Experimental Study And Numerical Simulation Of A Porous Floating Breakwater

Floating breakwater is a sort of floating structure moored on seabed, which provides port, coast with protection. Comparison with fixed breakwater, floating breakwater doesn't affect the water exchange and has little increase on cost with increscent water depth. So far, the cases of practical application are very few. The main reason is its poor performance on wave attenuation especially for long wave. Another one is the safety of mooring system, which is extremely significant for the design of floating structure. The contradiction between performance and mooring force has not been solved in the existing investigations. Therefore, this paper presents the investigations and results on configuration of floating breakwater influences performance and mooring force with lots of diamond blocks.First, this paper provides an analytical and experimental study of linear incident waves exerting on an articulated multi-module floating structure with the method of eigenfunction expansion for evaluating the feasibility of treating the large-scale flexible floating structure as floating breakwater. The matching equations are computed coupling with motion equation which can be obtained by using Lagrange's Equation. The results show that it can barely be used as floating breakwater owing to its poor stiffness and small draft.Secondly, using equal quantity of diamond blocks, the author has constructed more than ten kinds of floating breakwater models with different configurations and carried out experiments including of transmission coefficients and mooring force. The results of three sorts of dense structures with various aspect ratio and stiffness show that the amount in the same material and covered with diamond-shaped module assembly, the large width, shallow draft, high flexibility mat-shape and small width of the floating breakwater, deep draft, high-rigidity box wave properties of porous structure not very different, and in the mooring cable tension to zero when the first practical applications were difficult to meet the breakwater should have the effect of wave attenuation. In five different features of the outline and the internal structure of the floating breakwater structure of the experimental analysis, floating breakwater wave properties form the outline of its cross section has little to do, but the location and internal configuration present significant impact.In addition, the increased initial anchoring force can improve performance significantly, but under the action of the waves may have a greater cable capacity. This article is also carried out while the construction of four forms with same width of a distinct identity for rectangular floating breakwater model performance with the cable force and consumption wave experiments and found that the internal geometry of floating breakwater has significantly influence on the wave properties and mooring force. Overall, the outer surface of the windward and the leeward of the floating breakwater should have the appropriate hollow, whereas the central vertical plane should be more closed structure, which is conducive to the role of the time difference to the incident wave, to block wave energy directly through the structure and to reduce the "wave" effect while floating breakwater on the cover of water movement. Appropriate penetrability on the vertical is also advantageous to wave attenuation and force debasement.Base on the influential factors from aforementioned results, this paper presents an optimized configuration of floating breakwater and its performance in waves. Two mooring modes, directional mooring and bidirectional mooring are considered in the tests. The influence of an impermeable vertical sidewall on transmission coefficient is estimated. The results examined under the present investigations are:Kt, wave transmission coefficient (Kt=Ht/Hi, Ht-transmitted wave height, Hi-incident wave height); Kr, reflection coefficient (Kr=Hr/Hi, Hr-reflected wave height);Eloss (Eloss= (?)), the value of the dissipation of incident wave energy; and mooring force per unit length of the breakwater. For the case of floating breakwater with impermeable sidewall, measured transmission coefficient KT (KT=HT/H, HT-the measured wave height in front of the sidewall, H-the wave height without structure and sidewall) is offered. The experimental results show that the proposed floating breakwater can reduce incident wave height by dissipating wave energy more than reflecting it. It is propitious to not only reduce mooring force but also weaken accumulated energy with the role of impermeable sidewall.Lastly, the numerical model of the hydrodynamic characteristic is developed on moored porous floating breakwater with boundary element method.