Experimental study on the hydrodynamic performance of rectangular floating breakwater influenced by reef areas

Abstract

In this paper, series of experimental studies under regular wave actions to investigate the hydrodynamic performance of the rectangular floating breakwater (FB) affected by reefs with different slopes were carried out in a wave flume. The wave transmission coefficients, motion responses and mooring forces can be calculated on the basis of the data obtained from the experiments. A comparative experiment of the only rectangular FB is also conducted. The experimental results reveal that the rectangular FB with different reefs can make more positive effects on wave energy dissipation than that of the only rectangular FB, especially for short-period waves. The characteristics of three degrees of freedom of the rectangular FB affected by reefs are also observed, which can be used to further explain the variation tendency appeared in transmission coefficients. The roll motion of the FB influenced by reefs is intenser than that of the only FB and the changes of slopes have limited effects on the sway motion of the FB. Furthermore, the heave motion of the only rectangular FB is intenser than that of the FB affected by reefs for short-period waves and vice versa for long-period waves.     

V形防波堤与圆弧型防波堤之浅水波绕射作用的比较

应用椭圆余弦波的绕射理论,推导了V形防波堤的浅水波浪绕射解析解,从而对现有的Airy微幅波理论进行了有效拓展。据此理论对V形防波堤的浅水波绕射作用进行了解析计算,并与几何形状相近的圆弧型防波堤结果加以了对比。结果表明：椭圆余弦波理论计算的V形防波堤最大波浪力和最大绕射波面明显大于微幅波理论的对应值。本方法适用于张角180°的有限长直立薄壁防波堤的浅水波绕射作用计算,从而将无限长直立薄壁堤的反射波理论加以有效拓展。张角同为120°的V形堤与圆弧堤的堤后防浪效果相近,而180°圆弧堤的堤后防浪效果优于张角90°的V形堤。     

WEC-透空式防波堤集成装置能量转换效率研究

基于成本共享理念的波浪能发电装置(WEC)的开发与设计为降低建设成本提供了新的研究思路,应用计算流体力学方法对在透空箱式防波堤前附加垂荡浮子的集成装置进行数值模拟研究,主要研究了流体黏性和非线性PTO系统以及浮子形状对此类集成装置能量转换效率的影响。结果表明,此类集成装置可以获得较高的波能捕获宽度比(CWR),最高可达0.7,可以较好地利用反射波波能。共振区间上受黏性影响较大,相比于线性无黏理论解,CWR下降明显;实现了2种非线性PTO系统的模拟,有待于进一步的优化未获得更高的CWR值;浮子形状优化效果明显,采用圆底形浮子受黏性影响更小,可以获得更大的CWR值。此种集成模型的模拟和研究可以为新型防波堤设计和现有防波堤的改造提供思路和参考。     

连云港埒子口海域潮动力特征及其变化

为研究连云港埒子口海域潮流动力特征及其对周边海岸工程的响应,以及为治理埒子口闸下淤积问题提供参考,建立了基于有限体积法离散二维浅水方程的数值模型。采用实测水文资料对模型率定和验证,应用模型分析埒子口潮流动力特征和建设徐圩港防波堤和灌河口导堤后埒子口海域潮流动力的变化。模拟结果表明,建设工程后潮流动力变化较大,埒子口海域涨急流和落急流方向改变,涨、落潮平均流速均减小,距离工程区域越近,流速变化越大。埒子口海域潮流动力减弱将会加重上游挡潮闸的闸下淤积问题,致使埒子口排水不畅,进而增加沂北地区的洪涝风险,所以,相关部门应及时采取措施,保证埒子口排涝畅通。     

RANS Modeling of Solitary Wave Propagation over A Submerged Rectangular Breakwater

In this paper a series of numerical simulations are performed to investigate the vortex shedding mechanism for a solitary wave propagating over a submerged breakwater by use of Reynolds averaged Navier-Stokes (RANS) model combined with a k-ε model. Flows of different Reynolds numbers up to Re=1.4×105 corresponding to varying incident wave heights are considered in which the characteristic fluid velocity is represented by the maximum horizontal velocity above the submerged breakwater. For the verification of the accuracy of the numerical model, the incident waves and the velocity field in the vicinity of the breakwater are compared with experimental data. The result shows that the model is capable of describing vortex shedding for a solitary wave propagating over a rectangular submerged breakwater. Key features of vortex generation, evolution and dissipation are investigated. It is found that the vortex shedding and their evolution due to separated boundary layer over the breakwater are strongly related to the Reynolds number. A considerable number of vortices and complicated vortex pattern are observed as the Reynolds number increases.     

基于风险量化防波堤工程施工期保险费率厘定

如何对防波堤工程保险的保费进行厘定是国内外保险业和工程界共同面临的课题。利用蒙特卡罗技术建立模拟防波堤工程建设期间风险损失的模型,计算斜坡堤工程实例在建设期间的风险损失期望值,由此得到相应的纯保费率和商业保费率。     

波浪作用下堤前冲淤研究综述

总结了近年来国内外对波浪作用下堤前冲淤的研究状况,包括规则波和不规则波作用下堤前海床的冲淤形态、冲淤形态判别标准、冲淤机理等.针对该课题的研究现状,提出了需进一步研究的问题.     

Design weight of armour stone considering the effect of extreme waves

In this study, waves with the heights higher than H_1/3 in an irregular wave train are called as extreme waves and defined with the help of extreme wave parameter, α_extreme. In order to see the effect of extreme waves on the design weight of armour stone, stability analysis is carried out based on the hydraulic model test results. The test results of high α_extreme cases (HE) and low α_extreme cases (LE) are compared with currently used van der Meer's formulae with permeability factor P=0.4 and 0.45 and Hudson formula by using H_1/3 and H_1/10 in terms of the design weight of armour stone. As a result of the comparison, it is found that Hudson formula by using H_1/3 underestimates the necessary armour weight. Usage of H_1/10 instead of H_1/3 in Hudson formula doubles the weight which seems overestimated when Irribaren number is away from the transition zone in which both wave run-up and run-down forces become effective. However, it seems underestimated near the transition zone where experiment case HE gives higher armour weights. When the design weight of armour stone is calculated by van der Meer's formulae with P=0.4, it may be necessary to increase the weight up to 30% in the case of high extreme waves. On the other hand, van der Meer's formulae may overestimate the weight 14% when the extreme waves are low.     

Scaled Boundary Finite Element Analysis of Wave Passing A Submerged Breakwater

The scaled boundary finite element method （SBFEM） is a novel semi-analytical technique combining the advantage of the finite element method （FEM） and the boundary element method （BEM） with its unique properties. In this paper, the SBFEM is used for computing wave passing submerged breakwaters, and the reflection coeffcient and transmission coefficient are given for the case of wave passing by a rectangular submerged breakwater, a rigid submerged barrier breakwater and a trapezium submerged breakwater in a constant water depth. The results are compared with the analytical solution and experimental results. Good agreement is obtained. Through comparison with the results using the dual boundary element method （DBEM）, it is found that the SBFEM can obtain higher accuracy with fewer elements. Many submerged breakwaters with different dimensions are computed by the SBFEM, and the changing character of the reflection coeffcient and the transmission coefficient are given in the current study.     

Numerical Simulation on Hydraulic Performances of Quarter Circular Breakwater

Quarter circular breakwater （QCB） is a new-type breakwater developed from senti-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 finn 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.