No abstract

Several researchers working on the axes of solid particle transport, river flow, as well as the vulnerability of structures built on rivers have focused their work on the phenomenon of local scour, where many scour formulas have been proposed. Most of these formulas have been developed using laboratory data, estimated from simplified scaled-down models. This led to uncertainties and considerable inaccuracies in the scour estimation, sometimes causing serious consequences for the stability of structures subject to scour. These formulas were rarely tested using field data, where, until recently, there was very little data to validate them. This study aims to propose a new local scour formula using multiple nonlinear regression (MNLR). The data used is in situ data from an extensive database. The new proposed formula includes different parameters of the three fields involved in the triggering and development of the local scour, namely; the bridge, the flow, and the suspended characteristic of the eroded particle. The results obtained in the training phase and the validation show relatively better performances of the new formula compared to the existing empirical formulas.

Several studies have been conducted to assess local scour formulas in order to select the most appropriate one. Confronted to the limits of the previous formulas, further studies have been performed to propose new local scour formulas. Generalizing a single scour formula, for all soil classes, seems approximate for such a complex phenomenon depending on several parameters and may eventually lead to considerable uncertainties in scour estimation. This study aims to propose several new scour formulas for different granulometric classes of the streambed by exploiting a large field database. The new scour formulas are based on multiple non-linear regression (MNLR) models. Supervised learning is used as an optimization tool to solve the hyper-parameters of each new equation by using the ‘Gradient Descent Algorithm’. The results show that the new formulas proposed in this study perform better than some other empirical formulas chosen for comparison. The results are presented as seven new formulas, as well as abacuses for the calculation of local scour by soil classes.

No abstract

With the considerable use of pipelines and reactors in the engineering industry, determining the deposition velocity enabling hydraulic transport is of utmost importance. This has been investigated throughout the years, scrupulously in several types of reactors used in water treatment and solid transport. The primary focus has been extended to torus reactors, due to their significant advantage in chemical, biochemical and mixing processes. In the present work, we have studied the solid-liquid suspension in a torus reactor. We elaborated an experimental method based on visual assessment SBAM (Steady Bed Angle Method), which enabled us to analytically determine the just suspended speed ‘Njs’ at which no solid remains stationary at the bed and further parametrically study the effect of several parameters including solid loadings, particle sizes and densities. The just suspended speed values obtained experimentally have been compared to a modified Zwietering's correlation.