• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.373-374
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• 2004

산란체가 있을 때에 음장은 입사파와 산란파로 구분될 수 있다. 입사파는 산란체에 영향을 받지 않는다. 바꿔 말하면 음원으로부터 나온 소리는 청취자와 주위 환경에 무관하다. 이 논문에 제시된 입사음장 재생시스템은 주어진 공간내에서 입사음장을 재생하여 청취자에 독립적인 가상음장을 만드는 시스템이다. 입사음장 재생은 경계표면제어원칙에 기반하였다.

• 한국해양학회지
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• v.28 no.3
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• pp.177-185
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• 1993

The theory for long wave scattering (Proudman, 1914: Longuet-Higgins, 1970) is applied to a tidal-frequency Kelvin wave propagating around a small cylindrical island in a shelf sea of uniform depth. The theory includes the effects of bottom friction on wave propagation. The theoretical analysis of the Kelvin wave around the island. this amplitude change results in a uniform amplitude of the total wave along the circumference of the island in an inviscid fluid, and the dynamic cause of this is explained in terms of Coriolis effects. Bottom friction attenuates the amplitude of the total wave from the frontal side of the island to the leeward side, but the amplitude variation along the coast becomes symmetric to the line connecting both idea. The phase of the scattered wave contributes to more rapid travel of the total wave in the front and leeward side than farther offshore. The effects of bottom friction on the wave phase around the island are negligible.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.21 no.4
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• pp.334-344
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• 2009

In the present paper, analytic solutions are derived for scattering of obliquely incident waves by a semi-infinite breakwater or a breakwater gap of partial reflection. In order to examine the appropriateness of the derived solutions, they are compared with the solutions derived by McIver in 1999 and Bowen and McIver in 2002 for a semi-infinite breakwater and a breakwater gap, respectively, in the case of perfect reflection. The derived analytic solutions are used to investigate the effect of reflection coefficient of the breakwater and wave incident angle upon the tranquility at harbor entrance. The tranquility is deteriorated by the reflected waves as the reflection coefficient increases and as the waves are incident more obliquely.

• The Journal of the Acoustical Society of Korea
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• v.20 no.1
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• pp.68-76
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• 2001

Sonar is the system that detects objects and finds their location in water by using the echo ranging technique. In order to have excellent performance in variable environment, acoustic characteristics of this system must be analyzed accurately. In this paper, based on the finite element analysis, modeling and analysis of acoustic characteristics of underwater acoustic sensors are preformed. Couplings between piezoelectric and elastic materials, and fluid and structure systems associated with the modeling of piezoelectric underwater acoustic sensors are formulated. In the finite element modeling of unbounded acoustic fluid, IWEE (Infinite Eave Envelop Element) is adopted to take into account the infinite domain. When an incidence wave excites the surface of Tonpilz underwater acoustic sensor, the scattered wave on the sensor is founded by satisfying the radiation condition at the artificial boundary approximately. Based on this scattering analysis, the electrical response of the underwater acoustic sensor under incidence, so called RVS (Receiving Voltage Signal) is founded accurately. This will devote to design Sonar systems accurately.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.1
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• pp.45-53
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• 1991

The nonlinear forward diffraction of a modulated wave train by a thin wedge has been studied analytically. Since the physical variables involved in the problem have vastly different scales, the multiple scale expansion method has been used to obtain an approximate solution. To simplify the problem. the wedge is assumed to be thin and the parabolic approximation is utilized. The wave evolution can be described by a kind of the cubic Schrodinger equation. which consists of the linear time evolution. the lateral dispersion and the nonlinearity. Numerical results indicate that the nonlinearity. which it defined by the ratio of the ratio of the incident wave to the wedge angle. governs the amplitude and the stability of diffracted waves. The instability of dirffracted waves becomes more pronounced as the nonlinearity increases and the modulation ratio decreases. It is also found that the stem waves. initially developed along the wedge. can not sustain for a long time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.7
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• pp.647-652
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• 2016

Guided waves can be used for the inspection of long range pipelines. Surface corrosion is often found as a major defect type in pipelines. The reciprocity relation is a well-established theorem by which one can simplify complicated mathematical expressions. The approach has been already applied to plate and half-space structures to obtain the closed-form solutions of scattered amplitude. However, results for the case of cylindrical structures have not been reported yet. In this paper, the scattering of torsional waves, which is widely used in commercial applications, is explored by the reciprocity theorem approach. Obtaining closed-form solutions of the amplitudes of propagating waves is much simplified by using the reciprocal relation. The scattered amplitudes for elliptical and rectangular defect shapes are calculated with respect to defect depth and width, at frequencies between 0 and 500 kHz. The amplitude shows the periodic result as a function of frequency. The derived closed-form solutions can play a significant role in quantitative signal interpretation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.3
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• pp.183-193
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• 2007

Analytic solutions are derived for wave scattering by a semi-infinite breakwater or a breakwater gap with partially reflective front and fully reflective back. The water depth is constant and a regular wave train is normally incident to the breakwater. Wave scattering is studied based on the linear potential wave theory. The governing equation is transformed into ordinary differential equation by using the method of variation of parameters and coordinate transformation. Comparison with finite element numerical solution shows that the analytic solution obtained in this paper gives quite good results. Using the analytic solution, the tranquility of harbor entrance is investigated by changing the reflection coefficient at the breakwater.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.12
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• pp.2328-2339
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• 1992

The propagation of coherent time-harmonic elastic L-and SV-waves is studied in a medium with random distribution of cylindrical inclusions. The purpose of the research is to characterize the dynamic elastic moduli and the attenuation properties of fiber-reinforced composite materials. The cylindes representing the fibers are assumed to be distributed in parallel with each other and the direction of incident waves are normal to the cylinder axes. A multiple scattering formula using the single scattering coefficients in conjunction with the Lax's quasicrystalline approximation is derived from which the dispersion relation for such medium is obtained. In order to formulate the multiple scattering interaction between cylinders, the pair correlation functions are generated by the Monte Carlo simulation technique. From the numerically evaluated complex wavenumbers, the propagation speed of the average wave, the coherent attenuation and the effective elastic moduli are presented as functions of frequency and fiber volume fraction.

• Proceedings of the Acoustical Society of Korea Conference
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• 1992.11a
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• pp.69-76
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• 1992

섬유강화 복합재료의 동탄성계수와 감쇠특성을 규명하기 위하여 랜덤하게 분포된 무한 실린더 형상의 산란체를 가진 점탄성 매질내에서 , 축방향으로 분극되어 조화 운동을 하는 탄성파의 전파에 관하여 연구하였다. 다중 산란에 관한 이론으 이용하여 매질내에서의 파동전파 특성을 내포하는 분산관계식을 얻었다. 다중산란에 의한 실린더간의 상호작용을 수식화하기위하여 필요한 실린더의 쌍분포함수는 몬테카를로 모의 실험을 이용하여 구하였다. 수치적으로 구한 감쇠계수 및 유효전단강성을 주파수와 체적율의 함수로 제시하였다. 또한 감쇠계수의 주파수에 따른 변화에 있어서, 저주파에서는 매질의 점탄성 손실이 지배적이며, 고주파수로 갈수록 다중산란에 의한 손실이 지배적인 것으로 나타났다.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.93-96
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• 2000

수중 폭발성 음원(SUS)을 이용한 천해 저주파 잔향음 실험을 97년 제주 해역에서 실시하였다 측정된 신호를 고유음선 정보를 이용하여 시간영역에서 잡음, 반사, 산란 영역으로 구분하고 각 영역에 대해서 주파수별 스펙트럼 분석을 실시하였으며 각 영역이 갖는 확률적 특성을 분석하였다. 실험해역은 안정된 해저 형태를 갖는 천해였으므로 산란 신호는 일정한 크기를 갖고 지속적으로 수신되었다. 스펙트럼 분석 결과, 시간에 따른 안정성을 갖는 주파수 대역을 확인할 수 있었으며 구분된 영역별 위상은 반사영역과 산란영역의 위상 특성을 잘 반영하고 있었다. 구분된 각 영역에 대해 1/3 옥타브 벤드로 필터링 하여 확률 특성을 분석한 결과 주파수영역의 실수부와 허수부는 각각 정규 분포를 보였으며 그것의 진폭(envelope)은 레일리 분포를 나타냈다. 또한 산란신호의 위상은 저주파 대역에서 유니폼 분포 특성을 나타내어 잔향음의 기본적인 확률 특성을 잘 반영하고 있었다.