Enhancing the Design of Complex Hydraulic Structures Applying 3d Hydrodynamic Modelling
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Date
2019-10
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Addis Ababa University
Abstract
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.
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Keywords
velocity distributions, water surface profiles, computational fluid dynamics (CFD), 3D numerical models, spillway, superelevation