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چکیده
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Study and simulation of the flow hydraulics and sediments in bends in different ways have forever attracted engineers active in hydraulics science and river engineering. Flow mechanics are highly complicated in bended paths; therefore, the fluid dynamics numerical models, which represent a proper competition for experimental observations, can be greatly beneficial as efficient tools for predicting such a flow field. The erosion generated at the bend due to presence of helical flows can result in variations in the bend width. A review of earlier works indicates that so far the studies have been conducted solely on 180-degree bends with steady widths. Hence, with the aim of achieving a better understanding of the flow pattern and properties in convergent and divergent 180-degree river bends, SSIIM software has been utilized in this thesis, the flow and scour pattern around a circular bridge pier with a diameter of 5 cm at the apex of convergent and divergent 180-degree bends have been modeled and the effective parameters have been analyzed. This thesis first validated the numerical model by using the measurements on a U-shaped bend with a steady width of 1 meter. Then two similar, yet convergent and divergent, U-shaped bends with varied widths of 1 to 0.85 m and 1 to 1.15 m were simulated by a 3D SSIIM numerical model. Results of validation indicated that the model could predict the flow field and the proper amount and region of the maximum scour and sedimentation with a similar experimental model. The findings of the numerical modeling demonstrated that the maximum scour depth and the maximum sedimentation height had occurred in the second half of the bend in convergent models, while they had occurred in the first half in divergent models. Further, the maximum scour depth with the bridge pier installed at the bend apex was realized with 15% convergence. In this model, the maximum depth of the scour hole was equal to 0.76 times the pier diameter. Also, the maximum hei
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