Enhancing the Design of Complex Hydraulic Structures Applying 3d Hydrodynamic Modelling

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Addis Ababa University


Hydraulic structures are often complex and in many cases their designs require attention so that the flow behaviour around hydraulic structures and their influence on the environment can be predicted accurately. Currently, more efficient computational fluid dynamics (CFD) codes can solve the Navier–Stokes equations in three- dimensions and free surface computation in a significantly improved manner. CFD has evolved into a powerful tool in simulating fluid flows. In addition, CFD with its advantages of lower cost and greater flexibility can reasonably predict the mean characteristics of flows such as velocity distributions, pressure distributions, and water surface profiles of complex problems in hydraulic engineering. Meanwhile, performance assessment of FLOW-3D hydrodynamic model using physical model result has been done and it was found that the 3D numerical model results showed a good agreement with the results of the physical model as well as the designed results. In Ethiopia, Tendaho Dam Spillway was constructed recently, and one flood passed over the spillway. Using 3D hydrodynamic model Tendaho Spillway hydraulic performance was assessed and it is found stilling basin is inadequate. Because of this inadequacy the flood in 2011 created huge loses. It is recommended that the spillway bed level must be lowered by at least 15 m. Furthermore, the spillway size for its capacity to prevent overtopping of the dam has been checked with full Probable Maximum Flood (PMF) for a condition that if one of the gate malfunctions and the spillway crest length is reduced by one third. According to the result of 3D hydrodynamic model it is confirmed that the dam is safe from overtopping with the worst condition.The unconventional stilling basin of the Ribb dam spillway in Ethiopia was checked with 3D hydrodynamic model and found that the designed and constructed wall height will be overtopped. Hence, the wall height requires to be raised by an additional 7 m, otherwise the spillway as well as the dam are not safe for operation. The capacity of the U-shaped side channel spillway also checked with full PMF and is found that it is safe for the operation however it is uneconomical design. Hence, design of complex hydraulic structures using the state-of- art of 3D hydrodynamic modelling enhances the safety of the structures. Therefore, any complex hydraulic structure such as spillway, at least verification of its design must be done with 3D hydrodynamic numerical model before construction.



velocity distributions, water surface profiles, computational fluid dynamics (CFD), 3D numerical models, spillway, superelevation