بررسي خصوصيات هيدروليكي و كاهش نيرو ارتعاش جريان در شيب شكن ها به وسيله ي ميراگرها

چكيده انگليسي :

Hydraulic Characteristics and Reduction of Force and Vibration of Flow on Drops by Dampers Hamed Poursalehi h poursalehi@cv iut ac ir Date of Submission 2013 01 24 Department of Civil Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisors Mohammad Reza Chamani mchamani@cc iut ac ir Amir Mahdi Halabian mahdi@cc iut ac ir Abstract In irrigation channels and storm water systems structures are used to offset the elevation difference between the channel slope and the ground slope These structures usually lead to a sudden vertical change of channel slope and produce a free falling jet which impacts the drop floor downstream The impact force may damage the structures In addition extra dynamic force is developed in the downstream floor due to the free falling jet fluctuations Evaluation of the impact force in the downstream is an essential step in the design of drop structures downstream bed There are limited studies conducted to investigate the vibration problems of the hydraulic structures and this concept is still a baffling case If the vibration is not properly dissipated in addition to the structural instability it may produce environmental pollutions to the neighboring human communities The aim of the present study is to evaluate the dynamic force of the falling jet in a vertical drop This study consists of two parts i e experimental and analytical studies With subcritical flow in the upstream channel two physical models with drop heights of 0 226 m and 0 376 m are built in the Hydraulic Lab Department of Civil Engineering Isfahan University of Technology For verification the hydraulic properties of the flow on vertical drop are measured and the results are compared to previous studies Introducing a SDOF system for the downstream floor passive dampers were used to control the dynamic forces acting on the drop floor downstream The drop floor is allowed to have vertical degree of freedom and the absorbing system is designed to reduce the forces on the drop floor Three types of dampers with various stiffness and damping constants have been used based on the range of jet frequencies An instrumentation system including several load cells was used to record the fluctuating force time histories The hydraulic properties of flow on drops including brink depth pool depth length of pool surface flow depth at the downstream channel jet width at the pool level inclination and position of falling jet impact at the downstream channel and downstream floor pressure have been measured The results agreed well with those of the previous experimental data and analytical predictions The results of drops with dampers indicated that the vibrations could be lower than those in drop without dampers The results showed that damper type 3 has the best efficiency in terms of force and amplitude reductions Using damper type 3 the force amplitude and the mean value of dynamic force are reduced as much as 81 and 25 respectively In the analytical part a method is presented to estimate the dynamic force of falling jet on the downstream floor The results of the proposed method showed that if the sinusoidal variable pressure amplitude and steady pressure variance between two sides of the falling jet are known the proper value of dynamic force using the proposed method can be evaluated Keywords Drop Structure Vibration Damper Dynamic Force Frequency PDF created with pdfFactory trial version www pdffactory com

پورصالحي، حامد

بررسي خصوصيات هيدروليكي و كاهش نيرو ارتعاش جريان در شيب شكن ها به وسيله ي ميراگرها

سازه هاي هيدروليكي , شيب شكن قائم , نيروهاي ديناميكي