• The Journal of the Acoustical Society of Korea
• /
• v.23 no.1E
• /
• pp.24-30
• /
• 2004

This study is aimed to evaluate a tunneling effect in the laboratory measurement of sound transmission loss. Based on the formulation for sound transmission loss of a finite panel in the presence of tunnel, variations of the sound transmission loss with the parameters of panel location and tunnel depth are investigated. In comparison with the transmission loss of a finite plate in an infinite rigid baffle, the maximum difference occurs in the laboratory measurement when the panel is placed at the center of the tunnel, while a better estimation of true transmission loss is obtained when the panel is located at either end.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2000.06a
• /
• pp.1627-1632
• /
• 2000

Recently, piezoelectric materials have attracted considerable attention because of its self-sensing and actuating properties. To model smart structures, numerical modeling of structures with piezoelectric devices is essential. As many factors affect the performance of smart structures, optimization of these parameters is necessary. In this paper, the shape design sensitivity analysis of the 3D piezoelectric and structural elements is developed and shape optimization is performed. For the evaluation of the sensitivity, the finite element method is used. For the shape sensitivity, the domain velocity field is calculated. An acoustic cavity model is presented as a numerical example to study the feasibility of the formulation. The continuum sensitivity is compared with the results of the finite difference method by ANSYS. And the sequential linear programming (SLP) algorithm is used as the optimization algorithm.

• Structural Engineering and Mechanics
• /
• v.34 no.1
• /
• pp.109-133
• /
• 2010

This paper addresses the modified Dynamic Relaxation algorithm, called mdDR by minimizing displacement error between two successive iterations. In the mdDR method, new relationships for fictitious mass and damping are presented. The results obtained from linear and nonlinear structural analysis, either by finite element or finite difference techniques; demonstrate the potential ability of the proposed scheme compared to the conventional DR algorithm. It is shown that the mdDR improves the convergence rate of Dynamic Relaxation method without any additional calculations, so that, the cost and computational time are decreased. Simplicity, high efficiency and automatic operations are the main merits of the proposed technique.

• Structural Engineering and Mechanics
• /
• v.25 no.5
• /
• pp.501-518
• /
• 2007

In this work, a new approach is developed for dynamic analysis of a composite beam with an interply crack, based on finite element solution of partial differential equations with the use of the COMSOL Multiphysics package, allowing for fast and simple change of geometric characteristics of the delaminated area. The use of COMSOL Multiphysics package facilitates automatic mesh generation, which is needed if the problem has to be solved many times with different crack lengths. In the model, a physically impossible interpenetration of the crack faces is prevented by imposing a special constraint, leading to taking account of a force of contact interaction of the crack faces and to nonlinearity of the formulated boundary value problem. The model is based on the first order shear deformation theory, i.e., the longitudinal displacement is assumed to vary linearly through the beam's thickness. The shear deformation and rotary inertia terms are included into the formulation, to achieve better accuracy. Nonlinear partial differential equations of motion with boundary conditions are developed and written in the format acceptable by the COMSOL Multiphysics package. An example problem of a clamped-free beam with a piezoelectric actuator is considered, and its finite element solution is obtained. A noticeable difference of forced vibrations of the delaminated and undelaminated beams due to the contact interaction of the crack's faces is predicted by the developed model.

• Structural Engineering and Mechanics
• /
• v.1 no.1
• /
• pp.87-102
• /
• 1993

A $C^{\circ}$ continuous finite element formulation of a higher order displacement theory is presented for predicting linear and geometrically non-linear in the sense of von Karman transient responses of composite and sandwich plates. The displacement model accounts for non-linear cubic variation of tangential displacement components through the thickness of the laminate and the theory requires no shear correction coefficients. In the time domain, the explicit central difference integrator is used in conjunction with the special mass matrix diagonalization scheme which conserves the total mass of the element and included effects due to rotary inertia terms. The parametric effects of the time step, finite element mesh, lamination scheme and orthotropy on the linear and geometrically non-linear responses are investigated. Numerical results for central transverse deflection, stresses and stress resultants are presented for square/rectangular composite and sandwich plates under various boundary conditions and loadings and these are compared with the results from other sources. Some new results are also tabulated for future reference.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.13 no.6
• /
• pp.2773-2778
• /
• 2012

Formulation of finite difference method for analyzing seepage under concrete dam was carried out in order to find out characteristics of flow net. For the situation without curtain, slope of equipotential line of nonhomogeneous soil is greater in the region which has higher value of coefficient of permeability. By comparing analysis results between the situations with locating curtain at the center portion and left end, velocity of flow along with the face of the right hand side of the curtain for the situation with left end curtain is lower than that for the situation with center curtain. Considering flow in the region of the right of the curtain, streamline for the situation with left curtain gets horizontal relatively.

• Journal of the Korean Society of Hazard Mitigation
• /
• v.10 no.1
• /
• pp.49-55
• /
• 2010

This study describes a development of GIS-based program called Debris Flow Analyzer for simulating the hazard extent of debris flow on the assumption that is uniform continuous, incompressible, unsteady. The Debris Flow Analyzer was designed to process debris flow numerical simulation with Finite Difference Formulation; smoothed DEM, slope, debris flow directions, extract valley, debris volume, water volume, debris flow moving speed, effective viscosity, dynamic friction coefficient. Also, it is expected that we can be improved the inform of debris flow hazard map by Google Earth.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.7 no.2
• /
• pp.105-116
• /
• 1996

The design and analysis of the transversely fed EMC(electromagnetically coupled) microstrip dipole have been accomplished by using the integral equation and MOM(method of moment)in frequency domain in order to find the current distribution of the dipole. In this study, we proposed the possibilities for design and analysis of EMC micro-strip dipole array antenna by means of calculating the current distribution of each dipole directly using the FDTD(finite difference time domain) method. In this case, we applied the formulation which is the finite difference expression of the Maxwell's integral equation. From the current distribution of each dipole, we calculated the far field electric component and showed that the calculation process and running time was reduced with respect to the method which calculates the radiation field with surface electric and magnetic current density.

• Geomechanics and Engineering
• /
• v.23 no.4
• /
• pp.365-379
• /
• 2020

One of the leading causes for the damage of various underground structures during an earthquake is soil liquefaction, and among this liquefaction-induced uplift of these structures is a major concern. In this study, finite-difference modelling is carried out to study the liquefaction-induced uplift of an underground structure of 5 m diameter (D) with and without the replacement of the in-situ fine sand around the structure with the coarse sand. Soil replacements are carried out by three methods: replacement of soil above the structure, around the structure, and below the structure. The soil behaviour is represented using the elastic-perfectly plastic Mohr-Coulomb model, where the pore pressures were computed using Finn-Byrne formulation. The predicted pore pressure and uplift of the structure due to sinusoidal input motion were validated with the centrifuge tests reported in the literature. Based on numerical studies, an empirical equation is developed for the determination of liquefaction-induced maximum uplift of the underground structure without replacement of the in-situ sand. It is found that the replacement of soil around the structure with 2D width and spacing of D can reduce the maximum uplift by 50%.

• Korea-Australia Rheology Journal
• /
• v.13 no.1
• /
• pp.37-45
• /
• 2001

Numerical simulation of coextrusion process of viscoelastic fluids within a die has been carried out. In the coextrusion process velocity profile at the outflow boundary is not known a priori, which makes it difficult to impose the proper boundary condition at the outflow boundary. This difficulty has been avoided by using the open boundary condition (OBC) method. In this study, elastic viscous stress splitting (EVSS) formulation with streamline upwind (SU) method has been used in the finite element method. In order to test the validity of the OBC method, comparison between the results of fully developed condition at the outlet and those of OBC has been made for a Newtonian fluid. In the case of upper convected Maxwell (UCM) fluid, the effect of outflow boundary condition on the interface position has been investigated by using two meshes having different downstream lengths. In both cases, the results with the OBC method showed reasonable interface shape. In particular, for the UCM fluid the interface shape calculated with OBC was independent of the downstream length, while the results with the zero traction condition showed oscillation of interface position close to the outlet. Viscosity difference was found to be more important than elasticity difference in determining the final interface position. However, the overshoot of interface position near the con-fluent point increased with elasticity.