• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.153-166
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• 2004

This paper presents a comparative study of a fully coupled, upwind, compressible Navier-Stokes code with three two-equation models and the Baldwin-Lomax algebraic model in predicting transonic/supersonic flow. The k-$\varepsilon$ turbulence model of Abe performed well in predicting the pressure distributions and the velocity profiles near the flow separation over the axisymmetric bump, even though there were some discrepancies with the experimental data in the shear-stress distributions. Additionally, it is noted that this model has y$\^$*/ in damping functions instead of y$\^$＋/. The turbulence model of Abe and Wilcox showed better agreements in skin friction coefficient distribution with the experimental data than the other models did for a supersonic compression ramp problem. Wilcox's model seems to be more reliable than the other models in terms of numerical stability. The two-equation models revealed that the redevelopment of the boundary layer was somewhat slow downstream of the reattachment portion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.3
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• pp.294-301
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• 2003

We examine a problem in which porous/viscoelastic compliant thin plates are subject to pressure fluctuations under transitional or turbulent boundary layer. Measurements are presented of the frequency spectra of the near-field pressure and radiated sound by compliant surface. A porous plate consisting of 5mm thick. open-cell foam with fabric covering and a viscoelastic-painted plate of 1mm thick over an acoustic board of 4mm thick were placed over a rigid surface in an anechoic wind tunnel. Streamwise velocity and wall pressure measurements were shown to highly attenuate the convective wall pressure energy when the convective wavenumber (k$_{c}$h) was 3.0 or more. The sound source localization on the compliant walls is applied to the measurement of radiated sound by using an acoustic mirror system.

• Structural Engineering and Mechanics
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• v.48 no.2
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• pp.241-255
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• 2013

The receding contact problem for two elastic layers whose elastic constants and heights are different supported by two elastic quarter planes is considered. The lower layer is supported by two elastic quarter planes and the upper elastic layer is subjected to symmetrical distributed load whose heights are 2a on its top surface. It is assumed that the contact between all surfaces is frictionless and the effect of gravity force is neglected. The problem is formulated and solved by using Theory of Elasticity and Integral Transform Technique. The problem is reduced to a system of singular integral equations in which contact pressures are the unknown functions by using integral transform technique and boundary conditions of the problem. Stresses and displacements are expressed depending on the contact pressures using Fourier and Mellin formula technique. The singular integral equation is solved numerically by using Gauss-Jacobi integration formulation. Numerical results are obtained for various dimensionless quantities for the contact pressures and the contact areas are presented in graphics and tables.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.505-513
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• 2017

In this paper, a receding contact problem for an elastic layer resting on a half plane is considered. The layer is pressed by two rectangular stamps placed symmetrically. It is assumed that the contact surfaces are frictionless and only compressive traction can be transmitted through the contact surfaces. In addition the effect of body forces is neglected. Firstly, the problem is solved analytically based on theory of elasticity. In this solution, the problem is reduced into a system of singular integral equations in which half contact length and contact pressures are unknowns using boundary conditions and integral transform techniques. This system is solved numerically using Gauss-Jacobi integral formulation. Secondly, two dimensional finite element analysis of the problem is carried out using ANSYS. The dimensionless quantities for the contact length and the contact pressures are calculated under various stamp size, stamp position and material properties using both solutions. The analytic results are verified by comparison with finite element results.

• Computational Structural Engineering
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• v.9 no.4
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• pp.165-172
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• 1996

For thin elastic structures such as beams, arches, plates and shells, there may exist the boundary layer in the narrow thin region neighborhood of boundaries, where the solution displays the singular behavior exponentially decaying in the normal direction to the boundary. In the finite element analysis of these structures, finite element mesh patterns have a significant role to capture this singularity. This paper introduces the analytic study of this problem and provides a guideline to construct optimal mesh patterns together with numerical experiments.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.5
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• pp.81-88
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• 2002

An interface crack of a piezoelectric medium bonded between an elastic layer and a half-space is analyzed using the theory of linear piezoelectricity. Both out-of-plane mechanical and in-plane electrical loads are applied to the piezoelectric laminate. By the use of courier transforms, the mixed boundary value problem is reduced to a singular integral equation which is solved numerically to determine the stress intensity factors. Numerical analyses for various material combinations are performed and the results are discussed.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.112-122
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• 1996

A finite element scheme using the concept of PISO method has been developed to solve the Navier-Stokes viscous flows in all speed range. This scheme includes development of new pressure equation that retains both the hyperbolic term related with the density variation and the elliptic term reflecting the incompressibility constraint. The present method is applied to the incompressible two-dimensional driven cavity flow problems(Re=100, 400 and 1,000). For compressible flows, the Carter plate problem(M=3 and Re=1,000) is computed. Finally, we have simulated the shock-boundary layer interaction(M=2 and Re=2.96×10/sup 5/), a more difficult problem, and compared its results with the experiment to demonstrate the shock capturing capability of the present solution algorithm.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.3
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• pp.369-376
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• 2010

In this study, a radiation and a diffraction problems of a floating body in two-layer fluids were solved by the Numerical Wave Tank(NWT) technique in the frequency domain. In two-layer fluids, two different wave modes exist and the hydrodynamic coefficients can be obtained separately for each mode. The two-domain Boundary Element Method(BEM) in the potential fluid using the whole-domain matrix scheme was used to investigate the characteristics of wave forces, added mass and damping coefficients. The effects of the ratio of density and water depth in the lower domain were also evaluated and compared with given references.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.04a
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• pp.521-526
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• 2012

It is essential for the accurate time-domain prediction of broadband noise due to turbulence-cascade interaction to develop inflow/outflow boundary conditions to satisfy the following three requirements: to maintain the back ground mean flow, to nonreflect the outgoing disturbances and to generate the specified input gust. The preceding study(1) showed that Perfectly Matched Layer (PML) boundary condition was successfully applied to absorb the outgoing disturbances and to generate the specified gust in the time-domain computations of broadband noise due to interaction of incident gust with a cascade of flat-plates. In present study, PML boundary condition is extended in order to predict steady mean flow that is needed for the computation of noise due to interaction of incident gust with a cascade of airfoils. PML boundary condition is originally designed to absorb flow disturbances superimposed on the steady meanflow in the buffer zone. However, the steady meanflow must be computed before PML boundary condition is applied on the flow computation. In the present paper, PML equations are extended by introducing source term to maintain desired mean flow conditions. The extended boundary condition is applied to the benchmark problem where the meanflow around a cascade of airfoils is predicted. These illustrative computations reveal that the extended PML equations can effectively provide and maintain the target meanflow.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.7
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• pp.685-691
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• 2012

It is essential for the accurate time-domain prediction of broadband noise due to turbulence-cascade interaction to develop inflow/outflow boundary conditions to satisfy the following three requirements: to maintain the back ground mean flow, to nonreflect the outgoing disturbances and to generate the specified input gust. The preceding study showed that perfectly matched layer(PML) boundary condition was successfully applied to absorb the outgoing disturbances and to generate the specified gust in the time-domain computations of broadband noise due to interaction of incident gust with a cascade of flat-plates. In present study, PML boundary condition is extended in order to predict steady mean flow that is needed for the computation of noise due to interaction of incident gust with a cascade of airfoils. PML boundary condition is originally designed to absorb flow disturbances superimposed on the steady meanflow in the buffer zone. However, the steady meanflow must be computed before PML boundary condition is applied on the flow computation. In the present paper, PML equations are extended by introducing source term to maintain desired mean flow conditions. The extended boundary condition is applied to the benchmark problem where the meanflow around a cascade of airfoils is predicted. These illustrative computations reveal that the extended PML equations can effectively provide and maintain the target meanflow.