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Mixing process in opposing fow junction with diferent angles and junction radii

Mahmodinia Sharareh, Javan Mitra

Acta Geophysica

2020

Vol. 68, no. 3

795--809

Opposing fow junctions are considered as important elements in thermal and hydraulic equipment. This study numerically investigates the efects of angles and junction radii on coherent fow structures at opposing fow junctions with subcritical conditions. Hence, the three-dimensional unsteady Reynolds-averaged Navier–Stokes equations are solved with the k–ε turbulence model on a non-staggered grid using the indirect addressing treatment. After the verifcation of the numerical model, several numerical simulations are conducted for angles 35°, 40°, 45°, 50°, 60°, 70°, 80°, and 90° with diferent upstream Froude numbers and junction radii. The streamwise-oriented vortical cells only elongate into the branch channel of the opposing fow junction with angle 90°. By decreasing the angle between the main channel and confuent tributary, these cells decay in the main channel width, and one of the separation zones is gradually eliminated, as that does not form in the opposing fow junctions with angle 40°. The enhancement of junction radii decreases the dimensions of the separation and stagnation zones. Numerical simulation results of a curved-edge opposing fow junction with angle 80° indicate that any of the streamwise-oriented vortical cells in the main channel and separations zones in the branch channel are not formed. In such a condition, three vortical cells formed along the branch without decay, two cells are located near the side wall, and another cell is near the free surface.

Improvement of lumped models in multiple infows rivers by principal component analysis and reliability analysis

Pashazadeh Arash, Javan Mitra

Acta Geophysica

2019

Vol. 67, no. 4

1149--1161

Flood routing as an important part of food management is a technique for predicting the fow in downstream of a river channel or reservoir. Lumped, semi-distributed and distributed models have been devised in this regard. The convex and Att-Kin models are capable of simulating foods in single branches, while in reality, rivers and channels are multiple infows. The convex and modifed Att-Kin models as the simplest lumped models in terms of the storage equation were developed based on an equivalent infow for routing the multiple infows rivers in the present study. The genetic algorithm, a quite robust algorithm, was used for parameter estimation of the extended models. The ability of the extended models in simulating the outfow hydrograph of multiple infows systems was tested on two multiple infows case studies. The results of extended models were compared with the equivalent Muskingum infow model. Comparison of the extended models with the Muskingum model showed that the extended models with one parameter less than the Muskingum model could be suitable for use in food routing of multiple infows systems. The efect of infow hydrographs at diferent time steps was investigated by the principal component analysis (PCA) and reliability analysis. The results showed that the outfow hydrograph of the case study was precisely simulated and predicted by the gene expression programming (GEP) and multilayer perceptron (MLP) models. The PCA and reliability analysis results were adopted for the lumped, GEP and MLP models. The outfow hydrograph was precisely simulated and predicted by the GEP and MLP models, while the precision of lumped models (extended convex, extended modifed Att-Kin and Muskingum models) was not increased.