Investigation On The Separation Of Incident And Reflected Waves

Wave reflection is an important physical property of proceedding waves and it can alter the characteristics of wave field significantly. A physical experiment is one of the major means in ocean and coastal engineering. However, wave series measured in experiments are usually composed by incident and reflect waves. To assess the performance of marine structures, Determination on the reflection and transmission coefficients is the primary task to assess the performance of structures. Therefore, separation methods are needed to obtain the uninterfaced incident and reflected waves. Until now, there are many separation methods to deal with these problems. However, the existing methods have merits and shortcomings respectively, therefore, how to choose a proper method is a hard task. In this dissertation, the existing separation methods will be reviwed extensively. Then, the merits and disadvantages for each method are discussed and summarized as a reference for usage in practice.Firstly, the methods for separating two-dimensional free waves in both frequency and time domains are investigated. And the relating modifieds methods considering influence currents, bathymetry and damping are introducted. Then the virtues and limitations of each method are discussed. Eventually, a general procedure for separating two-dimensional free waves is concluded.In the shallow waters, higher-order waves including low frequency and higher harmonics of the primary waves can be enhanced mainly due to triad-order nonlinear interactions with decreasing water depth. After wave breaking or abrupt bathymetry changes, bond higher-order harmonics can be released as free waves. Accurate determination of wave components with different propagating characters is a key issue to reveal the generation mechanics of surf beat phenomonen. In this thesis, all existing methods for separating higher harmonics in both frequency and time domains are summeried. The advantanges and disadvantages of each method are later discussed extensively. And the points for application these methods are emphasized.Lastly, the separation methods for three-dimensional wave fields are introduced. For the oblique incident waves, there are separation methods in time and frequency domains. However, for mutile directional propagating waves, only separation methods in frequency domain are availale. Therefore, the modified maximum likelihood method (MMLM), the modified bayesian directional method (MBDM) and the wavelet-based method are summarized..