• Proceedings of the KSME Conference
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• 2003.11a
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• pp.103-108
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• 2003

In this paper, the current lead for superconducting device is studied by numerical method. The current lead is cooled by surrounded $N_{2}$ gas by natural convection. The heat conduction equation for current lead and boundary layer equation for $N_{2}$ gas must be solved simultaneously. The boundary layer equation for $N_{2}$ gas is highly nonlinear for varied temperature of current lead. So the linearization method is adopted for simplicity. Numerical results using natural convection cooling are compared with the conventional cooling methods such as conduction cooling and vapor cooling methods. The main difference of natural convection cooing is the non-zero temperature gradient at the top of current lead for the minimum heat dissipation into superconducting devices. For the optimized conduction-cooling and vapor-cooling current leads, the temperature gradient at the top of current lead is zero. Also, the heat flow at the cold end is much smaller than conduction cooling case.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.8
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• pp.802-808
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• 2013

Thermal barrier coating (TBC) is used to protect substrates and extend the operating life of gas turbines in power plant and aeronautical applications. The major causes of failure of such coatings is spallation, which results from thermal stress due to a thermal expansion coefficient mismatch between the top coating and the bond coating layers. In this paper, the effects of the material properties and the thickness of the top coating layer on thermal stresses were evaluated using the finite element method and the equation for the thermal expansion coefficient mismatch stress. In addition, we investigated a design technique for the top coating whereby thermal resistance is exploited.

• Journal of the Korean GEO-environmental Society
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• v.3 no.1
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• pp.57-66
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• 2002

Generally, the California Bearing Ratio(CBR) for the material of subgrade is estimated without considering the anti-frost layer into the subgrade layer when pavements are designed. A pavement structure is determined according to the CBR. However, recently the design method taking the anti-frost layer into the subgrade layer is getting prevail. It makes the top of the subgrade layer strengthen and the thickness of the road pavement structure decreased. By the way, some confusion may be caused because theoretically the general equation for the mean CBR to combine the material of the subgrade layer and anti-frost layer have not been developed well. In this paper, laboratory and field CBR tests were performed to estimate of the mean CBR for the subgrade layer including the anti-frost layer. From the basis of the test results, modified equation which is calculating the mean CBR of the subgrade layer has been proposed. Finally, economical efficiency was considered by comparing the pavement thickness with the road pavement design using CBR of the subgrade layer alone and the road pavement design using the mean CBR including the anti-frost layer.

• Journal of the Microelectronics and Packaging Society
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• v.7 no.2
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• pp.47-53
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• 2000

The fluxless wetting properties of TSM-coated glass substrate were evaluated by the wetting balance method. We could estimate the wettability of the TSM with new parameters obtained from the wetting balance test for one side-coated specimen. It was more effective in wetting to use Cu as a wetting layer and Au as a protection layer than to use Au itself as a wetting layer. The SnSb solder showed better wettability than SnAg, SnBi, and SnIn solders. The contact angle of the one side-coated glass substrate to the Pb-free solders could be calculated from the farce balance equation by measuring the static force and the tilt angle.

• Korean Journal of Metals and Materials
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• v.48 no.10
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• pp.901-906
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• 2010

The first stage blade of a gas turbine was operated under a severe environment which included both $1300^{\circ}C$ hot gas and thermal stress. To obtain high efficiency, a thermal barrier coating (TBC) and an internal cooling system were used to increase the firing temperature. The TBC consists of multi-layer coatings of a ceramic outer layer (top coating) and a metallic inner layer (bond coat) between the ceramic and the substrate. The top and bond coating layer respectively act as a thermal barrier against hot gas and a buffer against the thermal stress caused by the difference in the thermal expansion coefficient between the ceramic and the substrate. Particularly, the bondcoating layer improves the resistance against oxidation and corrosion. An inter-diffusion layer is generated between the bond coat and the substrate due to the exposure at a high temperature and the diffusion phenomenon. A thickness measurement result showed that the bond coat of the suction side was thicker than that of the pressure side. The thickest inter-diffusion zone was noted at SS1 (Suction Side point 1). A chemical composition analysis of the bond coat showed aluminum depletion around the inter-diffusion layer. In this study, we evaluated the properties of the bond coat and the degradation of the coating layer used on a $1300^{\circ}C$-class gas turbine blade. Moreover, the operation temperature of the blade was estimated using the Arrhenius equation and this was compared with the result of a thermal analysis.

• Journal of Korea Water Resources Association
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• v.45 no.4
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• pp.349-360
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• 2012

A horizontally curvilinear non-hydrostatic free surface model that was applicable to three-dimensional viscous flows was developed. The proposed model employed a top-layer equation to close kinematic free-surface boundary condition, and an isotropic k-${\varepsilon}$ model to close turbulence viscosity in the Reynolds averaged Navier-Stokes equation. The model solved the governing equations with a fractional step method, which solved intermediate velocities in the advection-diffusion step, and corrects these provisional velocities by accounting for source terms including pressure gradient and gravity acceleration. Numerical applications were implemented to the wind-driven currents in a two-dimensional closed basin, the flow in a steep-sided trench, and the flow in a strongly-curved channel accounting for secondary current by the centrifugal force. Through the numerical simulations, the model showed its capability that were in good agreement with experimental data with respect to free surface elevation, velocity, and turbulence characteristics.

• Geomechanics and Engineering
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• v.6 no.6
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• pp.517-530
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• 2014

Seismic ground response analysis is one of the most important issues in geotechnical earthquake engineering. Conventional seismic site response and free field analysis of layered soils does not consider the effect of surcharge mass which may be present on the top layer. Surcharge mass may develop extra inertial force to the soil and, hence, significantly affect on the results of seismic ground response analysis. Methods of analysis of ground response may also be categorized into time domain and frequency domain concepts. Simplicity in developing analytical relations and accuracy in considering soil dynamic properties dependency to loading frequency are benefits of frequency domain analysis. In this part of the paper, seismic ground response is analyzed using transfer function method for soil layers considering surcharge mass on the top layer. Equation of motion, wave equation, is solved using amended boundary conditions which effectively take the impact of surcharge mass into account. A computer program is developed by MATLAB software based on the solution method developed for wave equation. Layered soils subjected to earthquake loading were numerically studied and solved especially by the computer program developed in this research. Results obtained were compared with those given by DEEP SOIL computer program. Such comparison showed the accuracy of the program developed in this study. Also in this part, the effects of geometrical and mechanical properties of soil layers and especially the impact of surcharge mass on transfer function are investigated using the current approach and the program developed. The efficiency and accuracy of the method developed here is shown through some worked examples and through comparison of the results obtained here with those given by other approaches. Discussions on the results obtained are presented throughout in this part.

• 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.76 no.3
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• pp.325-336
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• 2020

In this study, the continuous and discontinuous contact problems of functionally graded (FG) layer resting on a rigid foundation were considered. The top of the FG layer was loaded by a distributed load. It was assumed that the shear modulus and the density of the layer varied according to exponential functions along the depth whereas the the Poisson ratio remained constant. The problem first was solved analytically and the results were verified with the ones obtained from finite element (FE) solution. In analytical solution, the stress and displacement components for FG layer were obtained by the help of Fourier integral transform. Critical load expression and integral equation for continuous and discontinuous contact, respectively, using corresponding boundary conditions in each case. The finite element solution of the problem was carried out using ANSYS software program. In continuous contact case, initial separation distance and contact stresses along the contact surface between the FG layer and the rigid foundation were examined. Separation distances and contact stresses were obtained in case of discontinuous contact. The effect of material properties and loading were investigated using both analytical and FE solutions. It was shown that obtained results were compatible with each other.

• Structural Engineering and Mechanics
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• v.66 no.3
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• pp.329-341
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• 2018

This paper considers the smooth receding contact problem between a homogeneous half-plane and a composite laminate composed of an inhomogeneously coated elastic layer. The inhomogeneity of the elastic modulus of the coating is approximated by an exponential function along the thickness dimension. The three-component structure is pressed together by either a concentrated force or uniform pressures applied at the top surface of the composite laminate. Both semianalytical and finite element analysis are performed to solve for the extent of contact and the contact pressure. In the semianalytical formulation, Fourier integral transformation of governing equations and boundary conditions leads to a singular integral equation of Cauchy-type, which can be numerically integrated by Gauss-Chebyshev quadrature to a desired degree of accuracy. In the finite element modeling, the functionally graded coating is divided into homogeneous sublayers and the shear modulus of each sublayer is assigned at its lower boundary following the predefined exponential variation. In postprocessing, the stresses of any node belonging to sublayer interfaces are averaged over its surrounding elements. The results obtained from the semianalytical analysis are successfully validated against literature results and those of the finite element modeling. Extensive parametric studies suggest the practicability of optimizing the receding contact peak stress and the extent of contact in multilayered structures by the introduction of functionally graded coatings.