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A series of process to make an acoustic lens for underwater imaging is reviewed and the method to evaluate characteristics of the lens is investigated. If the specification of lens is given, the making process consists of the material selection, evaluation of its properties, lens geometry design, prediction of lens characteristics, manufacturing, and evaluation by measurement. In this study, an actual acoustical lens is made by cutting polymethylpentene block. The characteristics of lens are predicted by the hybrid method, combination of ray tracing and Rayleigh integral. For this purpose, a simulation method based on the equivalent source method is suggested to reflect the actual radiation pattern of transducer used for measurements. Finally, the measurement is conducted in a small water tank to observe the actual characteristics of the manufactured lens.
Among poets representing this period are Cheung Ji Youg, Shin Seok Jeong, Shin Seok Cho and so on. Of them the most remarkable poet is Cheong Ji Youg, who is called a footprint of Korean poetry in the 1930's. He played a leading role of imagism developing the movement of pure poetry with Shin Seok Jeong against poetry's degrading to the instrument of materialistic dialectic conception and, also when losing a course of what Korean poetry should be, contribued to the success and development of traditional Korean poetry by creating 'philosphicalfeatured poetry' based upon Taoist ideas, the most art-oriented of Eastern ideas, but as a victim of the partition of the Korean peninsula a correct estimate on him and his poetry has not been made yet.<br/> This dissertation has been studied to contribute to development of contemporary Korean poetry by first estimating him and his poetry correctly and then rationalizing features of hie Taoist poetry objectively.<br/> First of all, Ji Yong, a believer in the spiritual world of Orientalism at his earlier period, was much devoted to Eastern ideas, first, to overcome the crisis of traditional poetry, preserving and developing natioal poetry under Japanese colony and then, to escape naturally from the limit of imagism which he had searched.<br/> It seems impossible and useless to find out which of two he had more importantly in his mind but the most obvious is that he escaped from aspects of struggle and restored a sense of gaiety and health again in his poetry. This fact could provide and history of Korean poetry with an opportunity of reflection and a foundation of an important turning point. It gave a realization that poetry should not be an express or a statement of simple emotion but a result of solidified thoughts, not an expressive instrument of thoughts but a substance of struggling and solving problems of life's realities.<br/> Especially Ji Yong's poetry prevented readers from not being moved though direct touching with objects and at the same time showed remarkable result of active embodiment by achieving a simple struture.<br/> As mentioned above, Taoist poetry has historical meanings and criticisms as follow:<br/> Firstly, when Korean poetry didn't move beyond a wall of sentimentalis or utilized an instrument of political ideology, and didn't overcome a limit of folloeing Western tendancy, Taoist poetry could be said to be a result of needs of the times, that is, a control of emotion, a removal of an intention and an equipment of Eastern ideas.<br/> Secondly, it can be estimated that Taoist poetry, connected closely with Eastren ideas and Eastern classical works, not only prevented following the Western-oriented tendancy one-sidedly but also contributed to achieving a traditional value.<br/> Thirdly, Taoist poetry, as a spiritual supporter in overcoming a crisis of devastating historical realities and national spirit of the times, made a great contribution to the that the solving to a sense of losing and a condition for the supreme bliss is not a material but a spirit.<br/> Fourthly' it can't be overlooked that Taoist poetry maximized the active taste of Korean poetry. Therefore Taoist poetry should have been valued correctly in terms of items mentioned above even if it didn't resist Japanese imperialism actively.<br/> From now, Taoist poetry and the achievements of poets absorbed in embodying its ends should be arranged more objectively and systematically and used as a foundation of development for contemporary Korean poetry.
A series of process to design an acoustic lens for underwater imaging is reviewed and the method to evaluate characteristics of the lens is investigated. If the target specification of lens is given, the design process consists of the material selection, evaluation of its properties, lens geometry design, prediction of lens characteristics, manufacturing, and evaluation by measurement. In this study, an actual acoustical lens is made by cutting polymethylpentene block. The characteristics of lens are predicted by the hybrid method, combination of ray tracing and Rayleigh integral. For the direct comparison between the prediction and measurement results, a simulation method based on the equivalent source method is suggested to reflect the actual radiation pattern of transducer used for measurements. Finally, the measurement is conducted in a small water tank to observe the actual characteristics of the manufactured lens.
원하는 복잡한 음장을 지정된 구역에 정확히 형성하는 것은 음향 어레이를 이용한 응용에 있어서 가장 어렵고도 중요한 일이다. 이를 해결하기 위해, 본 논문에서는 역 경계요소법을 원용한 음향홀로그래피 방법을 이용하여 원하는 음장의 특성을 얻기 위한 음원 어레이의 필터 계수를 설계하는 방법을 제안하였다. 음원 파악에 적용되는 음향 홀로그래피는 음장에서의 음압을 측정하여 표면에서의 음원 특성을 재구성하게 되는데, 이와 유사한 음원 설계 문제에서는 목적하는 음장 특성이 주어진 조건이 되며, 음원의 체적 속도는 이러한 음장을 얻기 위한 출력 신호가 된다. 설계 과정에 있어서 먼저 목표 음장의 특성 제한 조건을 갖는 음장 데이터를 구성하고, 음원과 공간을 경계요소법으로 모델링 한 뒤, 소요되는 음원의 정보를 역으로 유도한다. 예제로서 16개의 스피커를 갖는 어레이를 이용해 전방의 반은 평면파 전파, 나머지 반은 정숙공간을 동시에 갖도록 하는 목표 음장을 구현하였다. It is very difficult to form a desired complex sound field at a designated region precisely as an application of acoustic arrays, which is one of important objects of array systems. To solve the problem, a filter design method was suggested, which employed the concept of an inverse method using the acoustical holography based on the boundary element method. In the acoustical holography used for the source identification, the measured field data are employed to reconstruct the vibro-acoustic parameters on the source surface. In the analogous problem of source array design, the desired field data at some specific points in the sound field was set as constraints and the volume velocity at the surface points of the source plane became the source signal to satisfy the desired sound field. In the filter design, the constraints for the desired sound field are set, first. The array source and given space are modelled by the boundary elements. Then, the desired source parameters are inversely calculated in a way similar to the holographic source identification method. As a test example, a target field comprised of a quiet region and a plane wave propagation region was simultaneously realized by using the array with 16 loudspeakers.