سال انتشار: ۱۳۹۰
محل انتشار: اولین کنفرانس بین المللی و سومین کنفرانس ملی سد و نیروگاههای برق آبی
تعداد صفحات: ۱۰
S. A. SADRNEJAD – Dept of Civil Eng, KNToosi University of Tech, and Sapasad Engineering Co, Teheran,Iran
Flap gates are designed and provided at the end of draft tube bend, some 9m downstream of turbine axis, in power station section of Masjed-e-Soleiman (MIS)hydroelectric project. The function of these gates is to stop the tailrace water flowing back to the turbine space during repair and maintenance. In order to avoid vibrationof these gates, when they are in open position, the top parts are vacuumed. In addition to hydrostatic internal and external pressures to which flap gates andtheir steel linings are exposed to, the forces induced by vibration of the gate due to pressure fluctuation in draft tube flow, are of typical hydrodynamics unknown forces.The intention of the present work is to particularly define these forces as a cyclic loading which cause the gate as well as the servomotor (hydraulic cylinders for opening/closure of the gate) forces to oscillate while the gate is open. These changesof force must be considered in the design of servomotors. According to the results obtained from hydraulic model test scaled 1:30, the worsecondition of oscillation is quoted at frequency of 3.75 cycle/second, maximum and minimum measured pressure fluctuation H/H equal to 10% and 3.5% respectively.A normalized time function representing time variation of pressure to be multiplied by hydraulic unbalanced head is considered for the existing pressure fluctuation. The effectsof this dynamic load are added to the result of stability of the gate upon its weight.The obtained conclusions indicate that further to hydrostatic proof, the overall effects of pressure fluctuation on the gate provides a pushing action which only create somecompressive forces on the two existing servomotors and top support lines. However, this compression may not cause any change in the design of servomotors, i.e. toincrease the pushing force. Consequently, upon the existing conditions and pressurefluctuation no change is needed to be considered for the system. In this paper, the structure of the flap gate in open condition under the normal tailracehead in draft tube, applied top vacuum, keeping forces by servomotors and being supported by two pivots and top supports is to be oscillated due to pressurefluctuation. A structure-fluid dynamic interaction model based on added-mass solution is employed as an approximate solution procedure. An accurate added-mass approachmixed with implementation in finite element framework is proposed. In this work,experimental conclusions, supported by theory, led to presentation of more accurate results in vibration of flap gate. The obtained conclusion indicates that the overalleffects of pressure fluctuation on the gate is a pushing action that only create some compressive forces on two existing servomotors and top support lines. Thiscompression may not cause any change in the design of servomotors to increase the pushing force. Consequently, upon the existing conditions and pressure fluctuation nochange needed to be considered for the system.