Study on the Thermal Insulation Performance of a New Seabed Sediment Fidelity Sampler Based on ANSYS

A new seabed sediment fidelity sampler was developed and its thermal insulation performance was studied and analyzed. The temperature distribution simulation indicated that the sample quality could be insured by using this new sampler. Based on ANSYS10, the temperature finite element model of the sample cylinder was established. According to the law of conservation of energy, the unsteady heat transmit equation of the sampler under solid-liquid coupling condition was derived, then the mathematical model calculation was carried out by using a mixed finite-element finite-difference method, and two thermal insulation methods were used. The simulation was carried out by using the thickness of the thermal insulation layer and heat conductivity as the variable parameters and the temperature distribution of the sampler and related influencing factors were obtained. Optimization analysis was conducted using the simulation data and related parameters and the magnitude ranges of the parameters were obtained that could meet the design temperature requirements. The experimental data and simulation results indicated that the results were in good agreement with the realities, and this sampler might be of value for seabed sediment sampler design and manufacture.

Pollution of bed sediments and its changing process of Nansihu Lake

In order to research the changing process of the pollution from the formation of Nansihu Lake, this study determined the isotope age and depositional rate and analyzed the organic geo-chemical quotas and heavy metal quotas of two sedimentary profiles of Weishan and Dushan lakes. Research results showed that from the formation of Nansihu Lake, the change of the pollution could be divided into four phrases. At the early phrase of the formation, the organic matters of the lake mainly derived from the exotic matters and had a close relation to the effect on the water and sands from the Huanghe (Yellow) River. At the middle and late phrases of the development, the endogenous matters of the lake became the main and stable source of the organic matters. The overflow of the Huanghe River, the excavation of the Grand Canal and the cut of trees caused the changes of the historic pollution. In recent 20 years, the modern industrial pollution from the organic matters and heavy metals has an increasingly heavy tendency.

Influence of tributaries on downstream bed sediment grain sizes under flysch conditions

Tributaries are one of the most important factors contributing to variability in the downstream evolution of bed sediment grain size.The primary aim of this work is to evaluate the response of the bed sediment texture in the recipient channel induced by ten tributaries of the?ernáOstravice stream and find reach-scale and catchment-scale parameters that would be able to predict this response.The research was based on collecting information on the grain size distributions at sites adjacent to confluence zones.A significant change in sediment texture occurred in the vicinity of five confluences.Considering the other factors contributing to grain size variability(e.g.,local channel geometry,lithology,and lateral sediment sources),it was assumed that only four of them were associated with a sufficient bedload influx to alter the sediment calibre below the junction.Moreover,a significant morphological effect in the form of a large confluence bar was observed in one case.These tributaries had several common features:(i)they had a larger relative catchment area than that of nonsignificant tributaries;(ii)they were characterized by different bed grain sizes,with some exceptions;and(iii)they had a higher unit stream power close to the confluence in relation to that of the mainstream.These characteristics were represented by the proposed relative parameters,including the relative unit stream power and bed material texture,which allowed the best classification of significant and nonsignificant tributaries.In their simplified form,the parameters described the transport capacity and grain size distribution,which were generally considered to be primary factors responsible for a redefinition of the sediment texture in the recipient channel.However,it should be noted that these results are subject to some degree of uncertainty due to the relatively small sample size of only 10 tributaries.

Spatial Variation of Dissolved Nutrient and Heavy Metal Concentrations in River Bed Sediments as Influenced by Land-Use Patterns in Ogun-Osun River Basin, Nigeria

Evaluation of levels and spatial characteristics of dissolved nutrients and heavy metals in the river bed sediment within a basin are critical to understanding the extent of land-use impact on the river systems. Surface river bed sediments across eight rivers in the Ogun-Osun River Basin in Nigeria were collected and analyzed for Total N, , Total P, Total organic carbon, Cd, Hg, Pb, Zn, Cu, Fe, Mn and Cr. Pollution Load Index (PLI), Accumulation Factor (AF) and Hierarchical Clustering Analysis (HCA) were used to identify the impact of the pollutants and also define the spatial variation across the basin. The pollution load indices of heavy metals were moderately high ranging from 0.41 - 0.60, while AFs were 0.43 - 2.00 and 0.61 - 1.29 for heavy metals and nutrients from upstream to downstream in the rivers systems, respectively. The HCA identified 7 distinct spatial patterns describing pollutant input from the land-use in the basin. Although, heavy metals contents were low in relation to the background values, and the potential for redistribution and secondary pollution was high hence, there was need to impose checks on the activities across agricultural, urban and grazing land-uses that had impact negatively on the river systems in the basin.

Flow structure and phosphorus adsorption in bed sediment at a 90° channel confluence

The distribution of the phosphorus（P） adsorption in a bed sediment at channel confluences is an important issue for understanding the transport of contaminants in channel networks. In this study, the flow structure and its effect on the P distribution in the bed sediment were investigated in a 90° confluence flume. It is shown that the P adsorption amount in the sediment varies significantly in different hydrodynamic zones. The P adsorption amount is high in the flow separation zone where the horizontal velocity of the flow is very small, and it is low in the maximum velocity zone where the flow velocity reaches a maximum. The low P adsorption amount is observed in the downstream portion of the distorted shear layer, while the P enrichment is found in the upstream portion, as is related to the significant downwelling flow in this zone. Thus, the flow structure, especially, the flow velocity, has a significant effect on the distribution of the P adsorption in the bed sediment at the channel confluences.

The suspended sediment transport equation and its near-bed sediment flux

The suspended sediment transport equation and its near-bed sediment flux are one of the key problems of sediment transport research under nonequilibrium condition. Based on the three-dimensional primitive suspended transport equation, the two-dimensional suspended sediment transport equation is deduced. The derived process indicates that the physical essence of the near-bed sediment flux is right the bottom boundary condition for the suspended sediment transport equation. This paper analyzes the internal relations between the two methods of sediment carrying capacity and shear stress in common use, points out the consistency of these two methods in terms of form and physical meaning, and unifies these two methods theoretically. Furthermore, based on the analysis and comparison of the expressions of the near-bed sediment flux, this paper summarizes some problems to which attention should be paid, thus offering a novel approach to the study and the solution of the problems of suspended sediment transport and exchange flux of near-bed water sediment.

Non-capacity transport of non-uniform bed load sediment in alluvial rivers

Rivers often witness non-uniform bed load sedim ent transport. For a long tim e, non-uniform bed load transport has been assum ed to be at capacity regime determined exclusively by local flow. Yet whether the capacity assumption for non-uniform bed load transport is justified remains poorly understood. Here, the relative time scale of non-uniform bed load transport is evaluated and non-capacity and capacity models are compared for both aggradation and degradation cases with observed data. As characterized by its relative time scale, the adaptation of non-uniform bed load to capacity regime should be fulfilled quickly. However, changes in the flow and sedim ent inputs from upstream or tributaries hinder the adaptation. Also, the adaptation to capacity regime is size dependent, the finer the sediment size the slower the adaptation is, and vice versa. It is shown that the capacity model may entail considerable errors compared to the non-capacity model. For modelling of non-uniform bed load, non-capacity modelling is recommended, in which the temporal and spatial scales required for adaptation are explicitly appreciated.

Bed Forms and Sediment Characteristics along the Thalweg on the Tanana River near Nenana, Alaska, USA

Sediment sampling and longitudinal river-bottom surveys were conducted along the thalweg on the Tanana River near the city of Nenana, Alaska, USA, to provide basic information for the engineering design requirements of hydrokinetic devices to be deployed in the area. The study reach was located at approximately 64°33'50'N and 149°04'W. The Tanana is a large glacier-fed river, with open-water flow conditions from May to October. The river presents a single channel in the study area. Granulometric analyses of sediment moving near the riverbed reveals the coexistence of three distinctive types of sediment along the study reach: 1) nearly uniform fine sand;2) bimodal distributions containing fine sand and medium gravel;and 3) medium gravel. Preliminary relationships between sediment loads and discharge were developed. Dunes with small superimposed dunes were found along the reach. The basic geometric parameters (i.e., wavelength and height) of dunes were measured, and steepness was calculated. In general, dune wavelength increased with increasing discharge. Dune wavelengths ranged from 41 to 67 m, while small-dune wavelengths ranged from 13 to 16 m. Steepness increased slightly with increasing discharge.

Bed Load Transport Rate in Scouring and Armoring Process of Non-uniform Sediment River Bed

Flume experiments were carried out to study bed load transport rate during rive bed scouring and ar- moring.A theoretical differential equation linking the transport rate to the probability of incipient motion of non-uniform sediment is solved.The transport rate is shown to decrease exponentially with time,according to the theory,which is in good agreement with the experiment data.

Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

Incipient Motion of Bed Load Sediment and Its Application in the Three Gorges Hydro Project

A formula for the calculation of critical shear stress of non-uniform sediment was developed by on river bed has been established while considering the relative degree expose of grains.The values of the Coeffi- cients in the formula have been obtained.The formula has been verified with prototype observation data, flumes data of both nature and lightweight sand.The computed results fully reflect the characteristics of thresh- old motion of non-uniform sediment.The result have been used in some physical mo...

黄河下游平滩流量的模拟方法

在黄河流域水沙变异背景下,准确计算黄河下游平滩流量对于河道冲淤趋势预测与悬河治理十分重要。本文在比较分析已有多个黄河下游平滩流量计算方法基础上,首先建立了考虑非汛期水沙条件影响的平滩流量滞后响应模型,再提出了基于滞后响应模型和能量法的平滩流量模拟方法,结果表明:(1)小浪底运行后非汛期水沙条件发生了重要改变,已有研究提出的三种黄河下游平滩流量计算方法中,滑动平均法、滞后响应模型、能量法均无法有效模拟2000年后的黄河下游河道平滩流量。(2)建立了考虑非汛期水沙条件影响的滞后响应模型,以反映小浪底水库运行以来非汛期来水来沙条件的影响,虽然提高了平滩流量的模拟精度,但平滩流量平衡值的计算公式中部分参数差异较大,结构形式不稳定。(3)借鉴能量法的优点,改进了平滩流量平衡值计算公式,改进后的平滩流量计算方法不仅可反映全年来水来沙的影响,而且可同时反映以床沙中值粒径为代表的床面阻力的影响,新方法不仅具有一定的理论基础,而且提高了平滩流量的模拟精度。

泥沙输移模拟中垂向床沙分选模型比较分析

河床中非均匀泥沙的垂向分选影响河床表面泥沙分布及冲淤演变。目前研究中缺少连续性垂向床沙分选模型的具体计算方法,且连续性模型与离散层模型的对比研究较少。详细介绍了TELEMAC泥沙模块中连续性垂向床沙分选模型(C-VSM)的计算过程,并将其与离散层模型(HR-VSM)的计算方法进行比较,探讨垂向床沙分选模型对泥沙输移的影响,研究结果表明:C-VSM以多段线法表示垂向床沙分布,且分选过程与河床演变独立计算,提高了垂向床沙分布计算的准确性,避免了活动层与下层泥沙的垂向掺混问题,对河床冲淤及泥沙分布模拟较HR-VSM更准确。研究结果可为床沙垂向分选模型的开发提供参考。

钱塘江河口盐官段混合式丁坝修建对水沙及河床影响的实测研究

钱塘江北岸古海塘堤脚加固工程中,辅助围堰施工的临时性管袋黏土混合式丁坝对工程的顺利进行、提高施工效率起着至关重要的作用,然而目前对其周围水沙运动的研究较少,且缺乏相关实测资料。考虑混合式丁坝修建的动态过程,利用无人机拍摄水流视频结合LSPIV(粒子图像测速)处理技术对丁坝修建前、中、后期周围的流场进行分析,并对丁坝附近的地形进行跟踪测量,同时对不同潮差的水流含沙量进行现场测定。结果表明,丁坝具有改变水流方向,减少水流对河岸冲刷的作用,且丁坝越长,挑流作用越明显,为围堰施工提供了较为平缓的水流条件;混合式丁坝对坝后处的促淤效果明显,且坝后地形变化与含沙量密切相关,潮差越大,水体含沙量越高,丁坝后河床淤积幅度越大,有利于提高围堰的施工效率。研究成果对之后相关物理模型和数值模拟的研究提供数据支持。

SUSBED－1动床恒定非均匀全沙模型

本文介绍近期发展的一维恒定非均匀全沙（推移质、悬移质）ＳＵＳＢＥＤ—１数学模型，在前期和前人研究的基础上，同时嵌入了平衡和不平衡输沙两种计算模式，是一个可用于模拟水库及河道冲淤变形的通用模型，模型操作简便，易于掌握，计算速度快，所给出的计算信息既可进行基本问题的理论研究，又能够用于回答解决工程问题．

典型非均匀推移质输沙率公式适用性比较

基于等中值粒径的“单、双峰型级配”推移质输沙试验以及“驼峰”输沙率试验数据,选择Einstein、吴伟明、Wilcock和吴保生等4种典型非均匀推移质输沙率公式计算“单、双峰型级配”推移质输沙率,将两种级配的输沙率比值及曲线形态与试验成果对比分析。结果表明:吴伟明公式在反映“单、双峰型级配”推移质输沙差异上表现最好,这4种公式均无法反映“驼峰”输沙率现象。基于多参数考虑的Patel公式较这4种公式能更好地反映上述两种现象。充分考虑床沙级配对分组沙起动切应力和输沙有效Shields数的影响,是提高非均匀推移质输沙率公式精度和适用性的关键。

交汇区水流结构对底泥磷分布特征影响机制

交汇区的水流结构极为复杂,揭示交汇区底泥磷分布特征难度较大。设计交汇区底泥磷分布实验系统及其检测方法,测量交汇区的三维流场和底泥中总磷含量,分析交汇区水流分区与底泥中总磷空间分布的关系,并基于交汇水槽实验中204组水动力参数与底泥中总磷含量数据,建立人工神经网络模型,定量分析流场中水动力参数对底泥中总磷含量的影响,辨识其中的关键水动力参数。结果表明:分离区内水流水平流速较小,底泥磷含量较高;位于分离区外侧的加速区水平流速较大,底泥磷含量较低,但加速区的局部区域(剪切层区)存在显著的底泥磷含量偏高现象;通过人工神经网络模型的参数敏感性分析,定量解释局部底泥磷含量高值现象与该区域较大的向下水流有关。

三门峡水库原型试验以来渭河下游河床稳定性变化及其影响因素

为探究渭河下游河道形态演变特征及影响机理,基于多年水文观测资料分析渭河下游河床稳定性演变规律,探讨三门峡水库原型试验以来(2003~2020年),来水来沙条件、潼关高程变化、河道边界条件与河床稳定性的响应关系。结果表明,原型试验期内,渭河下游河道年均径流量呈缓慢增加趋势,年均含沙量均呈缓慢减小趋势,河段河槽呈扩张趋势,潼关高程呈逐年下降趋势。原型试验期前后,渭河下游河段河床横向、纵向和综合稳定性系数均增加,原型试验期内,河床稳定性呈逐年上升趋势。前期3年平均水流冲刷强度和潼关高程变化是影响渭河下游河床综合稳定性的重要因素,利用多元回归分析方法建立了渭河下游河床综合稳定性的经验计算公式,验证了所提经验公式的准确性和可靠性。研究成果可为渭河下游及类似河流管理提供参考。

零距离暗挖下穿既有车站控沉效果研究

研究目的:新建地铁车站换乘节点的施工不可避免地会对既有线的运营造成影响。本文通过列举新建车站零距离暗挖下穿既有线的案例,通过数值模拟,对比不同方案下的沉降影响分析,从而得出可靠的设计施工方案。研究结论:(1)按常规设计方案,先施工既有车站结构两侧主体结构,并在衔接处预留后浇带,暗挖完成后再进行后浇带施工,通过数值分析可以发现,下穿段施工过程中,对既有车站结构竖向变形影响相对显著,既有车站道床隆起,车站底板发生不均匀沉降,最大沉降值约2.1 mm,超过规范预警值,存在一定的安全风险;(2)针对传统连接做法,提出了零距离下穿既有车站暗挖施工托举法施工理念,直接将新建结构与既有结构连成整体,从而形成暗挖段施工过程的新建结构对既有结构的托举体系,通过数值分析,托举法施工结束后,既有车站道床沉降可减小50%,控沉效果显著;(3)本研究成果可为新建工程暗挖下穿既有工程提供指导。