• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.494-498
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• 2001

When supersonic jet impinges on wall from the nozzle, complex flow pattern appears such as Mach disc, expansion fan, and jet boundary. The numerical computation of this supersonic jet is important on flame deflecctor design for launch space especially. In this paper, we analyzed supersonic jet structure impinging on deflector wall using three dimensional steady and unsteady compressible equation and showed temperature and pressure distribution on the wall surface. As a result, some dominant factors of jet flows are discussed for conceptual design of flame deflector.

• 한국전산유체공학회지
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• 제17권3호
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• pp.25-32
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• 2012

This work was devoted to compare two different cavitation models to study the dependency of model constants. The cavitation model of Merkle et al.(2006) and Kunz et al.(2000) were used for the present computational study. The cavitation models were coupled with the incompressible unsteady Reynolds-Averaged Navier-Stokes solver to indicate the vaporization and condensation processes. For this purpose, a preconditioning method was added as the pseudo-time term to solve the unsteady stiffness problems. For the validation of the numerical simulation, the computation was performed for the cavitating flow in a converging-diverging channel. The present results show that Merkle's cavitation model is independent to the model constants, and the higher numerical accuracy over Kunz's cavitation model.

• 대한기계학회논문집
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• 제14권3호
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• pp.716-724
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• 1990

본 연구에서는 2차원 경사충돌분류에 대한 실험을 수행하였고, 이 결과를 수] 치해석에 의한 계산치와 비교하였다. 실험에서는 난류특성을 구명하기 위하여 열선 풍속계를 사용해 충돌각의 변화에 따른 평균속도, 각 난류응력성분, 압력등을 측정하 였다.수치해석을 위한 난류모델로는 표준 K-.epsilon.모델을 사용하였다.

• Earthquakes and Structures
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• 제10권3호
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• pp.495-521
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• 2016

Ancient monuments of Greek and Roman classical architecture usually consist of multi-drum columns that are constructed of stone blocks placed on top of each other. Several research studies deal with the seismic behaviour of such structures, since earthquakes are common causes of destruction of such monuments. This paper investigates the effect of multiple earthquakes on the seismic performance of multi-drum columns, through numerical simulations and parametric analyses. The Discrete Element Method and an appropriate contact model have been implemented in a specially developed software application that is able to efficiently perform the necessary simulations in two dimensions. Specifically, various strong ground excitations are used in series for the computation of the collective final deformation of multi-drum columns. In order to calculate this cumulative deformation for a series of ground motions, the individual deformation of the column for each excitation is computed and then used as initial conditions for the next earthquake excitation. Various multi-drum columns with different dimensions are also considered in the analyses in order to examine how the geometric characteristics of columns can affect their seismic sequence behaviour, in combination with the excitation frequency content.

• 지구물리와물리탐사
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• 제14권1호
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• pp.98-104
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• 2011

탐사 지구물리학에서 수치 모사는 지하매질에서의 탄성파 전파 현상을 이해하는데 중요한 통찰력을 제공한다. 탄성파 모사는 음향파 근사에 의한 수치 모사보다 계산시간이 많이 소요되지만 전단응력 성분을 포함하여 보다 현실적인 파동의 모사를 가능하게 한다. 그러므로 탄성파 모사는 탄성체의 반응을 탐사하는데 적합하다고 할 수 있다. 계산 시간이 길다는 단점을 극복하기 위해 본 논문에서는 그래픽 프로세서(GPU)를 이용하여 탄성파 수치 모사 시간을 단축하고자 하였다. GPU는 많은 수의 프로세서와 광대역 메모리를 갖고 있기 때문에 병렬화된 계산 아카텍쳐에서 사용할 수 있는 장점이 있다. 본 연구에서 사용한 GPU 하드웨어는 NVIDIA Tesla C1060으로 240개의 프로세서로 구성되어 있으며 102 GB/s의 메모리 대역폭을 갖고 있다. NVIDIA에서 개발된 병렬계산 아카텍쳐인 CUDA를 사용할 수 있음에도 불구하고 계산효율을 상당히 향상시키기 위해서는 GPU 장치의 여러 가지 다양한 메모리의 사용과 계산 순서를 최적화해야만 한다. 본 연구에서는 GPU 시스템에서 시간영역 유한차분법을 이용하여 2차원과 3차원 탄성과 전파를 수치 모사하였다. 파동전파 모사에 가장 널리 사용되는 유한차분법 중의 하나인 엇갈린 격자기법을 채택하였다. 엇갈린 격자법은 지구물리학 분야에서 수치 모델링을 위해 사용하기에 충분한 정확도를 갖고 있는 것으로 알려져 있다. 본 논문에서 제안한 모델링기법은 자료 접근 시간을 단축하기 위해 GPU 장치를 메모리 사용을 최적화하여 가능한 더 빠른 메모리를 사용한다. 이점이 GPU를 이용한 계산의 핵심 요소이다. 하나의 GPU 장치를 사용하고 메모리 사용을 최적화함으로써 단일 CPU를 이용할 경우보다 2차원 모사에서는 14배 이상, 3차원에서는 6배 이상 계산시간을 단축할 수 있었다. 세 개의 GPU를 사용한 경우에는 3차원 모사에서 계산효율을 10배 향상시킬 수 있었다.

• 한국지반공학회논문집
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• 제35권12호
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• pp.35-44
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• 2019

본 연구에서는 수직증축 공동주택 하부 신설 보강말뚝의 축강성(K_vr)을 기존말뚝의 열화를 고려한 이론적인 접근과 수치해석을 통하여 산정하였다. 3차원 유한요소 수치해석을 수행하는 과정에서, 이론적인 접근과 38본의 시험 말뚝계측 결과를 통하여 제안된 열화를 고려한 기존말뚝 축강성(K_ve)의 상한 값을 적용하였다. 이를 통해, 수직증축 리모델링으로 인하여 증가된 하중을 안정적으로 지지하기 위한 신설 보강말뚝의 최소 축강성을 산정하였다. 신설 보강말뚝의 축강성 제안은 선단지지 말뚝과 마찰말뚝에 대해 수행하였고, 다양한 세장비(L/D)에 따라 제안하였다. 해석기법은 기존말뚝의 설계 당시의 양호한 상태를 고려한 말뚝지지 전면기초 거동 해석과 열화가 고려된 기존말뚝의 축강성을 적용한 말뚝지지 전면기초 거동 해석을 수행하였다. 두 해석기법에 대한 검증을 수행한 결과 말뚝지지 전면기초 거동해석이 가능한 것으로 확인되었고, 이를 통하여 기존말뚝의 열화가 발생하였을 때 선단지지 신설 보강말뚝 축강성이 44 - 67% 증가되어야 수직증축 구조물의 안정성이 확보됨을 알 수 있었다.

• 한국전산유체공학회지
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• 제13권2호
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• pp.27-41
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulation of three-dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence-free flow field at each physical time step. An implicit time integration method with local time stepping was implemented to accelerate the convergence in the pseudo-time sub-iteration procedure. The one-equation Spalart-Allmaras turbulence model has been adopted to solve high-Reynolds number flow fields. The flow solver was parallelized to minimize the CPU time and to overcome the computational overhead. This method has been applied to calculate steady and unsteady flow fields around submarine configurations and a 3-D infinite cylinder. Validations were made by comparing the predicted results with those of experiments or other numerical results. It was demonstrated that the present method is efficient and robust for the prediction of steady and unsteady incompressible flow fields.

• Wind and Structures
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• 제10권6호
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• pp.511-532
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• 2007

The present study aims to generate turbulent inflow data to more accurately represent the turbulent flow around a square cylinder when the inflow turbulence level is significant. The modified random flow generation (RFG) technique in conjunction with a previously developed LES code is successfully adopted into a finite element based fluid flow solver to generate the required inflow turbulence boundary conditions for the three-dimensional (3-D) LES computations of transitional turbulent flow around a square cylinder at Reynolds number of 22,000. The near wall region is modelled without using wall approximate conditions and a wall damping coefficient is introduced into the calculation of sub-grid length scale in the boundary layer of the cylinder wall. The numerical results obtained from simulations are compared with each other and with the experimental data for different inflow turbulence boundary conditions in order to discuss the issues such as the synthetic inflow turbulence effects on the 3-D transitional flow behaviour in the near wake and the free shear layer, the basic mechanism by which stream turbulence interacts with the mean flow over the cylinder body and the prediction of integral flow parameters. The comparison among the LES results with and without inflow turbulence and the experimental data emphasizes that the turbulent inflow data generated by the present RFG technique for the LES computation can be a viable approach in accurately predicting the effects of inflow turbulence on the near wake turbulent flow characteristics around a bluff body.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2003년도 춘계학술발표대회 논문집
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• pp.184-187
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• 2003

Complete prediction of second order permeability tensor for three dimensional circular braided preform is critical to understand the resin transfer molding process of composites. The permeability can be predicted by considering resin flow through the multi-axial fiber structure. In this study, permeability tensor for a 3-D circular braided preform is calculated by solving a boundary problem of a periodic unit cell. Flow field through the unit cell is obtained by using a 3-D finite volume method (FVM) and Darcy's law is utilized to obtain permeability tensor. Flow analysis for two cases that a fiber tow is regarded as impermeable solid and permeable porous medium is carried out respectively. It is found that the flow within the intra-tow region of the braided preform is negligible if inter-tow porosity is relatively high but the flow through the tow must be considered when the porosity is low. To avoid checkerboard pressure field and improve the efficiency of numerical computation, a new interpolation function for velocity variation is proposed on the basis of analytic solutions. Permeability of the braided preform is measured through a radial flow experiment and compared with the permeability predicted numerically.

• 한국환경과학회지
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• 제3권4호
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• pp.367-372
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• 1994

A predictive model is demonstrated for gas removal rates from the aklosphere by dw deposition. Typical deposition velocities are complex functions of surface types, atmospheric stabilities, friction velocities, air pollutants, and so on. In this paper we simulated the calculation of dry deposition velocities near the earth surfaces, simultaneously we estimated real dry deposition velocities using the previous simulation. The measurement taken over a deciduous forest by Padro et d.(1988) were used to verify this model. In the comparison of the value of deposition velocity between numerical computation and observation, there are partially overestimations and underestimations between them, but we can speak that they are in a good accordance.