The Statistical Distribution And Spectrum Specialities Of Oblique And Multidirectional Irregular Wave Action On Vertical Breakwater

Vertical breakwater is one of typical maritime structures, which is mainly subjected to wave forces. Traditionally, the design of breakwater is based on the formulae developed for head-on unidirectional waves, very little attention has been addressed so far to the effects of wave obliquity and multi-directionality on the wave forces on vertical breakwaters. In fact, crude sea waves are multidirectional and irregular, further more usually attack a breakwater obliquely, and form short -crested waves ahead of mound ,thus exert larger forces than standing waves. There are four ways in dealing with action between irregular and construction ,they are ways of diagnostic wave and probability analysis and spectrum analysis and model test. The probability distribution of irregular wave force has been disquisitive emphasis by reliability design and optimize design used in maritime structures. The way of spectrum analysis study characteristic of spectrum structure and energy distribution of wave forces, moreover usually link with way of probability analysis, in order to confirm wave forces under different wave forces spectrum and different accumulative frequency . In this paper, the probability distribution and spectrum characteristic of obliquity and multi-directionality wave forces are studied systemically by a 3-D hydraulic model test.This paper is the partial accomplishments of the national fund project of natural science (5007900l).The physical model test was carried out in the multidirectional basin at the State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology. The JONSWAP spectrum suggested by Goda was used to simulate irregular waves, and directional spreading function of Guangyi-type was used in the test. Angles of incidence varied from 0 to 60, and three spreading parameters, s=10, 40, , three values of wave steepnesses Sop takes 0.02 , 0.03 and 0.04, and three values of wave heights Hs takes 0.06cm , 0.09cm and 0.12cm,water deepness d takes 0.45m.Through the analysis for experiment result, The form of probability distributions on the unit length of breakwater with attack angle is presented, and the effects of wave angle, multi-directionality, wave steepness, and relative wave height on wave parameters of probability distributions are analyzed. The rules of statistical distributions of oblique and multidirectional wave forces are presented. Spectrum specialities of oblique and multidirectional wave act on vertical breakwater are analyzed. Coherence between wave and wave forces on the unit length of breakwater are computed, the effects of wave angle, multi-directionality, wave steepness etc on rules of coherence are presented; The transferfunctions between oblique and multidirectional wave spectrum and wave forces spectrum are presented by ways of theory and model test, moreover the reliability of the formula of account and spectrum specialities of none linear system are discussed; Correlation between characteristic values of spectrum and characteristic values of statistics are studied, moreover the effects of wave angle and wave direction distribution on it are studied too, for wave spectrum , the correlation between characteristic wave height and spectrum quadrature mo is presented ,and compare with academic values, for wave forces spectrum, the correlation between characteristic wave forces and wave forces spectrum quadrature mo is presented.