• Geomechanics and Engineering
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• v.19 no.5
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• pp.463-472
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• 2019

The mode perturbation method (MPM) is suitable and efficient for solving the eigenvalue problem of a nonuniform soil deposit whose property varies with depth. However, results of the MPM do not always converge to the exact solution, when the variation of soil deposit property is discontinuous. This discontinuity is typical because soil is usually made up of sedimentary layers of different geologic materials. Based on the energy integral of the variational principle, a new mode perturbation method, the energy-based mode perturbation method (EMPM), is proposed to address the convergence of the perturbation solution on the natural frequencies and the corresponding mode shapes and is able to find solution whether the soil properties are continuous or not. First, the variational principle is used to transform the variable coefficient differential equation into an equivalent energy integral equation. Then, the natural mode shapes of the uniform shear beam with same height and boundary conditions are used as Ritz function. The EMPM transforms the energy integral equation into a set of nonlinear algebraic equations which significantly simplifies the eigenvalue solution of the soil layer with variable properties. Finally, the accuracy and convergence of this new method are illustrated with two case study examples. Numerical results show that the EMPM is more accurate and convergent than the MPM. As for the mode shapes of the uniform shear beam included in the EMPM, the additional 8 modes of vibration are sufficient in engineering applications.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.7
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• pp.1462-1470
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• 2003

According to the necessity about information security as well as the advance of IT system and the spread of the Internet, a variety of cryptography algorithms are being developed and put to practical use. In addition the technique about cryptography attack also is advanced, and the algorithms which are strong against its attack are being studied. If the linear transformation matrix in the block cipher algorithm such as Substitution Permutation Networks(SPN) produces the Maximum Distance Separable(MDS) code, it has strong characteristics against the differential attack and linear attack. In this paper, we propose a new algorithm which cm estimate that the linear transformation matrix produces the MDS code. The elements of input code of linear transformation matrix over GF$({2_n})$ can be interpreted as variables. One of variables is transformed as an algebraic formula with the other variables, with applying the formula to the matrix the variables are eliminated one by one. If the number of variables is 1 and the all of coefficient of variable is non zero, then the linear transformation matrix produces the MDS code. The proposed algorithm reduces the calculation time greatly by diminishing the number of multiply and reciprocal operation compared with the conventional algorithm which is designed to know whether the every square submatrix is nonsingular.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1069-1075
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• 2013

An effective method is necessary for the real-time analysis of an unmanned military robot. To achieve highly efficient simulations, a subsystem synthesis method has been developed. The subsystem synthesis method separately generates equations of motion for the base body and for the subsystem. The equations of motion are expressed by DAE, which consist of differential equations and algebraic equations. To increase the accuracy and efficiency of solutions, DAE solvers such as the Direct, CS (Constraint Stabilization), and GCP (Generalized Coordinate Partitioning) method are employed. In this study, the subsystem synthesis method is applied for effective multi-body dynamics analysis of an unmanned military robot, and a comparative study of three different DAE solvers is carried out.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.13-22
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• 2018

In this study, a governing differential equation for the bending problem of orthotropic rectangular plate is drived. It's exact solution for various boundary conditions is presented. This solution follows traditional method like Navier's solution or Levy's solution that transforms the governing differential equation into an algebraic equation by using trigonometric series. To obtain a solution by Levy's method, it is required that two opposite edges of the plate be simply supported. And the boundary conditions, for which the Navier's method is applicable, are simply supported edge at all edges. In this study, it overcomes the limitations of the previous Navier's and Levy's methods.This solution is applicable for any combination of boundary conditions with simply supported edge and clamped edge in x, y direction. The plate could be subjected to uniform, partially uniform, and line loads. The advantage of the solution is that it is the exact solution as well as it overcomes the limitations of the previous Navier's and Levy's methods. Calculations are presented for orthotropic plates with nonsymmetric boundary conditions. Comparisons between the result of this paper and the result of Navier, Levy and Szilard solutions are made for the isotropic plates. The deflections were in excellent agreement.

• The Journal of the Korea Contents Association
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• v.16 no.12
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• pp.1-9
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• 2016

Computational Fluid Dynamics(CFD) is a branch of fluid mechanics that solves partial differential equations which represent fluid flows by a set of algebraic equations using computers. Even though it requires multifarious variables, only selected ones are stored because of the lack of storage capacity. It causes the requirement of secondary variable calculations at analyzing time. In this paper, we suggest an efficient method to estimate optimal calculation paths for secondary variables. First, we suggest a converting technique from a dependency graph to a ordinary directed graph. We also suggest a technique to find the shortest path from any initial variables to target variables. We applied our method to a tool for data analysis and visualization to evaluate the efficiency of the proposed method.

• Membrane Journal
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• v.20 no.1
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• pp.29-39
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• 2010

This study focuses on the modeling of DMFC to predict the characteristics and to improve its performance. This modeling requires deep understanding of the design and operating parameters that influence on the cell potential. Furthermore, the knowledge with reference to electrochemistry, transport phenomena and fluid dynamics should be employed for the duration of mathematical description of the given process. Considering the fact that MEA is the nucleus of DMFC, special attention was made to the development of mathematical model of MEA. Multiscale modeling is comprised of process modeling as well as a computational fluid dynamics (CFD) modeling. The CFD packages and process simulation tools are used in simulating the steady-state process. The process simulation tool calculates theelectrochemical kinetics as well as the change of fractions, and at the same time, CFD calculates various balance equations. The integrated simulation with multiscal modeling explains experimental observations of transparent DMFC.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.4
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• pp.343-351
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• 2016

Cryogenic spray characteristics of a nitrogen swirl injector operating in supercritical environment have been numerically investigated. By comparing the equation of states(EOS) used for supercritical condition, SRK EOS was applied to predict the nitrogen thermodynamic property under supercritical environment. A Chung's method was implemented for the calculation of viscosity and conductivity and Takahashi's correlation based on Fuller's Theorem was implemented for the calculation of diffusion coefficient. By injecting the nitrogen with 5 bar differential pressure into 50 bar chamber filled with nitrogen, numerical simulation has been conducted. The dynamic Smagorinsky sub-grid scale (SGS) model has been compared with the algebraic Smagorinsky SGS model using FFT frequency analysis. The instability at the liquid film and gas core inside injector and the propagation of pressure oscillation into the injector has been investigated. The spreading angle of swirl injector obtained by numerical calculation has been validated with experimental result.