• 한국컴퓨터정보학회:학술대회논문집
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• 한국컴퓨터정보학회 2023년도 제67차 동계학술대회논문집 31권1호
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• pp.395-398
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• 2023

본 논문에서는 물리 기반 옷감 시뮬레이션과 SPH(Smoothed particle hydrodynamics) 기반의 유체 시뮬레이션 간의 상호작용에서 표현되는 다양한 물리적 효과를 GPU 기반으로 빠르게 표현할 수 있는 프레임워크를 제안한다. 기존 기법과는 다르게 수치적 안정성을 개선하기 위해 CCD(Continuous collision detection)를 활용하였으며, 모든 연산이 GPU에서 동작하기 때문에 매우 빠르게 옷감과 유체의 상호작용 장면인 다공성 재질, 기공 흐름, 흡수, 방사, 확산을 모델링할 수 있다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제9권4호
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• pp.390-403
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• 2017

Smoothed Particle Hydrodynamics (SPH) method has a good adaptability for the simulation of free surface flow problems. There are two forms of SPH. One is weak compressible SPH and the other one is incompressible SPH (ISPH). Compared with the former one, ISPH method performs better in many cases. ISPH based on Rankine source solution can perform better than traditional ISPH, as it can use larger stepping length by avoiding the second order derivative in pressure Poisson equation. However, ISPH_R method needs to solve the sparse linear matrix for pressure Poisson equation, which is one of the most expensive parts during one time stepping calculation. Iterative methods are normally used for solving Poisson equation with large particle numbers. However, there are many iterative methods available and the question for using which one is still open. In this paper, three iterative methods, CGS, Bi-CGstab and GMRES are compared, which are suitable and typical for large unsymmetrical sparse matrix solutions. According to the numerical tests on different cases, still water test, dam breaking, violent tank sloshing, solitary wave slamming, the GMRES method is more efficient than CGS and Bi-CGstab for ISPH method.

• 한국컴퓨터그래픽스학회논문지
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• 제23권1호
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• pp.9-16
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• 2017

젖은 헤어 또는 동물의 털 시뮬레이션에서 응집력과 강성(stiffness)을 처리하는 것은 어려운 문제이다. 격렬한 움직임을 갖는 헤어나 털이 물에 젖게 되면 끝이 뭉치고 빳빳해지는 현상이 나타나게 되는데, 이는 달리는 동물이나 헤드뱅잉 하는 장면 등에서 쉽게 관찰 할 수 있다. 기존의 방법들은 정해진 시뮬레이션 시나리오에서 이 문제를 해결하려고 했지만 여전히 젖은 헤어의 특징을 묘사하기 위한 일반적인 방법이 존재하지 않는다. 이 문제를 해결하기 위해 우리는 응집력과 강성에 대한 새로운 모델링 방법을 제안한다. 기존 연구들은 물이 모발에 흡수되는 현상을 모델링 하는데 초점을 맞춘 반면, 우리는 젖은 모발의 움직임을 사실적으로 표현하는데 집중한다. 젖은 헤어는 마른 헤어와는 다르게 인접한 모발들끼리 응집력이 작용하여 서로 뭉치는 형태를 띄며, 물의 포화도가 높아질수록 빳빳해지는 독특한 물리적 특성이 나타난다. 제안된 기법의 핵심은 SPH (smoothed particle hydrodynamics) 기반의 표면 장력 모델을 확장하여 응집력을 표현하고, 강성 제약을 두어 모발의 탄성력을 조절하는 것이다. 우리 기법은 젖은 모발이 격렬한 움직임에서도 응집력을 잘 유지할 수 있도록 도와주며, 물의 포화도에 따른 모발의 빳빳함을 표현하여 사실적인 젖은 헤어 시뮬레이션 결과를 보여준다.

• 한국지반신소재학회논문집
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• 제19권3호
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• pp.1-8
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• 2020

본 연구에서는 토석류 매커니즘 분석을 위해 SPH(Smoothed Particle Hydrodynamics) 기법을 사용하여 토석류 수치해석을 수행하고 선행연구와 비교하여 토질정수의 적용성을 검증하였다. 또한, 자굴산 유역 계곡부를 대상으로 드론을 이용하여 항공사진측량을 수행한 후 이를 기반으로 지형모델을 생성하고 NFLOW를 활용하여 토석류 수치해석을 수행한 후 결과값을 위성영상 기반의 기존의 방법과 비교·분석하였다. 본 연구 결과, 드론 영상 및 NFLOW를 활용한 수치해석 기법은 위성 영상기반의 기존 방법보다 실제 지형을 잘 반영할 수 있어 토석류 영향 예측에 적용성이 높은 것으로 나타났다. 따라서 드론영상 및 NFLOW를 활용한 토석류 분석 기법은 사방댐 위치선정 등 토석류 예방 대책 수립 시 기초자료로 활용될 수 있을 것으로 사료된다.

• 한국해양공학회지
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• 제28권2호
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• pp.93-101
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• 2014

In general, particle simulation methods such as the MPS(Moving Particle Simulation) or SPH(Smoothed Particle Hydrodynamics) methods have some serious drawbacks for pressure solutions. The pressure field shows spurious high fluctuations both temporally and spatially. It is well known that pressure fluctuation primarily occurs because of the numerical approximation of the partial differential operators. The MPS and SPH methods employ a pre-defined kernel function in the approximation of the gradient and Laplacian operators. Because this kernel function is constructed artificially, an accurate solution cannot be guaranteed, especially when the distribution of particles is irregular. In this paper, we propose a particle simulation method based on the moving least-square technique for solving the partial differential operators using a Taylor-series expansion. The developed method was applied to the hydro-static pressure and dam-broken problems to validate it.

• Journal of Astronomy and Space Sciences
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• 제29권1호
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• pp.51-55
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• 2012

A few high-mass X-ray binaries-consisting of an OB star plus compact companion-have been observed by Fermi and ground-based Cerenkov telescopes like High Energy Stereoscopic System (HESS) to be sources of very high energy (VHE; up to 30 TeV) ${\gamma}$-rays. This paper focuses on the prominent ${\gamma}$-ray source, LS 5039, which consists of a massive O6.5V star in a 3.9-day-period, mildly elliptical ($e{\approx}0.24$) orbit with its companion, assumed here to be an unmagnetized compact object (e.g., black hole). Using three dimensional smoothed particle hydrodynamics simulations of the Bondi-Hoyle accretion of the O-star wind onto the companion, we find that the orbital phase variation of the accretion follows very closely the simple Bondi-Hoyle-Lyttleton (BHL) rate for the local radius and wind speed. Moreover, a simple model, wherein intrinsic emission of ${\gamma}$-rays is assumed to track this accretion rate, reproduces quite well Fermi observations of the phase variation of ${\gamma}$-rays in the energy range 0.1-10 GeV. However for the VHE (0.1-30 TeV) radiation observed by the HESS Cerenkov telescope, it is important to account also for photon-photon interactions between the ${\gamma}$-rays and the stellar optical/UV radiation, which effectively attenuates much of the strong emission near periastron. When this is included, we find that this simple BHL accretion model also quite naturally fits the HESS light curve, thus making it a strong alternative to the pulsar-wind-shock models commonly invoked to explain such VHE ${\gamma}$-ray emission in massive-star binaries.

• 대한토목학회논문집
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• 제31권2A호
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• pp.71-77
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• 2011

본 논문은 고체의 동적 탄소성해석을 수행하기 위해 인장불안정이 제거된 SPH기법을 사용하였다. 인장불안정은 SPH 입자들이 인장력에 의해 서로 떨어져나가는 해석적 오류현상이며, 재료적 특성에 따라 해석결과에 큰 영향을 미치게 된다. 이와 같은 인장불안정을 제어하기 위한 방법으로 본 연구에서는 가상응력의 개념을 적용하였다. 본 연구에서 제시한 SPH에 의해 해석예제를 수행하여 해석법의 효율성을 검증하였으며, 해석예제로 원형 링의 충돌문제와, 절단, 균열과 같은 재료적 파괴문제를 수행하였다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.329-347
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• 2018

The Smoothed Particle Hydrodynamics (SPH) method has proved to have great potentials in dealing with the wave-structure interactions. Compared with the Weakly Compressible SPH (WCSPH) method, the ISPH approach solves the pressure by using the pressure Poisson equation rather than the equation of state. This could provide a more stable and accurate pressure field that is important in the study of wave-structure interactions. This paper improves the solid boundary treatment of ISPH by using a high accuracy Simplified Finite Difference Interpolation (SFDI) scheme for the 2D wave-structure coupling problems, especially for free-moving structure. The proposed method is referred as the ISPH_BS. The model improvement is demonstrated by the documented benchmark tests and laboratory experiment covering various wave-structure interaction applications.

• Smart Structures and Systems
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• 제15권2호
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• pp.299-314
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• 2015

Submersed rock-berm structures are frequently used for protection of underwater lifelines such as pipelines and power cables. During the service life, the rock-berm structure can experience several accidental loads such as anchor collision. The consequences can be severe with a certain level of frequency; hence, the structural responses should be carefully understood for implementing a proper structural health monitoring method. However, no study has been made to quantify the structural responses because it is hard to deal with the individual behavior of each rock. Therefore, this study presents a collision analysis of the submersed rock-berm structure using a finite element software package by facilitating the smoothed-particle hydrodynamics (SPH) method. The analysis results were compared with those obtained from the Lagrange method. Moreover, two types of anchors (stock anchor and stockless anchor), three collision points and two different drop velocities (terminal velocity of each anchor and 5 m/s) were selected to investigate the changes in the responses. Finally, the effect of these parameters (analysis method, anchor type, collision point and drop velocity) on the analysis results was studied. Accordingly, the effectiveness of the SPH method is verified, a safe rock-berm height (over 1 m) is proposed, and a gauge point (0.5 m above the seabed) is suggested for a structural health monitoring implementation.

• 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.