Numerical Investigations on Hydrodynamic Performance of An Open Comb-Type Breakwater Under Medium Water Levels

The comb-type breakwater(CTB)has been proposed and investigated in recent years due to its advantages in terms of deep-water adaptability,material saving and water exchanges.All existing empirical formulae for CTBs have been so far restricted to the water level above the bottom of the superstructure,which mainly occurs under the high tides or storm tides.However,based on recent engineering applications and experimental observations,the most severe conditions for CTBs are more likely to occur under a medium water level,because impulsive wave pressure may occur due to interactions between waves and the special chamber in CTBs.Meanwhile,during the most of construction and operation periods,the CTBs are mainly working under the medium water levels,i.e.,water levels below the bottom of the superstructure.In this study,the effects of main influence parameters on the horizontal wave force coefficient and wave transmission coefficient for open CTBs(with partially immersed side plates)under medium water levels were investigated based on a 3D numerical wave flume and corresponding empirical formulae were proposed.It is indicated that the location of the side plate related to the main caisson has significant influence on the hydrodynamic performance of CTBs.In engineering applications,the location of the side plate can be designed at b/L≤0.15 or b/L≥0.3(where b is the distance between the side plate and the front face of the main caisson and L is the incident wave length)for efficiently lowering the horizontal wave force and wave transmission.The flow mechanism of impulsive wave force on CTBs was revealed based on synchronous analyses of flow fields and pressure distribution.Through appropriate design of the height of the superstructure according to H/hD≤1.0 or H/hD≥1.5(where H is the incident wave height and hD is the distance between the still water level and the bottom of the superstructure),the likely impulsive wave pressure on the side plate can also be diminished.

An open cellular caisson breakwater

An open cellular caisson breakwater is a new type comoposite breakwater whose upper structure is an open chamfered caissons without bottom. It has the advantages of rational and compact configuration, good stability and low stress on its foundation ho.It is especially suitable for soft ground. The structural and hydraulic characteristics and the stability test results of this new type breakwater are presented in this paper.

EXPERIMENTAL STUDY ON A NEW KIND OF OPEN TYPE BREAKWATERS

A new kind of open type breakwaters was proposed based on the concept of wave energy conversion. The excellent feature of the structure is that it can absorb and utilize the wave energy to dissipate waves. The effects of some factors, such as the configuration insides, the geometrical parameters and the relative width (the ratio of the width to the wave length), on the performance of the breakwater were discussed based on a series of regular wave tests in the wave flume. The hydrodynamic characteristics of the new open type breakwater were analyzed in detail, and the structure was optimized to improve the performance of the breakwater to effectively dissipate the waves with long period. The variation of the coefficients of wave transmission and reflection along with attenuation with respect to relative width was examined. The results of the physical model tests indicate that the transmission coefficient significantly decreases by about twenty percent at the range of relative width from 0.1 to 0.2, compared with the traditional open type breakwaters.