• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.4 s.247
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• pp.320-327
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• 2006

The computations of chemically reacting laminar and turbulent flows are performed using the preconditioned Navier-Stokes solver coupled with turbulent transport and multi-species equations. A low-Reynolds number $k-\varepsilon$ turbulence model proposed by Chien is used. The presence of the turbulent kinetic energy tenn in the momentum equation can materially affect the overall stability of the fluids-turbulence system. Because of this coupling effect, a fully coupled formulation is desirable and this approach is taken in the present study. Choi and Merkle's preconditioning technique is used to overcome the convergence difficulties occurred at low speed flows. The numerical scheme used for the present study is based on the implicit upwind ADI algorithm and is validated through the comparisons of computational and experimental results for laminar methane-air diffusion flame and $ H_2/O_2$ reacting turbulent shear flow. Preconditioning formulation shows better convergence characteristics than that of non-preconditioned system by approximately five times as much.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.10-17
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• 2003

Dynamic stability is critically required to stabilize an airship which is statically unstable. Numerical computations were performed in order to support and confirm the foced oscillation wind tunnel tests. To analyze the low-speed flow filed around the airship, a low-Mach number preconditioned method was applied. Using two computation methods, variations of the dynamic damping coefficients were examined. Numerical results show that it is dynamically stable for three directional moments, but unstable for normal or side force. It is revealed that the damping coefficients are more sensitive to the direction of the angular rate than the angle of attack or the magnitude og angular rate.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.5
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• pp.30-40
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• 2004

In the present study, a numerical method has been developed for the calculation of the gust response of an airship using unstructured meshes. A preconditioning method is incorporated for accurate and efficient computations of the Euler equations at the low Mach number range. A simple sharp-edged gust is used as a gust model. The accuracy of the present method is demonstrated through comparisons with an exact line theory. The numerical results show that the variation of lift is relatively larger than that of moment. It is also shown that the static stability of the airship is enhanced with the use of control fins.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.195-202
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• 2001

In this paper, the convergence characteristics of preconditioned multigrid methods are investigated. The preconditioning method is introduced to reduce the condition number of discrete governing equations. 6 preconditioners including a point, line and diagonalized line solvers are implemented and applied to 2-dimensional inviscid flow problems. Theoretical fourier analyses and numerical results are presented for the preconditioners.

• 한국전산유체공학회:학술대회논문집
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• 2001.05a
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• pp.127-133
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• 2001

In this paper, the preconditioned multistage time stepping methods which are popular multigrid smoothers is studied for the compressible flow calculations. Fourier analysis on the local time stepping and block-Jacobi preconditioned residual operators is performed using the linearized 2-D Navier-Stokes equations. It fumed out that block-Jacobi preconditioner has better performance in eigenvalue clustering. They are implemented in the 2-D compressible Euler and Wavier-Stokes calculations with multigrid methods to verify that the block-Jacobi preconditioned multistage time stepping shows better performance in convergence acceleration.

• 한국전산유체공학회:학술대회논문집
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• 2001.10a
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• pp.20-30
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• 2001

A multigrid DADI method for low Mach number preconditioning method is presented. The eigenvalues of governing equations are modified by A low Mach number preconditioner developed by Choi & Merkle, and it results in an accurate solution and fast convergence In the low Mach number region. The convergence of numerical method is further accelerated by multigrid method. The efficient and accuracy of present method is shown by comparison with conventional solution method for the compressible flows.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.35-38
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• 2002

The convergence acceleration methods for the compressible Wavier-Stokes equations are studied ,which are multigrid method and implicit preconditioned multistage time stepping method. In this paper, the performance of implicit preconditioning methods are studied for the full-coarsening multigrid methods on the high Reynolds number compressible flow computations. The effect of numerical flux on the convergence are investigated for the inviscid and viscous calculations.

• Proceedings of the Speleological Society Conference
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• 1994.11a
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• pp.102-105
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• 1994

동굴은 관광개발과 동시에 그 환경은 점자 파괴오손 되는 것이 당연하다. 관광개발의 시설때문에 경관의 훼손은 물론이고, 그 밖에 입동객에 의한 이른바 오손공해는 우리들이 잘 아는 바이다. 그리고 조명시설에 의한 광도때문에 나타나는 녹색공해를 비롯한 흑색공해 등은 역시 무시할 수 없는 것이며, 이밖에도 대기질 변화, 건화현상 등에 유래되는 백색공해와 박리작용에 의한 퇴적물 오손 등은 참으로 개발에 따른 환경파괴와 오손현상이라 하겠다.(중략)

• Journal of the Speleological Society of Korea
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• v.35 no.36
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• pp.72-89
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• 1993

동굴은 관광개발과 동시에 그 환경은 점차 파괴오손 되는 것이 당연하다. 관광개발의 시설때문에 경관의 훼손은 물론이고, 그 밖에 입동객에 의한 이른바 오손공해는 우리들이 잘 아는 바이다. 그리고 조명시설에 의한 광도때문에 나타나는 녹색공해를 비롯한 흑색공해 등은 역시 무시할 수 없는 것이며, 이밖에도 대기질 변화, 건화현상 등에 유래되는 백색공해와 박리작용에 의한 퇴적물 오손 등은 참으로 개발에 따른 환경파괴와 오손현상이라 하겠다.(중략)

• 한국전산유체공학회:학술대회논문집
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• 2002.05a
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• pp.59-64
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• 2002

In this paper, the preconditioned multistage time stepping methods which are popular multigrid smoothers is implemented for the compressible Navier-Stokes calculation with full-coarsening multigrid method. The convergence characteristic of the point-Jacobi and Alternating direction line Jacobi(DDADI) preconditioners are studied. The performance of 2nd order upwind numerical fluxes such as 2nd order upwind TVD scheme and MUSCL-type linear reconstruction scheme are compared in the inviscid and viscous turbulent flow caculations.