Updated on 2024/04/22

写真a

 
IWAKAMI, Wakana
 
Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Assistant Professor(non-tenure-track)

Research Experience

  • 2024.04
    -
    Now

    Waseda University   School of Advanced Science and Engineering   Associate Professor

  • 2023.04
    -
    2024.03

    Tokyo University of Science   Postdoctoral Researcher

  • 2020.04
    -
    2023.03

    Waseda University   Research Institute for Science and Engineering

  • 2016.04
    -
    2020.03

    Kyoto University   Yukawa Institute for Theoretical Physics

  • 2013.04
    -
    2016.03

    Kyoto University   Yukawa Institute for Theoretical Physics

  • 2012.10
    -
    2013.03

    Waseda University   Research Institute for Science and Engineering

  • 2009.10
    -
    2012.09

    Tohoku University   Institute of Fluid Science   Assistant Professor

  • 2009.04
    -
    2009.09

    Waseda University   Faculty of Science and Engineering   Research Fellowship for Young Scientists

▼display all

Education Background

  • 2006.04
    -
    2009.03

    Tohoku University   Graduate School of Engineering  

  • 2004.04
    -
    2006.03

    Tohoku University   Graduate School of Engineering  

  • 2000.04
    -
    2004.03

    Tohoku University  

Professional Memberships

  • 2009.10
    -
    Now

    The Japan Society of Fluid Mechanics

  • 2007.06
    -
    Now

    Astronomical Society of Japan

  • 2007.06
    -
    Now

    The Physical Society of Japan

Research Areas

  • Theoretical studies related to particle-, nuclear-, cosmic ray and astro-physics / Fluid engineering

Research Interests

  • fluid dynamics

  • numerical simulation

  • supernova

  • neutrino

Awards

  • 日本機械学会三浦賞

    2005.03  

 

Papers

  • Physical mechanism of core-collapse supernovae that neutrinos drive.

    Shoichi Yamada, Hiroki Nagakura, Ryuichiro Akaho, Akira Harada, Shun Furusawa, Wakana Iwakami, Hirotada Okawa, Hideo Matsufuru, Kohsuke Sumiyoshi

    Proceedings of the Japan Academy. Series B, Physical and biological sciences   100 ( 3 ) 190 - 233  2024  [Domestic journal]

     View Summary

    The current understanding of the mechanism of core-collapse supernovae (CCSNe), one of the most energetic events in the universe associated with the death of massive stars and the main formation channel of compact objects such as neutron stars and black holes, is reviewed for broad readers from different disciplines of science who may not be familiar with the object. Therefore, we emphasize the physical aspects than the results of individual model simulations, although large-scale high-fidelity simulations have played the most important roles in the progress we have witnessed in the past few decades. It is now believed that neutrinos are the most important agent in producing the commonest type of CCSNe. The so-called neutrino-heating mechanism will be the focus of this review and its crucial ingredients in micro- and macrophysics and in numerics will be explained one by one. We will also try to elucidate the remaining issues.

    DOI PubMed

    Scopus

  • Protoneutron Star Convection Simulated with a New General Relativistic Boltzmann Neutrino Radiation Hydrodynamics Code

    Ryuichiro Akaho, Akira Harada, Hiroki Nagakura, Wakana Iwakami, Hirotada Okawa, Shun Furusawa, Hideo Matsufuru, Kohsuke Sumiyoshi, Shoichi Yamada

    Astrophysical Journal   944 ( 1 )  2023.02

     View Summary

    We investigate protoneutron star (PNS) convection using our newly developed general relativistic Boltzmann neutrino radiation hydrodynamics code. This is a pilot study for more comprehensive investigations later. As such, we take a snapshot of a PNS at 2.3 s after bounce from a 1D PNS cooling calculation and run our simulation for ∼160 ms in 2D under axisymmetry. The original PNS cooling calculation neglected convection entirely and the initial conditions were linearly unstable to convection. We find in our 2D simulation that convection is instigated there indeed and expands inward after being full-fledged. The convection then settled to a quasi-steady state after ∼100 ms, being sustained by the negative Y e gradient, which is in turn maintained by neutrino emissions. It enhances the luminosities and mean energies of all species of neutrinos compared to 1D. Taking advantage of the Boltzmann solver, we analyse the possible occurrence of neutrino fast flavor conversion (FFC). We found that FFC is likely to occur in regions where Y e is lower, and that the growth rate can be as high as ∼10−1 cm−1

    DOI

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    7
    Citation
    (Scopus)
  • Principal-axis Analysis of the Eddington Tensor for the Early Post-bounce Phase of Rotational Core-collapse Supernovae

    Wakana Iwakami, Akira Harada, Hiroki Nagakura, Ryuichiro Akaho, Hirotada Okawa, Shun Furusawa, Hideo Matsufuru, Kohsuke Sumiyoshi, Shoichi Yamada

    Astrophysical Journal   933 ( 1 )  2022.07

     View Summary

    Using full Boltzmann neutrino transport, we performed 2D core-collapse supernova simulations in axisymmetry for two progenitor models with 11.2 and 15.0 M ⊙, both rotational and nonrotational. We employed the results obtained in the early post-bounce phase (t 2 20 ms) to assess performance under rapid rotation of some closure relations commonly employed in the truncated moment method. We first made a comparison in 1D under spherical symmetry, though, of the Eddington factor p defined in the fluid rest frame (FR). We confirmed that the maximum entropy closure for the Fermionic distribution (MEFD) performs better than others near the proto-neutron star surface, where p < 1/3 occurs, but does not work well even in 1D when the phase-space occupancy satisfies e < 0.5 together with p < 1/3, the condition known to be not represented by MEFD. For the 2D models with the rapid rotation, we employed the principal-axis analysis of the Eddington tensor. We paid particular attention to the direction of the longest principal axis. We observed in FR that it is aligned neither with the radial direction nor with the neutrino flux in 2D, particularly so in convective and/or rapidly rotating regions, the fact not accommodated in the moment method. We repeated the same analysis in the laboratory frame and found again that the direction of the longest principal axis is not well reproduced by MEFD because the interpolation between the optically thick and thin limits is not very accurate in this frame.

    DOI

    Scopus

    3
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    (Scopus)
  • Multidimensional Boltzmann Neutrino Transport Code in Full General Relativity for Core-collapse Simulations

    Ryuichiro Akaho, Akira Harada, Hiroki Nagakura, Kohsuke Sumiyoshi, Wakana Iwakami, Hirotada Okawa, Shun Furusawa, Hideo Matsufuru, Shoichi Yamada

    Astrophysical Journal   909 ( 2 )  2021.03

     View Summary

    We develop a neutrino transfer code for core-collapse simulations that directly solves the multidimensional Boltzmann equations in full general relativity. We employ the discrete ordinate method, which discretizes the 6D phase space. The code is an extension of our special relativistic code coupled to a Newtonian hydrodynamics code, which is currently employed for core-collapse supernova simulations. In order to demonstrate our code's capability to treat general relativistic effects, we conduct some tests. We first compute the free streaming of neutrinos in the Schwarzschild and Kerr spacetimes and compare the results with the geodesic curves; in the Schwarzschild case, we deploy not only a 1D grid in space under spherical symmetry but also a 2D spatial mesh under axisymmetry in order to assess the capability of the code to compute the spatial advection of neutrinos. Second, we calculate the neutrino transport in a fixed matter background, which is taken from a core-collapse supernova simulation with our general relativistic but spherically symmetric Boltzmann hydrodynamics code, to obtain a steady neutrino distribution; the results are compared with those given by the latter code.

    DOI

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    7
    Citation
    (Scopus)
  • Simulations of the early postbounce phase of core-collapse supernovae in three-dimensional space with full boltzmann neutrino transport

    Wakana Iwakami, Hirotada Okawa, Hiroki Nagakura, Akira Harada, Shun Furusawa, Kosuke Sumiyoshi, Hideo Matsufuru, Shoichi Yamada

    Astrophysical Journal   903 ( 2 )  2020.11

     View Summary

    We report on the core-collapse supernova simulation we conducted for a 11.2M⊙ progenitor model in threedimensional space up to 20 ms after bounce, using a radiation-hydrodynamics code with full Boltzmann neutrino transport. We solve the six-dimensional Boltzmann equations for three neutrino species and the three-dimensional compressible Euler equations with Furusawa and Togashi's nuclear equation of state. We focus on the prompt convection at ∼10 ms after bounce and investigate how neutrinos are transported in the convective matter. We apply a new analysis based on the eigenvalues and eigenvectors of the Eddington tensor and make a comparison between the Boltzmann transport results and the M1 closure approximation in the transition regime between the optically thick and thin limits. We visualize the eigenvalues and eigenvectors using an ellipsoid, in which each principal axis is parallel to one of the eigenvectors and has a length proportional to the corresponding eigenvalue. This approach enables us to understand the difference between the Eddington tensor derived directly from the Boltzmann simulation and the one given by the M1 prescription from a new perspective. We find that the longest principal axis of the ellipsoid is almost always nearly parallel to the energy flux in the M1 closure approximation, whereas in the Boltzmann simulation it becomes perpendicular in some transition regions, where the mean free path is ∼0.1 times the radius. In three spatial dimensions, the convective motions make it difficult to predict where this happens and to possibly improve the closure relation there.

    DOI

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    21
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  • The Boltzmann-radiation-hydrodynamics Simulations of Core-collapse Supernovae with Different Equations of State: The Role of Nuclear Composition and the Behavior of Neutrinos

    Akira Harada, Hiroki Nagakura, Wakana Iwakami, Hirotada Okawa, Shun Furusawa, Kohsuke Sumiyoshi, Hideo Matsufuru, Shoichi Yamada

    Astrophysical Journal   902 ( 2 )  2020.10

     View Summary

    Using the Boltzmann-radiation-hydrodynamics code, which solves the Boltzmann equation for neutrino transport, we present the results of the simulations with the nuclear equations of state (EOSs) of Lattimer and Swesty (LS) and Furusawa and Shen (FS). We extend the simulation time of the LS model and conduct thorough investigations, though our previous paper briefly reported some of the results. Only the LS model shows the shock revival. This seems to originate from the nuclear composition: the different nuclear composition results in the different energy loss by photodissociation and hence the different strength of the prompt convection and the later neutrino-driven convection. The protoneutron star seen in the FS model is more compact than that in the LS model because the existence of multinuclear species softens the EOS. For the behavior of neutrinos, we examined the flux and the Eddington tensor of neutrinos. In the optically thick region, the diffusion of neutrinos and the dragging by the motion of matter determine the flux. In the optically thin region, the free-streaming determines it. The Eddington tensor is compared with that obtained from the M1-closure relation. The M1-closure scheme overestimates the contribution from the velocity-dependent terms in the semitransparent region.

    DOI

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    25
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  • Fast collective neutrino oscillations inside the neutrino sphere in core-collapse supernovae

    Milad Delfan Azari, Shoichi Yamada, Taiki Morinaga, Hiroki Nagakura, Shun Furusawa, Akira Harada, Hirotada Okawa, Wakana Iwakami, Kohsuke Sumiyoshi

    Physical Review D   101 ( 2 )  2020.01

     View Summary

    Neutrinos are believed to have a key role in the explosion mechanism of core-collapse supernovae as they carry most of the energy released by the gravitational collapse of a massive star. If their flavor is converted fast inside the neutrino sphere, the supernova explosion may be influenced. This paper is reporting the results of the extended work of our previous paper. We perform a thorough survey of the electron lepton number (ELN) crossing in one of our self-consistent, realistic Boltzmann simulations in two spatial dimensions under axisymmetry for the existence of the crossings between νe and νe angular distributions, or the ELN crossing. We report for the first time the positive detections deep inside the core of the massive star in the vicinity of neutrino sphere at r≈16-21 km. We find that low values of the electron fraction Ye produced by convective motions together with the appearance of light elements are critically important to give rise to the ELN crossing by enhancing the chemical potential difference between proton and neutron, and hence by mitigating the Fermi-degeneracy of νe. Since the region of positive detection are sustained and, in fact, expanding with time, it may have an impact on the explosion of core-collapse supernovae, observational neutrino astronomy, and nucleosynthesis of heavy nuclei.

    DOI

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    71
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  • Linear analysis of fast-pairwise collective neutrino oscillations in core-collapse supernovae based on the results of Boltzmann simulations

    Milad Delfan Azari, Shoichi Yamada, Taiki Morinaga, Wakana Iwakami, Hirotada Okawa, Hiroki Nagakura, Kohsuke Sumiyoshi

    Physical Review D   99 ( 10 )  2019.05

     View Summary

    Neutrinos are densely populated deep inside the core of massive stars after their gravitational collapse to produce supernova explosions and form compact stars such as neutron stars and black holes. It has been considered that they may change their flavor identities through so-called fast-pairwise conversions induced by mutual forward scatterings. If that is really the case, the dynamics of supernova explosion will be influenced, since the conversion may occur near the neutrino sphere, from which neutrinos are effectively emitted. In this paper, we conduct a pilot study of such possibilities based on the results of fully self-consistent, realistic simulations of a core-collapse supernova explosion in two spatial dimensions under axisymmetry. As we solved the Boltzmann equations for neutrino transfer in the simulation not as a postprocess but in real time, the angular distributions of neutrinos in momentum space for all points in the core at all times are available, a distinct feature of our simulations. We employ some of these distributions extracted at a few selected points and times from the numerical data and apply linear analysis to assess the possibility of the conversion. We focus on the vicinity of the neutrino sphere, where different species of neutrinos move in different directions and have different angular distributions as a result. This is a pilot study for a more thorough survey that will follow soon. We find no positive sign of conversion unfortunately at least for the spatial points and times we studied in this particular model. We hence investigate rather in detail the condition for the conversion by modifying the neutrino distributions rather arbitrarily by hand.

    DOI

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    59
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  • On the Neutrino Distributions in Phase Space for the Rotating Core-collapse Supernova Simulated with a Boltzmann-neutrino-radiation-hydrodynamics Code

    Akira Harada, Hiroki Nagakura, Wakana Iwakami, Hirotada Okawa, Shun Furusawa, Hideo Matsufuru, Kohsuke Sumiyoshi, Shoichi Yamada

    Astrophysical Journal   872 ( 2 )  2019

     View Summary

    With the Boltzmann-radiation-hydrodynamics code, which we have developed to solve numerically the Boltzmann equations for neutrino transfer, the Newtonian hydrodynamics equations, and the Newtonian self-gravity simultaneously and consistently, we simulate the collapse of a rotating core of the progenitor with a zero-age- main-sequence mass of 11.2 M and a shellular rotation of at the center. We pay particular attention in this paper to the neutrino distribution in phase space, which is affected by the rotation. By solving the Boltzmann equations directly, we can assess the rotation-induced distortion of the angular distribution in momentum space, which gives rise to the rotational component of the neutrino flux. We compare the Eddington tensors calculated both from the raw data and from the M1-closure approximation. We demonstrate that the Eddington tensor is determined by complicated interplays of the fluid velocity and the neutrino interactions and that the M1-closure, which assumes that the Eddington factor is determined by the flux factor, fails to fully capture this aspect, especially in the vicinity of the shock. We find that the error in the Eddington factor reaches ∼20% in our simulation. This is due not to the resolution but to the different dependence of the Eddington and flux factors on the angular profile of the neutrino distribution function, and hence modification to the closure relation is needed.

    DOI

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    30
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  • Simulations of Core-collapse Supernovae in Spatial Axisymmetry with Full Boltzmann Neutrino Transport

    Hiroki Nagakura, Wakana Iwakami, Shun Furusawa, Hirotada Okawa, Akira Harada, Kohsuke Sumiyoshi, Shoichi Yamada, Hideo Matsufuru, Akira Imakura

    Astrophysical Journal   854 ( 2 )  2018.02

     View Summary

    We present the first results of our spatially axisymmetric core-collapse supernova simulations with full Boltzmann neutrino transport, which amount to a time-dependent five-dimensional (two in space and three in momentum space) problem. Special relativistic effects are fully taken into account with a two-energy-grid technique. We performed two simulations for a progenitor of 11.2 M⊙, employing different nuclear equations of state (EOSs): Lattimer and Swesty's EOS with the incompressibility of K =220 MeV (LS EOS) and Furusawa's EOS based on the relativistic mean field theory with the TM1 parameter set (FS EOS). In the LS EOS, the shock wave reaches ∼700 km at 300 ms after bounce and is still expanding, whereas in the FS EOS it stalled at ∼200 km and has started to recede by the same time. This seems to be due to more vigorous turbulent motions in the former during the entire postbounce phase, which leads to higher neutrino-heating efficiency in the neutrino-driven convection. We also look into the neutrino distributions in momentum space, which is the advantage of the Boltzmann transport over other approximate methods. We find nonaxisymmetric angular distributions with respect to the local radial direction, which also generate off-diagonal components of the Eddington tensor. We find that the rθ component reaches ∼10% of the dominant rr component and, more importantly, it dictates the evolution of lateral neutrino fluxes, dominating over the θθ component, in the semitransparent region. These data will be useful to further test and possibly improve the prescriptions used in the approximate methods.

    DOI

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    83
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  • Three-dimensional Boltzmann-Hydro Code for Core-collapse in Massive Stars. II. the Implementation of Moving-mesh for Neutron Star Kicks

    Hiroki Nagakura, Wakana Iwakami, Shun Furusawa, Kohsuke Sumiyoshi, Shoichi Yamada, Hideo Matsufuru, Akira Imakura

    Astrophysical Journal, Supplement Series   229 ( 2 )  2017.04

     View Summary

    We present a newly developed moving-mesh technique for the multi-dimensional Boltzmann-Hydro code for the simulation of core-collapse supernovae (CCSNe). What makes this technique different from others is the fact that it treats not only hydrodynamics but also neutrino transfer in the language of the 3 + 1 formalism of general relativity (GR), making use of the shift vector to specify the time evolution of the coordinate system. This means that the transport part of our code is essentially general relativistic, although in this paper it is applied only to the moving curvilinear coordinates in the flat Minknowski spacetime, since the gravity part is still Newtonian. The numerical aspect of the implementation is also described in detail. Employing the axisymmetric two-dimensional version of the code, we conduct two test computations: oscillations and runaways of proto-neutron star (PNS). We show that our new method works fine, tracking the motions of PNS correctly. We believe that this is a major advancement toward the realistic simulation of CCSNe.

    DOI

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    50
    Citation
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  • A Parametric Study of the Acoustic Mechanism for Core-collapse Supernovae

    A. Harada, H. Nagakura, W. Iwakami, S. Yamada

    Astrophysical Journal   839 ( 1 )  2017.04

     View Summary

    We investigate the criterion for the acoustic mechanism to work successfully in core-collapse supernovae. The acoustic mechanism is an alternative to the neutrino-heating mechanism. It was proposed by Burrows et al., who claimed that acoustic waves emitted by g-mode oscillations in proto-neutron stars (PNS) energize a stalled shock wave and eventually induce an explosion. Previous works mainly studied to which extent the g-modes are excited in the PNS. In this paper, on the other hand, we investigate how strong the acoustic wave needs to be if it were to revive a stalled shock wave. By adding the acoustic power as a new axis, we draw a critical surface, which is an extension of the critical curve commonly employed in the context of neutrino heating. We perform both 1D and 2D parametrized simulations, in which we inject acoustic waves from the inner boundary. In order to quantify the power of acoustic waves, we use the extended Myers theory to take neutrino reactions into proper account. We find for the 1D simulations that rather large acoustic powers are required to relaunch the shock wave, since the additional heating provided by the secondary shocks developed from acoustic waves is partially canceled by the neutrino cooling that is also enhanced. In 2D, the required acoustic powers are consistent with those of Burrows et al. Our results seem to imply, however, that it is the sum of neutrino heating and acoustic powers that matters for shock revival.

    DOI

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    3
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  • LINKS between the SHOCK INSTABILITY in CORE-COLLAPSE SUPERNOVAE and ASYMMETRIC ACCRETIONS of ENVELOPES

    Kazuya Takahashi, Wakana Iwakami, Yu Yamamoto, Shoichi Yamada

    Astrophysical Journal   831 ( 1 )  2016.11

     View Summary

    The explosion mechanism of core-collapse supernovae (CCSNe) has not been fully understood yet, but multidimensional fluid instabilities such as standing accretion shock instability and convection are now believed to be crucial for shock revival. Another multidimensional effect that has been recently argued is the asymmetric structures in progenitors, which are induced by violent convections in silicon/oxygen layers that occur before the onset of collapse, as revealed by recent numerical simulations of the last stage of massive star evolutions. Furthermore, it has been also demonstrated numerically that accretions of such nonspherical envelopes could facilitate shock revival. These two multidimensional effects may hence hold a key to successful explosions. In this paper, we performed a linear stability analysis of the standing accretion shock in CCSNe, taking into account nonspherical, unsteady accretion flows onto the shock to clarify the possible links between the two effects. We found that such preshock perturbations can excite the fluid instabilities efficiently and hence help the shock revive in CCSNe.

    DOI

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    16
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  • Direct numerical simulation of aeroacoustic sound by volume penalization method

    Ryu Komatsu, Wakana Iwakami, Yuji Hattori

    Computers and Fluids   130   24 - 36  2016.05

     View Summary

    The volume penalization (VP) method for compressible flows is investigated as a tool of direct numerical simulation of aeroacoustic sound in problems where not only acoustic pressure but also hydrodynamic pressure depends on time and position. First, it is shown that the method proposed by Liu and Vasilyev (2007) [30] is not Galilean invariant. It is corrected to satisfy Galilean invariance. Next, numerical accuracy of the corrected VP method is investigated in problems of simple geometry which can be simulated also by a standard method on a body-fitted coordinate system: sound generation in (i) flow past a fixed square/circular cylinder, (ii) flow past an oscillating square/circular cylinder, and (iii) flow past two square cylinders. The results confirm that the corrected VP method gives reasonably accurate results for sound pressure which is much smaller than hydrodynamic pressure within 5% error. Finally, the corrected method is applied to two examples of complex geometry, which cannot be simulated by standard methods using body-fitted coordinate systems without considerable difficulty: sound generation in (i) flow past an oscillating cylinder and a fixed cylinder behind it and (ii) flow past a bundle of cylinders. The results show that the present method is in principle applicable to aeroacoustic problems in any complex geometry including practical engineering ones.

    DOI

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    35
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  • A new approach for error reduction in the volume penalizationmethod

    Wakana Iwakami, Yuzuru Yatagai, Nozomu Hatakeyama, Yuji Hattori

    Communications in Computational Physics   16 ( 5 ) 1181 - 1200  2014.11

     View Summary

    A new approach for reducing error of the volume penalization method is proposed. The mask function is modified by shifting the interface between solid and fluid by √νη toward the fluid region, where ν and η are the viscosity and the permeability, respectively. The shift length √νη is derived from the analytical solution of the one-dimensional diffusion equation with a penalization term. The effect of the error reduction is verified numerically for the one-dimensional diffusion equation, Burgers' equation, and the two-dimensional Navier-Stokes equations. The results show that the numerical error is reduced except in the vicinity of the interface showing overall second-order accuracy, while it converges to a non-zero constant value as the number of grid points increases for the original mask function. However, the new approach is effectivewhen the grid resolution is sufficiently high so that the boundary layer, whose width is proportional to √νη, is resolved. Hence, the approach should be used when an appropriate combination of ν and η is chosen with a given numerical grid.

    DOI

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    5
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  • Critical surface for explosions of rotational core-collapse supernovae

    Wakana Iwakami, Hiroki Nagakura, Shoichi Yamada

    Astrophysical Journal   793 ( 1 )  2014.09

     View Summary

    The effect of rotation on the explosion of core-collapse supernovae is investigated systematically in three-dimensional simulations. In order to obtain the critical conditions for explosion as a function of mass accretion rate, neutrino luminosity, and specific angular momentum, rigidly rotating matter was injected from the outer boundary with an angular momentum, which is increased every 500 ms. It is found that there is a critical value of the specific angular momentum, above which the standing shock wave revives, for a given combination of mass accretion rate and neutrino luminosity, i.e., an explosion can occur by rotation even if the neutrino luminosity is lower than the critical value for a given mass accretion rate in non-rotational models. The coupling of rotation and hydrodynamical instabilities plays an important role in characterizing the dynamics of shock revival for the range of specific angular momentum that are supposed to be realistic. Contrary to expectations from past studies, the most rapidly expanding direction of the shock wave is not aligned with the rotation axis. Being perpendicular to the rotation axis on average, it can be oriented in various directions. Its dispersion is small when the spiral mode of the standing accretion shock instability (SASI) governs the dynamics, while it is large when neutrino-driven convection is dominant. As a result of the comparison between two-dimensional and three-dimensional rotational models, it is found that m ≠ 0 modes of neutrino-driven convection or SASI are important for shock revival around the critical surface.

    DOI

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    25
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  • Parametric study of flow patterns behind the standing accretion shock wave for core-collapse supernovae

    Wakana Iwakami, Hiroki Nagakura, Shoichi Yamada

    Astrophysical Journal   786 ( 2 )  2014.05

     View Summary

    In this study, we conduct three-dimensional hydrodynamic simulations systematically to investigate the flow patterns behind the accretion shock waves that are commonly formed in the post-bounce phase of core-collapse supernovae. Adding small perturbations to spherically symmetric, steady, shocked accretion flows, we compute the subsequent evolutions to find what flow pattern emerges as a consequence of hydrodynamical instabilities such as convection and standing accretion shock instability for different neutrino luminosities and mass accretion rates. Depending on these two controlling parameters, various flow patterns are indeed realized. We classify them into three basic patterns and two intermediate ones; the former includes sloshing motion (SL), spiral motion (SP), and multiple buoyant bubble formation (BB); the latter consists of spiral motion with buoyant-bubble formation (SPB) and spiral motion with pulsationally changing rotational velocities (SPP). Although the post-shock flow is highly chaotic, there is a clear trend in the pattern realization. The sloshing and spiral motions tend to be dominant for high accretion rates and low neutrino luminosities, and multiple buoyant bubbles prevail for low accretion rates and high neutrino luminosities. It is interesting that the dominant pattern is not always identical between the semi-nonlinear and nonlinear phases near the critical luminosity; the intermediate cases are realized in the latter case. Running several simulations with different random perturbations, we confirm that the realization of flow pattern is robust in most cases.

    DOI

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    19
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  • Multimessengers from core-collapse supernovae: Multidimensionality as a key to bridge theory and observation

    Kei Kotake, Tomoya Takiwaki, Yudai Suwa, Wakana Iwakami Nakano, Shio Kawagoe, Youhei Masada, Shin Ichiro Fujimoto

    Advances in Astronomy   2012  2012

     View Summary

    Core-collapse supernovae are dramatic explosions marking the catastrophic end of massive stars. The only means to get direct information about the supernova engine is from observations of neutrinos emitted by the forming neutron star, and through gravitational waves which are produced when the hydrodynamic flow or the neutrino flux is not perfectly spherically symmetric. The multidimensionality of the supernova engine, which breaks the sphericity of the central core such as convection, rotation, magnetic fields, and hydrodynamic instabilities of the supernova shock, is attracting great attention as the most important ingredient to understand the long-veiled explosion mechanism. Based on our recent work, we summarize properties of gravitational waves, neutrinos, and explosive nucleosynthesis obtained in a series of our multidimensional hydrodynamic simulations and discuss how the mystery of the central engines can be unraveled by deciphering these multimessengers produced under the thick veils of massive stars. © 2012 Kei Kotake et al.

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  • Effects of rotation on stochasticity of gravitational waves in the nonlinear phase of core-collapse supernovae

    Kei Kotake, Wakana Iwakami-Nakano, Naofumi Ohnishi

    Astrophysical Journal   736 ( 2 )  2011.08

     View Summary

    By performing three-dimensional (3D) simulations that demonstrate the neutrino-driven core-collapse supernovae aided by the standing accretion shock instability (SASI), we study how the spiral modes of the SASI can impact the properties of the gravitational-wave (GW) emission. To see the effects of rotation in the nonlinear postbounce phase, we give a uniform rotation on the flow advecting from the outer boundary of the iron core, the specific angular momentum of which is assumed to agree with recent stellar evolution models. We compute fifteen 3D models in which the initial angular momentum and the input neutrino luminosities from the protoneutron star are changed in a systematic manner. By performing a ray-tracing analysis, we accurately estimate the GW amplitudes generated by anisotropic neutrino emission. Our results show that the gravitational waveforms from neutrinos in models that include rotation exhibit a common feature; otherwise, they vary much more stochastically in the absence of rotation. The breaking of the stochasticity stems from the excess of the neutrino emission parallel to the spin axis. This is because the compression of matter is more enhanced in the vicinity of the equatorial plane due to the growth of the spiral SASI modes, leading to the formation of the spiral flows circulating around the spin axis with higher temperatures. We point out that recently proposed future space interferometers like Fabry-Perot-type DECIGO would permit the detection of these signals for a Galactic supernova. © 2011. The American Astronomical Society. All rights reserved.

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    33
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  • Spiral mode of standing accretion shock instability in core-collapse supernovae

    Wakana Iwakami, Naofumi Ohnishi, Kei Kotake, Shoichi Yamada, Keisuke Sawada

    Astrophysics and Space Science   322 ( 1-4 ) 43 - 47  2009.08

     View Summary

    The study of standing accretion shock instability (SASI) in core-collapse supernova cores has been done with three-dimensional (3D) computer simulations. Rotations with various perturbations were introduced from outer boundary of an initial steady accreting flow. We found that one or two armed spiral accreting flow onto the proto-neutron star (PNS) is formed inside the shock wave depending on perturbations. The linear growth of spiral modes are clearly diagnosed by the mode analysis of the shock surface, and the lower m modes grow quickly in the linear regime. © 2008 Springer Science+Business Media B.V.

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    9
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  • Effects of rotation on standing accretion shock instability in nonlinear phase for core-collapse supernovae

    Wakana Iwakami, Kei Kotake, Naofumi Ohnishi, Shoichi Yamada, Keisuke Sawada

    Astrophysical Journal   700 ( 1 ) 232 - 242  2009.07

     View Summary

    We study the effects of rotation on standing accretion shock instability (SASI) by performing three-dimensional hydrodynamics simulations. Taking into account a realistic equation of state and neutrino heating/cooling, we prepare a spherically symmetric and steady accretion flow through a standing shock wave onto a proto-neutron star (PNS). When the SASI enters the nonlinear phase, we impose uniform rotation on the flow advecting from the outer boundary of the iron core, whose specific angular momentum is assumed to agree with recent stellar evolution models. Using spherical harmonics in space and Fourier decompositions in time, we perform mode analysis of the nonspherical deformed shock wave to observe rotational effects on the SASI in the nonlinear phase. We find that rotation imposed on the axisymmetric flowdoes not make any spiralmodes and hardly affects sloshingmodes, except for steady l = 2,m = 0 modes. In contrast, rotation imposed on the nonaxisymmetric flow increases the amplitude of spiral modes so that some spiral flows accreting on the PNS are more clearly formed inside the shock wave than without rotation. The amplitudes of spiral modes increase significantly with rotation in the progressive direction.

    DOI

    Scopus

    68
    Citation
    (Scopus)
  • Stochastic nature of gravitational waves from supernova explosions with standing accretion shock instability

    Kei Kotake, Wakana Iwakami, Naofumi Ohnishi, Shoichi Yamada

    Astrophysical Journal   697 ( 2 PART 2 )  2009

     View Summary

    We study the properties of gravitational waves (GWs) based on three-dimensional (3D) simulations, which demonstrate neutrino-driven explosions aided by standing accretion shock instability (SASI). Pushed by evidence supporting slow rotation prior to core collapse, we focus on the asphericities in neutrino emissions and matter motions outside the protoneutron star. By performing a ray-tracing calculation in 3D, we estimate accurately the gravitational waveforms from anisotropic neutrino emissions. In contrast to the previous work assuming axisymmetry, we find that the gravitational waveforms vary much more stochastically because the explosion anisotropies depend sensitively on the growth of SASI which develops chaotically in all directions. Our results show that the GW spectrum has its peak near 100 Hz, reflecting SASI-induced matter overturns of O(10) ms. We point out that the detection of such signals, possibly visible to the LIGO-class detectors for a Galactic supernova, could be an important probe into the long-veiled explosion mechanism. © 2009. The American Astronomical Society. All rights reserved.

    DOI

    Scopus

    75
    Citation
    (Scopus)
  • Ray-tracing analysis of anisotropic neutrino radiation for estimating gravitational waves in core-collapse supernovae

    Kei Kotake, Wakana Iwakami, Naofumi Ohnishi, Shoichi Yamada

    Astrophysical Journal   704 ( 2 ) 951 - 963  2009

     View Summary

    We propose a ray-tracing method to estimate gravitational waves (GWs) generated by anisotropic neutrino emission in supernova cores. To calculate the gravitational waveforms, we derive analytic formulae in a useful form, which are applicable also for three-dimensional computations. Pushed by evidence of slow rotation prior to core-collapse, we focus on asphericities in neutrino emission and matter motions outside the protoneutron star. Based on the two-dimensional models, which mimic standing accretion shock instability (SASI)-aided neutrino heating explosions, we compute the neutrino anisotropies via the ray-tracing method in a post-processing manner and calculate the resulting waveforms. For simplicity, neutrino absorption and emission by free nucleons, dominant processes outside the protoneutron stars, are only taken into account, while the neutrino scattering and the velocity-dependent terms in the transport equations are neglected. With these computations, it is found that the waveforms exhibit more variety in contrast to the ones previously estimated by the ray-by-ray analysis. In addition to a positively growing feature, which was predicted to determine the total wave amplitudes predominantly, the waveforms are shown to exhibit large negative growth for some epochs during the growth of SASI. These features are found to stem from the excess of neutrino emission in lateral directions, which can be precisely captured by the ray-tracing calculation. Reflecting the nature of SASI which grows chaotically with time, there is little systematic dependence of the input neutrino luminosities on the maximum wave amplitudes. Due to the negative contributions and the neutrino absorptions appropriately taken into account by the ray-tracing method, the wave amplitudes become more than one order of magnitude smaller than the previous estimation, thus making their detections very hard for a Galactic source. On the other hand, it is pointed out that the GW spectrum from matter motions have its peak near 100 Hz, reflecting the SASI-induced matter overturns of O(10) ms. Such a feature could be characteristic for the SASI-induced supernova explosions. The proposed ray-tracing method will be useful for the GW prediction in the first generation of three-dimensional core-collapse supernova simulations that do not solve the angle-dependent neutrino transport equations as part of the numerical evolution. © 2009. The American Astronomical Society. All rights reserved.

    DOI

    Scopus

    33
    Citation
    (Scopus)
  • Numerical methods for three-dimensional analysis of shock instability in supernova cores

    W. Iwakami, N. Ohnishi, K. Kotake, S. Yamada, K. Sawada

    Journal of Physics: Conference Series   112 ( Part 4 )  2008.06

     View Summary

    We studied the standing accretion shock instability (SASI) for a core-collapse supernova explosion. SASI induces a nonspherically symmetric motion of a standing spherical shock wave. In order to investigate the growth of SASI, we solved the three-dimensional compressible Euler equations using ZEUS-MP/2 code based on the finite-difference method with a staggered mesh of spherical polar geometry. Although the von Neumann and Richtmyer artificial viscosity is used in ZEUS-MP/2 code to capture shock waves, we propose utilizing a tensor artificial viscosity in order to overcome the numerical instability regarded as the carbuncle phenomenon. This numerical instability emerges around the grid polar axis and precludes mode analysis of SASI.

    DOI

    Scopus

    2
    Citation
    (Scopus)
  • Standing accretion shock instability: Numerical simulations of core-collapse supernova

    N. Ohnishi, W. Iwakami, K. Kotake, S. Yamada, S. Fujioka, H. Takabe

    Journal of Physics: Conference Series   112 ( Part 4 )  2008.06

     View Summary

    Standing accretion shock instability (SASI) is one of the candidates to solve the mystery of why we cannot reproduce the explosion with the present core-collapse supernova models. We have studied this phenomenon with including neutrino heating and realistic EOS and found that SASI may enhance neutrino heating. Although g-mode of proto-neutron star may enhance the SASI growth, the simulations just including the pressure perturbation as a mimic of g-mode induced sound wave reveal no significant effect on the shock dynamics. Moreover, we discuss the required conditions toward the possible laboratory experiment of SASI.

    DOI

    Scopus

    7
    Citation
    (Scopus)
  • Three-dimensional simulations of standing accretion shock instability in core-collapse supernovae

    Wakana Iwakami, Kei Kotake, Naofumi Ohnishi, Shoichi Yamada, Keisuke Sawada

    Astrophysical Journal   678 ( 2 ) 1207 - 1222  2008.05

     View Summary

    We have studied nonaxisymmetric standing accretion shock instabilities, or SASI, using three-dimensional (3D) hydrodynamical simulations. This is an extension of our previous study of axisymmetric SASI. We have prepared a spherically symmetric and steady accretion flow through a standing shock wave onto a proto-neutron star, taking into account a realistic equation of state and neutrino heating and cooling. This unperturbed model is meant to represent approximately the typical postbounce phase of core-collapse supernovae. We then added a small perturbation (∼1%) to the radial velocity and computed the ensuing evolutions. Both axisymmetric and nonaxisymmetric perturbations have been imposed. We have applied mode analysis to the nonspherical deformation of the shock surface, using spherical harmonics. We have found that (1) the growth rates of SASI are degenerate with respect to the azimuthal index m of the spherical harmonics Ylm, just as expected for a spherically symmetric background; (2) nonlinear mode couplings produce only m = 0 modes for axisymmetric perturbations, whereas m ≠= 0 modes are also generated in the nonaxisymmetric cases, according to the selection rule for quadratic couplings; (3) the nonlinear saturation level of each mode is lower in general for 3D than for 2D, because a larger number of modes contribute to turbulence in 3D; (4) low-l modes are dominant in the nonlinear phase; (5) equipartition is nearly established among different m modes in the nonlinear phase; (6) spectra with respect to l obey power laws with a slope slightly steeper for 3D; and (7) although these features are common to the models with and without a shock revival at the end of the simulation, the dominance of low-l modes is more remarkable in the models with a shock revival. © 2008. The American Astronomical Society. All rights reserved.

    DOI

    Scopus

    116
    Citation
    (Scopus)
  • Aeolian tones radiated from flow past two square cylinders in a side-by-side arrangement

    O. Inoue, W. Iwakami, N. Hatakeyama

    Physics of Fluids   18 ( 4 )  2006.04

     View Summary

    The sound generated by two square cylinders placed in a side-by-side arrangement in a uniform flow at low Mach numbers is studied by direct solution of the two-dimensional unsteady compressible Navier-Stokes equations. Special attention is paid to the effect of the spacing between the two cylinders on the generation mechanism of the sound. Results show that sound pressure fields as well as flow fields show different features depending on the spacing; six different wake patterns (nonsynchronized, antiphase and in-phase synchronized, flip-flopping, single bluff-body, and steady patterns) are observed and, depending on the wake pattern, sound pressure fields also show different features. Two types of bifurcation phenomenon are observed where two different wake patterns exist for the same spacing and either of the two patterns appears depending on an initial condition; different sound pressure fields appear in response to the wake patterns. Results also show that Curle's dipole solution does not predict well the direct numerical simulation results in the antiphase-synchronized pattern at a small spacing and the flip-flopping pattern, but that it gives a good approximation in the nonsynchronized, in-phase-synchronized, and single-bluff-body patterns. © 2006 American Institute of Physics.

    DOI

    Scopus

    61
    Citation
    (Scopus)

▼display all

Presentations

  • 三次元空間における重力崩壊型超新星のボルツマン輻射流体計算

    岩上わかな, 大川博督, 長倉洋樹, 原田了, 赤穂龍一郎, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会春季年会 

    Presentation date: 2024.03

  • The Boltzmann neutrino radiation hydrodynamic simulation of a core-collapse supernova in the three-dimensional space

    Wakana Iwakami

    Unraveling the History of the Universe and Matter Evolution with Underground Physics (UGAP2024) 

    Presentation date: 2024.03

    Event date:
    2024.03
     
     
  • A Simulation of Core-collapse Supernovae in Three-dimensional Space with Full Boltzmann Neutrino Transport on the Supercomputer FUGAKU

    Wakana Iwakami

    Unraveling the History of the Universe and Matter Evolution with Underground Physics (UGAP2022) 

    Presentation date: 2022.06

    Event date:
    2022.06
     
     
  • 三次元空間における重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 大川博督, 長倉洋樹, 原田了, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会2021年春季年会 

    Presentation date: 2021.03

  • 重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 大川博督, 長倉洋樹, 原田了, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会2020年春季年会 

    Presentation date: 2020.03

  • The Core-Collapse Supernova Simulations with the Full Boltzmann Neutrino Transport in Three-Dimensional Space

    Wakana Iwakami

    The Evolution of Massive Stars and Formation of Compact Stars: from the Cradle to the Grave (2020) 

    Presentation date: 2020.02

    Event date:
    2020.02
     
     
  • 重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 長倉洋樹, 大川博督, 原田了, 松古栄夫, 住吉光介, 山田章一

    日本天文学会2019年春季年会 

    Presentation date: 2019.03

  • Core-collapse supernovae simulations with Boltzmann-Hydro code

    Wakana Iwakami

    Physics of Core-Collapse Supernovae and Compact Star Formations (2018) 

    Presentation date: 2018.03

    Event date:
    2018.03
     
     
  • 重力崩壊型超新星のBoltzmann-Hydro Codeによるニュートリノ輻射流体計算

    岩上わかな, 長倉洋樹, 大川博督, 原田了, 松古栄夫, 住吉光介, 山田章一

    天文学会年会2018年春季年会 

    Presentation date: 2018.03

    Event date:
    2018.03
     
     
  • 重力崩壊型超新星で発生する流体力学的不安定性の数値計算

    犬塚慎之介, 岩上わかな, 山田章一

    平成29年度衝撃波シンポジウム 

    Presentation date: 2018.03

    Event date:
    2018.03
     
     
  • 重力崩壊型超新星爆発のボルツマン方程式によるニュートリノ輻射輸送計算

    岩上わかな, 長倉洋樹, 松古栄夫, 住吉光介, 山田章一

    日本天文学会2016年春季年会 

    Presentation date: 2016.03

    Event date:
    2016.03
     
     
  • ボルツマン方程式によるニュートリノ輻射流体計算コードを用いた重力崩壊型超新星爆発の二次元軸対称計算

    岩上わかな, 長倉洋樹, 松古栄夫, 住吉光介, 山田章一

    日本天文学会2016年春季年会 

    Presentation date: 2016.03

    Event date:
    2016.03
     
     
  • The Strategy for 6D Simulations of Core-Collapse Supernovae with Boltzmann-Hydro Code

    Wakana Iwakami

    Symposium on 'Quarks to Universe in Computational Science (QUCS2015) 

    Presentation date: 2015.11

    Event date:
    2015.11
     
     
  • Neutrino Radiation Hydrodynamic Simulations of Core Collapse Supernovae

    Wakana Iwakami

    Numazu Workshop 2015 

    Presentation date: 2015.09

    Event date:
    2015.09
     
     
  • 重力崩壊型超新星爆発と流体力学的不安定性に与える回転の影響

    岩上わかな, 長倉洋樹, 山田章一

    日本天文学会2014年秋季年会 

    Presentation date: 2014.09

    Event date:
    2014.09
     
     
  • Parametric Study of Explosion for Rotational Core-Collapse Supernovae

    Wakana Iwakami

    Multi-Messengers from Core-Collapse Supernovae (2013) 

    Presentation date: 2013.12

    Event date:
    2013.12
     
     
  • Various Flow Patterns behind the Accretion Shock wave for Core-Collapse Suprenovae

    Wakana Iwakami

    Supernovae and Gamma-Ray Bursts 2013 

    Presentation date: 2013.10

    Event date:
    2013.10
    -
    2013.11
  • 重力崩壊型超新星における定在降着衝撃波下流側の流れパターンの多様性

    岩上わかな, 長倉洋樹, 山田章一

    日本天文学会2013年秋季年会 

    Presentation date: 2013.09

    Event date:
    2013.09
     
     
  • The Effect of Rotation on the Shock Revival for the Core-Collapse Supernovae

    Wakana Iwakami

    1st Annual Symposium on "New Developments in Astrophysics Through Multi-Messenger Observations of Gravitational Wave Sources (2013) 

    Presentation date: 2013.03

    Event date:
    2013.03
     
     
  • Error Analysis for the Volume Penalization Method with Continuous Mask Functions

    Wakana Iwakami Nakano, Nozomu Hatakeyama, Yuji Hattori

    Ninth International Conference on Flow Dynamics (2012) 

    Presentation date: 2012.09

    Event date:
    2012.09
     
     
  • 連続型マスク関数を用いたVolume Penalization法の誤差解析

    中野わかな, 畠山望, 服部裕司

    日本流体力学会年会2012 

    Presentation date: 2012.09

    Event date:
    2012.09
     
     
  • Neutron Star Kicks Affected by Standing Accretion Shock Instability for Core-Collapse Supernovae

    Wakana Iwakami Nakano, Kei Kotake, Naofumi Ohnishi, Shoichi Yamada, Keisuke Sawada

    IAU Symposium 279, Death of Massive Stars: Supernovae & Gamma-Ray Bursts (2012) 

    Presentation date: 2012.03

    Event date:
    2012.03
     
     
  • Volume Penalization法の誤差低減法

    中野わかな, 畠山望, 服部裕司

    第25回数値流体力学シンポジウム 

    Presentation date: 2011.12

    Event date:
    2011.12
     
     
  • Error Reduction for the Volume Penalization Method

    Wakana Iwakami Nakano, Nozomu Hatakeyama, Yuji Hattori

    The eighth International Conference on Flow Dynamics (2011) 

    Presentation date: 2011.11

    Event date:
    2011.11
     
     
  • A Study of Volume Penalization Method Applied to High-Order Accurate Schemes

    Wakana Iwakami Nakano, Nozomu Hatakeyama, Yuji Hattori

    Seventh International Conference of Flow Dynamics (2010) 

    Presentation date: 2010.11

    Event date:
    2010.11
     
     
  • Development and Application of the Volume Penalization Method with Spectral-like Accuracy for Open Flow Conditions

    Wakana Iwakami Nakano, Nozomu Hatakeyama, Yuji Hattori

    Euromech Fluid Mechanics Conference - 8 (2010) 

    Presentation date: 2010.09

    Event date:
    2010.09
     
     
  • Volume Penalization法の高次精度スキームへの適用

    中野わかな, 畠山望, 服部裕司

    日本流体力学会年会2010 

    Presentation date: 2010.09

    Event date:
    2010.09
     
     
  • 力崩壊型超新星における定在降着衝撃波不安定性の数値シミュレーション

    中野わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本物理学会第65回年次大会 

    Presentation date: 2010.03

    Event date:
    2010.03
     
     
  • 定在降着衝撃波不安定性による中性子星キックの統計解析

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会2009年秋季年会 

    Presentation date: 2009.09

    Event date:
    2009.09
     
     
  • 超新星爆発における球状降着衝撃波の不安定性の三次元数値解析

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    第22回数値流体力学シンポジウム 

    Presentation date: 2008.12

    Event date:
    2008.12
     
     
  • 中性子星のキックやスピンに対する定在降着衝撃波の不安定性の影響

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会2008年秋季年会 

    Presentation date: 2008.09

    Event date:
    2008.09
     
     
  • Numerical Analysis of SASI by 3-D simulations

    Wakana Iwakami  [Invited]

    Asymmetric Instabilities in Stellar Core Collapse (2008) 

    Presentation date: 2008.07

    Event date:
    2008.06
    -
    2008.07
  • Effects of Shock Instability on Spin and Kick of Proto-Neutron Star in Supernova Cores

    Wakana Iwakami, Naofumi Ohnishi, Kei Kotake, Shoichi Yamada, Keisuke Sawada

    International Conference on HEDP/HEDLA-08 (2008) 

    Presentation date: 2008.04

    Event date:
    2008.04
     
     
  • 重力崩壊型超新星コアにおける定在降着衝撃波不安定性に対する回転の効果

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会2008年春季年会 

    Presentation date: 2008.03

    Event date:
    2008.03
     
     
  • 3D Simulations of Standing Accretion Shock Instability in Core-Collapse Supernovae"

    Wakana Iwakami

    14th Workshop on "Nuclear Astrophysics" (2008) 

    Presentation date: 2008.03

    Event date:
    2008.03
     
     
  • 重力崩壊型超新星コアで発生する停滞衝撃波の不安定性

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会2007年秋季年会 

    Presentation date: 2007.09

    Event date:
    2007.09
     
     
  • Three-Dimensional Simulations of Standing Accretion Shock Instability in Supernova Cores

    Wakana Iwakami, Naofumi Ohnishi, Kei Kotake, Shoichi Yamada

    Fifth International Conference on Inertial Fusion Sciences and Applications (2007) 

    Presentation date: 2007.09

    Event date:
    2007.09
     
     
  • 並列二角柱周りの流れから発生する音の直接数値計算と理論予測

    岩上わかな, 畠山望, 井上督

    第19回数値流体力学シンポジウム 

    Presentation date: 2005.12

    Event date:
    2005.12
     
     
  • Vortex Flow past a Pair of Square Cylinders and Sound Generation

    Wakana Iwakami, Nozomu Hatakeyama, Osamu Inoue

    The 3rd International Conference on Vortex Flows and Vortex Models (2005) 

    Presentation date: 2005.11

    Event date:
    2005.11
     
     
  • Sound Generation from a Pair of Square Cylinder

    Wakana Iwakami, Nozomu Hatakeyama, Osamu Inoue

    The 5th International Symposium on Advanced Fluid Information (2005) 

    Presentation date: 2005.11

    Event date:
    2005.11
     
     
  • 一様流中の並列二角柱周りから発生する音波

    岩上わかな, 畠山望, 井上督

    日本流体力学会年会2005 

    Presentation date: 2005.09

    Event date:
    2005.09
     
     
  • 一様流中の並列二角柱周りから発生する渦と音波

    岩上わかな, 今村綾花, 畠山望, 井上督

    第18回数値流体力学シンポジウム 

    Presentation date: 2004.12

    Event date:
    2004.12
     
     

▼display all

Research Projects

  • Non-modal stability of vortices and by-pass transition: towards general theory of hydrodynamic stability

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2012.04
    -
    2015.03
     

    HATTORI Yuji, FUKUMOTO Yasuhide, IWAKAMI Wakana

     View Summary

    Vortices are one of the fundamental structures in various flows. The stability of vortices is the starting point in understanding the nature of the flow. Transient growth and destabilization by localized disturbances in vortices are studied theoretically and numerically in order to understand the transition to turbulence in vortical flows. In transient growth vortex stretching by straining flow is shown to be a key mechanism. Numerical results of unstable growth of localized disturbances are in good agreement with theoretical prediction. The transition to turbulence occurs after several stages of growth.

  • Explosion mechanism of supernovae by 3D neutrino-radiation hydrodynamics

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2010.04
    -
    2015.03
     

    SUMIYOSHI Kohsuke

     View Summary

    We developed a new numerical code to perform numerical simulation of core-collapse supernovae by 3D neutrino-radiation hydrodynamics. This code is constructed, for the first time in the world, using the Boltzmann equation in the full 6 dimensions. This novel code is an essential tool to study the mechanism of supernova explosions, which is the final fate of massive stars, via the neutrino heating mechanism. We enabled ones to describe neutrino creation, propagation and annihilation for the neutrino heating in 3D space without approximations previously used. We revealed the characteristics of neutrino transfer in 3D space and its influence on the explosions.

  • 翼周りから発生する渦と音波に関する数値的研究

    前川報恩会  平成23年度第3回学術研究助成

    Project Year :

    2011.04
    -
    2012.03
     

    中野わかな

  • Quest for the unified picture of the explosion mechanism of supernovae and the central engine of gamma-ray bursts

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2007
    -
    2011
     

    SATO Katsuhiko, HASHIMOTO Masaaki, SUZUKI Hideyuki, YAMADA Shoichi, NAGATAKI Shigehiro, KOTAKE Kei, TAKIWAKI Tomoya, WATANABE Gentaro, OHNISHI Naohumi, SUMIYOSHI Kohsuke, FUJIMOTO Shinichiro, KIUCHI Kenta, IWAKAMI Wakana, SAWAI Hidetomo, YASUTAKE Nobutoshi, NISHIMURA Nobuya, SUWA Yudai, NAKAZATO Kenichiro, NAGAKURA Hiroki

     View Summary

    Advanced studies on the explosion mechanism of core-collapse supernovae and central engine of gamma-ray bursts were performed in this program, giving fruitful and state-of-the-art results. Lots of large-scale numerical simulations were done for the purpose, and in some cases cutting-edge simulations were performed using the K-computer. We also succeeded to obtain fruitful and noteworthy results on lots of phenomena accompanying core-collapse supernovae and gamma-ray bursts, such as gravitational waves, neutrino emissions, explosive nucleosynthesis including r-process nucleosynthesis, and ultra-high energy cosmic rays. For the above reasons, it is concluded that we could achieve great success to obtain cutting edge results in this program, which is more than we expected. Simultaneously, our five-year mission has ended successfully, leaving future works and direction of this field.

  • 三次元数値計算と模擬実験による重力崩壊型超新星爆発メカニズムの解明

    日本学術振興会  科学研究費助成事業

    Project Year :

    2008
    -
    2009
     

    中野 わかな

     View Summary

    本研究では、重力崩壊型超新星の爆発メカニズム、並びに爆発時に形成される原始中性子星のキック・スピン現象の解明を目的として、定在降着衝撃波の不安定性(SASI)の三次元数値流体シミュレーションを行っている。昨年度は、主に回転がSASIに与える影響と、SASIが原始中性子星のキック・スピン現象とどのようにかかわっているかについて調べた。本年度は、SASIが原始中性子星に与える運動量について統計解析を試み、2009年の9月に行われた天文学会で発表した。また、回転SASIのデータを使って、共同研究である重力波の解析も行った。
    中性子星は重力崩壊型超新星が爆発した後に形成される天体であり、周期的な電磁パルスを放出する観測可能な天体である。中性子星は、平均400km/sで並進運動しており、爆発前の星よりも速い固有速度を持っている。この現象を中性子星キックと呼ぶが、そのメカニズムはよくわかっていない。本研究では、中性子星キックが爆発の非球対称性によるものであり、その非球対称性はSASIによるものであると考える。SASIが原始中性子星に与える運動量を調べ、その統計的な性質を明らかにすることで、観測結果が示す統計的性質と比較する。もし、SASIが原始中性子星に与える運動量の統計的性質が、観測結果が示すものと同様であれば、爆発時にSASIが発生している可能性をより強く示唆することができる。SASIの直接観測は、ニュートリノや重力波による観測の可能性が提案されてはいるが、現時点では困難であり、中性子星キック現象との関連を示すことで間接的にSASIの存在を示すことは大変意義がある。

Misc

  • 三次元空間における重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 大川博督, 長倉洋樹, 原田了, 古澤峻, 赤穂龍一郎, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2021  2021

    J-GLOBAL

  • 重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 大川博督, 長倉洋樹, 原田了, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2020  2020

    J-GLOBAL

  • 重力崩壊型超新星のボルツマン方程式によるニュートリノ輻射流体計算

    岩上わかな, 岩上わかな, 長倉洋樹, 大川博督, 大川博督, 原田了, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2019  2019

    J-GLOBAL

  • 重力崩壊型超新星のBoltzmann-Hydro Codeによるニュートリノ輻射流体計算

    岩上わかな, 岩上わかな, 長倉洋樹, 大川博督, 大川博督, 原田了, 古澤峻, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2018  2018

    J-GLOBAL

  • 重力崩壊型超新星で発生する流体力学的不安定性の数値計算

    犬塚愼之介, 岩上わかな, 岩上わかな, 山田章一

    衝撃波シンポジウム講演論文集(CD-ROM)   2017  2018

    J-GLOBAL

  • ボルツマン方程式によるニュートリノ輻射流体計算コードを用いた重力崩壊型超新星爆発の二次元軸対称計算

    岩上わかな, 長倉洋樹, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2016  2016

    J-GLOBAL

  • 重力崩壊型超新星爆発のボルツマン方程式によるニュートリノ輻射輸送計算

    岩上わかな, 長倉洋樹, 松古栄夫, 住吉光介, 山田章一

    日本天文学会年会講演予稿集   2016  2016

    J-GLOBAL

  • 23pDJ-10 The Analysis of the Hydrodynamical Instabilities and Gravitional Waves in Core-collapse Supernovae

    Inutsuka S., Iwakami W., Yamada S.

    Meeting Abstracts of the Physical Society of Japan   70.1   466  2015

    DOI CiNii

  • 重力崩壊型超新星爆発と流体力学的不安定性に与える回転の影響

    岩上わかな, 長倉洋樹, 山田章一

    日本天文学会年会講演予稿集   2014  2014

    J-GLOBAL

  • 重力崩壊型超新星における定在降着衝撃波下流側の流れパターンの多様性

    岩上わかな, 長倉洋樹, 山田章一

    日本天文学会年会講演予稿集   2013  2013

    J-GLOBAL

  • Neutron star kicks affected by standing accretion shock instability for core-collapse supernovae

    Wakana Iwakami Nakano, Kei Kotake, Naofumi Ohnishi, Shoichi Yamada, Keisuke Sawada

    Proceedings of the International Astronomical Union   7 ( S279 ) 337 - 338  2011.04

     View Summary

    We investigate a proto-neutron star kick velocity estimated from kinetic momentum of a flow around the proto-neutron star after the standing accretion shock instability grows. In this study, ten different types of random perturbations are imposed on the initial flow for each neutrino luminosity. We found that the kick velocities of proto-neutron star are widely distributed from 40 km s -1 to 180 km s -1 when the shock wave reaches 2000 km away from the center of the star. The average value of kick velocity is 115 km s -1, whose value is smaller than the observational ones. The kick velocities do not depend on the neutrino luminosity. © 2012 International Astronomical Union.

    DOI

  • Volume Penalization法の誤差低減法

    中野わかな, 畠山望, 服部裕司

    数値流体力学シンポジウム講演論文集(CD-ROM)   25th  2011

    J-GLOBAL

  • Application of the volume penalization method to high-order accurate numerical scheme

    (Iwakami)Nakano,Wakana, Hatakeyama,Nozomu, Hattori,Yuji

      2010   268  2010.09

     View Summary

    The volume penalization method is one of applicable means to investigate numerically flows with complicated geometrical boundaries. In this study we research the behaviors of numerical errors occuring with the addition of volume penalization (VP) term to one-dimensional Burgers' equation, using 4th-order compact schemes in spacial discretization and the 4th-order runge-kutta method in time development. The volume penalization term has a mask function χ(x) describing boundary geometries and a parameter η called permeability. We adopted the step function as the χ(x) and changed the η from 10^<-2> to 10^<-5>. The results show that the numerical errors for Burgers' equation with VP term are much larger than that for it without one. The error becomes minimum at a number of grid points N which depend on η.

    CiNii

  • 22pEJ-6 Numerical simulation of spherical shock instability for core collapse supernovae

    Nakano Wakana, Ohnishi Naofumi, Kotake Kei, Yamada Shoichi, Sawada Keisuke

    Meeting Abstracts of the Physical Society of Japan   65.1.2   338  2010

    DOI CiNii

  • 定在降着衝撃波不安定性による中性子星キックの統計解析

    岩上わかな, 山田章一, 固武慶, 大西直文, 澤田恵介

    日本天文学会年会講演予稿集   2009  2009

    J-GLOBAL

  • 重力崩壊型超新星コアにおける定在降着衝撃波不安定性に対する回転の効果

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会年会講演予稿集   2008  2008

    J-GLOBAL

  • 中性子星のキックやスピンに対する定在降着衝撃波の不安定性の影響

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    日本天文学会年会講演予稿集   2008  2008

    J-GLOBAL

  • 超新星爆発における球状降着衝撃波の不安定性の三次元数値解析

    岩上わかな, 大西直文, 固武慶, 山田章一, 澤田恵介

    数値流体力学シンポジウム講演論文集(CD-ROM)   22nd  2008

    J-GLOBAL

  • 重力崩壊型超新星コアで発生する停滞衝撃波の不安定性

    岩上わかな, 大西直文, 固武慶, 山田章一

    日本天文学会年会講演予稿集   2007  2007

    J-GLOBAL

  • AM05-23-001 Sound Generated from a Pair of Square Cylinders in a Uniform Flow

    IWAKAMI,Wakana, HATAKEYAMA,Nozomu, INOUE,Osamu

      2005   297  2005.09

     View Summary

    The study of sound generated by a pair of square cylinders placed side by side in a uniform flow is performed. The sound expected by Curie's method containing the Doppler effect is compared to the sound obtained by a direct numerical simulation (DNS). When the distance between the centers of the cylinders is small, the sound expected by Curle's method agrees with the sound obtained by DNS for the in-phase vortex shedding, but does not for the antiphase vortex shedding.

    CiNii

  • Sound Generation from a Pair of Square Cylinders

    IWAKAMI Wakana, HATAKEYAMA Nozomu, INOUE Osamu

    International Symposium on Advanced Fluid Information   5th  2005

    J-GLOBAL

  • 並列二角柱周りの流れから発生する音の直接数値計算と理論予測

    岩上わかな, 畠山望, 井上督

    数値流体力学シンポジウム講演論文集(CD-ROM)   19th  2005

    J-GLOBAL

  • 一様流中の並列二角柱周りから発生する渦と音波

    岩上わかな, 今村綾花, 畠山望, 井上督

    数値流体力学シンポジウム講演論文集(CD-ROM)   18th  2004

    J-GLOBAL

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Syllabus

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Teaching Experience

  • Physics Exercises B

    Waseda University  

    2024.04
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  • Fundamental Engineering Experiment 1A

    Waseda University  

    2024.04
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  • Mechanics A

    Waseda University  

    2024.04
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