수중 기포집단의 음파산란에 관한 연구 = (A) study of sound scattering from bubble cloud in water

다국어 초록 (Multilingual Abstract)

The resonance frequency and scattering pattern of a bubblecloud containing a large number of bubbles in water are studied experimentally. To make a bubble cloud in water, a bubble maker was designed which consisted of forty nine 22-gauge hypodermic needles with square cut tips. The needles were arranged in concentric circular cross-section. With these bubble making system we were able to maintain a constant void fraction with a fixed geometrical configuration. Furthermore, the void fraction of the bubble culumn could be varied precisely by adjusting the flow rate through the flow meter and by controlling the needle number through stopcock.
In this paper, we made track for physical parameter that affect the scattering pattern. Fistly, the measured data and calculated results from function about elastic solid and hollow cylinder is compared.
From that point, we confirmed that the formula contained form function is so useful for analyzing the scattering pattern.
Not only the density of bubble cloud by a change of void fraction of bubble cloud but also the sound speed in bubble mixture is related to the previous formula.
It is shown that the resonance of the bubble column is significantly different from the natural resonant frequencies of the individual bubbles and the important parameter in the resonance of our column is the void fraction, not the bubble size. But, we don't have a projector that is able to emit experimentally, the lowest frequency near the resonance frequency, it is found that acoustical properties of a bubble cloud (any given void fraction) depend strongly on the degree of dispersion because of the complex interactions of the dynamics of the bubble with the whole flow.
As the result of measuring the scttering pattern by cylindrical bubble cloud in the water tank, a scattering pattern of bubble cloud is decided by a sound speed in the mixture among various acoustic characteristic which is changed by the void fraction of bubble column.
So as to analyze experimental results of scattering pattern by bubble column, we compared measuring data with calculating result which is obtained by a basis of form function, and then, we certified that it is in accord on a result using sound speed which simultaneously considered calibration term. It is also indicated that one of the most important factors, which decides what scattering pattern of bubble cloud is, must be sound propagation velocity in bubble mixture.
Finally, we have stated that bubble cloud which is built up with various size of single bubble should be a simple scatter.

목차 (Table of Contents)

• 목차
• Ⅰ. 서론 = 1
• Ⅱ. 이론적 배경 = 5
• 가) 수중에서의 단일 기포에 대한 산란이론 = 5
• 나) 기포 집단의 산란 이론 = 10
• 다) 원통 막대의 산란이론 = 15
• 라) 원통 쉘의 산란이론 = 21
• Ⅲ. 실험 방법 = 24
• 가) 원통형 탄성 산란체의 시료선택 = 24
• 나) 기포 집단의 발생 및 형태 = 26
• 다) 측정 장치 및 자료 처리 = 30
• Ⅳ. 결과 및 분석 = 36
• 가) 원통형 탄성 산란체의 산란 현상 = 36
• 나) 원통쉘의 산란현상. = 40
• 다) 원통형 기포집단의 공명 진동수 = 45
• 라) 기포 집단의 산란 현상 = 49
• 참고문헌
• Abstract
• Appendix 1
• Appendix 2
• Appendix 3