On the Study of Dynamic Mooring Line Damping

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Project title

Code/計畫編號

MOST106-2221-E006-113

Translated Name/計畫中文名

水下動態繫纜阻尼特性研究

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=12244345

Year

2017

Start date/計畫起

01-08-2017

Expected Completion/計畫迄

31-07-2018

Bugetid/研究經費

550千元

ResearchField/研究領域

土木水利工程

A mooring system is used for station keeping of an offshore floating structure and it is applied to resist external loadings via mooring line damping. The mooring line motions are classified as quasi-static and dynamic motions. Quasi-static motion is defined as a mooring line has a catenary shape and its lower end contacts with seabed, which usually occurs in a calm weather. On the other hand, dynamic motion means the mooring line is fully lifted from the seabed and it is in a stage of semi-taut or fully taut, which usually caused by an extreme event. The goal of this project is to study the static and dynamic mooring line damping and their importance for floating structures. The property of a single-point mooring line damping will be tested in an environment with various oscillating frequencies and amplitudes of driving forces. The tension force at top-end point and its trajectory will be measured or simulated, and they are further applied in the methodology of free decay and indicator diagram for calculating mooring line damping. These topics will be studied experimentally and numerically. There are three stages for experiments, including the establishment of devices for measuring mooring line damping, tests for static mooring line and dynamic mooring line. The spring, rotational disc and wave flume are used as driven forces to trigger static and dynamic mooring line motions, starting from a single freedom to multiple freedoms. Two time-domain numerical models, a direct forcing immersed boundary solver for Navier-Stokes equation and OrcaFlex, will be applied to study mooring line damping. Moreover, the drift, resonant condition, snap loads and statistical properties for mooring line will be investigated. We expect the results from this project have high impact to mooring dynamics and can be applied to floating offshore engineering. 繫纜系統為限制海洋浮式結構物在某一固定範圍內移動，並輔助其抵抗各種環境荷載的定位系統。在風波流外力作用下，繫纜運動行為可分為準靜態與動態兩大種類，前者發生於一般季風狀況下，繫纜仍保持懸鍊型狀，未完全離開底床；後者常發生於颱風或湧浪等極端氣候，繫纜歷經拉撐或緊繃循環。本計畫研究主題為繫纜於準靜態與動態運動行為下的阻尼特性，探討單錨鍊系統於不同震盪週期與振幅情況下，上端點張力大小與運動軌跡的變化，應用自由衰減法與指示圖法計算繫纜阻尼，進而比較靜態與動態繫纜阻尼特性。預計將以實驗與數值模擬方式進行研究，並進行交叉比對及驗證。本研究實驗將以三階段進行，分別為建構繫纜阻尼實驗平台與開發量測技術、進行準靜態繫纜實驗以及動態繫纜阻尼實驗。驅動外力預計以彈簧震盪、旋轉圓盤以及波浪水槽等方式進行，檢視繫纜從單自由度到多自由度的阻尼變化以及作為觸發靜態與動態繫纜運動的方法；數值分析則採用時域解析的虛擬直接力量沉浸邊界法(direct forcing immersed boundary，DFIB)以及Orcina 所開發的OrcaFlex 模組分別進行模擬計算。此外，本計畫也將研究靜態與動態繫纜情形下之漂移量、共振條件、瞬荷載張力與統計參數特性等。期待本計畫的成果除了能提升學術研究深度外，更能提供為相關海事工程實務做為參考之用。

Keyword(s)

錨碇系統
繫纜阻尼
浮式結構物
瞬荷載
漂移量
mooring system
mooring line damping
floating structure
snap load
drift

DSpace CRIS

On the Study of Dynamic Mooring Line Damping

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Description