• Proceedings of the Korea Concrete Institute Conference
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• 1989.10a
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• pp.53-58
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• 1989

Thicknesses of the base concrete blocks for large machines were estimated by analyzing the resonance modes of mechanical vibrations. The vibration was produced by the mechanical impact and detected by a wideband conical transcuder. There signals were analyzed by FET and thicknesses were obtained by the peaks of frequency spectrum. The estimated thickness upto 100cm are in good agreement with the real ones. For the layered concrete block, the estimated thickness is dependent on the acoustic reflective index at the boundary of the two layers.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.11a
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• pp.510-514
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• 2006

역경계요소법에 기초한 근접음장 음향홀로그래피는 근접 음장에서의 음압 측정과 음향경계요소법을 이용한 전달함수를 이용하여 소음원의 특성을 재구성하고, 임의 형상의을 갖는 소음원을 재구성 할 수 있는 강점이 있지만, 음압 측정에 많은 마이크로폰이 필요로 한다. 많은 실험 비용을 줄이기 위해, 본 연구에서는 마이크로폰이 고정된 상태에서 반사체를 추가하여 음장을 변화시키고, 이 상태에서 측정된 음압을 음원 재구성의 추가 정보로 이용하는 방법이 제안되고, 적용예제로서 모터의 표면 속도를 재구성 하였다. 직육면체 강체 반사체를 이용하여, 각 마이크로폰 위치에서 2 배수의 음압을 얻어, 이를 재구성에 이용하였다. 또한 수치유효랭크를 이용하여 재구성에 사용된 모우드의 개수를 계산하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.2
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• pp.141-147
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• 1995

Various numerical models for predicting wave deformation have been proposed. Among them a time-dependent mild-slope equation based on the line discharges and surface-elevation changes has been widely used in the wave fields with reflective waves. If applying this model to the case of obliquely-incident waves, not only the open-sea boundary but also one of the lateral boundaries should be treated as incident boundaries. In this study, Maruyama and Kajima (1985), Copeland (1985) and Ohnaka and Watanabe (1987)'s method are reviewed and the characteristics of these methods are analyzed using e normalized wave heights, wave angels and phases obtained from the numerical experiments. It is shown that Ohnaka and Watanabe(1987)'s method provides the most adequate driving boundary is the most suitable in e wave field with a general bottom slope.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.4
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• pp.846-856
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• 1998

In this paper, we have applied Berenger's perfectly matched layer(PML) absorbing boundary conditition(ABC) with three dimension at the propagation direction of field, side boundary and upper boundary in which evanescent and radiation field is exist. Even though the same computationaal domain is used, PML is superior to other ABC in the absorbing ability that is obtained reflective coefficient about $10^{-4}$ unit for the propagation wave, but PML is ineffective in absorbing evanescent field. Also we have compared dispersive characteristics of the microstrip with Kobayashi's emprical method, and obtaind very similar result, but 0.8% error is generated at the dc or near.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.396-401
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• 2019

A virtual rigid is modeled as the parallel structure of a virtual spring and a virtual damper. The reflective force from the virtual model is designed to be as large as possible to improve the realism of the virtual environment while maintaining the stable interaction. So, it is important to analyze the stability boundary of the virtual spring and damper. In the previous researches, the stability boundary is analyzed based on the zero-order-hold (ZOH) method, but it is analyzed based on the first-order-hold (FOH) method and the virtual damper in the paper. The boundary value of the stable virtual damper is inverse proportional to the sampling time and the maximum value of stable virtual stiffness is inverse proportional to the square of the sampling time. And the maximum value in the FOH method is increased to 110% of the value in the ZOH method. If the virtual damper is smaller than about 50% of the boundary value of the virtual damper in the FOH method, the stable virtual stiffness in the FOH method is several times larger than that in the ZOH method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.394-395
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• 2007

In order to make full color cholesteric displays, color filter-less R, G, B sub-pixel structured cholesteric LC cells have been studied. To make R, G, B colors, UV induced pitch variant chiral dopant was added to cholesteric LC mixtures. The concentration of the photo-sensitive chiral dopant was adjusted so that the initial state showed blue color and the color was changed from blue to green and red with increase of UV irradiation to the cholesteric cells. To prevent the mixing of R, G, B reflective sub-pixel liquid crystals, separation walls were formed using negative photo resister in boundary area between sub-pixels. Through the optimization of the material concentrations and UV irradiation condition, vivid R, G, B colors were achieved.

• Journal of Ocean Engineering and Technology
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• v.32 no.6
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• pp.447-457
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• 2018

In this study, a two-dimensional fully nonlinear transient wave numerical tank was developed using a desingularized indirect boundary integral equation method. The desingularized indirect boundary integral equation method is simpler and faster than the conventional boundary element method because special treatment is not required to compute the boundary integral. Numerical simulations were carried out in the time domain using the fourth order Runge-Kutta method. A mixed Eulerian-Lagrangian approach was adapted to reconstruct the free surface at each time step. A numerical damping zone was used to minimize the reflective wave in the downstream region. The interpolating method of a Gaussian radial basis function-type artificial neural network was used to calculate the gradient of the free surface elevation without element connectivity. The desingularized indirect boundary integral equation using an isolated point source and radial basis function has no need for information about the element connectivity and is a meshless method that is numerically more flexible. In order to validate the accuracy of the numerical wave tank based on the desingularized indirect boundary integral equation method and meshless technique, several numerical simulations were carried out. First, a comparison with numerical results according to the type of desingularized source was carried out and confirmed that continuous line sources can be replaced by simply isolated sources. In addition, a propagation simulation of a $2^{nd}$-order Stokes wave was carried out and compared with an analytical solution. Finally, simulations of propagating waves in shallow water and propagating waves over a submerged bar were also carried and compared with published data.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.1
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• pp.94-100
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• 2008

Noise barriers are being used more often to solve problems of noise pollution from traffic noise. Several types of noise barriers are being installed to increase the cost-effectiveness of noise barrier installation. In this study, the insertion loss is analyzed to evaluate the effectiveness of the noise barrier by using the BEM. In order to check the validity of the BEM, the BEM and Lam's theoretical analysis are compared with measurement, which is performed in the anechoic chamber for the 1/10 scale-down model, and good agreements are obtained. By using the two dimensional boundary element method, the insertion loss is calculated and analyzed for several typical noise barriers such as the vertical barrier, the barrier with an oblique edge on top, the T-shaped barrier and the barrier with interference device on top. With these analyses, it is possible to design more cost-effective noise barriers appropriate for a particular area.

• Nuclear Engineering and Technology
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• v.53 no.3
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• pp.732-740
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• 2021

Scattering resonance of medium mass nuclides leads complex spectrum in the fast reactor, which requires thousands of energy groups in the spectrum calculation. When the broad-group cross sections are collapsed, reaction rate cannot be completely conserved. To eliminate the error from energy collapsing, the Super-homogenization method in energy collapsing (ESPH) was employed in the fast reactor code SARAX. An ESPH factor was derived based on the ESPH-corrected SN transport equation. By applying the factor in problems with reflective boundary condition, both the effective multiplication factor and reaction rate were conserved. The fixed-source iteration was used to ensure the stability of ESPH iteration. However, in the energy collapsing process of SARAX, the vacuum boundary condition was adopted, which was necessary for fast reactors with strong heterogeneity. To further reduce the error caused by leakage, an additional conservation factor was proposed to correct the neutron current in energy collapsing. To evaluate the performance of ESPH with conservation factor, numerical benchmarks of fast reactors were calculated. The results of broad-group calculation agreed well with the direct full-core Monte-Carlo calculation, including the effective multiplication factor, radial power distribution, total control rod worth and sodium void worth.

• Magazine of the Korea Concrete Institute
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• v.3 no.3
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• pp.121-128
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• 1991

Thicknesses of the hase concrete blocks supportmg large machmes were estimated by analyzing the res- 0 ¬nance modes of mechanical Vibrations The vibration was produced by the mechanical impact with steel ball drop and detected by a wideband comcal piezoelectric transducei. The detected signals were analyzed by FFT and thicknesses of specimen were determined by the resonant frequency of vibratIon. For the layered concrete block, the estimated thickness is dependent on the acoustic reflective index at the boundary between layers. The estimated thickness up to 100em were in goo:l agreement with the real value. In additlOn. this technique could be applicable to the estimation of the bondmg status of the layered structures.