共查询到19条相似文献，搜索用时 110 毫秒
1.
《中国海洋工程》1987,(2)
There exists a wide tidal flat in the Qiantang Estuary. In this article the sediment concentrations in the mainstream and on the tidal flat are computed separately, taking into account the transverse exchange of sediment between them. The basic equation is similar to that used in Reference [2], but the ratio of the bottom sediment concentration to the vertical average is not taken as the same to the ratio of sediment transport capacity. The ratio of sediment concentration can be determined by the computational results of a simple model and checked by the field data. The formula of the sediment transport capacity for tidal flow can be obtained by statistical analysis directly using the measured values of sediment concentration.The verification of sediment concentration has been carried out with two sections both in the mainstream and on the tidal flat during twelve successive tidal cycles. The average discrepancy between the calculated and the measured is less than 20%. 相似文献
2.
Settling velocity is a fundamental parameter in sediment transport dynamics.For uniform Par-ticles,there are abundant formulas for calculation of their settling velocities.But in natural fields,sedi-ment consists of non-uniform particles.The interaction among particles is complex and should not be neg-lected.In this paper,based on the analysis of settling mechanism of non-cohesive and non-uniform parti-cles,a theoretical model to describe settling mechanism is proposed.Besides suspension concentration andupward turbulent flow caused by other particles,collision among particles is another main factor influ-encing settling velocity.By introducing the collision theory,equations of fall velocity before collision,colli-sion probability,and fall velocity after collision are established.Finally,a formula used to calculate the set-tling velocity of non-cohesive particles with wide grain gradation is presented,which agrees well with theexperimental data. 相似文献
3.
Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China 总被引：2，自引：1，他引：2
The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ～ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud. 相似文献
4.
You Yuming Hou Min Senior Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing Assistant Engineer River Harbour Department Nanjing Hydraulic Research Institute Nanjing 《中国海洋工程》1992,(3)
- The data of landsat TM of multi-temporal for Lingdingyang Estuary, Pearl River in China is firstly used with suspended sediment concentration of field measurement to establish a correlative model equation. After the ratio processing of TM data and atmospheric correction, the images of suspended sediment concentration of different temporals are exported from the image processing systems AREIS II and III. These images express the characteristics of suspended sediment distribution, the mode of sediment transport and the extent of dispersion under the actions of tidal current and wind condition of different seasons. 相似文献
5.
A theoretical analysis of velocity profiles in sediment-laden flows is presented by means of Prandtl-Karman mixing length theorem. The study shows that the upward velocity of liquid-phase caused by settling sediment leads to the invalidity of the log-law and Rouse equation. The theoretical analysis takes into account the upward velocity and shows: 1) the mean velocity in sediment-laden flows follows the log-law, but the Karman constant reduces in the main flow region, 2) sediment concentration reduces the mixing length of fluid particles, 3) flow resistance reduces with the presence of sediment concentration, and 4) the sediment concentration profile deviates from the well know Rouse equation. The experimental data agree well with the equations derived on the basis of non-zero wall velocity. It is found that the wall-normal velocity should not be neglected for density gradient flows because it induces more than for pure water flows. 相似文献
6.
In order to study the mechanism of flow-sediment movement, it is essential to obtain measured data of water hydrodynamic and sediment concentration process with high spatial and temporal resolution in the bottom boundary layer （BBL）. Field observations were carried out in the northwest Caofeidian sea area in the Bohai Bay. Near 2 m isobath （under the lowest tidal level）, a tripod system was installed with AWAC （Acoustic Wave And Current）, ADCP （Acoustic Doppler Current Profilers）, OBS-3A （Optical Backscatter Point Sensor）, ADV （Acoustic Doppler Velocimeters）, etc. The accurate measurement of the bottom boundary layer during a single tidal period was carried out, together with a long-term sediment concentration measurement under different hydrological conditions. All the measured data were used to analyze the characteristics of wave-current-sediment movement and the BBL. Analysis was performed on flow structure, shear stress, roughness, eddy viscosity and other parameters of the BBL. Two major findings were made. Firstly, from the measured data, the three-layer distribution model of the velocity profiles and eddy viscosities in the wave-current BBL are proposed in the observed sea area; secondly, the sediment movement is related closely to wind-waves in the muddy coast area where sediment is clayey silt： 1） The observed suspended sediment concentration under light wind conditions is very low, with the peak value generally smaller than 0.1 kg/m^3 and the average value being 0.03 kg/m^3; 2） The sediment concentration increases continuously under the gales over 6-7 in Beaufort scale, under a sustained wind action. The measured peak sediment concentration at 0.4 m above the seabed is 0.15-0.32 kg/m^3, and the average sediment concentration during wind-wave action is 0.08-0.18 kg/m^3, which is about 3-6 times the value under light wind conditions. The critical wave height signaling remarkable changes of sediment concentration is 0.5 m. The results show that the suspended load sediment concentration is mainly influenced by wave-induced sediment suspension. 相似文献
7.
In this paper,flume experiments are focused on sediment transport inside and outside the surf zone.According to the energy dissipation balance principle of sediment-laden flow and the similarity between energy dissipation of spilling breaking wave and hydraulic jump,formulas are proposed to predict time averaged suspended sediment concentration under both non-breaking and breaking waves.Assuming that the sediment diffusion coefficient,which is related with energy dissipation,is proportional to water depth,formulas are proposed to predict close-to-bed suspended sediment concentration and vertical distribution of suspended sediment under spilling breaking waves,and the prediction shows a good agreement with the measurement. 相似文献
8.
Based on a wave bottom boundary layer model and a sediment advection-diffusion model, seven turbulence schemes are compared regarding their performances in prediction of near-bed sediment suspension beneath waves above a plane bed. These turbulence algorithms include six empirical eddy viscosity schemes and one standard two-equation k-ε model. In particular, different combinations of typical empirical formulas for the eddy viscosity profile and for the wave friction factor are examined. Numerical results are compared with four laboratory data sets, consisting of one wave boundary layer hydrodynamics experiment and three sediment suspension experiments under linear waves and the Stokes second-order waves. It is shown that predictions of near-bed sediment suspension are very sensitive to the choices of the empirical formulas in turbulence schemes. Simple empirical turbulence schemes are possible to perform equally well as the two-equation k-ε model. Among the empirical schemes, the turbulence scheme, combining the exponential formula for eddy viscosity and Swart formula for wave friction factor, is the most accurate. It maintains the simplicity and yields identically good predictions as the k-ε model does in terms of the wave-averaged sediment concentration. 相似文献
9.
Modeling of suspended sediment transport with waveinduced longshore current in Huanghe (Yellow) River Delta 总被引：3，自引：2，他引：1
A three-dimensional suspended sediment model(SED)developed by the present authors is coupled with the combinatorial model of COHERENS(Luyten et al.,1999) (the three-dimensional coupled hydrodynamical-ecological model for Regional and Shelf Seas) and SWAN(Holthuijsen et al.,2004) (the third generation wave model).SWAN is regarded as a subroutine of COHERENS and gets time-and space-varying current velocity and surface elevation from COHERENS.COHERENS gets time-and space-varying wave relevant parameters provided by SWAN.Effects of wave on current are applied in bottom shear stress,wave-induced depth-dependent radiation stress and surface drag coefficient calculation.At the same time,the damping function of suspended sediment on turbulence is introduced into COHERENS.So the sediment model SED has feed back on circulation model COHERENS.The SED obtains current as sociated parameters from COHERENS.Then a couple dhydrodynamic-sediment model COHERENS-SED being able to account for interaction between wave and current is obtained.COHERENS-SED is adopted to simulate three-dimensional suspended sediment transport in the Huanghe River delta.In terms of simulation results,there is obvious diffierence between top and bottom layer of wave-induced longshore current.The values of time series of sediment concentration gotten by COHERENS-SED have,generally,an accepted agreement extent with measurement.Significant wave heights and wave periods obtained by COHERENS-SED show that wave simulation case with current’s effect can give better agreement extent with measurement than case without current’s effect.In the meantime,suspended sediment concentration distributing rule obtained by COHERENS-SED is similar to former researches and measurement. 相似文献
10.
The algorithms of extracting chlorophyll-a(Chl-a) concentration have been established for Chinese moderate resolution imaging spectrometer(CMODIS) mounted on Shenzhou-3 spaceship launched on 25 March 2002.The CMODIS is an ocean color sensor with 30 visible channels and 4 infrared channels,much different from other ocean color satellites and needs new algorithms to process data.Three models of Chl-a concentration were established based on Chl-a data retrieved from sea-viewing wide field-of-view sensor(SeaWiFS),with the average relative errors of 26.6%,24%.0% and 33.5%,respectively.This practical and economic approach can be used for developing the algorithms of Chinese ocean color and temperature sensor(COCTS) on the satellite Haiyang-1 to derive the Chl-a concentration concentration distribution.The applicability of the algorithms was analyzed using some in situ measurements.Suspended sediment is the main factor influencing the accuracy of the spectral ratio algorithms of Chl-a concentration.The algorithms are suitable to using in the regions where suspended sediment concentrations(SSC) are less than 5 g/m3 under the condition of relative error of Chl-a concentration retrieval within 35%.High concentration of suspended sediment leads to the overestimate remote sensing retrieval of concentration of Chl-a,while low-middle SSCs lead to the low Chl-a concentration values using the spectral ratio algorithms.Since the accuracy of Chl-a concentration by the spectral ratio algorithms is limited to waters of Case 2,it is necessary to develop semi-analytical models to improve the performance of satellite ocean color remote sensing in turbid coastal waters. 相似文献
11.
Observations of sediment contamination along the coast of Japan were analyzed. When the pollutant concentration is divided by the fine particle fraction in the sediment, a regular pattern is observed in the quantitative relationship among the degree and the area of contamination and the discharge rate of pollutant released continuously into the water along the coast. This regularity was observed with respect to COD,n-hexane soluble substances and heavy metals, and could be expressed by a formula.Polluted particles were supposed to disperse through suspension in the bottom water layer, and thus their distribution in the surface sediment is expected to become similar to effluent dispersion in the surface water. 相似文献
12.
ADCP对悬浮沉积物浓度的测量及其误差分析研究 总被引：6，自引：0，他引：6
为实时、连续地测量海水中悬浮沉积物，利用声学多普勒海流剖面仪(ADCP)，可以在测流的同时，测量海洋悬浮沉积物浓度。描述了利用后散射强度，估计悬浮沉积物浓度的原理。在现场测试中，利用采水器采集水样，通过水样分析并结合声信号的衰减特征对AI)CP的测量结果进行修正。作者还结合现场测试结果，对这一测量方法的精度进行了分析。现场实验表明，经公式校正后，ADCP测得的后散射强度与实测水样所获得的悬浮沉积物浓度之间有很好的相关性，相关系数达0．88，由此证明，此测量方法具有很好的实用价值和应用前景。 相似文献
13.
为实现对用海项目施工期悬浮泥沙扩散的实时跟踪监测,尝试采用无人机携带可见光、多光谱传感器对古雷围填海项目的围堰区进行遥感探测。利用Pix4d软件对无人机携带的可见光及多光谱照片进行处理,结果表明,可见光及多光谱影像对水体中的悬浮泥沙分布均具有一定的识别能力。通过研究分析多光谱影像的光谱特征发现,近红外波段对悬浮泥沙含量的升高较为敏感,运用波段比值公式计算结果显示,围堰内含沙水体经溢流口排入海域后浓度明显降低,并可向南继续扩散约300 m。该方法可克服遥感卫星影像时空分辨率低的特点,为用海项目资源环境影响跟踪监测提供新的技术手段。 相似文献
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15.
ADCP测量悬沙浓度的可行性分析与现场标定 总被引：18，自引：3，他引：18
根据现场观测数据，对ADCP测量悬浮沙浓度的进行标定实验。结果表明，在观测期间悬沙粒径变化较小的条件下，后散射强度与水样悬沙浓度之间存在较好的相关性。悬沙浓度剖面标定公式中的参数C′可用剖面实测水样浓度来确定，该参数与浓度密切相关：同一剖面不同浓度之间有一定的波动，但同一浓度不同潮时的变化很小。使用同一剖面参数C′的平均值计算出的剖面悬沙分布误差较大（29％－43％），而按不同深度段分别标定，误差可以小于20％，能够满足沉积动力学研究的需要。 相似文献
16.
近岸海域水沙界面通量与水流挟沙力研究 总被引：1，自引：0，他引：1
近岸海域的波浪、潮流及海流等动力因素具有周期性和时间、空间尺度差异大的特点,在综合考虑各动力因子的联合作用时具有较大的难度。本文根据平动动能叠加原理给出了一种近岸动力因子的表达形式,并提出了海洋波动有效速度的概念,结合水沙界面处泥沙通量的切应力与挟沙力关系,得到了水流挟沙力的新的计算公式。指出了水流挟沙力与水流临界速度有关,并且该水流临界速度随水深的增大及相对糙率的减小而增大。采用近岸实测数据和模拟结果,对本文的近岸水流挟沙力公式进行了验证,结果表明该公式的计算值与实测值吻合较好,可以适用于近岸海域。 相似文献
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黄河口悬浮泥沙时空动态及其驱动机制 总被引：1，自引：1，他引：0
受径流输沙、风浪、潮汐等影响,河口近岸海域悬浮泥沙具有显著的时空变化。本文基于小时分辨率的GOCI遥感影像,利用最优遥感反演算法,结合空间分析和统计方法,深入研究黄河口及邻近海域悬沙时空动态特征及驱动机制。结果表明,径流输沙对悬沙浓度的影响以河口近岸区为主,高径流输沙对悬沙浓度分布影响可达距岸约20 km,并向孤东近岸方向扩散。大风可引起清水沟老河口区泥沙强烈再悬浮,形成高浓度悬沙区。涨落潮对小时尺度的悬沙浓度影响显著,并影响悬沙的南北扩散。大潮悬沙浓度变化和扩散范围均大于小潮,潮流流速不同是造成该差异的主要原因。水深与悬沙浓度之间存在较明显的负相关关系,根据不同驱动因素的差异,悬沙浓度随着水深的增加呈现出指数型、幂函数型、线性3种关系。 相似文献
19.
对南海某海域深度100～400 m的海底浅层（约2 m埋深范围）沉积物柱状样在接近海底水压力下进行三轴应变-声学同步测量,结果表明沉积物纵波声速有两个特征:（1）从应变过程开始到结束,沉积物纵波声速不断变化;（2）平均声速随着平均静弹性模量的增加,由大变小又由小变大,存在声速最小值。这些结果与海底浅表层沉积物的物理力学性质、围压、颗粒的结合状态改变有关。此外,沉积物动弹性模量和孔隙度呈良好的负相关性,这与孔隙度增大含水量增大有关;动弹性模量是静弹性模量的10～100倍,这主要与三轴应变试验的应变数量级与声波振动产生的应变数量级的差异大有关。采用本论文实验测量的数据分别建立了双复合参数-声速和孔隙度-声速经验公式,分析结果表明双复合参数-声速公式声速预报误差约是孔隙度-声速公式的1/4,表明双复合参数-声速公式更加有效。 相似文献