考虑颗粒暴露角的宽级配泥沙起动流速公式研究

Incipient Velocity Formula Considering the Exposure Angle of Sediment Particles

堰塞坝坝料不均匀性强、级配范围宽,为了准确计算该工况条件下的泥沙起动问题,对泥沙颗粒暴露角进行了分析,引入底床坡度、泥沙颗粒的纵、横向暴露角,以泥沙滚动模型为基础建立了宽级配泥沙起动流速计算公式,并对计算式进行了合理性验证和敏感性分析。结果表明:底床坡度与泥沙颗粒的起动流速整体呈现负相关关系,但影响程度受颗粒暴露程度的影响明显,随着颗粒暴露度不断增加,底床坡度对其起动流速影响逐渐增强,泥沙颗粒纵、横向暴露角与其起动流速整体成负相关关系,但影响规律有所不同,床面粗颗粒处于暴露状态时,决定该颗粒起动的主控因素为颗粒粒径,处于隐蔽状态的细颗粒起动流速较大,床面坡度对其起动流速的影响较小。

The meso process of the barrier dam break is the scouring and transport movement of particles under the action of water flow. In essence, it is the interaction between unsteady overtopping flow and uneven earth rock materials in the breach, which belongs to a special form of sediment movement. The material of the barrier dam has strong heterogeneity and a wide grading range. The laws of incipient motion and transport are quite different from those of uniform sediments. If the existing theory of river sediment movement is directly applied to the calculation of the dam break accurately, the results will be different from the actual ones. In order to calculate the sediment incipient velocity under this condition, the exposure angle of sediment particles is analyzed. The bed slope, the longitudinal and transverse exposure angles of sediment particles are introduced. Based on the sediment rolling model, the instantaneous incipient velocity of sediment particles calculated is converted into the vertical average velocity of the section. The calculation formula of the incipient velocity of wide graded sediment is established, the rationality of the calculation formula is verified and the sensitivity is analyzed. The main conclusions are as follows: the incipient velocity of uniform and non-uniform sediment is selected for calculation, and compared with the measured data, it shows that the formula in this paper can accurately reflect the incipient law of sediment with the bed slope and particle exposure angle to a certain extent. There is a negative correlation between the bed slope and the incipient velocity of sediment particles. With the increase in the bed slope, the incipient velocity of sediment particles generally shows a decreasing trend, but the influence degree is affected by the particle exposure degree. With the increase in the sediment exposure degree, the influence of the bed slope on the incipient velocity gradually increases. There is a negative correlation between the transverse and longitudinal exposure angles of sediment particles and their incipient velocity, and the incipient velocity decreases with the increase in the transverse exposure of particles. When the studied particles are in the exposed state, ignoring the hydraulic elements and the surrounding water flow structure, whether the particles start or not will be mainly controlled by the particle size. The influence of the longitudinal and transverse exposure angles of the particles on the starting velocity of the particles is different. The transverse exposure angle of the particles has an exponential function relationship with the starting velocity, and the influence on the starting velocity gradually increases with the increase in the exposure angle. The relationship between the longitudinal exposure angle of particles and the starting velocity presents an S-curve. With the increase in exposure angles, the influence on the starting velocity first decreases and then increases. In addition, the composition of soil and stone materials at the mouth of the dam is very complex, and the particle shape, size, density, relative position are very different. To calculate the incipient transport of sediment at the breach accurately during overtopping, it is necessary to carry out further research on the generalized values of relevant parameters such as the exposure of sediment particles on the surface of the breach and the transport calculation method.