• Journal of the Korean Society for Advanced Composite Structures
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• v.1 no.4
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• pp.28-34
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• 2010

W e performed a geometrical nonlinear dynamic analysis of laminated skew plates made of advanced composite materials (ACM ) based on the first-order shear deformation plate theory (FSDT). The Newmark method and Newton-Raphson iteration are used for the nonlinear dynamic solution. The effects of skew angles and layup sequences on the nonlinear dynamic response for various parameters are studied using a nonlinear dynamic finite element program developed for this study. The several numerical results were in good agreement with those reported by other investigators for square composite and skew plates, and the new results reported in this paper show the significant interactions between the skew angle and layup sequence in the skew laminate. Key observation points are discussed and a brief design guideline is given.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.1392-1396
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• 2007

The governing equations in generalized curvilinear coordinates for 3D laminar flow are the Incompressible Navier-Stokes (INS) equations with the artificial dissipative terms. and continuity equation discretized using a second-order accurate, finite volume method on the nonstaggered computational grid. This method adopts a dual or pseudo time-stepping Artificial Compressibility (AC) method integrated in pseudo-time. Multigrid methods are also applied because solving the equations on the coarse grids requires much less computational effort per iteration than on the fine grid. The algorithm yields practically identical velocity profiles and secondary flows that are in excellent overall agreement with an experimental measurement (Humphrey et al., 1977).

• International Journal of Aeronautical and Space Sciences
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• v.2 no.2
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• pp.28-38
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• 2001

A numerical method for the assessment and correction of tunnel wall interference effects on forced-oscillation testing is presented. The method is based on the wall pressure signature method using computed wall pressure distributions. The wall pressure field is computed using unsteady three-dimensional full Navier-Stokes solver for a 70-degree pitching delta wing in a wind tunnel. Approximately-factorized alternate direction implicit (AF-ADI) scheme is advanced in time by solving block tri-diagonal matrices. The algebraic Baldwin-Lomax turbulence, model is included to simulate the turbulent flow effect. Also, dual time sub-iteration with, local, time stepping is implemented to improve the convergence. The computed wall pressure field is then imposed as boundary conditions for Euler re-simulation to obtain the interference flow field. The static computation shows good agreement with experiments. The dynamic computation demonstrates reasonable physical phenomena with a good convergence history. The effects of the tunnel wall in upwash and blockage are analyzed using the computed interference flow field for several reduced frequencies and amplitudes. The corrected results by pressure signature method agree well with the results of free air conditions.

• Transactions of the Korean Society of Automotive Engineers
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• v.5 no.6
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• pp.89-102
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• 1997

In this study, the steady state cornering behavior of a vehicle is investigated by using a numerical model that has parameters associated with roll motion. The nonlinear characteristics of tire cornering forces and aligning torques are presented in analytical forms using the magic formula. The sets of nonlinear algebraic equations that govern the cornering motion are solved by the Newton-Raphson iteration method. The vehicle design parameters are measured by SPMD(Suspension Parameter Measuring Device), and its results are verified by carrying out a skid pad test. The design parameters that are most affecting the steady state cornering behavior are classified into four factors, and the contributions of the factors to understeer gradient are then calculated.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.87-92
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• 1998

A nonlinear iterative scheme developed to reduce the computing time of the AFEN method was tested and applied to two benchmark problems. The new nonlinear method for the AFEN method is based on solving two-node problems and use of two nonlinear correction factors at every interface instead of one factor in the conventional scheme. The use of two correction factors provides higher-order accurate interface noes as well as currents which are used as the boundary conditions of the two-node problem. The numerical results show that this new method gives exactly the same solution as that of the original AEFEN method and the computing time is significantly reduced in comparison with the original AFEN method.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.112-117
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• 1998

A generalized perturbation program has been developed for the purpose of estimating zonal power variation of a CANDU reactor upon refueling operation. The forward and adjoint calculation modules of RFSP code were used to construct the generalized perturbation program. The numerical algorithm for the generalized adjoint flux calculation was verified by comparing the zone power estimates upon refueling with those of forward calculation. It was, however, noticed that the truncation error from the iteration process of the generalized adjoint flux is not negligible.

• Journal of the Korean Operations Research and Management Science Society
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• v.16 no.1
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• pp.135-146
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• 1991

This paper shows the infinite horizon model of Partially Observable Markov Decision Process with lagged information. The lagged information is uncertain delayed observation of the process under control. Even though the optimal policy of the model exists, finding the optimal policy is very time consuming. Thus, the aim of this study is to find an .eplison.-optimal stationary policy minimizing the expected discounted total cost of the model. .EPSILON.- optimal policy is found by using a modified version of the well known policy iteration algorithm. The modification focuses to the value determination routine of the algorithm. Some properties of the approximation functions for the expected discounted cost of a stationary policy are presented. The expected discounted cost of a stationary policy is approximated based on these properties. A numerical example is also shown.

• Journal of Advanced Marine Engineering and Technology
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• v.23 no.5
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• pp.637-653
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• 1999

In this study well-known burned rate expressions of Weibe function and double Wiebe function have been adopted for the combustion analysis of large two stroke marine diesel engine. A cycle simulation program was also developed to predict the performance and pressure waves in pipes using validated burned rate function,. Levenberg-Marquardt iteration method was applied to cali-brate the shape coefficients included in double Wiebe function for the performance prediction of two-stroke marine diesel engine. As a result the performance prediction using double Wiebe func-tion is well correlated withexperimental dta with the accuracy of 5% and pressure waves in intake and transport pipe are well predicted. From the results of this study it can be confirmed that the shape coefficients of burned rate function should be modified using the numerical method suggested for the accurated prediction and double Wiebe function is more suitable than Wiebe func-tion for combustion analysis of large two stroke marine engine.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.4
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• pp.17-29
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• 2004

Internal waves are computed using a ghost fluid method on an unstructured grid. Discontinuities in density and dynamic pressure are captured in one cell without smearing or oscillations along a multimaterial interface. A time-accurate incompressible Navier-Stokes/Euler solver is developed based on a three-point backward difference formula for the physical time marching. Artificial compressibility is introduced with respect to pseudotime and an implicit method is used for the pseudotime iteration. To track evolution of an interface, a level set function is coupled with the governing equations. Roe's flux difference splitting method is used to calculate numerical fluxes of the coupled equations. To get higher order accuracy, dependent variables are reconstructed based on gradients which are calculated using Gauss theorem. For each edge crossing an interface, dynamic pressure is assigned for a ghost node to enforce the continuity of total pressure along the interface. Solitary internal waves are computed and the results are compared with other computational and experimental results.

• Proceedings of the KIEE Conference
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• 1995.07b
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• pp.528-530
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• 1995

In the conventional power flow calculations, the slack bus is assumed to undertake the total transmission loss for the convenience of numerical computation. This is an unrealistic assumption because, in real power system, the transmission loss is supplied by all the generators and makes the power flow calculation results somewhat distorted. This paper proposes a new loss redistribution algorithm that can reduce the distortion of power flow results. In the proposed method, the system power loss redistribution algorithm is added to the conventional power flow equations and jacobian elements that are related the real power are newly constructed. In each iteration step, the power output of each generator is updated to consider the effect of calculated total power losses. Finally the usefulness of proposed method are tested through the some appropriate case studies.