Nonlinear Transformation of Waves above Submerged Structures

On the base of laboratory experiments the nonlinear wave transformation above submerged rectangular permeable and solid bars was investigated. A transmission coefficient and a change of mean wave period as parameters of wave transformation were considered. Both of these parameters can characterize an ability of submerged structure to reduce a wave impact in coastal zone. It was revealed that for decreasing of mean wave period solid submerged bar is more effective, but permeable bar is more effective for decreasing of wave height. The optimal relations for transmission coefficient and change of mean wave period in dependence of parameters of bar and waves were revealed. For decreasing of wave mean period the optimal length of solid bar must be 0.4 of initial wavelength and 0.1 - for permeable bar. For decreasing of wave height the length of bar for permeable bar must be 0.21 of initial wavelength and for solid bar - 0.55. It was revealed that maximal decreasing of mean wave period will be at relative depth of bar 1.25 independently of permeability of bar. The optimal relation between transmission coefficient and changes of mean wave period depends on wave steepness.