A series of regular and irregular wave experiments are conducted to study the reflective and transmitting performances of quarter circular breakwater (QCB) in comparison with those of semi-circular breakwater (SCB). Based on regular wave tests, the reflection and transmission characteristics of QCB are analyzed and a few influencing factors are investigated. Then, the wave energy dissipation as wave passing over the breakwater is discussed based on the hydraulic coefficients of QCB and SCB. In irregular wave experiments, the reflection coefficients of QCB and their spectrums are studied. Finally, the comparisons between the experimental results and numerical simulations for QCB under regular and irregular wave conditions are presented.
A numerical wave flume is constructed based on the Reynolds Averaged Navier-Stokes (RANS) equations with turbulence closure by a modified k-ε model to study the viscous interactions of waves with vertical breakwaters for different overtopping cases. The governing equations,the turbulence model,boundary conditions,and solution method for the numerical wave flume are introduced briefly. The reliability of the numerical wave flume is examined by comparing the numerical results with the experimental measurements,and good agreements between them indicate the validity of the present model. The developments of mean velocity fields,the contours of vorticity,and the influences of wave nonlinearity on turbulence field as wave passing through vertical breakwaters are discussed in detail based on the numerical results. It is noted that the vortices at the rear of the lower submerged breakwater are close to the bottom and maybe induce the scouring to the leeside toe of marine structure in practice. Over all,a conclusion can be obtained from this study that the turbulence in wave field around structure is induced directly by the development of boundary layer on the solid boundary,the nonlinear interaction of free surface with obstacle,and the plunging of overtopping waves.
The siltation induced by wind waves in an entrance channel is one of the prime factors influencing the operation efficiency of a port.It is necessary to predict the siltation accurately for dredging and ship operation passing through the entrance of the port.However,it is difficult to apply the traditional method to predicting entrance siltation because of its complex computational procedure and lacking the data of ocean dynamic elements in the specified sea area.From the view of energy conservation,a direct relationship between wind conditions and sediment deposition can be founded.On the basis of the above methodology,an empirical formula expressed by wind conditions for forecasting the siltation in the entrance channel is set up.The wind conditions are easily obtained from the local meteorological stations or weather maps,so the formula established in this paper is more convenient and practical than the traditional method.A case study is provided,in which the emopirical formula is calibrated and verified utilizing the measured wind and siltation conditions in the entrance channel of the port.Comparisons between computed values and measured data show satisfactory agreement.
Quarter circular breakwater(QCB)is a new-type breakwater developed from semi-circular breakwater(SCB).The superstructure of QCB is composed of a quarter circular front wall,a horizontal base slab and a vertical rear wall.The width of QCB's base slab is about half that of SCB,which makes QCB suitable to be used on relatively firm soil foundation.The numerical wave flume based on the Reynolds averaged Navier-Stokes equations for impressible viscosity fluid is adopted in this paper to simulate the hydraulic performances of QCB.Since the geometry of both breakwaters is similar and SCB has been studied in depth,the hydraulic performances of QCB are given in comparison with those of SCB.
