• 소성∙가공
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• 제6권5호
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• pp.408-415
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• 1997

The backward tracing scheme of the finite element analysis, which is counted to be unique and useful for process design in metal forming, has been developed and applied successfully in industry to several metal forming processes. Here the backward tracing scheme is implemented for process design of three-dimensional plastic deformation in metal forming, and it is applied to a precision coining process. The contact problem between the die and workpiece has been treated carefully during backward tracing simulation in three-dimensional deformation. The results confirm that the application of the developed program implemented with backward tracing scheme of the rigid plastic finite element leads to a reasonable initial piercing hole configuration. It is concluded that three-dimensional extension of the scheme appears to be successful for industrial applications.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.902-909
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• 2006

In this study, three-dimensional rotordynamic analyses have been conducted using equivalent beam, hybrid and fun three-dimensional models. The Present computational method is based on the general finite element method with rotating gyroscopic effects of a rotor system. General purpose commercial finite element code, SAMCEF which includes practical rotordynamics module with various types of rotor analysis methods and bearing elements is applied. For the purpose of numerical verification, comparison study for a benchmark rotor model with support bearings is performed first. Detailed finite element models based on three different modeling concepts are constructed and then computational analyses are conducted for the realistic and complex three-dimensional rotor system. The results for rotor stability and mass unbalance response are presented and compared with the experimental vibration test conducted in this study.

• 대한기계학회논문집A
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• 제29권7호
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• pp.990-997
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• 2005

The objective of this paper is to present the element connectivity parameterization (ECP) fur three dimensional problems. In the ECP method, a continuum structure is viewed as discretized finite elements connected by zero-length elastic links whose stiffness values control the degree of inter-element connectivity. The ECP method can effectively avoid the formation of the low-density unstable elements. These elements appear when the standard element density method is used for geometrical nonlinear problems. In this paper, this ECP method developed fur two-dimensional problems is expanded to the design of three-dimensional geometrical nonlinear structures. Among others, the automatic procedure converting standard finite element models to the models suitable for the ECP approach is developed and applied for optimization problems defined on general three-dimensional design domains.

• 대한기계학회논문집
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• 제18권1호
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• pp.101-112
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• 1994

The measurement of residual stress distribution of $Si_3N_4/SUS304$ joint was performed on 23 specimens with the same joint condition using PSPC type X-ray stress measurement system and the two-dimensional elastoplastic analysis using finite element method was also attempted. As results, residual stress distribution near the interface on the ceramic side of the joint was revealed quantitatively. Residual stress on the ceramic side of the joint was turned out to be tensional near the interface, maximum along the edge, varying in accordance with the condition of the joint and variance to be most conspicuous for the residual stress normal to the interface characterized by the stress singularities. In the vicinity of the interface, the high stress concentration occurs and residual stress distributes three-dimensionally. Therefore, the measured stress distribution differed remarkably from the result of the two-dimensional finite-element analysis. Especially at the center of the specimen near the interface, the residual stress, $\sigma_{x}$ obtained from the finite element analysis was compressive, whereas measurement using X-ray yielded tensile $\sigma_{x}$. Here we discuss two dimensional superposition model the discrepancy between the results from the two dimensional finite element analysis and X-ray measurement.

• 대한조선학회지
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• 제24권3호
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• pp.1-8
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• 1987

In this paper, the localized finite element method(LFEM) is applied to 3-dimensional ship motion problems in water of infinite depth. The LFEM used here is based on the functional constructed by Bai & Yeung(1974). To test the present numerical scheme, a few vertical axisymmetric bodies are treated by general 3-dimensional formulation. The computed results of hydrodynamic coefficients for a few vertical spheroids and vertical circular cylinders show good agreement with results obtained by others. The advantages of the present numerical method compared with the method of integral equation are as follows; (i) The cumbersome existence of irregular frequencies in the method of conventional integral equation is removed. (ii) The final matrix is banded and symmetric and the computation of the matrix elements is comparatively easier, whereas the size of the matrix in the present scheme is much larger. (iii) In the future research, it is possible to accommodate with the nonlinear exact free surface boundary condition in the localized finite element subdomain, whereas the linear solution is assumed in the truncated(far field) subdomain.

• 소음진동
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• 제9권3호
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• pp.544-553
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• 1999

A 3-dimensional helical rod finite element is devloped for the dynamic analysis of cylindrical springs. Element matrices are formulated using the Galerkin's method, and an exact static deflection curve is used as a shape function. Because the resultant mass and stiffness matrices of the model are symmetric, effective direct solution method can easily be applied for analysing dynamic behavior of springs. The model is used to analyze the dynamic characteristics of a typical automotive valve spring. The effectiveness of the developed helical rod element is verified by comparing the results of the proposed method with those of a classical theory and experiments. The helical element developed in this study is superior to a straight beam element and a 2-dimensional curved beam element for this problem.

• 대한기계학회논문집
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• 제17권5호
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• pp.1095-1105
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• 1993

본 연구에서는 앞서 개발된 3차원 강소성 유한요소법을 이용하여 H-형강 압연 공정을 해석하여 그 타당성을 검토하고 이를 실제의 공정 설계에 이용할 수 있도록 하였다.

• Journal of Advanced Marine Engineering and Technology
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• 제26권3호
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• pp.344-352
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• 2002

In the analysis of the 3 dimensional plate structures by the finite element method, the triangular elements are generally used for the global stiffness matrix of the analyzed system. But the triangular elements of the plates have some problems in the process of formulation and in the precision of analysis. The formulation of the finite element method to analyze 3 dimensional plate structures using quadrilateral elements is presented in this paper. The degree of freedom off nodal point is 6, that is, the displacements in the direction off-y-z is and the rotations about x-y-z axis and then the degree of freedom off element is 24. For the comparison of the analysis using triangular elements and quadrilateral elements, the rectangular plates subjected to the uniform load and a concentrated load on the centroid of the plate, for which the theoretical solutions have been obtained, are analyzed. The calculated deflections of the rectangular plates using the finite element method by the triangular elements and the quadrilateral elements are also compared with the deflections of the plates calculated by theoretical solutions. The defections of the rectangular plates calculated by the finite element method using the quadrilateral elements are closer to the theoretical solutions than the defections calculated by the finite element method using the triangular elements. The deflection of the centroid of plate, calculated by the finite element method, converges to that of theoretical solution as the number of elements is increased. This convergence is much more rapid for the case of using the quakrilateral elements than fir the case of using triangular elements.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 추계학술대회 논문집
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• pp.173-181
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• 1994

Process design is one of the most important fields in metal forming, where the finite element method has appeared a useful method for industrial applications. In this study, a program using the rigid plastic finite element has been developed for preform design in three-dimensional plastic deformation. The surface integration for calculation of the friction between die and workpiece has been implemented with care in numerical treatment. The developed program is applied to a precision coining process for designing an optimal punch.

• 한국항공우주학회지
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• 제30권6호
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• pp.39-45
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• 2002

본 논문에서는 복합재의 3차원 경화 수치모사를 위해 유한요소 정식과정을 제시하였다. 이 정식을 기초로 하여 유한요소 프로그램을 개발하였다. 개발한 프로그램을 검증하기 위해 참고문헌에 제시된 수치예제에 대한 해석을 수행하였다. 본 논문에서의 경화 수치모사결과가 측정된 경화온도와 잘 일치하였다. 본 3차원 경화 수치모사에서는 1, 2차원 해석과는 달리 복합재 구조물의 임의 지점에서의 수치모사 결과분석이 가능하다. 개발된 유한요소 프로그램을 이용하면 불규칙한 형상을 가진 복합재 구조물과 일정하지 않은 오토클레이브 내부 온도분포 하에서의 경화 수치모사를 할 수 있다.