Numerical investigation of non-cohesive seabed response around a mono-pile by crossing wave-current

The interaction between waves and currents in the ocean often complicates the flow field around structures. In this study, a three-dimensional integrated numerical model was established to investigate the seabed response and liquefaction around a mono-pile under different wave–current interaction angles. In the present model, the Reynolds-averaged Navier–Stokes equations were used to simulate the flow field, and the Biot's poro-elastic theory was adopted to calculate the seabed response caused by crossing wave-current loading. Unlike previous studies, the load on the mono-pile was considered, and the wave–current interaction angle was extended to 180°, which was more in line with practical engineering problems. The numerical results were in a good agreement with the experimental measurements. The results indicated that waves interacted with currents in a large angle could result in a large momentary liquefaction depth of the seabed. The parametric studies proved that the position of the front and two sides of the pile was relatively safer compared with that of the leeside of the pile, and the surface of the seabed downstream of the pile was liable to liquefy.     

Numerical analysis of seabed dynamic response in vicinity of mono-pile under wave-current loading

Pile foundations have been widely used in offshore engineering.In this study,a three-dimensional numerical model was used to investigate the seabed response around a mono-pile under wave-current loading.Reynolds-averaged Navier-Stokes equations were used to simulate the flow field,and Biot's consolidation equations were used for simulating the response of a porous seabed.The pore water pressure within soil and the effective stress along the depth of the seabed were simulated for various current velocities,with currents traveling either along or against the wave.Results indicate that the current has a significant effect on the effective stress and the pore water pressure distributions,which increases with the current velocity,and that the current traveling against the wave increases the liquefaction depth of the porous seabed.     

波浪作用下海床液化的数值分析

较大的风浪会使海床发生液化,波浪引起的海床液化问题是海岸及近海工程必须要考虑的关键问题之一。当海床内部土骨架的有效应力转移给孔隙水压力进而变为零时,土体将丧失剪切强度出现液化现象。基于Biot固结理论,利用软件FLAC,分析波浪作用下海床的动力响应,可推出波浪作用下海床最大液化深度,同时也可以得出波浪作用下海床液化的过程,即孔隙水压力上升、土层液化、液化后土层下沉压缩以及孔隙水压力消散,所得结果较好地反映了波浪作用下海床液化的规律。     

海上风电桩基局部冲刷试验研究

风电桩基既承担风机自身荷载,又受到叶片转动的侧向压力,桩基稳定性至关重要。海上风电桩基不仅受潮汐双向水流和波浪共同作用的影响,而且桩基尺度介于通常的桥墩和码头桩基之间,局部冲刷具有一定特殊性。通过建立1∶60的正态模型,研究了洋口海域海上风电桩基在波浪、潮流及波流共同作用下的局部冲刷。结果表明:潮流是控制该海域桩基局部冲刷的主导因素;往复流作用下的冲刷坑形态呈椭圆形,最大冲刷深度约为恒定流的80%;当波流共同作用时,由于桩前波浪振荡水流的作用,泥沙较水流作用时更易起动,局部冲刷显著增强,最大冲刷深度为潮流和恒定流作用下的2.0与1.7倍;韩海骞公式计算值按照系数0.75折算后与波流作用下的桩基冲刷深度试验值较为吻合。根据试验结果,建议对桩基周边局部冲刷坑进行抛石防护,确保海上风机的安全稳定。     

波流作用的近岸圆柱局部床面侵蚀

波浪流对近岸浅水带床面作用强烈,该区域结构物局部床面侵蚀显著,潜存致灾威胁。用三维数值方法研究了瞬态孤立波作用下非黏性沙海床上的近岸圆柱体局部冲刷规律,分析了波浪流冲刷的3类主要影响要素,讨论了近岸地形条件影响下的波流冲刷深度。研究认为,表征浅水波流特征和柱体尺度的无量纲数Urp与KC数存在非独立关系,二者均能分别反映波流冲刷的主要规律;表示泥沙运动的力学参数Shields数在波流动床条件下仍对柱体局部冲刷有贡献;近岸地形通过床面坡度对波破碎的增强及堤岸挡墙对波浪的反射,都会影响到局部冲刷。     

波浪加速度不对称性对海床液化的影响

为研究加速度不对称波浪作用下的海床响应特征,基于Biot多孔弹性介质理论建立了波浪作用下海床响应数学模型,采用水槽实验数据对模型进行了验证。通过引入加速度不对称波浪压力边界条件的计算方法,模拟分析了波浪加速度不对称性对海床内部孔隙水压力、有效应力以及土体液化的影响。结果表明,波浪加速度不对称性会引起海床表层正向孔压幅值的显著衰减,使孔压的空间分布变得偏斜,减小了液化深度和宽度,使海床液化区域变得窄而浅。     

波流作用下淹没圆柱局部冲深影响因素分析

淹没圆柱在海洋工程中运用广泛,局部冲刷对此类建筑物的安全有较大影响。为掌握该类型建筑物在波流作用下的冲刷特性,在波流水槽内开展了一系列试验研究。试验将圆柱模型安装在波流水槽中部的沙槽内,沙槽内铺设中值粒径0.22 mm的无黏性沙,形成平底海床。试验中圆柱处于淹没情况,改变入射波流条件,观测多种波流作用下,不同高度淹没圆柱周围的局部冲刷深度发展过程,分析了多种无量纲参数对局部冲刷深度的影响。结果表明:当KC数不变时,冲刷深度s/D随着相对流速U_cw和Fr的增大而增大,当Fr增大到一定程度时(Fr>0.80),冲刷深度s/D趋于稳定; U_cw在固定范围内时,冲刷深度s/D随KC数的增加而增加,增长速率逐渐变慢; 引入淹没因子K_s,得到了淹没圆柱与非淹没圆柱的冲刷深度计算关系式。     

大尺度柱状结构物波流荷载研究

大型深水工程往往面临水深、浪大以及流急等复杂自然条件,将受到巨大的水平波流力,在工程设计中需准确考虑波流力的大小.通过在波流水槽进行圆柱、方柱和矩形柱波流力系列试验,进行大尺度柱状结构物波流荷载研究,同时建立数学模型,应用边界元法求解大尺度柱体上的波浪荷载,编写了Fortran程序计算波浪力,运用柱体绕流理论计算水流力.对比分析试验结果和数值计算结果提出了波流力工程计算方法:对于深水大尺度柱状结构物波流力可由波浪力线性迭加水流力再乘以1.04得到,计算中波浪要素采用水流影响下的要素,水流力采用柱体绕流求得.按此方法计算波流力,并与物理模型试验结果进行对比,两者误差较小,满足工程设计的精度要求.     

波流耦合作用下紊流边界层水沙数学模型

在河口地区,波流相互作用下紊流边界层的泥沙起动输移规律非常复杂,深入探讨其泥沙运动规律很有必要。该文基于波浪边界层的控制方程,引入了时均水流压力,通过波流相互作用下的摩阻流速反映波浪与水流的夹角,用标准k-ε模型封闭方程,建立了波流叠加的紊流边界层内的弱耦合水流模型,分别讨论了波浪速度振幅、时均流速等的分布情况,与实测数据对比得到了较好的模拟结果。其次,基于水流模型建立了泥沙模型,采用对称振荡流和波流相互作用两种情况下的泥沙实测数据验证了泥沙模型的正确性,讨论了不同分布规律的涡黏系数对于模型的影响,为实际工程提供理论参考,结果具有一定的指导意义。     

WAVE-CURRENT INTERACTIONS WITH THREE-DIMENSIONAL FLOATING BODIES

A Time-domain Higher-Order Boundary Element Method (THOBEM) is developed for simulating wave-current interactions with 3-D floating bodies. Through a Taylor series expansion and a perturbation procedure, the model is formulated to the first-order in the wave steepness and in the current velocity, respectively. The boundary value problem is decomposed into a steady double-body flow problem and an unsteady wave problem. Higher-order boundary integral equation methods are then used to solve the proposed problems with a fourth-order Runge-Kutta method for the time marching. An artificial damping layer is adopted to dissipate the scattering waves. Different from the other time-domain numerical models, which are often focused on the wave-current interaction with restrained bodies, the present model deals with a floating hemisphere. The numerical results of wave forces, wave run-up and body response are all in a close agreement with those obtained by frequency-domain methods. The proposed numerical model is further applied to investigate wave-current interactions with a floating body of complicated geometry. In this work, the regular and focused wave combined with current interacting with a truss-spar platform is investigated.     

波浪引起海床土体液化的概率研究

摘要：评判海床土体能否液化大多采用有效应力法或液化势法，这些方法无法计算液化的概率，为解决这个问题，本文首先根据波浪荷载在海床内产生的循环应力比和海床土体的循环阻抗比，采用可靠性分析法，建立土体抗液化安全余量的表达式。根据一次二阶矩法，考虑波浪和土体参数的变异性，计算黄河水下三角洲埕岛海域某石油平台附近场地在6、8和10级风浪下的液化概率。风浪等级越大，抗液化安全系数越小，液化概率越大。如果该场地要求液化概率控制在5％以内，安全系数需大于1.8，可靠指标需大于1.6。然后分析了参数变异性对可靠指标的影响，得出波高比波长和土体标贯击数比粘粒含量对液化可靠指标的影响大的结论。最后研究参数之间的互相关性对液化可靠指标的影响，对可靠指标大于零的情况，忽略参数之间的互相关性会得到偏大的可靠指标，高估海床土体的抗液化性能。     

LOCAL SCOUR AROUND A LARGE-SCALE VERTICAL CIRCULAR CYLINDER DUE TO COMBINED WAVE-CURRENT ACTION

The local scour around a large scale vertical circular cylinder due to combined wave-current action was experimentally and numerically studied in the present paper. Experiments were carried out to research the affect of the wave height, current velocity and the diameter of the cylinder on the scour process. The topography near the cylinder in various cases during scour was measured. The cylinder diameter affects the distribution of scour and deposition area. The maximum scour depth increases evidently when the current velocity increases, The maximum scour depth does not increase after the wave height retains a certain value. A numerical model using a finite element method for simulating the scour process was established. And the numerical results agree well with the measured data. The numerical model is more applicable in the case of large-scale cylinders.     

波浪作用下砂质海床瞬时孔压特性的FLAC模拟

针对波浪荷载作用下砂质海床瞬时孔压响应问题,结合波流水槽模型试验实测结果,运用FLAC程序建立相应的流-固耦合本构模型,通过FISH函数使数值模型中的波浪加载与线性波理论相一致.并将数值模拟结果绘制成图和实测值进行比较分析,这是对FLAC渗流模块运用的拓展,以此进一步说明 FLAC有较好的模拟波浪加载下海床孔压特性的能力.     

应用Boussinesq方程对非线性波与流相互作用的理论研究

本文应用了Ｂｏｕｓｓｉｎｅｓｑ方程，对潮汐势流与规则波和不规则波共存时的非线性二阶波一流相互作用现象进行了理论分析，得到了在等水深条件下非线性相互作用二阶波流计算公式。应用此一公式可分析发现波受水流的非线性作用，不同于波受地形等水深变化的影响，其二阶波流频率不变，仍保持一阶线性入射波频率。本文最后采用所推导得到的二阶波流计算公式，对不规则波与势流相互作用等现象进行工程验算。得到了与物模实验较为一致的计算结果。应用本文的计算公式可以对现有工程规范中波与流计算公式进行修正和补充。由于其简便易行，势必会被工程界人士所接受     

波浪引起海床土体液化的概率研究

首先根据波浪荷载在海床内产生的循环应力比和海床土体的循环阻抗比,采用可靠性分析法,建立土体抗液化安全余量的表达式。根据一次二阶矩法,考虑波浪和土体参数的变异性,计算了黄河口水下三角洲埕岛海域某石油平台附近场地在6、8和10级风浪下的液化概率。风浪等级越大,抗液化安全系数越小,液化概率越大。如果该场地要求液化概率控制在5％以内,安全系数需大于1.8,可靠指标需大于1.6。然后分析了参数变异性对可靠指标的影响,得出波高比波长和土体标贯击数比黏粒含量对液化可靠指标的影响大的结论。最后研究了参数之间的互相关性对液化可靠指标的影响,对可靠指标大于零的情况,忽略参数之间的互相关性会得到偏大的可靠指标,高估海床土体的抗液化性能。     

波浪作用下海床孔隙水压力发展过程与液化的数值分析

为了探讨波浪作用下海床的液化特性与孔隙水压力发展过程，本文在海床动力响应弹性分析的基础上，将不排水条件下孔压增长模式与动力固结方程相结合，对波浪作用下海床中瞬态与残余孔隙水压力的发展过程与变化规律进行了有限元模拟与分析；对善功企与山崎浩之所提出的海床液化评判准则进行了修正，根据所估算的总孔隙水压力，对波浪作用下海床的液化势进行了评价。     

2D numerical modelling of bed profile changes due to tsunami effects on near shore coasts: Kadikoy case study.

This study was aimed at the investigation of tsunami effects on the seabed profile as these may be important for coastal structures, like sea outfalls or breakwaters. Tsunamis are well known with huge wave heights and destructive effects on the coastal region. A 2D numerical model was set using the software, COSMOS to calculate the cross-shore sediment transport and to evaluate profile changes in the coastal seabed. The study area is Kadikoy region, a densely populated industrial coastal area in South East Istanbul. The model was run for different kinds of tsunami waves. Not only the bed profile changes, but also the wave heights, breaker depths, peak wave bottom orbital velocities, wave set-up and cross-shore sediment transport rates were determined. The results indicated that, at a water depth around 40-50 m, some tsunamis were found to have a wave height of order of 15 m, which became about 5 m at a depth of 10 m. The wave set up near the coast was about 1.5-2 m. The results also implied that tsunami waves, with their destructive nature, could lead to dramatic vertical changes of the seabed.     

立波作用下海床的有效应力与液化分析

波浪作用下海床的稳定性与液化分析是海底管线、防波堤和海洋平台设计中必须仔细考虑的问题。本文推荐了一个循环荷载作用下土体的弹塑性实用本构模型，并给出了一种粉土的模型参数。该模型直接根据初始应力状态和循环应力的大小与作用时间计算土体的塑性应变增量，在有限元计算中不需要引入弹塑性矩阵。采用Biot理论和有限单元法，对海床有效应力的变化过程分析表明，波腹点下海床存在较大的液化可能性。波浪作用对海床存在一定的压密作用。     

THREE-DIMENSIONAL NUMERICAL MODELLING OF THE WAVE-IN- DUCED RIP CURRENTS UNDER IRREGULAR BATHYMETRY

A process-based 3-D hydrodynamic model is established to simulate the rip current structures under irregular bathymetry.The depth-varying wave-induced residual momentum,the surface rollers,the turbulent mixing and the wave-current interactions are considered.Experimental datasets are used to validate the model,and it is shown that the model can effectively describe the 3-D structures of the rip currents in both normal and oblique wave incident cases.The flow patterns of the rip currents see various characteristics for different incident wave directions.In the normal incident case,pairs of counter-rotating primary circulation cells are formed,and an offshore rip flow occurs in the embayment troughs.The peak seaward velocities occur at the top of the bed boundary layer,and the undertow is incorporated in addition to the rip currents.In the oblique incident case,the longshore currents are dominant,which result in a meandering flow along the depth contour,and the undertow is weaker compared to that in the normal incident condition.     

框架式海堤变形模拟与稳定性影响因素分析

以温州框架式海堤为背景,采用有限元强度折减法,分析密排桩结构参数和桩基周围淘蚀对框架式海堤变形及稳定性的影响。计算结果表明:随着密排桩桩长增加,密排桩桩身水平位移不断减小;密排桩径对桩身水平位移的影响较小;密排桩排间距对桩身水平位移基本没有影响;随着桩基周围淘蚀深度的增加,密排桩桩身水平位移不断增大,最大增幅位置都发生在桩顶;随着密排桩桩长和桩径的增加,框架式海堤整体稳定安全系数均增大;密排桩排间距为2.1 m时,框架式海堤整体稳定安全系数最小。