• 한국분말재료학회지
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• 제4권1호
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• pp.55-62
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• 1997

Flow and heat transfer characteristics of gas, and trajectories and cooling characteristics of droplets/particles in a gas atomizer were investigated by a numerical simulation using FLUENT code. Among several kinds of solution method, the k-$\varepsilon$ turbulent model, power-law scheme, SIMPLE algorithm is adopted in this study. Momentum and heat exchange between a continuous phase(gas) and a dispersed phase(particle) were taken into account. Particle trajectories are simulated using the Lagrangian method, and Rosin-Rammler formula is used for the particle size distribution. Streamlines, velocities and pressures of gas, and trajectories, velocities and cooling rates of particles have been investigated for the various gas inlet conditions. Small but very intensive recirculation is found just below the melt orifice, and this recirculation seems to cause the liquid metal to spread radially. Particle trajectory depends on the particle size, the location of particle formation and the turbulent motion of gas. Small particle cools down rapidly, while large diameter particles solidify slowly, and this is mainly due to the differences in thermal inertia.

• 한국연소학회:학술대회논문집
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• 한국연소학회 1999년도 제19회 KOSCO SYMPOSIUM 논문집
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• pp.139-148
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• 1999

In oder to analyze the effect of operating conditions on pulverized coal combustion, a numerical study is conducted at the pulverized coal combustor. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the particle phase. Turbulence is modeled using standard ${\kappa}-{\varepsilon}$ model. The description of species transport and combustion chemistry is based on the mixture fraction/probability density function(PDF) approach. Radiation is modeled using P-l model. The turbulent dispersion of particles is modeled using discrete random walk model. Swirl number of secondary air affects the flame front, particle residence time and carbon conversion. Primary/Secondary air mass ratio also affects the flame front but little affects the carbon conversion and particle residence time. Air-fuel ratio only affects the flame front due to lack of oxygen. Radiation strongly affects the flame front and gas temperature distribution because pulverized coal flame of high temperature is considered.

• Nuclear Engineering and Technology
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• 제56권7호
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• pp.2498-2515
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• 2024

In this study, we propose a fully parallelized adaptive particle refinement (APR) algorithm for smoothed particle hydrodynamics (SPH) to construct a stable and efficient multi-resolution computing system for nuclear safety analysis. The APR technique, widely employed by SPH research groups to adjust local particle resolutions, currently operates on a serialized algorithm. However, this serialized approach diminishes the computational efficiency of the system, negating the advantages of acceleration achieved through high-performance computing devices. To address this drawback, we propose a fully parallelized APR algorithm designed to enhance both efficiency and computational accuracy, facilitated by a new adaptive smoothing length model. For model validation, we simulated both hydrostatic and hydrodynamic benchmark cases in 2D and 3D environments. The results demonstrate improved computational efficiency compared to the conventional SPH method and APR with a serialized algorithm, and the model's accuracy was confirmed, revealing favorable outcomes near the resolution interface. Through the analysis of jet breakup, we verified the performance and accuracy of the model, emphasizing its applicability in practical nuclear safety analysis.

• Journal of Mechanical Science and Technology
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• 제20권9호
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• pp.1459-1474
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• 2006

The present study is focused on the development of the RIF (Representative Interactive Flamelet) model which can overcome the shortcomings of conventional approach based on the steady flamelet library. Due to the ability for interactively describing the transient behaviors of local flame structures with CFD solver, the RIF model can effectively account for the detailed mechanisms of $NO_x$ formation including thermal NO path, prompt and nitrous $NO_x$ formation, and reburning process by hydrocarbon radical without any ad-hoc procedure. The flamelet time of RIFs within a stationary turbulent flame may be thought to be Lagrangian flight time. In context with the RIF approach, this study adopts the Eulerian Particle Flamelet Model (EPFM) with mutiple flamelets which can realistically account for the spatial inhomogeneity of scalar dissipation rate. In order to systematically evaluate the capability of Eulerian particle flamelet model to predict the precise flame structure and NO formation in the multi-dimensional elliptic flames, two methanol bluffbody flames with two different injection velocities are chosen as the validation cases. Numerical results suggest that the present EPFM model has the predicative capability to realistically capture the essential features of flame structure and $NO_x$ formation in the bluff-body stabilized flames.

• 한국항공우주학회지
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• 제31권3호
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• pp.8-14
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• 2003

난류혼합층에서 속도비 변화에 따른 입자의 운동형태에 대하여 수치해석적 연구를 수행하였다. Turbulent closure를 목적으로 Subgrid모델을 바탕으로 한 LES를 적용하여고 입자 운동을 해석하기 위해 Lagrangian 방법을 적용하였다. 입자의 직경이 10, 50, 100, 150, 200${\mu}m$인 입자들이 분리판 끝단에서 정지한 상태로 혼합층에 유입이 되고, 큰-크기 와류구조에 영향을 받아 혼합층 내로 확산이 되어진다. 혼합층의 성장특성은 속도비 변화에 매루 민감하여, 입자의 확산은 혼합층의 속도비와 입자 직경의 변화에 따라 거동을 달리함을 알 수 있었다. 또한 Stokes 수와 입자확산의 관계를 나타내었다. 그 결과로 St~1인 경우 입자의 확산이 유동장의 확산보다 빠르게 일어나나, St<<1과 St>>1인 경우는 입자의 확산이 잘 일어나지 않음을 알 수 있다.

• 한국환경과학회지
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• 제25권9호
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• pp.1253-1267
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• 2016

After large-scale flooding damage occurred along the Imjin river in 1996, 1998, and 1999, the Hantan river flood control dam was planned, and it has since been under construction. Unlike existing dams in Korea, the Hantan river flood control dam will remain fully open except during high floods, when the dam will store flood water temporarily to reduce flood peaks and flood water volume downstream. During past flooding seasons, floating debris has caused difficulties in the management of large-scale dams. Most of the existing multipurpose dams in Korea have installed nets to collect floating debris based on many years of experience with and data about inflow and distribution of floating debris in the dams. For the Hantan river flood control dam, however, collection of data about inflow and distribution of floating debris is not possible as the dam is located near the border area between North and South Korea. In order to devise a preliminary plan to collect floating debris in the Hantan river flood control dam, an EFDC hydrodynamic model was used to analyze the behavior of floating debris during high floods. The Lagrangian particle tracking method was utilized to simulate the behavior of floating debris in the dam. Based on the analysis of paths and final destinations of the particles, seven collection points were selected where it seemed to be effective to collect floating debris, as debris is likely to accumulate there in high density.

• 한국해안해양공학회지
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• 제10권1호
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• pp.37-44
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• 1998

본 연구에서 제안하는 혼합 방법(hybrid method)은 흐름이 우세한 영역에서의 전송 문제를 정확하고 효과적으로 해결하기 위하여 개발된 것으로 오일러-라그란쥐적 방법과는 달리 전방추적에 의하여 이송 과정이 수행되므로 보간 기법이 불필요하고 무작위 행보에 의한 라그란쥐적 방법과 달리 유한 차분법에 의하여 확산 과정이 수행되므로 많은 입자가 요구되지도 않는다. 한 점에 순간적으로 부하되는 오염원과 연속적으로 부하되는 오염원에 대한 이론적인 해와 비교하여 확산 계수와 무관하게 상당히 만족할 만한 결과를 얻었다. 현 방법은 또한 2차원 상에서 주변 5격자로부터 보간하는 오일러-라그란쥐적 방법과 무작위 행보로 입자 추적하는 순수 라그란쥐적 방법과 비교하여 정확성은 물론 계산 시간에 있어서도 상당히 월등한 방법임이 입증되었다.

• 한국군사과학기술학회지
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• 제14권5호
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• pp.932-940
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• 2011

This study describes computational simulation results in 2-dimensional and 3-dimensional space concerning large scale gap test(LSGT) by using commercial hydrocode such as AUTODYN and LS-DYNA to analyze the detonation phenomenons of high explosives. To consider the possibilities of LSGT simulation, we used Lee - Tarver reaction rate model of PBX-9404 and Comp-B which were implemented AUTODYN's material library. Also we have tried the diverse numerical schemes such as Lagrangian, Eulerian and ALE(Arbitary Lagrangian Eulerian), SPH(Smoothed Particle Hydrodynamics) in LSGT simulations. After LSGT simulations, we compared the simulation results with published results to verify the LSGT simulations. According to the LSGT simulations, we have concluded as follows. In 2-dimensional and 3-dimensional space, Lagrangian solver provided the most reliable results based on analysis time and accuracy. When using two hydrocodes in 2-dimensional space, the simulation results are almost same except one explosive model. We have verified the modeling method and simulation results of the LSGT by using the commenrcial hydrocode in this study.

• 한국대기환경학회지
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• 제15권3호
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• pp.223-233
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• 1999

The wind-flow characteristics over a two-dimensional triangular prism with a porous windbreak are numerically investigated. The geometry is a simplified model of large outdoor stack with a frontal wall-type windbreak which is used to prevent particle dispersion by reducing wind speed over stak surface. In the present numerical model, the RNG k-$\varepsilon$ model, the orthogonal grid system and the QUICK scheme are employed for the successful simulation of separated flow. The predicted results are compared and validated with the associated wind-tunnel experiments. In addition, the trajectories of dispersed particles and their sedimentation characteristics are quantitatively investingated using a Lagrangian turbulent-dispersion model.

• 한국입자에어로졸학회지
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• 제8권1호
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• pp.1-8
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• 2012

In this study, the collection efficiency of inertial impactors was numerically simulated by employing the statistical Lagrangian particle tracking(SLPT) model. The SLPT model was proven to be correct in predicting the impactor collection efficiency, when the numerically obtained collection efficiencies were compared with the experimental data of Marple et al.(1987) at normal pressure level and the experimental data of $Marjam{\ddot{a}}ki$ et al.(2000) at low pressure level. Based on the validation results, balloon-borne impactors with the cut-off sizes of $1{\mu}m$, $2.5{\mu}m$, and $10{\mu}m$ were designed. Then, the sampling flowrates of the inertial impactors, required to keep the cut-off sizes constant at different pressures and temperatures, were estimated according to the altitude.