فهرست مطالب نسرین حسن پور

In present study, the effect of different cross-sections of bridge piers on reducing the bed erosion and the bed shear stress was experimentally and numerically evaluated. In experimental study, the bed erosion and the percentage of its resuction was calculated;also numerically, the flow around pier models was simulated three dimensionally, and the effect of each cross-section on reduction of bed shear stress was investigated. To determine the efficiency of suggested models, the circular model was selected as the reference model and the decreasing of maximum shear stresses in each model was compared with the decreased scour depth. Comparison of the velocity and water free surface profiles was conducted for verification of turbulence models and results showed that with model, more accuracy can be obtained. Among the presented models, the A2 model with decreasing scouring depth of 72 percent as copared to the refference model, was found to be best and most effective model. Also the B2 model lead to 8 percent reduction in scouring depth and can be suggested as a model that has the least effect on scouring. The D model causes the scouring depth increase by 7 percent relative to the reference model. Comparison of the numerical and experimental results was another objective of this study due to the complexities of experimental researches. The results showed that there are direct relationship between the bed shear stress and the equilibrium scour depths.

Abutments are used to protect erodible river banks. This structure is subjected to scouring due to flow convergence at the nose of structure. Therefore، countermeasure methods should be employed in order to prevent financial damages and life hazards. One of these methods is to use a slot. The main application of a slot is to deviate and change the down flow at the upstream region of an abutment. Also it reduces the power of vortices around the abutment. In this research، parameters such as depth، hole dimensions and time development of scoring process were measured around a vertical abutment. Operation of the slot was then evaluated at different height، depth، width and distance from the abutment nose and compared with unprotected abutment. The results showed that the models for which the slot was installed near the wall under the bed with the depth equal to the width of the abutment had the best performance. The amount of scour reduction for different models was 11. 8 to 43 percent.

Methods to control and reduce local scour are based on the scour mechanism. One of these methods is the application of collar around piers and using different bridge piers geometries. In this study eight different shapes of bridge piers were used with collar around them and the obtained scour depths and rates were compared with those of circular pier. The effect of airfoil shaped piers length was also investigated. The results showed that the airfoil shaped pier with relative length of 3. 85 was more effective than the other shapes of piers due to reduction of power of horseshoe and wake vortices and the maximum scour depth reduced 22% compared to the cylinderical pier. Furthermore، using a collar with a diameter two times greater than the pier diameter in the airfoil shaped piers decreased the maximum scour depth up to 80% in comparison with circular pier and the equilibrium time of scour also increased. Also، the airfoil shaped piers which were located in flow path in inverse direction، reduced the maximum scour depth in front of pier about 60%.