Unit stream power,minimum energy dissipation rate,and river engineering

Unit stream power is the most important and dominant parameter for the determination of transport rate of sand,gravel,and hyper-concentrated sediment with wash load.Minimum energy dissipation rate theory,or its simplified minimum unit stream power and minimum stream power theories,can provide engineers the needed theoretical basis for river morphology and river engineering studies.The Generalized Sediment Transport model for Alluvial River Simulation computer mode series have been developed based on the above theories.The computer model series have been successfully applied in many countries.Examples will be used to illustrate the applications of the computer models to solving a wide range of river morphology and river engineering problems.

CRITICAL UNIT STREAM POWER FOR SEDIMENT TRANSPORT

Yang's (1996) sediment transport theory based on unit stream power is one ofthe most accurate theories, but in his equations the use of product of slope and critical velocityinstead for critical unit stream power is not suitable. Dimensionless critical unit stream powerrequired at incipient motion can be derived from the principle of conservation of power as afunction of dimensionless particle diameter and relative roughness. Based on a lot of data sets,this new criterion was developed. By use of this new criteria, Yang's (1973) sand transport formulaand his 1984 gravel transport formula could be improved when sediment concentration is less thanabout 100 ppm by weight.

Counter-Rotating Type Horizontal-Axis Bidirectional Propellers for Tidal Stream Power Unit

Tidal stream power units with horizontal-axis propellers are one of promising technologies for generating the renewable green energy. The ebb and flow require that the power unit must operate in bidirectional tidal streams. Hence a tidal stream power unit with counter-rotating type horizontal-axis bidirectional propellers is proposed in this paper. The blades with fully-symmetrical hydrofoils were optimized numerically. The output and flow conditions predicted by the computational fluid dynamics simulations are compared with the results of the wind tunnel experiments at the higher tip speed ratios, which are of expected usual operating conditions of this unit. The numerical and experimental results show good agreements. It is also confirmed that the flow discharged from the counter-rotating type propellers has no swirling component, though the single propeller generates the unacceptable swirling component.

A Numerical Prediction of Tip Vortices from Tandem Propellers in the Counter-Rotating Type Tidal Stream Power Unit

Ocean energy has a potential of providing a large amount of renewable energy around the world. One of the forms of ocean energy, tidal stream power is widely recognized as the continuous, predictable and eco-friendly ocean energy source. Unique tandem propellers that can counter-rotate have been designed to generate electric power effectively from a tidal stream. This type of power unit has several advantages compare to the conventional unit with a single propeller. At the design of the tidal stream power unit, it is important to investigate the structure of the tip vortex tubes shedding to predict the load of the propeller. In this research, we investigated the tip vortex shedding using the CFD method for the conventional single propeller and counter-rotating type tandem propellers and estimated the performance efficiency using RANS (Reynolds Averaged Navier-Stokes) model and we confirmed the limitation of RANS model on the calculation of the tip vortex stretching.

最小水流能量损失率理论在河相关系中的应用

本文介绍最小水流能量损失率理论的变分法基础。用该理论导出了航道整治工程前后的河相关系式,并将之用于预估东平水道航道整治工程后的河相。实测值与预估值的比较表明,该理论和该河相关系式是可信的。

泥沙输移与水流强度指标

利用大量的实验室水槽和天然河道输沙资料 ,研究了各种水流强度指标与泥沙输沙强度的相关关系。结果表明 ,水流功率、平均流速、沙粒切应力能较好地预测输沙率而单位水流功率、佛汝德数、Velikanov参数则较好地预测输沙浓度。

输沙能力模式在坡面非恒定输沙过程中的应用

在坡面土壤侵蚀输沙计算中,可选用的输沙能力模式较多,但这些模式多运用于恒定输沙,在非恒定输沙中运用不多。建立了坡面土壤侵蚀非恒定输沙数学模型,模型中的输沙能力运用水流切应力、水流功率、单位水流功率3种模式,对模型过程采用有限差分格式离散求解。根据实测水沙资料进行模型参数率定,运用3种输沙能力模式于不同降雨强度、不同坡度的非恒定坡面输沙过程中。结果表明:在坡面非恒定输沙计算中,不同输沙能力模式对计算结果有明显影响,在降雨强度较小时,单位水流功率模式结果较其他两个模式为好,而在雨强较大时,切应力模式计算结果较好。

坡面草被覆盖对侵蚀产沙影响的模拟试验

为了探究坡面植被及其布设位置对坡面侵蚀动力过程的影响,通过室内放水冲刷试验,分析了不同植被覆盖度(0,30%,50%,70%,90%)和不同坡面覆盖位置(坡上、坡中和坡下)下的坡面产沙及其水动力学参数的变化。结果表明:植被覆盖度、径流动能、径流流速、弗汝德数、阻力系数、糙率系数、剪切力等与坡面侵蚀产沙量密切相关。随覆盖度的增加,径流流速、径流剪切力、单位水流功率和径流动能逐渐降低,曼宁糙率系数和阻力系数逐渐增加,产沙量呈直线下降。当覆盖度从0增长到50%时,植被的减沙效益显著提高,当盖度增加到70%时,植被保持水土的作用不随覆盖度的增加显著提高,不同坡面覆盖位置下坡面侵蚀产沙表现为植被位于坡面中下部的产沙量小于植被位于坡面上部的,可用包含植被覆盖度、单位水流功率和径流动能等参数建立的联合公式模拟预测坡面侵蚀产沙量。研究结果可为阐明植被减沙的临界盖度和合理位置以及黄土高原水土流失治理和黄河流域高质量发展提供参考。

电厂实时主蒸汽压力优化软件开发

为了实现节能降耗的目的,针对300MW大型火力发电机组,开发了主蒸汽压力实时优化系统。提出以热力系统矩阵方程为基础的机组运行状态重构方法。采用机理分析法和统计法相结合的混合建模思想,在保证运行参数规律的基础上提高了模型的计算精度。应用Delphi编程及Mysql数据库,实现了电厂机组主蒸汽压力实时优化,对电厂运行进行指导。软件应用表明:在100%负荷与80%负荷时,采用定压运行;在80%负荷以下采用滑压运行;热耗优化量随着负荷的升高逐渐减小。

基于能耗率的黄河下游河型变化趋势分析

利用黄河下游21a实测水文数据,逐年计算了其中6个河段的单位水流功率,分析了各河段的演化发展特征。研究结果表明:黄河下游弯曲河段的单位水流功率小于游荡河段的单位水流功率,过渡型河段的单位水流功率介于弯曲河段和游荡河段的单位水流功率之间;花-夹和夹-高游荡型河段21a的单位水流功率变化幅度较大,说明这两个河段的游荡特性至今没有得到改善,远离相对平衡状态;高-孙和孙-艾过渡型河段的单位水流功率逐渐下降,且自90年代中期以来变化幅度不大,其游荡特性已逐渐消失,越来越趋近于相对平衡状态;艾-泺和泺-利弯曲型河段21a的单位水流功率围绕着其平均值变化幅度越来越小,趋于相对平衡状态。

黄土坡面片蚀过程稳定含沙量及其影响因素

黄土高原地区坡面土壤侵蚀具有明显的垂直分带性,溅蚀片蚀带是坡面侵蚀的最上方地带,研究片蚀过程含沙量变化有助于阐明坡面侵蚀规律。本文采用人工模拟降雨试验方法研究了黄土坡面片蚀稳定含沙量及其影响因素;试验处理包括2种质地的黄土(塿土和黑垆土),2个雨强(90和120 mm/h)和4个坡度(10°、15°、20°和25°)。结果表明:在不同质地黄土、降雨强度和坡度条件下,水流含沙量均呈现先减小后平稳的规律;稳定含沙量与土壤颗粒体积分形维数、降雨强度和坡度呈幂函数关系,稳定含沙量随土壤颗粒体积分形维数的增大而减小,随降雨强度和坡度的增大而增大,影响程度依次为土壤颗粒体积分形维数、降雨强度和坡度;所分析的水动力学指标中单位水流功率与稳定含沙量关系最密切,降雨强度对稳定含沙量的影响大于单位水流功率。

草地坡面径流侵蚀动力特征模拟

坡面是土壤发生侵蚀的基本单元,坡面流是泥沙运动的载体,其水动力学特征直接影响坡面侵蚀的强度和时空分布。利用坡面放水冲刷试验,研究了不同植被覆盖下坡面流水力学参数和侵蚀产沙特征,结合灰色关联分析,确定影响坡面侵蚀产沙的关键水力学参数。结果表明:冲刷流量和植被覆盖对坡面流水力学参数和侵蚀产沙过程有显著影响,冲刷流量越大,径流流速越大,阻力系数、糙率系数和弗汝德数越小,径流剪切力和径流动能越大,侵蚀产沙量越大;随着植被覆盖度的增大,坡面径流平均流速、弗汝德数和单位水流功率呈指数减小,径流剪切力、平均阻力系数和糙率系数呈指数增大,径流动能呈直线减小。每增加1%的植被,径流流速平均降低1%~3%,不同覆盖下侵蚀减沙效益达到15%~89%。灰色关联分析结果表明,由于径流紊动性较小,在3.2 L·min-1冲刷流量下的各参数与侵蚀产沙量的相关系数均小于5.2 L·min-1,在不同冲刷流量下,弗汝德数和单位水流功率与侵蚀产沙量相关关系最为密切,其次是水流动能。侵蚀产沙量随着单位水流功率的增加呈现显著指数减小,可以预测不同覆盖下的侵蚀产沙量。