Acoustic Radiations of Infinite and Finite Ribbed Periodical Submerged Cylindrical Shells

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基本資料

Project title

Code/計畫編號

MOST104-2221-E019-042

Translated Name/計畫中文名

具有週期性加強肋之無限沿伸及有限長度之圓柱薄殼在水中噪音輻射之解析及計算

Project Coordinator/計畫主持人

Pei-Tai Chen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Systems Engineering and Naval Architecture

Website

https://www.grb.gov.tw/search/planDetail?id=11575550

Year

2015

Start date/計畫起

01-08-2015

Expected Completion/計畫迄

01-07-2016

Bugetid/研究經費

757千元

ResearchField/研究領域

機械工程

"本計畫分兩年期探討浸在水中之無限沿伸及有限長度之圓柱薄殼之噪音輻射，此薄殼在等間距位置具有環型加強肋，亦即為無限及有限週期結構。對於沒有水(即為聲音介質)的負荷下，眾所週知對於無限週期結構振動頻率變動時，具有通過區/停止區(pass band/stop band)之特性，有限週期結構也有類似的現象。本計畫探討的重點在於當結構浸入水中是否仍具有類似通過區/停止區之特性，亦即在聲音介質負荷下，因為結構振動而產生之聲音輻射，聲音由近場輻射至遠場時，使否仍具有通過/停止之特性，換言之，使否具有因為週期性加強肋的存在，使得遠場聲壓在某此頻率輻射較多的聲音功率，而另外某些頻率輻射較少或是明顯較少的聲音功率。這個重要的問題，迄今尚未有系統的建立出分析之理論架構。圓柱薄殼結構採用薄殼理論以及Love’s 假設，加強肋則是考慮由環形平板及內徑接著短柱型的圓柱薄殼所組成的T 型加強肋，聲音介質(水)對無線沿伸圓柱的負荷則是考慮圓柱表面之行進波所產生的輻射聲場，此聲場可以用漢克函數(Hankel function)來表示，而有限沿伸的圓柱聲音負荷則用傅立葉積分對表面波數(wave number) 轉換(Fourier integral transform)來表示。整個動態方程式的推導根據虛功原理，亦即圓柱薄殼及加強肋因位移產生的應變能之虛擬增量(virtual increment)等於圓柱表面聲押對圓柱表面位移所作虛功(virtual work)，此動態方程式之求解則是將未知之位移變數，用適當基底展開(Assumed modes expansion)，並應用前述之虛功原理，求得展開係數，從而解得圓柱薄殼之位移，以及遠場壓力。" "The proposal explores acoustic radiations submerged ribbed cylindrical shell with infinite and finite length cylinders .It is well known that infinite periodical structures, such as ribbed cylindrical shells, exhibit pass band/stop band characteristics where the vibration waves do not transmit for frequencies in a stop band. A similar phenomenon occurs for finite periodical structures. The present proposal intends to understand whether the pass /stop characteristics also occurs under heavy acoustic loading, such as water ,that is ,the acoustic power radiated from the vibrating shell structures shows frequency dependence where the power is small, on even significantly small at some frequency zones . The cylindrical shell is formulated based on thin shell theory together with Loves assumption, whereas the T shaped rib is composed by a ring shape plate connecting with an inner short length cylindrical shell. The acoustic loading for infinite cylinder is derived for a surface traveling wave propagating along the cylinder, with which an outward propagation wave represented by a Hankel function is obtained for describing acoustic field .The acoustic loading for finite cylinder can be represented by a Fourier integral transform with respect to the wave number of traveling wave along the surface. The equation for the ribbed cylindrical shell submerged in water is derived based on virtual work principle, where the virtual increment at strain energy by the cylindrical shell as well as the ribs equals the virtual work of the surface acoustic pressure done on the shell normal displacement. The equation is solved by a method of assumed modes expansion where the displacement variables are formed by a linear combination of a set assumed functions .The combination coefficients are obtained as the aforementioned virtual work is applied . Consequently, the surface displacements of the shell structures as well as the far field pressure are obtained."

DSpace CRIS

Acoustic Radiations of Infinite and Finite Ribbed Periodical Submerged Cylindrical Shells

基本資料

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