近自由水面水平板式防波堤消波特性及消波机理研究

Study on submerged plate type breakwater very close to free surface

近自由水面刚性水平薄板可作为一种新型的防波堤型式,文章通过应用完全非线性数值波浪水槽技术来探索这种型式防波堤的消波特性和消波机理。研究发现:水平板的浅水效应、透射波浪回流和板后波数分解成一系列高频短波是该种型式防波堤消波的三个重要原因。从工程应用的角度考虑,板的潜深与波高的比值以及板长与波长的比值是决定水平板消波的两个重要参数,合理地调整这两个参数,板式防波堤的透射系数可控制在0.2至0.5之间。由非线性数值模拟结果还可以发现,对于非常接近自由水面的水平板问题而言,会产生不少于3阶的高频短波,这说明用线性理论研究物体近自由水面问题是有局限性的。

A device system, composed of a submerged horizontal plate is proposed to be one type of breakwater. The plate is supposed to be thin, rigid and close to the free surface. Based on fully nonlinear theory, a numerical wave tank technique is utilized to investigate the wave elimination mechanism of the device. The shallow water effect,return flow and higher order high harmonic wave components behind plate,are three contributions to wave elimination.From the viewpoint of engineering application,the ratio of plate sub- mergence to wave height and the ratio of plate length to wavelength are two decisive coupling factors to wave transmitted coefficients.Carefully regulating these two factors,transmitted wave coefficient will be controlled under 0.2 to 0.5. From numerical simulation, for plate very close to free surface, at least third order wave elevation and hydrodynamic force should be considered which reveals the limitation of linear theory.