Flow resistance law under suspended sediment laden conditions
جریان قانون مقاومت تحت شرایط مملو از رسوب معلق-2020
The uniform flow resistance equation, in the form due to Manning or Darcy-Weisbach, is widely applied to establish the stage-discharge relationship of a river cross-section. The application of this equation, namely the slope-area method, allows to indirectly measure the corresponding river discharge by measurements of bed slope, water level, cross-section area, wetted perimeter and an estimate of channel roughness. In this paper, a recently deduced flow resistance equation for open channel flow was tested during conditions of suspended sediment-laden flow. First, the flow resistance equation was determined by dimensional analysis and by applying the condition of incomplete self-similarity for the flow velocity profile. Then the analysis was developed by the following steps: (i) for sediment-laden flows characterized by known values of mean diameter and concentration of suspended sediments, a relationship (Eq. (28)) between the Γ function of the velocity profile, the channel slope and the Froude number was calibrated by the available measurements; and (ii) a relationship for estimating the Γ function (Eq. (29)) which also takes into account the mean concentration of suspended particles was also established. The theoretical flow resistance law (Eq. (26)) coupled with the relationship for estimating the Γ function (Eq. (28) or Eq. (29)), which is characterized by the applicability of a wide range of flow conditions, allowed to estimate the Darcy-Weisbach friction factor for flows with suspended-load. The analysis showed that for large-size mixtures the Darcy-Weisbach friction factor can be accurately estimated neglecting the effect of mean concentration of suspended sediments while for small-size mixtures the friction factor decreases when the mean sediment concentration increases.
Keywords: Flow resistance | Suspended-load | Dimensional analysis | Self-similarity | Flow velocity profile
An expert system for predicting the velocity field in narrow open channel flows using self-adaptive extreme learning machines
یک سیستم خبره برای پیش بینی میدان سرعت در جریان کانال باریک باریک با استفاده از ماشینهای یادگیری افراطی خود سازگار-2019
This work investigates the ability of a new model based on powerful self-adaptive extreme learning machines to predict the velocity field in an open channel. A total of 363 velocity field data obtained in 8 different hydraulic conditions of a narrow open channel are used to develop the proposed model. The performance of the proposed model in predicting the velocity field is analysed for 3 different discharge rates that have no role in model development. According to the model prediction accuracy comparisons, the proposed model is more accurate than existing equations and can be employed successfully in velocity field predicting. Furthermore, the new model can more accurately predict the negative gradient of velocity near the free surface, which is the most significant/complex feature of a velocity distribution in narrow open channels. Moreover, a sensitivity analysis is done to surrey the effect of the proposed model on each input variable.
Keywords: Discharge | Field data | Flow velocity profile | Open channel | Sensitivity analysis | Velocity