斜坡上梯形潜堤附近流动结构的数值研究

波浪通过斜坡上潜堤时的波形和非线性特性均有显著变化,同时潜堤附近会出现涡流的生成及消散现象,有必要对其深入研究.基于1:20的斜坡上的波浪水槽实验,分析规则波在斜坡上不可渗梯形潜堤附近的动力特性.本文垂向二维波浪数学模型以RANS方程为控制方程,采用非线性涡黏性(各向异性) 紊流传输模型封闭雷诺应力项,利用VOF方法追踪自由表面以及采用源函数造波技术来模拟规则波对斜坡上潜堤的作用,数值计算结果与实验测量数据进行对比,吻合良好.利用数值计算进一步分析了流场、流线、紊动动能及紊动动能耗散率等特性,重点探讨了堤顶水深变化的影响,得到随堤顶水深增大,潜堤的消浪作用将明显减弱.     

波浪荷载对半圆型潜堤作用的数值分析

基于动量源数值造波原理,运用Fluent软件模拟了半圆型潜堤表面波压的分布及变化规律,采用π定理分析了波陡、水深及波长对半圆型潜堤表面波浪力的影响,并通过统计潜堤表面各点所受压力（最大波压力与最小波压力的差值）最大值的分布,给出了半圆型潜堤表面压力最大值出现的位置及概率.分析结果表明,在水深较深时,波陡的改变会使波压力在堤顶至背浪侧发生明显变化;水深波长比的改变,会引起半圆堤两侧波压力不同的变化;波压力的最大值一般发生在堤顶处及其偏向背浪侧附近;半圆堤面上的动波压力最大值主要出现在两侧堤脚附近,随着波高的增加,堤面上各点的动波压力由近似对称分布向两侧受力不同转变.     

防波堤透浪特性的研究

用大尺寸块石或人工块体建筑的斜坡式防波堤是港口工程中常用的一种形式。有时在防波堤一侧直接修筑码头,在这种情况下,不允许波浪从堤顶越过。由于堆石堤孔隙很大,波浪能量容易通过堤身将部分能量传递到堤的另一侧,这部分能量将产生一个新的波浪。 波能量在堤身内传递,工程上所关注的是波能量的传递规律,也就是波浪的衰减规律。若原始波高为H_0,传过堤身到达另一侧的波高为H,K_t=H/H_0称为透浪系数,K_t的大小直接与堤身尺寸和块石直径有关。     

规则波作用下潜堤透浪系数数值模拟

潜堤透浪系数是衡量潜堤削弱波浪能力的主要指标。基于Boussinesq型方程的MIKE21-BW模型建立波浪数值水槽,进行规则波作用下潜堤透浪系数的数值模拟。根据Dingemans物理模型试验结果对BW模型进行参数率定和验证,验证结果良好。在此基础上,进一步分析了影响潜堤透浪系数的无因次影响参数,包含相对淹没深度、波陡、相对堤顶宽度、斜坡堤坡度等,研究不同因素组合情况下潜堤透浪系数的变化规律。建立了规则波作用下潜堤透浪系数的计算式,应用MATLAB数学软件对式中的系数进行拟合,拟合式计算值与BW模型计算值相关系数为0.858,相关性较好。另外,将拟合式与杨正己公式进行比较,并分析数据的差异与原因。研究表明:MIKE21-BW模型可以进行规则波作用下潜堤透浪系数的数值模拟。     

斜坡平台上波浪破碎变形PIV试验研究

以斜坡平台上的波浪破碎区为研究对象,基于粒子图像测速技术PIV(Particle Image Velocimetry)研究了波浪在斜坡平台上的传播特性。通过分析破碎区流场、斜坡平台沿程波高分布及涡量场变化情况,探讨了波浪形态演变规律。利用谱分析研究了波浪倍频能量演变。结果显示,使用PIV可以良好地获得不同时段的流场完整瞬时信息。波浪在通过斜坡平台时,波形不对称性明显,波能在平台上剧烈衰减,破碎导致涡结构扩散。     

波浪作用下抛石堤的稳定性及消浪特性

波浪作用下抛石堤的稳定及消浪效果的确定是生产上迫切需要解决的问题。我们进行的试验,除通常所考虑的波高、波长、堤前水深和堤坡坡度等因素外,还考虑了静水位到堤顶的高度及堤顶宽度的影响,所得结果可用于出水堤(包括越浪与不越浪)和潜堤的稳定及消浪计算。     

孤立波作用下斜坡堤越浪量的实验研究

为了研究海啸等浅水大波对海堤等海岸结构物的作用,采用孤立波作为输入波形,在波浪水槽中进行了孤立波在斜坡堤上越浪过程的系列实验。通过物理模型实验,获得了孤立波作用下斜坡堤越浪量的测量结果,并基于PIV方法测量得到的海堤越浪流速度场计算了越浪量。以堤顶相对超高和来波相对波高为无量纲参数,基于越浪量实验数据建立了斜坡堤上孤立波越浪量的经验预报公式。孤立波堤顶越浪流的PIV测量结果表明,在实验工况条件下越堤流流场可近似为几乎平行的流动;基于PIV测量结果得到孤立波越浪量与越浪量的直接测量结果一致性较好。对简单斜坡堤而言,无量纲的孤立波越浪量随来波相对波高的增大而增加,随着堤顶相对超高的减小呈指数增大。     

植物护岸对波压力的影响试验研究

在堤外滩地上合理地种植适生植物能够起到保护岸滩、消减波浪的作用,是一种有效的生物护岸形式。该研究采用规则波和不规则波模拟河道中的波浪,通过不同滩地水深、不同波高和不同种树带宽度的组合试验,系统分析了防浪林宽度、滩地水深、浪高、波长等因素对刚性树干和带有柔性枝叶的模型树模拟堤外滩地防浪林消浪的影响,以及波高、最大波压力、波浪爬高及堤前底部波浪流速的分布规律; 该文重点研究植物护岸对最大波压力的影响。试验表明:在滩地上种植防浪树可以大大消减波浪能量,降低波浪对大堤的冲击力,从而起到保护堤岸的作用。     

改进的非线性波传播数值模型的验证和应用

基于吸收入射边界上反射波的方法,并通过将统一边界条件表达式推广到适应不规则波的情况,改进了非线性波传播的数值模型.将利用模型的线性版本(略去非线性项)所计算得到的台阶地形上波浪的反射和透射系数与相应的解析解进行了定量比较.在斜坡地形上数值模拟了不规则波的传播,并将数值结果和物理模型实验值进行了比较.在下游边界分别为开边界和全反射边界的等水深的水槽内数值模拟了不规则波的传播变形,讨论了非线性作用的影响.在侧边界和下游边界均为全反射的固壁边界、二维的等水深水域内,数值模拟了波浪斜向入射时所产生的波浪变形.计算结果表明,对上述各种算例,改进后的非线性波传播数值模型均能进行有效地数值模拟.     

斜坡堤砌体护面在波浪作用下稳定性的试验研究

本文根据对斜坡堤铺砌块体护面上法向波浪反压力的试验研究,分析了斜坡上最大反压力包络图,指出护坡块体失稳首先发生在破碎水深与打击点之间,该处法向波浪反压力最大。文中探讨了波高、波坦、相对水深、堤坡坡度等参数对该包络图图形的影响;反压力与波面的相位关系等。根据测试数据,应用数理统计方法,给出了反压力包络图的经验表达式和护坡块体最不利受力区域的范围。     

广西沿海水功能区水污染状况与水环境保护

在分析了广西沿海主要水功能区水污染现状及河流纳污量、等标污染负荷评价和水功能区达标分析的基础上,提出水功能区管理和水环境保护措施,并依据沿海经济发展对水资源需求,提出对水功能区调整及补充建议。     

Assessment of the levels of coastal marine pollution of Chennai city,Southern India

The levels of hydrological pollution of Chennai coastal zone in the southeastern part of India have been increased in the recent years by an uncontrolled disposal of wastewater and pollutants due to human activities. This study gave a special emphasis on the determination of the levels of pollution, the identification of vulnerable zones and providing some probable remedial measures for severely impacted coastal zone of Chennai city. During the period from September to November 2002, sampling was carried out along the shore in two traverses running in the seaside (surf zone) and landside (coastal aquifer). When sampling efforts took place the middle of the above period experienced a monsoonal storm over Chennai coast that significantly influenced large variations in the pollution level at both traverses in seaside and landside. Analysis of physical, chemical and biological parameter determinations indicated that the concentrations of dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), nutrients (nitrate, nitrite and phosphate), turbidity, maximum probable number (MPN) and chlorophyll a (Chl a) reached notably high levels at all sample locations before monsoonal storm prevailed over these areas during October 2002, which resulted in large fresh water input to the coastal system reducing the levels of pollution to some extent. Analysis of water samples collected during November apparently indicated that the concentrations of above parameters attained abnormal level and often exceeded the permissible limit of international standards. The concentrations of trace/toxic metals such as manganese, copper, nickel, lead, cadmium and cobalt also reached very high levels as a result of their sub-aqueous disposal to these areas, leading to further habitat and ecological destruction. On the other hand, analysis of groundwater samples collected from coastal aquifer for determination of certain chemical parameters such as Ca²⁺/Mg²⁺, Cl⁻/(CO²⁻ ₃+HCO ₃ ^-) and the ratio of total alkalinity (TA) and total hardness (TH) revealed that coastal groundwater appeared to be severely contaminated by saltwater intrusion as a result of overexploitation and enormous pressure imposed by monsoonal storm of October. Higher concentrations of toxic elements, for example, lead, nickel, cobalt and cadmium from the influence of industrial wastes and contaminated coastal waters, were also found to deteriorate the quality of coastal aquifer system. Based on detailed examination, four sites including Cuvum estuary, Adyar estuary, Kannikoil and Bharathiyar nagar are identified as highly venerable zones because of receiving a large quantity of municipal and industrial wastes. To reduce severe pollution levels in these areas it is therefore necessary to design and construct the submarine pipeline system to transport and disperse such a large quantity of waste materials to the deep open ocean areas.     

Linking integrated water resources management and integrated coastal zone management.

Some of the world's most valuable aquatic ecosystems such as deltas, lagoons and estuaries are located in the coastal zone. However, the coastal zone and its aquatic ecosystems are in many places under environmental stress from human activities. About 50% of the human population lives within 200 km of the coastline, and the population density is increasing every day. In addition, the majority of urban centres are located in the coastal zone. It is commonly known that there are important linkages between the activities in the upstream river basins and the environment conditions in the downstream coastal zones. Changes in river flows, e.g. caused by irrigation, hydropower and water supply, have changed salinity in estuaries and lagoons. Land use changes, such as intensified agricultural activities and urban and industrial development, cause increasing loads of nutrients and a variety of chemicals resulting in considerable adverse impacts in the coastal zones. It is recognised that the solution to such problems calls for an integrated approach. Therefore, the terms Integrated Water Resources Management (IWRM) and Integrated Coastal Zone Management (ICZM) are increasingly in focus on the international agenda. Unfortunately, the concepts of IWRM and ICZM are mostly being developed independently from each other by separate management bodies using their own individual approaches and tools. The present paper describes how modelling tools can be used to link IWRM and ICZM. It draws a line from the traditional sectoral use of models for the Istanbul Master Planning and assessment of the water quality and ecological impact in the Bosphorus Strait and the Black Sea 10 years ago, to the most recent use of models in a Water Framework Directive (WFD) context for one of the selected Pilot River Basins in Denmark used for testing of the WFD Guidance Documents.     

Hierarchical multi-scale classification of nearshore aquatic habitats of the Great Lakes: Western Lake Erie

Classification is a valuable conservation tool for examining natural resource status and problems and is being developed for coastal aquatic habitats. We present an objective, multi-scale hydrospatial framework for nearshore areas of the Great Lakes. The hydrospatial framework consists of spatial units at eight hierarchical scales from the North American Continent to the individual 270-m spatial cell. Characterization of spatial units based on fish abundance and diversity provides a fish-guided classification of aquatic areas at each spatial scale and demonstrates how classifications may be generated from that framework. Those classification units then provide information about habitat, as well as biotic conditions, which can be compared, contrasted, and hierarchically related spatially. Examples within several representative coastal or open water zones of the Western Lake Erie pilot area highlight potential application of this classification system to management problems. This classification system can assist natural resource managers with planning and establishing priorities for aquatic habitat protection, developing rehabilitation strategies, or identifying special management actions.     

Antecedent alluvial morphology and sea‐level controls on form‐process transition zones in the lower Trinity river,Texas

An important aspect of river science and management is the identification of key boundaries, transition zones and hinge points. Such critical areas are likely to be important foci or indicators of the effects of environmental change on river systems. While geological controls on such features are widely recognized in upland streams, inherited or antecedent forms may also be important controls of key transitional points or reaches in alluvial coastal plain rivers. The critical zone of the lower Trinity River, Texas marks an important transition in river channel and valley forms, dominant processes and resulting geomorphological, hydrological and ecological characteristics. Its location is not a transient result of upstream or downstream propagation of effects. Rather, the location marks the contemporary upstream extent of the effects of Holocene sea‐level rise, which in turn coincides with the point at which the Pleistocene upper Deweyville alluvial terrace surface is encountered. A more rapid rate of change and relatively sudden upstream displacement of this zone is likely when the upper Deweyville surface is flooded. Antecedent fluvial and alluvial topography inherited from previous aggradation, degradation and lateral migration episodes is likely to be an important control over modern fluvial forms and processes in other alluvial coastal plain rivers as well. Identification and mapping of such features may be extremely useful in pinpointing critical transition zones for water resource managers. Copyright © 2008 John Wiley & Sons, Ltd.     

How Subsurface Water Technologies (SWT) can Provide Robust,Effective, and Cost-Efficient Solutions for Freshwater Management in Coastal Zones

Freshwater resources in coastal zones are limited while demands are high, resulting in problems like seasonal water shortage, overexploitation of freshwater aquifers, and seawater intrusion. Three subsurface water technologies (SWT) that can provide robust, effective, and cost-efficient solutions to manage freshwater resources in the subsurface are evaluated using groundwater modelling and validation at field-scale: (1) ASR-coastal to store freshwater surpluses in confined brackish-saline aquifers for recovery in times of demand, (2) the Freshkeeper to counteract salinization of well fields by interception and desalination of upconing brackish groundwater, and (3) the Freshmaker to combine ASR and Freshkeeper to enlarge the volume of natural freshwater lenses for later abstraction. The evaluation indicates that SWT can be used in various hydrogeological settings for various hydrogeological problems like seawater intrusion, upconing, and bubble drift during ASR and have significant economic benefits. Although only sporadically applied to date, we foresee that SWT will stimulate (cost-)efficient and sustainable exploitation of various freshwater sources (like groundwater, rainwater, treated waste water, surface water) in coastal zones. Prolonged SWT testing in the current pilots, replication of SWT in other areas worldwide, and the development of technical and non-technical support tools are required to facilitate potential end-users in investment decision making and SWT implementation.     

Delineation of Groundwater Potential Zones of Coastal Groundwater Basin Using Multi-Criteria Decision Making Technique

Delineation of groundwater potential zones (GWPZ) has been performed for a coastal groundwater basin of eastern India. The groundwater potential zone index (GWPZI) map is generated by using Analytic Hierarchy Process (AHP) from different influencing features, e.g., Land Use/Land Cover (LU/LC), soil (S), geomorphology (GM), hydrogeology (HG), surface geology (SG), recharge rate (RR), drainage density (DD), rainfall (RF), slope (Sl), surface water bodies (SW), lineament density (LD), and Normalized Difference Vegetative Index (NDVI). Recharge rate values are estimated from hydrological water balance model. Overlay weighted sum method is used to integrate all thematic feature maps to generate GWPZ map of the study area. Four zones have been identified for the coastal groundwater basin [very good: 36.39 % (273.53 km², good: 43.57 % (327.47 km²), moderate: 18.27 % (137.30 km²), and poor: 1.77 % (13.27 km²)]. Areas in north to south-west and south-east direction show very good GWPZ due to the presence of low drainage density. GWPZ map and well yield values show good agreement. Sensitivity analysis reveals that exclusion/absence of rainfall and lineament density increases the poor groundwater potential zones. Omission of hydrogeology, soils, surface geology, and NDVI show maximum increase in good GWPZ. Obtained GWPZ map can be utilized effectively for planning of sustainable agriculture. This analysis demonstrates the potential applicability of the methodology for a general coastal groundwater basin.     

A linear hybrid model of MSE and BEM for floating structures in coastal zones

1. INTRODUCTION In coastal zones, wave propagation in water is considerably affected by the topography of the sea bottom, which may result in changes in the direction and shape of the waves and may cause redistribution of their energy in space, etc. Waves may also lose a certain amount of energy by wavebreaking or by other forms of dissipation. It can be easily seen that wave propagation in shallow waters is a very complicated process resulting from various mechanisms. The dominant mechan…     

Coastal wetland plant community responses to record-high Lake Superior water levels: An Allouez Bay case study

Here we present findings from a natural experiment to better understand coastal wetland plant community responses to rising water levels. Plant communities were monitored in three vegetation zones (submergent, emergent, and wet meadow) at Allouez Bay, a lacustrine coastal marsh, six times over years 2011–2020. Lake Superior water levels reached record-highs in 2017, and again in 2019. During our six sampling campaigns, we encountered eighty-four vascular plant species, seven of which were non-native. Except for reductions in total plant cover in the wet meadow zone, emergent and wet meadow plant communities were only marginally affected by rising water. Percent cover of non-native species did not increase in a clear pattern. Temporal changes in floristic quality were non-significant at the whole site level, and mean coefficient of conservatism values ranged from 5.3 to 6.0. Aquatic vegetation in the submergent zone was most affected by rising water. Submergent zone richness declined from sixteen plant species in 2011 to zero in 2020. Multivariate PERMANOVA analysis showed significant effects of year on site-wide plant composition. Temporal composition changes were predominately driven by species turnover in the submergent vegetation zone, whereby floating aquatic species were replaced by non-floating species from 2011 to 2017, and an absence of aquatic vegetation along research transects in 2020. Tracking regeneration of aquatic vegetation is a focus of future research as unknown effects from prolonged exposure to record-high water levels may affect natural regenerative processes at Allouez Bay, and potentially at other lacustrine Great Lakes wetlands throughout the basin.     

动力荷载作用下铁路过渡段工作特性分析

铁路路堤与桥、涵等结构物之间的过渡段处易出现明显的差异沉降,形成“跳车”,地基土体的固结和蠕变并不能完全解释这个现象。以往研究表明,过渡段处轨道顶面的不平顺和轨道基础刚度差异会导致轮轨动力荷载增大,进而引起轨道基础的附加压缩。首先确定了过渡段地基刚度的变化规律;然后采用动力计算模型分析了过渡段处的轮轨动力荷载,结果表明列车通过该过渡段时会产生很明显的动力荷载,最大可达列车静轮载的1．5倍。此外,计算还显示动力荷载主要由轨道沉降差和结构物刚度所控制;最后,采用压密模型对动力荷载下轨道基础的附加压缩量进行了预测。