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백경민,Baik, Kyungmin,Marston, Philip L. The Acoustical Society of Korea 2014 韓國音響學會誌 Vol.33 No.5
매끈한 물체에 의한 음향산란에 관한 수치해석은 발전해 왔으나 경계면에 위로 부분적으로 드러나 있는 물체에 의한 음향산란에 대한 수치해석은 여전히 드물다. 해저면에 부분적으로 파묻힌 실린더의 후방산란진폭을 결정함에 있어 경계면에 의한 잔향은 표적의 산란 함수 특성을 변화시킨다. 본 연구는 평탄한 경계면에 부분적으로 파묻힌 실린더의 후방산란진폭에 대한 수치해석을 제시하기 위하여 모멘트법(Method of Moments)을 채택하였다. 제시된 수치해석은 측정 및 키르히호프 근사법으로 얻은 해석적인 해와 상당한 일치를 보여주었다. 본 연구에서 기술된 수치해석은 해저면에서의 잔향과 표적으로부터의 산란파를 결합시킴으로써 해저면에 부분적으로 파묻힌 어떠한 형상의 표적에 대한 후방산란 문제에도 적용될 수 있다. Though there have been advances in the numerical analysis of the acoustic scattering by smooth objects, numerical analysis of the acoustic scattering by the objects that are partially exposed on the interface are still rare. In determining the backscattering amplitude by a partially buried cylinder on a seabed, reverberation by the interface changes the feature of the scattering form function. Current study adopted the Method of moments (MoM) to provide the numerical analysis on the backscattering amplitude for a partially buried cylinder on a flat interface. Suggested numerical analysis showed the good agreements with the measurements and the analytic solution obtained by the Kirchhoff approximation. Numerical analysis described in the current study can be applied to the backscattering problem of any shape of the objects partially imbedded on a seabed by combining the reverberation from the seabed with the scattered wave from the objects.
백경민,유정수,신구균,Baik, Kyungmin,Ryue, Jung-Soo,Shin, Ku-Kyun 한국음향학회 2016 韓國音響學會誌 Vol.35 No.1
Present study shows three different methods finding the eigenfrequencies of an infinite circular cylinder under free-vibration; Elasticity theory that can be applied to general case, thin-shell theory that can be effectively applied to the cylinders with small thickness, and numerical study using Finite Element Method (FEM). The results obtained from those methods were verified through the cross check among the calculations. Changing the thickness of the cylinder for a fixed outer radius, all the eigenfrequencies below 1 kHz were found and their dependences on the modal index and the thickness were observed. 본 논문은 무한 원통형 실린더의 자유진동에서 발생하는 고유진동수(eigenfrequency)를 구하는 3가지 방법에 대해 다루었다. 일반적인 경우에 적용될 수 있는 탄성 이론을 적용한 방법과 얇은 두께의 실린더에 효율적으로 적용될 수 있는 얇은 원통형 쉘 이론을 적용한 방법, 유한요소법(FEM: Finite Element Method)을 통한 수치 해석 방법을 통해 구해진 결과에 대한 비교 및 검증을 수행하였다. 주어진 실린더의 외반경에 두께를 서로 달리하여 1 kHz 이하에 존재하는 원통형 쉘의 고유진동수를 구하였고 모드수와 두께의 변화에 따른 이들 결과에 대해 관찰하였다.
Elmina Bernadette Carolina Fritzie,Baik Kyungmin,Kim Sung Mok,Kim Yong Tae 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.10
The water immersion through-transmission method is widely used owing to its simplicity and high precision in measuring sound speed. However, when measuring the sound speed of a compound material whose host medium is water, such as hydrogel tissue-mimicking material (TMM), the reproducibility and reliability of the measurements obtained under the state of water immersion method were found to be low. To solve this problem, the application of contact transmission method instead of the water immersion method was examined in this study. Unlike the water immersion method, the direct-contact method requires stability in target stiffness, which is difficult in TMM hydrogels due to their low-stiffness properties. Therefore, it is important to find a material that acts as a propagation medium, maintains thickness, and prevents percentage change of the material component in TMM. As a propagation medium, it is necessary for the material to have a low attenuation coefficient value to increase the signal-to-noise ratio. Among the investigated candidate materials, polymethyl methacrylate (PMMA) was selected, owing to its lowest signal attenuation value compared to other candidate materials. A measuring jig was designed and manufactured with this material. The sound speeds of agar and gelatin TMMs were measured by the conventional water immersion through-transmission method and the proposed indirect contact-type method for comparison. In the case of the conventional water immersion method, as the measurement was repeated, the measured sound speeds showed a decreasing trend. By contrast, the indirect contact-type measurements using the PMMA jig showed relatively high reproducibility and reliability.