• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.2 no.4
• /
• pp.61-66
• /
• 2003

An excellent mesh construction is of Importance in yielding good results of finite element analysis. The new mesh generation algorithm, which offsets boundaries inward, was developed on the basis of a looping method. An user interface technique and automatic splitting lines which both divide a given domain into subdomains manually or automatically, were used. In addition, the separation method has advantages to prevent the large scale of element size and to control numbers of nodes and elements. This new mesh generation algorithm was proved in practice.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.7 s.178
• /
• pp.1763-1770
• /
• 2000

A finite element interface system for the design of optimal spot welding locations has been developed. In order to find out the optimal locations of spot welding points, iterative finite element an alyses are necessary, and thus automatic generation of finite element model for the structures with spot welded pointsis required. In this interface system, quadrilateral shell elements are automatically generated for finite element analysis of spot welded structured, which employs a domain decomposition methodand adaptive mesh(h-method).

• Journal of the Korean Society of Fisheries and Ocean Technology
• /
• v.32 no.2
• /
• pp.164-176
• /
• 1996

The main intention of this paper is to develop and compare the algorithm based on finite element procedures for nonlinear transient dynamic analysis which has combined effects of material and geometric nonlinearities. Incremental equilibrium equations based on the principle of virtual work are derived by the finite element approach. For the elasto - plastic large deformation analysis of shells and the determination of the displacement-time configuration under time-varying loads, the explicit, implicit and combined explicit-implicit time integration algorithm is adopted. In the time structure is selected and the results are compared with each others. Isoparametric 8-noded quadrilateral curved elements are used for shell structure in the analysis and for geometrically nonlinear elastic behaviour, a total Lagrangian coordinate system was adopted. On the other hands, material nonlinearity is based on elasto-plastic models with Von-Mises yield criteria. Thus, the combined explicit-implicit time integration algorithm is benefit in general case of shell structure, which is the result of this paper.

• Structural Engineering and Mechanics
• /
• v.40 no.1
• /
• pp.121-148
• /
• 2011

Closed form solutions for equilibrium and flexibility matrices of the Mindlin-Reissner theory based eight-node rectangular plate bending element (MRP8) using Integrated Force Method (IFM) are presented in this paper. Though these closed form solutions of equilibrium and flexibility matrices are applicable to plate bending problems with square/rectangular boundaries, they reduce the computational time significantly and give more exact solutions. Presented closed form solutions are validated by solving large number of standard square/rectangular plate bending benchmark problems for deflections and moments and the results are compared with those of similar displacement-based eight-node quadrilateral plate bending elements available in the literature. The results are also compared with the exact solutions.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.20 no.3
• /
• pp.265-272
• /
• 2007

The finite element linear buckling analysis of folded plate structures using adaptive h-refinement methods is presented in this paper. The variable-node flat shell element used in this study possesses the drilling D.O.F. which, in addition to improvement of the element behavior, permits an easy connection to other elements with six degrees of freedom per node. The Box-typed structures can be analyzed using these developed flat shell elements. By introducing the variable-node elements some difficulties associated with connecting the different layer patterns, which are common in the adaptive h-refinement on quadrilateral mesh, can be overcome. To obtain better stress field for the error estimation, the super-convergent patch recovery is used. The convergent buckling modes and the critical loads associated with these modes can be obtained.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.36 no.10
• /
• pp.1139-1146
• /
• 2012

An alternative approach for topology optimization of steady incompressible Navier-Stokes flow problems is presented by using P1 nonconforming finite elements. This study is the extended research of the earlier application of P1 nonconforming elements to topology optimization of Stokes problems. The advantages of the P1 nonconforming elements for topology optimization of incompressible materials based on locking-free property and linear shape functions are investigated if they are also valid in fluid equations with the inertia term. Compared with a mixed finite element formulation, the number of degrees of freedom of P1 nonconforming elements is reduced by using the discrete divergence-free property; the continuity equation of incompressible flow can be imposed by using the penalty method into the momentum equation. The effect of penalty parameters on the solution accuracy and proper bounds will be investigated. While nodes of most quadrilateral nonconforming elements are located at the midpoints of element edges and higher order shape functions are used, the present P1 nonconforming elements have P1, {1, x, y}, shape functions and vertex-wisely defined degrees of freedom. So its implentation is as simple as in the standard bilinear conforming elements. The effectiveness of the proposed formulation is verified by showing examples with various Reynolds numbers.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2005.05b
• /
• pp.414-418
• /
• 2005

A finite element model is developed for the numerical simulation of bed elevation change in a curved channel. The SU/PG (Streamline-Upwind/Petrov-Galerkin) method is used to solve 2D shallow water equations and the BG (Bubnov-Galerkin) method is used for the Exner equation. For the time derivative terms, the Crank-Nicolson scheme is used. The developed model is a decoupled model in a sense that the bed elevation does not change simultaneously with the flow during the computational time step. The total load formula with is used for the sediment transport model. The slip conditions are described along the lateral boundaries. The effects of gravity force due to geometry change and the secondary flows in a curved channel are considered in the model. For the verification, the model is applied to two laboratory experiments. The first is $140^{\circ}$ bended channel data at Delft Hydraulics Laboratory and the second is $140^{\circ}$ bended channel data at Laboratory of Fluid Mechanics of the Delft University of Technology. The finite element grid is constructed with linear quadrilateral elements. It is found that the computed results are in good agreement with measured data, showing a point bar at the inner bank and a pool at the outer bank.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2009.05a
• /
• pp.815-821
• /
• 2009

하천의 2차원 흐름 및 하상변동, 오염확산 해석을 위한 유체의 수치해석법에는 유한요소법, 유한차분법, 유한차분법의 변형인 유한체적법, 경계적분법 등이 있으며, 국내의 경우 비구조적 요소망(unstructured mesh)을 이용하여 복잡한 형상을 표현하기가 상대적으로 용이한 유한요소법이 널리 사용되고 있다. 하천을 유한 요소화 하는 전처리 과정은 전체 해석 과정을 자동화 하는데 있어 필수적인 요소이며, 주로 삼각 요소망 또는 사각 요소망을 이용하여 해석을 수행하게 된다. 삼각 요소망의 경우 상대적으로 자동화하기 쉬운 반면 사각 요소망의 생성은 절점 생성 자체가 삼각 요소망 보다 더 많은 기하학적 제한 요소를 가지고 있기 때문에 상대적으로 완성도 높은 알고리즘을 구현하기가 어렵다 할 수 있다. 이에 따라 본 연구에서는 2차원 상에서 사각 요소망(quadrilateral elements)을 생성할 수 있는 Paving method를 중심으로 한 요소망 생성 알고리즘에 대해 고찰하고, 국내 최초의 범용 수치해석 모형인 RAMS(River Analysis and Modeling System)에 적용하였다. Paving method는 1990년에 Blacker and Stephenson에 의해 제안되었으며, Sandia National Laboratories에 의해 완성되었다. Paving Method는 advancing front style의 요소망을 생성하게 되고, 바깥쪽에서 안쪽으로 element layer를 생성하면서 채워나간다. 본 연구에서는 기존의 요소망 생성 프로세스에서 element 삽입 전의 검증 기능을 강화한 새로운 버전의 paving method를 적용하엿다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.7
• /
• pp.2148-2158
• /
• 1996

Uncoupled, quasi-static and linear thermoviscoelastic problems are analyzed in time domain by the finite element approximation which is developed using the principle of virtual work and viscoelasticity matrices instead of shear and bulk relaxation functions as in usual formulations. The material is assumed to be isotropic, homegeneous and thermorheologically simple, which means that the temperature-time equivalence postulate is effective. The stress-strain laws are expressed by relaxation-type hereditary integrals. In spatial and time discritizations, isoparametric quadratic quadrilateral finite elements and linear time variations are adopted. For explicit derivations, the viscoelastic material is assumed to behave standard linear solid in shear and elastically in dilatation. Two-dimensional examples are solved under general temperature distributions T = T(x, t), and compared with other opproximate solutions to show the versatility of the presented analysis.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.20 no.7
• /
• pp.2067-2077
• /
• 1996

In adaptive finite element analysis, r- and h-methods are generally used on the basis of a discretization error estimator. In this paper, an rh-method is proposed as a new adaptive method which can improve the adaptivity performance by using both of them. This suggested rh-method moves nodal coordinates of initially given model to adjust element discretization errors and thereafter performes the h-method tdo obtain the specified accuracy of finite element solutions. Numerical experiments for various plane problems were performed using 4-noded isoparametric quadrilateral elements. As a result, the rh-method has been shown to be an accurate and efficient adaptive analysis method to obtain as improved solution.