Updated on 2022/05/17

写真a

 
TAKEZAWA, Akihiro
 
Affiliation
Faculty of Science and Engineering, School of Fundamental Science and Engineering
Job title
Professor

Concurrent Post

  • Faculty of Science and Engineering   Graduate School of Fundamental Science and Engineering

Research Institute

  • 2020
    -
    2022

    理工学術院総合研究所   兼任研究員

Education

  • 2009.03
     
     

    博士(工学) 取得 京都大学  

  • 2003.04
    -
    2005.03

    Kyoto University   Graduate School of Engineering  

  • 1999.04
    -
    2003.03

    Kyoto University   Faculty of Engineering   School of Engineering Science  

Degree

  • 京都大学   博士(工学)

Research Experience

  • 2020.04
    -
    Now

    Waseda University

  • 2010.09
    -
    2020.03

    Hiroshima University   Graduate School of Engineering

  • 2009.08
    -
    2010.08

    Hiroshima University   Graduate School of Engineering

  • 2007.04
    -
    2009.07

    Hiroshima University   Graduate School of Engineering

  • 2005.04
    -
    2007.03

    ファナック株式会社

 

Research Areas

  • Control and system engineering

  • Mechanics of materials and materials

  • Manufacturing and production engineering

  • Machine elements and tribology

  • Design engineering

Research Interests

  • 積層造形

  • 構造最適化

Papers

  • Design optimization of functionally graded lattice infill total hip arthroplasty stem for stress shielding reduction

    J. Nomura, A. Takezawa, H. Zhang, M. Kitamura

    Proc. Inst. Mech. Eng. H   in press  2022  [Refereed]

    Authorship:Corresponding author

  • スパースモデリングを用いた構造物の設計形状における重要部位の抽出手法に関する研究

    本田 正徳, 目良 貢, 河村 力, 竹澤 晃弘, 北村 充

    日本機械学会論文集   in press  2022  [Refereed]

  • Numerical and Experimental Analysis of Additively Manufactured Particle Dampers at Low Frequencies

    Honghu Guo, Kazuo Ichikawa, Hiroyuki Sakai, Heng Zhang, Xiaopeng Zhang, Kenji Tsuruta, Kanjuro Makihara, Akihiro Takezawa

    Powder Technology   396B   696 - 709  2022.01  [Refereed]

    Authorship:Last author, Corresponding author

  • 動的問題における繊維強化複合材のトポロジー最適化

    野沢 修矢, Zhang Heng, 宇恵野 章, 柳原 一貴, 竹澤 晃弘

    日本機械学会論文集   87 ( 904 ) 21-00234  2021.12  [Refereed]

    Authorship:Last author, Corresponding author

  • Optimally Variable Density Lattice to Reduce Warping Thermal Distortion of Laser Powder Bed Fusion

    A. Takezawa, Q. Chen, A. C. To

    Additive Manufacturing   48B   102422  2021.12  [Refereed]

    Authorship:Lead author, Corresponding author

  • Topology optimization of composite macrostructure with multi-phase viscoelastic composite microstructures for enhanced structural damping

    H. Zhang, A. Takezawa, X. Ding, H. Guo, W. Ni, X. Zhang

    Composite Structures   278   114712  2021.12  [Refereed]

    Authorship:Corresponding author

  • Bi-material microstructural design of biodegradable composites using topology optimization

    H. Zhang, A. Takezawa, X. Ding, S. Xu, P. Duan, H. Li, H. Guo

    Materials & Design   209   109973  2021.11  [Refereed]

    Authorship:Corresponding author

    DOI

  • ラティス体積分率分布最適化と金属積層造形による傾斜機能構造体の温度分布設計

    宇惠野 章, Guo Honghu, 森豊 亮太, 竹澤 晃弘, 北村 充

    精密工学会誌   87   827 - 833  2021.10  [Refereed]

  • Island scanning pattern optimization for residual deformation mitigation in laser powder bed fusion via sequential inherent strain method and sensitivity analysis

    Q. Chen, H. Taylor, A. Takezawa, X. Liang, X. Jimenez, R. Wicker, A. C. To

    Additive Manufacturing   46   102116  2021.10  [Refereed]

    DOI

  • Topology optimization of degradable composite structures with time‐changeable stiffness

    H. Zhang, A. Takezawa, X. Ding, S. Xu, H. Li, H. Guo

    International Journal for Numerical Methods in Engineering   122 ( 17 ) 4751 - 4773  2021.09  [Refereed]

    Authorship:Corresponding author

    DOI

  • 高強度・薄板中空フレーム曲げ強度の質量効率を向上させる断面形状の研究

    本田 正徳, 河村 力, 竹澤 晃弘, 北村 充

    日本機械学会論文集   87   21-00096  2021.08  [Refereed]

  • Temperature Distribution Design Based on Variable Lattice Density Optimization and Metal Additive Manufacturing

    A. Ueno, H. Guo, A. Takezawa, R. Moritoyo, M. Kitamura

    Symmetry   13 ( 7 ) 1194  2021.07  [Refereed]  [Invited]

    Authorship:Corresponding author

     View Summary

    Additive manufacturing (AM) is employed for fabricating industrial products with complex geometries. As topological optimization is suitable for designing complex geometries, studies have combined AM and topological optimization, evaluating the density optimization of lattice structures as a variant of topological optimization. The lattice structures of components fabricated via AM comprise voids. Models designed using topological optimization should be modified to ensure structures suitable for AM. As the lattice unit can be easily fabricated using AM with fewer design modifications, this study uses lattice density optimization for an industrial AM product. We propose a method of optimizing the lattice distribution for controlling the surface temperature uniformity of industrial products, such as molds. The effective thermal conductivity of the lattice is calculated using the homogenization and finite element methods. The effective thermal conductivity changes depending on the internal pore sizes. The proposed methodology is validated using a 3D example; the minimization problem of surface temperature variations in the target domain is considered. The variable density of the embedded lattice in the target domain is optimized, and we experimentally validated the performance of the lattice unit cell and optimal 3D structure using metal powder bed fusion AM.

    DOI

  • Construction of Design Guidelines for Optimal Automotive Frame Shape Based on Statistical Approach and Mechanical Analysis

    M. Honda, C. Kawamura, I. Kizaki, Y. Miyajima, A. Takezawa, M. Kitamura

    Computer Modeling in Engineering & Sciences   128 ( 2 ) 731 - 742  2021.07  [Refereed]

    Authorship:Corresponding author

    DOI

  • Study on damping performance for granular damper using fine particles

      87 ( 896 ) 20-00389  2021.04  [Refereed]

    DOI

  • Mechanical behavior of in-situ alloyed Ti6Al4V(ELI)-3 at.% Cu lattice structures manufactured by laser powder bed fusion and designed for implant applications

    A. M. Vilardell, A. Takezawa, A. du Plessis, N. Takata, P. Krakhmalev, M. Kobashi, M. Albu, G. Kothleitner, I. Yadroitsava, I. Yadroitsev

    Journal of the Mechanical Behavior of Biomedical Materials   113   104130 - 104130  2021.01  [Refereed]

    DOI

  • Sensitivity analysis and lattice density optimization for sequential inherent strain method used in additive manufacturing process

    A. Takezawa, A. C. To, Q. Chen, X. Liang, F. Dugast, X. Zhang, M. Kitamura

    Computer Methods in Applied Mechanics and Engineering   370   113231  2020.10  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Method to systemically order welding sequence to efficiently mitigate welding displacement of a general ship grillage structure

    D. Woo, M. Kitamura, A. Takezawa

    Ships and Offshore Structures   15 ( 7 ) 753 - 768  2020.08  [Refereed]

    Authorship:Last author

    DOI

  • アディティブマニュファクチャリングによる最適化構造の創製

    竹澤晃弘

    精密工学会誌   86 ( 6 ) 405 - 408  2020.06  [Invited]

    Authorship:Lead author, Corresponding author

  • Systematic method for positioning clamps and strongbacks based on their influence on welding displacements

    D. Woo, M. Kitamura, A. Takezawa

    Ocean Engineering   202   107084 - 107084  2020.04  [Refereed]

    Authorship:Last author

    DOI

  • Finite element simulation of the compressive response of additively manufactured lattice structures with large diameters

    H. Guo, A. Takezawa, M. Honda, C. Kawamura, M. Kitamura

    Computational Materials Science   175   109610  2020.04  [Refereed]

    Authorship:Corresponding author

    DOI

  • Topology optimisation of a porous unit cell in a fluid flow considering Forchheimer drag

    A. Takezawa, X. Zhang, T. Tanaka, M. Kitamura

    International Journal of Computational Fluid Dynamics   34 ( 1 ) 50 - 60  2020.01  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Compressive Behaviors of 3-D Additive Manufactured Shock Absorption Material

    Satou Yasutaka, Otsuki Masatsugu, Baba Mitsuhisa, Tobe Hirobumi, Ishimura Kosei, Kitazono Koichi, Takezawa Akihiro

    JOURNAL OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES   67 ( 6 ) 218 - 224  2019.12  [Refereed]

    Authorship:Last author

     View Summary

    <p>This paper addresses shock absorption behavior of 3-D additive manufactured truncated octahedron for the landing gear of lunar and planetary explores. The deformation modes of truncated octahedron were predicted by the form finding analyses. The collapse load of each deformation load was calculated by the plastic hinge theory. The predicted load--displacement curve agreed with the experimental results, and thus, the proposed prediction method was verified. </p>

    DOI CiNii

  • Optimization of an Additively Manufactured Functionally Graded Lattice Structure with Liquid Cooling Considering Structural Performances

    A. Takezawa, X. Zhang, M. Kitamura

    International Journal of Heat and Mass Transfer   143C   118564  2019.11  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • 金属3Dプリンティングにおけるトポロジー最適化の活用法

    竹澤晃弘

    機械技術   67   28 - 33  2019.11  [Invited]

    Authorship:Lead author, Corresponding author

  • Topology optimization and characterization of Ti6Al4V ELI cellular lattice structures by laser powder bed fusion for biomedical applications.

    A. M. Vilardell, A. Takezawa, A. du Plessis, N. Takata, P. Krakhmalev, M. Kobashi, I. Yadroitsava, I. Yadroitse

    Materials Science and Engineering: A   766   138330  2019.10  [Refereed]

    DOI

  • トポロジー最適化と金属AM を用いた冷却ラティス構造の開発

    竹澤晃弘

    砥粒加工学会誌   63 ( 7 ) 353 - 356  2019.10  [Invited]

    Authorship:Lead author, Corresponding author

  • Method to Optimize an Additively-Manufactured Functionally-Graded Lattice Structure for Effective Liquid Cooling

    A. Takezawa, X. Zhang, M. Kato, M. Kitamura

    Additive Manufacturing   28   285 - 298  2019.08  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Structural optimization of stiffener layout for stiffened plate using hybrid GA

    G. L. Putra, M. Kitamura, A. Takezawa

    International Journal of Naval Architecture and Ocean Engineering   11   809 - 818  2019.07  [Refereed]

    Authorship:Last author

    DOI

  • A phase-field based robust topology optimization method for phononic crystals design considering uncertain diffuse regions

    X. Zhang, A. Takezawa, Z. Kang

    Computational Materials Science   160   159 - 172  2019.04  [Refereed]

    Authorship:Corresponding author

    DOI

  • An objective function for the topology optimization of sound-absorbing materials

    A. Takezawa, T. Yamamoto, X. Zhang, K. Yamakawa, S. Nakano, M. Kitamura

    Journal of Sound and Vibration   443   804 - 819  2019.03  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Numerical study on the effective stiffness of topology-optimized lattice structures made of orthotropic crystal grains with optimal orientation

    A. Takezawa, X. Zhang, Y. Koizumi

    Computational Materials Science   159   202 - 209  2019.03  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    © 2018 Elsevier B.V. Controlling the orientation of crystal grains in metal additive manufacturing is an active field of research. Assuming that three-dimensional control of orthotropic metal crystal grain can be achieved, we numerically studied the effective performance of a topology-optimized lattice made of crystal grains with optimal directions in orientation. The objective function is maximized for an effective isotropic stiffness. The effective properties of the lattice are calculated using the homogenization method. Each discretized finite element is regarded as a crystal grain and its artificial density and orientation are optimized. Through several numerical studies using a single orthotropic crystal of Ni exhibiting large anisotropy in its single crystal stiffness, the optimization and the usefulness of the lattice structure composed of optimal orientation crystal grains is confirmed. In the design of a lattice with effective isotropic stiffness, an improvement in stiffness was observed compared with that using equivalent isotropic Ni as a material.

    DOI

  • Robust topology optimization of vibrating structures considering random diffuse regions via a phase-field method

    X. Zhang, A. Takezawa, Z. Kang

    Computer Methods in Applied Mechanics and Engineering   344   766 - 797  2019.02  [Refereed]

    Authorship:Corresponding author

    DOI

  • Study on sliding-window length based on Rayleigh backscattering spectrum correlation in distributed optical-fiber strain measurement

    L. Suo, Z. Lei, S. Zhao, Z. Wu, A. Takezawa

    Optical Fiber Technology   47   126 - 132  2019.01  [Refereed]

    Authorship:Last author

    DOI

  • Reliability-Guided Rayleigh Backscattering Spectrum Correlation Method for Distributed Strain Measurements in Optical Fibers

    L. Suo, Z. Lei, S. Zhao, Z. Wu, A. Takezawa

    Journal of Modern Optics   66   512 - 520  2019.01  [Refereed]

    Authorship:Last author

    DOI

  • Two-stage layout–size optimization method for prow stiffeners

    Z. Liu, S. Cho, A. Takezawa, X. Zhang, M. Kitamura

    International Journal of Naval Architecture and Ocean Engineering   11   44 - 51  2019.01  [Refereed]

    Authorship:Corresponding author

     View Summary

    Designing sophisticate ship structures that satisfy several design criteria simultaneously with minimum weight and cost is an important engineering issue. For a ship structure composed of a shell and stiffeners, this issue is more serious because their mutual effect has to be addressed. In this study, a two-stage optimization method is proposed for the conceptual design of stiffeners in a ship's prow. In the first stage, a topology optimization method is used to determine a potential stiffener distribution based on the optimal results, whereupon stiffeners are constructed according to stiffener generative theory and the material distribution. In the second stage, size optimization is conducted to optimize the plate and stiffener sections simultaneously based on a parametric model. A final analysis model of the ship-prow structure is presented to assess the validity of this method. The analysis results show that the two-stage optimization method is effective for stiffener conceptual design, which provides a reference for designing actual stiffeners for ship hulls.

    DOI

  • トポロジー最適化と金属積層造形の金型開発への応用

    竹澤晃弘

    ぷらすとす   1 ( 11 ) 758 - 762  2018.08  [Invited]

    Authorship:Lead author, Corresponding author

  • Isotropic Ti–6Al–4V lattice via topology optimization and electron-beam melting

    A. Takezawa, K. Yonekura, Y. Koizumi, X. Zhang, M. Kitamura

    Additive Manufacturing   22   634 - 642  2018.08  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    © 2018 Elsevier B.V. Electron-beam melting (EBM) exhibits advantages over other metal-additive manufacturing techniques owing to its low residual stress, rapid fabrication speed, and high energy efficiency. However, in EBM, metal powder is preheated and sintered to stabilize the temperature gradient and powder position during melting with a high-power electron beam. When making a lattice structure by EBM, a certain size of the powder-removing hole is required to remove the sintered remaining metal powder from the lattice. However, a large powder-removing hole can reduce the lattice mechanical performance. We conducted topology optimization to derive an optimal lattice structure shape with high isotropic stiffness assuming fabrication by EBM and minimizing the performance reduction owing to fixed large powder-removing holes. The optimized structure was fabricated via the EBM of a Ti–6Al–4V alloy. The optimal lattice structure achieved 83% of the performance of the Hashin–Shtrikman upper bound in numerical simulations, but an approximate 20% stiffness reduction was observed in the experiments. The isotropy was high with an error in Young's modulus and a strength of less than 9% and 6%, respectively. These results are discussed based on numerical and experimental results.

    DOI

  • Topology optimization of piezoelectric smart structures for minimum energy consumption under active control

    X. Zhang, A. Takezawa, Z. Kang

    Structural and Multidisciplinary Optimization   58 ( 1 ) 185 - 199  2018.07  [Refereed]

     View Summary

    This paper investigates topology optimization of the electrode coverage over piezoelectric patches attached to a thin-shell structure to reduce the energy consumption of active vibration control under harmonic excitations. The constant gain velocity feedback control method is employed, and the structural frequency response under control is analyzed with the finite element method. In the mathematical formulation of the proposed topology optimization model, the total energy consumption of the control system is taken as the objective function, and a constraint of the maximum allowable dynamic compliance is considered. The pseudo-densities indicating the distribution of surface electrode coverage over the piezoelectric layers are chosen as the design variables, and a penalized model is employed to relate the active damping effect and these design variables. The sensitivity analysis scheme of the control energy consumption with respect to the design variables is derived with the adjoint-variable method. Numerical examples demonstrate that the proposed optimization model is able to generate optimal topologies of electrode coverage over the piezoelectric layers, which can effectively reduce the energy consumption of the control system. Also, numerical comparisons with a minimum-volume optimization model show the advantage of the proposed method with respect to energy consumption. The proposed method may provide useful guidance to the layout optimization of piezoelectric smart structures where the energy supply is limited, such as miniature vibration control systems.

    DOI

  • Current and future trends in topology optimization for additive manufacturing

    J. Liu, A. T. Gaynor, S. Chen, Z. Kang, K. Suresh, A. Takezawa, L. Li, J. Kato, J. Tang, C. C. L. Wang, L. Cheng, X. Liang, A. C. To

    Structural and Multidisciplinary Optimization   57 ( 6 ) 2457 - 2483  2018.06  [Refereed]

     View Summary

    Manufacturing-oriented topology optimization has been extensively studied the past two decades, in particular for the conventional manufacturing methods, for example, machining and injection molding or casting. Both design and manufacturing engineers have benefited from these efforts because of the close-to-optimal and friendly-to-manufacture design solutions. Recently, additive manufacturing (AM) has received significant attention from both academia and industry. AM is characterized by producing geometrically complex components layer-by-layer, and greatly reduces the geometric complexity restrictions imposed on topology optimization by conventional manufacturing. In other words, AM can make near-full use of the freeform structural evolution of topology optimization. Even so, new rules and restrictions emerge due to the diverse and intricate AM processes, which should be carefully addressed when developing the AM-specific topology optimization algorithms. Therefore, the motivation of this perspective paper is to summarize the state-of-art topology optimization methods for a variety of AM topics. At the same time, this paper also expresses the authors’ perspectives on the challenges and opportunities in these topics. The hope is to inspire both researchers and engineers to meet these challenges with innovative solutions.

    DOI

  • Inverse analysis of giant macroscopic negative thermal expansion of Ca2RuO4%y ceramics based on elasticity and structural topology optimization

    A. Takezawa, K. Takenaka, X. Zhang

    Applied Physics Express   11 ( 5 ) 055801  2018.05  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    Ca2RuO4%y ceramics exhibit a large volumetric negative thermal expansions (NTE), although the crystallographic volume contraction on heating is much smaller than the NTE. Therefore, we examine the differences in the mechanisms underlying the volumetric thermal expansion for ruthenate ceramics and crystals in the context of the elasticity. We identify the possible microstructure of ruthenate ceramics composed of crystal grains and cavities using structural topology optimization. We conclude that the measured large volumetric NTE of ruthenate ceramics is certainly possible via anisotropic crystallographic thermal expansion through an elastic mechanism.

    DOI

  • Robust topology optimization of phononic crystals with random field uncertainty

    X. Zhang, J. He, Z. Kang, A. Takezawa

    International Journal for Numerical Methods in Engineering   115   1154 - 1173  2018.05  [Refereed]

    Authorship:Last author, Corresponding author

    DOI

  • Design methodology of magnetic fields and structures for magneto-mechanical resonator based on topology optimization

    A. Takezawa, J. Lee, M. Kitamura

    Optimization and Engineering   19 ( 1 ) 19 - 38  2018.03  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    Magneto-mechanical resonators—magnetically-driven vibration devices—are used in many mechanical and electrical devices. We develop topology optimization (TO) to configure the magnetic fields of such resonators to enable large vibrations under specified current input to be attained. A dynamic magneto-mechanical analysis in the frequency domain is considered where we introduce the surface magnetic force calculated from the Maxwell stress tensor. The optimization problem is then formulated involving specifically the maximization of the dynamic compliance. This formulation is implemented using the solid-isotropic-material-with-penalization method for TO by taking into account the relative permeability, Young’s modulus, and the mass density of the magnetic material as functions of the density function. Through the 2D numerical studies, we confirm that this TO method works well in designing magnetic field patterns and providing matching between the external current frequency and eigenfrequency of the vibrating structure.

    DOI

  • Lattice structure design with topology optimization and additive manufacturing

    Takafumi Nishizu, Tomoya Tanitsugu, Akihiro Takezawa, Kazuo Yonekura, OsamuWatanabe, Mitsuru Kitamura

    Transactions of the JSME   83 ( 855 )  2017.12  [Refereed]

    DOI

  • Design methodology for porous composites with tunable thermal expansion produced by multi-material topology optimization and additive manufacturing

    A. Takezawa, M. Kobashi

    Composites Part B: Engineering   131   21 - 29  2017.12  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    To realize negative thermal expansion (NTE), porous composites made of two materials with different coefficients of thermal expansion are being actively researched. NTE can be realized by taking advantage of the thermal deformation mechanisms of a composite material's internal geometry. However, in addition to negative thermal expansion, materials with anisotropic and large positive thermal expansion are also desirable for various applications. Also, additive manufacturing provides new ways to fabricate composites by layering multiple materials at arbitrary points in three-dimensional space. In this study, we developed a design methodology for porous composites, which showed defined thermal expansion characteristics, including negative and positive thermal expansion as well as isotropic and anisotropic thermal expansion. Our approach was tested based on the fabrication of a multi-material photopolymer by additive manufacturing. The internal geometries required to produce such characteristics were designed by topology optimization, which is the most effective structural optimization method for realizing macroscopic inward deformation and for maintaining stiffness. The designed structures were converted to three-dimensional models and fabricated by multi-material photopolymer additive manufacturing. Using laser scanning dilatometry, we measured the thermal expansion of these specimens, revealing well-ordered thermal expansion, from anisotropic positive thermal expansion to anisotropic negative thermal expansion, over a wide range of about -3 x 10(-4) K-1 to 1 x 10(-3) K-1. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI

  • High-stiffness and strength porous maraging steel via topology optimization and selective laser melting

    A. Takezawa, Y. Koizumi, M. Kobashi

    Additive Manufacturing   18   194 - 202  2017.12  [Refereed]

     View Summary

    © 2017 Elsevier B.V. Recent additive manufacturing technologies can be used to fabricate porous metals with precise internal pore structures and effective performance. We use topology optimization to derive an optimal pore structure shape with high stiffness that is verified experimentally. The design maximizes the effective bulk modulus and isotropic stiffness, and the performance is compared with Hashin–Shtrikman (HS) bounds. The optimized structure is fabricated via selective laser melting of maraging steel, which is a high-strength, iron-nickel steel that cannot easily be made porous with conventional methods. The optimal porous structure achieved 85% of the performance of the HS upper bound in numerical simulations, and at least 90% of them were realized in compressive testing. Finally, the performance is discussed relative to that of other metals.

    DOI

  • ここまできたCAE 第5回 最適設計

    竹澤晃弘

    KANRIN   72   45 - 48  2017.05  [Invited]

    Authorship:Lead author, Corresponding author

  • AM 技術を活かすトポロジー最適化

    竹澤晃弘

    スマートプロセス学会誌   6 ( 3 ) 119 - 124  2017.05  [Refereed]  [Invited]

    Authorship:Lead author, Corresponding author

  • Eigenfrequecy-based damage identification method for non-destructive testing based on topology optimization

    T. Nishizu, A. Takezawa, M. Kitamura

    Engineering Optimization   49 ( 3 ) 417 - 433  2017.03  [Refereed]

    Authorship:Corresponding author

     View Summary

    Non-destructive testing (NDT) detects damage according to a difference in a physical phenomenon between a normal structure and damaged structure. As a solution avoiding human errors in NDT, a numerical method based on a dynamical numerical analysis model and a structural optimization algorithm was proposed. This method automatically derives a structure with a response that is equal to that of a damaged structure through an optimization procedure. Among structural optimization methods, topology optimization can optimize the structure fundamentally by changing the topology and not just the shape of a structure. Thus, topology optimization is employed together with eigenfrequency analysis, which is the most fundamental methodology of NDT. The proposed method derives a structure that has the same eigenfrequencies as a damaged structure employing topology optimization. The shape and location of damage can be identified through the optimal shape obtained.

    DOI

  • Porous metal produced by selective laser melting with effective isotropic thermal conductivity close to the Hashin-Shtrikman bound

    A. Takezawa, M. Kobashi, Y. Koizumi, M. Kitamura

    International Journal of Heat and Mass Transfer   105   564 - 572  2017.02  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    Additive manufacturing may be a novel method for fabricating porous materials. These materials can achieve effective performance because of their internal geometries. Metal-additive manufacturing is expected to utilize thermal conduction materials and devices. We have developed a porous metal with effective isotropic thermal conductivity by using metal-selective laser melting additive manufacturing. The internal pore structure was designed by topology optimization, which is the most effective structural optimization technique to maximize effective thermal conductivity. The designed structure was converted to a three-dimensional STL model, which is a native digital format of additive manufacturing, and assembled as a test piece. Effective thermal conductivity was measured by a steady-state method in which the effective thermal conductivity was calculated from a one-dimensional temperature gradient and the heat flux of the test pieces. The test pieces showed an effective thermal conductivity close to the Hashin-Shtrikman or Maxwell-Eucken bound, which is the theoretical limit of effective performance with an error less than 10%. (C) 2016 Elsevier Ltd. All rights reserved.

    DOI

  • Cellular lattices of biomedical Co-Cr-Mo-alloy fabricated by electron beam melting with the aid of shape optimization

    Yuichiro Koizumi, Arata Okazaki, Akihiko Chiba, Takahiko Kato, Akihiro Takezawa

    Additive Manufacturing   12   305 - 313  2016.10  [Refereed]

     View Summary

    © 2016 Elsevier B.V. With a view to developing a highly biocompatible and highly reliable material for artificial hip joints, cellular lattice structures with high strength and low Young's modulus (E) were designed using computational shape optimization. These structures were fabricated from a biomedical Co-Cr-Mo alloy via electron beam melting. As a starting point for shape optimization, inverse body-centered-cubic (iBCC)-based structures with different porosities and aspects were fabricated. The strength tended to increase with increasing E. Then, the structures were re-designed using shape optimization based on the traction method, targeting a simultaneous increase in yield strength with retention of the low E. The shapes were optimized through minimization of the maximum local von Mises stress and control of E to 3/2 or 2/3 of the original value, while maintaining constant porosity. The re-designed cellular structures were fabricated and subjected to mechanical testing. The E values of the porous structures were comparable to the design values, but the strength of the cellular lattice with E = 2/3 (design value) was lower than expected. This discrepancy was attributed to inhomogeneities in the microstructures and their impact on the lattice mechanical properties. Thus, shape optimization considering crystal orientation is a significant challenge for future research, but this approach has considerable potential.

    DOI

  • 振動ハーベスティングにおける発電エネルギ増加制御の研究

    槙原幹十朗, 吉水謙司, 竹澤晃弘

    日本機械学会論文集   82 ( 835 ) Article No. 15-00499  2016.03  [Refereed]

    DOI

  • Topology optimization of damping material for reducing resonance response based on complex dynamic compliance

    Akihiro Takezawa, Masafumi Daifuku, Youhei Nakano, Kohya Nakagawa, Takashi Yamamoto, Mitsuru Kitamura

    JOURNAL OF SOUND AND VIBRATION   365   230 - 243  2016.03  [Refereed]

     View Summary

    In this research, we propose a new objective function for optimizing damping materials to reduce the resonance peak response in the frequency response problem, which cannot be achieved using existing criteria. The dynamic compliance in the frequency response problem is formulated as the scalar product of the conjugate transpose of the amplitude vector and the force vector of the loading nodes. The proposed objective function methodology is implemented using the common solid isotropic material with penalization (SIMP) method for topology optimization. The optimization problem is formulated as maximizing the complex part of the proposed complex dynamic compliance under a volume constraint. 2D and 3D numerical examples of optimizing the distribution of the damping material on the host structure are provided to illustrate the validity and utility of the proposed methodology. In these numerical studies, the proposed objective function worked well for reducing the response peak in both lower and upper excitation frequencies around the resonance. By adjusting the excitation frequency, multi-resonance peak reduction may be achieved with a single frequency excitation optimization. (C) 2015 Elsevier Ltd. All rights reserved.

    DOI

  • Design methodology using topology optimization for anti-vibration reinforcement of generators in a ship's engine room

    Masafumi Daifuku, Takafumi Nishizu, Akihiro Takezawa, Mitsuru Kitamura, Haruki Terashita, Yasuaki Ohtsuki

    PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART M-JOURNAL OF ENGINEERING FOR THE MARITIME ENVIRONMENT   230 ( 1 ) 216 - 226  2016.02  [Refereed]

     View Summary

    Structural optimization for reinforcing the anti-vibration characteristics of the generators in the engine room of a ship is presented. To improve the vibration characteristics of the structures, topology optimization methods can be effective because they can optimize the fundamental characteristics of the structure with their ability to change the topology of the target structure. Topology optimization is used to improve the characteristics of the anti-vibration reinforcement of the generators in the engine room. First, an experimentally observed vibration phenomenon is simulated using the finite element method for frequency response problems. Next, the objective function used in topology optimization is set as the dynamic work done by the load based on the energy equilibrium of the structural vibration. The optimization problem is then constructed by adding the volume constraint. Finally, based on finite element analysis and the optimization problem, topology optimization is performed on several vibration cases to improve their performance and reduce weight.

    DOI

  • Optimization of Ship Structure Considering Stiffener Layout

    Ryouta Nonami, Mitsuru Kitamura, Akihiro Takezawa, Shinichi Hirakawa

    Journal of the Japan Society of Naval Architects and Ocean Engineers   22   129 - 135  2015.12  [Refereed]

    DOI

  • Structural optimization of the large structure with stiffeners by hybrid genetic algorithms

    Ryouta Nonami, Mitsuru Kitamura, Akihiro Takezawa

    Transactions of the Japan Society of Mechanical Engineers   81 ( 832 ) 15-00437  2015.11  [Refereed]

    DOI CiNii

  • エネルギー回生式セミアクティブ振動制御装置に対するSRS制約を導入した圧電アクチュエータ最適配置

    中野陽平, 竹澤晃弘, 槙原幹十朗, 北村充

    日本機械学会論文集   81 ( 830 ) Article No. 15-00191  2015.10  [Refereed]

    Authorship:Corresponding author

    DOI

  • Stiffness maximization for thermal deformation under thermal conductivity constraint using topology optimization

    Takafumi NISHIZU, Akihiro TAKEZAWA, Mitsuru KITAMURA

    Transactions of the JSME   81 ( 828 )  2015.08  [Refereed]

    DOI CiNii

  • Porous composite with negative thermal expansion obtained by photopolymer additive manufacturing

    Akihiro Takezawa, Makoto Kobashi, Mitsuru Kitamura

    APL MATERIALS   3 ( 7 ) 076103 (6 pages)  2015.07  [Refereed]

    Authorship:Lead author, Corresponding author

     View Summary

    Additive manufacturing (AM) could be a novel method of fabricating composite and porous materials having various effective performances based on mechanisms of their internal geometries. Materials fabricated by AM could rapidly be used in industrial application since they could easily be embedded in the target part employing the same AM process used for the bulk material. Furthermore, multi-material AM has greater potential than usual single-material AM in producing materials with effective properties. Negative thermal expansion is a representative effective material property realized by designing a composite made of two materials with different coefficients of thermal expansion. In this study, we developed a porous composite having planar negative thermal expansion by employing multi-material photopolymer AM. After measurement of the physical properties of bulk photopolymers, the internal geometry was designed by topology optimization, which is the most effective structural optimization in terms of both minimizing thermal stress and maximizing stiffness. The designed structure was converted to a three-dimensional stereolithography (STL) model, which is a native digital format of AM, and assembled as a test piece. The thermal expansions of the specimens were measured using a laser scanning dilatometer. Negative thermal expansion corresponding to less than -1 x 10(-4) K-1 was observed for each test piece of the N = 3 experiment. (C) 2015 Author(s).

    DOI

  • Power evaluation of advanced energy-harvester using graphical analysis

    K. Makihara, A. Takezawa, D. Sigeta, Y. Yamamoto

    Mechanical Engineering Journal   2   14-00444 (12 pages)  2015.07  [Refereed]

    DOI

  • Cross-Sectional Optimization of Whispering-Gallery Mode Sensor With High Electric Field Intensity in the Detection Domain

    Akihiro Takezawa, Masanobu Haraguchi, Toshihiro Okamoto, Mitsuru Kitamura

    IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS   20 ( 6 ) 5300110 (10 pages)  2014.11  [Refereed]

     View Summary

    Optimal cross-sectional shapes for whispering-gallery mode sensors with prescribed emission wavelengths and resonance modes are generated through topology optimization based on the finite element method. The sensor is assumed to detect the state of the domain surrounded by the sensor. We identified the integral of the square of the electric field intensity over the detection domain and the quality factor (Q factor), which should be maximized, as key values for the sensor sensitivity, representing the detection limit for the relative permittivity change of the test object. Based on this, the integral of the square of the electric field intensity over the detection domain and the Q factor are studied as the optimization targets. In our numerical study, their optimal configuration characteristics are identified and analyzed. The resulting device has a small radius, a small detection domain and a concave shape with a center located next to the detection domain. We also succeeded in performing simultaneous optimization of the integral of the square of the electric field intensity over the detection domain and the Q factor.

    DOI

  • トポロジー最適化と金属3D プリンタを用いたポーラス材料の設計・製造

    竹澤晃弘

    日本機械学会誌   117   697  2014.10  [Invited]

    Authorship:Lead author, Corresponding author

  • Structural topology optimization with strength and heat conduction constraints

    Akihiro Takezawa, Gil Ho Yoon, Seung Hyun Jeong, Makoto Kobashi, Mitsuru Kitamura

    COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING   276   341 - 361  2014.07  [Refereed]

     View Summary

    In this research, a topology optimization with constraints of structural strength and thermal conductivity is proposed. The coupled static linear elastic and heat conduction equations of state are considered. The optimization problem was formulated; viz., minimizing the volume under the constraints of p-norm stress and thermal compliance introducing the qp-relaxation method to avoid the singularity of stress-constraint topology optimization. The proposed optimization methodology is implemented employing the commonly used solid isotropic material with penalization (SIMP) method of topology optimization. The density function is updated using sequential linear programming (SLP) in the early stage of optimization. In the latter stage of optimization, the phase field method is employed to update the density function and obtain clear optimal shapes without intermediate densities. Numerical examples are provided to illustrate the validity and utility of the proposed methodology. Through these numerical studies, the dependency of the optima to the target temperature range due to the thermal expansion is confirmed. The issue of stress concentration due to the thermal expansion problem in the use of the structure in a wide temperature range is also clarified, and resolved by introducing a multi-stress constraint corresponding to several thermal conditions. (C) 2014 Elsevier B.V. All rights reserved.

    DOI

  • Development of the beam and shell elements for stress evaluation of a joint of structural components

    Mitsuru Kitamura, Yoshifumi Ueshige, Akihiro Takezawa

    Journal of the Japan Society of Naval Architects and Ocean Engineers   19   111 - 121  2014.06  [Refereed]

    DOI

  • Smooth operators iron out engine room vibrations

    M. Daifuku, A. Takezawa, M. Kitamura, H. Terashita, Y. Ohtsuki

    The Naval Architect   February 2014   62 - 64  2014.02  [Invited]

    Authorship:Corresponding author

  • Development of a novel phase-field method for local stress-based shape and topology optimization

    Seung Hyun Jeong, Gil Ho Yoon, Akihiro Takezawa, Dong-Hoon Choi

    COMPUTERS & STRUCTURES   132   84 - 98  2014.02  [Refereed]

     View Summary

    This research develops a stress-based topology optimization method (STOM) using the phase-field method representing topological changes. This research shows that to apply the phase field method, regional and localized stress constraints should be addressed. Thus, we use an Augmented Lagrange multiplier approach for the stress constraints and present a new numerical solution for the Lagrange multipliers inside the Allen-Cahn equation with the topological derivatives. Through several two dimensional illustrative problems, the results of the phase-field method have larger objective values, but are robust from a stress point of view compared with the results of the STOM by the density method. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

  • Design methodology of piezoelectric energy-harvesting skin using topology optimization

    A. Takezawa, M. Kitamura, S. L. Vatanabe, E. C. N. Silva

    STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION   49 ( 2 ) 281 - 297  2014.02  [Refereed]

     View Summary

    This paper describes a design methodology for piezoelectric energy harvesters that thinly encapsulate the mechanical devices and exploit resonances from higher-order vibrational modes. The direction of polarization determines the sign of the piezoelectric tensor to avoid cancellations of electric fields from opposite polarizations in the same circuit. The resultant modified equations of state are solved by finite element method (FEM). Combining this method with the solid isotropic material with penalization (SIMP) method for piezoelectric material, we have developed an optimization methodology that optimizes the piezoelectric material layout and polarization direction. Updating the density function of the SIMP method is performed based on sensitivity analysis, the sequential linear programming on the early stage of the optimization, and the phase field method on the latter stage of the optimization to obtain clear optimal shapes without intermediate density. Numerical examples are provided that illustrate the validity and utility of the proposed method.

    DOI

  • Layout optimization methodology of piezoelectric transducers in energy-recycling semi-active vibration control systems

    Akihiro Takezawa, Kanjuro Makihara, Nozomu Kogiso, Mitsuru Kitamura

    JOURNAL OF SOUND AND VIBRATION   333 ( 2 ) 327 - 344  2014.01  [Refereed]

     View Summary

    An optimization methodology is proposed for the piezoelectric transducer (PZT) layout of an energy-recycling semi-active vibration control (ERSAVC) system for a space structure composed of trusses. Based on numerical optimization techniques, we intend to generate optimal location of PZTs under the constraint for the total length of PZTs. The design variables are set as the length of the PZT on each truss based on the concept of the ground structure approach. The transient problems of the mechanical and electrical vibrations based on the ERSAVC theory are considered as the equations of state. The objective is to minimize the integration of the square of all displacement over the whole analysis time domain. The sensitivity of the objective function is derived based on the adjoint variable method. Based on these formulations, an optimization algorithm is constructed using the fourth-order Runge-Kutta method and the method of moving asymptotes. Numerical examples are provided to illustrate the validity and utility of the proposed methodology. Using the proposed methodology, the optimal location of PZTs for the vibration suppression for multi-modal vibration is studied, which can be benchmark results of further study in the context of ERSAVC systems. (C) 2013 Elsevier Ltd. All rights reserved.

    DOI

  • Phase field method to optimize dielectric devices for electromagnetic wave propagation

    Akihiro Takezawa, Mitsuru Kitamura

    JOURNAL OF COMPUTATIONAL PHYSICS   257   216 - 240  2014.01  [Refereed]

     View Summary

    We discuss a phase field method for shape optimization in the context of electromagnetic wave propagation. The proposed method has the same functional capabilities as the level set method for shape optimization. The first advantage of the method is the simplicity of computation, since extra operations such as re-initialization of functions are not required. The second is compatibility with the topology optimization method due to the similar domain representation and the sensitivity analysis. Structural shapes are represented by the phase field function defined in the design domain, and this function is optimized by solving a time-dependent reaction diffusion equation. The artificial double-well potential function used in the equation is derived from sensitivity analysis. We study four types of 2D or 2.5D (axisymmetric) optimization problems. Two are the classical problems of photonic crystal design based on the Bloch theory and photonic crystal wave guide design, and two are the recent topics of designing dielectric left-handed metamaterials and dielectric ring resonators. (C) 2013 Elsevier Inc. All rights reserved.

    DOI

  • Enhancement of non-resonant dielectric cloaks using anisotropic composites

    Akihiro Takezawa, Mitsuru Kitamura

    AIP ADVANCES   4 ( 1 ) 017106 (10 pages)  2014.01  [Refereed]

     View Summary

    Cloaking techniques conceal objects by controlling the flow of electromagnetic waves to minimize scattering. Herein, the effectiveness of homogenized anisotropic materials in non-resonant dielectric multilayer cloaking is studied. Because existing multilayer cloaking by isotropic materials can be regarded as homogenous anisotropic cloaking from a macroscopic view, anisotropic materials can be efficiently designed through optimization of their physical properties. Anisotropic properties can be realized in two-phase composites if the physical properties of the material are within appropriate bounds. The optimized anisotropic physical properties are identified by a numerical optimization technique based on a full-wave simulation using the finite element method. The cloaking performance measured by the total scattering width is improved by about 2.8% and 25% in eight-and three-layer cylindrical cloaking materials, respectively, compared with multilayer cloaking by isotropic materials. In all cloaking examples, the optimized microstructures of the two-phase composites are identified as the simple lamination of two materials, which maximizes the anisotropy. The same performance as published for eight-layer cloaking by isotropic materials is achieved by three-layer cloaking using the anisotropic material. Cloaking with an approximately 50% reduction of total scattering width is achieved even in an octagonal object. Since the cloaking effect can be realized using just a few layers of the laminated anisotropic dielectric composite, this may have an advantage in the mass production of cloaking devices. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

    DOI

  • Damage identification in non-destructive testing based on topology optimization and eigenfrequency analysis

    T. Nishizu, A. Takezawa, M. Kitamura

    Journal of the Japan Society of Naval Architects and Ocean Engineers   18   73 - 80  2013.12  [Refereed]

     View Summary

    The non-destructive testing for detecting structural damage at the earliest possible stage is significant in the safe and long life operation of large marine structure such as ships. In the non-destructive testing, the variation in structural characteristics from the original one to the damaged one is used to identify the damage. Vibration characteristic is one of the most popular criteria used for it due to its sensitivity for the structural damage. In this paper, a damage identification method used in non-destructive testing is proposed based on topology optimization focusing on the difference of eigenfrequency between the original structure and the damaged one. Eigenfrequency analysis of a structure is considered. A inimization of the least squared error between the eigenfrequency of the damaged structure and the target eigenfrequency is set as an objective function. An optimization algorithm is constructed based on the topology optimization and the method of moving asymptotes (MMA). The validity and the usefulness of the proposed method is confirmed by several numerical examples.

    DOI CiNii

  • Sensitivity analysis and optimization of vibration modes in continuum systems

    Akihiro Takezawa, Mitsuru Kitamura

    JOURNAL OF SOUND AND VIBRATION   332 ( 6 ) 1553 - 1566  2013.03  [Refereed]

     View Summary

    The sensitivity analysis of objective functions including the eigenmodes of continuum systems governed by scalar Helmholtz equations is carried out in continuum form. In addition, based on the sensitivity, the mode shapes are specified through numerical optimization. Using the continuum sensitivity and adjoint equation, the physical nature of them can be analyzed, which helps to explain the nature of the target optimization problem. Moreover, the continuum sensitivity and adjoint equation contribute to the quick numerical implementation of sensitivity analysis using software that can solve an arbitrary partial differential equation directly. A scalar Helmholtz equation in 1D or 2D domain is considered. The sensitivity analysis is performed, for the general objective function formulated as a function of the eigenmode in continuum form. A minimization problem using the least squared error (i.e., difference) between the eigenvector and target mode shape is set as a sample objective function for both the first and second eigenmodes. The sensitivity and the adjoint equation are derived for this objective function. 1D and 2D numerical sensitivity analysis and optimization examples are studied to illustrate the validity of the derived sensitivity. (C) 2012 Elsevier Ltd. All rights reserved.

    DOI

  • Cross-Sectional Shape Optimization of Whispering-Gallery Ring Resonators

    Akihiro Takezawa, Mitsuru Kitamura

    JOURNAL OF LIGHTWAVE TECHNOLOGY   30 ( 17 ) 2776 - 2782  2012.09  [Refereed]

     View Summary

    Optimal cross-sectional shapes of whispering-gallery ring resonators with prescribed emission wavelength and resonance mode are generated using topology optimization based on the finite element method. The two critical performance indices, the quality factor (Q factor) and mode volume of a resonator, are treated as the objective functions in the optimization. In our numerical study, characteristics of optimal configurations are identified and analyzed. Since the Q factor and mode volume have a tradeoff relationship, i.e., an increasing Q factor increases mode volume, a Pareto-optimal set of solutions can be identified under certain device specifications. These configurations achieve better performances than existing shapes in producing both a high Q factor and low mode volume.

    DOI

  • Designing piezoresistive plate-based sensors with distribution of piezoresistive material using topology optimization

    L. A. M. Mello, A. Takezawa, E. C. N. Silva

    SMART MATERIALS AND STRUCTURES   21 ( 8 ) 085029 (13 pages)  2012.08  [Refereed]

     View Summary

    Piezoresistive sensors are commonly made of a piezoresistive membrane attached to a flexible substrate, a plate. They have been widely studied and used in several applications. It has been found that the size, position and geometry of the piezoresistive membrane may affect the performance of the sensors. Based on this remark, in this work, a topology optimization methodology for the design of piezoresistive plate-based sensors, for which both the piezoresistive membrane and the flexible substrate disposition can be optimized, is evaluated. Perfect coupling conditions between the substrate and the membrane based on the `layerwise' theory for laminated plates, and a material model for the piezoresistive membrane based on the solid isotropic material with penalization model, are employed. The design goal is to obtain the configuration of material that maximizes the sensor sensitivity to external loading, as well as the stiffness of the sensor to particular loads, which depend on the case (application) studied. The proposed approach is evaluated by studying two distinct examples: the optimization of an atomic force microscope probe and a pressure sensor. The results suggest that the performance of the sensors can be improved by using the proposed approach.

    DOI

  • Geometrical design of thermoelectric generators based on topology optimization

    A. Takezawa, M. Kitamura

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING   90 ( 11 ) 1363 - 1392  2012.06  [Refereed]

     View Summary

    This paper discusses an application of the topology optimization method for the design of thermoelectric generators. The proposed methodology provides the optimized geometry in accordance with various arbitrary conditions such as the types of materials, the volume of materials, and the temperature and shape of the installation position. By considering the coupled equations of state for the thermoelectric problem, we introduce an analytical model subject to these equations, which mimics the closed circuit composed of thermoelectric materials, electrodes, and a resistor. The total electric power applied to the resistor and the conversion efficiency are formulated as objective functions to be optimized. The proposed optimization method for thermoelectric generators is implemented as a geometrical optimization method using the solid isotropic material with penalization method used in topology optimizations. Simple relationships are formulated between the density function of the solid isotropic material with penalization method and the physical properties of the thermoelectric material. A sensitivity analysis for the objective functions is formulated with respect to the density function and the adjoint equations required for calculating it. Depending on the sensitivity, the density function is updated using the method of moving asymptotes. Finally, numerical examples are provided to demonstrate the validity of the proposed method. Copyright (C) 2012 John Wiley & Sons, Ltd.

    DOI

  • Topology optimization of compliant circular path mechanisms based on an aggregated linear system and singular value decomposition

    A. Takezawa, M. Kitamura

    INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING   89 ( 6 ) 706 - 725  2012.02  [Refereed]

     View Summary

    This paper proposes a topology optimization method for the design of compliant circular path mechanisms, or compliant mechanisms having a set of output displacement vectors with a constant norm, which is induced by a given set of input forces. To perform the optimization, a simple linear system composed of an input force vector, an output displacement vector and a matrix connecting them is constructed in the context of a discretized linear elasticity problem using FEM. By adding two constraints: 1, the dimensions of the input and the output vectors are equal; 2, the Euclidean norms of all local input force vectors are constant; from the singular value decomposition of the matrix connecting the input force vector and the output displacement vector, the optimization problem, which specifies and equalizes the norms of all output vectors, is formulated. It is a minimization problem of the weighted summation of the condition number of the matrix and the least square error of the second singular value and the specified value. This methodology is implemented as a topology optimization problem using the solid isotropic material with penalization method, sensitivity analysis and method of moving asymptotes. The numerical examples illustrate mechanically reasonable compliant circular path mechanisms and other mechanisms having multiple outputs with a constant norm. Copyright (C) 2011 John Wiley & Sons, Ltd.

    DOI

  • Shape Optimization System of Bottom Structure of Ship Incorporating Individual Mesh Subdivision and Multi-Point Constraint

    Mitsuru Kitamura, Kunihiro Hamada, Akihiro Takezawa, Tetsuya Uedera

    INTERNATIONAL JOURNAL OF OFFSHORE AND POLAR ENGINEERING   21 ( 3 ) 209 - 215  2011.09  [Refereed]

     View Summary

    A structural optimization system using the Finite Element Method (FEM) for the initial design stage of a ship is presented in this paper. A general bulk carrier is selected as the object for the optimization. Some dimensions determining the shapes of the ship&apos;s bottom structure are taken as design variables. Since the design variables affect the shape of the structure, the FEM model needs to be updated during the optimization. Further, the structure of the ship is so large and complicated that optimizing the shape of the ship&apos;s structure is very difficult. The individual mesh subdivision technique and the multi-point constraint method are introduced to make this optimization possible. However, creating the FEM datasets for the ship&apos;s structure requires a lot of manpower. To remove this drawback, Prime Ship-Hull is used because it has a function for recognizing the ship&apos;s structural members. The FEM dataset which can be applied to the individual mesh subdivision technique and the multi-point constraint method is made automatically from the structural members categorized by Prime Ship-Hull. Five key design variables for shape optimization of the ship&apos;s bottom structure-height and width of the double bottom, height of the bilge hopper tank, and the 2 widths of the lower stool-are considered here. A numerical example shows that the proposed method makes it possible to optimize the shape of the ship&apos;s bottom structure.

  • Topology optimization for worst load conditions based on the eigenvalue analysis of an aggregated linear system

    Akihiro Takezawa, Satoru Nii, Mitsuru Kitamura, Nozomu Kogiso

    COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING   200 ( 25-28 ) 2268 - 2281  2011.06  [Refereed]

     View Summary

    This paper proposes a topology optimization for a linear elasticity design problem subjected to an uncertain load. The design problem is formulated to minimize a robust compliance that is defined as the maximum compliance induced by the worst load case of an uncertain load set. Since the robust compliance can be formulated as the scalar product of the uncertain input load and output displacement vectors, the idea of "aggregation" used in the field of control is introduced to assess the value of the robust compliance. The aggregation solution technique provides the direct relationship between the uncertain input load and output displacement, as a small linear system composed of these vectors and the reduced size of a symmetric matrix, in the context of a discretized linear elasticity problem, using the finite element method. Introducing the constraint that the Euclidean norm of the uncertain load set is fixed, the robust compliance minimization problem is formulated as the minimization of the maximum eigenvalue of the aggregated symmetric matrix according to the Rayleigh-Ritz theorem for symmetric matrices. Moreover, the worst load case is easily established as the eigenvector corresponding to the maximum eigenvalue of the matrix. The proposed structural optimization method is implemented using topology optimization and the method of moving asymptotes (MMA). The numerical examples provided illustrate mechanically reasonable structures and establish the worst load cases corresponding to these optimal structures. (C) 2011 Elsevier B.V. All rights reserved.

    DOI

  • A Structural Optimization Method Incorporating Level Set Boundary Expressions Based on the Concept of the Phase Field Method

    T. Yamada, K. Izui, S. Nishiwaki, M. Yoshimura, A. Takezawa

    Journal of Environment and Engineering   6   567 - 578  2011.06  [Refereed]

    DOI

  • Robust Topology Optimization Based on an Aggregated Linear System and Eigenvalue Analysis

    Satoru Nii, Akihiro Takezawa, Mitsuru Kitamura, Nozomu Kogiso

    Transactions of the Japan Society of Mechanical Engineers   A-77 ( 775 ) 472 - 482  2011.03

  • A topology optimization method based on the level set method incorporating a fictitious interface energy

    Takayuki Yamada, Kazuhiro Izui, Shinji Nishiwaki, Akihiro Takezawa

    COMPUTER METHODS IN APPLIED MECHANICS AND ENGINEERING   199 ( 45-48 ) 2876 - 2891  2010.11  [Refereed]

     View Summary

    This paper proposes a new topology optimization method, which can adjust the geometrical complexity of optimal configurations, using the level set method and incorporating a fictitious interface energy derived from the phase field method. First, a topology optimization problem is formulated based on the level set method, and the method of regularizing the optimization problem by introducing fictitious interface energy is explained. Next, the reaction-diffusion equation that updates the level set function is derived and an optimization algorithm is then constructed, which uses the finite element method to solve the equilibrium equations and the reaction-diffusion equation when updating the level set function. Finally, several optimum design examples are shown to confirm the validity and utility of the proposed topology optimization method. (C) 2010 Elsevier B.V. All rights reserved.

    DOI

  • Topology optimization for designing strain-gauge load cells

    Akihiro Takezawa, Shinji Nishiwaki, Mitsuru Kitamura, Emilio C. N. Silva

    STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION   42 ( 3 ) 387 - 402  2010.09  [Refereed]

     View Summary

    Load cells are used extensively in engineering fields. This paper describes a novel structural optimization method for single- and multi-axis load cell structures. First, we briefly explain the topology optimization method that uses the solid isotropic material with penalization (SIMP) method. Next, we clarify the mechanical requirements and design specifications of the single- and multi-axis load cell structures, which are formulated as an objective function. In the case of multi-axis load cell structures, a methodology based on singular value decomposition is used. The sensitivities of the objective function with respect to the design variables are then formulated. On the basis of these formulations, an optimization algorithm is constructed using finite element methods and the method of moving asymptotes (MMA). Finally, we examine the characteristics of the optimization formulations and the resultant optimal configurations. We confirm the usefulness of our proposed methodology for the optimization of single- and multi-axis load cell structures.

    DOI

  • Phase-Field法による形状最適化

    竹澤晃弘

    計算工学   15   20 - 23  2010.04  [Invited]

    Authorship:Lead author, Corresponding author

  • Shape and topology optimization based on the phase field method and sensitivity analysis

    Akihiro Takezawa, Shinji Nishiwaki, Mitsuru Kitamura

    JOURNAL OF COMPUTATIONAL PHYSICS   229 ( 7 ) 2697 - 2718  2010.04  [Refereed]

     View Summary

    This paper discusses a structural optimization method that optimizes shape and topology based oil the phase field method. The proposed method has the same functional capabilities as a structural optimization method based oil the level set method incorporating perimeter control functions. The advantage of the method is the simplicity of computation, since extra operations such as re-initialization of functions are not required Structural shapes are represented by the phase field function defined in the design domain, and optimization of this function is performed by solving a time-dependent reaction diffusion equation. The artificial double Well potential function used in the equation is derived from sensitivity analysis The proposed method is applied to two-dimensional linear elastic and vibration optimization problems Such as the minimum compliance problem, a compliant mechanism design problem and the eigenfrequency maximization problem. The numerical examples provided Illustrate the convergence of the various objective functions and the effect that perimeter control has oil the optimal configurations (C) 2009 Elsevier Inc All rights reserved.

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  • フェーズフィールド法と感度解析に基づく構造最適化

    竹澤晃弘, 西脇眞二, 北村充

    日本機械学会論文集(A編),76巻761号(2010)     1 - 9  2010.01  [Refereed]  [Invited]

    DOI

  • レベルセット法に基づく熱電効果を利用した熱アクチュエータ設計問題に関するトポロジー最適化

    岡本由仁, 山田崇恭, 泉井一浩, 西脇眞二, 竹澤晃弘

    日本計算工学会論文集   2009 ( 20090024 )  2010.01  [Refereed]

  • Research on anti-vibration design of bridge wing based on topology optimization

    Akihiro Takezawa, Yuri Kaneno, Mitsuru Kitamura, Kunihiro Hamada, Yasuaki Ohtsuki

    Journal of the Japan Society of Naval Architects and Ocean Engineers   10   227 - 230  2009.12  [Refereed]

    DOI

  • フェーズフィールド法に基づく構造最適化(ペリメータ制約効果の検証とコンプライアントメカニズム創生問題・固有振動数最大化問題への拡張)

    竹澤晃弘, 西脇眞二, 北村充

    日本機械学会論文集(A編),75巻760号(2009)     1784 - 1793  2009.12  [Refereed]  [Invited]

    DOI

  • Optimization of Block Division Using Nodal Cut Set Method

    K.V. Karottu, K. Hamada, A. Takezawa, M. Kitamura

    Ship Technology Research   56   142 - 153  2009.07  [Refereed]

    DOI

  • A Multi-step Design Optimization Method for Mid-ship Section

    K. Hamada, A. Takezawa, M. Kitamura, K. Kanaikari

    Ship Technology Research   56   110 - 120  2009.07  [Refereed]

    DOI

  • レベルセット法による形状表現を用いたフェーズフィールド法の考え方に基づくトポロジー最適化

    山田崇恭, 西脇眞二, 泉井一浩, 吉村允孝, 竹澤晃弘

    日本機械学会論文集(A編)   75 ( 753 ) 550 - 558  2009.05  [Refereed]

    Authorship:Last author

    DOI

  • A Shape Optimization System of Ship Structures Using a Function Recognizing Structure Members : Shape Optimization of Double Bottom Part of Ship Structure

    Mitsuru Kitamura, Testuya Uedera, Kunihiro Hamada, Akihiro Takezawa, Takahiro

    Journal of the Japan Society of Naval Architects and Ocean Engineers   8   273 - 281  2008.12  [Refereed]

    Authorship:Last author

  • トポロジー最適化法を用いたひずみゲージ式変換器構造の最適化

    竹澤晃弘, 西脇眞二, 北村充

    日本機械学会論文集(A編),74巻747号(2008)   74 ( 747 ) 1459 - 1468  2008.11  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • 特異値分解に基づく多軸荷重変換器構造のトポロジー最適化

    竹澤晃弘, 西脇眞二, 北村充, Emilio Carlos Nelli Silva

    日本機械学会論文集(C編),74巻746号(2008)     2462 - 2470  2008.10  [Refereed]

    Authorship:Lead author, Corresponding author

    DOI

  • Shape and Size Optimization of Bottom Part of Ship Structure by Independent Mesh-subdivision Technique with Aide of Multiple Point Constraint

    Mitsuru Kitamura, Kunihiro Hamada, Akihiro Takezawa, Takahiro Takaki, Kunpei Kanaya, Yasuaki Ohtsuki

    Journal of the Japan Society of Naval Architects and Ocean Engineers   7   89 - 96  2008.06

  • 離散構造要素を用いたバンドギャップ構造の最適化

    竹澤晃弘, 最上克哉, 西脇眞二, 泉井一浩, 吉村允孝, 北村充

    日本機械学会論文集(C編),74巻740号(2008)   74 ( 740 ) 780 - 788  2008.04  [Refereed]  [Invited]

    DOI

  • Structural optimization based on topology optimization techniques using frame elements considering cross-sectional properties

    A. Takezawa, S. Nishiwaki, K. Izui, M. Yoshimura

    STRUCTURAL AND MULTIDISCIPLINARY OPTIMIZATION   34 ( 1 ) 41 - 60  2007.07  [Refereed]

    Authorship:Lead author

     View Summary

    This paper discusses a new structural optimization method, based on topology optimization techniques, using frame elements where the cross-sectional properties can be treated as design variables. For each of the frame elements, the rotational angle denoting the principal direction of the second moment of inertia is included as a design variable, and a procedure to obtain the optimal angle is derived from Karush-Kuhn-Tucker (KKT) conditions and a complementary strain energy-based approach. Based on the above, the optimal rotational angle of each frame element is obtained as a function of the balance of the internal moments. The above methodologies are applied to problems of minimizing the mean compliance and maximizing the eigen frequencies. Several examples are provided to show the utility of the presented methodology.

    DOI

  • Structural optimization using function-oriented elements to support conceptual designs

    Akihiro Takezawa, Shinji Nishiwaki, Kazuhiro Izui, Masataka Yoshimura

    JOURNAL OF MECHANICAL DESIGN   128 ( 4 ) 689 - 700  2006.07  [Refereed]

    Authorship:Lead author

     View Summary

    This paper presents a new structural optimization method that supports decision-making processes to obtain innovative designs at the conceptual design phase. This method is developed based on structural and function-oriented elements, such as frame and panel elements that have specific functions. For each of the frame elements, the rotational angle denoting the principal direction of the second moment of inertia is included as a design variable, and a procedure to obtain the optimal angle is derived from Karush-Kuhn-Tucker conditions. For the panel elements, two types of panel elements are introduced based the assumed stress method. Several examples are provided to show the utility of the methodology presented here for mechanical design engineers.

    DOI

  • フレーム要素を用いたトポロジー最適化(固有振動数最大化を目的とした場合)

      71 ( 710 ) 3018 - 3025  2005.10  [Refereed]

    Authorship:Lead author

    DOI

  • 離散構造要素を用いたトポロジー最適化(フレーム要素の断面主軸方向を設計変数として考慮した場合)

    竹澤晃弘, 西脇眞二, 泉井一浩, 吉村允孝

    日本機械学会論文集C編   71   172 - 179  2005.06  [Refereed]

    Authorship:Lead author

  • Concurrent design and evaluation based on structural optimization using structural and function-oriented elements at the conceptual design phase

    A Takezawa, S Nishiwaki, K Izui, M Yoshimura, H Nishigaki, Y Tsurumi

    CONCURRENT ENGINEERING-RESEARCH AND APPLICATIONS   13 ( 1 ) 29 - 42  2005.03  [Refereed]

    Authorship:Lead author

     View Summary

    Computer-aided engineering (CAE) has been successfully used in mechanical industries such as automotive industries. CAE enables us to quantitatively evaluate the mechanical performances of products and to propose an effective way to improve their performances using optimization techniques without building physical prototypes. However, CAE tools are usually utilized not at the conceptual design phase, but at the evaluation phase following the detailed design phase. This is because current CAE tools require detailed design data that does not yet exist at the conceptual design phase, and such tools also inhibit the provision of useful design suggestions that, ideally, match the way of thinking and insight of design engineers. Thus, at present, no CAE tools exist that can assist the conceptual design decision making process of design engineers. On the other hand, conceptual design processes are of great significance when seeking to create innovative and high-performance products and to shorten their development time. In order to fulfill the designer's needs during the conceptual design phase, a new type of CAE method must be constructed, one that enables concurrent design support and evaluation, and fits the way design engineers think and explore design insights.
    This article presents a new structural optimization method that supports concurrent decision making so that design engineers can work to obtain innovative designs and evaluate the mechanical design details of mechanical structures at the conceptual design phase. This method is developed based on the concept of product-oriented analysis and discrete, function-oriented elements, such as beam and panel elements, since these can provide design suggestions concerning the structural evaluation of reasons as to why certain design ideas obtained are reasonable or optimal in the design sense.
    The basic ideas and specifications needed to construct the method are explained and the construction of the structural optimization design method is discussed. The optimization algorithm is developed using the ground structure approach and CONLIN sequential convex programming. The examples provided demonstrate the utility of the proposed methodology for supporting design engineers' concurrent decision making, so that innovative mechanical designs can be evaluated at the conceptual design phase.

    DOI

  • 離散化構造要素を用いたトポロジー最適化

    竹澤晃弘, 西脇眞二, 泉井一浩, 吉村允孝, 西垣英一, 鶴見康昭

    日本機械学会論文集C編   70   1008 - 1015  2004.04  [Refereed]

    Authorship:Lead author

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Books and Other Publications

  • 産業用3Dプリンターの最新技術と先進分野への応用

    竹澤晃弘( Part: Contributor, 第7章第7節:3Dプリンターとトポロジー最適化の連携事例)

    技術情報協会  2018.06 ISBN: 9784861047091

  • 熱膨張制御材料の開発と応用

    竹澤晃弘( Part: Contributor, 第10章:人口構造体)

    シーエムシー出版  2018.01 ISBN: 9784781313160

  • 自動車用制振・遮音・吸音材料の最新動向

    竹澤晃弘( Part: Contributor, 第3章第4節:トポロジー最適化による減衰材料の最適配置)

    シーエムシー出版  2018.01 ISBN: 9784781313184

Awards

  • 文部科学大臣表彰若手研究者賞

    2017.04   動的問題に対する構造最適化法とその応用に関する研究

    Winner: 竹澤晃弘

Research Projects

  • 振動低減ラティス構造の生産性向上に関する研究

    JST  A-STEP「産学共同フェーズ(シーズ育成タイプ)」

    Project Year :

    2019.10
    -
    2022.03
     

    マツダ株式会社

  • 構造最適化と指向性エネルギー堆積法に基づく負熱膨張金属複合材料の開発

    JSPS  科学研究費助成事業 国際共同研究加速基金(国際共同研究強化(A))

    Project Year :

    2019.03
    -
    2022.03
     

    竹澤晃弘

  • 構造最適化・積層造形・毛管現象による三次元負熱膨張Ti/Mg複合材料の開発

    JSPS  科学研究費助成事業 基盤研究(B)

    Project Year :

    2018.04
    -
    2021.03
     

    竹澤晃弘

  • 構造最適化を活用した高減衰ラティス構造の応用研究

    JST  研究成果展開事業 地域産学バリュープログラム

    Project Year :

    2017.10
    -
    2018.09
     

    竹澤晃弘

  • カスタムメイド多孔質金属人工関節最適設計システム

    JSPS  科学研究費助成事業 挑戦的萌芽研究

    Project Year :

    2015.04
    -
    2017.03
     

    竹澤晃弘

  • 加工性を考慮した構造最適化に関する研究

    JST  研究成果展開事業 マッチングプランナープログラム

    Project Year :

    2015.10
    -
    2016.09
     

    竹澤晃弘

  • 海洋構造物に対するセルフパワード振動制御装置の研究

    JSPS  科学研究費助成事業 若手研究(B)

    Project Year :

    2013.04
    -
    2015.03
     

    竹澤晃弘

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Specific Research

  • 金属積層造形の熱変形を抑制するラティス構造の実験検証

    2021  

     View Summary

    近年,次世代の加工技術として金属積層造形が注目を集めており,試作のみならず量産最終製品にも使用されるようになっている.しかし,金属積層造形においては熱変形が問題になる.この熱変形を近似的に推定する方法として、固有ひずみ法が近年開発されている.本研究では、熱変形の抑制に密度・剛性分布を適所で変更可能なラティス構造を適用することを考え,固有ひずみ法とラティス構造の密度分布を最適化する構造最適化法を組み合わせ,金属積層造形における低熱変形構造の最適設計法を構築した.そして,最適解の妥当性を実験により検証した.一連の成果は国際学術誌Additive Manufacturingで発表した.

  • 金属積層造形の熱変形抑制に向けたラティス構造最適化法の研究とその実験検証

    2021  

     View Summary

    近年,次世代の加工技術として金属積層造形が注目を集めており,試作のみならず量産最終製品にも使用されるようになっている.しかし,金属積層造形においては熱変形が問題になる.この熱変形を近似的に推定する方法として、固有ひずみ法が近年開発されている.本研究では、熱変形の抑制に密度・剛性分布を適所で変更可能なラティス構造を適用することを考え,固有ひずみ法とラティス構造の密度分布を最適化する構造最適化法を組み合わせ,金属積層造形における低熱変形構造の最適設計法を構築した.そして,最適解の妥当性を実験により検証した.一連の成果は国際学術誌Additive Manufacturingで発表した.

  • 金属積層造形の熱変形抑制に向けた高精度固有ひずみ法とラティス構造最適化法の研究

    2020  

     View Summary

     近年,次世代の加工技術として金属積層造形が注目を集めており,試作のみならず量産最終製品にも使用されるようになっている.しかし,金属積層造形においては熱変形が問題になる.この熱変形を近似的に推定する方法として、固有ひずみ法が近年開発されている.本研究では、熱変形の抑制に密度・剛性分布を適所で変更可能なラティス構造を適用することを考え,固有ひずみ法とラティス構造の密度分布を最適化する構造最適化法を組み合わせ,金属積層造形における低熱変形構造の最適設計法を構築した.具体的には,固有ひずみ法は有限要素解析と実際の金属積層造形の熱変形計測を通じてモデルを構築した.そのモデルをラティス構造の密度分布最適化アルゴリズムに組み込み,最適設計法を構築した.

 

Syllabus

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