عنوان مقاله [English]
Background and objectives: Many built structures in rivers have been destroyed or damaged due to lack of proper understanding of scouring. Therefore, predicting the maximum scour around structures in the river has a great importance. Groins widely are designed and constructed in order to river training in the country. This method, which is one of the most effective ways to stabilize the river banks are expanding day by day. In this research, bed deformation around permeable and close groins with different percentage of permeability was numerically simulated by using some of turbulence closure models. Then numerical simulation results were compared with experimental advantages.and at leastAnd, by using the best model of turbulence and calculating the transverse flow criteriaes created by the presence of a groin, the effect of the permeability of groine on the transverse flow power and the longitudinal distance in the downstream of which the continuity of the transverse flow continues is determined.
Materials and methods: In other to compare the obtained results from numerical simulation with laboratory advantages, laboratory results around close and permeable groins with 30, 50 and 70 percent of permeability in a flume were used.
The length of mentioned flume was 14m, the flume width and height’s was respectively 2 and 0.5m. The slope of its floor was near Zero. Discharge is 50 liters per second, and the average diameter of the bed materials is 0.26 mm and clear water conditions. For numerical modeling, Flow-3D software was used.
Results: The comparison of results of numerical simulation and experimental advantages shows that numerical simulation can predict the bed topography around permeable groins with different percentage of permeability and close groins in channel by live bed as well. In the following, the effect of permeability on power of vortices created around the permeable groins was studied. For this purpose, some criteria that demonstrate the power of secondary flows were computed. Then the changes and continuity of these criteria before and after the permeable groins with different permeability was studied. In the following the same criteria were predicted by ANN method and the advantages of ANN method was compared with results of numerical simulation method.
Conclusion: numerical simulation and especially Flow-3D software can predict the location and maximum scouring around impermeable and permeable groins with different percentage as well. And also the changes of power of secondary flow at the upstream and downstream of groin have a relation with percent of permeability of groin. The ANN results for predicting the criteria of power of secondary flow in different cross section and for different percent of permeable groin shows that this method also has good performance. The results for the calculated cross-flow criteria also indicate that the deviation of the flow by a groin can be roughly ignored with a permeability percentage of more than fifty percent, and for impermeable groin, cross flow continue to extend over 1.4 times the length of the groin.
Keywords: permeable and close groins, scour, secondary flow, vortex, numerical simulation, ANN