حيدر سامي محمد الخياط

Computational Fluid Dynamics (CFD) modelling in field of hydraulic structures and river engineering is continuously growing in recent years, through applied this powerful tool for modeling several types of multiphase flow. The objective of current study, it is to extends clear understanding of multiphase flow around stepped spillway for different steps configuration and to test the capabilities of the CFD Model (Fluent 18.2) to represent these phenomena. VOF method adopted to capture interface between water and air, k-ε turbulent model for turbulence parameters and (PISO) Pressure Implicit with Splitting of Operator algorithm is used. Experimental study is carried out for four model configuration according to the steps aspect ratio Hs/Ls (1, 0.75, 0.6 and 0.5) for flow rate range (10, 15 and 20 L sec–1). physical model made from plywood with smooth surface. CFD Model demonstrated an acceptably recorded result in predicting the energy dissipation rate for different steps configuration compering with the experimental results. Also, it is obtained that the energy dissipation rate is increases with increase the steps aspect ratio. time steps size it about 0.005 sec or less are recommend to capture the flow pattern and secondary flow around stepped spillway.

Rockfill gabions considered one of important self-spillway hydraulic structures, used as water distributor, regulator and other purposes. An experimental investigation was carried out to note the effect of the change of longitudinal slope and the change of rockfill size on the velocity at downstream side of gabion, all tests carried out under through flow regime type, the monosized of rockfill were used (-76, +64), (-64, +50) and (-50, +37.5) mm with three longitudinal slope 0, 0.014 and 0.028. Wooden frame meshed-side gabion with constant dimensions, 220 cm length of the bottom side 150 cm length of upper side of gabion, 0.3 m width and 0.35 m height. The result showed that the effective of discharge increasing on the value of velocity of downstream by increasing of rockfill size for same longitudinal slope and the effect of discharge decreasing on the velocity at downstream by increasing the longitudinal slope for the same rockfill size, a dimensional analysis concept used and non-linear regression by using IBM SPSS 21 program, to develop an empirical formula to estimate the velocity at downstream.

ABSTRACT This study was initiated to better understand the sediment transport capacity of a reach on Euphrates river at downstream of Al-Abbasia City bridge’s in a length of 6 km approximately which is have a combined characteristic of straight and meander morphology. A one of arithmetical model for representing flow and calculating transportation of sediment capacity of the elaborated reach was carried out and run by utilizing the HECRAS (4.1.0) program and making use of measuring of field for carrying out and running standardization processes. Flow velocity and sediment transport capacity were estimated for a range of discharge from 40 to 100 m3/sec. Locations of the low flow velocity were specified. The comparison between sediment potential rating curves of these locations showed that the sediment transport potential of the reach cross sections at distance from 1000 to 1200, 2200 to 3000 and 3580 m from the end of the reach, is less than that of the other cross sections of this reach were under 50 tones/day. Also observes that for the straight parts on the studied reach the discharge increasing gives less sediment transport capacity while the meandering parts of the reach were in reverse behavior.

An unsteady one dimensional mathematical model was calibrated for simulating the flow and estimating the water surface profiles for Al-Kufa River. The Hydraulic Model for the studied river was implemented and run by using the HEC-RAS (Version 4) software. The calibrations and verification processes of the model have been carried out by making use of the field measurements. Al- Kufa River was selected so that the numerical results can be compared with available measured flows and stages data. The appropriate value of Manning’s roughness coefficient (n) is chosen through the process of calibration