• Wind and Structures
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• 제23권4호
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• pp.313-350
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• 2016

Taipei 101 Tower, which has 101 stories with height of 508 m, is located in Taipei where typhoons and earthquakes commonly occur. It is currently the second tallest building in the world. Therefore, the dynamic performance of the super-tall building under strong wind actions requires particular attentions. In this study, Large Eddy Simulation (LES) integrated with a new inflow turbulence generator and a new sub-grid scale (SGS) model was conducted to simulate the wind loads on the super-tall building. Three-dimensional finite element model of Taipei 101 Tower was established and used to evaluate the wind-induced responses of the high-rise structure based on the simulated wind forces. The numerical results were found to be consistent with those measured from a vibration monitoring system installed in the building. Furthermore, the equivalent static wind loads on the building, which were computed by the time-domain and frequency-domain analysis, respectively, were in satisfactory agreement with available wind tunnel testing results. It has been demonstrated through the validation studies that the numerical framework presented in this paper, including the recommended SGS model, the inflow turbulence generation technique and associated numerical treatments, is a useful tool for evaluation of the wind loads and wind-induced responses of tall buildings.

• Journal of Biosystems Engineering
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• 제30권3호
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• pp.185-191
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• 2005

Importance of alternative energy has been increasing due to environmental issues and lack of fossil fuels. In addition, heating cost that occupies from 30 to $40\%$ of the total production cost in the protected cultivation sector in Korea needs to be reduced for profitability and global competition. But, study on geothermal energy to solve these problems has not been activated for Korean protected cultivation. This study was conducted to develop an optimized geothermal exchange system through fundamental test of heat transfer characteristics in soil such as thermal diffusivity, changes in soil temperature during heating and cooling operations, and restorations of soil temperature after the heater was fumed off, These issues were investigated using computer simulation for different depths. The simulated characteristics were evaluated through controlled tests. Simulated characteristics of heat transfer in the soil at different depths showed a reasonable agreement with the results of the controlled tests. All of computer simulation and controlled tests, soil temperatures changed at 10cm and 20cm distance from pipe. but don't change at more than 30cm distance. It means that distances of heat transfer of the soil ranged from 20 to 30cm a day. Based on these results, the optimum spacing between adjacent heat exchange pipes and the pitch were selected as 50 and 40cm, respectively.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.3049-3052
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• 2008

MCFC(molten carbonate fuel cell) power generation system is prime candidate for the utilization of fossil based fuels to generate ultra clean power with a high efficiency. In the MCFC power plant system, a combustor performs a role to supply high temperature mixture gases for cathode and heat for reformer by using the stack off-gas of the anode which includes a high concentration of $H_2O$ and $CO_2$. Since a combustor needs to be operated in a very lean condition and to avoid excessive local heating, catalytic combustor is usually used. The catalytic combustion is accomplished by the catalytic chemical reaction between fuel and oxidizer at catalyst surface, different from conventional combustion. In this study, a mathematical model for the prediction of internal flow and catalytic combustion characteristics in the catalytic combustor adopted in the MCFC power plant system is suggested by using the numerical methods. The numerical simulation models are then implemented into the commercial CFD code. After verifying result by comparing with the experimental data and calibrated kinetic parameters of catalytic combustion reaction, a numerical simulation is performed to investigate the variation of flow and combustion characteristics by changing such various parameters as inlet configuration and inlet temperature. The result show that the catalytic combustion can be effectively improved for most of the case by using the perforated plate and subsequent stable catalytic combustion is expected.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2021년도 학술발표회
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• pp.60-60
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• 2021

Investigating Backward-Facing Step(BFS) flow is important in that it is a representative case for separation flows in various engineering flow systems. There have been a wide range of experimental, theoretical, and numerical studies to investigate the flow characteristics over BFS, such as flow separation, reattachment length and recirculation zone. However, most of such previous studies were concentrated only on the perpendicular step angle. In this study, several numerical investigations on the flow pattern over BFS with various step angles (10° ~ 90°) and expansion ratios (1.48, 2 and 3.27) under different Reynolds numbers (5000 ~ 64000) were carried out, mainly focused on the reattachment length. The numerical simulations were performed using an open source 3D CFD software, OpenFOAM, in which the velocity profiles and turbulence intensities are calculated by RANS (Reynolds Averaged Navier-Stokes equation) and 3D LES (Large Eddy Simulation) turbulence models. Overall, it shows a good agreement between simulations and the experimental data by Ruck and Makiola (1993). In comparison with the results obtained from RANS and 3D LES, it was shown that 3D LES model can capture much better and more details on the velocity profiles, turbulence intensities, and reattachment length behind the step for relatively low Reynolds number(Re < 11000) cases. However, the simulation results by both of RANS and 3D LES showed very good agreement with the experimental data for the high Reynolds number cases(Re > 11000). For Re > 11000, the reattachment length is no longer dependent on the Reynolds number, and it tends to be nearly constant for the step angles larger than 30°.) Based on the calibrated and validated numerical simulations, several additional numerical simulations were also conducted with higher Reynolds number and another expansion ratio which were not considered in the experiments by Ruck and Makiola (1993).

• 대한기계학회논문집B
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• 제35권7호
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• pp.723-733
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• 2011

본 연구에서는 비정렬격자계와 체적포착법을 사용하여 표면장력이 지배적인 다상유동의 수치해석 방법을 제시하였다. 먼저 표면장력에 대한 CSF(Continuum Surface Force) 모델을 비정렬격자계에 적용할 수 있도록 수치해석 방법을 확립시켜 Myong(2009)이 개발한 비정렬격자계와 체적포착법을 사용한 수치 해석코드에 삽입하였다. 테스트 문제로 오직 표면장력만이 존재하는 평형상태의 정적(static) 액적 및 비평형상태의 동적(dynamic) 액적 문제에 적용하여, 이 해석방법의 유용성과 정확도를 평가하였다. 연구결과, 매끄러운 곡률 계산을 위해 필요한 필터로 본 연구에서 제안한 Laplacian 필터와 함께 CSF 모델로는 밀도보정(density-scaled)한 CSF 모델이 예측성능이 우수한 것으로 나타났다. 또한 표면장력 계산을 위한 이 모델을 채용한 본 수치해석방법은 표면장력이 지배적인 다상유동인 평형상태의 정적 액적 및 비평형상태의 동적 액적 문제 모두에 대해 정확성과 유용성이 입증되었다.

• Wind and Structures
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• 제31권2호
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• pp.85-102
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• 2020

Accurate load evaluation is essential in any performance-based design. Design wind speeds and associated wind loads are well defined for synoptic boundary layer winds but not for thunderstorms. The method presented in the current study represents a new approach to obtain design wind speeds associated with thunderstorms and their gust fronts using historical data and Monte Carlo simulations. The method consists of the following steps (i) developing a numerical model for thunderstorm downdrafts (i.e. downbursts) to account for storm translation and outflow dissipation, (ii) utilizing the model to characterize previous events and (iii) extrapolating the limited wind speed data to cover life-span of structures. The numerical model relies on a previously generated CFD wind field, which is validated using six documented thunderstorm events. The model suggests that 10 parameters are required to describe the characteristics of an event. The model is then utilized to analyze wind records obtained at Lubbock Preston Smith International Airport (KLBB) meteorological station to identify the thunderstorm parameters for this location, obtain their probability distributions, and utilized in the Monte Carlo simulation of thunderstorm gust front events for many thousands of years for the purpose of estimating design wind speeds. The analysis suggests a potential underestimation of design wind speeds when neglecting thunderstorm gust fronts, which is common practice in analyzing historical wind records. When compared to the design wind speed for a 700-year MRI in ASCE 7-10 and ASCE 7-16, the estimated wind speeds from the simulation were 10% and 11.5% higher, respectively.

• 한국산학기술학회논문지
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• 제12권2호
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• pp.1005-1012
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• 2011

본 연구에서는 혁신적인 연소시스템의 최적 연소조건을 도출하기 위해 반응기 내부 유동 특성, 온도분포, 속도분포 및 체류시간 등에 대해 전산유체역학(CFD)을 이용한 3차원 모사를 수행하였다. 연료 투입량 1.5 ton/hr, 체류시간 1.25초, 공기비 2.1의 조건에서 연소시킬 때 로의 출구의 면적가중(area-weighted) 평균온도는 $1,077^{\circ}C$로 나타나 에너지 회수 및 유해가스 처리에 적합한 온도임을 알 수 있었다. 배가스는 연소실 중앙부위에서 강한 선회류를 따라 최고속도 약 40~50 m/s로 덕트를 통해 배출되므로 연소실의 중심부에 강한 난류가 형성되어 연소 속도 및 연소 효율이 향상되는 것으로 나타났다. 본 시스템의 경우, 불완전 연소를 방지하고 또한 thermal NOx의 생성도 억제하기 위한 적정 조업조건은 공기비 1.9~2.1, 연료 투입량 1.25~1.5 ton/hr 정도인 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제36권2호
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• pp.93-103
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• 2023

수많은 함정용 채프들은 폭발에 의해 확산되어 채프운을 형성하며, 채프운은 허위 레이더 반사 단면적을 생성하여 적의 레이더를 기만한다. 본 논문에서는 전산유체역학-이산요소법 단방향 연동 기법을 기반으로 공기 중에 분포하는 함정용 채프운의 시공간 분포를 해석하는 수치적 프레임워크를 구축하고 바람의 방향과 속도, 채프 카트리지의 초기 각도와 폭발 압력이 채프운 분포에 미치는 영향을 분석하였다. 채프운의 확산은 폭발에 의한 방사형 확산, 난류와 충돌에 의한 전 방향 확산, 낙하 속도 차이에 의한 중력 방향 확산과 같이 세 단계로 구분되는 것을 확인하였다. 바람은 채프운의 평균 위치를 이동시켰으며, 항력에 의한 확산 효과는 나타나지 않았다. 카트리지 초기 각도에 따라 폭발에 의한 방사형 확산 방향이 달라졌으며, 각도가 지면과 수직에 가까울수록 더 넓게 확산되었다. 폭발 압력이 증가할수록 채프운은 더 넓게 확산되었으나 중력 방향으로는 분포 차이가 작았다.

• 한국항행학회논문지
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• 제21권6호
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• pp.537-543
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• 2017

수중글라이더(UG; underwater glider)는 지속적인 해양관측 탐사를 목적으로 개발된 장기운용 가능한 수중로봇이다. 원통형의 일반적인 수중글라이더는 단일 부력엔진과 자세제어기를 통해 추진하기 때문에, 운동조종성능 측면에서 효율적이지 못하다. 본 논문에서는 기존 원통형 수중글라이더의 부력제어 및 운동제어성능을 개선하기 위해 이중부력엔진을 탑재한 가오리 형태의 수중글라이더를 소개한다. CFD(computational fluid dynamics) 해석을 수행하여 설계된 형상의 글라이드 운동에 대한 유체저항성능을 해석한다. 산출한 유체력 계수를 바탕으로 운동 시뮬레이션을 수행하여 운동성능을 비교 분석한다. 가오리 형태의 수중글라이더 소형 축소모델을 제작하고, 제어시스템을 구성하여 기초 성능시험을 수행한다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권3호
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• pp.276-284
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• 2014

본 연구의 목적은 ORC(Organic Rankine Cycle) 반경류터빈의 설계기법을 확립하는 것이다. 이를 위하여 반경류터빈의 예비설계프로그램인 RTDM(Radial Turbine Design Modeler) Ver.2.1를 개발하였다. RTDM Ver.2.1의 정확성을 검증하기 위해 R32를 이용한 200kW급 OTEC(Ocean Thermal Energy Conversion)용 반경류터빈을 설계하였고 이에 대해 CFD(Computational Fluid Dynamics) 수치해석을 수행하였다. 그 결과 RTDM Ver.2.1의 정확성은 설계한 반경류터빈의 전엔탈피 강하를 기준하여 약 94.6%로 나타났다. 본 연구에서는 반경류터빈의 설계요구조건인 출력조건과 로터출구조건을 충족시키기 위해 질량유량조정 방법을 도입하였다. 이에 따라 RTDM Ver.2.1을 이용하여 설계한 200kW급 OTEC용 반경류터빈의 질량유량은 21.2kg/s이며 이 때 Total to Total과 Total to Static 효율은 각각 89.8%, 85.3%이다.