• Tribology and Lubricants
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• v.32 no.1
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• pp.1-8
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• 2016

This paper focuses on the thermal deformation induced preload change in the tilting pad journal bearing, using a three-dimensional (3D) thermo-hydro-dynamic (THD) approach. Preload is considered as a critical factor in designing the tilting pad journal bearing. The initial preload measured under nil external load and nil thermal gradient is influenced by two factors, namely, the thermal deformation and elastic deformation. Thermal deformation is due to a temperature distribution in the bearing pads, whereas the elastic deformation is due to fluid forces acting on the pads. This study focuses on the changes induced in preload and film clearance due to thermal deformation. The generalized Reynolds equation is used to evaluate the force of the fluid and the 3D energy equation is used to calculate the temperature of the lubricant. The abovementioned equations are combined by establishing a relationship between viscosity and temperature. The heat transfer within the bearing pads, the lubricant, and the spinning journal is calculated using the heat flux boundary condition. The 3D Finite Element Method (FEM) is used in modeling the (1) heat conduction in the spinning journal and bearing pads, (2) thermal gradient induced thermal distortion of the spinning journal and pads, and (3) viscous shearing, and heat conduction and convection in a thin film. This evaluation method has an increased fidelity, and it can prove to be a cost-effective tool that can be used by designers to predict the dynamic behavior of a bearing.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.5
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• pp.387-395
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• 2015

A technique for calculating the additive drag of the inlet in supersonic flow was studied using commercial CFD software, STAR-CCM+, which provides a efficient way of 3 dimensional flow analysis with polyhedron-shaped grid system. Three configurations were chosen and applied to the calculation with various flow conditions of two different free stream Mach No. and some mass flow ratios. Comparisons with results from wind tunnel test gave good agreements. Though computation were carried out with the inviscid and compressible flow around the supersonic inlet for the supercritical condition, ignoring the viscous effects is concluded to give little effects on the accuracy of the additive drag calculation and to make the calculation more efficient owing to less effort and time consumed for grid system build-up and for iteration because of less grid number and simpler boundary condition.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.6
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• pp.65-71
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• 2008

A one-dimensional site response analysis program (KODSAP) was developed using cyclic soil behavior model by using the modified parallel IWAN model. The model is able to predict the cyclic hardening and degradation of soil through the adjustment of the internal slip stresses of its elements beyond the cyclic threshold, and satisfies Bauschinger's effect and the Masing rule in terms of its own behavior characteristics. The program (KODSAP) used the direct integration method in the time domain. The elasticity of the base rock was considered as a viscous damper boundary condition. The effects of cyclic hardening or degradation of soil on site response analysis were evaluated through parametric studies. Three types of analyses were performed to compare the effect of analysis and cyclic parameter on site response. The first type was equivalent linear analysis, the second was nonlinear analysis, and a third was nonlinear analysis using the cyclic hardening or degradation model.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• 한국전산유체공학회:학술대회논문집
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• 2008.10a
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• pp.177-180
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• 2008

The objective of this study is to get simulation data about pulsatile flow of a non-Newtonian fluid through a bifurcated tube. All the process was based on CFD method, with a commercial FVM code, SC/Tetra ver. 6.0 for solving, and with CATIA R16 for generating geometries. To define a non-Newtonian fluid, the following viscous models are used; the Powell-Eyring model, the modified Powell-Eyring model, the Cross model, the modified Cross model, the Carreau model, the Carreau-Yasuda model and the modified Power Law model. The flow calculation data using each model were compared with the other data of a existing paper. Finally, the Carreau model was recognized to give the best result with the SC/Tetra code, and the succeeding simulations are made with the model. For the pulsating flow condition, the sine wave type velocity profile is given as the inlet boundary condition. To investigate the effect of geometries and mesh, the pre-test is carried out with various curvature conditions of the bifurcated corner, and then with various mesh conditions. The final process is to calculate flow variables such as the wall shear stress (WSS) and the wall shear stress gradient (WSSG). To validate all the result, the simulation is compared with the existing data of the other papers. Generally speaking, there is a noticeable difference in the maximum and minimum value of WSS. It is not sure that the values in each data are on the exactly same location. However, the overall trend is similar. The next study needs to investigate the same situation by experimental method. Furthermore, if the flow is simulated with more pulsatile conditions, more data of flow field through a bifurcated tube could be achieved.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.66-71
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• 2013

In this paper, the supersonic flows around space launch vehicles have been numerically simulated by using a 3-D RANS flow solver. The focus of the study was made for investigating plume-induced flow separation(PIFS). For this purpose, a vertex-centered finite-volume method was utilized in conjunction with 2nd-order Roe's FDS to discretize the inviscid fluxes. The viscous fluxes were computed based on central differencing. The Spalart-Allmaras model was employed for the closure of turbulence. The Gauss-Seidel iteration was used for time integration. To validate the flow solver, calculation was made for the 0.04 scale model of the Saturn-5 launch vehicle at the supersonic flow condition without exhaust plume, and the predicted results were compared with the experimental data. Good agreements were obtained between the present results and the experiment for the surface pressure coefficient and the Mach number distribution inside the boundary layer. Additional calculations were made for the real scale of the Saturn-5 configuration with exhaust plume. The flow characteristics were analyzed, and the PIFS distances were validated by comparing with the flight data. The KSLV-1 is also simulated at the several altitude conditions. In case of the KSLV-1, PIFS was not observed at all conditions, and it is expected that PIFS is affected by the nozzle position.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2000.10a
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• pp.189-195
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• 2000

New concept of LNG-FPSO ship with moonpool and bilge step in bottom is considered and investigated in the point of motion reduction and sloshing phenomena of the cargo and operation tanks. The cargo capacity of the ship of which principle dimensions is L x B x D x t(design) =270.0 x 51.0 x 32.32 x 13.7(m) 16K at 98% loading condition. The two moonpools and rectangular step at bilge part are setted up specially for getting the effect of motion decrease. For the motion analysis, linearized three dimensional diffraction theory with the simplified boundary conditions is used. The six-degree of freedom coupled motion responses are calculated for the LNG-FPSO ship. Viscous effects on the roll motion responses of a vessel are taken into account in this calculation program using an empirical formula suggested by Ikeda, Himeno and Tanaka is used. The case study for the moonpool size had been carried out by theoretical estimation and experimental method. For the optimization of the moonpool size and effect of the step, 9 cases of its size and with and without step are considered. From the results of calculation and experiment, it can be concluded that this designed LNG-FPSO ship have possibility to carry out her missions in the rough sea as for the owner's demand waves condition. The motion responses, especially roll motion, for the designed LNG-FPSO ship are much lower than those of another drillship and shuttle tanker and limit criterions are satisfied. For the check of the cargo tank and operation tank sizes we have performed sloshing analysis in the irregular waves which focuses on the pressure distribution on the tank wall and the time history of pressure and free surface for No.2 and No5. tanks of LNG-FPSO with chamfers. Finally we got the tank size which has no resonance and no impact pressure in all filling in the bow quartering and beam sea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.484-491
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• 2007

Numerical experiments using a numerical wave tank have been performed to verier the nonlinear interaction between monochromatic waves and a submerged horizontal plate. As a model for numerical wave tank, we used a higher-order Boundary Element Method(BEM) based on fully nonlinear potential flow theory and CADMAS-SURF for solving Navier Stokes equations and exact free surface conditions. Both nonlinear models are able to predict the higher harmonic generation in the shallow water region over a submerged horizontal plate. CADMAS-SURF, which involves the viscous effect, can evaluate the higher harmonic generation by flow separation and vortices at the each ends of plate. The comparison of reflection and transmission coefficients with experimental results(Patarapanich and Cheong, 1989) at different lengths and submergence depths of a horizontal plate are presented with a good agreement. It is found that the transfer of energy from the incident fundamental waves to higher harmonics becomes larger as the submergence depth ratio decreases and the length ratio increases.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.6
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• pp.852-860
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• 1986

The effect of placing a worktable in a vertical laminar flow clean room is invesgiated by a numerical simulation. The model clean room is assumed to be a rectangular square of 2m*2m, in which a worktable of 0.8m long and 0.1m thick is located at 0.7m above the floor. Major parameters are the horizontal position of the table and the inlet flow velocity. The flow is assumed to be laminar throughout the clean room. Navier-Stokes equations with the pressure terms are directly solved by the SIMPLE algorithm. Boundary conditions at the two exits are given in terms of pressure conditions. The flow pattern, pressure loss due to viscous friction, the ratio of flow rates through each exit and pressure imbalance at the exits are calculated. All of the flow characteristics are seen to vary substantially with the location of the table, but are quite insensitive to the inlet flow velocity(Reynolds number). As an example, the flow rate through each exit can very by as much as 30% depending on the location of the table.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.2
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• pp.150-162
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• 2010

Assessment of hydrodynamic performance of a ship hull has been focused on a model ship rather than a full-scale ship. In order to design the propeller of a ship, model-scale wake is often extended to full-scale based upon an empirical method or designer's experience, since wake measurement data for a full-scale ship is very rare. Recently modern CFD tools made some success in reproducing wake field of a model ship, which implicates that there are some possibilities of the accurate prediction of full-scale wakes. In this paper firstly the evaluation of model-scale wake obtained by Fluent package was performed. It was found that CFD calculation with the Reynolds-stress model (RSM) provided much better agreement with wake measurement in the towing tank than with the realizable k-$\varepsilon$ model (RKE). In the next full-scale wake was calculated using the same package to find out the difference between model and full-scale wakes. Three hull forms of KLNG, KCS, KVLCC2 having measurement data open for the public, were chosen for the comparison of resistance, form factor, and propeller plane wake between model ships and full-scale ships.