研究者詳細 - 河野晴彦

論文 - 河野晴彦

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2次元移流問題におけるCIP法に基づく離散化手法の比較

河野雄太，河野晴彦

日本機械学会九州支部講演論文集 ( 日本機械学会 ) 2017.70 259 - 260 2017年01月

An improved rf-sheath boundary condition and implications for ICRF modeling 査読有り国際誌

J. R. Myra, H. Kohno

26th IAEA Fusion Energy Conference, Kyoto, Japan, 17-22 October 2016, paper IAEA-CN-234/TH/P4-31 2016年10月

Erratum: "Numerical investigation of fast-wave propagation and radio-frequency sheath interaction with a shaped tokamak wall" [Phys. Plasmas 22, 072504 (2015)] 査読有り国際誌

H. Kohno, J. R. Myra, D. A. D'Ippolito

Physics of Plasmas ( AIP Publishing ) 23 ( 8 ) 089901-1 - 089901-4 2016年08月

流れの有限要素法による自由表面の変形を有する電磁流体の数値解析

梶山祐甫，河野晴彦

日本機械学会九州支部講演論文集 ( 日本機械学会 ) 2016.69 351 - 352 2016年01月

CUDAによる電磁熱流体解析の高速化

迫田卓，河野晴彦

日本機械学会九州支部講演論文集 ( 日本機械学会 ) 2016.69 349 - 350 2016年01月

An efficient, high-order finite element method using the nodal averaging technique for incompressible fluid flows 査読有り国際誌

Haruhiko Kohno

Computer Physics Communications ( Elsevier B.V. ) 195 68 - 76 2015年10月

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 new finite element method is presented for use of quadrilateral nine-node elements in the solution of the incompressible Navier-Stokes equations. In a conventional predictor-corrector scheme, the method applies the nodal averaging technique to discretize the Poisson equation used for the simultaneous relaxation of velocity and pressure. Additionally, efficient approximation procedures are devised to increase the speed of computation without deteriorating solution accuracy. The proposed numerical schemes are evaluated on two-dimensional test problems including a classical lid-driven cavity flow and a flow over a backward-facing step in a flow channel. The results show good accuracy even when distorted elements are used for calculation.

DOI： 10.1016/j.cpc.2015.05.002

Scopus

Numerical investigation of fast-wave propagation and radio-frequency sheath interaction with a shaped tokamak wall 査読有り

H. Kohno, J. R. Myra, D. A. D'Ippolito

Physics of Plasmas ( AIP Publishing ) 22 ( 7 ) 072504-1 - 072504-12 2015年07月

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）

Interactions between propagating fast waves and radio-frequency (RF) sheaths in the ion cyclotron range of frequencies are numerically investigated based on a cold fluid plasma model coupled with a sheath boundary condition. In this two-dimensional study, the capability of the finite element code rfSOL, which was developed in previous numerical work, is extended to analyze self-consistent RF sheath-plasma interaction problems in a tokamak with a non-circular cross-section. It is found that a large sheath voltage is generated near the edges of the limiter-shaped deformation as a result of the conversion from fast to slow waves on the sheaths. The sheath voltage associated with this conversion is particularly significant in the localized region where the contact angle between the magnetic field line and the conducting wall varies rapidly along the curved sheath surface, which is consistent with the results in previous one-dimensional theoretical work. The dependences of the RF sheaths on various parameters in plasma such as the toroidal wavenumber, edge plasma density, and the degree of the RF wave absorption in the core region are also examined in detail.

DOI： 10.1063/1.4926449

Scopus

直流磁場下における上昇気泡の数値解析

田中宏幸，河野晴彦

日本機械学会九州支部講演論文集 ( 日本機械学会 ) 2015.68 3 - 4 2015年01月

ハイブリッド並列による電磁熱流体解析の高速化

迫田卓，宇都信一，河野晴彦

日本機械学会九州支部講演論文集 ( 日本機械学会 ) 2015.68 1 - 2 2015年01月

Calculation of contact angles at triple phase boundary in solid oxide fuel cell anode using the level set method 査読有り国際誌

Xiaojun Sun, Yosuke Hasegawa, Haruhiko Kohno, Zhenjun Jiao, Koji Hayakawa, Kohei Okita, Naoki Shikazono

Materials Characterization ( Elsevier B.V. ) 96 100 - 107 2014年10月

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.

DOI： 10.1016/j.matchar.2014.07.020

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84905373556&origin=inward

Role of magnetic field tangency points in ICRF sheath interactions 査読有り国際誌

J. R. Myra, D. A. D'Ippolito, H. Kohno

AIP Conference Proceedings ( AIP Publishing ) 1580 ( 1 ) 322 - 325 2014年02月

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

ICRF waves can sometimes interact with plasma-facing surfaces in tokamak fusion experiments causing degradation of core heating efficiency, impurity injection and even component damage. While presently available low dimensionality if sheath models are useful in understanding many features of these interactions, more quantitative modeling will require attention to realistic geometrical details of the boundary plasma and surfaces. In this paper, we explore the situation in which there exists a tangency point of the background magnetic field with a surface. We find that the rf interactions are strongly influenced by the generation and propagation of sheath-plasma waves (SPW) along the surface. It is found that these waves preferentially propagate towards, and accumulate at, a convex tangency point. An analytical theory of SPW propagation is developed to understand these features.

DOI： 10.1063/1.4864553

Detailed transport-reaction models for SOFC Ni-YSZ patterned anodes: A critical inquiry 査読有り国際誌

Haruhiko Kohno, Shixue Liu, Teppei Ogura, Takayoshi Ishimoto, Dayadeep S. Monder, Kunal Karan, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 2821 - 2830 2013年10月

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 two-dimensional 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.

DOI： 10.1149/05701.2821ecst

Scopus

その他リンク： https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84905040215&origin=inward

Molecular dynamics simulation studies of H diffusion in SOFC anode using reactive force field 査読有り国際誌

Leton C. Saha, Kazuhide Nakao, Haruhiko Kohno, Takayoshi Ishimoto, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 2649 - 2654 2013年10月

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）

Employing reactive molecular dynamics simulation, we investigated diffusion pathways of H-atoms into the bulk from the Ni(100) surface. We found that surface pathway is dominant compared to bulk pathway for H atoms diffusion. Our simulation suggests that H atoms can diffuse into the bulk Ni. From 973 to 1273 K, H atoms migration into bulk is observed, but number of H atom is influenced by the temperature. At 1273 K, 30 % H atoms move into the bulk region. Diffusion barrier of H into bulk is calculated higher than the surface pathway. Diffusion coefficient of H between bulk and surface pathway is calculated to be one order of magnitude discrepancy.

DOI： 10.1149/05701.2649ecst

Molecular dynamics study for sintering property analysis of Ni-YSZ cermet 査読有り国際誌

Kazuhide Nakao, Haruhiko Kohno, Takayoshi Ishimoto, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 1407 - 1413 2013年10月

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）

Microstructural change of porous electrodes in SOFC caused by sintering affected by materials and impurities is one of the main factors of the long-term degradation. Since it is difficult to clarify the effects of materials and impurities on sintering by experiments, atomistic scale simulation is important. In this study, we performed molecular dynamics (MD) simulation of porous structure of Ni and analyzed sintering properties of porous structure by employing master sintering curve theory. We have succeeded to obtain the sintering activation energy and its size dependency and to identify the dominant sintering mechanism by comparing sintering activation energy with activation energy of surface diffusion on each facet.

DOI： 10.1149/05701.1407ecst

First-principles calculations of the anodic oxidation reactions of solid oxide fuel cell: Oxygen potential effect on Nickel (111) surface 査読有り国際誌

Shixue Liu, Takayoshi Ishimoto, Haruhiko Kohno, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 2429 - 2436 2013年10月

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）

The anodic reactions of solid oxide fuel cells are examined by density functional theory method under different oxygen coverage on the Ni(111) surface. The oxidation reactions H, OH and CO are calculated and the reaction barriers are affected by the oxygen potential. The concept of oxygen potential is introduced to discuss the effect of the surface chemical potential to the oxidation reactions. The results are valuable for estimating the reaction rate of anodic reactions under different oxygen potential near the anodic three phase boundary.

DOI： 10.1149/05701.2429ecst

Density functional theory calculation of spin-state transition in LaCoO3 査読有り国際誌

Takayoshi Ishimoto, Yumi Ito, Haruhiko Kohno, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 2655 - 2660 2013年10月

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）

We analyzed the dependence of X-ray absorption spectra for Co 2p orbital of LaCoO3 on the Hubbard U and lattice parameters by using the density functional theory (DFT) method. The X-ray absorption spectra and partial density of states (PDOS) are studied with the different U parameters ranging from 2.5 to 7.8. The characteristic peak position of X-ray absorption spectra is also investigated for different structures: i.e., the O atom positions assuming the displacement by thermal vibrations, the lattice expansion and the crystalline lattice distortion. The effect of the above parameters on the X-ray absorption spectra are discussed on the basis of theoretical calculation results.

DOI： 10.1149/05701.2655ecst

Detailed kinetic modeling for SOFC Ni pattern anodes fuelled by methane 査読有り国際誌

Teppei Ogura, Haruhiko Kohno, Shixue Liu, Takayoshi Ishimoto, Michihisa Koyama, Hisayoshi Tsukikawa, Masaki Tajima

ECS Transactions ( IOP Publishing ) 57 ( 1 ) 2865 - 2870 2013年10月

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）

High SOFC operating temperature allows direct internal reforming (DIR) of methane within the SOFC anode. However, carbon formation reduces considerably the performance and durability of the cells. A key step towards improving SOFC performance is to understand the detailed surface kinetics and electrochemistry for DIR of methane at the triple phase boundaries (TPBs) in SOFC anodes. In this study, we have performed kinetic simulations with a numerical model on Ni pattern anode, combined with surface reactions, charge transfer reactions, and diffusions for DIR of methane. The I-V characteristics of SOFC near TPBs are discussed.

DOI： 10.1149/05701.2865ecst

Radio-frequency sheath-plasma interactions with magnetic field tangency points along the sheath surface 査読有り国際誌

H. Kohno, J. R. Myra, D. A. D'Ippolito

Physics of Plasmas ( AIP Publishing ) 20 ( 8 ) 082514-1 - 082514-9 2013年08月

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）

Computer simulations of radio-frequency (RF) waves propagating across a two-dimensional (2D) magnetic field into a conducting boundary are described. The boundary condition for the RF fields at the metal surface leads to the formation of an RF sheath, which has previously been studied in one-dimensional models. In this 2D study, it is found that rapid variation of conditions along the sheath surface promote coupling of the incident RF branch (either fast or slow wave) to a short-scale-length sheath-plasma wave (SPW). The SPW propagates along the sheath surface in a particular direction dictated by the orientation of the magnetic field with respect to the surface, and the wave energy in the SPW accumulates near places where the background magnetic field is tangent to the surface.

DOI： 10.1063/1.4818991

A new method for the level set equation using a hierarchical-gradient truncation and remapping technique 査読有り国際誌

Haruhiko Kohno, Jean-Christophe Nave

Computer Physics Communications ( Elsevier B.V. ) 184 ( 6 ) 1547 - 1554 2013年06月

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）

We present a novel numerical method for solving the advection equation for a level set function. The new method uses hierarchical-gradient truncation and remapping (H-GTaR) of the original partial differential equation (PDE). Our strategy reduces the original PDE to a set of decoupled linear ordinary differential equations with constant coefficients. Additionally, we introduce a remapping strategy to periodically guarantee solution accuracy for a deformation problem. The proposed scheme yields nearly an exact solution for a rigid body motion with a smooth function that possesses vanishingly small higher derivatives and calculates the gradient of the advected function in a straightforward way. We will evaluate our method in one- and two-dimensional domains and present results to several classical benchmark problems.

DOI： 10.1016/j.cpc.2013.02.002

Scopus

Molecular dynamics study for sintering characteristics of solid oxide fuel cell anode 査読有り国際誌

Kazuhide Nakao, Haruhiko Kohno, Takayoshi Ishimoto, Michihisa Koyama

ECS Transactions ( IOP Publishing ) 50 ( 30 ) 1 - 9 2013年05月

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）

The prediction of long-term durability of SOFC anode is important to understand the sintering phenomena in the anode, which are affected by microstructure, materials, and impurities. To understand the sintering phenomena considering the effects of materials and chemical species, molecular dynamics (MD) simulation is one of the most effective computational methods. In this study, we developed a theoretical methodology based on the master sintering curve to analyze the sintering property. We performed MD simulation for the densification of both Ni and YSZ porous structures. The sintering activation energy obtained from our proposed method was in reasonable agreement with the experimental result.

DOI： 10.1149/05030.0001ecst

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