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최덕기(D.K.Choi),김재윤(J.Y.Kim) 한국자동차공학회 1998 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1998 No.11_1
Molecular dynamics is emerging with the recent development of high -performance computers. Molecular dynamics has been used for materials simulation and various fracture simulations. In this paper, a study on an application of molecular dynamics technique to optimization problems is presented. A Potential energy of molecular system is mapped into its equivalent objective function, which is to be optimized. Also each molecule is considered a design variable, which lead the objective function to be a minimum value. An advantage of the present method over others is to find global minima instead local minima. Three different objective functions are selected to show the performance of the present method, which yields good accuracy and convergence speed in optimization.<br/>
삼각격자모델을 사용한 응력확대계수에 대한 분자동역학적 해석
최덕기(D.K.Choi),신현제(H.J.Shin) 한국자동차공학회 1997 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1997 No.6_2
The use of molecular dynamics simulation on materials is examined to study stress intensity factors calculation. To carry out materials simulation using molecular dynamics, the potential, which interacts between molecules, must be known and be accurate. There are several potential models and the Hooke’s model is selected in this paper for simplicity. The simulations of a tension test are performed. The energy release rate can be calculated from the potential and the crack length. Also the stress intensity factor may be obtained from the energy release rate. Three different cases are discussed to show the validity of the simulations.<br/>
최덕기(D. K. Choi),류한규(H. K. Ryu) 한국자동차공학회 1997 한국자동차공학회 학술강연초록집 Vol.1997 No.4
A hole located at the crack tip is used to suppress the crack growth. Being microscopic phenomena, it cannot be materialized easily through conventional ap-proachs. Molecular dynamics is emerging with recent development of computer technology. Even it being a useful tool for analysis molecular dynamics simulation requires vast computer resources. In this study, quasi molecules, which are aggregates of molecules are used to reduce amount of computation so that all the simulation may be performed at reasonable computation time. Through quasimolecular dy-namics approach in the present study, it is clearly shown that present approach can be used to simulate the crack grow retardation due to a hole at the crack tip.
최덕기(D. K. Choi),김창수(C. S. Kim) 한국자동차공학회 1997 한국자동차공학회 학술강연초록집 Vol.1997 No.4
This paper addresses a procedure which can be used for designing functionally graded materials(FGM) using semi-analytical approach. The FGM is a nonhomogeneous material whose compoaition. changes continuously from a metal surface to a ceramic surface. An FGM that decreases thermal stresses at the interface has been developed for structural components and mechanical elements such as nuclear, aircraft, and space engineering. The temperature distribution in the FGM is obtained by approximate Green's function solution. Thermal stresses are obtained in elastic boundary conditions on elongation and radius of curvature. The stress difference is calculated for various parameters, volume fraction of each element and porosity. The stress ratio can be used for determining the appropriate parameters.