سید حامد معراجی

Piers install in the flow path creates a complex and three dimensional pattern of flow such that it disturbs the normal flow of the river and the turbulence resulting from it causes erosion of sedimentary materials around the pier. This mechanism becomes more complicated around series piers in bended paths. The growing power of computers and development of powerful numerical models that they are able to stimulate sediment transport in form of 3D in complex geometry, and the difficulty and also the high cost of doing experiments in this field has caused that the use of these numerical models for engineers is inevitable. In this thesis the flow and scour pattern in a 180 degree bend, without pier, with single pier and with triple series piers was simulated by using SSIIM model and compared to laboratory results. Also the effect of change in the relative curvature radius, distance between piers, position of piers in the channel and with the abutment are investigated on the flow and scour pattern. The results showed that SSIIM model is well able to simulate bed changes and flow pattern. The most important results of this research are: By increasing the relative curvature radius from 2 to 6, maximum scouring and sedimentation are reduced about 20% and 30%, respectively. By increasing the distance between the piers, the maximum scour is reduced about 20%, however there is no significant change in the maximum amount of sedimentation. The maximum amount of scouring occurs at the position of piers and abutments at the 90 degree angle. Maximum transverse, longitudinal and vertical velocity by increasing the relative curvature radius is reduced 40%, 70% and is increased 30%, respectively. Increasing the distance between the piers causes a change in the value of the velocity parameters in such a way that transverse, longitudinal and vertical velocities is increased 30%, is reduced 50% and is increased 40%, respectively. Also maximum transverse, longitudinal and vertical velocit