• 수산해양기술연구
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• 제38권2호
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• pp.164-171
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• 2002

본 연구에서는 중층 트롤 어구 시스템의 운동을 예측하기 위한 운동방정식을 정의하였고 중층 트롤 어구 시스템의 운동을 유체역학적으로 해석하여 시뮬레이션에 적용하여 계산한 결과를 해상에서 실험한 결과들과 비교하여 시뮬레이션의 정확도를 검증하였다. 해상실험은 1997년 8월 28일부터 1997년 8월 30일까지 동해상(36$^{\circ}$05'N, 130$^{\circ}$25'2E~36$^{\circ}$20'N,130$^{\circ}$47'E)에서 부경대 실습선 가야호를 이용하여 실시하였다. 그 결과는 다음과 같다. 1. 중층 트롤 시스템의 운동을 해석하기 위해 사용된 운동 방정식은 m$_{i}$equation omitted/=f$_{i}$으로 기술하였고, 여기서 m과 /equation omitted/는 각각 질점 i의 질량과 가속도이며, f$_{i}$는 질점에 작용하는 힘이다. 2. 각 질점에 작용하는 힘은 내력과 외력으로 구성되며, 내력은 질점 사이에서 작용하는 힘으로 어구 시스템 구성에 사용된 각 종 줄과 그물실의 탄성에 의한 힘이며, 외력은 질점에 작용하는 저항, 부력 그리고 중력 등이다. 3. 시뮬레이션의 결과를 해상실험의 결과와 정량적으로 비교하기 위해 끌줄길이 250m, 예망속력 2m/s에서의 전개판 간격, 전개판 수심 망고 그리고 망폭을 비교하였다. 이 때 전개판 사이의 간격과 망폭은 계산치와 실험치가 거의 일치하며, 전개판의 수심과 망고는 각각 5m와 4m의 오차를 가지고 있었다. 4. 시뮬레이션 도중 끌줄의 길이, 예망속력, 부력 그리고 전개판 면적을 증가시키면서 어구의 형상을 계산한 결과를 앞선 해상 실험들의 결과와 비교하였다. 이 때 끌줄길이를 증가시킨 경우 어구의 예망수심이 깊어졌으며 전개판의 간격이 증가하였다. 예망속력을 증가시킨 경우 어구가 수면으로 부상하였으며 전개판의 간격이 줄어들었다. 부력을 증가시킨 경우에도 어구가 수면으로 부상하였으며 전개판의 간격과 망폭이 줄어들었다. 마지막으로 전개판의 면적을 증가시킨 경우에는 전개판의 전개력이 증가하여 전개판 사이 간격이 커지고 망폭이 증가하였다.

• 한국해안해양공학회지
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• 제17권3호
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• pp.166-177
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• 2005

본 연구에서는 정체수역에서 유입이론과 일부 형상계수의 조정을 통해 근역에서의 하$\cdot$폐수 혼합거동을 해석할 수 있는 근역제트적분모형을 개발하기위해 총 6개의 상미분 보존방정식에 6개의 미지수를 가지는 문제를 수치적으로 풀기 위한 4차의 Runge-Kutta기법을 사용하였다. 또한, LIF 시스템을 이용하여 검정과정을 통해서 단일수평부력제트의 수리실험을 수행하였다. 그리고 기존의 모형 CORMIX 1, WSJET,그리고 본 모형의 계산결과를 수리실험결과와 서로 비교하였다. VISJET모형에 의해 예측된 중심선 제적이 운동량과 부력이 지배적인 구간에서는 실험결과와 근접한 반면에 본 제트적분모형에 의해 예측된 결과는 천이영역에서 측정된 궤적과 잘 일치하였다. 중심선희석률에 있어서 운동량과 부력이 지배적인 구간에서 CORMIX1 모형의 결과와 잘 일치하는 반면에 초기영역과 천이 영역에서 본 모형의 결과와 대체로 잘 일치하는 경향을 보였다.

• 한국수자원학회논문집
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• 제50권9호
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• pp.637-646
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• 2017

본 연구에서는 중층 밀도류를 모의할 수 있는 $k-{\varepsilon}$ 난류모형의 지배방정식을 제시하고 수치모의를 수행하였다. 깊은 수체에 모형을 적용하여 중층 밀도류를 모의하고 게산된 유속과 초과밀도 분포를 분석하였다. 밀도류의 주 흐름방향을 따라 물 연행으로 인해 유속이 감소되는 것과 Richardson 수의 증가로 인해 유속 변화율이 감소되는 것을 관찰하였다. 유속과 초과밀도의 유사성을 확인하였으나, 난류운동에너지와 소산율의 유사성에서는 보이지 않았다. $k-{\varepsilon}$ 모형의 모의 결과를 이용하여 중층 밀도류의 층적분 모형에서 사용될 수 있는 형상계수를 계산하였다. 또한, 층적분 모형을 이용하여 $k-{\varepsilon}$ 모형에서 사용되는 부력관련 모형상수 ($c_{3{\varepsilon}}$)와 부피팽창계수 (${\beta}_0$)를 계산하였다.

• 한국항해항만학회지
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• 제34권4호
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• pp.271-279
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• 2010

The Mobile Harbor(MH) is a new transportation platform that can load and unload containers to and from very large container ships in the sea. This loading and unloading by crane can be performed with only very small movements of the MH in waves because MH is operated outside of the harbor. For this reason, an anti-rolling tank(ART) and an active mass driving system(AMD) were designed to reduce MH's roll motion, especially at the natural frequency of MH. In the conceptual design stage, it is difficult to confirm the design result of theses anti-rolling devices without modeling and simulation tools. Therefore, the coupled MH and anti-rolling devices' dynamic equations in waves were derived and a simulation program that can analyze the roll reduction performance in various conditions, such as sea state, wave direction, and so on, was developed. The coupled equations are constructed as an eight degrees of freedom (DOF) motion that consists of MH's six DOF dynamics and the ART's and AMD's control variables. In order to conveniently include the ART's and AMD's control dynamics in the time domain, MH's radiated wave force was described by an impulse response function derived by the damping coefficient obtained in the frequency domain, and wave exciting forces such as Froude-Krylov force and diffraction force and nonlinear buoyancy were calculated at every simulation time interval. Finally, the roll reduction performances of the designed anti-rolling devices were successfully assessed in the various loading and wave conditions by using a developed simulation program.

• 한국응용과학기술학회지
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• 제30권3호
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• pp.540-550
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• 2013

Various efforts have been explored to save the cost in many industrial fields. In order to recover the residual thermal energy from the flue gas, an extreme high efficiency heat exchanger is planning to install at a power plant. The gas temperature will be reduced to $40^{\circ}C$ from $115^{\circ}C$. Thus gas buoyancy decreases, and dispersion of nitrogen oxides is expected to deteriorate as increasing relative humidity. In this study, the conversion of nitrogen monoxide to nitrogen dioxide and dispersion regime are investigated through computational modeling. Nitrogen dioxide which indicates 0.1 ppm at 85 m from the ground could be propagated to 620 m at $115^{\circ}C$ of the flue gas, whilst when cooled down to $40^{\circ}C$, it expands up to 750 m. The ground level influence area showed more expansion of dispersion, approximately to 930 m.

• 대한기계학회논문집B
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• 제32권3호
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• pp.173-180
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• 2008

Diurnal variation of the flow over a forest canopy on a mountain slope is simulated numerically. In the daytime, the earth surface is heated by the solar radiation and the flow goes up the mountain due to the buoyancy force, and during the night, the air is drained downward along the slope owing to the cooling of the surface by radiation. In this flow process the forest canopy that consists of leaf region and the trunk region plays a dominant role as a momentum sink to the flow, thus the modeling of the leaf area region and trunk region is critical to the successful flow simulation. In the present study, a field measurement in an experimental forest in the State of Oregon in the United States is numerically analyzed. The resistance to the flow in the leaf region is directly related to the leaf area density (LAD), and the trunk is modeled as a cylinder.

• 한국해양공학회지
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• 제27권6호
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• pp.7-15
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• 2013

Eco-friendly and sustainable seaweed biomass energy have been under the spotlight as the future of renewable energy. However, seaweed culture is primarily conducted inshore, with the research on offshore culture still in an early stage. For massive biomass production, a systematic engineering approach is required to devise offshore seaweed culture facilities rather than the conventional empirical ones. To establish the fundamental behavior of seaweed culture facilities, the dynamic characteristics of a seaweed culture facility were analyzed in the study. For this purpose, numerical analyses of the seaweed culture facility (a frame type) were carried out by using the hydrodynamic simulation program ANSYS-AQWA. For the analysis, environmental loads were considered using the wave spectra and co-linear current; mooring variables were selected as parameters; and time domain analyses were carried out to acquire the time series responses and eventually the dynamic characteristics. Finally, the mooring performance was evaluated. It was found that the motion could be controlled by adjusting the buoyancy and mooring slope.

• 한국군사과학기술학회지
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• 제26권2호
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• pp.159-170
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• 2023

In the present study, the dynamic behavior characteristics of an amphibious assault vehicle during water entry were analyzed using STAR-CCM+, a commercial computational fluid dynamics(CFD) code. All computations were performed using an overset mesh system and a RANS based flow-solver coupled with dynamic fluid-body interaction(DFBI) solver for simulating three degrees of freedom motion. For numerical validation of the solver, a water entry simulation of inclined circular cylinder was conducted and it was compared between an existing experiment data and CFD results. The pitch angle variation and the trajectory of the circular cylinder during water entry shows good agreement with previous experimental and numerical studies. For the water entry simulations of the amphibious assault vehicle, the analysis of dynamic behaviors of the amphibious assault vehicle with different slope angles, submerged depths and initial velocities were conducted. It is confirmed that the steep slope angle increases the submerged volume of the amphibious assault vehicle, so the buoyancy acting on the vehicle is increased and the moved distance for the re-flotation is decreased. It is also revealed that the submerged volume is increased, bow-up phenomenon occur earlier.

• Nuclear Engineering and Technology
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• 제55권10호
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• pp.3754-3767
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• 2023

Turbulent jet discharges in subcooled water pools are essential for safety systems in nuclear power plants, specifically in the pressure suppression pool of boiling water reactors and In-containment Refueling Water Storage Tank of advanced pressurized water reactors. The gas and liquid flow in these systems is investigated using multiphase flow analysis. This field has been extensively examined using a combination of experiments, theoretical models, and Computational Fluid Dynamics (CFD) simulations. ANSYS CFX offers two approaches to model multiphase flow behavior. The non-homogeneous Eulerian-Eulerian Model has been used in this work; it computes global information and is more convenient to study interpenetrated fluids. This study utilized the Large Eddy Simulation Model as the turbulence model, as it is better suited for non-stationary and buoyant flows. The CFD results of this study were validated with experimental data and theoretical results previously obtained. The figures of merit dimensionless penetration length and the dimensionless buoyancy length show good agreement with the experimental measurements. Correlations for these variables were obtained as a function of dimensionless numbers to give generality using only initial boundary conditions. CFD numerical model developed in this research has the capability to simulate the behavior of non-condensable gases discharged in water.

• 한국초전도ㆍ저온공학회논문지
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• 제3권1호
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• pp.16-21
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• 2001

Bubble behavior is studied with an electrode system which consists of coaxial spiral coil-to-cylindrical electrode with an insulation barrier and spacers and is immersed in liquid nitrogen for simulation of insulation environments in high temperature superconducting(HTS) coils The results show that the bubble behavior Is affected severely by electric field: (1) under low applied voltage bubbles rise by buoyancy, but at higher applied voltage they are trapped in a lower electric field region below the coil electrode, and (2) the trapped bubble flows along the downside of coil electrode if no obstruction is in a groove between coil turns. but it splashes out of the groove after its growing if the obstruction such as spacer-exists.