Mechanics of nonlinear short-wave generation by a moored near-surface buoy
Mechanics of nonlinear short-wave generation by a moored near-surface buoy
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DOI：
10.1017/s0022112098003826
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发表时间：
1999-02
影响因子：
3.7
通讯作者：
Q. Zhu;Yuming Liu;A. A. Tjavaras-A.;M. Triantafyllou;D. Yue
中科院分区：
文献类型：
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作者：
Q. Zhu;Yuming Liu;A. A. Tjavaras-A.;M. Triantafyllou;D. Yue
我们考虑面波与系留近水面浮标的非线性相互作用问题。我们的目标是研究在这个完整的波浪-浮标-缆绳耦合动力系统中产生非线性短面波的机制。我们开发了一种有效的数值模拟能力，用于非线性波浮标相互作用问题的高效高分辨率高阶谱方法和用于缆索浮标动力学的稳健隐式有限差分方法。数值格式考虑了波浪陡度上任意高阶的非线性波-波和波-体相互作用，并能处理包括负索力条件在内的缆索的极端运动。系统仿真表明，在入射波幅阈值较小的情况下，浮标会发生混沌运动，其特征是拉索折断。混沌响应的根本原因是电缆的折断和表面波的产生之间的相互作用，表面波提供了一个强(辐射)衰减的来源。由于这种相互作用，混沌浮标运动在两种相互竞争的模式之间切换：一种具有较大的平均峰值幅度和较低的特征频率，另一种具有较小的幅度和较高的频率。一旦混沌运动开始，产生的高次谐波/短波将被极大地放大。对辐射波谱的分析表明，在较高频率下的能量很大，这比在规则运动下的非线性产生所能预期的能量大几个数量级。
We consider the nonlinear interaction problem of surface waves with a tethered near-surface buoy. Our objective is to investigate mechanisms for nonlinear short surface wave generation in this complete coupled wave–buoy–cable dynamical system. We develop an effective numerical simulation capability coupling an efficient and high-resolution high-order spectral method for the nonlinear wave–buoy interaction problem with a robust implicit finite-difference method for the cable–buoy dynamics. The numerical scheme accounts for nonlinear wave–wave and wave–body interactions up to an arbitrary high order in the wave steepness and is able to treat extreme motions of the cable including conditions of negative cable tension. Systematic simulations show that beyond a small threshold value of the incident wave amplitude, the buoy performs chaotic motions, characterized by the snapping of the cable. The root cause of the chaotic response is the interplay between the snapping of the cable and the generation of surface waves, which provides a source of strong (radiation) damping. As a result of this interaction, the chaotic buoy motion switches between two competing modes of snapping response: one with larger average peak amplitude and lower characteristic frequency, and the other with smaller amplitude and higher frequency. The generated high-harmonic/short surface waves are greatly amplified once the chaotic motion sets in. Analyses of the radiated wave spectra show significant energy at higher frequencies which is orders of magnitude larger than can be expected from nonlinear generation under regular motion.