• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2101-2108
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• 2008

Most of train fires which occur in usual cases do not grow up significantly on a large scale enough to bring about casualties and harmful damages. However, the consequence of some train fire accidents can be devastating disaster so that it would be even recorded in history in unusual cases. Accordingly, such a probability of fire disaster cannot be ignored in aspect of the railway safety assesment. A scale of injury and damage is very difficult to predict and analyze. Because it is depend on various factors, i.e. fire load, burning period, facilities, environment condition, and so on. Thus, a prediction of fire load could be understood as a one methodology to estimate railway safety assesment. The summation method which is one of them is used to evaluate the overall fire load by assuming that sum of heat release rate per unit area or mass of each composite material equals the total. However, since the train fire is classified into a compartment fire in under-ventilation condition. The summation method do not estimate a fire load completely. In this journal, Various methods to predict fire load are introduced and evaluated. Especially the fire simulation tool FDS(Fire Dynamics Simulator)which is based on the CFD(Computational Fluid Dynamics) is introduced, too. Through the FDS simulation, numerical analyses for the fire load and flame spread are performed. Then, these results of the simulation are validated through the comparison study with the experimental data. Then, limitations and approximations including in simulation process are discussed. The future direction of research is proposed.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.3
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• pp.215-226
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• 2017

This paper presents numerical results of the performance of a marin propeller in cavitating and non-cavitating flow conditions. The geometry and experimental validation data of the propeller are provided in Potsdam Propeller Test Case(PPTC) in the framework of the second International Symposium on Marine Propulsors 2011(SMP'11) workshop. The PPTC includes open water tests, velocity field measurements and cavitation tests. The present numerical analysis was carried out by using the Reynolds averaged Navier-Stokes(RANS) method on a wall-resolved grid ensuring a y+=1, where the SST k-${\omega}$ model was mainly used for turbulence closure. The influence of the turbulence model was investigated in the prediction of the wake field under a non-cavitating flow condition. The propeller tip vortex flows in both cavitating and non-cavitating conditions were captured through adaptation of additional grids. For the cavitation flows at three operation points, Schnerr-Sauer's cavitation model was used with a Volume-Of Fluid(VOF) approach to capture the two-phase flows. The present numerical results for the propeller wake and cavitation predictions including the open water performance showed a qualitatively reasonable agreement with the model test results.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.2
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• pp.99-107
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• 2016

Test research on Infra-Red Thermography(IRT) technique in a supersonic wind tunnel has been conducted. Inadvertent technical difficulties and their solutions associated with the technique in running of the facility were examined. Two flow conditions at Mach number of 3 and 4 were considered. A double compression ramp model, that replicates realistic high-speed vehicle configuration, was used as test model. The present IR data were compared with shadowgraph visualization images and laminar computational fluid dynamics(CFD) results. It has been shown that the IRT technique can be used in quantifying various fluid dynamic features such as flow transition, separation and three-dimensional phenomena around the double compression ramp model.

• Tribology and Lubricants
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• v.33 no.6
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• pp.288-295
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• 2017

In order to improve the efficiency and reliability of the machine, the friction should be minimized. The most widely used method to minimize friction is to maintain the fluid lubrication state. However, we can reduce friction only up to a certain limit because of viscosity. As a result of several recent studies, surface texturing has significantly reduced the friction in highly sliding machine elements, such as mechanical seals and thrust bearings. Thus far, theoretical studies have mainly focused on isothermal/iso-viscous conditions and have not taken into account the heat generation, caused by high viscous shear, and the temperature conditions on the bearing surface. In this study, we investigate the effect of dimple depth and film-temperature boundary conditions on the thermohydrodynamic (THD) lubrication of textured parallel slider bearings. We analyzed the continuity equation, the Navier-Stokes equation, the energy equation, and the temperature-viscosity and temperature-density relations using a computational fluid dynamics (CFD) code, FLUENT. We compare the temperature and pressure distributions at various dimple depths. The increase in oil temperature caused by viscous shear was higher in the dimple than in the bearing outlet because of the action of the strong vortex generated in the dimple. The lubrication characteristics significantly change with variations in the dimple depths and film-temperature boundary conditions. We can use the current results as basic data for optimum surface texturing; however, further studies are required for various temperature boundary conditions.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2173-2182
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• 2020

Control valves are widely used to regulate fluid flux in nuclear power plants, and there are more than 1500 control valves in the primary circuit of one nuclear power plant. With their help, the flux can be regulated to a specific level of water or steam to guarantee the energy efficiency and safety of the nuclear power plant. The flux characteristics of the control valve mainly depend on the valve core shape. In order to analyze the effects of valve core shapes on flux characteristics of control valves, this paper focuses on the valve core shapes. To begin with, numerical models of different valve core shapes are established, and results are compared with the ideal flux characteristics curve for the purpose of validation. Meanwhile, the flow fields corresponding to different valve core shapes are investigated. Moreover, relationships between the valve core opening and the outlet flux under different valve core shapes are carried out. The flux characteristics curve and equation are proposed to predict the outlet flux under different valve core openings. This work can benefit the further research of the flux control and the optimization of the valve core for control valves in nuclear power plants.

• Progress in Superconductivity and Cryogenics
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• v.24 no.3
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• pp.62-67
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• 2022

Liquid hydrogen (LH₂) has a higher density than gaseous hydrogen, so it has high transport efficiency and can be stored at relatively low pressure. In order to use efficient bulk hydrogen in the industry, research for the LH₂ supply system is needed. In the high-pressure hydrogen station based on LH₂ currently being developed in Korea, a heat exchanger is used to heat up supercritical hydrogen at 700 bar and 60 K, which is pressurized by a cryogenic high-pressure pump, to gas hydrogen at 700 bar and 300 K. Accordingly, the heat exchanger used in the hydrogen station should consider the design of high-pressure tubes, miniaturization, and freezing prevention. A helical heat exchanger generates secondary flow due to the curvature characteristics of a curved tube and can be miniaturized compared to a straight one on the same heat transfer length. This paper evaluates the heat transfer performance through parametric study on the distance between coils, guide effect, and anti-icing design of helical heat exchanger. The helical heat exchanger has better heat transfer performance than the straight tube exchanger due to the influence of the secondary flow. When the distance between the coils is uniform, the heat transfer is enhanced. The guide between coils increases the heat transfer performance by increasing the heat transfer length of the shell side fluid. The freezing is observed around the inlet of distribution tube wall, and to solve this problem, an anti-icing structure and a modified operating condition are suggested.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.4
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• pp.641-648
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• 2023

Recently, the rapid growth of artificial intelligence among the 4th industrial revolution has progressed based on the performance improvement of semiconductor, and circuit integration. According to transistors, which help operation of internal electronic devices and equipment that have been progressed to be more complicated and miniaturized, the control of heat generation and improvement of heat dissipation efficiency have emerged as new performance indicators. The DUT(Device Under Test) Shell is equipment which detects malfunction transistor by evaluating the durability of transistor through heat dissipation in a state where the power is cut off at an arbitrary heating point applying the rating current to inspect the transistor. Since the DUT shell can test more transistor at the same time according to the heat dissipation structure inside the equipment, the heat dissipation efficiency has a direct relationship with the malfunction transistor detection efficiency. Thus, in this paper, we propose various method for PCB configuration structure to optimize heat dissipation of DUT shell and we also propose various transformation and thermal analysis of optimal DUT shell using computational fluid dynamics.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.149-149
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• 2020

하천에서 물 흐름이 보와 댐과 같은 수공구조물을 지날 때 일반적으로 흐름상태에 다양하고 급진적인 변화가 발생한다. 특히 흐름이 구조물을 지나면서 사류(supercritical flow)로 변하고 다시 상류(subcritical flow)로 복원되면서 일어나는 도수(hydraulic jump) 현상은 수위의 급변화, 흐름 에너지 소산, 변동성이 강한 압력 분포 등이 특징이다. 이러한 흐름 특성들은 보나 여수로와 같은 수공구조물 자체의 성능뿐만 아니라 이들 수공구조물의 하류에서 발생하는 국부세굴로 인해 구조물의 안정성에 부정적인 영향을 줄 수 있다. 따라서 수공구조물을 설계할 때는 이들 구조물을 통과하는 흐름의 비정상 난류 흐름 특성을 정확하게 해석하여 반영하여야 한다. 이 연구에서는 k-omega SST 난류 모형과 자유수면의 급격한 변동을 해석하기 위한 하이브리드-VOF(hybrid volume of fluid)기법을 이용하여 도수현상을 수치적으로 재현하고자 한다. 기존 CFD(computational fluid Dynamics) 모델링에서는 자유수면 변동의 영향을 고려하기 위해 VOF 기법을 많이 사용하였다. 하지면 전통적인 VOF 기법은 다상흐름(multiphase flow)을 오직 부피분율(volume fraction)의 함수로만 고려하며 모의함으로써 강한 수면변동뿐만 아니라 공기연행(air entrainment)를 동반하는 난류 흐름을 모의하는데는 한계가 있다. 이 연구에서 이용하는 Eulerian 기법인 하이브리드 VOF 기법은 물과 공기의 각 상에 대하여 흐름 특성들을 개별적으로 계산하기 때문에 공기연행을 포함한 급변류 흐름에서 전통적인 VOF 기법보다 적용성이 우수하다. 이와 같은 난류모형과 자유수면 포착기법을 이용하여 3차원 비정상 난류 흐름 수치모형을 구축하여 수공구조물 주변에서 발생하는 강한 공기연행과 난류 특성를 보이는 급변류를 수치적으로 재현한다. 이 연구는 계산된 수치해석 결과를 기존 수리실험 결과와 비교하여 수치모형의 적용성을 평가하고 도수 현상에서 발생하는 독특한 흐름 특성을 제시한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.203-203
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• 2022

일반적으로 지진해일은 지진, 화산에 의한 융기 또는 침강에 따른 급작스러운 해저지각 운동에 의해 발생하며, 이에 따른 수위변동과 유체운동을 일컫는다. 그 밖에 해안/해저 산사태, 운석 낙하, 빙하 붕괴와 같이 암석, 토사, 얼음, 운석이 바다, 호수의 수면과 충돌하여 해일이 발생하기도 한다. 이 산사태 해일의 피해사례는 많지 않지만, 대부분 인명피해를 동반한다. 이에 과거부터 수리모형실험을 통해 산사태로 생성된 해일의 전파과정을 조사하는 연구들이 수행되었다. 최근에는 컴퓨터 성능향상과 다양한 수치모델이 개발됨에 따라 수치해석이 많이 수행되고 있다. 그러나 산사태 해일의 생성을 직접 모의하기 위해서는 유체-구조 상호작용(FSI; fluid-structure interaction)을 고려할 수 있는 전산유체역학(CFD; computational fluid dynamics)해석이 요구되는 관계로 활발한 연구가 진행되지 않고 있다. 본 연구에서는 FSI에 기초하여 충돌모의에 특화된 LS-DYNA를 이용하여 산사태 해일의 생성, 전파 그리고 직립벽(댐)에서의 처오름 및 파압 등을 검토한다. 그리고 낙하물의 형상, 낙하 높이에 따라 생성된 해일이 댐에 미치는 영향을 분석한다. 또한, 이용하는 LS-DYNA 해석의 타당성 및 유효성을 확인하기 위하여 기존 수리모형실험에서 생성된 산사태 지진해일과 비교·검증한다. 수치해석 결과, 동일한 체적의 낙하물에서는 폭이 좁을수록 최대파고가 낙하물에 근접해 생성되었고, 폭이 넓을수록 파장이 길어지는 것을 확인할 수 있었다. 낙하물의 낙하높이가 높을수록 산사태 지진해일의 파고가 크게 생성되었다. 낙하물로부터 600m 지점에서 설치한 댐에서의 산사태 지진해일의 처오름은 파고 및 파장이 클수록 증가하였다. 산사태 지진해일의 파압 역시 처오름에 상응하게 나타났다. 그러므로 호소에서 산사태 해일이 발생한다면, 댐 및 제방의 안정성에 영향을 미칠 수 있을 것으로 판단된다.

• KIPS Transactions on Computer and Communication Systems
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• v.10 no.10
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• pp.261-268
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• 2021

Cloud computing is a computing paradigm in which users can utilize computing resources in a pay-as-you-go manner. In a cloud system, resources can be dynamically scaled up and down to the user's on-demand so that the total cost of ownership can be reduced. The Modeling and Simulation (M&S) technology is a renowned simulation-based method to obtain engineering analysis and results through CAE software without actual experimental action. In general, M&S technology is utilized in Finite Element Analysis (FEA), Computational Fluid Dynamics (CFD), Multibody dynamics (MBD), and optimization fields. The work procedure through M&S is divided into pre-processing, analysis, and post-processing steps. The pre/post-processing are GPU-intensive job that consists of 3D modeling jobs via CAE software, whereas analysis is CPU or GPU intensive. Because a general-purpose desktop needs plenty of time to analyze complicated 3D models, CAE software requires a high-end CPU and GPU-based workstation that can work fluently. In other words, for executing M&S, it is absolutely required to utilize high-performance computing resources. To mitigate the cost issue from equipping such tremendous computing resources, we propose HEMOS-Cloud service, an integrated cloud and cluster computing environment. The HEMOS-Cloud service provides CAE software and computing resources to users who want to experience M&S in business sectors or academics. In this paper, the economic ripple effect of HEMOS-Cloud service was analyzed by using industry-related analysis. The estimated results of using the experts-guided coefficients are the production inducement effect of KRW 7.4 billion, the value-added effect of KRW 4.1 billion, and the employment-inducing effect of 50 persons per KRW 1 billion.