• 한국음향학회지
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• 제34권6호
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• pp.493-498
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• 2015

물로 채워진 음향 펄스 튜브 내에는 가진 조건들에 따라 복잡한 형태의 음향 신호들이 형성될 수 있다. 이는 펄스 튜브를 이용해 저주파수 대역에서 평면파 반사계수를 측정하는 것을 어렵게 한다. 본 연구에서는 COMSOL Multiphysics를 이용하여 튜브 벽이 가진되는 경우 펄스 튜브 내에 평면파 뿐 아니라 비평면파 모우드의 복잡한 음장이 발생됨을 보였다. 모우드 분리 방법인 이차원 푸리에 필터링으로 입사 또는 반사하는 평면파 모우드만을 각각 분리할 수 있었다. 이에 시간 게이팅을 적용하므로 음향 시편의 평면파 반사계수를 보다 정확하게 결정할 수 있게 하였다.

• 대한조선학회논문집
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• 제53권4호
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• pp.307-314
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• 2016

Energy flow analysis(EFA) is a representative method that can predict the statistical energetics of structures at high frequencies. Generally, as the frequency increases, the shear distortion and rotatory inertia effects in the out-of-plane motion of beams or plates become important. Therefore, to predict the out-of-plane energetics of coupled structures in the high frequency range, the energy flow analyses of Timoshenko beam and Mindlin plate are required. Unlike the energy flow model of Kirchhoff plate, the energy flow model of Mindlin plate is composed of three kinds of energy governing equations(out-of-plane shear wave, bending dominant flexural wave, and shear dominant flexural wave). This paper performed the energy flow finite element analysis(EFFEA) of coplanar coupled Mindlin plates. For EFFEA of coplanar coupled Mindlin plates, the energy flow finite element formulation of out-of-plane energetics in the Mindlin plate was performed. The general EFFEA program was implemented by MATLAB® language. For the verification of EFFEA of Mindlin plate, the various numerical applications were done successfully.

• 한국해안·해양공학회논문집
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• 제22권3호
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• pp.163-170
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• 2010

평면파 근사식에 기초한 지형에 의한 파랑변형 모형인 산란체법과 변환행렬법을 비교하여 특성을 분석하였다. 산란체법의 결과가 기존 엄밀해에 보다 근접하고 내재한 물리현상을 보다 명확히 설명하는 것으로 평가된다. 이들은 해석해로 계산이 빠르고 용이하며 지형이 비교적 단순한 경우에는 상당한 정밀도를 보인다.

• 대한기계학회논문집B
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• 제27권6호
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• pp.766-772
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• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• 물과 미래
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• 제29권5호
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• pp.139-150
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• 1996

본 논문에서는 수리학적 유역추적 모형인 선형 Muskingum-Cunge(M-C)법에 있어서 격자간격과 같은 수치적 인자의 변화가 단위폭사면에서의 유출수문곡선에 미치는 영향을 소개한다. 수치계산의 결과에 의하면, 유출특성은 수치적 또는 물리적으로 의미를 갖는 Courant 수 C 및 cell Reynolds 수 D의 값에 좌우되는데, C 값은 1에 접근할수록 D 값은 증가할수록 수치분산에 의한 진동은 발생하기 어렵다. C<1인 경우는 수치진동이 이동파의 전방에 발생한다. C>1인 경우는 파의 후방에 발생하는데, 이 때는 수치확산의 효과로 인해 수치진동은 작아지거나 사라진다. 특성구간길이 L의 값이 작은 사면(예, 급경사사면)의 경우, M-C법은 kinematic 법과 마찬가지로 파의 감쇠를 보이지 않는다. 한편 L의 값이 큰 사면(예, 완경사 사면)에서는 M-C법은 큰 거리격자간격 (Δx)에서도 큰 D(= L/ΔX)의 값을 갖게 되어 C에 거의 관계없이 diffusion wave를 잘 재현한다. 따라서 완경사 유역의 추적에 있어 M-C 법의 적용은 매우 유효하리라고 생각된다.

• 비파괴검사학회지
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• 제26권3호
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• pp.162-168
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• 2006

Speckle interferometry with phase-shifting method has been applied to measurement of micro-scale displacement through optical signal processing. Four-step phase-shifting method by PZT is used to measure out-of-plane displacement in spot-welded cantilever and results of optical experiments are comparable to those of FEM. Phase-shifting method using Fourier transform by PZT is applied to measurement of in-plane displacement on rectangular steel plate with a circular hole. The results of optical experiment agree well with theoretical calculation. New phase-shifting method in speckle interferometry has been implemented with a quarter wave plate. In-plane displacement of specimen is measured by the new phase-shifting method. Results of optical experiment show that the quarter wave plate can be used for phase-shifting method that is cheap and easy to use in speckle interferometry.

• Geomechanics and Engineering
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• 제17권3호
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• pp.295-305
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• 2019

The bedding plane has a significant influence on the effect of blasting fragmentation and the overall performance of underground mining. This paper explores the effects of fragmentation of the bedding plane and different angles by using the numerical analysis. ANSYS/LS-DYNA code was used for the implementation of the models. The models include a dynamic compressive and tensile failure which is applied to simulate the fractures generated by the explosion. Firstly, the cracks propagation with the non-bedding plane in the coal with two boreholes detonated simultaneously is calculated and the particle velocity and maximum principal stress at different points from the borehole are also discussed. Secondly, different delay times between the two boreholes are calculated to explore its effects on the propagation of the fractures. The results indicate that the coal around the right borehole is broken more fully and the range of the cracks propagation expanded with the delay time increases. The peak particle velocity decreases first and then increases with the distance from the right borehole increasing. Thirdly, different angles between the bedding plane and the centerline of the two boreholes and the transmission coefficient of stress wave at a bedding plane are considered. The results indicated that with the angles increase, the number of the fractures decreases while the transmission coefficient increases.

• The Journal of the Acoustical Society of Korea
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• 제17권2E호
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• pp.53-58
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• 1998

In this paper, we study the response of several anisotropic systems to buried transient line loads. The problem is mathematically formulated based on the equations of motion in the constitutive relations. The load is in form of a normal stress acting with arbitrary axis on the plane of monoclinic symmetry. Plane wave equation is coupled with vertical shear wave, longitudinal wave and horizontal shear wave. We first considered the equation of motion in reference coordinate system, where the line load is coincident with symmetry axis of the orthotrioic material. Then the equation of motion is transformed with respect to general coordiante system with azimuthal angle by using transformation tensor. The load is first described as a body force in the equations of the motion for the infinite media and then it is mathematically characterized. Subsequently the results for semi-infinite spaces is also obtained by using superposition of the infinite medium solution together with a scattered solution from the free surface. Consequently explicit solutions for the displacements are obtained by using Cargniard-DeHoop contour. Numerical results which are drawn from concrete examples of orthotropic material belonging to monoclinic symmetry are demonstrated.

• 대한조선학회지
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• 제17권1호
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• pp.31-37
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• 1980

Herein the flow past a submerged circular cylinder with a free surface is mapped onto a reference plane, in which the free surface is transformed to a straight line and the cylinder to a certain shape. A global mapping function between two planes is sought in a manner that linear free-surface elevation is generated in the physical plane. Hereby the Froude mumber $F_h$, based on the submergence depth h', is assumed to be of order 0(1) and the ratio a'/h'(a'=cylinder radius) of order o(1). Wave thus obtained are slightly different in magnitude and phase from usual linear solution. The resulting free wave starts advanced ahead compared to the classical result and its amount depends on Froude number. Based on the present concept wave forces are calculated. In this type of approach the body boundary condition gives more influence on wave resistance than that by the free surface in the speed range $F_h>1$.

• Journal of electromagnetic engineering and science
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• 제15권2호
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• pp.120-122
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• 2015

This study presents a new, simple method for improving the front-to-back (F/B) ratio of a microstrip patch antenna (MSA) based on surface wave suppression. The back radiation of the MSA is significantly reduced by using the meandered ground plane edges and placing split-ring resonators (SRRs) in the middle of the meandered slots. By loading SRRs near the center of the meandered ground plane edges, some parts of the diffracted back-lobe power density can be reduced further. Compared to the F/B ratio of a conventional MSA with a full ground plane of the same size, an improved F/B ratio of 18 dB has been achieved experimentally for our proposed MSA.