共查询到20条相似文献，搜索用时 171 毫秒
1.
Yee-Meng Chiew 《天津大学学报(英文版)》2008,14(4):289-295
This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer＇s ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour. 相似文献
2.
郭俊克 《天津大学学报(英文版)》2009,15(2):79-94
Bridge pressure flow scour at clear water threshold condition is studied theoretically and experimentally. The flume experiments reveal that the measured scour profiles under a bridge are more or less 2-dimensional; all the measured scour profiles can be described by two similarity equations, where the horizontal distance is scaled by the deck width while the local scour by the maximum scour depth; the maximum scour position is located just under the bridge about 15% deck width from the downstream deck edge; the scour begins at about one deck width upstream the bridge while the deposition occurs at about 2.5 deck widths downstream the bridge; and the maximum scour depth decreases with increas-ing sediment size, but increases with deck inundation. The theoretical analysis shows that: bridge scour can be divided into three cases, i.e. downstream unsubmerged, partially submerged, and totally submerged. For downstream unsubmerged flows, the maximum bridge scour depth is an open-channel problem where the conventional methods in terms of critical velocity or bed shear stress can be applied; for partially and totally submerged flows, the equilibrium maximum scour depth can be described by a scour and an inundation similarity number, which has been confirmed by experiments with two decks and two sediment sizes. For application, a design and field evaluation procedure with examples is presented, including the maximum scour depth and scour profile. 相似文献
3.
Modeling on flash flood disaster induced by bed load 总被引：1，自引：0，他引：1
Flash floods result from a complex interaction among hydro-meteorological, hydrological, and hydraulic processes across various
spatial and temporal scales. Sichuan Province suffers flash floods frequently owing to mountain weather and topography. A
flash flood and gravel bed load transport are two key relative problems in mountain river engineering. Bed materials are often
encountered in alternate scouring and deposition in mountain fluvial processes during a flash flood. In this circumstance,
CRS-1 bed load numerical model jointly with scale physical model is employed to predict water level and gravel bed scour and
deposition for design of flood control dykes and flash flood disaster mitigation. A case study on the mechanism of a flash
flood disaster induced by bed load transport for a hydropower station in Sichuan Province is conducted. Finally, suggestions
to protect the hydropower station are proposed.
Supported by the key project of National Natural Science Foundation of China(No.50739002).
CAO Shuyou, born in 1945, male, Dr, Prof. 相似文献
4.
对调关至八十丈河段抛石后局部冲刷进行验证测量 ,结果表明 ,抛石总体效果是明显的 ,但在特殊河段、特殊水流条件下抛石后河床局部有冲刷现象。对长江堤防工程的正常运行提出了安全监测建议。 相似文献
5.
大坝使世界上的许多大江大河差不多都变成了水库搭起来的台阶,彻底改变了河流自然的季节流量模式,引起河水的温度和化学成分变化;滋生诸如蚊子类的传播媒介,使疾病四处蔓延,将河谷生命网络间的联系切断,使生物多样性减少;搅乱了河流的侵蚀、搬运和沉积地质作用过程,引起河岸滑塌,而且诱发水库地震;拦住了淤积洪泛平原与入海的沉积物,使河道形态发生变化,对流域生态环境造成严重影响,甚至破坏。呼吁人类关注大坝对环境的影响,放弃解决水资源问题的唯一方法就是修建大型水利工程的传统观念,用明智的治水 策略使用流域,保证河流的健康。 相似文献
6.
For a channel-shoal system in a funnel-shaped basin the impact of dredging and dumping is investigated using a complex process-based
model. First, the residual flow and sediment transport circulations are analysed for the channel-shoal pattern, which has
emerged after a long-term model simulation. Results are compared to the Western Scheldt estuary, which forms the inspiration
for this study. Subsequently, different dredge and dump scenarios are modelled, according to a conceptual model, in which
ebb-and flood-channels and enclosed shoals form morphodynamic units (cells) with their own sediment circulation. Model results
show that dumping sediment in a channel further reduces the channel depth and induces erosion in the opposite channel, which
enhances tilting of the cross-section of the cell and eventually can lead to the degeneration of a multiple channel system
into a single channel. The impact of different dredging and dumping cases agrees with results from a stability analysis. This
means that this type of model applied to a realistic geometry can potentially be used for better prediction of the impact
of human interventions. 相似文献
7.
The power of hydraulic piston engines is much affected by the on-off valves which control the fuel injection of the piston assembly. Therefore, the opening time of the seat valve used as the on-off valve is optimized by minimizing the axial flow forces on the spool. A damping sleeve with orifices is proposed to change the valve internal geometry. Experimental and numerical investigations of the flow forces acting on the spool with and without the proposed damping sleeve are carried out to identify the differences in the flow field and to minimize the forces’ effect. The simulated results fit the experimental results well. Both results show that the proposed damping sleeve affects the pressure distribution along the spool cone surface and the jet stream direction significantly. The effects of the orifice’s width, height, and relative sleeve installation positions on the flow field and cavitation are assessed using simulation methods. As a result of the flow field changing, the damping sleeve can reduce the flow forces significantly and even reverse the forces’ direction at the cost of a little flow loss. The opening time of the seat valve can be reduced by 31% to 0.67 ms by using the proposed damping sleeve. 相似文献
8.
通过计算机仿真模拟,研究了各向异性粒种扩散沉积集团的维数与多重分形谱.研究结果表明,各向异性粒种扩散沉积集团具有随机分叉、开放的结构,明显的多重分形性质.集团的维数与质量分布非均匀性随着各向异性的增加而增加. 相似文献
9.
The grating eddy current displacement sensor （GECDS） for distance or position measurement used in watertight electronic calipers was described. The sensor relies on repetitive variation of inductance against displacement caused by the change of coupling areas between moving coils and static reflectors. The investigations focused on setting up and utilizing a computer model of the 3D eddy current fields and geometry to analyze causes of the production of measurement blind areas, and to investigate effects of the sensor parameters, such as axial gap between coils and reflectors, reflector length and reflector width on characteristics of the sensor. Simulation results indicated that the sensor has the smallest nonlinearity error of 0.15%, which agrees well with the experimental results. 相似文献
10.
As hybrid vehicles introduced the motor, the vehicle structure has a significant change in the power matching. Adriver-vehicle-road closed-loop semi-physical simulation system, which makes real driving parts together with the simulation car,will bring convenience to the new car design. We used the computer software to simulate the road with a slope, curve and someother features based on the actual road condition, and analyzed the whole road scene in addition to geometry and physicalcharacteristics. Analyzing and constructing the vehicle dynamics basic template, appropriate changes to the template can obtainthe desired vehicle dynamics model with an external device to control the model vehicle. It combined the physical operation system with visual display, which gave us real driving feelings and increased the vehicle design predictive accuracy. 相似文献
11.
P. P. Mujumdar 《Resonance》2001,6(5):66-73
In this article, we will discuss the specific problem of how a flood wave propagates along a channel-a stream, a river or any open channel, and present the theoretical framework available for forecasting the propagation of the flood wave. 相似文献
12.
同步流密码在保密通信中具有很大优势,但在实际应用中,同步丢失的危险并不能被完全消除,因此,在某些应用当中使用了固定重同步方法．本文通过对此方法进行研究分析,指出在有噪低速可靠传感器网络中使用同步流密码,其加密安全性能至少等价于固定重同步系统,甚至有所加强.研究设计了新的重同步方法,同时进行仿真实验,结果表明,新设计的方法相对于固定重同步来讲对信道状态依赖得比较少,所以在有噪信道中比固定重同步方法更加有效。 相似文献
13.
徐小华 《潍坊教育学院学报》2011,(6):86-88
在对干线运输实际背景作合理假设的基础上,建立了较完整的干线运输车辆调度问题的数学模型。将基本遗传算法在交叉、变异等操作方面进行了一系列改进,使之适用于运输企业的干线运输车辆调度问题的求解。同时,对改进的遗传算法进行计算机数值仿真实验,并对实验结果进行分析和评价。 相似文献
14.
田雯的山水田园诗给我们展示了祖国西南山水的壮丽,表现了泉城济南和鲁北地区的风光以及诗人晚年田园生活的恬静,或隐或显地反映了诗人这几个人生阶段的心路历程,在表现题材的宽度、深度方面有突破,浓郁的人文意蕴成为其山水田园诗的重要艺术特征. 相似文献
15.
在基于固定窗口宽度滑动窗口模型的基础上。提出了一种基于回归参数存储的预测模型,该模型设置了计算区、数据区和参数区。计算区用于获得最近一个滑动窗口中的数据。数据区用于接收新数据,参数区存储最近若干组滑动窗口数据所计算得到的线性回归参数值,作为计算预测结果的原始数据集。按照这种模型的处理思路。提出了一种基于数据平滑技术的回归预测算法,随着窗口的滑动。对数据区中的数据进行回归分析,获得前面若干组滑动窗口数据的回归函数并存入参数区中,检验当前窗口中数据获得的回归函数预测效果。实验分析表明。通过修正当前回归函数的参数。可以使预测函数的预测精度得到很大程度的提高。 相似文献
16.
1IntroductionThe most popular multi-level topology is the three-level inverter[1-4],first proposed as“neutral-point-clamped(NPC)inverter”,selectingrelativelylarge ca-pacitors for the capacitor bank.The performance ofoutput voltage of inverter is mainly determined by thepulse width modulation strategy.Space vector pulsewidth modulation(SVPWM)is widely applied becauseof such advantages as convenient realization and fullDC-link voltage utilization.The schematic of a three-level inverter is … 相似文献
17.
通过理论分析和数值模拟方法,研究了高功率宽频带皮秒级(亚皮秒量级)脉冲激光非线性"热像"效应。根据宽频带光脉冲包络演化的非线性傍轴方程,在远场近似及光学薄近似条件下,得出了高功率宽频带激光非线性"热像"出现的位置及强度满足的解析关系。结果表明,"热像"形成在非线性介质后与衍射物对称的位置,"热像"强度随脉冲时间发生变化,最大强度通常发生在脉冲峰值功率时刻。通过计算机模拟,并与理论预测结果进行比较,显示两者符合较好。同时对宽频带"热像"的形成过程给出了解释,指出宽频带脉冲光束"热像"的形成类似于时间分片的连续单色光"热像"形成过程。 相似文献
18.
本文通过对目前提出的无线MIMO信道进行总结,详细分析了MIMO信道的空时模型。为了对MIMO无线通信技术进行有效的研究与评估,在基于3GPP中的TR25.996协议的基础上,根据接收信号的平均到达角、扩展角和收发两端天线的拓扑结构,创建了一个基于时延的无线MIMO信道仿真方法。通过对时延无线MIMO模型的仿真,验证了基于时延无线MIMO信道特性。 相似文献
19.
Effect of water and sediment regulation on lower Yellow River 总被引：1，自引：0，他引：1
According to the results of the water and sediment regulations of the Yellow River in year 2002-2007, the effect of erosion and deposition on the lower reaches, the amount and distribution of erosion and deposition in the river mouth area, the adjustment of river regime, the effect of river regulation projects and changes of flowing capacity of the channel are analyzed. It is revealed that the water and sediment regulation is efficient to reduce deposition and improve the flowing capacity and the conditions of sediment transport. 相似文献
20.
陈晶晶 《宁波职业技术学院学报》2009,13(5):32-33,91
介绍了无线MIMO系统信道容量的计算方法,重点分析和比较了在瑞利衰落信道下,发射端已知或未知,但接收端完全未知的信道状态信息时的独立同分布的多入多出各态历经容量特性。并利用Matlab对其进行仿真。结果表明,在低信噪比时,采用自适应功率分配得到的信道容量特性要优于采用平均功率分配。并且信道容量随收、发天线数目的最小值呈线性增长。 相似文献