不规则立波的特性及其对沙底的作用

根据波浪水槽中的模型试验结果,在本文中探讨了不规则波经直立墙反射后的一些特性以及墙前沙底的冲刷形态。为了便于比较,文中也简要地提及了规则立波对直立墙前沙底作用的主要结论。分析表明,若采用有效波高作为规则波试验中的等值波高,则由此得出的最终冲刷深度是偏于安全的。     

立波作用下堤前冲刷特性及预报

本文对立波作用下堤前海床的冲刷进行了系统的研究,指出了立波作用下直立堤前海庆的冲刷形态;分析堤前冲刷机理;提出了堤前冲刷形态的判别标准;给出了反映粒径效应的堤前冲刷深度公式;研究了突基床尺度对堤前冲刷的影响规律.     

波浪作用下直立堤前床面边界层内传质速度

本文研究立波作用下的层流、紊流边界层内的流速和传质速度,并采用谱法将传质速度推广到不规则波情况.根据实验与计算分析,研究了床面边界层内传质速度在堤前冲刷中的应用.研究结果表明,在传质速度的峰值附近形成底沙的冲刷坑;由于不规则波作用下堤前传质速度的峰值沿程递减,因此相应冲刷坑的深度沿程减少.     

直立式防波堤前护底层宽度设计的新方法

直立式防波堤可因堤前海底被冲刷的影响而发生破坏。过去对于在立波作用下的直立堤,一般认为由于在堤前四分之一波长,即波节点处发生最大底流速,将引起海底泥沙的被冲刷,因此要求堤前护底块石层的宽度采用为1/4～3/8倍设计波长。然而一些模型试验表明,冲刷并不一定发生在节点位置。而且我们认为即使是在节点发生冲刷的情况下,也不应当简单地规定必须防止在第一个节点处形成冲刷坑。在确定直立堤前的护底措施时,应当首先判断冲刷坑可能发生的位置,估计冲刷坑的深度及大小,然后在地基整体稳定计算(如圆弧滑动方法)中,具体考虑存在冲刷坑后对稳定安     

埕岛油田海域波—底相互作用

基于1976，1993年埕岛油田海域测深资料，应用HISWA浅水海浪数值计算模式，研究风暴浪入侵该海域导致的波-底相互作用后果。数值计算结果表明，海区固定点海底冲刷导致波场强化；波参数增量与冲刷深度有关；海底水质点轨道流速峰值，底摩擦耗散峰值及临界波高值相对水深分布均表明，该海域深水区海底冲刷将减弱，浅水区海底冲刷将加强。     

半潮堤前的反射形态与时均流速场分析

采用模型试验和数值模拟研究了不同水深工况下半潮堤前的反射形态及时均流速场。基于Hilbert变换建立了叠合波的时频分离技术,同时获取了入射波和反射波的波面过程及相位关系,通过试验数据证明其适用于不同反射程度的波浪信号分析。不同水深工况下,半潮堤前形成了部分立波系统,腹点和节点分别以四分之一波长的偶数倍和奇数倍交替增加。半潮堤前底床水质点水平速度包络图与波面包络图相差四分之一周期的相位,水平速度的极大值和极小值分别出现在波面包络图的节点和腹点,意味着节点处易形成冲刷,腹点处易形成淤积。3种工况的周期平均速度场均在迎浪基床上方的堤脚处存在一个小型环流系统,可能引起局部冲刷,此处需加强防护。淹没工况下,半潮堤前的周期平均速度场形成一个大型环流系统,表层水流向堤后,中下层水流向海侧,意味着底床悬起的泥沙很可能向离岸方向流失。     

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。     

直立式防波堤前的冲刷形态及其对防波堤整体稳定的影响

由于水波作用而在海岸建筑物前(或周围)引起的冲刷问题,是海岸工程领域中的一个重要课题,已经有很多研究工作者针对不同类型建筑物前的冲刷问题开展了不少研究, 为了确定在立波作用下直立堤前冲刷剖面的形状和尺度,作者在荷兰德尔夫特工业大学流体力学实验室的两条波浪水槽中,用四种不同的沙径进行了模型试验,在大部分的试验组次中采用规则波,少数几组采用不规则波.     

直立堤前海床的局部冲刷

对不规则波作用下直立堤前海床的局部冲刷进行了研究。研究了由于波浪作用导致床面的底沙运动,从而造成提前海床的局部冲刷,即所谓的“相对粒沙”的情况。报导了;(1)堤前海床面为水平、堤下无基床情况下的堤前局部冲刷,以及堤下有明基床时基床尺度对堤前局部冲刷的影响;(2)堤前海床面为斜坡面时堤前的局部冲刷,以及当堤下有明基床时基床尺度对堤前局部冲刷的影响;(3)从波浪作用下床面边界层的理论分析出发,对于在不规则波作用下,离堤面愈远处的冲刷坑深度愈小的事实给出了解释。     

海啸波作用下直立堤局部冲刷实验研究

基于波浪水槽动床实验,开展海啸波作用下直立堤局部冲刷实验研究。对海啸波上爬和回落过程、岸滩演变和直立 堤局部冲刷形态进行测量。在利用实测数据验证基础上,结合 FLOW 3D 进行数值模拟流场计算分析。研究结果表明,直立堤 的修建对岸滩起到明显的保护作用,但是直立堤两侧会出现明显的局部冲刷。直立堤向岸侧局部冲刷主要发生在海啸上爬时 刻,堤脚处形成的涡流是局部冲刷形成的主要原因。直立堤离岸侧的局部冲刷主要由海啸波回落水流越过堤顶生成水跌形成 的,随着直立堤堤顶高度的增加,最大局部冲刷深度会逐渐减小。     

潮流场对渤、黄、东海陆架底质分布的控制作用

运用二维潮流数学模型，模拟了渤、黄、东海陆架的M2潮汐、潮流。结果表明，渤、黄、东海陆架的潮流有强弱之分以及往复流和旋转汉之别。在此基础上，计算了8种粒径沙的湖平均悬移输沙率、潮平均推移输沙以及相应的输沙率散度。根据输沙率散度的正负，划分了海底冲刷区与淤积区。根据不同粒径泥沙输沙率散度的相对大小，确定出海底的主要底质类型为砂质沉积、粉砂质泥沉积和以粉砂为主的混合沉积。计算结果表明，海底3种主要底负类型的分布格局与海底的冲淤格局以及与输沙率矢量的发散和聚合状况基本一致。在渤、黄、东海陆架，沙脊主要在强往复流区形成，沙席主要在强或较强的旋转流区形成，泥质沉积主要在弱潮流区形成。砂质沉积、泥质沉积以及混合沉积这3种主要底质类型并非孤立存在，而是受渤、黄、东海陆架潮流场控制而形成的一个完整的潮流沉积体系。渤、黄、东海陆架的砂质沉积与泥质沉积并非残留沉积，而是潮流沉积。在没有冷涡的情况下，黄、东海陆架的典型泥质沉积在弱潮流环境中同样可以形成，因此，认为冷涡并非黄、东海陆架典型泥质沉积形成的必要条件。     

黄河三角洲河口区滨海湿地面积动态变化与影响因素分析

采用遥感和地理信息系统技术,根据遥感影像数据和实测水深数据,分析了现代黄河三角洲河口区滨海湿地面积的变化规律,并计算了研究区湿地面积与黄河入海沙量之间的相关性。结果表明,黄河改道清水沟流路初期,三角洲河口区滨海湿地面积呈快速增长之势,但滩涂面积变化较复杂,1996年实施清8出汉工程后,低潮线至水下-2,-5和-6m湿地...     

潮间浅滩泥沙运移的现场观测和冲淤量的估算

首先介绍了在潮间浅滩观测泥沙远移的两种新工具──标志桩和沉沙盘的基本结构、工作原理和使用方法。然后通过实例阐明了利用标志桩、沉沙盘观测资料研究潮间浅滩冲淤变化及冲淤量估算的途径及方法。     

前进波作用下沙纹床面的净输沙方向与净输沙强度

在沙纹床面输沙过程中，假设水流从涡中取出并搬运的悬移质数量与推移质运动的沙星成比例，由12组细沙实验结果得到了沙纹床面净输沙的方向和输沙强度公式，并与他人的实验结果进行对比。     

Sediment Deposition and Resuspension in Mouth Bar Area of the Yangtze Estuary

—A comprehensive analysis is conducted based on observations on topography.tidal current.salinity.suspended sediment and bed load during the years of 1982.1983.1988.1989.1996 and 1997 in theYangtze Estuary.Results show that the deformation of tidal waves is distinct and the sand carrying capaci-ty is large within the mouth bar due to strong tidal currents and large volume of incoming water and sedi-ments.Owing to both temporal and spatial variation of tidal current.deposition and erosion are extremelyactive.In general a change of up to 0.1 m of bottom sediments takes place during a tidal period.The maxi-mum siltation and erosion are around 0.2 m in a spring to neap tides cycle.The riverbed is silted duringflood when there is heavy sediment load.eroded during dry season when sediment load is low.The annualaverage depth of crosion and siltation on the riverbed is around 0.6 m.In particular cases.it may increaseto 1.4 m to 2.4 m at some locations.     

Two-Dimensional Mathematical Model of Tidal Current and Sediment for Oujiang Estnary and Wenzhou Bay

A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the WenzhouBay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport arepresented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with theirinitial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of thecritical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested.The model verification computation shows that, the tidal levels computed from the model are in good agreement with the fielddata at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measuredalong the totally 52 synchronously observed verticals distributed over 8 cross sections. The computed tidal water throughputsthrough the Huangda‘ao cross section are close to the measured data. And the computed values of bed deformation fromYangfushan to the estuary outfall and in the outer-sea area are in good agreement with the data observed from 1986 to 1992.The changes of tidal volumes through the estuary, velocities in different channels and the bed form due to the influence of thereclamation project on the Wenzhou shoal are predicted by means of this model.     

In situ flume measurements of resuspension in the North Sea

The in situ annular flume, Voyager II, was deployed at three sites in the North Sea in order to investigate resuspension events, to determine the physical characteristics of the seabed, to determine the threshold of resuspension of the bed and to quantify erosion rates and erosion depths. These are the first controlled, in situ flume experiments to study resuspension in the North Sea, and were combined with long-term measurements of waves and currents. Resuspension experiments were undertaken at two muddy, and one sandy site: north of the Dogger Bank (DG: water depths ∼80 m, very fine, poorly sorted, very fine-skewed sediment experiencing seasonal thermal stratification of the water column along with oxygen depletion); the Oyster Grounds (OG: ∼40 m, similar bed properties, year round water column thermal stratification, Atlantic forcing); and in the Sean Gas Field (SGF: ∼20 m, moderately sorted, very coarse-skewed sand, and well mixed water column). The erosion thresholds of the bed were found to be 0.66-1.04 Pa (DG) and 0.91-1.27 Pa (OG), with corresponding erosion depths of 0.1-0.15 mm and 0.02-0.06 mm throughout the experiments.Evaluation of a year of current velocities from 2007 indicated that at OG, resuspension of the consolidated bed was limited to on average ∼8% of the time as a result of tidal forcing alone for short (<30 min) durations, but would potentially increase during the winter as a result of wave influences. At DG, under similar conditions this would increase to 13%, and in the SGF, wave-induced resuspension events occurred throughout the year, with the potential exceedance of the threshold for suspension greater than 50% in January and March.Resuspension of bed material and erosion rates were closely related to applied bed shear stresses, and eroded depths were significantly correlated with the physical properties of the bed. Therefore, while complex variations in biogeophysical factors affected the critical threshold of erosion, once exceeded, erosion rates were related to the nature of the sediment.     

Two-Dimensional Mathematical Model of Tidal Current and Sediment for Oujiang Estuary and Wenzhou Bay

A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the Wenzhou Bay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport are presented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with their initial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of the critical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested. The model verification computation shows that, the tidal levels computed from the model are in good agreement with the field data at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measured along the totally 52 synchronously ob     

Test Study on Erosion and Siltation Patterns of Sandy Bottom Before Mound Breakwater Under the Effect of Waves

In this paper, the effect of waves on erosion of the sandy bottom before mound breakwaters is studied. The sandy bottom basically presents two erosion patterns, between which there is a transitional state, under the action of partially standing waves. The two erosion patterns can be determined by dimensionless parameter Us, defined in this paper. The erosion locations, depths and lengths can be estimated by a series of equations presented in the text. Irregular waves are employed in the test besides regular waves, and the effect of the irregular waves can be estimated by the element of equivalent waves, such as T1/3, H1/3.