• 한국전산유체공학회지
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• 제17권1호
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• pp.44-53
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• 2012

Immersed boundary method(IBM) is a numerical scheme proposed to simulate flow field around complex objectives using simple Cartesian grid system. In the previous studies, the IBM has mostly been implemented to fractional step method based Navier-Stokes solvers. In this study, we implement the IBM to an incompressible Navier-Stokes solver which uses SIMPLE algorithm. The weight coefficients of the bi-linear and quadratic interpolation equations were formulated by using only geometric information of boundary to reconstruct velocities near IB. Flow around 2D circular cylinder at Re=40 and 100 was solved by using these formulations. It was found that the pressure buildup was not observed even when the bi-linear interpolation was adopted. The use of quadratic interpolation made the predicted aerodynamic forces in good agreement with those of previous studies. For an analysis of moving boundary, we smulated an oscillating circular cylinder with Re=100 and KC(Keulegan-Carpenter) number of 5. The predicted flow fields were compared with experimental data and they also showed good agreements.

• Geomechanics and Engineering
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• 제18권6호
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• pp.651-659
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• 2019

The IB-SEM numerical method combines the spectral/hp element method and the rigid immersed boundary method. This method avoids the problems of low computational efficiency and errors that are caused by the re-division of the grid when the solids move. Based on the Fourier transformation and the 3D immersed boundary method, the 3D IB-SEM system was established. Then, using the open MPI and the Hamilton HPC service, the computational efficiency was increased substantially. The flows around a cylinder and a sphere were simulated by the system. The surface of the cylinder generates vortices with alternating shedding, and these vortices result in a periodic force acting on the surface of the cylinder. When the shedding vortices enter the flow field behind the cylinder, a recirculation zone is formed. Finally, the three-dimensional pore flow was successfully investigated.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.608-608
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• 2008

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.41-42
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• 2006

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.141-148
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• 2007

We present an immersed boundary (IB) method for 3D simulation of flappingflags in a uniform flow. The proposed formulation is manipulated on the basis of an efficient Navier-Stokes solver adopting the fractional step method and a staggered Cartesian grid system. A direct numerical method is developed to calculate the flag motion, with the elastic force treated implicitly. The fluid motion defined on an Eulerian grid and the flag motion defined on a Lagrangian grid are independently solved and the mass of flag is handled in a natural way. An additional momentum forcing is formulated from the flag motion equation in a way similar with the direct-forcing IB formulation and acts as the interaction force between the flag and ambient fluid. A series of numerical tests are performed and the present results are compared qualitatively and quantitatively with previous studies. The instantaneous flag motion is analyzed under different conditions and surrounding vortical structures are identified. The effects of physical parameters on the flapping frequency are studied.

• 한국전산유체공학회지
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• 제12권2호
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• pp.14-20
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• 2007

We present an improved immersed boundary method for computing incompressible viscous flow around an arbitrarily moving body on a fixed computational grid. The main idea is to incorporate feedback forcing scheme of virtual boundary method with Peskin's regularized delta function approach in order to use large CFL number and transfer quantities between Eulerian and Lagrangian domain effectively. From the analysis of stability limits and effects of feedback forcing gains, optimum regions of the feedback forcing are suggested.

• 한국전산유체공학회지
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• 제18권3호
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• pp.34-41
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• 2013

We develop a novel immersed boundary (IB) method based on implicit direct forcing scheme for incompressible flows. The proposed IB method is based on an iterative procedure for calculating the direct forcing coupled with the momentum equations in order to satisfy no-slip boundary conditions on IB surfaces. We perform simulations of two-dimensional flows over a circular cylinder for low and moderate Reynolds numbers. The present method shows that the errors for estimated velocities on IB surfaces are significantly reduced even for low Reynolds number with a fairly large time step while the previous methods based on direct forcing failed to provide no-slip boundary conditions on IB surfaces.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.23-29
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• 2007

We present an improved immersed boundary method for computing incompressible viscous flow around an arbitrarily moving body on a fixed computational grid The main idea is to incorporate feedback forcing scheme of virtual boundary method with Peskin's regularized delta function approach in order to use large CFL number and transfer quantities between Eulerian and Lagrangian domain effectively. From the analysis of stability limits and effects of feedback forcing gains, optimum regions of the feedback forcing are suggested.

• 한국전산유체공학회지
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• 제14권4호
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• pp.41-47
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• 2009

An immersed boundary method(IBM, Kim et al.(2001)) for simulating flows over complex geometries is applied to computation of three-dimensional Floquet stability of a periodic wake. Floquet stability analysis is employed to extract different modes of three-dimensional instability. To verify the present method, a fully-resolved Floquet stability calculation for flow past a circular cylinder is considered. There are two different instability modes with long(mode A) and short (mode B) spanwise wavelengths for the periodic wake of a circular cylinder. The critical Reynolds number and the most unstable spanwise wavelengths of modes A and B are computed using the present method, and compared with other authors' results currently available.

• 한국전산유체공학회지
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• 제17권1호
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• pp.8-15
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• 2012

A code developed using the flux-difference splitting scheme on the hybrid Cartesian/immersed boundary method is applied to simulate three-dimensional internal waves. The material interface is regarded as a moving contact discontinuity and is captured on the basis of mass conservation without any additional treatment across the interface. Inviscid fluxes are estimated using the flux-difference splitting scheme for incompressible fluids of different density. The hybrid Cartesian/immersed boundary method is used to enforce the boundary condition for a moving three-dimensional body. Immersed boundary nodes are identified within an instantaneous fluid domain on the basis of edges crossing a boundary. The dependent variables are reconstructed at the immersed boundary nodes along local normal lines to provide the boundary condition for a discretized flow problem. The internal waves are simulated, which are generated by an pitching ellipsoid near an material interface. The effects of density ratio and location of the ellipsoid on internal waves are compared.