• Structural Engineering and Mechanics
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• 제78권4호
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• pp.497-518
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• 2021

In this study, a new method for treating the wall boundary in smoothed particle hydrodynamics (SPH) is proposed to simulate free surface flows effectively. Unlike conventional methods of wall boundary treatment through boundary particles, in the proposed method, the wall boundary condition is directly imposed by adding boundary truncation terms to the mass and momentum conservation equations. Thus, boundary particles are not used in boundary modeling. Doing so, the wall boundary condition is accurately imposed, boundary modeling is simplified, and computation is made efficient without losing stability in SPH. Performance of the proposed method is demonstrated through several numerical examples: dam break, dam break with a wedge, sloshing, inclined bed, cross-lever rotation, pulsating tank and sloshing with a flexible baffle. These results are compared with available experimental results, analytical solutions, and results obtained using the boundary particle method.

• 한국항공우주학회지
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• 제44권11호
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• pp.957-964
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• 2016

본 연구에서는 발사체를 보관하고 사출하는 수직 발사대에서 발사체의 화염에 의해 변형되는 발사대 후방덮개의 응답을 유체-고체 연성해석 기법을 이용하여 해석하였다. 발사체의 화염은 Eulerian 기법을 이용하여 해석하였고, 탄소성 변형이 일어나는 후방 덮개는 9절점 유한 요소 기법을 사용하여 해석하였다. 유체와 고체 물질간의 경계면 추적은 레벨 셋 기법을 사용하였고 경계값은 가상유체 기법을 이용하여 결정하였다. 각 해석 기법들은 이론값들을 통하여 검증되었고, 후방 덮개의 해석 결과는 후방 덮개가 변형되는 시간을 비교하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2879-2884
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• 2007

Dynamic responses of electrorheological (ER) fluids in steady pressure flow to stepwise electric field excitations are investigated experimentally. The transient periods under various applied electric fields and flow velocities were determined from the pressure behavior of the ER fluid in the flow channel with two parallel-plate electrodes. The pressure response times were exponentially decreased with the increase of the flow velocity, but increased with the increase of the applied electric field strength. In order to investigate the cluster structure formation of the ER particles, it was verified using the flow visualization technique that the transient response of ER fluids in the flow mode is assigned to the densification process in the competition of the electric field-induced particle attractive interaction forces and the hydrodynamic forces, unlike that in the shear mode determined by the aggregation process.

• 한국해양공학회지
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• 제21권4호
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• pp.8-14
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• 2007

A particle method recognized as one of gridless methods has been developed to investigate incompressible viscous flaw. The method is more feasible and effective than conventional grid methods for solving the flaw field with complicated boundary shapes or multiple bodies. The method is consists of particle interaction models representing pressure gradient, diffusion, incompressibility and the boundary conditions. In the present study, the models in case of various simulation condition were checked with the analytic solution, and applied to the two-dimensional Poiseuille flow in order to validate the developed method.

• 한국해양공학회지
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• 제24권5호
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• pp.31-38
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• 2010

The Floating storage and re-gasification unit (FSRU), which has large cargo storage tanks, is a floating liquefied natural gas (LNG) import terminal. The sloshing motion in tanks that are partially filled with LNG can cause impact pressure on the containment system and affect the global motion of the FSRU. Therefore, the accurate prediction of sloshing motion has been a significant issue in the offshore gas production industry. In this paper, a particle method based on the moving particle semi-implicit (MPS) method proposed by Koshizuka and Oka (1996) has been modified to predict sloshing motion accurately in a rectangular tank with the filling ratio of water. The simulation results, including the violent sloshing of the fluid, were validated by comparison with the original MPS method.

• 한국해양공학회지
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• 제21권6호
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• pp.53-58
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• 2007

A particle method, recognized as one of gridless methods, has been developed to investigate non-linear free-surface motions interacting with structures. This method is more feasible and effective than conventional grid methods for solving flow fieldswith complicated boundary shapes. The method consists of particle interaction models representing pressure gradient, diffusion, incompressibility, and the free-surface boundary conditions without grids. In the present study, broken dam problems with various viscosity values are simulated to validate the developed method.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제28회 추계학술대회
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• pp.82-90
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• 1998

Machines that normally operate under fluid film lubricated condition also experience surface damage. This is largely due to the failure of the lubricant film which leads to boundary lubrication. Thus, it is important to have a good understanding of boundary lubrication behavior. In this paper the major tribological parameters that influence the boundary lubrication properties are evaluated. It is shown that disk roughness, hardness and normal load affect the friction and wear of metals in boundary lubrication. Also, the mechanism of surface damage is attributed to abrasion and wear particle interaction.

• International Journal of Aerospace System Engineering
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• 제5권1호
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• pp.1-8
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• 2018

Military rotorcrafts are constantly exposed to risk from bullet impacts because they operate in a battle environment. Because bullet impact damage can be deadly to crews, the fuel tanks of military rotorcraft must be designed taking extreme situations into account. Fuel tank design factors to be considered include the internal fluid pressure, the structural stress on the part impacted, and the kinetic energy of bullet strikes. Verification testing using real objects is the best way to obtain these design data effectively, but this imposes substantial burdens due to the huge cost and necessity for long-term preparation. The use of various numerical simulation tests at an early design stage can reduce the risk of trial-and-error and improve the prediction of performance. The present study was an investigation of the effects of bullet impacts on a fuel tank assembly using numerical simulation based on SPH (smoothed particle hydrodynamics), and conducted using the commercial package, LS-DYNA. The resulting equivalent stress, internal pressure, and kinetic energy of the bullet were examined in detail to evaluate the possible use of this numerical method to obtain configuration design data for the fuel tank assembly.

• 한국지반공학회논문집
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• 제38권10호
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• pp.41-48
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• 2022

전단파 속도를 기반으로 포화 지반의 최대 전단탄성계수를 산정하는데 이용되는 매질의 밀도가 명확하지 않아 이를 결정하고자 검증식을 구성하고, 시나리오를 수립하여 실내 실험결과와 비교하였다. 매질의 밀도는 포화, 습윤, 건조, 수중 밀도 조건으로 가정하였고, 각 경우별 건조지반 전단파속도 대비 포화지반 전단파속도의 비를 산정하였다. 포화 밀도 가정시 전단파속도 비는 공진주 실험 결과에 의한 전단파속도 비와 일치하였고, 습윤 밀도 가정시에는 벤더엘리먼트 실험 결과에 의한 값과 일치하였다. 이는 특성 주파수를 경계로 흙입자와 유체의 거동을 정의하는 Biot(1956)의 이론과 일치하는 결과이며, 일반적으로 고려되는 지진의 주파수 범위를 고려한다면 포화 지반에서는 포화 밀도를 적용하는 것이 타당할 것으로 사료된다.

• 드라이브 ㆍ 컨트롤
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• 제15권3호
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• pp.1-7
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• 2018

Humanoid robots have fascinated many researchers since they appeared decades ago. For the requirement of both accurate tracking control and the safety of physical human-robot interaction, torque control is basically desirable for humanoid robots. Humanoid robots are highly nonlinear, coupled, complex systems, accordingly the calculation of robot model is difficult and even impossible if precise model of the humanoid robots are unknown. Therefore, it is difficult to control using traditional model-based techniques. To realize model-free torque control, time-delay control (TDC) for humanoid robot was proposed with time-delay estimation technique. Using optimal walking trajectory obtained by particle swarm optimization, TDC with proposed scheme is implemented on whole body of a humanoid, not on biped legs even though it is performed by a virtual humanoid robot. The simulation results show the validity of the proposed TDC for humanoid robots.