波浪在沙质海床上传播波长变化

沙质海床具有渗透性,会引起波浪的波长变化。基于线性波浪理论,采用Mendez提出的摄动方法,在已知波浪周期、水深和海床渗透系数的条件下,数值求解了渗透海床上的波浪色散方程,得到相应的波长,进而研究不同渗透系数和相对水深的沙质海床上波长的变化规律。结果表明,波浪在沙质海床上传播时的波长大于海床不可渗透的情况,且随着渗透系数的增大而增大;波浪在向岸传播过程中会发生浅水变形而波长减小,相比海床不可渗透的情况,沙质海床上的波长减小程度相对较小,这种现象随着相对水深的减小而愈加明显。因此,沙质海床的渗透性对波长的影响相当于1个“海床水深”Δh,它随渗透系数的增大和相对水深的减小而增大,当波浪在水深为h的沙质海床上传播时,其波长等于水深为h+Δh的不可渗透海床的波长。     

WAVE FORCE ACTION ON A PIER SITTING ON DEFORMABLE SEABED

In this paper,the seepage action on the bottom of a pier resting on a porous elas-tic seabed is obtained by numerical method.The seabed is assumed to be homogeneous,isotropicand linearly elastic porous medium,and can be described by Darcy's law,and the pore water isassumed to be compressible.The governing equations are Biot consolidation equation and storageequation.Considering the wave force acting directly on the pier,the seepage force and soil skele-ton displacement are computed by iterative calculation with the motion of the pier.In the calcu-lating process,it is divided into a diffraction problem and a radiation problem.Superposition oftwo solutions gives the final result.     

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.     

ANALYTICAL SOLUTION OF WAVE-INDUCED SEEPAGE PRESSURE ACTING ON THE BASE OF BREAKWATER

The wave loads acting on a breakwater resting on seabed include not only the waveforce from the wave field around the structure but also the wave-induced seepage pressure actingon the base of breakwater.The latter is also a circumstance load which can not be neglected inengineering design.This paper presents a closed-form analytical solution of wave-induced seep-age pressure acting on the base of breakwater resting on an infinite-depth porous elastic seabed.Based on the Biot's consolidation theory,the soil deformation and the compressibility of pore wa-ter are considered.The water wave pressure on sea bottom is determined by the linear waterwave theory.The numerical results of uplifting force and moment caused by the wave-inducedseepage pressure are given and the influences of soil deformation and pore water compressibilityon the calculation results are discussed.     

Lifting of a large object from a rigid porous seabed

This study investigates the flow field induced by the tilting lift of a large object from a rigid porous seabed and the induced force acting on the object using an analytical approach. In the corners between the object and the seabed, we assume the flow is a corner flow with a low Reynolds number, and the porous media flow in the seabed obeys Brinkman equations. The complete boundary conditions for viscous flow, including the continuity of velocities and stresses, are utilized at the seabed-water interface. The Helmholtz decomposition theorem, which decomposes the flow field into irrotational and rotational parts, and a perturbation expansion are employed to solve the boundary-value problem. Leading-order analytical solutions for the flow in the water and in the porous seabed are presented, indicating that the flow inside the corners is not a parallel flow, and the porous media flow inside the seabed is a Stokes boundary layer flow that does not obey Darcy’s law.

     

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.     

水平多孔板导致之近岸陷波

在本文中，利用线性水波理论和本征函数展开方法，我们研究了附有一沉放在一定深度水下的水平多孔介质板之垂直岸壁的水波反射问题，数值模拟了水平多孔板的消浪特性，我们发现，通过在岸会加一水平的多孔人质薄板之后，将增加近岸处波浪反射和散射过程的复杂性，导致陷波现象发生，具有恰当可渗性能的多孔介质薄板将具有消浪特性，这时板的行为就象一个波浪吸收器一样，从而减少了岸壁的反射能力，降低了岸壁处及其临近的波高，板越     

Extreme wave loads on submerged water intakes in shallow water

This paper provides new guidance concerning the hydrodynamic loads on submerged intake structures located in shallow water under breaking and non-breaking waves. Results from a series of experiments conducted in a large wave flume at 1:15 scale to study the hydrodynamic forces exerted on a generic intake structure located on a sloping seabed in shallow water below breaking and non-breaking irregular waves are presented. Based on analysis of the experimental data, empirical relationships are developed to describe the peak loads in terms of characteristic wave parameters such as significant wave height and peak wave period. The distribution of the peak loads across different parts of the intake structure is also described. Drag and inertia force coefficients for the horizontal forcing on the intake structure and for the main structural sub-components are derived and presented. It is shown that the well-known Morison equation, with appropriate drag and inertia force coefficients, can provide reasonable estimates of the moderate horizontal loads, but the peak loads are less well predicted.     

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。     

波浪对圆柱外接圆弧型防波堤绕射的解析计算

在微幅波绕射理论的基础上,使用特征函数展开法,推导了圆柱外接圆弧型防波堤复合结构的水波绕射的解析解,并据此计算了该结构所受到的波浪载荷以及绕射波面分布。计算结果表明:与单一圆柱相比,外接圆弧型防波堤的存在可明显降低作用于圆柱的波浪载荷和圆柱表面的波浪爬高;采用外接堤表面密实或透空而内圆柱表面透空的结构形式可以取得圆柱防浪的较佳效果;结构透空系数、波浪入射角度、外接堤张角、外堤半径与水深比、水深与波长比等因素的变化对绕射波浪作用均存在一定影响。     

An integrated model of wave-seabed-structure interactions

The phenomenon of wave-seabed-structure interactions have occurred in the marine environment with a coastal permeable (or partially permeable) structure, which has attracted great attention from coastal engineers involved in the design of marine structures. In this study, a porous seabed model based on Biot’s consolidation equation and pore-elastic theory is integrated into the COBRAS wave-structure model. This integrated model is verified by the laboratory experiments. Some dominant factors affecting the wave motion and its induced seabed response are examined by using this model, including wave parameters and structure properties.

     

REFLECTION OF OBLIQUE INCIDENT WAVES BY PERFORATED CAISSONS WITH TRAVERSE WALL

The interaction of oblique incident waves with infinite number of perforated caissons is investigated. The fluid domain is divided into infinite sub-domains by the caissons, and eigen-function expansion is applied to expand velocity potentials in each domain. A phase relation is introduced for wave oscillation in each caisson, and the structure geometry is considered in constructing the models of reflection waves. The reflected waves with the present analysis include all of the waves traveling in different directions when incident wave period is short. Numerical examinations show that velocities at the inner and outer sides of the front walls of caissons are close to each other, and reflection coefficients satisfy the energy conservation relation very well when porous effect parameter is infinite. Numerical results show that the reflection coefficients of oblique incident waves are smaller for shorter caissons at low frequency, and decrease with the increase of wave incident angle.     

Cyclic strength of sand under a nonstandard elliptical rotation stress path induced by wave loading

The principal stress rotation is one of the most important features of the stress state in a seabed subjected to wave loading. Most prior investigations focused their attention on the cyclic behaviour of soil deposits under the circular rotation stress path based on the analytical solutions for a seabed of infinite thickness. In this paper, the nonstandard elliptical, i.e., non-circular, rotation stress path is shown to be a more common state in the soil sediments of a finite seabed with an alternating changeover in stress due to a travelling regular wave. Then an experimental investigation in a hollow cylinder triaxial-torsional apparatus is conducted into the effect of the nonstandard elliptical stress path on the cyclic strength. A special attention is placed on the difference between the circular rotation stress path and the elliptical rotation stress path. The results and observations show that the shear characteristics for the circular rotation stress path in the literature are not applicable for analyzing the cyclic strength of sand in a finite seabed, and also indicate that due to the influence of three parameters about the size and the shape of a nonstandard ellipse, the cyclic strength under a nonstandard elliptical rotation stress path is evidently more complex and diversified as compared with that under a circular rotation stress path. Especially the influence of the initial phase difference on the cyclic strength is significant.     

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。     

波浪作用下黏性土海床动力响应数值分析

波浪作用下黏性土海床的动力响应对于海洋建筑物的稳定性具有重要的影响。在大型有限元软件ABAQUS平台上进行二次开发,根据重复性原理(repeatability principle)在有限元模型中设置侧向边界条件,采用Carter等(1982)提出的改进剑桥动力本构模型模拟海床土体。首先通过与有关弹性海床在波浪荷载作用下力学响应的解析解的对比,在一定程度上验证了有限元模型的合理性。进而通过参数对比研究,探讨了波高、波浪周期、海床土体的渗透系数等因素对于弹塑性黏性土海床力学响应的影响。计算结果表明,在波高较大、周期较短、土的渗透系数较低情况下,容易导致黏性土海床丧失稳定性。     

ELEMENT-FREE GALERKIN METHOD FOR RESPONSE OF STRATIFIED SEABED UNDER WAVE ACTION

A numerical model for the dynamic response of anisotropic and inhomogeneous seabed under wave action is developed based on the element-free Galerkin method for Biot's dynamic consolidation equations. Variations of the permeability and the elasticity of the soil in the vertical direction, which is an intrinsic feature of the stratified seabed, are considered. The numerical model is validated under isotropic and homogeneous conditions. The effects of the cross-anisotropy and inhomogeneity on the seabed response and shear failure are found to be remarkable. If the vertical increase of elastic modulus is taken into account, a significant decrease of the depth of shear failure can be expected.     

Experimental study on wave-current structure around a pneumatic breakwater

A model of a pneumatic breakwater comprised of perforated pipes placed on a wave flume bottom and connected to a piston-type air compressor is installed in a wave flume. Ascending air bubbles form an aerial barrier which dissipates wave energy and reduces the height of transmitted waves. The model is exposed to regular waves with fixed parameters, and its properties are modified by changing the amount of air supplied to the pipes. Particle Image Velocimetry and Acoustic Doppler Velocimetry methods are employed to measure a wave-current velocity field in the close vicinity of a submerged aerial barrier used as a breakwater. The measurements are supported by free-surface elevation registration in order to evaluate the effectiveness of the pneumatic breakwater in damping waves and to identify processes responsible for wave energy dissipation. Basing on the measurements, the performance of the pneumatic breakwater in different wave conditions is analysed. The results indicate that the dissipation of energy inside a region of a turbulent flow induced by ascending air bubbles may be considered the main mechanism of wave energy attenuation by pneumatic breakwaters.     

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。     

南海北部海域海底沙波演化特征

在对沙波的成因、形态以及运移机制充分探讨的基础上,给出了预测计算海底沙波形成与运移规律的理论模式。以此为基础建立了南海北部海域海底沙波波长及沙波移动的数学模型,对较大范围内的沙波形态及其运移规律进行了计算,成果表明计算区域海底沙波在正常水流条件下迁移速率相对较小,可视为比较稳定的地貌类型,为该海域海底工程实施提供参考。     

复杂河口汊道封堵水沙问题研究

摘 要：对复杂分汊河口次要汊道进行封堵围垦可以获得土地资源。以瓯江口南口封堵为例研究了复杂河口汊道封堵问题。首先对复杂的瓯江口的自然条件和冲淤演变进行了分析；其次，使用二维波浪潮流泥沙数学模型、波浪潮流泥沙物理模型及三维潮流数学模型等研究手段，对瓯江南口现潜堤加高进行了封堵后的二维潮流场、泥沙场、地形冲淤变化和三维潮流场进行了模拟研究，对瓯江泄洪排涝的影响进行了计算和分析。研究结果表明，从对周围水沙环境和瓯江泄洪排涝的影响角度考虑，将现潜堤加高进行南口封堵的方案是可行的。