The seawater intrusion (SWI) into rivers can lead to many negative consequences, especially on ag... more The seawater intrusion (SWI) into rivers can lead to many negative consequences, especially on agricultural activities and live ecosystems in upstream areas of rivers. One solution to prevent SWI is using air bubble curtains (ABCs). The objective of this study is to investigate the optimal location of ABCs and airflows. To this end, several tests with different flow and salinity rates were performed and effect of ABC location on SWI investigated. The results show that, when the ratio of seawater to freshwater densities increased from 1.006 to 1.010, the ratio of saline wedge tip velocity to seawater velocity, airflow to seawater discharge ratio for first and second ABCs are raised 60, 58, and 70%, respectively. Also, when the Froude number (Fr) > 0.031, seawater density changes do not significantly affect the process of SWI. Besides, results of the study show that the closer the ABC is to the river downstream, the higher the airflow rates required. In addition, the optimal value ...
The present study aims to evaluate the effects of the arrangement of the teeth in terms of angle,... more The present study aims to evaluate the effects of the arrangement of the teeth in terms of angle, arrangement and radius on the eddy currents, kinetic energy dissipation and turbulence dissipation rate. Four groups of models were created for this purpose. In the first group, each model contained a bucket with two teeth with different angles. The second group included three models where each bucket had two teeth with the same angle, but the angle was different for each bucket. The third group contained three models with different bucket radii. In addition, the last group consisted of two models where each model had two teeth with an angle of 45°. The result showed that the use of teeth with unequal angles plays a significant role in increasing the total turbulence loss. Moreover, the angle of the teeth has a much larger effect on increasing the turbulence loss than changing the bucket radius. In addition, the use of unequal angles in the design of the teeth can significantly increase the loss. The loss can be significantly increased if a larger radius and unequal tooth angles are used simultaneously. Using equal tooth angles with a larger angle result in more loss compared to the case where the angles are small but different. Finally, buckets with larger radius and unaligned and larger tooth angles are considered as the factors that increase the energy loss in buckets, which leads to an increase in the efficiency of the bucket.
The numerical solution of flows with a freely moving boundary is of great importance in practical... more The numerical solution of flows with a freely moving boundary is of great importance in practical application such as ship hydrodynamics. Details are given of the development of a two-dimensional vertical numerical model for simulating unsteady and steady free-surface flows on a nonstaggered grid in curvilinear coordinates, using a non-hydrostatic pressure distribution. In this model, Reynolds equation and the kinematic free-surface boundary condition are solved simultaneously, so that the water-surface elevation can be integrated into the solution and solved for, together with the velocity and pressure field. In computational space, the Cartesian velocity components and the pressure are defined at the center of a control volume, while the volume fluxes are defined at the midpoint on their corresponding cell faces. Detailed numerical results are presented for the wave generation above an obstacle and resonant motion standing wave. The results show that the numerical algorithm descri...
Particle movement will occur when the instantaneous fluid force on a particle is just larger than... more Particle movement will occur when the instantaneous fluid force on a particle is just larger than the instantaneous resisting force. One of the most important issues in this regard is the influence of different hydrodynamic forces on threshold of motion. In the present study, effects of different forces; such as non-linear drag force, the shear lift force, Magnus force, the buoyancy force, the added mass force, Basset history force and torque; on the initiation of motion of sediment grains were studied by developing a 3D Lagrangian numerical model. The particle-wall collision were included using Discrete Element Method (DEM) and a random process. The non-cohesive sediments grains for the range of sand to gravel were considered. The verification step was performed using different particle diameters and flow conditions. The results indicated that the drag force is the dominating force. Also, it is observed that the influence of lift force increase by increasing grain diameter. Keyword...
Submerged vanes are installed in waterways bed. These structures are usually used in groups and t... more Submerged vanes are installed in waterways bed. These structures are usually used in groups and their main performance is to create an eddy current which leads to change in stream flow pattern and the bed topography in waterways. Performance of submerged vanes group depends on their arrangement and size. In this study using SSIIM numerical model, hydrodynamic analysis of flow pattern and bed topography around a single submerged vane in a straight channel was done and tried to estimate proper arrangement of submerged vanes group. The geometry of arrangement consisted of longitudinal distance between consecutive vanes, transverse distance of two adjacent vanes, and transverse distance of submerged vanes from the outer wall. Therefore, after verification of the results of numerical model with experimental data, flow pattern and topography of the bed around a vane with different dimensions and angles (in suggested domain) were investigated and analyzed. In this order, values of transverse and longitudinal distances of scouring hole at high-pressure and low-pressure sides of the vane from center of the vane were measured. Also values of transverse and longitudinal locations of the maximum scouring hole and maximum sedimentation downstream of the vane were determined. The results of these parameters were used to estimate the location of adjacent vanes. To reduce number of modes, the Taguchi method is used in design of simulations. Finally, mathematical relations are derived for geometry of arrangement versus vanes dimensions and angles. Comparison of the results of this research with the results of previous researchers, who have studied submerged vanes groups, showed that accuracy of the method used in this study is acceptable. The numerical results showed that the values obtained for the transverse and longitudinal distances of vanes are almost in the same range of previous laboratory studies.
Hydraulic characteristics of the flow and sediment transport conditions are among the most import... more Hydraulic characteristics of the flow and sediment transport conditions are among the most important issues in design of the lateral intakes in order to minimize the flow loss. In this study, a 3D numerical model has been employed in a parametric study to study the performance of a lateral pipe intake. Observations indicated that the flow was affected by the pipe intake so that the recirculation area was close to the wall of the main channel, the wall of the lateral pipe intake and back of the lateral pipe intake. The pipe intake in vertical direction to the main channel showed the highest performance, although sedimentation behind the pipe intake in this diversion angle was higher. In addition, pipe intake showed a quite acceptable performance for almost 40% intrusion to the main channel width. Relationships for the coefficient of discharge were also developed.
The seawater intrusion (SWI) into rivers can lead to many negative consequences, especially on ag... more The seawater intrusion (SWI) into rivers can lead to many negative consequences, especially on agricultural activities and live ecosystems in upstream areas of rivers. One solution to prevent SWI is using air bubble curtains (ABCs). The objective of this study is to investigate the optimal location of ABCs and airflows. To this end, several tests with different flow and salinity rates were performed and effect of ABC location on SWI investigated. The results show that, when the ratio of seawater to freshwater densities increased from 1.006 to 1.010, the ratio of saline wedge tip velocity to seawater velocity, airflow to seawater discharge ratio for first and second ABCs are raised 60, 58, and 70%, respectively. Also, when the Froude number (Fr) > 0.031, seawater density changes do not significantly affect the process of SWI. Besides, results of the study show that the closer the ABC is to the river downstream, the higher the airflow rates required. In addition, the optimal value ...
The present study aims to evaluate the effects of the arrangement of the teeth in terms of angle,... more The present study aims to evaluate the effects of the arrangement of the teeth in terms of angle, arrangement and radius on the eddy currents, kinetic energy dissipation and turbulence dissipation rate. Four groups of models were created for this purpose. In the first group, each model contained a bucket with two teeth with different angles. The second group included three models where each bucket had two teeth with the same angle, but the angle was different for each bucket. The third group contained three models with different bucket radii. In addition, the last group consisted of two models where each model had two teeth with an angle of 45°. The result showed that the use of teeth with unequal angles plays a significant role in increasing the total turbulence loss. Moreover, the angle of the teeth has a much larger effect on increasing the turbulence loss than changing the bucket radius. In addition, the use of unequal angles in the design of the teeth can significantly increase the loss. The loss can be significantly increased if a larger radius and unequal tooth angles are used simultaneously. Using equal tooth angles with a larger angle result in more loss compared to the case where the angles are small but different. Finally, buckets with larger radius and unaligned and larger tooth angles are considered as the factors that increase the energy loss in buckets, which leads to an increase in the efficiency of the bucket.
The numerical solution of flows with a freely moving boundary is of great importance in practical... more The numerical solution of flows with a freely moving boundary is of great importance in practical application such as ship hydrodynamics. Details are given of the development of a two-dimensional vertical numerical model for simulating unsteady and steady free-surface flows on a nonstaggered grid in curvilinear coordinates, using a non-hydrostatic pressure distribution. In this model, Reynolds equation and the kinematic free-surface boundary condition are solved simultaneously, so that the water-surface elevation can be integrated into the solution and solved for, together with the velocity and pressure field. In computational space, the Cartesian velocity components and the pressure are defined at the center of a control volume, while the volume fluxes are defined at the midpoint on their corresponding cell faces. Detailed numerical results are presented for the wave generation above an obstacle and resonant motion standing wave. The results show that the numerical algorithm descri...
Particle movement will occur when the instantaneous fluid force on a particle is just larger than... more Particle movement will occur when the instantaneous fluid force on a particle is just larger than the instantaneous resisting force. One of the most important issues in this regard is the influence of different hydrodynamic forces on threshold of motion. In the present study, effects of different forces; such as non-linear drag force, the shear lift force, Magnus force, the buoyancy force, the added mass force, Basset history force and torque; on the initiation of motion of sediment grains were studied by developing a 3D Lagrangian numerical model. The particle-wall collision were included using Discrete Element Method (DEM) and a random process. The non-cohesive sediments grains for the range of sand to gravel were considered. The verification step was performed using different particle diameters and flow conditions. The results indicated that the drag force is the dominating force. Also, it is observed that the influence of lift force increase by increasing grain diameter. Keyword...
Submerged vanes are installed in waterways bed. These structures are usually used in groups and t... more Submerged vanes are installed in waterways bed. These structures are usually used in groups and their main performance is to create an eddy current which leads to change in stream flow pattern and the bed topography in waterways. Performance of submerged vanes group depends on their arrangement and size. In this study using SSIIM numerical model, hydrodynamic analysis of flow pattern and bed topography around a single submerged vane in a straight channel was done and tried to estimate proper arrangement of submerged vanes group. The geometry of arrangement consisted of longitudinal distance between consecutive vanes, transverse distance of two adjacent vanes, and transverse distance of submerged vanes from the outer wall. Therefore, after verification of the results of numerical model with experimental data, flow pattern and topography of the bed around a vane with different dimensions and angles (in suggested domain) were investigated and analyzed. In this order, values of transverse and longitudinal distances of scouring hole at high-pressure and low-pressure sides of the vane from center of the vane were measured. Also values of transverse and longitudinal locations of the maximum scouring hole and maximum sedimentation downstream of the vane were determined. The results of these parameters were used to estimate the location of adjacent vanes. To reduce number of modes, the Taguchi method is used in design of simulations. Finally, mathematical relations are derived for geometry of arrangement versus vanes dimensions and angles. Comparison of the results of this research with the results of previous researchers, who have studied submerged vanes groups, showed that accuracy of the method used in this study is acceptable. The numerical results showed that the values obtained for the transverse and longitudinal distances of vanes are almost in the same range of previous laboratory studies.
Hydraulic characteristics of the flow and sediment transport conditions are among the most import... more Hydraulic characteristics of the flow and sediment transport conditions are among the most important issues in design of the lateral intakes in order to minimize the flow loss. In this study, a 3D numerical model has been employed in a parametric study to study the performance of a lateral pipe intake. Observations indicated that the flow was affected by the pipe intake so that the recirculation area was close to the wall of the main channel, the wall of the lateral pipe intake and back of the lateral pipe intake. The pipe intake in vertical direction to the main channel showed the highest performance, although sedimentation behind the pipe intake in this diversion angle was higher. In addition, pipe intake showed a quite acceptable performance for almost 40% intrusion to the main channel width. Relationships for the coefficient of discharge were also developed.
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