Iranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122Use of a Simple Repulsive Force in Simulating Fluid Flow under a Hypo-Elastic Gate by Smoothed Particle HydrodynamicsUse of a Simple Repulsive Force in Simulating Fluid Flow under a Hypo-Elastic Gate by Smoothed Particle Hydrodynamics1141017210.30482/jhyd.2014.10172FAH. SabahiM.Sc. Student, Mechanical Engineering, Shiraz University of Technology, Shiraz, Iran.A. H. NiksereshtAssociate Professor, Mechanical Engineering, Shiraz University of Technology, Shiraz, Iran.S. J. RouzegarAssistant Professor, Mechanical Engineering, Shiraz University of Technology, Shiraz, Iran.Journal Article20141003Re-meshing in grid dependent CFD methods in large deformation problems has a high computational cost. Smoothed Particle Hydrodynamics (SPH) is a robust mesh-free method to deal with the problems of large deformation in fluid-solid interactions. Also SPH is a fully Lagrangian particle method, which has a good ability to capture the free surface in two phase flows. In this paper, at first, fluid flow under a gate is solved with the present SPH method and the results are compared with the VOF scheme. For validating the solid part of the code, vibration of a hypo-elastic plate is simulated. Comparing the results with the previous researches show a good agreement. Finally a coupled fluid flow under a hypo-elastic gate is simulated with the present SPH method and the interaction between fluid and solid is obtained with a proposed simple model. In this paper also a simple repulsive force which is independent of the pressure distribution is introduced to prevent the penetration of fluid particles into the solid parts. The results also show the high ability of the present SPH method to follow the fluid- solid interface accurately.Re-meshing in grid dependent CFD methods in large deformation problems has a high computational cost. Smoothed Particle Hydrodynamics (SPH) is a robust mesh-free method to deal with the problems of large deformation in fluid-solid interactions. Also SPH is a fully Lagrangian particle method, which has a good ability to capture the free surface in two phase flows. In this paper, at first, fluid flow under a gate is solved with the present SPH method and the results are compared with the VOF scheme. For validating the solid part of the code, vibration of a hypo-elastic plate is simulated. Comparing the results with the previous researches show a good agreement. Finally a coupled fluid flow under a hypo-elastic gate is simulated with the present SPH method and the interaction between fluid and solid is obtained with a proposed simple model. In this paper also a simple repulsive force which is independent of the pressure distribution is introduced to prevent the penetration of fluid particles into the solid parts. The results also show the high ability of the present SPH method to follow the fluid- solid interface accurately.https://jhyd.iha.ir/article_10172_97498ff22ec53ef103fb9d806b73334e.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122Effect of Hydrograph Peak Time on Local Scour around Bridge PierEffect of Hydrograph Peak Time on Local Scour around Bridge Pier15321017310.30482/jhyd.2014.10173FAM. Karimaee TabarestaniPhD Graduate, Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran.0000-0001-9673-1315A. R. ZarratiProfessor, Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran.Journal Article20141115In the present study effect of hydrograph peak time on local scour around bridge pier is studied. Hydrographs with one discharge peak as well as double discharge peaks were generated in the labaratory. The duration time for some of these hydrographs were so short that could be considered as flash flood occuring in arid or semi-arid zone rivers. In each experiment, development of scour depth with time was measured by small cameras. Results showed that for hydrogaphs with similar duration, parameter of peak time or sequence of peaks in double discharge peak has negligible effect on final scour depth but considerable effect on time development of scour depth. Furthermore, time developmet of scour depth for present hydrographs are calculated by stepped- hydrograph model and empirical equations presented in the literature for steady flow. Results also showed high descrepancy between calculated and measured data for time development of scour depth and all of the final calculated scour depths are larger than experimental ones. In the best case, the average error for final calculated scour depth is about 10%.In the present study effect of hydrograph peak time on local scour around bridge pier is studied. Hydrographs with one discharge peak as well as double discharge peaks were generated in the labaratory. The duration time for some of these hydrographs were so short that could be considered as flash flood occuring in arid or semi-arid zone rivers. In each experiment, development of scour depth with time was measured by small cameras. Results showed that for hydrogaphs with similar duration, parameter of peak time or sequence of peaks in double discharge peak has negligible effect on final scour depth but considerable effect on time development of scour depth. Furthermore, time developmet of scour depth for present hydrographs are calculated by stepped- hydrograph model and empirical equations presented in the literature for steady flow. Results also showed high descrepancy between calculated and measured data for time development of scour depth and all of the final calculated scour depths are larger than experimental ones. In the best case, the average error for final calculated scour depth is about 10%.https://jhyd.iha.ir/article_10173_8d71457e33633cbc26d3ff03a4ed6e21.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122Analysis of Shear Stress in Rectangular Open Channels Using Force Balance MethodAnalysis of Shear Stress in Rectangular Open Channels Using Force Balance Method33441017410.30482/jhyd.2014.10174FAB. Lashkar-AraAssistant Professor of Civil Engineering Department, Jundi-Shapur University of Technology, Dezful, Iran.M. Fathi-MoghadamProfessor in College of Water Science Engineering, Shahid Chamran University of Ahwaz, Iran.Journal Article20140113One of the most important problems in open channel flow is determination of shear stress. It is difficult to determine boundary shear distributions in real life applications. Laboratory flume studies have still been serving to deal with this problem. This study is focused on experimental measurement of the bed and wall shear stresses as well as estimation of hydraulic resistance coefficient for flow in rectangular open channels. The energy and momentum approaches were used to determine contribution of wall and bed shear forces on total boundary shear. The hydraulic grade line was measured using an indirect method while a frictionless system (knife edge flume) was used for the momentum measurements. The local boundary shear stress was measured using a 4-mm diameter Preston tube connected to a differential pressure transducer and a data acquisition system. The calibration curves proposed by Patel were used to convert pressure reading to shear stress. The results were adjusted by the total shear force calculated from the energy and momentum methods. A nonlinear regression-based technique was carried out to develop equations and to determine the percentage of wall and bed shear stresses on the wetted perimeter of a smooth rectangular open channel. Comparison of results for shear stress measurement by direct and indirect methods shows maximum errors of 4 and 8 percent respectively.One of the most important problems in open channel flow is determination of shear stress. It is difficult to determine boundary shear distributions in real life applications. Laboratory flume studies have still been serving to deal with this problem. This study is focused on experimental measurement of the bed and wall shear stresses as well as estimation of hydraulic resistance coefficient for flow in rectangular open channels. The energy and momentum approaches were used to determine contribution of wall and bed shear forces on total boundary shear. The hydraulic grade line was measured using an indirect method while a frictionless system (knife edge flume) was used for the momentum measurements. The local boundary shear stress was measured using a 4-mm diameter Preston tube connected to a differential pressure transducer and a data acquisition system. The calibration curves proposed by Patel were used to convert pressure reading to shear stress. The results were adjusted by the total shear force calculated from the energy and momentum methods. A nonlinear regression-based technique was carried out to develop equations and to determine the percentage of wall and bed shear stresses on the wetted perimeter of a smooth rectangular open channel. Comparison of results for shear stress measurement by direct and indirect methods shows maximum errors of 4 and 8 percent respectively.https://jhyd.iha.ir/article_10174_8f68e6fc48541446a4d849fe8f16db5b.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122Estimating Scour Hole Dimensions of Ski Jump Downstream of Dams Using Granular Computing ModelEstimating Scour Hole Dimensions of Ski Jump Downstream of Dams Using Granular Computing Model45601017510.30482/jhyd.2014.10175FAAli NaghikhaniM.Sc. Student of Environmental Engineering-Water Resources, Faculty of Environment, University of Tehran, Iran.Roohollah NooriAssistant professor of Environmental Engineering, Faculty of Environment, University of Tehran, Iran.Hossien SheikhianM.Sc. Student, Surveying and Civil Engineering, College of Engineering, University of Tehran, IranBehzad GhiasiM.Sc. Student of Environmental Engineering-Water Resources, Faculty of Environment, University of Tehran, Iran.Journal Article20150228Accurate estimation of scour parameters such as length, depth and width, have a major role in the management of this quite nonlinear phenomenon. The main goal of this study is to present a method based on granular computing model (GRC) to estimate scour parameters. For this purpose, scour hole of ski jumps downstream of dams (goal functions) were considered to be affected by hydraulic, morphological and geotechnical variables, and GRC model was used for calibration and verification of the phenomena. The implemented linear analysis showed that the goal functions are affected by flow rate variations, waterfall height and deposited particles average size, rather than lip angle. This fact was in compliance with the previous researches. The results also showed the GRC model results in predicting the goal functions had values very close to the measured ones, or with small discrepancies. More investigations showed that the GRC model was superior for estimation of scour depth of ski jumps downstream of dam to the well-known empirical formula proposed by other researchers.Accurate estimation of scour parameters such as length, depth and width, have a major role in the management of this quite nonlinear phenomenon. The main goal of this study is to present a method based on granular computing model (GRC) to estimate scour parameters. For this purpose, scour hole of ski jumps downstream of dams (goal functions) were considered to be affected by hydraulic, morphological and geotechnical variables, and GRC model was used for calibration and verification of the phenomena. The implemented linear analysis showed that the goal functions are affected by flow rate variations, waterfall height and deposited particles average size, rather than lip angle. This fact was in compliance with the previous researches. The results also showed the GRC model results in predicting the goal functions had values very close to the measured ones, or with small discrepancies. More investigations showed that the GRC model was superior for estimation of scour depth of ski jumps downstream of dam to the well-known empirical formula proposed by other researchers.https://jhyd.iha.ir/article_10175_be388d6703892d9d07917321294980d5.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122Three Dimensional Hydrodynamics of Arced Piano Key SpillwaysThree Dimensional Hydrodynamics of Arced Piano Key Spillways61791017610.30482/jhyd.2014.10176FAA. SafarzadehAssistant Professor, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabili, Iran.0000-0003-4515-2078B. NorooziM.Sc. of Hydraulic Structures, Faculty of Engineering, University of Mohaghegh Ardabili, Ardabili, Iran.Journal Article20150727In this paper 3D free surface flow over the arced Piano Key spillway (APK) was numerically simulated and its hydraulic performance curves determined for various geometrical and hydraulic conditions. Three dimensional flow pattern around various types of APK were also determined and the differences between their performance with rectangular and trapezoidal piano key spillways discussed. The arced Piano Key spillways necessarily have trapezoidal keys and they should have advantages of trapezoidal weirs due to the increased inlet key area. Furthermore, the arced plan, bulged into the reservoir, eliminates the approaching flow channel mode and flow approaches perpendicularly to the spillway crest, from all directions. These phenomena lead to substantially increase of the discharge coefficient of the Piano Key spillways. By increasing the arced spillway angle, the discharge capacity increases. This is mainly due to the decrease of the local submergence over the outlet keys and increase of the inlet key area and modification of the overflow pattern. In this paper 3D free surface flow over the arced Piano Key spillway (APK) was numerically simulated and its hydraulic performance curves determined for various geometrical and hydraulic conditions. Three dimensional flow pattern around various types of APK were also determined and the differences between their performance with rectangular and trapezoidal piano key spillways discussed. The arced Piano Key spillways necessarily have trapezoidal keys and they should have advantages of trapezoidal weirs due to the increased inlet key area. Furthermore, the arced plan, bulged into the reservoir, eliminates the approaching flow channel mode and flow approaches perpendicularly to the spillway crest, from all directions. These phenomena lead to substantially increase of the discharge coefficient of the Piano Key spillways. By increasing the arced spillway angle, the discharge capacity increases. This is mainly due to the decrease of the local submergence over the outlet keys and increase of the inlet key area and modification of the overflow pattern. https://jhyd.iha.ir/article_10176_aed000578bd7f739c485452bb395368e.pdfIranian Hydraulic AssociationJournal of Hydraulics2345-42379320141122» Research Note «
Experimental Investigation on Local Scour around Conical and Pyramidal Piers» Research Note «
Experimental Investigation on Local Scour around Conical and Pyramidal Piers81891017710.30482/jhyd.2014.10177FAM. Pourahmadi.Sc. in Marine Structures, Faculty of Civil Engineering, Sahand University of TechnologH. HakimzadehProfessor of Coastal Engineering, Faculty of Civil Engineering, Sahand University of Technology.Journal Article20140805The present study was conducted to investigate the use of conical and pyramidal piers in reducing local scour risk at the bridge piers. The efficacy of different diameters on the bed and water surface (i.e. different lateral structural slopes of piers ranging from 1:60 to 1:10) with constant projected areas was studied. The experimental results for the two flow intensities (velocity of flow to critical velocity of flow) of 0.92 and 0.86 showed that the scour depth in bridges with conical or pyramidal piers decreased significantly in comparison to those with cylindrical and cubical piers. For the flow intensity of 0.92, it was found from the experimental data that by making a very mild slope (1:60) in conical piers, the absolute (maximum measured depth of scour) and relative (ratio of maximum measured depth of scour to diameter on the bed) scour depths were reduced about 15.8% and 25.1%, respectively when compared to the cylindrical one. For the same conditions in pyramidal piers, the absolute and relative scour depths were reduced about 8.9% and 18.4%, respectively, in comparison with the cubical one. In the case of other piers with steeper slopes and consequently larger diameters on the bed, in spite of considering the same criteria, the side walls and wake vortex behind the pier altered the process of experiments and therefore the reduction ratThe present study was conducted to investigate the use of conical and pyramidal piers in reducing local scour risk at the bridge piers. The efficacy of different diameters on the bed and water surface (i.e. different lateral structural slopes of piers ranging from 1:60 to 1:10) with constant projected areas was studied. The experimental results for the two flow intensities (velocity of flow to critical velocity of flow) of 0.92 and 0.86 showed that the scour depth in bridges with conical or pyramidal piers decreased significantly in comparison to those with cylindrical and cubical piers. For the flow intensity of 0.92, it was found from the experimental data that by making a very mild slope (1:60) in conical piers, the absolute (maximum measured depth of scour) and relative (ratio of maximum measured depth of scour to diameter on the bed) scour depths were reduced about 15.8% and 25.1%, respectively when compared to the cylindrical one. For the same conditions in pyramidal piers, the absolute and relative scour depths were reduced about 8.9% and 18.4%, respectively, in comparison with the cubical one. In the case of other piers with steeper slopes and consequently larger diameters on the bed, in spite of considering the same criteria, the side walls and wake vortex behind the pier altered the process of experiments and therefore the reduction rathttps://jhyd.iha.ir/article_10177_f5c7f233596f29df4451bc08d26c0e6e.pdf