• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.517-518
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• 2006

Transient and asymmetric density distributions have been investigated by three-dimensional digital speckle tomography with a novel integration method. Multiple CCD images captured movements of speckles in three angles of view simultaneously because the flows were asymmetric and unsteady. The speckle movements which have been formed by a ground glass between no flow and downward butane flow from a circular half opening have been calculated by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. A novel integration method has been developed to obtain projection data from the deflection angles for the speckle tomography.'The three-dimensional density fields have been reconstructed from the accurate projection values by a real-time multiplicative algebraic reconstruction technique (MART) with the developed integration method.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.465-470
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• 2003

In this study, the state-space Newmark method based on average velocity is presented to analyse the transient dynamic response for general dynamic system. The conventional Newmark method based on average acceleration cannot he directly to the first-order state-space differential equations introducing the state-space vector. To overcome this problem, the time-step integration algorithm, based on average velocity concept, suitable for the first-order state-space differential equations is proposed In results, the proposed method has %he numerical stability and order of accuracy, which is proved analytically, equal to those of the conventional Newmark method based on average acceleration. Also, the formulation for numerical solution is very simple and the calculation time Is nearly equal to that of the conventional Newmark method based on average acceleration in spite of an increase of two times over matrix size. This method will be look forward to applying the general dynamic system to calculate the transient dynamic response.

• Structural Engineering and Mechanics
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• v.26 no.5
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• pp.545-556
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• 2007

In this paper, a hybrid boundary element technique is implemented to analyze nonlinear transient pile soil interaction in Gibson type nonhomeogenous soil. Inelastic modeling of soil media is presented by introducing a rational approximation to the continuum with nonlinear interface springs along the piles. Modified $\ddot{O}$zdemir's nonlinear model is implemented and systems of equations are coupled at interfaces for piles and pile groups. Linear beam column finite elements are used to model the piles and the resulting governing equations are solved using an implicit integration scheme. By enforcing displacement equilibrium conditions at each time step, a system of equations is generated which yields the solution. A numerical example is performed to investigate the effects of nonlinearity on the pile soil interaction.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.497-502
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• 2004

This paper presents applications of the objective stress rates to stress update algorithms for transient shell dynamic analysis within the context of explicit time integration. The hypo elasto-plastic materials are assumed in establishing constitutive equations. The derivation of the objective stress rates are investigated by use of the Lie derivative. Comparison results are given between the Kirchhoff and Cauchy stress formulation. The Jacobian determination algorithm proposed in this paper is presented in association with the Belytschko-Lin-Tsay shell theory. Several numerical examples are demonstrated including contact and non-contact examples, by which proposed algorithms are compared with respect to the accuracy and effectiveness.

• 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.

• Earthquakes and Structures
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• v.14 no.1
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• pp.45-53
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• 2018

A family of the structure-dependent methods seems very promising for time integration since it can simultaneously have desired numerical properties, such as unconditional stability, second-order accuracy, explicit formulation and numerical dissipation. However, an unusual overshoot, which is essentially different from that found by Goudreau and Taylor in the transient response, has been experienced in the steady-state response of a high frequency mode. The root cause of this unusual overshoot is analytically explored and then a remedy is successfully developed to eliminate it. As a result, an improved formulation of this family method can be achieved.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.8
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• pp.1180-1185
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• 2015

This paper describes the accurate inductance measurement of a switched reluctance motor (SRM). Conventionally, the inductance of the SRM is measured using the equivalent circuit of a stator phase or time constant of exponential current transient. This paper presents an effective method to measure the SRM inductance accurately and rapidly using automated voltage integration. The proposed method is validated experimentally by comparison with the existing equivalent circuit method (ECM) and the FEA(finite element analysis) simulation.

• Nuclear Engineering and Technology
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• v.52 no.2
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• pp.230-237
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• 2020

In this part, an implicit time dependent solution is presented for the Boltzmann transport equation discretized by the analytic coarse mesh finite difference method (ACMFD) over the spatial domain as well as the simplified P₃ (SP₃) for the angular variable. In the first part of this work we proposed a SP₃-ACMFD approach to solve the static eigenvalue equations which provide the initial conditions for temp dependent equations. Having solved the 3D multi-group SP₃-ACMFD static equations, an implicit approach is resorted to ensure stability of time steps. An exponential behavior is assumed in transverse integrated equations to establish a relationship between flux moments and currents. Also, analytic integration is benefited for the time-dependent solution of precursor concentration equations. Finally, a multi-channel one-phase thermal hydraulic model is coupled to the proposed methodology. Transient equations are then solved at each step using the GMRES technique. To show the sufficiency of proposed transient SP₃-ACMFD approximation for a full core analysis, a comparison is made using transport peers as the reference. To further demonstrate superiority, results are compared with a 3D multi-group transient diffusion solver developed as a byproduct of this work. Outcomes confirm that the idea can be considered as an economic interim approach which is superior to the diffusion approximation, and comparable with transport in results.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.122-124
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• 2003

Power system analysis is generally based on computer simulation and time-domain simulation is used to assess it's dynamic performance. This paper deals with the selection of proper integration engine for large-scale power system dynamic simulation. Simulation results obtained from the selected algorithm are compared to those of commercial program.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.4
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• pp.375-382
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• 2008

The particular integral formulation for two(2D) and three(3D) dimensional inelastic transient dynamic stress analysis is presented. The elastostatic equation is used for the complementary solution. Using the concept of global shape function, the particular integrals for displacement and traction rates are obtained to approximate acceleration of the inhomogeneous equation. The Houbolt time integration scheme is used for the time-marching process. The Newton-Raphson algorithm for plastic multiplier is used to solve the system equation. Numerical results of four example problems are given to demonstrate the validity and accuracy of the present formulation.