• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.117-121
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• 2005

In this paper, an approximate time-effective approach to rigid-plastic finite element method is presented with its solution scheme and a volume compensation method is proposed to simulate rotary forging processes. The applicability is examined by comparing the results obtained by the presented approach with those by the conventional approach. The approach is applied to simulation of a rotary forging process fur a wheel bearing assembly. The analyzed results are compared with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.2
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• pp.322-330
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• 1987

Isotropic linear viscoelasticity problems are analyzed numerically in time domain by Boundary Element Method with quadratic isoparametric boundary elements. Viscoelastic fundamental solutions are newly derived by using the elastic-viscoelastic correspondence principle and corresponding boundary integral equations are also presented. Numerical results of two examples are compared with the derived exact solutions to verify the accuracy and validity of the method. A detailed study on the accuracy of displacement and stress in terms of time integration step is given.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.10
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• pp.1995-1999
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• 2009

A partial discharge(PD) measurement is a very effective method to assess the insulation condition of high-voltage machines. It is necessary that the life time of the on-line PD measurement sensor is assessed. Therefore, the electrical life time assessment method of ceramic element was reviewed in order to estimate the life time of the on-line PD measurement sensor. The samples were prepared according to the reviewed method and were tested at 8kV, 9kV and 10kV. Based on the obtained results, the life time constant is shown above 59. Also, it is assumed that the estimated life time constant can be used to anticipate the life time and to assess the conformity of the on-line PD measurement sensor.

• Journal of Power Electronics
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• v.15 no.2
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• pp.431-442
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• 2015

Dead-time element must be set into space vector pulsed width modulation signals to avoid short circuits of the inverter. However, the dead-time element distorts the output voltage vector, which deteriorates the performance of electrical machine drive system. In this paper, dead-time effect and its compensation control strategy are analyzed. Based on the analysis, the voltage distortion caused by dead-time is regarded as two disturbances imposed on dq axes in the rotor reference frame, which degenerates the current tracking performance. To inhibit the adverse effect caused by the dead-time, a control scheme using two linear extended state observers is proposed. This method provides a strong ability to suppress dead-time effects. Simulations and experiments are conducted on a permanent magnet synchronous motor drive system to demonstrate the effectiveness of the proposed method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.85-89
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• 2005

For the analysis of a vibrating two dimensional structure such as the simply supported rectangular plate, Spectral Finite Element Method (SFEM) has been studied. Under the condition that two parallel edges are simply supported at least and the other two edges can be arbitrary, Spectral Finite Element has been developed. Using this element SFEM is applied to the vibrating rectangular plate which all edges are simply supported, and obtain the frequency response function in frequency domain and the dynamic response in time domain. To evaluate these results normal mode method and finite element method (FEM) are also accomplished and compared. It is seen that SFEM is more powerful analysis tool than FEM in high frequency range.

• Structural Engineering and Mechanics
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• v.57 no.3
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• pp.389-402
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• 2016

Based on the traditional mechanical model of thin-walled straight beam, the paper makes analysis and research on the pre-twisted thin-walled beam finite element numerical model. Firstly, based on the geometric deformation differential relationship, the Saint-Venant warping strain of pre-twisted thin-walled beam is deduced. According to the traditional thin-walled straight beam finite element mechanical model, the finite element stiffness matrix considering the Saint-Venant warping deformations is established. At the same time, the paper establishes the element stiffness matrix of the pre-twisted thin-walled beam based on the classic Vlasov Theory. Finally, by calculating the pre-twisted beam with elliptical section and I cross section and contrasting three-dimensional solid finite element using ANSYS, the comparison analysis results show that pre-twisted thin-walled beam element stiffness matrix has good accuracy.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.789-794
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• 2007

Recently, the necessity of efficient and exact method to analyze structures is increasing with the importance of the seismic analysis. But the finite element method used in many field do not give the exact solution unless the length of the element is very short enough to represent the deformation of the element. Because the amount of computer calculation increase with the increasing of the number of degree of freedoms, the finite element method for the exact dynamic analysis of structures would not be efficient. To solve these problems, spectral clement method combined spectral method using the principle of wave mechanics and finite element method for the analysis of discrete models is applied to evaluate the behavior of the spatial structures. As a result of analysis. it becomes clear that the spectral element method is faster and more exact than the finite clement method.

• Transactions of Materials Processing
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• v.3 no.2
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• pp.156-166
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• 1994

An arbitrary Lagrangian-Eulerian (ALE) finite element method has been developed. The finite element formation is derived and implemented for rigid-viscoplastic materials. The developed computer program is applied to the analysis of axisymmetric square die extrusion, which has many difficulties with updated Lagrangian approach. The results are compared with those from updated Largrangian approach. The results are compared with those from updated Lagrangian finite element program. Updating scheme of time dependent variables and mesh control are also examined.

• Structural Engineering and Mechanics
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• v.24 no.6
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• pp.683-698
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• 2006

The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient procedure is proposed which simplifies this procedure amazingly, and results in great computational time saving. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that efficient procedure is incredibly accurate under all practical conditions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.1-10
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• 1991

Two-dimensional explicit finite element code was developed. The transient dynamics code can analyse large deformations of non-linear materials subjected to extremely high strain rates. The Lagrangian finite element program uses an explicit time integration operator to integrate the equations of motion, thus the stiffness matrix is not introduced. Cylinder upsetting and ring compression problems are simulated to check the effects of friction and inertia force. It is shown that (1) calculated results agree very well with experimental results, (2) constant shear friction method overestimates the decrease of inner ring radius and then underestimates after on in comparison with the Coulomb friction method, and (3) the effect of the increase in initial strain rate is similar to the effect of higher frictional coefficient.