• Journal of computational fluids engineering
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• v.18 no.3
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• pp.79-86
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• 2013

Preconditioned compressible Navier-Stokes equations are solved for almost incompressible flows. Unstructured meshes are utilized for spatial discretization of complex flow domain. Effectiveness of the current preconditioning algorithm, with respect to various Reynolds numbers and Mach numbers, is demonstrated by the solution of canonical problems for incompressible flows, e.g. driven cavity flows.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.2
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• pp.40-49
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• 1999

A Finite Volume Method for the two-dimensional incompressible, two-fluids Navies-Stokes equation and level-set scheme are used to analyse the interface of two fluids, free-surface flow. The numerical characteristics and the applicability of level-set scheme are brief1y investigated and appraised by solving oscillating small surface wave in a water tank and dam break problems. In the numerical results, a method for improving the convergence of the solution is presented.

• Journal of Ocean Engineering and Technology
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• v.25 no.5
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• pp.9-14
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• 2011

The divergence-free finite elements introduced in this paper are derived from Hermite functions, which interpolate stream functions. Velocity bases are derived from the curl of the Hermite functions. These velocity basis functions constitute a solenoidal function space, and the gradient of the Hermite functions constitute an irrotational function space. The incompressible Navier-Stokes equation is orthogonally decomposed into its solenoidal and irrotational parts, and the decoupled Navier-Stokes equations are then projected onto their corresponding spaces to form appropriate variational formulations. The degrees of the Hermite functions we introduce in this paper are bi-cubis, quartic, and quintic. To verify the accuracy and convergence of the present method, three well-known benchmark problems are chosen. These are lid-driven cavity flow, flow over a backward facing step, and buoyancy-driven flow within a square enclosure. The numerical results show good agreement with the previously published results in all cases.

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.98-105
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• 1999

The Pressure-based Unstructured-grid Navier-Stokes Solver PUNS-2/3D for incompressible steady and unsteady viscous flows has been developed. It is based on nonstaggered cell-centered finite volume method. Second-order upwind scheme with least-square reconstruction is used for convective fluxes. The SIMPLE method is implemented to couple the pressure and velocity fields. And the time derivatives in the momentum equations are discretised using a second-order Euler backward-differencing scheme. The discretised linear equations are solved by the preconditioned Biconjugate Gradient Stabilized method(Bi-CGSTAB). The developed solver is applied to validation problems using hybrid meshes.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.508-511
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• 2010

본 논문에서는 정상상태 유체-구조 연성문제를 연속체 기반으로 정식화하고 유한요소법을 이용하여 완전 연성된 해를 구하였다. 대 변형을 고려하기 위하여 토탈 라그란지안 정식화를 사용하였으며 유체 및 구조의 비선형성이 고려되었다. 유체와 구조 영역의 형상을 NURBS 곡면을 이용하여 매개화하여 표현하였으며, 형상 최적화를 위해 효율적인 설계민감도 해석법인 애조인 기법을 이용하여 압력, 속도, 변위 등에 대한 설계민감도를 구하였다. 이를 이용하여 최소 컴플라이언스를 갖게 하는 구조물 내부의 유체영역의 설계 등의 수치예제를 통하여 개발된 방법론의 타당성을 확인하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.05a
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• pp.331-334
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• 2010

The supersonic speeds slowing down by shock waves is a common problem during the transonic region. So how to study the status of shock on the surface of airplane and wings is crucial adjective during transonic region. However, the theoretical and computational transonic flow problems were very hard. This paper introduced using Navier-Stokes Schemes to study characteristics of AGARD Wing 445.6 by ANSYS CFX in transonic region. From simulations results, as the Mach number increases, shock waves appear in the flowfield, getting stronger as the speed increases, these shock waves will lead to a rapid increase in drag.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2002.10a
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• pp.174-180
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• 2002

A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D-Numerical Wave Tank. The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation, and the Marker-Density function technique is adopted to implement the fully-nonlinear free-surface kinematic condition. The marine environmental situations, i.e. waves, currents, wind, etc., are reproduced by use of multi-segmented wavemaker on the basis of the so-called "snake-principle". In this paper, some numerical reproduction techniques for regular and irregular waves, multi-directional waves, Bull's-eye wave, wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.11 no.4
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• pp.55-68
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• 2007

First-order least-squares method of a distributed optimal control problem for the incompressible Navier-Stokes equations is considered. An optimality system for the optimal solution are reformulated to the equivalent first-order system by introducing velocity-flux variables and then the least-squares functional corresponding to the system is defined in terms of the sum of the squared $L^2$ norm of the residual equations of the system. The optimal error estimates for least-squares finite element approximations are obtained.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1061-1071
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• 2015

In the present study, the Navier-Stokes (N-S) equations delineating water flows inside porous media were derived applying Reynolds transport theorem in order to provide a basis for analyzing water wave problems inside the porous media. Then, the derived N-S equations were compared with the same species of equations in existing researches. Based on the N-S equations, a set of Boussinesq equations was then derived in such a form that the dispersiveness and nonlinearity of water waves inside the porous media can be properly reproduced. Finally, numerical analyses were carried out to demonstrate the validity of the equations. The reflection and transmission coefficients of porous breakwaters were calculated and compared with the results of existing hydraulic experiments. The numerical results showed a rather sensitive dependency on the virtual mass coefficient of grains constituting the porous media. The selection of the coefficient with zero turned out to give nice agreements with numerical and experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.386-391
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• 1983

Two-dimensional slow viscous flow due to a stokeslet near a slit is investigated on the basis of Stokes approximation. Velocity fields and stream function are obtained in closed forms by finding two sectionally holomorphic functions which are determined by reducing the problem to Riemann-Hilbert problems. The force exerted on a small cylinder is calculated for the arbitrary position of the cylinder translating in an arbitrary direction. The features of fluid flow are also investigated.