循环荷载下饱和粉土中伞式吸力锚水平承载性能研究

利用ABAQUS有限元软件构建模型,对伞式吸力锚施加水平循环荷载,研究伞式吸力锚的承载性能。在固定荷载大小的情况下,研究锚体位移以及不同位置土体的应力应变。分析可得,在水平循环荷载的作用下,土体的最大塑性应变出现在筒裙位置,筒裙和锚支的结合发挥了主要的承载作用。改变荷载工况,研究不同荷载大小对伞式吸力锚的影响。研究发现,随着循环波浪荷载作用强度的增大,筒裙的稳定作用愈加明显,且这种作用在循环波浪荷载的后期阶段相对更加突出。     

海上风电伞式吸力锚基础结构优化设计及承载优势分析

海上风电基础是制约海上风电发展的一个重要因素,大力发展经济与效用兼备的新型基础刻不容缓。本文基于新型的海上风电伞式吸力锚基础(USAF)的已有结构,借助大型通用有限元软件ABAQUS构建出一系列不同尺寸的伞式吸力锚基础(USAF)有限元模型,并通过模态分析等动力分析得到最佳伞式吸力锚基础(USAF)结构尺寸,最后,将最佳伞式吸力锚基础(USAF)与常规单筒吸力锚基础在单一荷载下的极限承载力进行比较,证明了伞式吸力锚基础(USAF)具有良好的承载优势。     

波致液化海床土中伞式吸力锚承载特性试验研究

伞式吸力锚作为一种新型海上风电基础,现已在数值模拟方面进行了大量的研究,但缺少相应的室内试验。本文对伞式吸力锚(USAF)水平静力承载特性和波致土体液化中伞式吸力锚承载特性进行了室内模型试验,并与无锚枝吸力锚(SAF)进行了对比试验。研究发现,USAF的锚枝使得锚体转动中心升高,锚体承载性能得到提升;在波致液化海床土中,USAF的承载性能优于SAF,并且具有一定的防冲刷效果。     

单向流作用下伞式吸力锚基础的冲刷特征

伞式吸力锚(USAF)是一种新型的海上风电基础,与单桩基础相比,吸力锚基础(SAF)局部冲刷对风机稳定性的影响更为显著.因此,研究其冲刷特性对海上风电项目的建设具有重要意义.本文基于FLOW-3D软件,采用VOF法描述水体自由面,移动网格捕获冲刷形态随时间的变化,建立了三维USAF冲刷模型,并且与冲刷模型试验对比,验证...     

黄河三角洲海上风机新型吸力锚基础型式分析

海上风力发电是未来风电产业的主要趋势,黄河三角洲沿海滩涂地带风能蕴藏量丰富,多为风能富集型,具有很大的开发潜力。但水下黄河三角洲地域条件复杂,广泛发育着不稳定地形地貌,加上波浪荷载和风荷载的联合作用,极易引起海床土体侵蚀液化,直接影响海上风机基础的安全稳定性。在分析了现有海上风电风机基础的优缺点后,针对现有风机基础存在的弊端,提出了一种新型伞式吸力锚基础,并对其结构优势和安装方法做了说明,该新型吸力锚基础独特的结构设计在黄河三角洲地区风电开发中具有一定的应用前景。     

组合荷载作用下伞式吸力锚基础承载特性数值分析

针对用于海上风力发电机的伞式吸力锚基础(USAF)实际条件下的受力特点,采用数值模拟方法,基于大型通用有限元软件ABAQUS构建数值计算模型,对伞式吸力锚基础在H-V、H-T、V-T荷载平面内以及H-V-T非共面复合加载模式下的承载特性进行分析,进而推导其破坏包络面数学表达式。分析中采用固定位移比加载法进行复合加载,并将桶顶位移作为失效破坏标准。结果表明：(1)拟定的应力归一化复合加载破坏包络面椭圆曲线方程可以较好地模拟不同主筒长径比USAF在不同荷载空间内的破坏包络面形式;(2)H-T空间内USAF复合承载性能随主筒长径比(L/D)的增大而提高,而H-V、V-T空间内变化不明显;(3)绘制了H-V-T空间内USAF三维破坏包络面,可根据实际受荷状态与包络面之间的相对位置关系,评价实际工况下伞式吸力锚基础的稳定性。     

波、流及其共同作用下桩墩局部冲刷问题试验研究现状

要研究波流共同作用下桩墩的基础冲刷问题,首先需要了解水流和波浪单独作用下桩墩冲刷的机理和特征。针对波、流及其共同作用下桩墩的局部冲刷问题,从流速、水深、桩径、波长、波高、相对底层流速、粒径和粒径级配等方面系统地简述了恒定流、波浪和波流作用下桩、墩局部冲刷的研究进展。根据实验资料比较了各家经典计算公式的计算结果发现我国规范65-1式计算值偏大,65-2式计算值偏小等结论。桩墩局部冲刷是一个复杂的过程,今后可以针对淤泥质海岸底床、粉沙质海岸底床、复杂桩群结构、物理模型比尺效应、非恒定水动力条件、复杂基础形式方面对波流作用下基础冲刷的最大冲刷深度、冲刷过程、冲刷范围进行研究,以弥补桩墩局部冲刷在这些方面的不足。     

离岸裙式吸力基础在砂土地基中沉贯性研究

吸力基础是海洋工程中新型的一种基础型式,广泛应用于海洋平台、海洋浮动式结构等,近年来,也被作为浅海离岸风力发电工程的基础。吸力基础易遭受较大的水平动力荷载和弯矩,从而可能产生较大水平位移和转角;同时,由于海床冲刷,会降低其承载能力。为克服这些不足,提出了一种新型吸力基础———裙式吸力基础,把分析传统吸力基础砂土中的沉贯方法,拓广到裙式吸力基础中,研究该基础型式在砂土中的可沉贯性以及所需的吸力;并与同情况下的传统吸力基础进行了比较,证明了所提出的裙式吸力基础具有较好的沉贯性能,具有工程实践推广价值。     

复合加载下桶形基础循环承载性能数值分析

作为一种新型基础形式,吸力式桶形基础除了承受海洋平台结构及自身重量等竖向荷载的长期作用之外,往往还遭受波浪等所产生的水平荷载及其力矩等其它荷载分量的瞬时或循环作用。对复合加载模式下软土地基中桶形基础及其结构的循环承载性能尚缺乏合理的分析与计算方法。应用Andersen等对重力式平台基础及地基所建议的分析方法,基于软黏土的循环强度概念,在大型通用有限元分析软件ABAQUS平台上,通过二次开发,将软土的循环强度与Mises屈服准则结合,针对吸力式桶形基础,基于拟静力分析建立了复合加载模式下循环承载性能的计算模型,并与复合加载作用下极限承载性能进行了对比。由此表明,与极限承载力相比,桶形基础的循环承载力显著降低。     

新鹤海湾的演变特征及水沙模拟分析

为准确把握新鹤海湾的演变特征和水动力条件,采用现场观测和GIS技术对其地形变化、冲淤分布和冲淤量进行探讨,并利用数值模拟分析波浪、潮流和泥沙共同作用对海湾演变的影响。结果表明:海湾演变对连续台风的响应不同,表现为先冲后淤,其中苏拉作用下的冲刷量为台风过境后全年的2倍左右;受东南季风的影响,春夏冲淤幅度较大,海湾冲淤分布为南冲北淤,波高分布不均与涨潮流入湾时的向北偏转是其主要原因;波流共同作用下的底床切应力约为潮流单独作用时的10倍,波浪是导致海湾冲刷的主要因素,常浪下底床切应力小于临界冲刷应力,泥沙不易起动,因此海湾冲刷主要是由极端天气时的大浪所导致的。     

Local Scour Around Piles Under Wave Action

The model tests are performed with regular waves, and the effect of wave height, wave period, water depth, sediment size and pile diameter is evaluated. The shape and size of local scour around piles are studied. There are three typical scour patterns due to wave action. It is found that a relationship exists between the erosion depth and the wave number. An empirical formula of the maximum local scour is thus derived.     

A wave-flume study of scour at a pile breakwater: Solitary waves

Understanding the sediment transport and the resulting scour around coastal structures such as pile breakwaters under local extreme wave conditions is important for the foundation safety of various coastal structures. This study reports a wave-flume experiment investigating the scour induced by solitary waves at a pile breakwater, which consists of a row of closely spaced large piles. A wave blacking gate with a simple operation procedure in the experiment was designed to eliminate possible multiple reflections of the solitary wave inside the flume. An underwater laser scanner and a point probe were used in combination to provide high-resolution data of the bed profile around the pile breakwater. Effects of incident wave height and local water depth on the maximum scour depth, the maximum deposition height and the total scour and deposition volumes were examined. An existing empirical formula describing the evolution of the scour at a single pile in current or waves was extended to describe the scour at the pile breakwater under the action of multiple solitary waves, and new empirical coefficients were obtained by fitting the formula to the new experimental data to estimate the equilibrium scour depth. It appears that the maximum scour depth and the total scour volume are two reliable quantities for validation of numerical models developed for the scour around pile breakwaters under highly nonlinear wave conditions.     

Numerical investigation of local scour below a vibrating pipeline under steady currents

Local scour below a vibrating pipeline under steady current is investigated by a finite element numerical model. The flow, sediment transport and pipeline response are coupled in the numerical model. The numerical results of scour depths and pipeline vibration amplitudes are compared with measured data available in literature. Good agreement is obtained. It is found that pipeline vibrations cause increases of scour depth below the pipeline. The scour pit underneath a two-degree-of-freedom vibrating pipeline is deeper than that under a pipeline vibrating only in the transverse flow direction. The effects of water depth are also investigated. The present numerical result shows that water depth has weak effect on the scour depth. However it does affect the time scale of the scour. The shallower the water depth is, the less time it requires to reaches the equilibrium state of scour. It is found that the vibration forces vortices to be shed from the bottom side of the pipeline. Then vortex shedding around a vibrating pipeline is closer to the seabed than vortex shedding around a fixed pipeline. This contributes to the increase of the scour depth.     

港珠澳大桥青州航道桥桥墩基础冲刷试验研究

桥墩基础冲刷是桥梁毁坏的重要因素,是桥梁基础设计的关键指标之一。目前国内外对于桥墩基础在复杂动力条件下冲刷深度的研究常采用物理模型试验方法,利用正态系列模型方法,在波流水槽中研究了水流、潮流和波流共同作用下青州航道桥索塔基础周围流态变化和局部冲刷特征。研究结果表明,桥墩最大冲刷深度和冲淤范围与水流流速、桥墩轴线与水流夹角和波浪等因素有关;在潮流最大流速和恒定流流速一致情况下,桥墩局部冲刷深度达到平衡后,将会达到与恒定流基本一致的最大冲深;波流共同作用下的最大冲刷深度比恒定流增加10%左右。设计桥墩形状在100年一遇水流和波浪共同作用下桥墩基础局部最大冲刷深度为13.7 m。     

波浪作用下大尺径圆柱周围局部冲刷

通过系列模型试验，对波浪作用下墩柱周围局部冲刷地形及其形成机理进行了分析，认为最大冲刷深度发生在墩柱前方，与防波堤前冲淤形态类似，分为细沙型和粗沙型。在对各影响因子分析基础上，提出墩柱周围最大冲刷深度计算公式，试验资料表明，该公式与试验值有着良好的一致性。     

Scour and Burial Mechanics of Objects in the Nearshore

A process-based, numerical, hydrodynamic vortex lattice mine scour/burial model (VORTEX) is presented that simulates scour and burial of objects of arbitrary shape resting on a granular bed in the nearshore. There are two domains in the model formulation: a far-field where burial and exposure occur due to changes in the elevation of the seabed and a near-field involving scour and transport of sediment by the vortices shed from the object. The far-field burial mechanisms are based on changes in the equilibrium bottom profiles in response to seasonal changes in wave climate and accretion/erosion waves spawned by fluxes of sediment into the littoral cell. The near-field domain consists of one grid cell extracted from the far-field that is subdivided into a rectangular lattice of panels having sufficient resolution to define the shape of the object. The vortex field induced by the object is constructed from an assemblage of horseshoe vortices excited by local pressure gradients and shear over the lattice panels. The horseshoe vortices of each lattice panel release a pair of vortex filaments into the neighboring flow. The induced velocity of these trailing vortex filaments causes scour of the neighboring seabed and induces hydrodynamic forces on the object. Scour around the object and its subsequent movement into the scour depression contribute to burial, while far-field changes in local sand level may increase burial depth or expose the object. Scour and burial predictions of mines and mine-like objects were tested in field experiments conducted in the nearshore waters off the Pacific coast of California at Scripps Pier, the Gulf Coast of Florida at Indian Rocks, and off the Atlantic coast of Massachusetts at Martha's Vineyard. Model predictions of mine scour and burial are in reasonable agreement with field measurements and underwater photographs.     

植物对孤立波作用下直立堤局部冲刷影响实验研究

基于水槽实验,研究植物对孤立波作用下直立堤局部冲刷的影响。通过改变实验入射波高、植物带的宽度和密度,分析各要素对直立堤局部冲刷的影响。实验对波高沿程变化、孤立波越堤、回落过程以及地形演变进行全程的测量和记录,并进行有无植物带保护的直立堤局部冲刷对比分析。结果表明,植物带的存在,使得堤后相对最大冲刷深度显著减小,堤前冲刷形态由单峰式"L"型变为双峰式淤积沙坝形态,且冲刷位置由原堤脚前移至植物带所在位置,冲刷范围大幅增加。减小植物带密度或者植物带宽度会使近岸侧或是离岸侧的相对最大冲刷深度和相对最大淤积高度有增大的趋势,但是当入射波高增大时,二者的影响不显著。该研究对实际工程中植物带的合理布置提出了具有参考性的建议,对减少堤防工程的冲刷和损失有一定现实意义。     

新型旋转减冲装置对桩基局部冲刷防护试验研究

为减轻海上风电单桩基础周围局部冲刷对其结构安全的影响,提出了一种新型旋转减冲装置。在波流水槽中开展物理模型试验,改变波流条件、装置安装高度、安装距离,记录桩周冲刷发展历时,运用激光地形仪扫描冲刷坑形态,分析各工况下冲刷坑形态差异,验证装置不同安装距离、安装高度下的冲刷防护效果,提出了不同安装位置下的防护效率公式。结果表明：新型旋转减冲装置具有较好的冲刷防护效果,本试验工况下,桩周最大冲刷深度可减小44%左右。装置安装距离对冲刷防护效果影响较小,波流作用下的冲刷防护效果受装置安装高度影响显著,冲刷防护效果随装置安装高度的增加而减弱。     

Experimental Study on Local Scour Around A Large Circular Cylinder Under Irregular Waves

1 .IntroductionWiththedevelopmentofexploitationofmarineresources ,theconstructionofoffshorestructuresdevelopsrapidly ,suchasmarineoilplatforms ,deep waterbreakwaters ,marinebridges ,largehar bors,etc .Thesestructureswillchangesurroundingwaveandcurrentconditionsandleadtolocalscourofseabed ,resultinginstructuraldamage .Therefore ,localscouraroundmarinestructuresaswellastheirprotectionhasdrawnmuchattentionfromrelativeengineeringfields .Manyscholarshaveconduct edtheoreticalanalysisandexperimentals…     

Scour below pipelines and around vertical piles in random waves

An approach by which the scour depth and scour width below a fixed pipeline and scour depth around a circular vertical pile in random waves can be derived is presented. Here, the scour depth formulas by Sumer and Fredsøe [ASCE J. Waterw., Port, Coastal Ocean Eng. 116 (1990) 307] for pipelines and Sumer et al. [ASCE J. Waterw., Port, Coastal Ocean Eng. 114 (1992) 599] for vertical piles as well as the scour width formula by Sumer and Fredsøe [The Mechanics of Scour in the Marine Environment, World Scientific, Singapore, 2002] for pipelines combined with describing the waves as a stationary Gaussian narrow-band random process are used to derive the cumulative distribution functions of the scour depths and width. Comparisons are made between the present approach and random wave scour data. Tentative approaches to related random wave scour cases are also suggested.