• Transactions of Materials Processing
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• v.8 no.1
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• pp.22-28
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• 1999

The explicit and implicit time integration methods are applied effectively to analyze sheet metal stamping processes, which include the forming stage and the springback stage consecutively. The explicit time integration method has better merits in the forming stage including highly complicated three-dimensional contact conditions. By contrary, the implicit time integration method is better for analyzing springback since the complicated contact conditions are removed and the computing time to get the final static state is short. In this work, brief descriptions of the formulation and the factor study for springack simulations are presented. Further, the simulated results for the S-rail and the roof panel stamping processes are shown and discussed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.136-140
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• 2000

It is desirable to predict springback quantitatively and accurately for the tool and process design in sheet stamping operations, however, it is blown very difficult. The result of springback analysis by the finite element method is sensitively influenced by numerical factors such as blank element size, number of integration point, punch velocity, contact algorithm etc. In the present work, a parametric study by Taguchi method is performed in order to evaluate the influence of numerical factors on springback Quantitatively and to obtain the combination of numerical factors which yields the best approximation to experimental data. Since springback is determined by the residual stress after forming process, it is important to evaluate stress distribution accurately. The oscillation in the time history curve of stress obtained by explicit FEM says that the stress solution at termination time is in very unstable state. Therefore, a variability study is also carried out in this study in order to assess the stability of implicit springback analysis starting from the stress solution by explicit forming simulation. The 2D draw bending process, one of the NUMISHEET '93 benchmark problems, is adopted as an application model.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.4
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• pp.1-9
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• 2012

Dynamic application lower mode response is of interest, however the higher modes of spatially discretized equations generally do not represent the real behavior. Some implicit algorithms, therefore, are introduced to filter out the high-frequency modes. The objective of this study is to introduce the P-method and PC ${\alpha}$-method to compare that with dissipation method and Newmark method through the stability analysis and numerical example. PC ${\alpha}$-method gives more accuracy than other methods because it based on the ${\alpha}$-method inherits the superior properties of the implicit ${\alpha}$-method. In finite element analysis, the PC ${\alpha}$-method is more useful than other methods because it is the explicit scheme and it achieve the second order accuracy and numerical damping simultaneously.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.9
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• pp.74-81
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• 2002

Recently tube hydroforming has been widely applied to the automotive industries due to its several advantages over conventional methods. In this paper, attention is paid to comparison of an implicit and an explicit finite element method widely used for numerical simulation of a hydroforming process. For an explicit FEM, a huge amount of computational time is required because of the very small time increment to solve a quasi-static problem. Hence, when an explicit FEM is used fDr a hydroforming process, it is general to convert the real problem to a virtual problem with a different processing time and mass density by appropriate scaling factor. However it is difficult to figure out how large the scaling should be adopted enough to ignore the dynamic effects and maintain the desired accuracy. In this paper, the comparison of the results obtained from both methods focus on the accuracy of the predicted geometrical shape and the stress with various scaling factors which are applied to analyze hydroforming process of an automobile lower arm.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.625-628
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• 1995

A static/implicit finite element code for sheet forming (ITAS3D) is parallelized on IBM SP 6000 multi-processor computer. Computing-load-balanced domain decomposition method and the direct solution method at each subdomain (and interface) equation are developed. The system of equations for each subdomain are constructed by condensation and calculated on each processor. Approximated operation counts are calculated to set up the nonlinear equation system for balancing the compute load on each subdomain. Th esquare cup tests with several numbers of elements are used in demonstrating the performance of this parallel implementation. This procedure are proved to be efficient for moderate number of processors, especially for large number of elements.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.989-996
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• 2001

High-speed and low-speed flows are simulated numerically by flowfield-dependent mixed explicit-implicit (FDMEI) method. This algorithm depends on implicitness parameters of convection, diffusion, diffusion gradients, and source terms which are calculated from the changes of local Mach, Reynolds, Peclet, and Damkohler numbers between adjacent nodes. Convection phenomena or shock waves are resolved from Mach number-dependent implicitness parameters whereas diffusion or viscous actions are simulated by Reynolds number or Peclet number-dependent implicitness parameters. Fluctuation components of all variables are properly accommodated spatially and temporally in the FDMEI procedure. To illustrate, some benchmark example problems are presented for comparisons of the FDMEI results with other available data. These results appear to be encouraging and point toward the need for further investigations of the FDMEI theory.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.369-379
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• 2023

Reliability-Based Design Optimization (RBDO) is an appropriate framework for obtaining optimal designs by taking uncertainties into account. Large-scale problems with implicit limit state functions and problems with discrete design variables are two significant challenges to traditional RBDO methods. To overcome these challenges, this paper proposes a hybrid method to perform RBDO of structures that links Firefly Algorithm (FA) as an optimization tool to advanced (finite element) reliability methods. Furthermore, the Genetic Algorithm (GA) and the FA are compared based on the design cost (objective function) they achieve. In the proposed method, Weighted Simulation Method (WSM) is utilized to assess reliability constraints in the RBDO problems with explicit limit state functions. WSM is selected to reduce computational costs. To performing RBDO of structures with finite element modeling and implicit limit state functions, a First-Order Reliability Method (FORM) based on the Direct Differentiation Method (DDM) is utilized. Four numerical examples are considered to assess the effectiveness of the proposed method. The findings illustrate that the proposed RBDO method is applicable and efficient for RBDO problems with discrete and continuous design variables and finite element modeling.

• Proceedings of the Korea Water Resources Association Conference
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• 1982.07a
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• pp.91-98
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• 1982

The formulation of depth-averaged two-dimensional mathematical model for the analysis of tide induced circulation in a harbor by the Galerkin finite element techique is presented. In integration of the Galerkin approach in time both explicit and implicit method have been tested for one and two dimentional water bodies, and the two step Lax-Wendroff explicit method is found to be effective than the implicit in reducing computing time. The essential characteristics of the tide induced flow in Busan Harbor with two open boundaries has been foccud to be reproduceable in the numerical model and the simulated results encourage that the model can be used as a predictive tool.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.53-58
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• 2017

In this paper, we propose a new method to debond between mixed finite elements for porous media in ABAQUS (2014). ABAQUS just provides debonding algorithm for the u-p model using cohesive elements in standard version. However, this approach has a drawback that it is hard to simulate complex debonding problems like element separation, rigid body motion, and contact between separated elements in standard version. ABAQUS-explicit can resolve these complex problems, but cohesive elements for the u-p model cannot be applied. We introduce a new algorithm for debonding for porous media instead of using cohesive elements. In this method, subroutines VUMAT to apply constitutive models and VDISP to separate elements in ABAQUS are used to simulate debonding problems. In addition, a simple 2-D example is demonstrated in the ABAQUS-explicit solver.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.38-47
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• 2000

Recently, finite element method has been used as an effective tool in the design process of sheet metal forming. In the present study, an implicit method and an explicit method have been developed for 2D analysis and 3D analysis, respectively, and applied to several processes including plane strain draw bending and TWB sqaure cup drawing. Also, commercial codes are used for geometrically complex problems, such as tube hydroforming, "L" cup deep drawing and side frame forming. In this paper, basic formulations used in the methods are introduced and results obtained from the applications are discussed.discussed.