine operation. This study aims to develop a small size gas engine system with biomass gas by modifying the control system of a conventional spark ignition engine. In this paper, effect of fuel composition on combustion was clarified experimentally to get guideline for the engine control system. Copyright © 2007 Society of Automotive Engineers of Japan, Inc.

One approach to achieving 99% combustion efficiency (C.E.) and 10 ppmV or lower NOx (at 15%O-2) in a micro gas turbine (MGT) combustor fueled by biomass gas at a variety of operating conditions is with the use of flameless combustion (FLC). This paper compares experimentally obtained results and CHEMKIN analysis conducted for the developed combustor. As a result, increase the number of stage of FLC combustion enlarges the MGT operation range with low-NO, emissions and high-C.E. The composition of fuel has a small effect on the characteristics of ignition in FLC. In addition, NO, in the engine exhaust is reduced by higher levels Of CO2 in the fuel.

Dynamic pressure type foil bearings are expected to serve as shaft bearings for Micro Gas Turbines (MGT). In this study, in order to establish design guidelines of radial foil bearings, dynamical modeling of multi wounded foil bearing was carried out employing leakage flow induced vibration theory. Taking frictional forces due to attached part of the foil and the protrusion, etc. into consideration, static and dynamic characteristics were analyzed to examine the performance and the stability of radial foil bearings.

Foil bearings are supposed to be one of the best candidates of supporting component for turbo-machineries because of their design simplicity, reduced weight and size, high speed and temperature capability, and easy maintenance. Among various types of foil bearings, multi wound foil bearing (MWFB), which had been designed and fabricated in our lab, is easy to analyze static characteristics even though load capability of which is small compared with other types of foil bearings.<br>In this study, a theoretical model of MWFB taking account of the effect of the foil deformation is developed to predict its static performance. Reynolds equation is solved using Finite Difference Method (FDM) to yield air pressure distribution, while the elastic deformation equation is solved by Finite Element Method (FEM) to predict the deformation of the foil. Then, the above two equations are coupled by several iterations until the convergence criterion is reached. Based on such calculations, static characteristics of MWFB such as load capacity, torque are presented.

Thermal reaction of lean to ultra-lean premixed mixtures supported by the hot burned gas from the upstream stage can be used for obtaining a better trade-off between ultra-low-NOx and high combustion efficiency over a wide range of operations of a gas turbine. A three-stage model combustor designed based on this concept is being developed for a biomass gas-fueled regenerative cycle 10 kW micro-gas turbine. Tubular flame combustion is used for the primary stage and mixtures of lean to ultra-lean compositions are injected into the cross-flowing hot burned gas from the up-stream stage in the secondary and tertiary stages. The emissions and combustion characteristics are evaluated with methane and simulated biomass gas of different CO2 contents at atmospheric pressure and inlet air temperatures up to 700 K.
In the experiments, the fuel flow for the secondary mixture was gradually increased while maintaining the fuel flow to the primary stage in the two-stage combustion mode and the fuel flow for the tertiary mixture was gradually increased while maintaining the fuel flows to the primary and secondary stages in the three-stage combustion mode. The combustor exit NOx concentration corrected to 15% O-2 remained at or slightly lower than the level that was achieved at the start of fuel staging as far as the injected mixture was leaner than the primary mixture and NOx emissions in the 10 ppm level were achieved at gas temperatures less than 1700 K. In contrast, the NOx concentration increase steeply with equivalence ratio in non-staged combustion mode. The reaction of the injected mixture was completion when the reaction zone temperature was higher than 1500 K regardless of inlet air temperature and equivalence ratio of the primary stage. The results show that, the multi-stage combustion where mixtures of ultra-lean to lean compositions are injected into the hot burned gas from the up-stream stage achieved low-NOx emissions and high combustion efficiency over a wide range of overall equivalence ratios or combustor exit gas temperatures. It is found that the CO2 in the simulated biomass gas suppresses the NO formation by slowing down the progress of combustion reaction, especially at high temperature conditions. (c) 2006 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Micro grid energy system is consisted of various kind of generator (ex: wind power system that use natural energy, gas engine, storage battery and etc.). These devices are needed to be operated in line for the electricity demand change. Fuel composition also changes in assuming biomass use in the micro grid. So, it is important to understand their transient response properties for designing and managing the micro grid. In this study, transient response characteristics of a small size existent gas engine were investigated in experiment and engine dynamics model was developed. Influence of fuel condition on transient response was also investigated. It was clarified that fuel condition did not affect load following time though thermal efficiency was changed.

This paper deals with both linear and nonlinear analyses of sheet flutter in a narrow passage caused by fluid-structure interaction. The sheet is considered as a combination of massless beam elements, springs and discrete mass particles, in which the mass of each particle and spring coefficients are calculated based on the beam model. In the linear analysis, equations of motion of the system are obtained by formulating fluid dynamic forces and moments acting on each sheet element, yielding an eigenvalue problem. To show the validity of the proposed method, calculated results were compared with previously reported experimental ones. In the nonlinear analysis, nonlinear fluid dynamic forces are introduced to simulate the behavior of the sheet, showing the appearance of limit-cycle vibration in high flow speed. (c) 2005 Elsevier Ltd. All rights reserved.

This paper describes the characteristics of fluid forces and wake patterns of a circular cylinder oscillating in the streamwise direction in a cross-flow, on the basis of precise measurements and flow-visualizations in forced-oscillation tests in a water tunnel at subcritical Reynolds numbers. The added mass and added damping coefficients of a circular cylinder in a streamwise oscillation were calculated. The results of the forced-oscillation tests confirmed that two reduced-velocity ranges with negative added damping exist. The two ranges agree well with the two streamwise excitation regions observed in the free-oscillation tests in several previous studies. The added mass coefficient for the streamwise vibration varies greatly, depending on the reduced velocity, and that can affect the dynamic behavior of the streamwise vibration under low mass-ratio conditions. Furthermore, the mean drag coefficient attains its maximum at the reduced velocity between the first and second excitation regions where the added damping coefficient reaches its local maximum. This suggests that the increase in the mean drag coefficient induced by the formation of alternate vortices magnifies the fluid damping effect and contributes to the damping region between the first and second excitation region. (c) 2005 Elsevier Ltd. All rights reserved.

It was hypothesized that indicators of a subject entering a sleep state are captured in the gradient time series waveform of the square of the amplitude of the finger plethysmogram which show a fluctuation of changes in a blood pressure and also captured in the largest Lyapunov value's gradient time series waveform which show a fluctuation in a diameter of the blood vessels in the skin, and that these indicators exist in the VLF and ULF.
This hypothesis was verified by sleep experiments on subjects in sitting position. Indicators were detected of predicting subject's transition to the first stage in the sleep state during wakefulness. These indicators required about 30 minutes to be detected for a measurement and were identified by transition state in the power value's gradient amplitude and gradients of both the largest Lyapunov coefficient and the power values exhibiting a phase difference of 180 degrees.

睡眠パターンの特徴は体温リズムなどに代表される概日リズムやホメオスタシスなどで決まる. 本研究では, 概日リズムやホメオスタシスの影響による末梢循環系の変化を, 指尖容積脈波の極超低周波成分 (ULF) と超低周波成分 (VLF) から捉える方法を考案した. 臥位および座位での睡眠導入実験により, 指尖容積脈波を採取した. 採取した指尖容積脈波をカオス解析により求めた最大リアプノブ指数とパワー値の各傾きの時系列変化の分析により, 覚醒期における睡眠第1段階移行を予兆する現象を検出した. この予兆現象は, パワー値の傾きの振幅の遷移状況及び最大リアプノフ指数とパワー値の傾きが180度位相差をもつことにより捉える事ができる.

In order to study aerodynamic characteristics of a carriage arm equipped on hard magnetic disks, water tunnel tests with 10 times enlarged model of an actual carriage arm were conducted under Reynolds number similitude, which allows the time scale of the tests to expand approximately 1300 times larger than that under actual condition in the air. In the tests, flow visualization around the carriage arm model with fluorescent dye injection and Laser-light sheet technique was carried out. Fluid dynamic drag, lift and torque on the model were also measured. Effects of incident flow velocity and incident flow angle were investigated.

It was hypothesized that indicators of a subject entering a sleep state are captured in the gradient time series wave form of the square of the amplitude of the finger plethysmogram pressure, and also are captured in the fluctuation in diameters of the blood vessels in the skin as evidenced in the largest Lyapunov value's gradient time series wave form, and that indicators of entering a sleep state exist in the VLF and ULF.
This hypothesis was verified in sleep studies on subjects in both lying and sitting positions, and indicators were detected when the subject went from a waking state to the first stage of entering a sleep state. These indicators required a measurement timeframe of 30-50 minutes, and were captured when the power value's gradient amplitude, the largest Lyapunov coefficient and the power value's gradient exhibited a phase difference of 180 degrees.

At present, curriculum in engineering graduate school has the following issues to be solved; there are few student laboratories aiming at acquiring experimental skills, few opportunities to experience experiments in other laboratories besides their proper laboratories and few chances to learn technical writing and documentation. In the Mechanical Engineering Department, the University of Tokyo, we started new laboratory course entitled "Dynamics and Control Laboratory for graduate students" in 2002 to improve such situations. After finishing the first trial, we immediately carried out students' evaluation, improved the scheme and reflected the planning of 2003. In this paper, first we introduce the activities, analyze the results of students' evaluation and finally show the effectiveness of newly proposed laboratory course for graduate students.

For the purpose of the effective utilization of the biomass, a low calorific value gas fueled micro gas turbine generating system is being developed. The micro gas turbine is a twin shaft gas turbine with regenerative cycle, and its output is about 10 kW. City gas and low calorific value gas are used as fuel. The low calorific value gas simulated the gas composition of the biogas, and its calorific value is about 4,000 kcal/m^3. In order to operate and evaluate the generating system, the development of the control system is also being carried out. In this paper, the outline of the generating system and its start-up control method are introduced.

Dynamic pressure type foil bearings are expected to serve as bearings for micro gas turbine use because its maintenanceability. However, details of design guidelines have not yet been clarified although this technology is already used in APC for aircraft units. In this study, as an extension of leakage flow theory, dynamic modeling of the fluid coupled thin film is conducted. Taking fluid dynamic forces as well as frictional forces acting on the attachment part of the foil through the protrusions on the thin metal foil into consideration, static and dynamic characteristic of foil journal bearing were analyzed to examine performance and stability of the radial foil bearing.

This paper deals with nonlinear analyses of sheet flutter in a narrow passage caused by fluid-structure interaction. Attention is paid to the behavior of sheet when flow velocity exceeds critical, flow velocity. With discretization, the sheet is modeled as a combination of mass less beam elements, springs and discrete mass particles, in which the mass of each particle and spring coefficients are calculated based on the beam model. Nonlinear fluid forces acting on the mass particles are formulated then coupled with equations of motions of structure. After that the behavior of large-amplitude vibration of cantilevered sheet is simulated using numerical computation, showing that Vibration of sheet grows into a limit cycle oscillation then becomes unstable with increasing flow velocity.

Fluid force acting on a circular cylinder oscillating in the streamwise direction in a cross flow was measured by forced oscillation test in a water tunnel under the condition of low reduced velocity and small cylinder amplitude. Added mass and added damping coefficients were calculated based on the measured dynamic drag. They reasonably explain the characteristics of the in-line oscillation such as soft oscillator in the 1st excitation region and hysteresis in the 2nd excitation region. The mean drag coefficient and dynamic lift coefficient attain to their maximum at the reduced velocity between the 1st and 2nd excitation region where the added damping coefficient has its local maximum. It suggests that the increase of the mean drag coefficient induced by the formation of alternate vortices magnifies fluid damping effect and it contributes to the damping region between the 1st and 2nd excitation region.

Recently, much attention is paid to foil bearings for micro gas turbine use because these bearings are indispensable elements for realizing maintenance free small size gas turbines. We designed and manufactured a small size radial and thrust foil bearing for the shaft the size of which is 20mm in diameter. In this test apparaturs, the shaft is equipped with radial turbine blades and is driven by compressed air. As a result, we succeeded to operate it at the speed of 60000rpm and measured vibration characteristics.

The flow-induced vibration for an annular leakage-flow system is studied theoretically and experimentally. The annular leakage-flow system consists of a fixed duct, a flexibly mounted inner cylinder allowed to move translationally and rotationally inside the duct, and a viscous fluid flow in the annular passage between the duct and the inner cylinder. A numerical method is developed to analyze the flutter instability of the flow-induced vibration of the inner cylinder. In the method, a critical flow rate is introduced to describe the flutter instability. The experiment on the annular leakage-flow-induced vibration is carried out, and a critical flow rate of the flutter instability is obtained for some annular leakage-flow systems with different passage increment ratios as well as the eccentricities. The calculated results are in good agreement with the experimental results. (C) 2002 Elsevier Science Ltd. All rights reserved.

This paper deals with a new countermeasure against wind-induced cable vibrations called "changing vibration modes method", in which growth of the unstable fundamental vibration mode is suppressed by dissipating vibration energy in higher mode generated by a permanent magnet installed near the lower end of the cable. In this paper, first, a parameter design method for "changing vibration modes method" is proposed and we showed its effectiveness by simulation results. Second, the proof that this countermeasure was effective against rain-wind induced vibration is demonstrated by trial application to an actual bridge.

Optical fiber cables constitute one the key elements supporting current information technology society. Recently, the price reduction is becoming competitive among optical fiber manufacturers. In order to meet such a need, the manufacturers are now trying to increase the operating process speed when they manufacture optical fiber cables. Under these circumstances, severe vibrations were observed on a fiber cable traveling at a high speed during coating process. This paper summarizes a case study concerning traveling optical fiber vibrations and the examination results on the mechanism of vibrations. First, we outline the characteristics of traveling cable vibrations, secondly, we explain the results of model cable vibration tests and finally, we describe the theory to clarify the mechanism of the traveling cable vibrations. In the analytical part, we start with the equation of motion of a traveling cable together with the effect of the fluid force due to the leakage flow induced in a coating dice. The effect of the leakage flow in a coating dice is formulated based on annular leakage flow theory developed by author's group where the effect of viscosity of the coating material on the instability is taken into account. Then, the equation of a traveling cable under the effect of the leakage flow at the supporting point is successfully formulated. Based on the linearized equation of motion for the traveling cable, eigenvalue analysis was performed which leads to instability criteria selecting dice configuration and the temperature of the coating material as parameters. Finally, calculated results were compared with test experimental results and discussion on the design parameters for the stable operation is made.

In order to suppress vibrations of stay cables in cable-stayed bridges, the authors developed a new vibration reduction method called "Changing vibration modes method" using a permanent magnet. With this method, growth of the unstable fundamental vibration mode is prevented by dissipating energy of higher stable modes. The authors have confirmed in former reports that the proposed method effectively reduces the self-induced cable vibrations by both theoretical analyses and wind tunnel tests and design method of the device was proposed. In this report, first, the design process of a prototype of a control device is described. Second, higher mode vibrations generated by the action of the device were confirmed from the results of free vibration tests. Finally, efficiency of the proposed countermeasure against rain-wind-induced vibrations of an actual cable is clarified.

In order to suppress vibrations of stay cables in cable-stayed bridges, the authors developed a new vibration reduction method called "Changing vibration modes method" using a permanent magnet. The authors have confirmed its effectiveness in former reports by both theoretical analyses and wind tunnel tests. In second report, the authors analyzed cable vibrations by taking account of only an unstable mode and clarified how the design parameters such as a gap and magnetic force affect the control efficiency. In this report, accuracy of the analysis is further improved by introducing the higher modes effects as an "equivalent aerodynamic damping". Then, a design procedure of the parameters is proposed on the basis of the improved analysis, and its validity is shown by wind tunnel test results.

It is known that flutter of a traveling sheet may occur during its manufacturing process under the influence of leakage flow between the traveling sheet and a guide. In order to avoid the quality defectiveness like wrinkle due to the unsteady phenomenon happening on the sheet, a nonlinear stability analysis of sheet subjected to a leakage flow are performed to study the behavior of sheet in this paper. Concretely, sheet is described as a model consisting of mass less beam elements, springs and discrete mass particles, in which the mass of each particle and spring coefficients are calculated based on the beam model. During the formulation of fluid dynamic forces, nonlinear terms are taken into account for simulation of large-amplitude vibration of sheet, showing the appearance of limit cycle vibration in high flow velocity.

In order to identify the mechanism of a swirling leakage flow induced turbo pump axial vibration, as a first step, we analyzed steady and unsteady pressure distribution along the conical narrow passage when the vibration of an elastically supported center body is excited. In this work, we applied leakage flow theory to the conical leakage path taking the effect of inlet flow boundary conditions in to account. Then, we made comparison between calculated and measured value and found that our proposed method of calculating steady and unsteady pressure gives reasonable result.

Vibrations of stay cables are often induced by wind because of their aerodynamic instability. They must be suppressed to prevent cable fatigue and to allay passenger fear. Although various countermeasures have been developed, totally effective one has not yet been established. The authors have proposed a new vibration reduction method called “Vibration modes changing method” using a permanent magnet. A magnet installed near the end of the cable changes the vibration modes passively by repeating motions of constraining and releasing cables. With this method, growth of the unstable fundamental vibration mode is prevented by dissipating energy of higher stable modes. Comparing with other methods, it is expected to improve low temperature characteristics, maintenance and manufacturing cost. Considering only unstable fundamental vibration modes, the vibration analyses were carried out taking account of gap effects. The results agree well with wind tunnel tests and the design conditions were obtained. © 2001, The Japan Society of Mechanical Engineers. All rights reserved.

This paper presents an analytical model for the self-excited sloshing due to the fluid discharge over a flexible weir, as observed in the cooling circuit of the French fast breeder reactor, Super-Phenix-1. To clarify the instability mechanism, we analyzed the case in which a rectangular reservoir was divided into an upstream and a downstream plenum by a flexible plate weir. The kinematic and dynamic effects of the discharged fluid on downstream plenum sloshing are discussed in details. Calculations are presented for the rectangular fluid-structure model with successively increasing fluid level difference between the upstream and downstream plenums, and the instability mechanism is examined. [S0094-9930(00)00302-4].

Self-excited oscillations of the structure coupled with inner fluid occurred in the insulation wall cooling system of the fast breeder reactor Super-Phenix-l (SPX-1) in France during test operations. In this system, lower temperature sodium going up along the inside of the main vessel in a feeding plenum brims over a cylindrical flexible weir shell and flows into a restitution plenum. It is reported that the self-excited oscillations were found to occur at the same natural frequency of the sloshing in the restitution plenum, the free surface of the fluid in both feeding and restitution plenums oscillated at large amplitudes, and the cylindrical shell was found to oscillate with an oval vibration mode instability. Such an instability is called a coupled sloshing mode. In this study, the authors analyzed and performed experiments on the instability of a multiple cylindrical structure system that has dual flexible weir shells. They measured self-excited oscillations changing various parameters such as discharge flow rate, difference of the liquid heights between feeding and restitution plenums, and so on. In the experiment, it was found that dual cylindrical shells oscillate in and out of phase with each other with an oval vibration mode under the specific conditions. Comparison between theoretically and experimentally obtained instability regions was made showing good agreement.

This paper presents an analytical model for the self-excited sloshing due to the fluid discharge over a flexible weir, as observed in the cooling circuit of the French fast breeder reactor, Super-Phenix-1. To clarify the instability mechanism, we analyzed the case in which an annular reservoir wad divided into an upstream and a downstream plenum by a flexible cylindrical weir. The kinematic and dynamic effects of the discharged fluid on downstream plenum sloshing are discussed in details. Calculations are presented for the cylindrical fluid-structure model with successively increasing fluid level difference between the upstream and downstream plenums, and the instability mechanism is examined. [S0094-9930(00)00901-X].

An analytical model for describing the effectiveness of a deepwater-type cylindrical tuned liquid damper (TLD) with a submerged net for suppressing horizontal vibration of structures is first proposed. In this study, we performed calculations to estimate the effectiveness of a deepwater-type cylindrical TLD based on a proposed dynamical model and compared with experimental results obtained by shaking table experiments and free oscillation tests. In particular, the effect of hydraulic resistance produced by a submerged net and the liquid depth ratio (the ratio of the liquid depth to the diameter of the cylindrical tank) are examined intensively. In the analysis, employing finite amplitude wave theory and Galerkin method in the case of cylindrical tank, we obtained hydrodynamic forces and the free surface elevations. Then, combining the hydrodynamic forces with the equation of motion of the structure, damped transient responses were calculated. The calculated results thus obtained were compared with the experimental results, by which the validity of the modeling methodology was confirmed. [S0094-9930(00)00101-3].

Pager sheet nutter observed in paper manufacturing machines is the subject of this work. To analyze the basic mechanism of the problem, we discuss the case where a sheet of paper with both ends cramped is fixed in the center of the channel and the airflow is running parallel to the sheet in a narrow passage between a rigid wall and a flexible sheet. The sheet is modeled as a beam like structure subjected to tension and FEM is employed to formulate the problem. To obtain fluctuating fluid force acting on the sheet, unsteady fluid dynamic analysis based on the leakage-flow approximation is applied. Combining FEM based structural equation together with fluctuating fluid force vector acting on each element, fluid-structure coupled vibration is analyzed and the characteristic equation determining the stability of the system is derived. Then, eigen-value analysis is performed to calculate the critical flow velocity and the frequency of the nutter. Comparison with experimental results show that unstable behavior of the sheet coupled with running flow can be predicted by the method of calculation proposed in this paper.

This research deals with the vibration of rotors containing liquid, such as rotors of washing machines with a fluid balancer, and is intended to predict the occurrence of self-excited vibration and to evaluate some other characteristics of these rotors by analysis. We developed an analytical method using the assumption of shallow-water sloshing to predict the motion of liquid contained in a whirling ring, and made some calculations for various whirling rates. These calculations confirmed the validity of the method, and yielded following results. (a)Not only major resonances, but also secondary resonances peculiar to nonlinear systems occur when multiples of the exciting frequency correspond to natural frequencies of sloshing. (b)There are some isolated waves(or solitons)near resonance points, and the number of solitons changes when whirling rates changes slightly.

Vibrations of stay cables are often induced by wind because of their aerodynamic instability. They must be suppressed to prevent cable fatigue and to allay passenger fear. Although various countermeasures have been developed, totally effective one has not yet been established. In this paper, the authors propose a new method using a permanent magnet. A magnet installed near the end of the cable changes the vibration modes passively by repeating motions of constraining and releasing cables. With this method, growth of the unstable fundamental vibration mode is prevented by dissipating energy of higher stable modes. Comparing with other methods, it is expected to improve low temperature characteristics, maintenance and manufacturing cost. After describing the principle, fundamental studies on energy transferring mechanism were carried out and it was verified that the lower modes energy is distributed to the higher modes when the cable is released from the magnet. The effectiveness of this method was confirmed by wind tunnel tests and numerical simulations. © 2000, The Japan Society of Mechanical Engineers. All rights reserved.

An analytical model for describing the effectiveness of deepwater-type tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed. TLD is a damping device for suppressing the vibration of long-period structures such as high-rise buildings, tall towers, the pylons of cable stayed bridges, and so on. The damping force is created by the hydrodynamic force caused by the sloshing of water contained in rectangular tanks located on top of such structures. In this study, we proposed the dynamical model for analyzing deepwater-type TLD (DTLD) where the liquid depth is deep compared with the length of the rectangular tank. In particular, the effect of hydraulic resistance produced by submerged nets installed in the tank is examined intensively. In the analysis of DTLD, employing finite amplitude wave theory, we obtained the hydrodynamic force and the dissipation energy by using Galerkin method, taking the effect of submerged nets into account. The calculated results thus obtained are compared with experimental results, by which the validity of the modeling methodology is confirmed. Finally, the case in which DTLD with nets is installed on an actual structure is investigated both theoretically and experimentally and the the performance of DTLD is illustrated.

An analytical model for describing the effectiveness of tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed Dissipation energy due to the liquid motion under sinusoidal excitations is calculated bused on nonlinear shallow water wave theory. In particular, the effects of hydraulic resistance produced by nets installed in a tank on the performance of TLDs are examined. The results of dissipation energy theoretically obtained are confirmed by experiments. To show the effectiveness of the proposed analytical model for TLD-structure interaction problems, the case in which TLD with nets is installed on top of a pylon of a cable-stayed bridge is described and the calculated results are compared with the actual experimental data. In the calculation, it is shown that the optimal damping factor, as is the case for tuned mass dumpers (TMD), can be produced by the nets, and the effectiveness of TLD with nets are demonstrated.

An analytical mode for the self-excited vibration of an overflow flexible weir as observed in the French demonstration fast breeder reactor, Super Phenix-1, is proposed. The instability condition was derived for the case in which the plate vibrates at the frequency of the downstream rank sloshing. In this analysis, the flexible plate weir is modeled as a simply supported-free-simply supported-clamped rectangular plate. Eigenfunction expansions were applied for analyzing both plate vibrations and the downstream rank sloshing. The effect of an overflow liquid is formulated based on the assumption that the momentum change due to the collision of apr overflow liquid partly transmitted to the pressure,ise on the free surface. As a result, the characteristic equation of the system yielding the theoretical stability boundary, ms obtained The stability boundary thus derived agreed well with experimental results.

In this study, the stability of annular Ieakage- flow- induced vibrations was investigated theoretically and experimentally for a translationally and rotationally coupled two- degree- of- freedom system. The critical flow rate was both theoretically and experimentally obtained as a function of the passage increment ratio and the eccentricity of the passage. A good agreement between the theoretical and experimental results was obtatined. It was discovered both theoretically and from the experiments that instability will occur in the case of a divergent passage: the eccentricity of the passage lowers the stability of the systems.

This study reports the stability of annular leakage-flow-induced vibrations. The pressure distribution of fluid between a fixed outer cylinder and a vibrating inner cylinder was obtained in the case of a translationally and rotationally coupled motion of the inner cylinder. The unsteady fluid force acting on the inner cylinder in the case of translational and rotational single-degree-of- freedom vibrations was then expressed in terms proportional to the acceleration, velocity, and displacement. Then the critical flow rate (at which stability was lost) was determined for an annular leakage-flow-induced vibration. Finally, the stability was investigated theoretically. It is known that instability will occur in the case of a divergent passage, but the critical flow rate depends on the passage increment in a limited range: the eccentricity of the passage and the pressure loss factor at the inlet of the passage lower the stability.