هيدروليك جريان در حوضچه هاي آرامش شيب شكن هاي قائم مجهز به مستهلك كننده هاي شياري-شبكه اي

چكيده انگليسي :

Hydraulics of Flow in Stilling Basins of Vertical Drops Using Grating and Netting Dissipaters Elham Bakhshian e bakhshian civil@yahoo com Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor Dr A R Kabiri SamaniAbstract Abrupt changing the channel bed elevation in hydraulic systems due to e g chutes drops andsteeped spillways tends to create a sever flow kinematic energy This excess energy results differentunfavorable phenomena including tremendous forces on hydraulic structures scouring and degradingthe channel bed which results to destruction of the downstream structures These phenomena wouldintensify while a number of vertical drops constructed consecutively along the channel The main goal of the present study is to explore methods for increasing the energy dissipationefficiency of vertical drops by installing new types of dissipaters namely Grating and Nettingdissipaters based on model experimentation These types of dissipaters could be established over thedrop crest looking like a bottom racks In addition the features of hydraulic jump created in thestilling basins of these types of vertical drops are compared with those of a simple vertical drop Byassembling the above mentioned structures over the stilling basins of vertical drops the jet flowdirection is changed the degree of turbulence is increased that tend to increase the head loss Inaddition the length of the hydraulic jump decreases Both these consequences enhance the stillingbasin efficiency and are of interest in practice The enhanced efficiency of the proposed structures wasquantified based on the achieved experimental data Both analytical and experimental investigations were performed in the present study Experimentswere conducted based on three different drop heights five different netting dissipaters with certaingrid s dimension and three different grating dissipaters with special slot widths The range of Yc hratios where Yc is the critical depth and h is the vertical drop height was considered between 0 14and 0 325 Based on the model experimentation data empirical equations were presented to estimatethe depth and length of the pool downstream of the drop the force acting on the basin floor optimumlength of the dissipaters and relative head loss With respect to the results of the former investigationsand their assumptions new semi analytical models were developed for estimating the abovementioned hydraulic parameters of the vertical drops which were equipped by netting or gratingdissipaters To expand the present semi analytical model more logical assumptions were applied anddata of the present model experimentation were used The proposed semi analytical model comparedwell with the experimental results However there are small discrepancies between the analytical andexperimental results of netting dissipaters This is partly due to the flow high turbulence andcomplicated phenomena exist in the stilling basins of netting dissipaters Also the air bubbleentrainment is another source of the difference between the two sets of results Overall installinggrating dissipaters increases the head loss efficiency by up to 30 and decreases the hydraulic jumplength by about 30 35 compared with simple vertical drops However for the netting dissipaters thehead loss increases by up to 45 and the jump length decreases by about 60 75 Keywords Energy Dissipater Hydraulic Jump Netting Grating Vertical Drop

بخشيان، الهام

هيدروليك جريان در حوضچه هاي آرامش شيب شكن هاي قائم مجهز به مستهلك كننده هاي شياري-شبكه اي

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