• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1999.03b
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• pp.253-256
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• 1999

The Streamline Upwind Petrov-Galerkin(SUPG) finite element method is used to solve the two-dimensional laminar and turbulent flow. The flow is simulated by averaged Navier-Stokes equations with a penalty function approach and the lograithmic(k-$\varepsilon$) turbulent model is employed to take into account its turbulent behavior. The near-wall viscous sub-layer model is employed to approach the dominant viscous effects in the near wall zones. To find a good-enough initial guess of the Newton-Raphson iteration solving Nonlinear Matrix the Incremental method is considered for momentum and the Incomplete logarithmic turbu-lent equations for Turbulence. The validation of our method is investigated in comparision with published experimental data.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.785-794
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• 2015

To obtain low resistance and high efficiency energy-saving ship, minimum total resistance hull form design method is studied based on potential flow theory of wave-making resistance and considering the effects of tail viscous separation. With the sum of wave resistance and viscous resistance as objective functions and the parameters of B-Spline function as design variables, mathematical models are built using Nonlinear Programming Method (NLP) ensuring the basic limit of displacement and considering rear viscous separation. We develop ship lines optimization procedures with intellectual property rights. Series60 is used as parent ship in optimization design to obtain improved ship (Series60-1) theoretically. Then drag tests for the improved ship (Series60-1) is made to get the actual minimum total resistance hull form.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.309-314
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• 1999

This paper is concerned with the viscous interaction between rotor and stator The viscous interaction is caused by wakes from upstream blades. The cascade was composed with five blades and cylinders were placed to make wakes and their location was about 50 percent of blade chord upstream. The location of cylinders were varied in the cascade axis with 0, 20, 40, 60 and 80 percent of pitch length. The velocity distribution in the cascade passage were measured using single slanted hot-wire and the ones in the boundary layer using boundary probe. As a result, wakes decay more rapidly at suction surface and more slowly at pressure surface. And the measurement of momentum thickness of cascade shows that the momentum thickness is larger near the blade surface. From measurement of blade boundary layer, turbulent intensity is also larger near the blade surface because wakes collide the boundary layer And wakes make boundary layer thickness smaller and delay flow separation.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.2
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• pp.313-324
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• 1992

Two-dimensional Navier-Stokes code has been developed for analysis of turbomachinery blade rows and other internal flows. The Navier-Stokes equations are written in a Cartesian coordinate system, then mapped into a generalized body-fitted coordinate system. All direction of viscous terms are incorporated and turbulent effects are modeled using the Baldwin-Lomax algebraic model. Equation are discretized using finite difference method on the C-type grids and solved using implicit LU-ADI decomposition scheme. Calculations are made at a VKI turbine cascade flow in a transonic wind-tunnel and compared to experimental data. Present numerical scheme is shown to be in good agreement with the previous experimental results and simulates the two-dimensional viscous flow phenomena.

• Journal of the korean Society of Automotive Engineers
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• v.8 no.1
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• pp.52-61
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• 1986

An iterative viscous-potential flow procedure has been developed and used to predict aerodynamic characteristics of automobiles in ground proximity. The method is capable of predicting the effects of separated flows. The viscous-potential flow iteration procedure provides the connection between potential flow, boundary layer and wake modules. The separated wake is modeled in the potential flow analysis by thin sheets across which exists a jump in velocity potential. The ground effect is properly accounted for by placing a body image in the potential flow calculation. The agreement between theory and experiment is good and, thus, demonstrates that the method can be used in the preliminary design stage.

• 한국가시화정보학회:학술대회논문집
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• 2002.11a
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• pp.49-50
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• 2002

In micro-channels, the electro-viscous effect is caused by the electrical double layer on pressure-driven liquid flow. Velocity fields of flow inside micro-channels were measured using micro-PIV system for investigating the electro-viscous effect. De-ionized water and aqueous NaCl solutions with four different concentrations were used as working fluid in a PDMS micro-channel of $100{\mu}m$ width and $66{\mu}m$ height. The pressure gradient, dP/dx, was determined from the pre-determined input flow rate Q of syringe pump. The mean velocity $u_m$ used for calculating Reynolds number was obtained from the PIV velocity field data. These are used to plot the pressure gradient as a function of Reynolds numbers. The pressure gradient far lower concentration solution $(10^{-5}\;M)$ was higher than that for the higher concentration solution. The increase of flow resistance was about $30\%\;and\;37.5\%$ at Re=0.02 and 0.06, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.2
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• pp.194-200
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• 2002

A method for simulating flow of extremely low Reynolds number in a vortex-in-cell (VIC) was studied. The viscous diffusion was represented by the random walk method. The validity of this method was proven by applying it to the flows passing over a fence placed vertically at an extremely low Reynolds number. The effects of parameters of the VIC method on the random walk method, such as the number of point vortices, the mesh density and the time increment, were investigated by numerical analysis using a one-dimensional diffusion equation. Changes in the relative error of vorticity depending on those parameters were clarified.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.639-650
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• 2019

Time-domain commercial codes are widely used to evaluate the seismic behavior of tunnels. Those tools offer a good insight into the performance and the failure mechanism of tunnels under earthquake loading. Viscous damping is generally employed in the dynamic analysis to consider damping at very small strains in some cases, and the Rayleigh damping is commonly used one. Many procedures to obtain the damping parameters have been proposed but they are seldom discussed. This paper illustrates the influence of the Rayleigh damping formulation on the tunnel visco-elastic behavior under earthquake. Four Rayleigh damping determination procedures and three soil shear velocity profiles are accounted for. The results show significant differences in the free-field and in the tunnel response caused by different procedures. The difference is somewhat decreased when the soil site fundamental frequency is increased. The conventional method which consists of using solely the first soil natural mode to determine the viscous damping parameters may lead to an unsafe seismic design of the tunnel. In general, using five times site fundamental frequency to obtain the damping formulation can provide relatively conservative results.

• Geomechanics and Engineering
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• v.16 no.6
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• pp.609-618
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• 2018

A new mechanical model for predicting the vibration of a pipe pile embedded in longitudinally layered visco-elastic media with radial inhomogeneity is proposed by extending Novak's plain-strain model and complex stiffness method to consider viscous-type damping. The analytical solutions for the dynamic impedance, the velocity admittance and the reflected signal of wave velocity at the pile head are also derived and subsequently verified by comparison with existing solutions. An extensive parametric analysis is further performed to examine the effects of shear modulus, viscous damping coefficient, coefficient of disturbance degree, weakening or strengthening range of surrounding soil and longitudinal soft or hard interbedded layer on the velocity admittance and the reflected signal of wave velocity at the pile head. It is demonstrated that the proposed model and the obtained solutions provide extensive possibilities for practical application compared with previous related studies.

• Earthquakes and Structures
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• v.20 no.2
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• pp.225-238
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• 2021

Supplemental passive dampers are widely employed to improve the structural performance of buildings under seismic excitations. Nevertheless, the added damping could be counter-productive if the axial forces induced by the damper reaction forces are not routed properly in the columns. A few researchers engaged to optimize the width-wise damper arrangement to improve the delivered path of the axial column forces. However, most of these studies are limited under the design-based seismic level and few of them has evaluated the collapse performance of buildings under strong earthquakes. In this paper, the strategic width-wise placement method of viscous dampers is explored regarding the building performance under collapse state. Two realistic steel buildings with different storeys are modelled and compared to explore higher mode effects. Each building is designed with four different damper arrangement scenarios based on a classic damper distribution method. Both a far-fault and a near-fault seismic environment are considered for the buildings. Incremental Dynamic Analysis (IDA) is performed to evaluate the probability of collapse and the plastic mechanism of the retrofitted steel buildings.