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沉积物颗粒与下覆颗粒间转动角是制约沉积物颗粒起动的一个重要因素。本文样品采集于1987年。作者通过一系列实验探明了沉积物转动角同颗粒形状、相对粒径比以及迭瓦状构造等因素之间的相互关系。在均匀粒径条件下,球状砾石转动角的测量数值同理论数值相吻合,但随粒径的减小而增大。这一结果同前人利用球状砂粒进行实验所获得的结果相一致。利用球状、椭球状及棱角状砾石进行的实验表明,沉积物转动角φ随相对粒径的增大而减小,随颗粒扁平度及颗粒棱角度的增大而增大。扁平砾石的迭瓦状构造将导致转动角的增大,其增大值约等于砾石的迭瓦角。若其它因素相同,沉积物起动的难度自球状、椭球状、棱角状及迭瓦状构造而依次增强。这些结果将有助于对颗粒粒径、形状、构造同沉积物搬运临界状态以及沉积物选择性起动之间的相互关系进行定量分析。 相似文献
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本文基于尖点突变理论,针对泥沙运动的复杂特征,建立了波浪作用下的泥沙起动模式,确定了希尔兹极值、相对粒径和反映波浪与泥沙之间相互作用参数的非线性方程,并对该方程进行了拓扑变换。该模式的计算结果与波浪水槽试验资料的对比分析说明,该模式尽管存在一定的系统误差,但是对于波浪作用下的泥沙起动流速的求解和运动状态判别与试验值基本吻合,进而证明了泥沙起动的突变特性和该模型的适用性。 相似文献
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南汇东滩沉积物粒度特征及其与水动力的关系 总被引：2，自引：0，他引：2
沉积物粒度参数可以用来反演沉积物沉积的水动力条件和沉积环境。根据对南汇边滩采集的表层沉积物粒度资料进行分析,结果表明:沉积物类型以黏土质粉砂为主;随着沉积物平均粒径Mz的减小,分选逐渐变好,偏态由极正偏向正偏转变,并向近对称接近。运用Pe- jurp的三角图式对沉积环境进行划分,结果表明南汇东滩的水动力条件总体上较强,沉积物粒径总体上偏粗,属于径流—潮流共同作用的河口浅滩沉积环境。对潮流底应力和沉积物临界起动切应力的计算进一步印证了该区水动力较强,对应沉积物颗粒偏粗的现象。 相似文献
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沉积物的粒度是最重要的沉积物参数之一，在河床中，表层沉积物缺乏砂–砾过渡粒级（即1～10 mm）的沉积物，被称为Grain size gap，得到广泛关注。海滩沉积物是否也是如此，是一个基本而又未知的问题。本文分析了中外228处海滩共456个表层沉积物平均粒径数据，发现海滩大概率或是平均粒径几十毫米的砾石滩，或是平均粒径几百微米的砂滩，也缺乏砂–砾过渡粒级沉积物，其粒度范围是-3.5～-1?（2～11 mm），这一结果和河床的情况基本相同。造成砂–砾过渡粒级缺乏的原因应从物源、颗粒磨损和分选以及广义的物质收支分析中去寻找。 相似文献
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天然砾石海滩作为一种高能环境下的海岸堆积体,因其粒径粗、孔隙度大等特征,是良好的海岸防护屏障。了解砾石海滩形成过程离不开砾石形貌这一重要参数,但要快速、准确获得大量砾石的定量参数比较困难。本文对山东北长山岛3个砾石海滩(九丈崖、月牙湾、长滩)、南长山岛的4个砾石海滩(仙境源、林海、长山尾和明珠广场)进行现场剖面测量并采集砾石样品及砾石图像,应用ImageJ软件对砾石进行原位无干扰数字图像测算,可以快速大量分析砾石粒径、磨圆度等形貌参数。结果显示:砾石的粒径范围为4～79 mm,主要集中在中砾,各海滩分选较好;其中,北长山岛海滩的砾石平均粒径略小于南长山岛,北长山岛九丈崖海滩的砾石平均粒径最大,南长山岛的仙境源海滩砾石平均粒径最小。向海方向从滩肩到高潮线平均粒径逐渐减小,但在水边线处增大。砾石磨圆度介于0.59～0.75之间,等级均为圆状,砾石海滩均已达到较成熟阶段;其中北长山岛的月牙湾海滩砾石磨圆最好,长滩海滩砾石的磨圆最差,由陆向海磨圆度值呈增大的趋势。形状比率范围介于1.36～1.77之间,与磨圆度呈明显负相关(R2=0.98),砾石由陆向海从长条状渐变为椭圆状。南、北长山岛的砾石海滩的砾石形貌受到物源、动力条件和人为活动的影响。研究区砾石海滩坡度范围为16%～35%,海滩坡度与沉积物粒径呈正相关。 相似文献
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粒径趋势分析是一种用于判断海洋环境中沉积物净输运方向的方法，但是至今粒径趋势形成的物理机制尚不够清楚，因而影响了粒径趋势分析适用条件的确定。针对这个问题，本文通过建立一维、推移质、往复流（近岸潮流）条件下的数值模型，采用正演方法模拟粒度参数在输运方向上的分布．以评价沉积动力过程的影响，初步探讨粒径趋势形成的物理机制。数值模型实验的初步结果显示，水动力条件的空间差异导致的沉积物粒度参数的空间分布符合粒径趋势分析的假设，粒径趋势分析中定义的两种粒径趋势可由沉积物输运强度的空间梯度而形成，并且在沉积物净输运方向上出现的频率最高。 相似文献
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苏北潮滩不同生态带沉积物分布特征 总被引：7，自引：0，他引：7
利用2004年1月3日在江苏盐城珍禽国家级自然保护区核心区新洋港采集到的表层和柱状沉积物样品,采用矩值法对该潮滩沉积物粒度和粒度参数进行了分析和计算,并对潮滩沉积物的水平和垂向分布特征以及不同植被对沉积物分布的影响进行了研究,结果表明:(1)自海向陆,光滩、互花米草滩、互花米草盐蒿混合滩、盐蒿滩和芦苇地5个亚带中,光滩沉积物的粒径明显较其它4个亚带处的粒径大,在接近互花米草滩时沉积物的粒径迅速变小,而互花米草滩等其它4个亚带处的沉积物粒径则变化不大。较低部位光滩沉积物的频率分布曲线呈不明显双峰分布,而较高部位的光滩及其它生态带内的沉积物频率分布曲线均为单峰,显示出物源较为单一的特点。(2)沉积物自海向陆粒度特征的变化规律反映了潮滩水动力条件对沉积物分布的影响,尤其是反映了盐沼植物在潮滩的发育过程中所起的重要作用。(3)周期性变化的潮动力作用、潮流不对称作用、植被以及潮滩不同部位淤积演化差异的影响造成了潮滩不同部位沉积物敏感组分粒度垂向变化的差异。 相似文献
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黄河三角洲孤东海域沉积物及水动力 总被引：7，自引：0，他引：7
根据黄河三角洲孤东近岸海域表层沉积物取样、水文泥沙观测和风浪资料推算,分析沉积物特征和运移趋势,并通过水动力条件(潮流和波浪)探讨沉积物起动和输移特征。结果表明,孤东海域沉积物多为粉砂类物质,由内向外逐渐变细,分选变差,丁坝的修建对周围粒径分布影响明显;沉积物运移趋势受风成余流、岸线轮廓和丁坝工程修建的影响,不同区域表现为不同的输移方向;研究区水动力表现为波浪掀沙、潮流输沙的特征,由于潮流较小,不足以引起泥沙的起动,泥沙起动主要由波浪引起。 相似文献
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Chandralata Raghukumar G. Sheelu P. A. Loka Bharathi Shanta Nair C. Mohandass 《Marine Georesources & Geotechnology》2001,19(1):1-16
In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance. 相似文献
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Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
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海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。 相似文献
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Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification
An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm. 相似文献
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Shigehisa Nakamura 《Marine Geodesy》2000,23(1):55-61
Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone. 相似文献
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The effect of different fixation and storage protocols on the flow cytometric (FCM) simultaneous analysis of bacterioplankton and phytoplankton in coastal seawater samples (Mediterranean coastal lagoons) was investigated. FCM measurements (cell number, fluorescence and scatter characteristics) were obtained through DAPI staining. Three fixatives [glutaraldehyde (GA), formaldehyde (FA) and paraformaldehyde (PFA)] and two storage (3 months duration) methods (5 °C and −196 °C) were tested. Two dominant populations were detected in studied samples: bacteria and eukaryotic picophytoplankton. Adding fixatives (2% final concentration) appears necessary to obtain FCM exhaustive counts of all the bacteria and phytoplanktonic cells. This was related to the permeation effect of fixatives which allowed a better DAPI staining of the cells. Maximum fluorescence, i.e. optimal staining of the cells was obtained with FA or PFA, and significant lower fluorescences with GA. Fixed samples stored at 5 °C induced rapid cell loss. Only storage in liquid nitrogen of samples fixed with FA or PFA, allows mid-term (≥4 months) preservation of bacteria or picophytoplankton cell numbers, and limited evolution of DAPI-induced fluorescence and scatter characteristics. 相似文献
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《海洋学报(英文版)》2014,(9):F0003-F0003
<正>Acta Oceanologica Sinica(AOS)is a comprehensive academic journal edited by the Editorial Committee of Acta Oceanologica Sinica and is designed to provide a forum for important research papers of the marine scientific community which reflect the information on a worldwide basis.The journal publishes scholarly papers on marine science and technology,including physics,chemistry,biology, 相似文献
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Oedometer tests have been carried out on 70 undisturbed surficial clays (at approximately 250 mm below the mudline), mostly collected by free-fall corers from sites widely scattered throughout the deep-sea North Atlantic. Acoustic measurements were also made, initially on contiguous samples and ultimately on the same sample using a geophysically instrumented oedometer which also collected electrical resistivity data. Apart from those quiescent areas below the carbonate compensation depth, such as north of the West Indies where very fine clays exist, most of the samples are silty clays whose geotechnical-geophysical properties are dependent on the type of clay minerals present (and their ability to take in moisture), the sand-size fraction, and the quantity of carbonate present. Thus the pure clays have high compressibilities which decrease on the addition of coarse particles, while the converse is true for the acoustic parameters, these increasing with the sand fraction. Using the notion of the intrinsic compression line for all samples, and comparison to it of the measured compression curves, it is clear that, contrary to some previously held ideas, most deep-sea clays are normally consolidated; the addition of carbonate has the effect of creating an open, stronger sediment skeleton. Interestingly, where information is available, the variation with depth of a sample's acoustic velocity follows the void ratio pressure relationship of the compression curve. This allows the construction of an in-situ sediment compression curve using the in-situ geophysical observations. 相似文献