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چكيده انگليسي :

Omission of Hydraulic Jump during Transition from Supercritical to Subcritical Flow Mohamad Hosein Rabiei m rabiei@cv iut ac ir Date of Submission March 7 2011 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisors Dr Abdorreza Kabiri Samani akabiri@cc iut ac ir Dr Hamid Reza Safavi hasafavi@cc iut ac ir Adviser Dr Seyed Mahmood Borghei mahmood@sharif edu AbstractIn order to reduce the flow energy of weirs to preserve downstream dams raise the water surface inchannels increase the underflow gates discharge diminish the uplift pressure under the hydraulicstructures and create a control section for discharge measurement the flow must be transmitted fromsupercritical to subcritical Quick transition of the flow regime accompanies by expansion turbulence water circulation and local head loss together with a hydraulic jump Hydraulic jump is a type ofrapidly varied flows and must be controlled and restrained By employing a proper transition structurethe total water head would be reduced gradually and flow regime would be changed uniformly alongthe transition Afterward the hydraulic jump could be eliminated and consequently the supercriticalflow would be transmitted to a subcritical flow regime In the present study in order to change the flow regime from supercritical to subcritical and to reach anuniform gradually varied flow a special transition is introduced based on the energy principle andChow s 1959 suggested method Linear water surface profile and energy gradient line was assumedto estimate the transition surface profile Different flow discharge with upstream Froude numbersbetween 1 5 and 6 5 were tested The proposed transition is suitable for irrigation and drainage systems For obtaining all unknown transition geometrical parameters three programs were written usingMatlab software ver 7 1 Regarding to a comprehensive theoretical analysis the transition profileequations were obtained based on complete omission of hydraulic jump Results of the theoreticalmodels show that for high values of the transition length the downstream depth is not depended on thetransition length and is almost higher than the downstream depth of the equivalent classic hydraulicjump In addition the total head loss during flow transition is lower than that of the equivalent classichydraulic jump In order to validate the analytical models a comprehensive experimental investigationis conducted Analytical results show good agreement with those of model experimentation Based ontheoretical results six experimental transition models were constructed of galvanized iron Differenthydraulic and geometrical aspects of flow were studied over the transition structures during transitionof flow regime Transition length height surface profile upstream and downstream depths flowdischarge and pressure distribution along the transition were the considered parameters Observationsshowed that for all the constructed models the hydraulic jump was completely omitted for a certaindesign Froude number By increasing the upstream Froude number roller waves were generated yielded to forming partial hydraulic jump over the positive slope of transition structure with a lengthlower than equivalent classic hydraulic jump Based on the experimental results of partial hydraulicjump an algorithm was proposed for calculating all the partial hydraulic jump unknown parameters Inthis situation the downstream depth was approximately equal to the downstream depth of theequivalent classic hydraulic jump Key words Supercritical flow Subcritical flow Omission of hydraulic jump Partial hydraulic jump Transition

ربيعي، محمد حسين

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