• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.534-541
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• 2010

A high-order accurate Euler flow solver based on a discontinuous Galerkin method has been developed for the numerical simulation of unsteady flows on unstructured meshes. A multi-level solution-adaptive mesh refinement/coarsening technique was adopted to enhance the resolution of numerical solutions efficiently by increasing mesh density in the high-gradient region. An acoustic wave scattering problem was investigated to assess the accuracy of the present discontinuous Galerkin solver, and a supersonic flow in a wind tunnel with a forward facing step was simulated by using the adaptive mesh refinement technique. It was shown that the present discontinuous Galerkin flow solver can capture unsteady flows including the propagation and scattering of the acoustic waves as well as the strong shock waves.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.120-125
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• 2006

Piezoelectric actuators have been investigated for flow control in the field of fluid dynamics. Numerical simulation for a single diaphragm piezoelectric actuator operating in quiescent air is performed to investigate the complex flow field around the slot exit. A periodic velocity transpiration condition is applied to simulate the effect of the moving diaphragm. The computational results for the flow field around the slot exit agree well with the experimental data. The results also show that low pressure regions due to the vortex pairing cause non-monotonic variations in the vertical velocity.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.22-25
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• 2006

Direct simulations of aerodynamic sound, especially sound emitted by rapidly rotating elliptic cylinder by the finite difference lattice Boltzmann method (FDLBM). Effect of pile-fabrics for noise reduction is also studied by the finite volume LBM (FVLBM) using an unstructured grid. Second order time integration and third order upwind scheme are shown to be enough for these simulations. Sound sources are detected to be doublets for both cases. For the elliptic cylinder, the doublet is generated in the interaction between the vortex and the edge. For the circular cylinders, they are generated synchronizing with the Karman vortex street, and it is also shown that the pile-fabrics covering the surface of the cylinder reduces the strength of the source.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2273-2283
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• 2004

The vortical flows over sharp-edged delta wings with and without a leading edge extension have been investigated using a computational method. Three-dimensional compressible Reynolds-averaged Navier-Stokes equations are solved to provide an understanding of the effects of the angle of attack and the angle of yaw on the development and interaction of vortices and the aerodynamic characteristics of the delta wing at a freestream velocity of 20 m/s. The present computations provide qualitatively reasonable predictions of vortical flow characteristics, compared with past wind tunnel measurements. In the presence of a leading edge extension, a significant change in the suction pressure peak in the chordwise direction is much reduced at a given angle of attack. The leading edge extension can also stabilize the wing vortex on the windward side at angles of yaw, which dominates the vortical flows over yawed delta wings.

• Journal of Power System Engineering
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• v.9 no.1
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• pp.23-29
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• 2005

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages was carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry was accurately modeled adopting the embedded H grid system. An explicit four-stage Runge-Kutta scheme was used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, were interpreted and compared with the experimental data from the Penn State turbine stage. The predictions for major features of the flow field have been found to be in good agreement with the experimental data.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.171-175
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• 2003

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages is carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry is accurately modeled adopting the embedded H grid topology. An explicit four-stage Runge-Kutta scheme is used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, are interpreted and compared with the experimental data from the Penn State turbine stage. Good agreement between the experimental data and the numerical prediction was achieved in the sense of the major features of the flow fields.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.382-386
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• 2013

본 연구에서는 Main Rotor Blade Tip 형상 변화에 따른 후류해석을 통해 와류 생성 및 주변 유동을 분석하여 블레이드 팁 형상의 변화가 와류 간섭을 감소시키는지의 여부를 확인하였다. EDISON CFD를 이용하여 블레이드 Blade Tip 형상에 따라 유동이 어떻게 나타나며, Blade 후류의 압력과 점성의 변화를 분석하여 와류의 양상을 해석하였다. 비교 Blade 형상은 2세대 긴 직사각형 모형, KUH 수리온의 Blade, 유로콥터사의 'Blue Edge'로 비교적 최근에 개발된 대표적인 Blade Tip 형상 3개로 정하였다. 결과를 토대로 블레이드 뒷전의 와류흐름 양상을 확인하여 블레이드 와류 간섭현상의 감소를 확인하였다.

• Interaction and multiscale mechanics
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• v.5 no.2
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• pp.131-144
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• 2012

We study a radial basis function collocation method (RBFCM) to discretize a coupled nonlinear Schr$\ddot{o}$dinger equation (CNLSE) that governs a two dimensional rotating Bose-Einstein condensate (BEC) with an angular momentum rotation term. We exploit a RBFCM-continuation method (RBFCM-CM) to trace the solution curve of the CNLSE. We compare the performance of the RBFCM-CM with the FEM-CM. We observe that the RBFCM-CM is very robust in a coarse grid for resolving the ground state solution with many vortices when the angular momentum rotation is close to the limit. Numerical results demonstrate the efficiency and accuracy of the RBFCM-CM for computing the superfluid density of the ground level of the BEC.

• 한국전산유체공학회:학술대회논문집
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• 2009.11a
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• pp.151-158
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• 2009

To implement the insects' flapping flight for developing flapping MAVs(micro air vehicles), the unsteady flow characteristics of the insects' forward flight is investigated. In this paper, two-dimensional FSI(Fluid-Structure Interaction) simulations are conducted to examine realistic flow features of insects' flapping flight and to examine the flexibility effects of the insect's wing. The unsteady incompressible Navier-Stokes equations with an artificial compressibility method are implemented as the fluid module while the dynamic finite element equations using a direct integration method are employed as the solid module. In order to exchange physical information to each module, the common refinement method is employed as the data transfer method. Also, a simple and efficient dynamic grid deformation technique based on Delaunay graph mapping is used to deform computational grids. Compared to the earlier researches of two-dimensional rigid wing simulations, key physical phenomena and flow patterns such as vortex pairing and vortex staying can still be observed. For example, lift is mainly generated during downstroke motion by high effective angle of attack caused by translation and lagging motion. A large amount of thrust is generated abruptly at the end of upstroke motion. However, the quantitative aspect of flow field is somewhat different. A flexible wing generates more thrust but less lift than a rigid wing. This is because the net force acting on wing surface is split into two directions due to structural flexibility. As a consequence, thrust and propulsive efficiency was enhanced considerably compared to a rigid wing. From these numerical simulations, it is seen that the wing flexibility yields a significant impact on aerodynamic characteristics.

• Structural Engineering and Mechanics
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• v.65 no.5
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• pp.557-572
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• 2018

The academic research works about liquid storage tanks are reviewed for the purpose of providing valuable reference to the engineering practice on their aseismic design. A summary of the performance of tanks during past earthquakes is described in this paper. Next, the seismic response of tanks under unidirectional earthquake is reported, supplemented with the dynamic response under multidirectional motions. Then, researches on the influence of soil-structure interaction are brought out to help modify the seismic design approach of tanks in different areas with variable properties of soils. Afterwards, base isolation systems are reported to demonstrate their effectiveness for the earthquake-resistant design of liquid storage tanks. Further, researches about the liquid-structure interaction are reviewed with description of simplified models and numerical analytical methods, some of which consider the elastic effect of tank walls. Moreover, the liquid sloshing phenomenon on the hydrodynamic behaviors of tanks is presented by various algorithms including grid-based and meshfree method. And then the impact of baffles in changing the dynamic characteristics of the liquid-structure system is raised, which shows the energy dissipation by the vortex motion of liquid. In addition, uplifting effect is given to enhance the understanding on the capacity of unanchored tanks and some assessment of their development. At last, the concluding remarks and the aspects of extended research in the field of liquid storage tanks under seismic loads are provided, emphasizing the thermal stress analysis, the replaceable system for base isolation, the liquid-solid interaction and dynamic responses with stochastic excitations.