• Journal of Navigation and Port Research
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• v.27 no.5
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• pp.473-478
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• 2003

Numerical study was made on the flow characteristics around a circular pipeline between parallel walls. The incompressible Navier-Stokes equations were solved by using a third-order upwind differential scheme. When the distance near a wall is small enough, the vortex shedding is almost completely suppressed because of the interaction with the wall boundary layer separation. This study aims to clarify the characteristics of the vortex shedding regime as the body approaches a wall as Reynolds number varies. The feature of separated vorticity dynamics is analyzed at different conditions with particular attention to the interaction between the pipeline wake and the induced separation on the plane walls.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.38-42
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• 2009

Recently, various particle based simulation techniques, which solve the Navier Stokes and continuity equations, have been developed and applied to complicated engineering problems. However, although progress is being made on their visualization or rendering techniques, these are still insufficient. In this study, to render a smooth configuration for a free surface, a rendering technique was developed that included the generation of density fields from the location information for simulated particles and the creation model for a polygonal surface. The developed rendering technique was applied to the visualization of a dynamic free surface flow interacting with a structure using a particle based simulation technique.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2002.07a
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• pp.182-187
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• 2002

국내 저온저장고의 주류를 이루고 있는 컨테이너 박스형 저온저장고의 문제점은 재래식 제어방식으로 인한 성능저하 외에도 자체 구조적인 설계상의 문제점을 가지고 있다 이러한 구조적인 문제점을 열거하면 다음과 같다. 첫째, 한 축 방향에 설치되어있는 유니트 쿨러에서 토출되는 냉기에 의해 저장고 내의 공기를 냉각하는 형태이기 때문에 냉기의 분포가 고르지 못하여 균일한 온도 분포를 이루기 어렵다는 단점을 가지고있다. 둘째, 한 축 방향에서 토출되는 냉기가 맞은 편 벽면까지 도달해야 하기 때문에 풍속이 강해야 하며 이로 인해 저장 청과물이 냉해를 쉽게 입고 심한 증산작용에 의해 쉽게 표면건조나 중량감소를 가져온다. 셋째, 천장부와 측벽부가 90$^{\circ}$의 경사각을 가지고 있어 공기의 유동이 원활하지 못하여 에디현상으로 인한 온도나 풍속의 불균일 구간을 피해서 청과물을 저장해야 하기 때문에 그만큼 버려지는 공간이 많아 비경제적이다. 넷째, 위와 같은 문제점들 때문에 중ㆍ대형의 저온저장고를 컨테이너 박스형으로 설비 할 경우 보다 심한 온도 불균일과 냉기유동 분포를 보여 경제적인 손실이 더 커지게 되는 악순환을 낳게된다. 이에 따라 본 연구에서는 국내 저온저장고의 구조적인 설계상의 문제점을 인식하고 이를 해결하고자 3차원 CFD 시뮬레이션을 이용하여 저온저장고의 새로운 모델을 설계하였다. 이론 바탕으로 직접 저온저장고의 시작기를 개발하여 저장고 내부의 역 유동과 난류유통을 해석하였다. (중략)

• Journal of the Society of Naval Architects of Korea
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• v.33 no.2
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• pp.1-12
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• 1996

Hydrodynamic characteristics of shipping water on deck are investigated by using a simplified two-dimensional model. Formulation of the shipping water on deck leads to a nonlinear hyperbolic system of equations based on the shallow-water wave theory. Time-domain solution of these equations are obtained numerically using a finite difference method which adopts predictor-corrector method for time-marching and 2nd upwind differencing method for convection term calculation. To confirm the validity of the present numerical method, we calculated some shallow-water wave problems accompanying a bore and compared the obtained results with the analytic solutions. We found good agreements between them. Though the calculation results of shipping water on deck, we show that the shipping water flows into the deck as a rarefying wave arid grows into a bore after colliding with a deck structure. Also we examined the effects of acceleration and slope of deck and found that they have significant influences on the flow of shipping water.

• Journal of the Korea Society for Simulation
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• v.23 no.2
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• pp.17-24
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• 2014

This study attempts to show an example of developing and applying thermal hydraulic simulation model for Aircraft-EHA. The overview of research procedure is as in the following. First, The unit hydraulic simulation model, which reflects physical quantity answering engineer's purpose is developed. Second, The unit hydraulic simulation model is combined, and then branched out to EHA hydraulic model. Third, a simulation model including flow thermal is developed, and then oil temperature rise time according to 'initial temperature and load' is examined. Finally, the master graph that can be used for designing EHA combined with thermal hydraulic analysis results in several cases is compiled, and suggested. AMESim, commercial software, is used through whole procedure.

• Journal of the Korea Concrete Institute
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• v.26 no.6
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• pp.671-677
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• 2014

In this research, flow experiments and simulation of highly flowable concrete has been attempted using a viscoplastic particle method varying with dosages of SP admixture and water-cement (W/C) ratios. Rheological and flow characteristics of flowable concrete manufactured in domestic products of cement, aggregates, and SP admixtures were investigated by experimental programs varying with mix proportions. From experiment, the predictive model of rheological characteristics of flowable concrete has been newly proposed considering with the effects of the W/C ratio and the dosage of SP admixture, and the effect of mixing proportion has also been incorporated into shear stress and strain rate curve of flowable concrete in the current method. A series of L-box flow test of highly flowable concrete varying with dosages of SP admixture and W/C ratios was compared with the proposed model.

• Smart Media Journal
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• v.8 no.4
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• pp.38-45
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• 2019

When there is a spray flow such as from a pesticide nozzle, winds affect the droplet flow of a rotary-wing drone accompanied by a strong wake, with a severe oscillation. Especially, during forwarding flights or when winds come from the side, compare to a simple hovering flight as the droplet is in the effect of aerodynamic drag force, the effect of spraying region becomes even larger. For this reason, the spraying of pesticides using drones may cause a greater risk of scattering or a difference in droplet dispersion between locations, resulting in a decrease in efficiency. Therefore, through proper numerical modeling and its applied simulation, an indication tool is required applicable for the various flight and atmospheric conditions. In this research, we completed both experiment and numerical analysis for the strong downwash from the rotor and flight velocity of the drone by comparing the probability density function of droplet distribution to build a spraying system that can improve the efficiency when spraying droplets in the pesticide spray drone.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.5
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• pp.398-407
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• 2002

An experimental and analytical study was made on the heat transfer characteristics of one small (150 W), two medium (60 and 1,500 W, respectively) and two large (7,500and 100,000 W) two-phase loop thermosyphons (TLT), and the results from the experiments were used to see if a computer simulation code alone for such TLT heat transfer systems would give any meaningful quantitative results without being accompanied with some benchmark experimental verification. Two simulation methods were used for the analysis of the systems, i.e., the lumped and the sectorial thermal resistance methods. The study clearly shows that the computer simulation for the three TLTs can predict the most cases of the affecting parameters involved, provided that correct empirical correlations are used. To do so, however, the interior temperature distribution had to be verified by experiment.

• Journal of the Korea Computer Graphics Society
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• v.9 no.1
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• pp.1-2
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• 2003

본 논문에서는 액체와 기체가 상호작용 하는 현상들에 대한 새로운 유체 애니메이션 기법을 액체 속 공기방울의 예를 사용하여 제시한다. 기존의 자유표면 시뮬레이션 기법들과는 달리 액체와 기체를 함께 시뮬레이션 할 경우에는 기체의 유동과 액체의 유동을 동시에 다루어야 하며 비중 차에 의한 부력과 경계면에서의 표면장력 등을 추가적으로 고려해야 한다. 유체의 토폴로지 변화를 쉽게 다루면서도 수치적 분산을 막기 위하여 유체 역학 분야의 VOF (Volume of Fluid) 기법과 프론트 추적 (Front-tracking) 기법을 혼합하여 사용하였다. 액체와 기체의 경계면은 마칭 큐브즈 알고리즘을 사용하여 폴리곤으로 복원된 후 버텍스 쉐이더 기술들을 사용하여 액체-기체 경계면의 광학적인 특성을 표현할 수 있었다.

• The KSFM Journal of Fluid Machinery
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• v.9 no.5 s.38
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• pp.22-27
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• 2006

Sedimentation phenomenon of suspended solids occurs by the gravitational force. Pollution particles are separated from slowly flowing waste water in clarifier. Recently, the sludge suction collector is Preferred rather than the scraper type sludge collector due to the enhancement of the clarifier efficiency. The sludge suction collector is usually operated by the user's experiences without any scientific and/or technical consideration. To evaluate the performance of sludge suction collector, the three dimensional numerical simulation was conducted by the finite volume method. To analyze the performance, the velocity vectors and the suction flow rates of the orifices were investigated. The result showed that each suction flow rate through out the collector was equivalent in the sludge suction collector and the efficiency of suction collector was good to remove high concentrated sludge in clarifier.