Estimation of hydraulic jump characteristics of channels with sudden diverging side walls via SVM Kiyoumars Roushangar, Reyhaneh Valizadeh and Roghayeh Ghasempour ABSTRACT Sudden diverging channels are one of the energy dissipaters which can dissipate most of the kinetic energy of the flow through a hydraulic jump. An accurate prediction of hydraulic jump characteristics is an important step in designing hydraulic structures. This paper focuses on the capability of the support vector machine (SVM) as a meta-model approach for predicting hydraulic jump characteristics in different sudden diverging stilling basins (i.e. basins with and without appurtenances). In this regard, different models were developed and tested using 1,018 experimental data. The obtained results proved the capability of the SVM technique in predicting hydraulic jump characteristics and it was found that the developed models for a channel with a central block performed more successfully than models for channels without appurtenances or with a negative step. The superior performance for the length of hydraulic jump was obtained for the model with parameters F 1 (Froude number) and (h 2— h 1 )/h 1 (h 1 and h 2 are sequent depth of upstream and downstream respectively). Concerning the relative energy dissipation and sequent depth ratio, the model with parameters F 1 and h 1 /B (B is expansion ratio) led to the best results. According to the outcome of sensitivity analysis, Froude number had the most significant effect on the modeling. Also comparison between SVM and empirical equations indicated the great performance of the SVM. Kiyoumars Roushangar (corresponding author) Department of Civil Engineering, University of Tabriz, Tabriz, Iran E-mail: kroshangar@yahoo.com Reyhaneh Valizadeh Roghayeh Ghasempour Department of Civil Engineering, University of Tabriz, Tabriz, Iran Key words | central block, empirical equations, hydraulic jump, stilling basin, sudden diverging side walls, SVM INTRODUCTION The purpose of the design of energy dissipators is to dissipate part of the kinetic energy of the inflowing flow in order to return safely the flow to the downstream channel or river and prevent scour below overflow spillways, chutes and sluices. Based on the energy dissipating action of hydraulic jumps, stilling basins are one of the possible solutions which may be adopted. The performance or efficiency of any stilling basin is usually assessed in terms of characteristics of the jump allocated (Negm ). The length of the hydrau- lic jump is mostly taken as a design parameter or as an indicator of the length of the paved downstream section, i.e. the stilling basin. The hydraulic jump is a natural phenom- enon that occurs when supercritical flow is forced to change to subcritical flow by an obstruction to the flow. Depending on the geometry of the channel and tailwater con- ditions, the hydraulic jump can assume several distinct forms. The hydraulic jump is a useful means of dissipating the excess energy of supercritical flow so that scour in the downstream is minimized. It has also been used to raise the water level on the downstream to provide the requisite head for diversion into canals. However modeling hydraulic jump character- istics has great importance since it plays an important role in designing hydraulic structures. So far, various studies have been carried out to explain the complex phenomenon of the hydraulic jump and to estimate its characteristics. Hughes & Flack () studied the effect of various roughness designs on the hydraulic jump characteristics in a stilling basin. Hager & Bremen () investigated the influence of wall friction on the sequent depths ratio. Bhutto et al. () developed analytical solutions for computing sequent depth and relative energy loss for free hydraulic jump in slop- ing and horizontal rectangular channels. Finnemore & Franzini () stated that the characteristics of the hydraulic jump depend on the Froude number. Negm () studied the hydraulic performance of rectangular and radial stilling basins, where the latter stand for the diverging channels. 1614 © IWA Publishing 2017 Water Science & Technology | 76.7 | 2017 doi: 10.2166/wst.2017.304 Downloaded from https://iwaponline.com/wst/article-pdf/76/7/1614/449938/wst076071614.pdf by guest on 26 May 2020