Theoretical Calculation of Floating Breakwater Performance

- In this paper, the theoretical calculation of floating breakwater performance in regular waves with arbitrary wave direction is discussed. Under the hypothesis of linearized system and applying the strip theory, we can solve the boundary condition problems of diffraction potential and radiation potential. Introducing the asymptotic expression of the wave velocity potential at infinity and using wave energy conservation, we can separately calculate the transmitted waves generated by the sway, heave and roll motion of the floating breakwater and by the fixed breakwater. Finally, we define the amplitude ratio of the transmitted wave to the incident wave as the transmitted wave coefficient CT which describes the floating breakwater effectiveness. Two examples are given and the theoretical results obtained by the present method agree well with experimental results.     

Infragravity Waves Produced by Wave Groups on Beaches

The generation of low frequency waves by a single or double wave groups incident upon two plane beaches with the slope of 1/40 and 1/100 is investigated experimentally and numerically. A new type of wave maker signal is used to generate the groups, allowing the bound long wave (set-down) to be included in the group. The experiments show that the low frequency wave is generated during breaking and propagation to the shoreline of the wave group. This process of generation and propagation of low frequency waves is simulated numerically by solving the short-wave averaged mass and momentum conservation equations. The computed and measured results are in good agreement. The mechanism of generation of low frequency waves in the surf zone is examined and discussed.     

基于海冰物理和力学参数的渤海冰工程分区

根据渤海海冰物理和力学参数分布建立渤海海冰工程分区.其特点是将作用到相同直径或宽度的直立结构物上冰的作用力范围相同的区域划分为同一分区内,因此不同重现期设计冰厚度和峰值压缩强度之积作为区划指标.为了获得不同重现期渤海海冰物理和力学性质参数,利用渤海历史资料建立用气温、水温、冰期和冰厚表达非变形平整冰层和冰样温度、盐度、密度的关系,进而获得冰的孔隙率;利用渤海海冰单轴压缩强度同孔隙率的试验关系计算相应峰值压缩强度;然后发展渤海不同重现期平整冰层物理和力学参数的平面分布.在此基础上以新区划指标做不同重现期的海冰工程分区.作为新区划的实例,给出25、50、100年重现期的渤海海冰工程分区.     

Numerical simulation of tidal current and erosion and sedimentation in the Yangshan deep-water harbor of Shanghai

Yangshan near-shore sea area is the multi-island and multi-channel area with strong flow velocity and high suspended sediment concentration. Based on the characteristics of tidal currents, waves, and sediment in the Yangshan area, a two-dimensional numerical model of tidal currents, sediment transport, and sea bed deformation is developed. In the model, the effects of tidal currents and wind waves on sediment transport are considered. According to characteristics of the study area, unstructured grids are applied to fit the boundaries of the near-shore sea area. The results show that the calculated values are in good agreement with the measured data. The field of tidal currents, suspended sediment concentrations, and the deformation of the seabed can be successfully simulated.     

Numerical Model of Cnoidal Wave Flume

The volume of fluid(VOF)method is used to set up a wave flume with an absorbing wavemaker of cnoidal waves.Based on the transfer function between wave surface and paddle velocity obtained bythe shallow water wave theory,the velocity boundary condition of an absorbing wave maker is introduced toabsorb reflected waves that reach the numerical wave maker.For H/d ranging from 0.1 to 0.59 and T(g/d)~(1/2)from 7.9 to 18.3,the parametric studies have been carried out and compared with experiments.     

开孔沉箱与斜向波作用的理论研究和实验验证

应用透空壁内流体速度与壁两侧的压力差成正比的线性模型,研究了无限多个开孔沉箱在斜向波作用下的反射问题。整个流域被分成无限多个子域,在每个子域内应用特征函数展开法对速度势进行展开。对于沉箱内的波浪运动,根据沉箱位置引入相位差概念。在构造反射波模型时,考虑了结构物几何形状周期性的影响。结果表明,当孔隙系数无限大时,开孔墙前后的速度非常接近,反射系数符合能量守恒定律。在低频入射波作用下,沉箱越短,其反射系数越小,反射系数随着角度的变大而减小。     

船体曲面几何表达及水动力性能计算的NURBS方法

采用非均匀有理B样条(NURBS)对船体曲面形状进行几何表达,所生成的网格直接用于后续的有关船体水动力性能计算工作中。对Wigley船型的线性兴波阻力和斜航操纵运动的船体,结合近似的Kutta条件作了相应的数值计算,从与试验结果的比较来看,该方法具有较好的工程精度,对船舶及海洋工程领域中的计算机辅助设计(CAD)与计算流体动力学(CFD)之间的相互集成,具有推动与促进作用。     

Nonlinear Model of Mean Free Surface of Waves

-A nonlinear model of mean free surface of waves or wave set-up is presented.The model isbased on that of Roelvink(1993),but the numerical techniques used in the solution are based on theWeighted-Average Flux(WAF)method(Watson et al,1992),with Time-Operator-Splitting(TOS)usedfor the treatment of the source terms.This method allows a small number of computational points to beused,and is particularly efficient in modeling wave set-up.The short wave(or primary wave)energy equa-tion is solved by use of a more traditional Lax-Wendroff technique.A nonlinear wave theory(James,1974)is introduced.The model described in this paper is found to be satisfactory in most respects whencompared with the measurements conducted by Stive(1983)except in modeling the mean free surface veryclose to the mean shoreline.     

Numerical Simulation of Waves Interaction with A Submerged Horizontal Twin-Plate Breakwater

The numerical investigation of regular waves interacting with a submerged horizontal twin-plate breakwater is presented in this paper. A numerical model with an absorbing wave-maker is established based on the VOF method. The validity of the model is verified by experimental results. Comparisons between the numerical and experimental results show that both the water surface profiles and the wave-induced pressures can be modeled accurately. Wave deformation over the breakwater,water particle velocities aroun...