非線性波浪作用下繫纜之動力分析

本研究目的在於分析水底纜繩在規則波列通過下受波力作用非線性的動態行爲。求解的概念爲將纜繩結構分離爲有限的元素，每個元素的平衡則必須滿足虛功方程式。由於離散化的方程式是高度非線性的，在求解過程應用到增量與疊代的技巧。在進行動態分析之前，纜繩的初始平衡形態可藉由黏滯鬆弛的技巧於靜態分析中獲得；而在動態分析中，本研究採用隱式的Newmark法來積分運動方程式。驅使纜繩運動的流體力量乃根據Morison公式，而波浪下流體的運動採用勢函數理論，非線性波浪則引用至Stokes二階解。本研究成果顯示在繫纜靜態平衡形態的計算與解析解比較有良好的一致性，在動態分析上當前的數值模式可合理地模擬繫纜繩於非線性波浪下之動態行爲。

關鍵字

纜繩；非線性波；虛功；有限元素

並列摘要

In this study, the dynamic problem of a mooring cable fixed at two ends and subjected to wave forces is investigated. The governing equation for cable structure is derived from the principle of virtual work. A finite element method is then used to obtain the discrete equations for numerical computation. Due to highly nonlinearity of the discrete equations of motion for cables, further manipulations, including incremental and iterative schemes, are used in solution procedures. Before performing dynamic analysis, the initial equilibrium configuration of cable structure is calculated by the viscous relaxation technique in static analysis. In this study, the implicit Newmark's method is chosen for integration of the equations of motion in nonlinear dynamic analysis. To describe the wave forces, the Morison equation is used to calculate the drag forces on cables, and the fluid motion generated by water wave is based on potential wave theory, in which the nonlinear Stokes waves is applied up to the second-order solution. Good agreements between numerical results and analytic solutions are shown in calculation of equilibrium configurations. The present numerical model can be used to simulate dynamic motions of mooring cables starting from initial static equilibrium position.

並列關鍵字

Cable ； Nonlinear Waves ； Virtual Work ； Finite Elements

國際替代計量

非線性波浪作用下繫纜之動力分析

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