共查询到17条相似文献，搜索用时 140 毫秒
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考虑渗流力的海床临界冲刷机理及计算方法 总被引：1，自引：0，他引：1
从波浪引起的海床内部渗流与床面泥沙运动耦合的角度出发,研究波浪作用下海床临界冲刷机理及计算方法。研究表明,波浪作用下床面泥沙起动及冲刷是一个不断向下发展的过程,最终达到一个临界冲刷深度。波浪引起的渗流力能够显著降低泥沙的临界起动切应力,促进泥沙起动,是影响海床冲刷的一个重要因素。将渗流力引入到传统泥沙起动公式中,推导并给出了波浪作用下海床临界冲刷深度的计算方法。结合室内和现场两个算例,很好地解释了波浪水槽试验中海床"流化"现象和黄河水下三角洲粉砂流冲沟等灾害地貌特征及成因,初步验证了该方法用于评价和计算海床冲刷的有效性。 相似文献
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从波浪引起的海床内部渗流与床面泥沙运动耦合的角度出发,研究波浪作用下海床临界冲刷机理及计算方法。研究表明,波浪作用下床面泥沙起动及冲刷是一个不断向下发展的过程,最终达到一个临界冲刷深度。波浪引起的渗流力能够显著降低泥沙的临界起动切应力,促进泥沙起动,是影响海床冲刷的一个重要因素。将渗流力引入到传统泥沙起动公式中,推导并给出了波浪作用下海床临界冲刷深度的计算方法。结合室内和现场两个算例,很好地解释了波浪水槽试验中海床"流化"现象和黄河水下三角洲粉砂流冲沟等灾害地貌特征及成因,初步验证了该方法用于评价和计算海床冲刷的有效性。 相似文献
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黄河三角洲粉质土海床临界起动切应力影响因素研究 总被引：1，自引：0，他引：1
在黄河口潮滩和室内环形土槽模拟新沉积的海床土体,观测固结过程中沉积物临界起动切应力的变化及对应的土体重度、含水率、贯入阻力、剪切强度指标值的变化,分析黄河三角洲粉质类土临界起动切应力的影响因素与变化规律。研究发现：黄河三角洲粉土的临界起动切应力与重度、贯入阻力和抗剪强度之间呈正相关关系,而与含水率呈负相关关系,并且与干密度、抗剪强度之间具有非常好的定量关系。将黄河三角洲粉土临界侵蚀切应力的试验结果与其他学者建立的计算公式进行了比较,发现在固结开始试验与计算结果间的吻合性较好,随着固结时间差异性变大,表现出黄河口粉质土的独特性。 相似文献
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为揭示内部渗流对海岸冲流带泥沙起动的影响,系统地开展了斜坡海床冲流特性与泥沙起动机理研究。通过室内水槽开展了孤立波在可渗透和不可渗透斜坡海床上的冲流试验,测试了冲流过程中波高、波速等变化规律;建立了渗透海床冲流数值模型并通过试验结果进行验证;深入分析了床面渗流对其波浪流场动态特征以及床面泥沙起动的影响机理。研究表明,床面渗流作用加剧波浪的不对称性,在波浪上冲过程中因床面强入渗作用而增大了床面切应力;回流过程因入渗所造成流量损失而导致床面切应力减小。床面渗流引起床面颗粒有效重度和切应力变化而导致泥沙希尔兹数大大增加,加剧了泥沙起动现象,且床面切应力改变是引起泥沙希尔兹数变化的主要因素。 相似文献
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河口入海泥沙沉积固结过程中抗侵蚀性的变化直接决定着沉积物的再悬浮和二次迁移,对河口岸滩的稳定具有重要决定作用。在现代黄河三角洲潮滩模拟入海泥沙快速沉积,现场测试不同固结时间沉积物的抗侵蚀性和物理力学指标的变化。研究发现,黄河入海泥沙沉积物的抗侵蚀性随固结时间增长迅速提高,当沉积固结时间达8h时,其临界侵蚀切应力就超过了原状潮滩表层沉积物;新沉积泥沙的临界侵蚀切应力与其重度、贯入阻力、剪切强度呈良好的正相关关系,与含水率呈良好的负相关关系。黄河入海泥沙临界侵蚀流速的试验值随固结时间的增长速率要高于各泥沙起动公式计算值的增长速率,前者是后者的1.5～4.1倍。 相似文献
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分析了现有起动标准的不足之处。在制定起动标准时,不但要考虑水流条件,还必须考虑泥沙颗粒在床面的相对位置。对同一粒径的泥沙颗粒,其起动条件不是一个常量,而是位于一个区间,它随颗粒在床面的相对暴露度而变化。根据力学原理,推导了泥沙颗粒起动时的临界无量纲切应力公式,并对其系数取值进行了理论计算。计算结果表明,对同一粒径、在同一起动状态下,泥沙颗粒的起动临界条件并非一个常量。并从理论上分析得到了临界值的范围,对个别及少量起动,其无量纲临界切应力为0.021～0.042及0.041～0.062。 相似文献
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为研究淤泥质河口的水沙运动规律,建立了用于模拟淤泥质河口水沙运动的二维数学模型。该模型采用基于无结构三角网格下的有限体积法对方程组进行离散,结合Roe-MUSCL方法及时间方向的预测-校正格式,使模型在时空方向具有二阶计算精度。模型中分别采用不同方法计算粘性和非粘性泥沙的输移源项,并引入粘性泥沙的起动流速和冲刷率计算公式。采用已有的概化水槽试验数据对模型进行了初步验证。然后模拟了1995年10月小潮及大潮期间海河口的潮流运动与泥沙输移过程,计算得到的潮位、潮流速及含沙量过程与实测过程符合较好,结果表明模型能够用来模拟淤泥质河口粘性和非粘性泥沙的不平衡输移过程。同时还比较了泥沙输移源项的不同处理方式对计算结果的影响,计算表明在淤泥质河口水沙运动数学模型中必须同时考虑粘性和非粘性泥沙的输移。 相似文献
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粘性土体具有较强的抗冲能力,其抗冲性强弱决定了河岸的侵蚀速率。为了估算河岸的侵蚀速率,确定粘性土体的起动条件、侵蚀系数及两者之间的数量关系非常重要,为此开展了荆江段河岸粘性土体起动条件与冲刷特性的水槽试验研究。根据试验结果获得了粘性土体的起动流速与土体液限/自然含水率之间关系以及起动切应力与干密度、起动切应力与液性指数之间的定量表达式,综合反映了粘性土起动条件与其物理性质指标之间的关系;结合冲刷特性试验结果,还获得了土体侵蚀系数随起动切应力的变化规律,并与已有其他试验结果进行了比较。结果表明:荆江河岸粘性土侵蚀系数均比相同条件下其他公式计算值偏大,这与该试验土体中粘粒含量相对较低、土体结构受到扰动等因素有关;根据试验结果,拟合得到了荆江河岸粘性土侵蚀系数与起动切应力之间定量关系式,其相关系数R2=0.90,故该关系式能为荆江段崩岸过程的计算提供参考依据。 相似文献
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为了通过实验测量泥沙起动概率,基于封闭槽道内开展的泥沙起动实验,系统论述了基于高速摄影的起动概率测量方法所涉及的起动概率定义、相机采样频率、图像处理方法、起动比例与运动比例的关系等关键问题.根据泥沙在水流紊动猝发作用下起动的物理机制,定义实测起动概率为单个紊动猝发周期内,从一定面积床面上冲刷外移的泥沙比例.根据推移质运动概念模型,提出高速图片拍摄间隔应小于推移质运动的中间时间尺度,以捕获泥沙的每一次起动.在高速图像处理时,通过连续两帧图片之间的灰度差实现运动比例的无偏差提取.进一步分析表明,运动泥沙可处于起动、止动或滑翔状态,运动比例等于起动比例、止动比例和滑翔比例之和,起动比例与运动比例之比等于两张图片之间的时间间隔除以推移质运动的中间时间尺度.基于上述关键技术,将高速摄影测量方法用于泥沙起动概率的测量,结果表明,临界起动水流条件时,床沙处于少量起动现象,对应的临界起动概率与窦国仁所推导的2.28%接近. 相似文献
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天然水体中泥沙颗粒表面容易生长生物膜,生物膜的生长会对泥沙颗粒的运动特性产生显著影响。设计了泥沙颗粒表面生长生物膜的实验,以及生长生物膜后泥沙颗粒的起动水槽实验。在水槽观测段分别放置由去离子水浸泡和天然水培养的两种泥沙,对比观察两种泥沙起动过程的区别,分析起动流速的差异和随培养时间的变化规律。结果表明,天然富营养水体中生物膜生长繁茂,对泥沙起动特性有着显著的影响,能够增强泥沙颗粒的抗冲性,并随时间呈现出先逐步增强到一个最优值后有所削弱的钟形曲线的变化趋势,表明在研究天然河流和湖泊尤其是污染严重的水域的泥沙起动时,需要考虑到生物膜的作用。 相似文献
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床面上泥沙颗粒的起动测量一直是泥沙运动规律研究的难题。为此,提出了一种基于B超成像技术的泥沙起动流速测量方法。在模型试验水槽中,该方法利用B超仪获取水下地形及其附近粒子的运行图像,通过图像处理技术分析统计床面附近运动粒子的成像光斑个数,并分析其与流速之间的关系。结果表明,B超成像光斑个数在泥沙起动过程中存在一个突变过程,且该突变过程与泥沙起动运动相对应,可用来判定泥沙起动及其对应的起动流速,并利用该流速下的床面地形变化验证了该方法的正确性。该方法具有无扰动无干扰、适合于清水和浑水、易于实现自动化测量的特点。 相似文献
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The concept of the wave-graded continental shelf, with sea floor sediment coarsening from offshore mud to shoreface sand, has been well known from the time of Johnson (1919) . Although most of the modern shelf shows textures unrelated to water depth on account of relict features or sediment starvation, the geological record is more likely to preserve sites where sediment is being fed to a subsiding inner-shelf. These consistently show the landward-coarsening pattern of the wave-graded shelf, recording past water depth history in accumulated sea floor sediment. The landward-coarsening pattern is driven primarily by wave-induced bed shear stress, which increases shoreward exponentially, although it also varies from place to place with wave climate, and can be influenced by sediment concentration and currents. In this study, the relationship between bed shear stress, sediment texture and water depth has been investigated by comparing per cent mud and wave climate data from shore-normal transects of three modern wave-graded coastal settings: Wellington Harbour (low energy) and the Manawatu coast (moderate energy) in New Zealand, and Monterey Bay in California (moderate–high energy). Samples from all three locations show a progressive change from poorly sorted mud offshore to well-sorted fine sand nearshore, with the sand–mud transition ranging from 3 m (low energy) to 50 m (moderate–high energy), reflecting differences in average bed shear. Repeat measurements of per cent mud on seasonal, annual and decadal time scales along a Manawatu coastal transect showed no measurable change, demonstrating equilibrium between sediment supply, wave energy, water depth and sediment texture. A simple model based on the relationship between wave climate, shear stress and per cent mud, and using data and conditions from the modern Manawatu coast, is applied to two mid-Pliocene cyclothems exposed 50 km inland, giving results comparable with estimates from foraminifera and the deep-sea isotope record. Per cent mud offers more detail for palaeobathymetric trends in shallow water shelf strata than other proxy depth recorders, although it is limited to depths above wave base and requires an independent estimate of wave climate if depths are to be quantified. 相似文献
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Bed forms were studied in Goodwin Creek and a laboratory flume channel. The bed sediment of the field site and flume had median diameters of 8·3 (modes of 0·4, 22·6 mm) and 1·82 mm (modes of 0·5, 5·6 mm), respectively. The laboratory and field channels had similar values of bimodal parameters, ratios of flow depth to median bed material diameter, and ratios of shear stress to critical shear stress and were judged to be comparable in the transport of bed load sediment and the resulting bed forms. Three groupings of bed forms from the laboratory flume experiments (ripple-like bed forms, bed load sheets, low-relief bed waves) were identified using the height and period of the bed forms. For the range of flow depths and discharges investigated in the flume, bed forms became higher and longer with increasing bed shear stress. Bed forms from Goodwin Creek were similar to those from the flume with comparable ratios between bed form length, height, and flow depth. The bed forms in the flume provide a positive link between rate and size fluctuations measured in the field and the bed forms. The smaller bed forms identified were sediment starved and are not considered to be dunes, while the largest bed forms in which all of the bed material sizes were mobilized in the field and laboratory were judged to be dunes. 相似文献
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On experimentally deposited kaolinite, illite, and Ca-bentonite consolidated under their own load or by additional vertical pressure, the progress of compaction in relation to excess pore water pressure, mass physical properties, gravitational mass movements in a tilted tank, and erodibility under running water in a flume were studied. The very low consolidated sediments near the mud/water interface do not obey the generally used theory in soil mechanics. They show a different, non-linear relationship between void ratio or water content and depth below the sedimentary surface on the one hand, or effective overburden pressure and shear strength on the other. The same is true of other physical properties such as permeability, which changes considerably with depth and time of consolidation. High sedimentation rates on slopes induce shallow sediment flow, whereas at low rates and critical slope angles different types of slope failures including the breaking up of water-rich sediment into sharp boundered blocks are observed. Flume studies on soft clay muds show three different types of erosion: continuously suspending, discontinuous erosion of crumbs or shreds, and wavy deformation of the clay surface with disintegration of particles from the crests. The critical tractive stress depends not only on clay type, void ratio, and shear strength, but significantly also on the ‘geologic history’of the clay (i.e. deposition from thin suspension or dense slurry, fabric, consolidation and swelling generating minute inhomogeneities etc.). The experiments may lead to a better understanding of all mechanical processe's including pore-water flow taking place near or not far below the sediment/ water interface. 相似文献
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根据无粘性均匀沙起动的力学条件,在已有研究成果基础上,推导出泥沙起动概率与水流条件之间的关系式,得到考虑起动概率的起动切应力及起动流速公式,并将起动条件与起动标准联系分析.通过对现有几个典型无粘性均匀沙起动条件公式分析表明,本文公式较为合理. 相似文献