• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.629-640
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• 2007

In this paper an analytical study is carried out to improve the capacity of absorbing boundary using dashpot, one of the most widely used absorbing boundaries in FEM. Using 2-D harmonic plane wave equation, absorbing boundary condition is modified to maximize its capacity according to the incident angle. Validity of the absorbing boundary conditions which is modified is investigated by adopting the solution of Miller and Pursey. The Miller and Pursey's problem is then numerically simulated using the finite element method. The absorption ratios are calculated by comparing the displacements at the absorbing boundary to those at the free field without the absorbing boundary. The numerical study is carried out through comparison of displacement at the interior region and the boundary of the numerical model.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2751-2761
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• 1994

A numerical investigation on the three-dimensional laminar natural convection heat transfer in the periodically fully developed PCB channel has been performed. When heat generating blocks mounted on the adiabatic wall make a channel with their facing shrouding wall, the flow inside the channel becomes periodically fully developed. A single module in the periodically fully developed region is chosen for computational domain in order to save computer storage and computational time. The periodic boundary condition is applied in the anlaysis. The effects of the parameters such as the Rayleigh number, the number of the modules, and the height of channel are examined to obtain the optimum condition for the enhancement of the cooling effectiveness. The result shows that the cooling effect is improved with increasing Rayleigh number and channel height, and decreasing the number of the module. The result also indicates that increasing the height of the channel and number of the module is recommended for a limited space.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.9 no.2
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• pp.63-71
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• 1989

The objective of this study is to enhance the reliability of the computed results by setting up of an improved treatments onto the open boundary condition for tidal motion in finite domain. By the $L^2-norm$ and RMS error tests, it was revealed that Sommerfeld's radiating condition gives better result than a forced boundary condition. In the numerical tests for a long wave in a simplified rectangular bay, it was found that the computational accuracy of the newly improved technique to the Sommerfeld condition, suggested in this study with the 2 dimensional shallow finite element model, could be improved by 30% of RMS error to the existing Sommerfeld condition.

• Journal of Energy Engineering
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• v.21 no.2
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• pp.138-143
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• 2012

The present study has been carried out to elucidate the unsteady temperature characteristics of a refrigerator near gasket region by measuring time dependent temperature measurements. From the measured values of the time dependent temperature inside and outside region of a refrigerator, one could see that the temperature varies periodically with time from the effect of refrigerator operation. The measured mean temperatures at the wall had great different value from the previous other research results conducted by numeric ofheat transfer using improperfheat transfer boundary condition. The present study could give the experiment ofdata for the properfnumeric ofheat transfer an oysis and suggest more accuratefheat transfer boundary conditions for the inside and outside of a refrigerator.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.3
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• pp.440-448
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• 1999

This paper describes a full wave analysis of the scattering from electromagnetic absorbers which can be approximated as infinite periodic structure using hybrid finite element method. By introducing fictitious boundaries, equivalent finite region is defined and proper boundary conditions of each boundary are obtained by Floquet theorem. Since higher-order Floquet modes are employed, the method presented in this paper can be readily applied to the periodic structure haying a relatively long period. To reduce difficulty in evaluating the surface integral, the normal component to the surface were represented with the tangential component to the surface. Comparisons of calculated results with analytical or published ones show the validation of the method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.6
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• pp.931-939
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• 2001

The slot coupling characteristics was analysed in a radial-line slot antenna for its design. The previously proposed waveguide model with a periodic boundary condition on its narrow walls and periodically arranged slots on its wide wall was used. The magnetic field integral equation and two dyadic Green\`s functions for respective regions was derived and the method of moments was used. To maximize the efficiency of numerical analysis and to extract singularities, two different kinds of basis functions, the entire domain basis function and the sub-domain one, are used. In addition, the Ewald sum technique for the rectangular waveguide and the Shanks transform for the half space were used to accelerate the computation of the slowly convergent potential Green\`s functions. Simulation results expressed the effects of the various design parameters on the slot coupling.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.1
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• pp.47-54
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• 1993

For the numerical analysis of free oscillation characteristics in a harbor with general boundary and bottom topography, finite element method is applied. The governing Helmholtz equation is transformed into a generalized matrix eigenvalue problem using the standard finite element procedure. A computer code is developed for the numerical evaluation of natural frequencies and free oscillation modes. In the eigensolution process, a shifting strategy is devised for the treatment of numerical singularity. Scaling of coefficient matrix is also found to be effective for the alleviation of numerical ill-conditioning. For the test problems, firstly, analytical and numerical solutions are compared and validity of the code is obtained. Hence the method is successfully applicable for the real-world problems with general geometric boundaries and bottom topography.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.38 no.11
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• pp.1075-1080
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• 2010

For the aeroelastic analysis of a wing with friction damping, coupled time integration method was used to obtain time responses in the subsonic and transonic regions. To take into account aerodynamic nonlinearity induced by shock wave on the lifting surface, transonic small disturbance equation with in-phase periodic boundary condition was used for unsteady aerodynamic calculation. For 2-DOF airfoil system with displace-dependent friction dampers, the effects of normal load slope and Mach number on flutter boundary were investigated.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.1 s.118
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• pp.41-47
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• 2007

Scattering fields of two dimensional acoustic waves by a circular cylinder are investigated. The present numerical approach for the acoustic scattering problem has difficulties of numerical robustness, long-time stability and suitability of far-field boundary treatments. The time-dependent periodic acoustic source is used to analyze Interference patterns between incident waves and waves reflected by the cylinder. Characteristic boundary algorithms coupled with 4th order Modified-Flux-Approach ENO(essentially non-oscillatory) schemes are employed in generalized coordinates to examine the effect of the wane frequency on the interference patterns. Non-reflecting boundary conditions, which is crustal for accurate computations of aeroacoustic problems, are used not to contaminate scattering fields by reflected waves at the outer boundary. Computed scattering fields show the circumferential acoustic modes generated by interacting between acoustic sources and scattered waves. At a lower frequency, the wave passes almost straight through the cylinder without Interacting with circular cylinder. Simulation results are presented and compared with the analytic solution. Computed RMS-pressure distribution on the cylinder wall is good agreement with exact solution.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.21-27
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• 2011

In this paper, the diagonal implicit harmonic balance method is applied to analyze helicopter rotor blade flow. The periodic boundary condition for Fourier coefficients is also applied in hover and forward flight conditions. It is available enough to simulate the forward flight problem with only one rotor blade using the periodic boundary condition in the frequency domain. In order to demonstrate the present method, Caradonna & Tung's rotor blades were used and the results were compared to the time-accurate method and experimental data.