Study On Wave Attenuation Mechanism Of Surface Vertical Multi-plates

Breakwater plays an important role in protecting marine structures,and the main function of breakwater is to reduce the negative effect of out-sea waves and storm on structures in protected area.Nowadays,marine economy developed gradually to deep sea where traditional breakwater is not suitable.Floating breakwater which is usually positioned near the water surface has got much attention for some of its applications at deep water locations.Numerical study on the interaction of regular wave with surface vertical multi-plates is carried out.Numerical wave flume is established in Fluent software,using piston wave maker to generate waves,VOF method to capture free surface movement.Numerical method is verified by good agreement of numerical wave with analytical wave.In order to calculate the reflection coefficients,two new methods are proposed in this paper based on wave superposition principle.using these two methods to deal with the reflection coefficients of two different models,one is a complete reflection experiment model,the results of this model obtained by those two methods are quite close to the ideal value;the other one is a numerical model,compare the numerical results with experiment results of this model,their coincident indicates that these two methods are valid in calculating reflection coefficients.Four factors are considered to analyze the wave attenuation mechanism of surface vertical multi-plates:plate number and immersion depth,incident wave length and wave steepness.Reflection coefficient _rC,transmission coefficient_tC and energy loss coefficient_lC of the numerical model versus with dimensionless plate spacing 2S L is analyzed.Flow field materials:phase contour,velocity contour and velocity vector near plate are presented.The results show that:_rC increase with plate number and immersion depth increasing and decrease with an increase of incident wave length and wave steepness;Results of transmission coefficient_tC show a decrease with plate number,immersion depth and wave steepness increasing,and an increase as wave length increase;The energy loss coefficient_lC increases with an increase of plate immersion depth and incident wave steepness.Near the condition of 2S L=1and 2S L=2,_rC increase,_tC and_lC decrease obviously,which means that there exist Bragg resonant phenomena when regular waves interact with surface vertical multi-plates,and Bragg resonance can enhance wave reflection and reduce wave transmission and wave energy loss.When the incident wave length and nonadjacent plate spacing satisfy Bragg resonance condition,the phenomena of reflection enhancement,transmission and energy loss descent also occur.The flow field materials show that eddies occur near plates which cause viscous dissipation.A numerical simulation method is used to study the mechanism of wave attenuation of interaction between regular wave and surface vertical multi-plates,which lays a foundation for further study of breakwater with variable plate spacing,perforated breakwater and flexible membrane floating breakwater.