• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.29-34
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• 1999

A two-dimensional Navier-Stokes code based on AUSMPW+ scheme has been developed to simulate the hypersonic flowfield of hypersonic shock-shock interaction. AUSMPW+ scheme is a new hybrid flux splitting scheme, which is improved by introducing pressure-based weight functions to eliminate the typical drawbacks of AUSM-type schemes, such as non-monotone pressure solutions. To study the real gas effects, three different gas models are taken into account in this paper: perfect gas, equilibrium flow and nonequilibrium flow. It has been investigated how each gas model influences on the peak surface loading, such as wall pressure and wall heat transfer, and unsteady flowfield structure in the region of shock-shock interaction. With the results, the value of peak pressure is not sensitive to the real gas effects nor to the wall catalyticity. However, the value of peak heat transfer rates is affected by the real gas effects and the wall catalyticity. The structure of the flowfield also changes drastically in the presence of real gas effects.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.83-105
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• 2013

In this paper, a multi-scale meshfree-enriched finite element formulation is presented for the analysis of acoustic wave propagation problem. The scale splitting in this formulation is based on the Variational Multi-scale (VMS) method. While the standard finite element polynomials are used to represent the coarse scales, the approximation of fine-scale solution is defined globally using the meshfree enrichments generated from the Generalized Meshfree (GMF) approximation. The resultant fine-scale approximations satisfy the homogenous Dirichlet boundary conditions and behave as the "global residual-free" bubbles for the enrichments in the oscillatory type of Helmholtz solutions. Numerical examples in one dimension and two dimensional cases are analyzed to demonstrate the accuracy of the present formulation and comparison is made to the analytical and two finite element solutions.

• 대한기계학회논문집
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• 제19권11호
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• pp.3031-3040
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• 1995

Two-dimensional incompressible Navier-Stokes equations have been solved by the node-centered finite volume method with the unstructured triangular meshes. The pressure-velocity coupling is handled by the artificial compressibility algorithm due to its computational efficiency associated with the hyperbolic nature of the resulting equations. The convective fluxes are obtained by the Roe's flux difference splitting scheme using edge-based connectivities and higher-order differences are achieved by a reconstruction procedure. The time integration is based on an explicit four-stage Runge-Kutta scheme. Numerical procedures with local time stepping and implicit residual smoothing have been implemented to accelerate the convergence for the steady-state solutions. Comparisons with experimental data and other numerical results have proven accuracy and efficiency of the present unstructured approach.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 1999년도 유체기계 연구개발 발표회 논문집
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• pp.179-186
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• 1999

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67), and to evaluate the performances of k-$\epsilon$ and Baldwin-Lomax turbulence models. A finite volume method is used for spatial discretization. And, the equations are solved implicitly in time with the use of approximate factorization. Upwind difference scheme is used for inviscid terms, but viscous terms are centrally differenced. The flux-difference-splitting of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. And, the results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, we conclude that k-$\epsilon$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost same.

• 대한전기학회논문지
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• 제41권7호
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• pp.735-741
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• 1992

This paper presents a parallel algorithm for the finite element analysis using relatively inexpensive transputer parallel system. The substructure method, which is highly parallel in nature, is used to improve the parallel computing efficiency by splitting up the whole structure into substructures. The proposed algorithm is applied to a simple two-dimensional magnetostatic problem. It is found that the more the number of transputer is increased, the more the total computation time is reduced. And the computational efficiency becomes better as the number of internal boundary nodes becomes smaller.

• 한국자기공명학회논문지
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• 제24권1호
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• pp.16-22
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• 2020

Based on quantum transport theory, we investigated theoretically the magnetic field dependence of the quantum optical transition of quasi 2-dimensional Landau splitting system, in CdS and ZnO Through the analysis of the current work, we found the increasing properties of the cyclotron resonance line-profiles (CRLPs) which show the absorption power and the cyclotron resonance line-widths (CRLWs) with the magnetic field in CdS and ZnO We also found that that CRLWs, γ_total(B) of CdS < γ_total(B) of ZnO in the magnetic field region B < 15 Tesla.

• Earthquakes and Structures
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• 제8권6호
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• pp.1325-1348
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• 2015

Real-time hybrid testing (RTHT) involves virtual splitting of the structure into two parts: physical substructure that contains the key region of interest which is tested in a laboratory and numerical substructure that contains the remaining part of the structure in the form of a numerical model. This paper numerically assesses four step-by-step integration methods (Central difference method (CDM), Operator splitting method (OSM), Rosenbrock based method (RBM) and CR-integration method (CR)) which are widely used in RTHT. The methods have been assessed in terms of stability and accuracy for various realistic damping ratios of the physical substructure. The stability is assessed in terms of the spectral radii of the amplification matrix while the accuracy in terms of numerical damping and period distortion. In order to evaluate the performance of the methods, five carefully chosen examples have been studied - undamped SDOF, damped SDOF, instantaneous softening, instantaneous hardening and hysteretic system. The performance of the methods is measured in terms of a non-dimensional error index for displacement and velocity. Based on the error indices, it is observed that OSM and RBM are robust and performs fairly well in all the cases. CDM performed well for undamped SDOF system. CR method can be used for the system showing softening behaviour. The error indices indicate that accuracy of OSM is more than other method in case of hysteretic system. The accuracy of the results obtained through time integration methods for different damping ratios of the physical substructure is addressed in the present study. In the presence of a number of integration methods, it is preferable to have criteria for the selection of the time integration scheme. As such criteria are not available presently, this paper attempts to fill this gap by numerically assessing the four commonly used step-by-step methods.

• 대한전자공학회논문지SD
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• 제40권7호
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• pp.518-525
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• 2003

본 논문은 리프팅 스킴(lifting scheme)의 분할 방법을 개선하여 고속 병렬 처리가 가능한 2차원 DWT(Discrete Wavelet Transform) 하드웨어 구조를 제안한다. 2차원 DWT 변환은 2차원 입력 데이터 전체에 대하여 연산이 수행되고 순차적으로 2차원 처리가 됨에 따라서 초기 및 전체 지연시간(latency)이 많이 걸린다. 본 논문에서는 처리속도와 지연 시간을 향상시키기 위해 개선된 분할 방법과 새로운 자원 공유 하드웨어 구조를 제안한다. 상호 연관성이 없는 데이터들을 4 개의 데이터 집합으로 분할하여 병렬 처리에 적합하도록 새로운 분할 방법을 제안하였다. 병렬처리 하드웨어 구조는 하드웨어의 자원 공유가 가능하도록 하기 위해 필터연산의 중간 값을 메모리에 저장할 수 있는 파이프라인 구조를 갖도록 설계하였다. 제안된 구조를 효율적으로 동작시킬 수 있도록 하드웨어 자원의 공유를 스케쥴링하여 초기지연과 전체지연 시간을 줄였다. 제안하는 구조는 기존의 병렬 처리 구조에 비해 초기 지연 및 전체 지연 시간을 각각 50%와 66%감소시키는 결과를 얻을 수 있었다.

• 한국결정성장학회지
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• 제31권2호
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• pp.96-101
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• 2021

Developing effective and earth-abundant electrocatalyst for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is critical for the commercialization of a water splitting system. In particular, the overpotential of the OER is relatively higher than the HER, and thus, it is considered that one of the important methods to enhance the performance of the electrocatalyst is to reduce the overpotential of the OER. We report effects of incorporation of metalloid into Ni(OH)2 microcrystal on electrocatalytic activities. In this study, Te incorporated Ni(OH)2 (��Te-Ni(OH)2) were grown on three-dimensional porous NF by a facile solvothermal method with �� = 1, 3 and 5. Homogeneous microplate structure on the NF was clearly observed for the Ni(OH)2/NF and ��Te-Ni(OH)2/NF samples. However, irregular and collapsed nanostructures were found on the surface of nickel foam when Te precursor ratio is (��) over 3. Electrocatalytic OER properties were analysed by Linear sweep voltammetry (LSV) and Electrochemical impedance spectroscopy (EIS). The amount of Te incorporation used in the electrocatalytic reaction was found to play a crucial role in improving catalytic activity. The optimum Te amount (��) introduced into the Ni(OH)2/NF was discussed with respect to their OER performance.

• 대한토목학회논문집
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• 제14권5호
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• pp.1145-1158
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• 1994

물의 유동(流動)에 관한 계산상 효율성(效率性)을 갖는 자유수면(自由水面)을 고려한 3차원(次元) 유한차분(有限差分) 수직모형(數値模型)을 개발하였다. 수직모형(數値模型)은 연직방향(鉛直方向)에 대해 정규화(正規化)한 좌표(座標)(${\sigma}$-coordinate)를 사용하며, 시간(時間) 적분방법(積分方法)으로는 반음해법(半陰解法)(semi-implicit)을 사용하여 계산시간(計算時間)의 효율성(效率性)을 도모하였다. 모드분리(mode-splitting)개념을 도입하여 내부모드(internal mode)에 대해서는 양해법(陽解法)을 사용하였으며, 외부모드(external mode)는 수평방향(水平方向) 운동량방정식(運動量方程式)들과 연속방정식(連續方程式)의 차분식(差分式)으로부터 구한 타원형(楕圓型) 차분방정식(差分方程式)을 SOR방법에 의하여 해석하였다. 이와 같은 방법은 계산(計算) 시간간격(詩間間隔)이 표면(表面) 중력파(重力波)에 대한 CFL(Courant-Fredrich-Lewy)조건에 의해 제약을 받지 않아 계산시간(計算時間)의 효율성을 도모할 수 있다. 개발된 모형은 1차원(次元) 수로(水路)에서 취송유(吹送流)의 연직분포(鉛直分布)에 대한 해석해(解析解)와 비교(比較) 및 연직(鉛直) 가변격자(可變格子)의 도입에 따른 오차분석(誤差分析) 정사각형(正四角形) 호수(湖水)에서 취송유(吹送流) 계산(計算) 및 차분화(差分化) 상수(常數)들의 민감도(敏感度) 분석(分析)을 수행하였다.