• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.435-447
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• 2019

Energy Flow Finite Element Analysis (EFFEA) is a promising tool for predicting dynamic energetics of complicated structures at high frequencies. In this paper, the Energy Flow Finite Element (EFFE) formulation of complicated Mindlin plates was newly developed to improve the accuracy of prediction of the dynamic characteristics in the high frequency. Wave transmission analysis was performed for all waves in complicated Mindlin plates. Advanced Energy Flow Analysis System (AEFAS), an exclusive EFFEA software, was implemented using $MATLAB^{(R)}$. To verify the general power transfer relationship derived, wave transmission analysis of coupled semi-infinite Mindlin plates was performed. For numerical verification of EFFE formulation derived and EFFEA software developed, numerical analyses were performed for various cases where coupled Mindlin plates were excited by a harmonic point force. Energy flow finite element solutions for coupled Mindlin plates were compared with the energy flow solutions in the various conditions.

• 대한기계학회논문집A
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• 제26권10호
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• pp.2201-2210
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• 2002

The accurate analysis of ultrasonic wave propagation and scattering plays an important role in many aspects of nondestructive evaluation. A numerical analysis makes it possible to perform parametric studies, and in this way the probability of detection and reliability of test results can be improved. In this paper, a finite element method was employed for the analysis of ultrasonic wave propagation in anisotropic materials, and the accuracy of results was checked by comparing with analytical predictions. The element size and the integral time step, which are the critical components for the convergence of finite element solutions, were determined using a commercial finite element code. Some differences for wave propagation in anisotropic media were illustrated when plane waves are propagating in a unidirectionally reinforced composite materials. When plane waves are propagating in nonsymmetric directions in a symmetric plane, deviation angles between the wave vector and the energy vector were found from finite element analyses and the results agreed well with analytical calculations.

• 한국전자파학회논문지
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• 제8권6호
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• pp.665-680
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• 1997

본 논문에서는 350 MHz와 900 MHz 평면파에 노출된 다양한 모델의 인체 두부 내 비흡수율(specific abs sorption rate, SAR)의 분포를 해석하였다. 해석 방법은 유한차분시간영역(finite-difference time-domain, FDTD) 방법이며, 인체 두부 모델로서 균질 매질의 구형모델, 균질의 실질적인 형태를 갖는 모텔 그리고 실질적인 형태를 갖는 비균질 모델이 사용된다. 입사 평면파의 편파는 인체 길이방향과 일치하며, 진행방향은 뒤에서 암으로, 그리고 앞에서 뒤로 향하는 두 가지 경우를 다룬다. 얻어진 연구결과는 다음과 같다. 1) 세 가지 모델의 평균 SAR은 비슷하나 국부 SAR은 큰 차이가 있다. 2) 주파수가 900 MHz보다 두부의 공진이 일어나는 대역인 350 MHz에서 복사전력이 더 깊이 침투한다. 3) 후방입사 평변파의 경우에는 두부가 아닌 목 부근에서 "hot spot"이 일어난다. 4) 전방입사 평면파의 경우에는 900 MHz에서는 코, 350 MHz의 경우에는 입술 위와 턱 부분에 "hot spot"이 나타난다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권1호
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• pp.174-194
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• 2015

In this paper, an Energy Flow Analysis (EFA) for coplanar coupled Mindlin plates was performed to estimate their dynamic responses at high frequencies. Mindlin plate theory can consider the effects of shear distortion and rotatory inertia, which are very important at high frequencies. For EFA for coplanar coupled Mindlin plates, the wave transmission and reflection relationship for progressing out-of-plane waves (out-of-plane shear wave, bending dominant flexural wave, and shear dominant flexural wave) in coplanar coupled Mindlin plates was newly derived. To verify the validity of the EFA results, numerical analyses were performed for various cases where coplanar coupled Mindlin plates are excited by a harmonic point force, and the energy flow solutions for coplanar coupled Mindlin plates were compared with the classical solutions in the various conditions.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.820-823
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• 2007

In the wavenumber domain, each point on a radiation sphere indicates a plane wave of the frequency corresponding to radius of the sphere and the position on the sphere shows propagating direction of the plane wave. This concept is extended from the research by Choi[1] where he focus acoustic potential energy at a point on a radiation sphere. Here we propose the method to focus the energy at a point on the radiation sphere, as a result, we can easily generate a plane wave which propagates to any direction that we want.

• 한국해안·해양공학회논문집
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• 제20권5호
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• pp.439-451
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• 2008

단일 계단지형에 대한 반사파와 투과파의 해를 이용하여 다중 계단지형에서의 파랑변형을 계산할 수 있는 새로운 산란체법의 모형을 구성하였다. 산란체법의 근사해를 보다 정밀한 Kirby and Dalrymple(1983)이 제시한 EFEM의 해와 비교검증하였다. 진행파만의 근사에서는 산란체법과 EFEM의 해는 동일하다. 계산된 반사율과 투과율에 대한 위상의 경우 억류파를 포함한 산란체법의 해는 진행파만의 근사해보다 훨씬 우수하다. 억류파의 영향이 감소할수록 산란체법의 해는 EFEM의 해로 접근한다.

• 전자공학회논문지A
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• 제32A권2호
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• pp.19-30
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• 1995

Diffraction patterns of the copolarized and the crosspolarized total electric fields by a spherical air cavity in a dielectric medium are analyzed in the forward near-field region when the wavelength of the incident plane wave is comparable to one half of the cavity radius. It is shown that double nulls and dips of the copolarized and the crosspolarized total electric fields exist in the measurement plane tansverse to the propagating direction of the incident field, and their dependences on the frequency, the distance of the measurement plane, and the measurement angle are analyzed.

• 한국소음진동공학회논문집
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• 제20권9호
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• pp.863-875
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• 2010

The vibration of a cylindrical shell is generated due to elastic waves propagating on the shell. Those elastic waves include propagating waves such as flexural, longitudinal and shear waves. Those also include non-propagating decaying waves, i.e. evanescent waves. In order to separate contributions of each type of waves to the data for the vibration of the cylindrical shell, spatial signal processing techniques for wavenumber analysis are investigated in this paper. Those techniques include Fast Fourier transform(FFT) algorithm, Extended Prony method and Overdetermined Modified Extended Prony method(OMEP). Those techniques have been applied to identify the waves from simulated vibration signals with various signal-to-noise ratios. Futhermore, the experimental data for in-plane vibration of the cylindrical shell has been processed with those techniques to identify propagating waves(longitudinal, shear and flexural waves) and evanescent waves.

• The Journal of the Acoustical Society of Korea
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• 제20권3E호
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• pp.31-37
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• 2001

Finite element model of a cMUT is constructed using the commercial code ANSYS to analyze the cross talk mechanism. Calculation results of the complex load impedance seen by single capacitor cells are presented, and then followed by a calculation of the plane wave real load impedance seen by a parallel combination of many cells that are used to make a transducer. Cross talk between 1-D array elements is found to be due to two main sources: coupling through a Stoneley wave propagating at the transducer-water interface and coupling through Lamb waves propagating in the substrate. To reduce the cross talk level, the effect of various structural variations of the substrate are investigated, which include a change of its thickness and etched trenches or polymer walls between array elements.

• 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.