• Structural Engineering and Mechanics
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• v.10 no.2
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• pp.157-164
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• 2000

This paper discusses the error propagation characteristics of the Newmark explicit method, modified Newmark explicit method and ${\alpha}$-function dissipative explicit method in pseudodynamic tests. The Newmark explicit method is non-dissipative while the ${\alpha}$-function dissipative explicit method and the modified Newmark explicit method are dissipative and can eliminate the spurious participation of high frequency responses. In addition, error propagation analysis shows that the modified Newmark explicit method and the ${\alpha}$-function dissipative explicit method possess much better error propagation properties when compared to the Newmark explicit method. The major disadvantages of the modified Newmark explicit method are the positive lower stability limit and undesired numerical dissipation. Thus, the ${\alpha}$-function dissipative explicit method might be the most appropriate explicit pseudodynamic algorithm.

• Transactions of the Korean Society of Automotive Engineers
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• v.3 no.3
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• pp.19-28
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• 1995

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solutions since it improves the convergency problem, memory size and computational time especially for the case of complicated geometry and large element number. The explicit schemes in general use are based on the elastic-plastic modelling of material requiring large computation time. In the present work, rigid-plastic explicit finite element method is introduced for analysis of sheet metal forming processes in which plane strain normal anisotropy condition can be assumed by dividing the whole piece into sections. The explicit scheme is in good agreement with the implicit scheme for numerical analysis and experimental results of auto-body panels. The proposed rigid-plastic explicit finite element method can be used as robust and efficient computational method for prediction of defects and forming severity.

• Journal of the Korean housing association
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• v.15 no.3
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• pp.93-99
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• 2004

This study was conducted to estimate the solar energy, as an alternative energy evaluating an effect of solar radiation on indoor space of residential building. The basic data of solar radiation which is useful for architectural design was suggested using theoretical and experimental analysis. Accordingly, this study was carried out measuring the solar energy using Explicit Method. These results were compared with the results using steady state heat transfer method. The results of this study are summarized as follows; Based on the results using Explicit Method and steady state heat transfer on the indoor space of building, it was shown that an analysis on heat transfer using Explicit Method is more sensitive to the outdoor environmental changes. The results using Explicit Method to analysis and evaluate the solar radiation should be used for residential building design.

• The KIPS Transactions:PartA
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• v.13A no.2 s.99
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• pp.177-184
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• 2006

Since well-known explicit methods for cloth simulation were regarded unstable for large time steps or stiff springs, implicit methods have been proposed to achieve the stability. Large time step makes the simulation fast, and large stiffness enables a less elastic cloth property. Also, there have been efforts to devise so-called semi-implicit methods to achieve the stability and the speed together. In this paper we improve Kang's method (Kang and Cho 2002), and thus devise a scalable method for cloth simulation that varies from an almost explicit to a full implicit method. It is almost as fast as explicit methods and, more importantly, almost as stable as implicit methods allowing large time steps and stiff springs. Furthermore, it has a less artificial damping than the previously proposed semi-implicit methods.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.783-788
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• 2000

Hydroforming is a method for forming circular tubes. If this technology is to be applied economically, it is essential to have knowledge of the avoidance of failure cases as well as of the behavior of the tube in the tool under the compressive stress and forces that are exerted by the machine. A finite element simulation for manufacturing of lower arm from straight tubes, using the hydroforming method, was performed to investigate the effects of varying process parameters. Explicit method is used to simulate hydroforming in many cases, but that is not included flow rule. And then it needs simulation for implicit method. It was simulated by two methods, implicit and explicit, to compare the result of the hydroforming.

• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1687-1692
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• 2002

The problem analyzed here is a sheet metal forming process which requires a drawbead. The drawbead provides the sheet metal enough tension to be deformed plastically along the punch face and consequently, ensures a proper shape of final products by fixing the sheet to the die. Therefore, the optimum design of drawbead is indispensable in obtaining the desired formability. A static-explicit finite element analysis is carried out to provide a perspective tool for designing the drawbead. The finite element formulation is constructed from static equilibrium equation and takes into account the boundary condition that involves a proper contact condition. The deformation behavior of sheet material is formulated by the elastic-plastic constitutive equation. The finite element formulation has been solved based on an existing method that is called the static-explicit method. The main features of the static-explicit method are first that there is no convergence problem. Second, the problem of contact and friction is easily solved by application of very small time interval. During the analysis of drawbead processes, the strain distribution and the drawing force on drawbead can be analyzed. And the effects of bead shape and number of beads on sheet forming processes were investigated. The results of the static explicit analysis of drawbead processes show no convergence problem and comparatively accurate results even though severe high geometric and contact-friction nonlinearity. Moreover, the computational results of a static-explicit finite element analysis can supply very valuable information for designing the drawbead process in which the defects of final sheet product can be removed.

• Structural Engineering and Mechanics
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• v.85 no.5
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• pp.607-620
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• 2023

The classical optimal control (COC) method has been widely used for linear quadratic regulator (LQR) problems of structural control. However, the equation of motion of the structure is incorporated into the optimization model as the constraint condition for the LQR problem, which needs to be solved through the Riccati equation under certain assumptions. In this study, an explicit optimal control (EOC) method is proposed based on the explicit time-domain method (ETDM). By use of the explicit formulation of structural responses, the LQR problem with the constraint of equation of motion can be transformed into an unconstrained optimization problem, and therefore the control law can be derived directly without solving the Riccati equation. To further optimize the weighting parameters adopted in the control law using the gradient-based optimization algorithm, the sensitivities of structural responses and control forces with respect to the weighting parameters are derived analytically based on the explicit expressions of dynamic responses of the controlled structure. Two numerical examples are investigated to demonstrate the feasibility of the EOC method and the optimization scheme for weighting parameters involved in the control law.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.206-211
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• 1993

The explicit scheme for finite element analysis of sheet metal forming problems has been widely used for providing practical solution since it improves the convergency problem,memory size and computational time especially for the case of complicated geometry and large element number. In the present work, a basic formulation for rigid-plastic explicit finite element analysis of plain strain sheet metal forming problems has been proposed. The effect of some basic parameters involved in the dynamic analysis has been studied in detail. A direct trial-and-error method is introduced to treat contact and friction. In order to show the validity and effectiveness of the proposed explicit scheme, computation are carried out for cylindrical punch stretching and the computational results are compared with those by the implicit scheme as well as with a commercial code. The proposed rigid-plastic explicit element method can be used as a robust and efficient computational method for analysis of sheet method forming.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.145-162
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• 1995

A damped trapezoidal rule method for numerical time-integration is presented, and its application in analyses of dynamic response of damped structures is discussed. It is shown that the damped trapezoidal rule method has features that make it an attractive approach for applications in dynamic analyses of structures. Accuracy and stability analyses are developed for the damped single-degree-of-freedom systems. Error analyses are also performed for the Newmark beta method and compared with the damped trapezoidal rule method as a basis for discussion of the relative merits of the proposed method. The procedure is fully explicit and easy to implement. However, since the method is an explicit method, it is conditionally stable. The methodology is applied to several example problems to illustrate its strengths, limitations and inherent simplicity.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.10-22
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• 1998

In the present work the elastic-plastic FE formulations using dynamic explicit time integration schemes are used for numerical analysis of a large auto-body panel stamping processes. For analyses of more complex cases with larger and more refined meshes, the explicit method is more time effective than implicit method, and has no convergency problem and has the robust nature of contact and friction algorithms while implicit method is widely used because of excellent accuracy and reliability. The elastic-plastic scheme is more reliable and rigorous while the rigid-plastic scheme require small computation time. In finite element simulation of auto-body panel stamping processes, the roobustness and stability of computation are important requirements since the computation time and convergency become major points of consideration besides the solution accuracy due to the complexity of geometry conditions. The performnce of the dynamic explicit algorithms are investigated by comparing the simulation results of formaing of complicate shaped autobody parts, such as a fuel tank and a rear hinge, with the experimental results. It has been shown that the proposed dynamic explicit elastic-plastic finite element method enables an effective computation for complicated auto-body panel stamping processes.