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1.
海底浊流在坡道转换处的流动及沉积的数值模拟 总被引：2，自引：1，他引：1
根据一经多项试验数据验证的基于三维不可压缩流体Navier-Stokes方程和湍流 k-ε 模型的重力流数值计算的数学模型,模拟并分析了单粒径沉积物的海底浊流沿不同斜坡流至近似平坦坡的流动及沉积特征。模拟结果显示了有关海底浊流的一些重要特征:连续入流的浊流在斜坡上的流速随着斜坡的增大而增大,同时浊流厚度由于对环境水体的夹带而渐渐增厚,坡度越大,增厚越快;流至近水平坡时,流速均有明显的降低,但大斜坡入流依然保持相对较高的流速。在沉积方面,初步的模拟结果显示对给定的沉积物来说存在一相对应的临界坡度:当坡度小时,坡上沉积多,坡下少,这样整体的坡度有逐渐增大之势;当坡度大时,坡上沉积少或为侵蚀,而坡下沉积相对较多,坡度有整体减小之势。了解了不同坡度转换的浊流沉积的上述特点,对于我们根据实测的浊流沉积的剖面特征推测其形成的环境,进而推测相关油气储层的分布状况会有一定的参考作用。 相似文献
2.
浊流形成条件的水动力学模拟及其在储层预测方面的作用 总被引：3，自引：0，他引：3
在对浊流形成条件地质背景研究的基础上,应用水动力学模拟原理正演模拟了由不同粒级沉积物形成的浊流的几何形态,并通过与地震资料的对比来达到储层预测的目的.采用该方法分别对莺歌海和琼东南盆地的浊流沉积进行了模拟研究,模拟结果表明:①浊流发育的最理想的坡度是1.5～3.0°;②浊流沉积一般都会形成斜坡扇和盆底扇,且单个浊积体在坡角处沉积最厚,向盆地方向逐渐减薄;③在其它参数不变的情况下,固体颗粒越大,形成的浊积体越厚,但展布范围越小;固体颗粒越小,形成的浊积体越薄,但展布范围越大.模拟结果与钻井的实际情况吻合良好. 相似文献
3.
准噶尔盆地沙湾凹陷早二叠世沉积期发育大面积的砂岩,主要发育砂质碎屑流、浊流等重力流砂体。砂质碎屑流沉积以块状层理为主,单砂体厚度大,浊流沉积以粒序层理为主,砂泥互层频繁。通过陆相湖盆、野外露头剖面、岩心、测井等资料分析,结合重力流沉积背景下各成因砂体测井曲线形态、垂向的发育厚度、连续性及组合特征,确定了沙湾凹陷西斜坡受重力流形成机制、坡折带形态、坡折带古地貌和同沉积断裂的影响,重力流不呈经典的扇形。按形态可分为水道-湖底扇、扇形2大类。并从坡折带及平面形态和地震属性上进行了精细刻画。研究结果表明,扇三角洲前缘亚相水下分流河道为沉积优势相带。砂质碎屑流沉积区虽是油气藏有利聚集分布带,但分布面积较广。进一步确定规模储层发育带,明确了“北河南扇”的沉积特征,为有利区的优选提供了新的研究方向。 相似文献
4.
在野外放水试验条件下,利用染色法和侵蚀针法分别观测坡面流速和侵蚀产沙空间变异性。结果表明,坡面各横向断面的流速与距坡顶距离之间呈正相关,且相关性随流量增大逐渐变得显著,纵向断面流速的变异程度明显强于横向断面。总体上,上、下坡位侵蚀程度较重,而中坡位最轻;小流量时沉积作用明显,大流量时距坡顶0~2 m范围为净侵蚀区;各坡段侵蚀量与其距坡顶距离之间呈负相关;发生泥沙沉积部位随流量增大逐渐下移,细沟侵蚀量占坡面总侵蚀量的比例随流量增大不断增加。试验条件下流速为0.30 m/s时,细沟侵蚀产沙大于细沟间侵蚀,且坡面侵蚀量迅速增大。随流量增大,流速和侵蚀产沙量呈增大趋势;但在流量较大时,坡面各坡位侵蚀量与流速呈负相关,这可能与坡面中下部位粗颗粒泥沙沉积以及含沙水流的挟沙能力基本达到饱和有关。 相似文献
5.
海底浊流的运动及其沉积,是目前浊流研究的热点之一。根据经过验证的基于雷诺平均纳维尔-斯托克斯方程及浮力项修正 k-ε 湍流模型的三维数值计算模型模拟了海底弯曲圆弧形峡谷内的浊流的流动和沉积,结果表明:（1）浊流在运动过程中由于对环境水体的夹带厚度不断增加,浊流厚度一般会超过峡谷深度,溢出峡谷,使浊流产生密度和动量损失;（2）浊流到达弯道部分后,由于离心力的作用会产生剥离,溢出更多的浊流至漫滩区域。浊流剥离的最大处为弯道顶点外岸下游处,其过量密度可达入流的37.5%;（3）对于模拟的横剖面为圆弧型的峡谷内的浊流来说,弯道顶点处的二次流在底部形成一个顺时针的循环圈,靠近峡谷底部从外岸指向内岸;（4）在峡谷中间及弯道顶点内岸下游处形成沉积,在弯道顶点外岸下游处形成侵蚀。这些特征对根据浊流的沉积观察推测其形成环境及油气储层的调查等方面有一定的参考意义。 相似文献
6.
深水环境多级地貌坡折控制下的重力流动力学的演变 总被引：4，自引：0，他引：4
台湾浅滩陆坡具有活跃的重力流机制,发育了壮观的重力流沉积体系,是研究重力流动力学作用过程的理想场所。自陆架前缘直至深海的马尼拉海沟,发育了三个地貌坡折（包括一个陆架坡折和两个陆坡坡折）。这些地貌坡折控制了重力（流）的启动和整个演化过程,控制了各种重力流沉积体系的空间分布格局。其中陆架坡折控制了重力滑塌的产生,第一和第二陆坡坡折则分别控制了重力滑塌体、碎屑流、浊流的转换。论文利用重力流沉积物波的波形参数恢复了重力流流体有关参数,实证了研究区的确存在有非常活跃的重力流机制。而多级地貌坡折代表着陆坡地貌的不均衡和向均衡的演化,重力流的侵蚀－沉积效应只是陆坡体系调整过程的表现。 相似文献
7.
大型坳陷湖盆坡折带背景下的重力流沉积模式 总被引：6，自引：0，他引：6
沉积盆地的坡折带是重力流发育的最有利场所,湖盆发育有和陆坡特征相似的坡折带,开展大型坳陷湖盆坡折带背景下的重力流沉积模式及其分布规律的研究具有重要意义。松辽盆地的龙虎泡—大安阶地具有明显的坡折带特征,且发育两级坡折。湖底扇是由沉积物重力流所搬运的沉积物在湖底堆积形成的沉积体,松辽盆地南部湖底扇主要由滑坡、碎屑流、浊流搬运的碎屑堆积而成。以松辽盆地为例,建立了短缓坡和长缓坡两种类型的重力流沉积模式,两种模式的湖底扇和下切水道的形态和分布模式均存在明显不同。 相似文献
8.
夏万云 《中国地质灾害与防治学报》2022,33(1):99-106
黄土坡面侵蚀特性研究对于铁路边坡及路基防护具有重要的意义。通过银西高铁董志塬段某路基护坡坡面冲刷试验,获得了不同冲刷历时、冲刷流量、坡度等条件下的坡面冲刷结果,并对坡面流水动力学特性、坡面产沙规律、坡面产沙机理进行了分析,得出以下结论:（1）坡顶和坡底比坡面中部更易受侵蚀;30°～60°斜坡在较小的冲刷强度下也能产生较明显的侵蚀沟,宜采取45°左右的多级矮坡来减弱侵蚀强度。（2）坡面流水动力学特性分析表明,试验工况水流主要处于过渡流区;平均流速与冲刷流量、坡度呈幂函数关系;达西阻力系数与冲刷流量、坡度呈负相关,且与雷诺数相关性较低。（3）平均含沙量随冲刷流量与坡度的增大而增大,随历时近似线性增加,约20 min以后,含沙量基本稳定,此过程为坡面沟道发展阶段。（4）坡面侵蚀产沙量与侵蚀切应力、有效水流功率都呈正相关,与前者近似呈线性增大关系,而与后者近似呈幂函数关系。 相似文献
9.
在恢复乌里雅斯太凹陷南洼早白垩世古地貌的基础上,分析了调节构造—坡折带特征与沉积体系和储集层分布的关系。结果表明：该复合型构造组合对砂体形态和储集层分布具有控制作用。研究区发育调节构造—上坡折、调节构造—中坡折和调节构造—下坡折,平面上呈北北东向展布。调节构造—坡折带控制沉积体系的发育,形成大规模扇三角洲—湖底扇沉积体系;调节构造—坡折带也控制砂体的形态,形成了7个呈舌状分布的小型湖底扇砂体;多级坡折带提供沉积物堆积的空间,调节构造对物源和水系也具有控制作用。在调节构造—坡折带的控制作用下,南洼储集体类型主要为扇三角洲前缘和湖底扇砂体,且不同级别的复合构造的储集体类型和物性存在差异。 相似文献
10.
本文基于对覆盖全区的二维地震资料研究,在珠江口盆地识别出了大型的陆架坡折及多种小型坡折带,包括侵蚀坡折带、沉积坡折带、断裂坡折带和挠曲坡折带。不同的构造背景发育了不同的坡折带类型。自30Ma年以来,坡折带总体呈向北迁移的趋势。古近纪一早中新世中期以各种小型坡折带为主,主要控制三角洲及扇三角洲等浅水沉积的展布;早中新世中期至今,由于陆架一陆坡体系已形成,坡折带以陆架坡折为主,控制了陆架边缘三角洲及海底扇等较深水沉积的发育。 相似文献
11.
Quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope 总被引：2，自引：0，他引：2
Two-dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows. The results suggest that in natural flows, turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser-grained beds in the bottomsets of Gilbert-type fan deltas. Experimental flows were generated on 0°, 3°, 6° and 9° slopes of equal length which terminated abruptly on a horizontal bed. Two-component velocities were measured on the slope, at the slope break and downstream of the slope break. Flows were depositional and non-uniform, visibly slowing and thickening with distance downstream. One-dimensional continuous wavelet transforms of velocity time series were used to produce time-period variance maps. Peaks in variance were tested against a background red-noise spectrum at the 95% level; a significant period banding occurs in the cross-wavelet transform at the slope break, attributed to increased formation of coherent flow structures (Kelvin–Helmholtz billows). Variance becomes distributed at progressively longer periods and the shape of the bed-normal-velocity spectral energy distribution changes with distance downstream. This is attributed to a shift towards larger turbulent structures caused by wake stretching. Mean velocity, Reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents. A turbulent kinetic energy transfer balance shows that flow non-uniformity arises through the transfer of mean streamwise slowing to mean bed-normal motion through the action of Reynolds normal stresses. Net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed-normal motion is limited. At the slope break, an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free-shear boundaries at the bottom and top of the flows, respectively. A rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope. The increased turbulent kinetic energy, limited bed-normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period. Thus, mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break. The internal effects of flow non-uniformity therefore can be separated from the external influence of the slope break. 相似文献
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Alluvial fans and fan deltas can, in principle, have exactly the same upstream conditions, but fan deltas by definition have ponding water at their downstream boundary. This ponding creates effects on the autogenic behaviour of fan deltas, such as backwater adaptation, mouth bars and backward sedimentation, whereas alluvial fans may lack these effects. Hence the present authors hypothesize that morphodynamics on alluvial fans are determined primarily by upstream boundary conditions, whereas morphodynamics on fan deltas are determined by both the upstream and the downstream boundary condition and changes therein. To isolate the effects of the upstream and downstream boundaries, five new alluvial fan experiments are compared with the details of three fan deltas published earlier that were formed under very similar and simple conditions. Similar to the fan deltas, the alluvial fans build up by sheet flow, whilst quasi‐regular periods of incision cause temporary channelized flow. Incision is followed by channel backfilling, after which the fan returns to sheet flow. The channelization and backfilling in alluvial fans is markedly less pronounced and more prone to autogenic disturbance than in fan deltas. The difference is caused by morphodynamics at the downstream boundary. In a fan delta, the flow expansion of the channel causes deposition of all the sediment, which forms a mouth bar and causes strong backfilling. In an alluvial fan, on the other hand, the slope break at the fan perimeter causes some deposition, but transport is not reduced to zero. Consequently, the backfilling in alluvial fans is less pronounced than in fan deltas. Other published experiments support this trend: removal of the mouth bar by a river leads to permanent channelization, whilst pronounced mouth‐bar formation in highly channelized deltas promotes backward sedimentation. The experimental results for this study predict that, when alluvial fans prograde into lakes or deep rivers, they transition to fan deltas with increasingly deeper channels and thicker backfill deposits. 相似文献
14.
通过多组次水槽试验,应用声速多普勒测速仪研究入汇角为90°时,不同汇流比水流条件下支流入汇区域及其附近的水面比降变化和时均流速分布特征。试验表明,入汇口上游的干支流水面坡降取决于干支流相互顶托影响,而入汇口处及其下游合流掺混区水面坡降随干流流量增大而增大,随汇流比增大而有所减小。不同位置垂线时均流速分布主要受主支汇流比和水流流态的双重影响,随着汇流比的增大,入汇口上游断面时均流速逐渐减小,而入汇口下游断面产生了明显的高、低流速带,形成回流分离区。 相似文献
15.
Flow and sediment dynamics in a low sinuosity, braided river: Calamus River, Nebraska Sandhills 总被引：1，自引：0，他引：1
The interaction between channel geometry, flow, sediment transport and deposition associated with a midstream island was studied in a braided to meandering reach of the Calamus River, Nebraska Sandhills. Hydraulic and sediment transport measurements were made over a large discharge range using equipment operated from catwalk bridges. The relatively low sinuosity channel on the right-hand side of the island carries over 70% of the water discharge at high flow stages and 50–60% at low flow stages. As a result, mean velocity, depth, bed shear stress and sediment transport rate tend to be greater here than in the more strongly curved left-hand channel. The loci of maximum flow velocity, depth and bed shear stress are near the centre of the channel upstream of the island, but then split and move towards the outer banks of both channels downstream. Variations in these loci depend on the flow stage. Topographically induced across-stream flows are generally stronger than the weak, curvature-induced secondary circulations. Water surface topography is controlled mainly by centrifugal accelerations and local changes in downstream flow velocity. The averaged water surface slope of the study reach varies very little with discharge, having values between 0·00075 and 0·00090. As bed shear stress generally varies in a similar way to mean velocity, friction coefficients vary little, normally being in the range 0·07–0·13. These values are similar to those in straight channels with sandy dune-covered beds. Bedload is moved mainly as dunes at all flow stages. Grain size is mainly medium sand with coarse sand moved in thalwegs adjacent to the cut banks, and with fine sand at the downstream end of the island. These patterns of flow velocity, depth, water surface topography, bed shear stress, bedload transport rate and mean grain size can be accurately predicted using theoretical models of flow, bed topography and sediment transport rate in single river bends, applied separately to the left and right channels. During high flow stages deposition occurs persistently near the downstream end of the island, and cut banks are eroded. Otherwise, erosion and deposition occurs only locally within the channel as discharge varies. Abandonment and filling of a strongly curved channel segment may occur by migration of an upstream bar into the channel entrance at a high flow stage. 相似文献
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A.K. Singh 《Geomechanics and Geoengineering》2016,11(2):125-134
Consideration of the average pore water pressure and average unit weight of soil in the slope of a levee, ignoring the position of phreatic line for stability analysis is not correct. In addition, the influence of a rock-filled portion on the upstream slope, ignored in Kozeny analysis, plays a significant role in the stability of the downstream slope. In this study, levees resting on an impervious base, without a filter and with a filter, taking into consideration a realistic pore water pressure and corresponding seepage force, with unsaturated and saturated unit weights of soil above and below the phreatic line, respectively, by taking into account the capillary effect, location of the inverted filter and rock-filled portion of the upstream slope have been analysed. A numerical technique has been applied to compute the elevation of the phreatic line and a computer program was developed. The appropriate unit weight of soil above and below the phreatic line, taking into consideration the capillary effect, and actual pore water pressure ensure greater safety of the downstream slope. The factor of safety has been found to be 16.5% more for a levee with a filter than a levee without a filter for an upstream pondage depth of 18 m, this is increased by 22.0% in cases where there is an upstream rock-filled portion. 相似文献
18.
基于野外调查与室内分析,应用图解法和矩值法,分别对金沙江上游雪隆囊古滑坡堰塞湖溃坝堆积物的50个样品的粒度参数进行定量计算,并对两种方法所得结果进行对比研究。结果表明:溃坝堆积物的上、中、下游三个区段的两种计算结果的平均粒径具有高度相关性,相关系数分别为0948、0994、0991,分选性相关系数分别为0824、0959、0901,表明两种方法得到的平均粒径基本相等,可以互相代替;标准偏差（分选系数）除上游区段存在较大偏差外,其它两区段分选系数基本相等,可以相互替代。整个溃坝堆积物粒度的偏态和峰态较离散,相关性较差。针对溃坝型沉积物,建议优先选用矩值法计算粒度参数,该方法能全面涵盖样品信息,反映整个沉积过程中水动力条件的变化。该研究结果与其它类型沉积物研究结果产生差异的主要原因是粒度组分分布情况、沉积动力条件及沉积环境不同。 相似文献
19.
Alitabar Abbas Noorzad Reza Qolinia Afshin 《Geotechnical and Geological Engineering》2021,39(6):4237-4251
Embankment dams are one of the most important geotechnical structures that their failures can lead to disastrous damages. One of the main causes of dam failure is its slope instability. Slope Stability analysis has traditionally been performed using the deterministic approaches. These approaches show the safety of slope only with factor of safety that this factor cannot take into account the uncertainty in soil parameters. Hence, to investigate the impact of uncertainties in soil parameters on slope stability, probabilistic analysis by Monte Carlo Simulation (MCS) method was used in this research. MCS method is a computational algorithm that uses random sampling to compute the results. This method studies the probability of slope failure using the distribution function of soil parameters. Stability analysis of upstream and downstream slopes of Alborz dam in all different design modes was done in both static and quasi-static condition. Probability of failure and reliability index were investigated for critical failure surfaces. Based on the reliability index obtained in different conditions, it can be said that the downstream and upstream slope of the Alborz dam is stable. The results show that although the factor of safety for upstream slope in the state of earthquake loading was enough, but the results derived from probabilistic analysis indicate that the factor of safety is not adequate. Also the upstream slope of the Alborz dam is unstable under high and uncontrolled explosions conditions in steady seepage from different levels under quasi-static terms.
相似文献20.
The Hanjiang River Basin is the source area of the Middle Route Project of the South-to-North Water Diversion Project, and the vegetation coverage in this basin directly affects the quality of the ecological environment. This study is based on long time series of Moderate Resolution Imaging Spectroradiometer (MODIS) Normalized Difference Vegetation Index (NDVI) data synthesized over 16 days from 2000 to 2016 in the Hanjiang River Basin. Major climatic data (temperature and rainfall) and topographic data (elevation, slope, and aspect) are employed to analyze the driving forces of NDVI changes. The results demonstrate the following: for the 2000–2016 period, the average annual NDVI is 0.823, with a change trend of 0.025 year?1. The overall NDVI upstream is higher than that downstream. The average annual value of NDVI upstream is 0.844, with a change trend of 0.036 year?1, and that of downstream is 0.799, with a change trend of 0.022 year?1. The spatial distribution of NDVI was significantly increased in the area around the upstream section of the river and near the Danjiangkou Reservoir, and the distribution of NDVI around the central city was significantly reduced. The NDVI was positively correlated with temperature and rainfall, and the impacts differed among different regions. At elevations below 2000 m, the NDVI shows an increasing trend with increasing elevation, and at elevations exceeding 2000 m, the NDVI is negatively correlated with elevation. Slope is positively correlated with the NDVI. The influence of aspect on the NDVI was small. 相似文献