Experimental and Numerical Study on Dynamics of Mooring System

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Project title

Code/計畫編號

MOST105-2218-E006-020

Translated Name/計畫中文名

三維水下繫纜動態實驗與數值複合型研究

Project Coordinator/計畫主持人

Wen-Yang Hsu

Funding Organization/主管機關

National Science and Technology Council

Co-Investigator(s)/共同執行人

陳明志
楊瑞源

Department/Unit

Tainan Hydrotech Laboratory,NCKU

Website

https://www.grb.gov.tw/search/planDetail?id=11918233

Year

2016

Start date/計畫起

01-08-2016

Expected Completion/計畫迄

31-07-2017

Bugetid/研究經費

820千元

ResearchField/研究領域

820千元

The floating platforms have been successfully applied to support cage aquacultures and floating breakwater. In recent years, the floating platforms were further used to carry heavy turbines to extract energy from the wave, current and wind. The balance mechanisms of the floater came from ballast water, the position of gravity/buoyancy and mooring system. The mooring dynamic is highly nonlinear and fully coupled system when it is subjected to a natural environment. Based on the literature review, we identify the mechanical behaviors of mooring line in quasi-static and dynamic states. However, most experimental studies only focus on the tension force of mooring line at the fairlead. The limitation of instruments and measurement technology has hindered us to examine the mooring line dynamic together with coupled external forces in time domain. As a result, we will develop a synchronized 3-D underwater image tracking system to measure the instantaneous tension force and the corresponding geometry of mooring line. Under a quasi-static or dynamic forcing, the technique allow us to study the mooring line dynamics, such as change of mooring line shape, tension force, mooring line damping, energy dissipation, snap load and its probability. On the other hand, we will develop a fluid-structure model for the mooring line. The framework is based on the direct forcing immersed boundary simulation of the hydroelastic behavior of a mooring line in a periodic displacement. The model-data comparison will be made for improving the accuracy of the model. The results obtained from this project can provide a better insight into the complex fluid-structure interactions and provide sufficient data for designing a floater. 海上浮動式載台過去常應用於箱網養殖、蚵架與浮式防波堤等輕載重，近年因再生能源興起，浮式結構物廣泛被應用於搭載海流或波浪發電機以及風機等重荷載。海上浮動式載體之平衡來自壓艙水、結構重心/浮心設計與錨碇系統等平衡機制。在風浪與流等外力作用下，繫纜動態為高度非線性與多項耦合作用，對於浮動載體穩定性扮演極重要腳色。為深入探討繫纜動態，本計畫先進行繫纜破壞因素、繫纜及浮體平台間交互作用等相關文獻回顧，整理出繫纜於準靜態(強制位移)或動態外力(風波流)作用下繫纜之力學行為。然而，往昔實驗多數僅在浮台與繫纜間安裝張力計(load cell)，並受限於實驗儀器與量測技術等，難將繫纜動態行為與耦合外力進行時域分析。有鑑於此，本計畫擬開發水下3維繫纜動態擷取系統，量測繫纜受力與幾何形狀變化，並與其他量測儀器同步，針對繫纜於靜態或動態的作用下，探討繫纜之幾何形狀變化、張力大小、繫纜阻尼、能量衰減、瞬荷載大小與發生機率等。另一方面，本計畫將透過合作方式，共同開發適於繫纜之流固耦合模式，採用具虛擬力的直接力量沉浸邊界法(direct forcing immersed boundary，DFIB)求解Navier-Stokes 方程式，與實驗結果交互驗證。上述研究成果期能對浮體載台之錨碇系統，完整地呈現繫纜-水動力-浮體運動等耦合力學機制，提供浮體載台開發時所需之參考與驗證。

Keyword(s)

水下三維質點影像追蹤
繫纜動態
浮動式平台
瞬荷載
直接力量
沉浸邊界法
3-D underwater particle tracing
mooring line dynamics
floating platform
snap load
direct forcing immersed boundary (DFIB)

DSpace CRIS

Experimental and Numerical Study on Dynamics of Mooring System

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