• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제23권2호
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• pp.65-92
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• 2019

We survey a recently developed immersed finite element method (IFEM) for the interface problems. The IFEM uses structured grids such as uniform grids, even if the interface is a smooth curve. Instead of fitting the curved interface, the bases are modified so that they satisfy the jump conditions along the interface. The early versions of IFEM [1, 2] were suboptimal in convergence order [3]. Later, the consistency terms were added to the bilinear forms [4, 5], thus the scheme became optimal and the error estimates were proven. For elasticity problems with interfaces, we modify the Crouzeix-Raviart based element to satisfy the traction conditions along the interface [6], but the consistency terms are not needed. To satisfy the Korn's inequality, we add the stabilizing terms to the bilinear form. The optimal error estimate was shown for a triangular grid. Lastly, we describe the multigrid algorithms for the discretized system arising from IFEM. The prolongation operators are designed so that the prolongated function satisfy the flux continuity condition along the interface. The W-cycle convergence was proved, and the number of V-cycle is independent of the mesh size.

• 한국해안해양공학회지
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• 제17권4호
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• pp.294-306
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• 2005

지금까지 침매터널에 대한 대부분의 연구들은 건설기술자의 경험에 바탕을 둔 연구들이었다. 공학적인 관점에서 파랑하중에 의한 침매터널의 안정성은 지반기초의 거동에 큰 영향을 받으므로 파${\cdot}$지반${\cdot}$침매터널의 상호작용에 대한 이해는 매우 중요하다. 본 연구에서는 파${\cdot}$지반${\cdot}$침매터널의 상호작용의 메커니즘에 대한 이해를 위하여 부산-거제간 연결도로 민간투자사업 구간 중 침매터널 구간에 직접수치해석기법을 적용하여 침매터널 주변의 지반 및 피복층 내에서 파랑하중에 의한 간극수압, 와도 및 흐름의 특성을 종합적으로 살펴보았다. 또한 다양한 파랑조건 및 피복층의 평균입경변화에 따른 비선형성의 파랑과 침매터널 및 지반의 상호작용이 침매터널의 안정성과 관련하여 논의되었다.

• 한국전산유체공학회지
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• 제17권3호
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• pp.68-74
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• 2012

Near-wall effect on wakes behind particles is one of the important factors in precise tracking of particles in turbulent flows. However, most aerodynamic force models for particles did not fully consider the wall effect. In the present study, we focused on changes of hydrodynamic forces acting on a particle depending on wall proximity. To this end, we developed an immersed boundary method with multi-direct forcing incorporated to a fully implicit decoupling procedure for incompressible flows. We validate the present immersed boundary method through two-dimensional simulations of flow over a circular cylinder. Comprehensive parametric studies on the effect of the wall proximity on the drag and lift forces acting on an immersed circular cylinder in a channel flow are performed in order to investigate general flow patterns behind the circular cylinder for a wide range of Reynolds number (0.01 ${\leq}$ Re ${\leq}$ 200). As the cylinder is closer to the wall, the drag coefficient decreases while the lift coefficient increases with a local maximum. Maximum drag and lift coefficients for different wall proximities decrease with increment of Reynolds number. Normalized drag and lift coefficients by their maximum values show universal correlations between the coefficients and wall proximity in a low Reynolds number regime (Re ${\leq}$ 1).

• Journal of Mechanical Science and Technology
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• 제20권12호
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• pp.2292-2314
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• 2006

Efficient numerical method is developed for the prediction of aerodynamic noise generation and propagation in low Mach number flows such as aeolian tone noise. The proposed numerical method is based on acoustic/viscous splitting techniques of which acoustic solvers use simplified linearised Euler equations, full linearised Euler equations and nonlinear perturbation equations as acoustic governing equations. All of acoustic equations are forced with immersed surface dipole model which is developed for the efficient computation of aerodynamic noise generation and propagation in low Mach number flows in which dipole source, originating from unsteady pressure fluctuation on a solid surface, is known to be more efficient than quadrupole sources. Multi-scale overset grid technique is also utilized to resolve the complex geometries. Initially, aeolian tone from single cylinder is considered to examine the effects that the immersed surface dipole models combined with the different acoustic governing equations have on the overall accuracy of the method. Then, the current numerical method is applied to the simulation of the aeolian tones from twin cylinders aligned perpendicularly to the mean flow and separated 3 diameters between their centers. In this configuration, symmetric vortices are shed from twin cylinders, which leads to the anti-phase of the lift dipoles and the in-phase of the drag dipoles. Due to these phase differences, the directivity of the fluctuating pressure from the lift dipoles shows the comparable magnitude with that from the drag dipoles at 10 diameters apart from the origin. However, the directivity at 100 diameters shows that the lift-dipole originated noise has larger magnitude than, but still comparable to, that of the drag-dipole one. Comparison of the numerical results with and without mean flow effects on the acoustic wave emphasizes the effects of the sheared background flows around the cylinders on the propagating acoustic waves, which is not generally considered by the classic acoustic analogy methods. Through the comparison of the results using the immersed surface dipole models with those using point sources, it is demonstrated that the current methods can allow for the complex interactions between the acoustic wave and the solid wall and the effects of the mean flow on the acoustic waves.

• 대한기계학회논문집B
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• 제38권1호
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• pp.95-101
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• 2014

본 연구는 고속 회전형(~10,000 rpm) 기어펌프의 질량유량과 효율을 예측하기 위해서 2 차원 immersed solid method(ISM)를 이용한 수치해석을 수행하였다. 기어펌프와 하우징의 순환유동을 고려하기 위하여 유체 유동을 난류 유동으로 가정하였고, 기어 펌프의 입 출구의 일정 압력 조건하에 기어펌프의 회전 속도를 부가하였다. 기어펌프의 다양한 회전 속도 및 기어 끝 단과 하우징 사의의 서로 다른 간극에 대한 질량유량 및 효율을 검토하였다. 해석 결과로서, 회전 속도가 증가할수록 평균 질량유량 및 효율은 증가하였고, 기어펌프와 하우징의 간격이 증가할수록 평균 질량유량 및 효율은 감소하였다. 간격이 없는 조건하의 6,000 rpm, 8,000 rpm, 10,000 rpm 회전속도에의 효율은 각각 85.11 %, 90.94 %, 93.62 % 를 얻었고, 간격이 0 m, 0.00001 m, 0.00003 m 에 대해서 효율은 각각 93.62 %, 93.29 %, 92.74 % 를 얻었다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1989년도 가을 학술발표회 논문집
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• pp.25-30
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• 1989

In this paper, morter and concrete specimens made with four cements were immersed in Mgcl2, MgSO4 Solution and artifical Seawater which was corresponded with Seawater. The hydration products of immersed cement pastes were looked over by using SEM, EDS and X-ray diffraction method. The results show that the concrete made with domestic flyash cement and blast-frrnace slag cement is superior to that of ordinary portland cement in resistance to chloride and sulphate solution. Especially, it is found that the attack of Cl-ion on the concrete plays an important role of the deterioration of concrete.

• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1899-1903
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• 2018

The effects of introducing hybrid lipids to a lipid bilayer containing saturated and unsaturated lipids immersed in water were studied. The lipid and water molecules were modeled as coarse-grained particles. All particles were simulated by using the dissipative particle dynamics method. The results showed that the hybrid lipids accumulated at the interface between the saturated and the unsaturated lipid domains. The relation between the hybrid lipid concentration and the equilibrium domain size was obtained. Moreover, the sizes of the simulated lipid domains are consistent with that given by the lipid raft definition.

• 조명전기설비학회논문지
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• 제30권2호
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• pp.20-25
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• 2016

This paper describes the effectiveness of continuous water removal in oil immersed transformers. Insulation oil in which insulation papers were immersed were prepared for tests and water concentrations in oil with heating time were measured at five oil temperatures. Also, the tests that water dissolved in $100^{\circ}C$ oil was removed at once and continuously at $50^{\circ}C$ and $100^{\circ}C$ were performed for consideration of effective method for water removal. Test results indicated that the oils for water measurement have to be extracted at similar temperatures and water in oil has to be continuously removed at higher temperatures for more effective water management of transformers.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.51-58
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• 2008

The George Massey immersed tunnel passes the Fraser River near Vancouver, Western Canada. In this paper, dynamic analysis of the tunnel on sandy soils was performed using an effective stress constitutive model called UBCSAND. This model is able to calculate pore pressure rise and resulting tunnel deformation due to cyclic loading. Centrifuge tests conducted at RPI are used to verify the model performance. Centrifuge tests consist of 3 models: Model 1 is designed for an original ground condition, Model 2 for a ground improvement by compaction method, Model 3 for a ground improvement by gravel drainage. The results of centrifuge Model 1 are presented and compared with predictions of UBCSAND model. This model well captured the results of centrifuge test and therefore can be used to predict dynamic behavior of similar tunnels or underground structures on sandy soils.

• Nuclear Engineering and Technology
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• 제35권1호
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• pp.1-13
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• 2003

In this study, an effective method to estimate the fundamental frequencies of co-axial cylinders immersed in fluid is proposed. The proposed method makes use of the equivalent mass or density that is derived from the added mass matrix caused by the fluid-structure interaction (FSI) phenomenon. The equivalent mass is defined from the added mass matrix based on a 2-D potential flow theory. The theory on two co-axial cylinders extended to the case of three cylinders. To prove the validity of the proposed method, the eigenvalue analyses upon coaxial cylinders coupled with fluid gaps are peformed using the equivalent mass. The analyses results upon various fluid gap is conditions reveal that the present method could provide accurate frequencies and be suitable for expecting the fundamental frequencies of fluid coupled cylinders in beam mode vibration.