防波堤的人工神经网络Monte Carlo法可靠性分析

防波堤建设费用巨大,且一旦遭到破坏,后果甚为严重,因此,如何准确地计算防波堤的可靠性意义重大.随着人工神经网络理论的快速发展,人工神经网络方法在结构可靠性分析中的应用逐渐得到重视.基于神经网络的Monte Carlo法计算直立式防波堤的可靠性,概率意义明确.以秦皇岛典型直立堤为算例,采用基于神经网络的Monte Carlo法对直立式防波堤进行可靠性分析时,将直立堤滑动破坏和倾覆破坏的极限状态方程中的所有参数均作为变量处理,并将计算结果与Monte Carlo模拟的直接抽样法、重要抽样法以及独立变量JC法的计算结果进行对比.结果表明:基于神经网络的Monte Carlo法和Monte Carlo模拟的直接抽样法、重要抽样法计算结果相近,而比独立变量JC法的计算结果略低.     

直立式防波堤可靠性分析

防波堤一旦破坏,会严重影响港口的正常使用功能,准确计算防波堤的可靠度指标对港口工程意义重大。防波堤所受主要荷载为水平波浪力及波浪浮托力,计算可靠度应考虑两者的相关性。结合Gumbel-Houggard Copula函数与对数正态边缘分布构造二维的Copula分布可以很好地描述荷载间的相关性。本文以秦皇岛直立式防波堤为例,用二维Copula分布计算防波堤的可靠度,并与JC独立法、JC相关法进行了比较,结果显示:用Copula分布计算的结构可靠度指标远小于JC独立法计算结果,与JC相关法接近。     

矩形开孔沉箱防波堤可靠性分析

为研究矩形开孔沉箱防波堤的可靠性,本文提出了一种新的直立式防波堤结构可靠性计算方法,考虑波高同周期的相关性,将波高、周期和抗力作为随机变量处理,构造隐式功能函数,采用直接抽样法生成随机样本进行模拟,作为中间变量的波浪荷载不做统计分析处理,根据功能函数的响应直接判断是否滑移或倾覆失效,计算失效概率和可靠指标。计算结果表明:新的计算方法与传统直接抽样法相比结果数值非常接近,验证了新方法的有效性;同传统JC法相比,新方法相对保守。本计算方法在波浪要素资料充足时可为矩形开孔沉箱防波堤的设计提供参考。     

荷载变量相关下直立式防波堤的可靠度

为了探讨独立或相关荷载变量对结构可靠指标(β)值的影响,利用广义随机空间极限状态曲面上任一点处切平面法线来确定可靠指标,从而将在欧洲通用的确定直立式防波堤可靠指标的Hasofer和Lind方法推广至适用于波浪水平力与浮托力之间相关的情况.对一座直立堤实例的核算表明,在变量相关情况下采用改进的JC法或推广的HL法得出可靠指标值符合良好,而荷载相关时的可靠指标值则明显低于假定荷载独立时的结果.     

港口工程结构可靠度研究进展

本文系统地总结了结构可靠度理论在港口工程领域的研究和应用,对国内外工程结构可靠性设计标准的发展历程进行了回顾,介绍了中国港口工程结构可靠度设计的基本原则和方法,并从四个方面总结了港口工程结构可靠度的研究发展和现状:(1)港口工程结构荷载与抗力的统计分析;(2)防波堤的可靠度计算与可靠性设计;(3)重力式、板桩、高桩和开敞式码头的可靠性设计;(4)桩基基础和边坡稳定研究。目前,港工结构可靠性研究正在从近似概率设计向全概率设计转变。新方法和新技术的发展和应用将推动港口工程可靠性设计理论和实践的变革。     

基于可靠度理论的防波堤设计方法

文中综合了不规则波试验和统计分析的结果,提出一个以可靠度理论为基础的新的直立式防波堤设计方法。频率分析表明,对数正态和极值Ⅰ型[耿贝尔(Gumbel)]分布可用来描述直立堤上波浪力的长期分布。     

边坡整体稳定的可靠性分析方法

边坡整体滑动稳定性的可靠性分析是建立在土体具有的抗力大于荷载效应的概率基础上进行设计和校验的。在条分法的基础上推导出了进行边坡稳定可靠性分析的统一极限状态方程 ,将土的容重γ、内摩擦角φ、粘聚力 c作为随机变量 ,当其为非正态分布时 ,进行当量正态化 ,考虑变量相关的情况 ,用简化相关法对随机变量进行统计分析 ,并以 Bishop圆弧滑动法为例 ,用 JC法求解边坡的可靠性指标及失效概率 ,给出计算安全系数和可靠性指标的算法程序。并就影响可靠性指标的因素如抗剪强度指标、变量分布形式、土性参数的变异性等进行了讨论。     

基于粘性流模型的筒型基础防波堤波浪力数值分析

筒型基础防波堤是一种新型港口海岸工程结构,其基础上部是由连续排列的圆筒构成的直立防浪墙.采用粘性流数值模型,研究连续圆筒防波堤上波浪力竖向分布、水平(沿圆筒环向)分布和波浪力合力特性,并对粘性流数值模型计算的平面直墙波浪力与海港水文规范方法计算结果;粘性流数值模型计算的连续圆筒墙面波浪力与平面直墙波浪力;无限长连续圆筒墙面波浪力与有限长连续圆筒墙面波浪力进行比较分析.针对所选工程算例,建议按<海港水文规范>中平面直墙波浪力计算方法确定连续圆筒防波堤上的波浪力时,波峰时考虑0.90左右的折减系数,波谷时考虑0.95左右的折减系数.     

中日直立式双板桩防波堤设计方法比较研究

直立式双板桩防波堤是一种对深水软土地基有较强适应性的防波堤结构,但是目前尚无系统的设计方法。本文以某外海深水直立式双板桩防波堤为例,分别采用国内规范和日本规范给出的方法计算直立式双板桩防波堤的入土深度和桩身内力。结果表明,中日规范在直立式双板桩防波堤的设计中均有一定的局限性:对于国内规范,当堤顶宽度较小时,其墙后主动土压力的计算会与实际情况有较大差别;对于日本规范,当堤顶宽度较大时,墙后填土产生的抵抗弯矩不符合实际情况。由此,对直立式双板桩防波堤的设计,建议同时采用中日两种计算方法进行设计并相互验证,共同拟定合理的结构断面。     

直立式防波堤兼码头水工结构设计与试验研究

基于青岛崂山前海直立式防波堤兼码头工程的设计,通过规范计算值与断面物理模型试验数据的对比分析,合理确定断面尺度、堤顶高程和越浪量等重要设计参数。特别是通过多组试验的数据分析,对挡浪墙的外形尺度和护底宽度进行优化,采用通过增大护底块体重量的方式有效地减小护底长度,充分运用试验手段对于设计规范的护底相关规定做出了有益的探索和补充,为深水直立式防波堤的设计改进提供了借鉴。     

Meshless Method for Analysis of Permeable Breakwaters in the Proximity of A Vertical Wall

In the present work, the improved version of the meshless singular boundary method(ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method(BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater's width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.     

On front slope stability of berm breakwaters

The short communication presents application of the conventional Van der Meer stability formula for low-crested breakwaters for the prediction of front slope erosion of statically stable berm breakwaters with relatively high berms. The method is verified (Burcharth, 2008) by comparison with the reshaping of a large Norwegian breakwater exposed to the North Sea waves. As a motivation for applying the Van der Meer formula a discussion of design parameters related to berm breakwater stability formulae is given. Comparisons of front erosion predicted by the use of the Van der Meer formula with model test results including tests presented in Sigurdarson and Van der Meer (2011) are discussed. A proposal is presented for performance of new model tests with the purpose of developing more accurate formulae for the prediction of front slope erosion as a function of front slope, relative berm height, relative berm width, method of armour stone placement, and hydraulic parameters. The formulae should cover the structure range from statically stable berm breakwaters to conventional double layer armoured breakwaters.     

Long wave reflection from submerged trapezoidal breakwaters

This study addresses the reflection and transmission of long waves from a trapezoidal breakwater and a series of trapezoidal breakwaters, using the matching method. A systematic shape transfer is derived to determine wave reflection and transmission. The peak Bragg reflection of long waves from a series of trapezoidal breakwaters is shifted toward low frequency. In spite of the spacing between any pair of breakwaters, the top plane width and the arrangement of the series of breakwaters are found to be the two major parameters in designing multiply composite Bragg breakwaters.     

Experimental study of strong reflection of regular water waves over submerged breakwaters in tandem

A series of laboratory experiments was carried out to investigate the strong reflection of regular water waves over a train of submerged breakwaters. Rectangular and trapezoidal shapes of submerged breakwaters are employed and compared for reflecting capability of incident waves. Measured reflection coefficients of regular waves over impermeable submerged breakwaters are verified by comparing with those of the eigenfunction expansion method. A very good agreement is observed. Reflection coefficients of permeable submerged breakwaters are less than those of impermeable breakwaters. The trapezoidal shape is recommended for a submerged breakwater in terms of reflecting capability and practical application.     

港内波浪要素计算方法研究

为分析不同计算方法在推算港内波要素中的适用性,分别采用JTS 145-2-2013《海港水文规范》计算方法和数学模型计算方法计算了防波堤为单突堤、双突堤和岛式堤三种典型布置型式的港内波浪.将计算结果与物理模型试验结果进行了对比,分析了不同布置型式时3种方法得到的结果之间的差异性,给出了在计算不同防波堤布置型式下的港内波浪要素时上述3种方法的适用程度.     

Application of Importance Sampling Method in Sliding Failure Simulation of Caisson Breakwaters

It is assumed that the storm wave takes place once a year during the design period, and N histories of storm waves are generated on the basis of wave spectrum corresponding to the N-year design period. The responses of the breakwater to the N histories of storm waves in the N-year design period are calculated by mass-spring-dashpot mode and taken as a set of samples. The failure probability of caisson breakwaters during the design period of N years is obtained by the statistical analysis of many sets of samples. It is the key issue to improve the efficiency of the common Monte Carlo simulation method in the failure probability estimation of caisson breakwaters in the complete life cycle. In this paper, the kernel method of importance sampling, which can greatly increase the efficiency of failure probability calculation of caisson breakwaters, is proposed to estimate the failure probability of caisson breakwaters in the complete life cycle. The effectiveness of the kernel method is investigated by an example. It is indicated that the calculation efficiency of the kernel method is over 10 times the common Monte Carlo simulation method.     

Brief Account of Breakwater Construction in China

-The construction of breakwaters in China in more than 40 years since the founding of the People's Republic of China is reviewed. The construction of two main types of breakwater, upright breakwaters and rubble mound breakwaters, and the way in which they are built are expounded. Recommendations to improve the technology for future breakwater construction are presented.     

Bragg reflection of sinusoidal waves due to trapezoidal submerged breakwaters

Numerical and laboratory experiments are performed to investigate characteristics of the Bragg reflection due to multi-arrayed trapezoidal submerged breakwaters. The numerical model is based on the Reynolds averaged Navier–Stokes equations with the VOF method and the k–ε turbulence closure model. As expected, the reflection coefficients increase as the array of submerged breakwaters increases in both laboratory measurements and numerical results. The resonant periods provide similar relative wave numbers regardless of the permeability and the number of arrays. The reflection coefficients due to porous breakwaters are smaller than those due to non-porous breakwaters. The velocity contours for two and three arrays are also described.     

Deformation of breakwater armoured artificial units under cyclic loading

Rubble mound breakwaters usually consist of armour, filter and core layers. The units used in the armour layer are natural rock or concrete. Although natural rock is usually preferred, it is not always possible to apply it. There are some advantages to using concrete units: they have a high stability coefficient under wave attack, and they are easily produced at work sites. Tetrapod and cube blocks are widely used in breakwaters as armour units.Rubble mound breakwaters are subjected not only to wave activity but also other types of environmental loading, such as earthquakes. Although rubble-mound breakwaters are most likely the most common type of breakwaters, they have received little attention regarding their response to seismic activity. The objective of this study is to present the dynamic response of a breakwater armoured by tetrapods placed by two different placement methods and armoured by cubes during seismic loadings experimentally and numerically. A shaking tank was developed for the experimental study. The breakwater models sit on a rigid bed, and the model scale is 1/50. A one-dimensional shaking tank was used to understand simple responses of the rubble mound breakwaters under seismic loads. The tank allows only one degree of freedom. A raining crane system was developed to achieve the same packing density and porosity for the core material. The shape of the model breakwater before and after the tests was measured using a profiler and was recorded by computer. However, crest lowering and the level of damage on slopes were determined from profiler records. The dynamic responses of the model breakwaters were also investigated using an image processing technique. For numerical simulation, software using finite element method was used.The results obtained from the experiment and numerical model may help designers build breakwaters armoured by artificial units.