有限水深下独立波群的能量变化试验研究

Experimental investigation on energy evolution of single wave group at finite water depth

为了研究独立高斯型波群在中等水深条件下的非线性演化情况,进行了多种波况的物理试验,重点分析了波浪各要素对波群非线性演化的影响。试验结果表明,波陡在波群演化中占主导作用,其次是波群的谱宽,前者引起的非线性主要体现在高阶谐波的能量变化而后者引起的非线性主要体现在自由波能量的变化。频带下移现象只在大波陡情况下才会发生,随着波陡的增加,频带下移发生的相对更早,随着波群的谱变窄,频带下移相对越明显。波陡的增加会使得波群更早的开始分裂。大波陡的波群在演化中会发生破碎,破碎的类型以崩破为主,并且崩破是间歇发生的,连续崩破发生的距离约为1.0～1.5倍波长。此外,破碎引起的能量损耗主要来源于主频和高频成分波,耗散率约10%～18%,平均每个崩破能耗约为初始能量的2%。

A set of experiments were carried out to investigate the nonlinear evolution of a single wave group consistent with a Gaussian spectral form at finite water depth,with emphasis on the effect of wave characteristics.It is found that wave steepness is the leading factor for wave group evolution,and the spectrum width comes the second;the nonlinearity induced by the former and the latter is reflected mainly in the energy variation of the high order harmonic and free wave respectively.It is observed that frequency downshift only occurs for the wave group with a large wave steepness;it appears relatively early with increasing wave steepness and relatively obvious with decreasing spectrum width.The increase in wave steepness leads to a earlier split of a wave group.Additionally,the discontinuous occurence of spilling breaker is observed for wave groups with a larger wave steepness.The distance between two succesive spilling breakers is approximately 1~1.5 times wavelength.In addition,the energy dissipation due to breaking comes from the dominant and high frequency components,this energy dissipation rate is about 10%~18%,and energy loss due to each spilling accounts for about 2%of the initial energy averagely.