• Journal of Power System Engineering
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• v.11 no.1
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• pp.82-91
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• 2007

기존의 2차원 FDLB 모델(D2Q21)에서 비열비 ${\gamma}$는 공간의 차원수(D)에 의존한다. 즉, 2차원 공간의 계산에서는 ${\gamma}=(D+2)/D=2.0$밖에 취할 수 없으며, 공기와 같은 실체기체를 전산모사 하기에는 여러 어려움이 있다. 이러한 이유 때문에 문헌[1]의 LBM에서 제안된 조정 가능한 비열비 모델을 2차원 FDLB모델에 적용하여 자려발생 에지톤(edgetone)의 수치계산이 수행되었다. wedge의 선단각도가 ${\alpha}=23^{\circ}$(Case I) 및 $20^{\circ}$(Case II)를 갖는 2가지 모델이 설정되었으며, 노즐출구에서 wedge선단까지의 거리 w/d는 $3d{\sim}12d$사이에서 주어졌다. edgetone은 노즐로부터 나온 분류와 edge의 상호작용으로 이난 음압(sound pressure)의 차에 의해서 소음이 발생하며, 이 음압은 다시 상류의 분류에 영향을 미쳐 분류의 변동을 가져온다. w/d가 ??9d이하인 경우, 피드백(feedback) 메커니즘에 기인한 주기적인 운동이 발생하지만, w/d가 큰 ??9d이상인 경우에는 분류의 불안정성 때문에 규칙적인 분류의 운동은 보이질 않으며, 이는 기존의 연구결과들과 잘 일치함을 보였다. 본 연구에서 적용된 모델을 이용하여 공기와 같은 2원자 기체의 비열비 ??${\gamma}=1.4$를 갖는 유체에 있어서 공력 소음의 수치예측이 가능하다는 것을 확인하였다.

• Korean Journal of Food Science and Technology
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• v.41 no.3
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• pp.272-277
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• 2009

In this research, three dimensional mathematical models were developed to predict the shelf life of tofu packaged in a semi-rigid plastic container. A model combining oxygen transfer through the package and oxygen consumption within the package was considered. According to the results, the model simulations estimated that the number of microorganisms in the filled water was higher than that in the tofu, suggesting the shelf life of packaged tofu was not affected by the number of microorganisms in the tofu product, but rather by the number of organisms in the filled water. Additionally, the effects of the physical properties of the packaging material, such as oxygen permeability through the package, oxygen diffusion coefficient, the initial oxygen concentration in the filled water, and the depth of the filled water in the packaged tofu, were also observed.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.10a
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• pp.170-174
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• 2002

In this study, the material characterization and the dynamic behavior of 3D orthogonal woven composite materials has been studied under transverse central low-velocity impact condition by means of the micromechanical model using finite elements. To build up the micromechanical model considering tow spacing and waviness, an accurate unit structure is stacked in x-y-z direction repeatedly. First, the mechanical properties of 3D orthogonal woven composites are obtained by means of virtual experiment using full scale Finite Element Analysis based on the DNS concepts, and the computed elastic properties are validated by comparison to available experimental results[9]. Second, using the implementation of this validated micromechanical model, 3D transient finite-element analysis is performed considering contact and impact, and the impact behavior of 3D orthogonal woven composite is investigated. A comparison study will be carried out in terms of energy absorption capabilities.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.179-182
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• 2007

The new KOMPSAT in preliminary design phase will utilize 4.45 N monopropellant thrusters for attitude and orbit control. In this paper, a numerical plume analysis is performed to verify the effects of thruster plume on the satellite with a 3-D satellite base region model by DSMC. As a result, plume behaviors such as overall plume temperature, total density and thermal radiation to solar array are estimated.

• The Journal of the Acoustical Society of Korea
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• v.41 no.6
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• pp.713-722
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• 2022

In this paper, the flow performance and aero-acoustic noise generated by the target centrifugal fan system were investigated numerically and experimentally. Also, the numerical method for Computational Aero-Acoustics were evaluated by comparing each method. To analyze the performance of the centrifugal fan experimentally, the acoustic power level was measured in the semi-anechoic chamber using microphones, and the active frequency range for the noise performance was identified and that frequency range was applied for Computational Aero-Acoustics (CAA) techniques as sampling frequency. Then, Navier-Stokes equation and the Ffowcs Williams&Hawking equations were used to analyze the flow and sound power numerically, respectively, and a virtual acoustic radiation plane was designed and used for the implementation of the sound field. The accuracy and numerical characteristics of the numerical methods were validated by comparing simulated acoustic power levels with acoustic power levels measured.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 2003.05a
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• pp.601-604
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• 2003

본 연구의 목표는 현재 복수기의 운전상황을 반영한 열유동 해석을 수행하여 저압터빈후드 온도의 좌우 편차가 발생하는 원인을 분석하는 것이다. 그러나 실제 복수기가 기하학적 형상이 복잡하고, 운전조건의 명확한 설정이 어려우며, 또한 수치해석에도 포함되는 오차 등을 고려하면, 단순히 현재의 운전조건 만을 반영한 해석에 의하여서는 원인의 규명이 어렵게 된다.(중략)

• Tunnel and Underground Space
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• v.30 no.4
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• pp.320-334
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• 2020

This study presents an application of hydro-mechanical coupled Particle Flow Code 3D (PFC3D) to simulation of fluid injection induced fault slip experiment conducted in Mont Terri Switzerland as a part of a task in an international research project DECOVALEX-2019. We also aimed as identifying the current limitations of the modelling method and issues for further development. A fluid flow algorithm was developed and implemented in a 3D pore-pipe network model in a 3D bonded particle assembly using PFC3D v5, and was applied to Mont Terri Step 2 minor fault activation experiment. The simulated results showed that the injected fluid migrates through the permeable fault zone and induces fault deformation, demonstrating a full hydro-mechanical coupled behavior. The simulated results were, however, partially matching with the field measurement. The simulated pressure build-up at the monitoring location showed linear and progressive increase, whereas the field measurement showed an abrupt increase associated with the fault slip We conclude that such difference between the modelling and the field test is due to the structure of the fault in the model which was represented as a combination of damage zone and core fractures. The modelled fault is likely larger in size than the real fault in Mont Terri site. Therefore, the modelled fault allows several path ways of fluid flow from the injection location to the pressure monitoring location, leading to smooth pressure build-up at the monitoring location while the injection pressure increases, and an early start of pressure decay even before the injection pressure reaches the maximum. We also conclude that the clay filling in the real fault could have acted as a fluid barrier which may have resulted in formation of fluid over-pressurization locally in the fault. Unlike the pressure result, the simulated fault deformations were matching with the field measurements. A better way of modelling a heterogeneous clay-filled fault structure with a narrow zone should be studied further to improve the applicability of the modelling method to fluid injection induced fault activation.

• Journal of Power System Engineering
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• v.15 no.6
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• pp.27-34
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• 2011

The increasing capabilities of the computers enable us to utilize various numerical schemes for the time-domain simulations concerned with 3-dimensional free-surface wave problems. There are still difficulties to solve such kind of problems, however. That's because long time simulations with large computational domain are needed in time-domain analysis. So, we need faster and more efficient numerical schemes to get the solutions practically for these problems. In this paper, a high-order spectral/boundary-element method is used for the numerical investigation of physics involved in wave-body interaction. This method is one of the most efficient numerical methods by which the nonlinear gravity waves can be simulated and hydrodynamic forces also can be calculated in time-domain. To get the robust study in these topics, various numerical tests are performed and compared with others' works.

• Korean Journal of Optics and Photonics
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• v.31 no.2
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• pp.59-70
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• 2020

We discuss a modified numerical model based on the Monte Carlo radiative transfer (MCRT) method, i.e., the MCRT matrix method, for the analysis of atmospheric scattering effects in three-dimensional flash LIDAR systems. Based on the MCRT method, the radiative transfer function for a LIDAR signal is constructed in a form of a matrix, which corresponds to the characteristic response. Exploiting the superposition and convolution of the characteristic response matrices under the paraxial approximation, an extended computer simulation model of an overall flash LIDAR system is developed. The MCRT matrix method substantially reduces the number of tracking signals, which may grow excessively in the case of conventional Monte Carlo methods. Consequently, it can readily yield fast acquisition of the signal response under various scattering conditions and LIDAR-system configurations. Using the computational model based on the MCRT matrix method, we carry out numerical simulations of a three-dimensional flash LIDAR system operating under different atmospheric conditions, varying the scattering coefficient in terms of visible distance. We numerically analyze various phenomena caused by scattering effects in this system, such as degradation of the signal-to-noise ratio, glitches, and spatiotemporal spread and time delay of the LIDAR signals. The MCRT matrix method is expected to be very effective in analyzing a variety of LIDAR systems, including flash LIDAR systems for autonomous driving.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.524-524
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• 2023

하천 내 식생의 분포는 흐름저항의 증가와 수위상승에 큰 영향을 미치는 요소 중 하나이다. 동일한 단면정보를 가졌더라도 식생이 분포하는 하도는 식생이 없는 하도에 비해 흐름저항으로 인해 유속이 현저히 느려져 홍수위 상승을 유발하기 때문이다. 따라서 식생의 종류, 크기, 분포 형태, 잎의 밀도 등에 따라 흐름저항계수를 정량화하며 흐름을 정확히 예측하는 것이 필요하다. 본 연구에서는 2019년 한국건설기술연구원 하천실험센터에서 진행된 식생하도에 대한 실규모 실험의 조건과 지형정보를 HEC-RAS(Hydrologic Engineering Center's River Analysis System) 1차원 수치모형에 입력하고, 식생 패치의 분포를 고려한 Manning's n의 공간적 분포 및 적용방식에 따른 수면 경사 재현 정확도에 대한 민감도 분석을 수행하였다. 실험은 상단 폭 11 m, 경사 1:2(V:H)의 사다리꼴 단면을 가진 실규모 수로에서 70 m 길이의 구간을 대상으로 진행되었다. 실험 구간 내 6개의 압력식 수위계를 설치해 수위 측정 및 수면 경사 산정을 실행하였다. 실험 조건으로 적용된 인공 식생패치의 분포 및 밀도 조건은 3가지로 큰 패치와 작은 패치로 구성된 조밀한 조건, 단일 패치로 구성된 조밀한 조건, 단일 패치로 구성된 성긴 조건이었으며, 모두 정수(emergent)상태로 진행되었다. 적용된 패치의 형상은 내성천에서 조사된 자연 형태의 식생패치 형태를 참고하였으며, 버드나무 종을 모사하였다. 실험 조건에 따라 유량은 각각 평균 1.5 cms와 2.7 cms로 공급하였으며, 평균 수심은 약 1 m로 측정되었다. 위 실험 내용을 바탕으로 수치모의를 위한 경계조건과 지형정보를 수립하였으며 모의 케이스는 크게 두 가지로, 수로 내 식생의 분포를 종방향으로 고려한 케이스와 횡방향으로 고려하여 조도계수를 적용한 케이스로 분류하였다. 모의에 적용된 조도계수는 실험에서 획득한 데이터와 베르누이 방정식을 활용하여 산정되었으며, 두 케이스에 대한 모의 결과는 실험에서 관측된 수위와 비교하였다. 본 연구에 따르면 여러 개의 식생패치가 정수상태로 존재하는 하천에 대한 1차원 수치모의 시 식생의 분포를 종방향으로 고려하여 하나의 구간조도계수를 적용하는 방식이 종횡단면의 식생패치 위치를 고려한 조도계수를 세분화하여 적용하는 방식에 비해 수위 계산 정확도가 상대적으로 높은 것으로 나타났다.