• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.5
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• pp.460-469
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• 2010

This paper presents the analysis of a time reversal process for $A_0$ Lamb wave mode($A_0$ mode) on a rectangular plate. The dispersion characteristic equation of the $A_0$ mode is approximated using the Timoshenko beam theory. A virtual sensor array model is developed to consider the effects of reflections occurring on the plate boundary on the time reversal process. The time reversal process is formulated in the frequency domain using the virtual sensor array model. The reconstructed signal is obtained in the time domain through an inverse fast Fourier transform. The validity of the proposed method is demonstrated through the comparison to the numerical simulation results computed by the finite element analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.30 no.2
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• pp.58-67
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• 2018

This study investigated the effect of variation in the angle of the elliptic cylinder as well as the presence of circular cylinder on natural convection inside a square enclosure. The Rayleigh number was varied between $10^3$ and $10^6$, and the Prandtl number was fixed to 0.7. In the present study, the angle of the elliptic cylinder was changed from $0^{\circ}$ to $90^{\circ}$, and the perimeter of the elliptic cylinder was same as that of the circular cylinder. The immersed boundary method was used to capture the virtual wall boundary of the inner cylinder. With the increasing angle of the elliptic cylinder, the surface-averaged Nusselt numbers on the cylinder and the enclosure increased. In the Rayleigh number range considered in the present study, the surface-averaged Nusselt number on the elliptic cylinder over = $45^{\circ}$ was higher than that of the circular cylinder. The effect of elliptic cylinder's angle on natural convection in the enclosure was analyzed according to the flow and thermal fields, and the distributions of the Nusselt number.

• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3491-3500
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• 2024

In this work, the hybrid vibro-acoustic model reduction technique that is a physical-modal combined formulation is proposed to accelerate the finite element model updating process of the vibro-acoustic pipeline system. Particularly, the new formulation could provide an effective way of the model updating by preserving the physical DOFs for the direct calibration of the undetermined boundary conditions. The sensitivity based vibro-acoustic model updating is first conducted, and then the undetermined spring constant at the displacement boundary condition is then directly and effectively calibrated by using the proposed hybrid model reduction formulation. The proposed method is implemented in the real nuclear facility to evaluate its performance. In addition, an experimental implementation test using the inverse force identification process is also conducted to demonstrate the reliability of the generated vibro-acoustic FE model through the proposed method.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.272-276
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• 2007

In this paper, we researched a parametric study in flow control system using louver with numerical method. Generally, for the large fans with constant rotational speed, the louver can be used to control the flow rate. The opening and closing of louver can make a some change of flow properties generated by a large fan. To develope the relation between the opening angle of louver and flow rate(or pressure difference), we simulated the flow past the modelled louver installed in a virtual wind tunnel. For the various angles, the mean flow properties are investigated and parameterized with a given boundary condition. The research result can be used directly to design the flow control system of large constant-speed fans, which are often applied to petrolic refinery system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.4
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• pp.1813-1818
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• 2014

This paper presents the stability analysis of the haptic system including a human impedance using the Routh-Hurwitz criterion. The reflective force is computed from a virtual spring model and is transferred to a human operator using the first-order-hold method. The stability boundary conditions are induced and the relation among a virtual spring ($K_w$), the mass ($M_h$), the damping ($B_h$) and the stiffness ($K_h$) of a human impedance is analyzed. Hence the stability boundary of the virtual spring ($K_w$) is proposed as $K_w{\leq}54413{\sqrt{(M_h+M_d)(B_h+B_d)}}-0.486K_h$ when the sampling time is 1 ms. The average relative error is about 0.5% when the mathematical analysis results are compared with the results of the stability boundary model.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.891-896
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• 2007

Noise radiated from the powertrain is an important factor of the vehicle interior noise. In this paper, Finite Element(FE) model and Boundary Element(BE) models were created. The FE model was updated by doing a correlation between experimental modal analysis(EMA) values and finite element analysis(FEA) values. Main bearing forces were calculated using a running modal data. The forced vibration analysis was simulated using the software MSC/NASTRAN, and the radiated noise was predicted using the software LMS/VIRTUAL.LAB.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.93-107
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• 2017

The article presents the vibration and acoustic responses of un-baffled doubly curved laminated composite panel structure under the excitation of a harmonic point load. The structural responses are obtained using a simulation model via ANSYS including the effect various geometries (cylindrical, elliptical, spherical and hyperboloid). Initially, the model has been established by solving adequate number of available examples to show the convergence and comparison behaviour of the natural frequencies. Further, the acoustic responses are obtained using an indirect boundary element approach for the coupled fluid-structure analysis in LMS Virtual.lab by importing the natural frequency values. Subsequently, the values for the sound power level are computed using the present numerical model and compared with that of the available published results and in-house experimentally obtained data. Further, the acoustic responses (mean-square velocity, radiation efficiency and sound power level) of the doubly curved layered structures are evaluated using the current simulation model via several numerical experimentations for different structural parameters and corresponding discussions are provided in detail.

• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.79-88
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• 1999

The purpose of this paper is to develop a mathematical expression for computing crack angles based on reinforcement volumes in the longitudinal and transverse directions, member end-fixity and length-to-width aspect ratio. For this a reinforced concrete beam-column element is assumed to possess a series of potential crack planes represented by a number of differential truss elements. Depending on the boundary condition, a constant angle truss or a variable angle truss is employed to model the cracked structural concrete member. The truss models are then analyzed using the virtual work method of analysis to relate forces and deformations. Rigorous and simplified solution schemes are presented. An equation to estimate the theoretical crack angle is derived by considering the energy minimization on the virtual work done over both the shear and flexural components the energy minimization on the virtual work done over both the shear and flexural components of truss models. The crack angle in this study is defined as the steepest one among fan-shaped angles measured from the longitudinal axis of the member to the diagonal crack. The theoretical crack angle predictions are validated against experimentally observed crack angle reported by previous researchers in the literature. Good agreement between theory and experiment is obtained.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.7
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• pp.1294-1306
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• 1992

In order to determine the design parameters and processing conditions in injection molding, it is very important to establish the theoretical model with scientific base. In this study, a two dimensional model has been developed for the purpose and flow simulations of filling process are carried out. The moving boundary transient flow problem along the flat plane is solved efficiently by the Iterative Boundary Pressure Reflection Method which rearranges the impinged melt front along the physical boundary in scientific manner. The two dimensional modeling of filling process is applied to two examples : a three dimensional cover with two screw holes and a two-gated flat cavity with unbalanced runners. The numerical results show good agreement with experimental short shots, especially for the weldline locations and the pressure traces at various locations. They also provide the temperature, clamp force, and velocity field in the mold at different times during filling of cavity.

• Structural Engineering and Mechanics
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• v.81 no.6
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• pp.769-780
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• 2022

This paper studies the dynamic behavior of laminated composite circular cylindrical shells interacting with a fluid. The mathematical formulation of the dynamic problem for an elastic body is developed based on the variational principle of virtual displacements and the relations of linear elasticity theory. The behavior of an ideal compressible fluid is described by the potential theory, the equations of which together with boundary conditions are transformed to a weak form. The hydrodynamic pressure exerted by the fluid on the internal surface of the shell is calculated according to the linearized Bernoulli equation. The numerical implementation of the mathematical formulation has been done using the semi-analytical finite element method. The influence of the ply angle and lay-up configurations of laminated composites on the natural vibration frequencies and the hydroelastic stability boundary have been analyzed for shells with different geometrical dimensions and under different kinematic boundary conditions set at their edges. It has been found that the optimal value of the ply angle depends on the level of filling of the shell with a fluid. The obtained results support the view that by choosing the optimal configuration of the layered composite material it is possible to change upwards or downwards the frequency and mode shape, as well as the critical velocity for stability loss over a wide range.