Mathematical Modelling of Streamwise Velocity Profile in Open Channels Using Tsallis Entropy

Abstract

This study derived the vertical distribution of streamwise velocity in wide open channels by maximizing Tsallis entropy, in accordance with the maximum entropy principle, subject to the total probability rule and the conservation of mass, momentum, and energy. Entropy maximizing leads to a highly nonlinear differential equation for velocity which was transformed into a relatively weaker nonlinear equation and then solved analytically using a non-perturbation approach that yielded a series solution. The convergence of the series solution was proved using both theoretical and numerical procedures. For the assessment of velocity profile, the Lagrange multipliers and the entropy index were obtained by solving a system of nonlinear equations by Gauss-Newton method after approximating the constraint integrals using Gauss-Legendre quadrature rule. The derived velocity profile was validated for some selected sets of experimental and field data and also compared with the existing velocity profile based on Tsallis entropy. The incorporation of the above constraints and the effect of entropy index were found to improve the velocity profile for experimental as well as field data. The methodology reported in this study can also be employed for addressing other open channel flow problems, such as sediment concentration and shear stress distribution.