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Hydrodynamic Analysis of Floating Structures Characteristics with Skirts
|Authors: ||Tran Duc Tru|
|Contributors: ||NTOU:Department of Harbor and River Engineering|
Floating structure;Boundary Element Method;rigid skirt;response amplitude operators;Flexible
|Issue Date: ||2017-05-24T08:40:43Z
|Abstract: ||本研究利用對偶邊界元素法(Dual Boundary Element Method , DBEM)建立一個數值模式來模擬設有翼板及繫纜浮體的運動行為，包括：前後移動、垂直移動、縱轉、波浪反射率、透射係數、繫留力及能量損失。 從結果發現，在矩形浮體下方加裝兩個翼板，可以增加浮體的附加質量，在波浪作用時給浮體結構物一個緩衝的作用力，因此浮體較容易受長週期波影響。這些現象增加了浮體對抗波浪的能力。本研究翼板和垂直軸的夾角設計為（00、300、600、900），當翼板角度為０度時，反應振福運算子(Response Amplitude Operators , RAO)呈現出來的模擬結果跟Mohamed R. Gesraha的結果吻合；所計算出來的結果也跟實驗數據相近。另外，本篇論文亦有討論拖曳係數C¬¬¬¬¬d¬ 、翼板數量及翼板的長度。當長週期波通過設有較長翼板的浮體結構物時會產生共振。 另一方面，本文也專注在柔性翼板的研究，包括：結構物的運動模式、繫纜力、透過係數及反射係數。假設浮式結構物在水面上的變化是微小而且線性的，加裝在浮體下方的柔性翼板厚度可以忽略並且為均勻抗彎。本文在此選擇四種彈性模數進行討論，分別為 = 0.001, 0.05, 0.5 和 5。結果顯示當柔性翼板的彈性模數逐漸減少時，浮體震盪的自然頻率、繫留力、波浪反射力和波浪繞射情況會落在短週期波的區間內。此外，本研究也發現浮體結構物的繫留力和垂直運動有正相關。|
In this study, the Dual Boundary Element Method (DBEM) has been applied to numerical simulations of the dynamic behavior of floating bodies with rigid skirt and mooring lines such as: pitch RAO (response amplitude operators), surge RAO and heave RAO; reflection and transmission coefficients; forces on mooring lines, and energy loss. The results show that the double skirts mounted beneath a rectangular floating structure, which together comprise a floating structure, can increase the added mass and thus cause the response of the floating structure to be less sensitive, thus the floating structure can only be excited by waves of a longer period waves. Such phenomenon enhances the ability of the floating structure to resist the wave forces. The angles between the rigid skirts and the vertical axis of the wave tank varied from 00 to 900 with 300 degree difference between two adjacent designs. When the angle is 00 degrees, the numerical results of the response amplitude operators agree well with the results done by Mohamed R. Gesraha. In other cases, the calculated results also agree well with the experimental data. The drag coefficient C¬¬¬¬¬d¬ also is reported and discussed in this study. The number of rigid skirts and the length of the rigid skirts also are considered in this research. The resonant frequency of the floating structure with longer rigid skirts corresponds with the long wave period. On the other hand, this study focused on the change in the structure’s motion in each mode; forces on the mooring lines; transmission and reflection coefficients induced by the flexible rigidity. The motions of the structure were assumed to be small and linear. The flexible skirts mounted beneath the structure were assumed to be of uniform flexural rigidity and the thickness of the skirts was negligible. The flexible rigidities selected were 0.001, 0.05, 0.5 and 5 for simulation. The results show that the natural frequencies of the structure’s oscillation, moored force, wave reflection and transmission tended to the region of short-period waves when the flexible rigidity gradually decreases. Positive correlation exists between the aft mooring force and the pitch motion of the floating structure.
|Appears in Collections:||[河海工程學系] 博碩士論文|
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