担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

In this study, we investigate the stability required for a two-dimensional sloshing analysis with the use of an arbitrary Lagrangian–Eulerian (ALE) method. Here, two well-known upwind methods are employed for the discretization of the kinematic condition on the free surface: SUPG and CIP methods. On the other hand, the Navier-Stokes equations are discretized by a finite element scheme without any upwind method to see whether the stability is retained solely by introducing an appropriate upwind method into the calculation on the free surface. It is shown in both primary and tertiary modes that stable results are obtained when the CIP method is employed, while unstable grid-scale oscillations are observed at some point when the SUPG method is used. This suggests that a semi-Lagrangian scheme is essential for stable computation based on the ALE formulation.

DOI： 10.1299/jsmecmd.2019.32.073

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007817141

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

In our previous work, a three-dimensional numerical scheme for analyzing magnetohydrodynamic (MHD) flows under alternating-current magnetic fields was constructed, which takes into account the coupling with the electromagnetic fields in the solid and gas regions. In this study, a periodic boundary condition and an external traveling-wave magnetic field are introduced into the numerical scheme to investigate the dependences of the MHD flow in a square duct on the Hartmann number and the phase velocity of the external magnetic field. It is shown that the flow in the axial direction is encouraged with the increase in the Hartmann number or the angular frequency, while an opposite behavior is observed in terms of the oscillation amplitude of the fluid flow.

DOI： 10.1299/jsmecmd.2019.32.103

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007817254

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

Three-dimensional numerical simulation of incompressible, magnetohydrodynamic flows under traveling magnetic fields are carried out, which takes into account the coupling with the electromagnetic field in the solid and gas regions. A numerical scheme is constructed by combining the Galerkin finite element method and the edge-element based finite element method, which are applied to the discretizations of Navier-Stokes equations and the electromagnetic field equations, respectively. The solution algorithm for fluid flow is based on an explicit fractional step approach and the simultaneous relaxation of velocity and pressure to satisfy the continuity equation. The electromagnetic field equations are formulated with the use of the magnetic vector potential which is defined on the edge elements. Numerical simulations of the MHD flows in an annular channel are carried out under traveling magnetic fields. It is confirmed that the magnitude and oscillation amplitude of the z-component of the velocity becomes larger with the increase in the Hartmann number. It is also shown that the frequency of the velocity pulsation is doubled than the frequency of the externally applied traveling magnetic field.

DOI： 10.1299/jsmecmd.2019.32.028

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007817209

記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 IOP Publishing Ltd. In ion cyclotron range of frequency (ICRF) experiments in fusion research devices, radio frequency (RF) sheaths form where plasma, strong RF wave fields and material surfaces coexist. These RF sheaths affect plasma material interactions such as sputtering and localized power deposition, as well as the global RF wave fields themselves. RF sheaths may be modeled by employing a sheath boundary condition (BC) in place of the more customary conducting wall (CW) BC; however, there are still many ICRF computer codes that do not implement the sheath BC. In this paper we present a method for post-processing results obtained with the CW-BC. The post-processing method produces results that are equivalent to those that would have been obtained with the RF sheath BC, under certain assumptions. The post-processing method is also useful for verification of sheath BC implementations and as a guide to interpretation and understanding of the role of RF sheaths and their interactions with the waves that drive them.

DOI： 10.1088/1361-6587/ab2f41

Kyutacar

Scopus

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記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Author(s). Radio frequency (RF) sheaths form near surfaces where plasma and strong RF fields coexist. The effect of these RF sheaths on wave propagation near the boundary can be characterized by an effective sheath impedance that includes both resistive and capacitive contributions describing RF sheath rectification and RF power absorption in the sheath [J. R. Myra and D. A. D'Ippolito, Phys. Plasmas 22, 062507 (2015)]. Here, we define a dimensionless parameter, the ratio of incoming wave impedance to the sheath impedance, which determines the characteristics of the interaction, ranging from quasi-conducting to quasi-insulating, or in the case of matched impedances, to either perfect absorption or a sheath-plasma resonance. A semi-analytical analysis is carried out for electrostatic slow waves in the ion cyclotron range of frequencies. For the propagating slow wave case, where the incident wave is partially reflected, the fraction of power dissipated in the sheath is calculated. For the evanescent slow wave case, which admits a sheath-plasma resonance, an amplification factor is calculated. Using the impedance ratio approach, RF sheath interactions are characterized for a range of RF wave and plasma parameters including plasma density, magnetic field angle with respect to the surface, wave frequency, and wave-vector components tangent to the surface. For a particularly interesting example case, results are compared with the rfSOL code [H. Kohno and J. R. Myra, Comput. Phys. Commun. 220, 129 (2017)]. Finally, electromagnetic effects, absent from the semi-analytical analysis, are assessed.

DOI： 10.1063/1.5088343

Kyutacar

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

© 2019 Author(s). The physics of interactions between waves in plasmas and sheaths for background magnetic fields which make oblique angles with sheath surfaces is studied with the use of the self-consistent finite element code rfSOL incorporating the recently developed sheath impedance model [J. R. Myra, Phys. Plasmas 24, 072507 (2017)]. The calculation based on this model employs the generalized sheath boundary condition (sheath BC), which surpasses the previously used capacitive sheath BC in reliability by taking into account the contributions of the ion and electron currents in the sheath and the displacement current. A series of numerical simulations is carried out in two-dimensional slab geometry with a flat or curved sheath surface as part of the boundary. It is shown that the sheath-plasma wave appears when the equilibrium magnetic field line angle with respect to the sheath surface is small, the absolute value of the radio-frequency (RF) sheath voltage is large, and the plasma density is slightly higher than the lower hybrid resonance density (LHR density), all of which bring the sheath property closer to being capacitive. It is also shown that the sharp variation of the magnetic field line angle along the sheath surface can sensitively affect the maximum absolute value of the RF sheath voltage at a plasma density slightly lower than the LHR density.

DOI： 10.1063/1.5054920

Kyutacar

Scopus

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担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

Three-dimensional (3D) numerical simulation of incompressible, magnetohydrodynamic (MHD) flows under alternating-current (AC) magnetic fields are carried out, which takes into account the coupling with the electromagnetic fields in the solid and gas regions. A numerical scheme is constructed by combining the Galerkin finite element method and the edge-element based finite element method, which are applied to the discretizations of the Navier–Stokes equations and the electromagnetic field equations, respectively. The solution algorithm for fluid flow is based on an explicit fractional step approach and the simultaneous relaxation of velocity and pressure to satisfy the continuity equation. The electromagnetic field equations are formulated with the use of the magnetic vector potential which is defined on the edge elements. In the proposed numerical scheme, the advection term in the induction equation is not neglected, because the scheme needs to deal with the condition where the advection term is the same order with the diffusion term in that equation. The validity of the numerical scheme is verified through the analysis of the electromagnetic field under a direct-current magnetic field, and numerical simulations of the MHD flows under spatially uniform AC magnetic fields are carried out. It is confirmed that the spatio-temporal mean Lorentz force in the conducting fluid becomes weaker with the increase in the dimensionless frequency due to the skin effect. It is also shown that the flow pattern in a hexahedral closed domain is largely changed when the frequency is getting higher, which is associated with the change in the Lorentz force profile.

DOI： 10.1299/transjsme.17-00589

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007419065

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

A finite element code that solves self-consistent radio-frequency (RF) sheath-plasma interaction problems is improved by incorporating a generalized sheath boundary condition in the macroscopic solution scheme. This sheath boundary condition makes use of a complex sheath impedance including both the sheath capacitance and resistance, which enables evaluation of not only the RF voltage across the sheath but also the power dissipation in the sheath. The newly developed finite element procedure is applied to cases where the background magnetic field is perpendicular to the sheath surface in one- and two-dimensional domains filled by uniform low- and high-density plasmas. The numerical results are compared with those obtained by employing the previous capacitive sheath model at a typical frequency for ion cyclotron heating used in fusion experiments. It is shown that for sheaths on the order of 100 V in a high-density plasma, localized RF power deposition can reach a level which causes material damage. It is also shown that the sheath-plasma wave resonances predicted by the capacitive sheath model do not occur when parameters are such that the generalized sheath impedance model substantially modifies the capacitive character of the sheath. Possible explanations for the difference in the maximum RF sheath voltage depending on the plasma density are also discussed.

DOI： 10.1016/j.cpc.2017.06.025

Scopus

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

© 2017 The authors, published by EDP Sciences. For applications of ICRF power in fusion devices, control of RF sheath interactions is of great importance. A sheath boundary condition (SBC) was previously developed to provide an effective surface impedance for the interaction of the RF sheath with the waves. The SBC enables the surface power flux and rectified potential energy available for sputtering to be calculated. For legacy codes which cannot easily implement the SBC, or to speed convergence in codes which do implement it, we consider here an approximate method to simulate SBCs by post-processing results obtained using other, e.g. conducting wall, boundary conditions. The basic approximation is that the modifications resulting from the generalized SBC are driven by a fixed incoming wave which could be either a fast wave or a slow wave. The method is illustrated in slab geometry and compared with exact numerical solutions; it is shown to work very well.

DOI： 10.1051/epjconf/201715703037

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

Copyright © 2016 John Wiley & Sons, Ltd. A new mixed-interpolation finite element method is presented for the two-dimensional numerical simulation of incompressible magnetohydrodynamic (MHD) flows which involve convective heat transfer. The proposed method applies the nodal shape functions, which are locally defined in nine-node elements, for the discretization of the Navier–Stokes and energy equations, and the vector shape functions, which are locally defined in four-node elements, for the discretization of the electromagnetic field equations. The use of the vector shape functions allows the solenoidal condition on the magnetic field to be automatically satisfied in each four-node element. In addition, efficient approximation procedures for the calculation of the integrals in the discretized equations are adopted to achieve high-speed computation. With the use of the proposed numerical scheme, MHD channel flow and MHD natural convection under a constant applied magnetic field are simulated at different Hartmann numbers. The accuracy and robustness of the method are verified through these numerical tests in which both undistorted and distorted meshes are employed for comparison of numerical solutions. Furthermore, it is shown that the calculation speed for the proposed scheme is much higher compared with that for a conventional numerical integration scheme under the condition of almost the same memory consumption. Copyright © 2016 John Wiley & Sons, Ltd.

DOI： 10.1002/fld.4292

Scopus

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担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.1299/jsmekyushu.2017.70.817

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007099690

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.1299/jsmekyushu.2017.70.818

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007099682

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.1299/jsmekyushu.2017.70.816

CiNii Article

その他リンク： https://ci.nii.ac.jp/naid/130007099749

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Japan   Kyoto   2016年10月17日  -  2016年10月22日

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4960384

Scopus

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

その他リンク： http://ci.nii.ac.jp/naid/110010054797

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

その他リンク： http://ci.nii.ac.jp/naid/110010054798

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.cpc.2015.05.002

Scopus

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4926449

Scopus

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.1299/jsmekyushu.2015.68.3

CiNii Article

CiNii Research

その他リンク： https://ci.nii.ac.jp/naid/130006576105

担当区分：最終著者,　責任著者   記述言語：日本語   掲載種別：研究論文（学術雑誌）

DOI： 10.1299/jsmekyushu.2015.68.1

CiNii Article

CiNii Research

その他リンク： https://ci.nii.ac.jp/naid/130006575966

記述言語：英語   掲載種別：研究論文（学術雑誌）

A level set method is applied to characterize the three dimensional structures of nickel, yttria stabilized zirconia and pore phases in solid oxide fuel cell anode reconstructed by focused ion beam-scanning electron microscope. A numerical algorithm is developed to evaluate the contact angles at the triple phase boundary based on interfacial normal vectors which can be calculated from the signed distance functions defined for each of the three phases. Furthermore, surface tension force is estimated from the contact angles by assuming the interfacial force balance at the triple phase boundary. The average contact angle values of nickel, yttria stabilized zirconia and pore are found to be 143°-156°, 83°-138° and 82°-123°, respectively. The mean contact angles remained nearly unchanged after 100 hour operation. However, the contact angles just after reduction are different for the cells with different sintering temperatures. In addition, standard deviations of the contact angles are very large especially for yttria stabilized zirconia and pore phases. The calculated surface tension forces from mean contact angles were close to the experimental values found in the literature. Slight increase of surface tensions of nickel/pore and nickel/yttria stabilized zirconia were observed after operation. Present data are expected to be used not only for the understanding of the degradation mechanism, but also for the quantitative prediction of the microstructural temporal evolution of solid oxide fuel cell anode. © 2014 Elsevier Inc.

DOI： 10.1016/j.matchar.2014.07.020

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.4818991

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.cpc.2013.02.002

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

Understanding the detailed physicochemical mechanisms for the electro-oxidation of fuel at the triple phase boundaries (TPBs) in solid oxide fuel cell (SOFC) anodes is a key step towards improving SOFC performance. Significant efforts have been directed toward this goal via both experimental and computational modeling studies. In particular, patterned Ni anode on a planar YSZ substrate has been examined because of its well-defined twodimensional geometry that in principle offers the advantages of known TPB length and minimization of mass transport effects. A common formulation for such patterned anodes considers modeling of surface reactions and diffusion on both electrode and electrolyte surfaces, along with charge-transfer reactions at the TPBs based on elementary kinetics. In this study, we review the theoretical approaches proposed by several authors and offer a critique of their methods. © The Electrochemical Society.

DOI： 10.1149/05701.2821ecst

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.cpc.2012.05.014

Scopus

担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1063/1.3677262

Scopus

記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）

A new quantitative approach for computing the rf sheath potential is described, which incorporates plasma dielectric effects and the relative geometry of the magnetic field and the material boundaries. The new approach uses a modified boundary condition ("rf sheath BC") that couples the rf waves and the sheaths at the boundary. It treats the sheath as a thin vacuum region and matches the fields across the plasma-vacuum boundary. When combined with the Child-Langmuir Law (relating the sheath width and sheath potential), the model permits a self-consistent determination of the sheath parameters and the rf electric field at the sheath-plasma boundary. Semi-analytic models using this BC predict a number of general features, including a sheath voltage threshold, a dimensionless parameter characterizing rf sheath effects, and the existence of sheath plasma waves with an associated resonance. Since the sheath BC is nonlinear and dependent on geometry, computing the sheath potential numerically is a challenging computational problem. Numerical results will be presented from a new parallel-processing finite-element rf wave code for the tokamak scrape-off layer (called "rfSOL"). The code has verified the physics predicted by analytic theory in 1D, and extended the solutions into model 2D geometries. The numerical calculations confirm the existence of multiple roots and hysteresis effects, and parameter studies have been carried out. Areas for future work will be discussed. © 2011 American Institute of Physics.

DOI： 10.1063/1.3664959

Scopus

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担当区分：筆頭著者,　責任著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.compstruc.2009.05.001

Scopus

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.ijengsci.2007.03.016

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1016/j.physleta.2006.12.074

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1002/cnm.861

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）

DOI： 10.1002/fld.1246

開催期間： 2021年11月08日 - 2021年11月12日   記述言語：英語   開催地：Pittsburgh, Pennsylvania   国名：アメリカ合衆国  

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開催期間： 2014年12月11日 - 2014年12月12日   記述言語：英語   開催地：九州大学 筑紫キャンパス   国名：日本国  

開催期間： 2014年03月04日   記述言語：日本語   開催地：九州大学 伊都キャンパス   国名：日本国  

開催期間： 2014年03月04日   記述言語：日本語   開催地：九州大学 伊都キャンパス   国名：日本国  

開催期間： 2014年03月04日   記述言語：日本語   開催地：九州大学 伊都キャンパス   国名：日本国  

開催期間： 2014年03月04日   記述言語：日本語   開催地：九州大学 伊都キャンパス   国名：日本国  

開催期間： 2013年12月19日 - 2013年12月20日   記述言語：英語   開催地：九州大学 筑紫キャンパス   国名：日本国  

開催期間： 2013年08月19日 - 2013年08月20日   記述言語：英語   開催地：京都大学 百周年時計台記念館   国名：日本国  

開催期間： 2013年06月25日 - 2013年06月28日   記述言語：英語   開催地：Hotel Parco dei Principi, Sorrento   国名：イタリア共和国