Research On Plane Gate-closing Vibration And Its Influence On Holding Force

A large number of water conservancy projects with high head and large discharge capacity have been built with the great development of hydropower in China.The plane gate is often used as the emergency gate or fast gate,which can quickly close the gate and block the water flow when there are engineering problems or accidents.The gate-closing vibration and failure of gate-closing often occur,which poses a serious threat to the safe and stable operation of water conservancy projects.Thus,the gate-closing vibration and holding force have become vatial research topics.Based on this,this paper carried out hydraulic model test of plane gate under different supporting forms,focused on the characteristic analysis of vertical vibration and the holding force under the condition of gate fixed opening and gate closing process,and discussed the source of gate-closing vibration.Afterwards,the control equation of plane gate-closing vibration was established through analogy dry friction self-excited vibration theory.The influence of various parameters on the characteristics of the gate-closing vibration was analyzed.Finally,based on the control eqution of gate-closing vibration,the macro document by the user-defined functions in FLUENT was used to control the gate vibration response.Then,the numerical simulation model of holding force,considering influence of gate-closing vibration,was established in the plane gate closing process.The main research achievements of this article are as follows:Firstly,through hydraulic model test,two plane gates by supported sliding block and roller were carried out to study the characteristics of gate vibration and holding force under different working conditions.The model results show that the two plane gate models supported by sliding block and roller have gate-closing vibration phenomenon.Under the condition of free outflow behind the gate supported by sliding block,as the gate falls and the gate opening ratio decreases,the intensity and period of vertical gate vibration increase gradually.The mean of gate holding force decreases and its fluctuation amplitude increases gradually with the decrease of gate opening ratio.Gate vibration has little effect on the maximum holding force in this model.The variation characteristics of the vertical vibration and the holding force is consistent and their dominant frequency gradually decreases from 14 Hz to 7 Hz,indicating that the gate vertical vibration can be regarded as a rigid one-degree-of-freedom vibration.When the lubrication material was applied to the plane gate supported by the sliding block,the intensity of gate-closing vibration is significantly reduced,indicating that the friction factor between the gate support and the track has an important influence on the vibration.For the model test of plane gate supported by roller and with the variation of outflow conditions behind the gate,the vertical vibration intensity of the gate increases gradually and the vibration frequency gradually decreases from 7.43 Hz to 5.15 Hz.The variation range of vibration frequency in model test and natural frequency of gate equivalent system is consistent,which suggests that the gate-closing vibration is self-excited vibration.The maximum of closing force and opening force increased by 7.63～14.23% and 5.02～8.64%respectively due to the gate vibration.Comparing the variation characteristics between the fluid load on the gate bottom and the holding force,there is a big difference between them in the variation numerical magnitude and frequency,indicating that the gate-closing vibration is mainly affected by the instability of gate movement,but less by the instability of fluid.Secondly,by analogy with the dry friction self-excited vibration theory in tribology,the dynamic control equation of the dry friction self-excited vibration between the gate support and the track was constructed,and then the plane gate-closing vibration response was inverted.On this basis,the influences of gate mass,closing speed and friction coefficient on gate-closing vibration were analyzed.The results show that the plane gate-closing vibration is a special nonlinear self-excited vibration caused by interface friction.The greater the coefficient difference of static-slide friction and the panel water thrust,the smaller the equivalent stiffness,the greater the gate closing-vibration response.The critical closing speed,related to the static friction coefficient,can be regarded as the demarcation point of whether the gate is vibrating or not.With the increase of gate mass,the initial deformation of steel rope and the closing time increase,and the gate vibration intensity increases gradually.As the gate closes,the release length of steel rope increases,which leads to the gradual decrease of equivalent system stiffness.It is the direct reason for the increase of the gate-closing vibration period.Plane gate-closing vibration could induce strong vibration of hoist equipment and the vibration intensity can reach 2.08 mm.The key to solve the gate-closing vibration is to effectively deal with the the nonlinear variation of friction coefficient between the gate and the track.The key to solve the failure of gate-closing is to effectively reduce the static friction coefficient between the gate support and the track and improve the problem of insufficient closing force.Thirdly,combined with the physical model test and the control equation of gate-closing vibration,this paper utilized the user-defined functions in FLUENT to define the gate-closing vibration response and established the holding force numerical model of the plane gate.The fluid load of the gate body and the flow discharge of the gate were monitored,and the effect of gate vibration on hydraulic physical quantity was explored.The numerical simulation results show that the continuous vortex shedding phenomenon does not occur on the gate bottom because the water flow behind the gate gradually changes from full flow to open flow in gate closing process,indicating that the gate-closing vibration is less affected by the fluid instability.Compared with the numerical results of the direct gate-closing process,it is found that the gate has no obvious vibration in large gate opening ratio,and the variation trends of fluid load of the gate body and the flow discharge are consistent.When the plane gate opening ratio is small,the gate has a significant vibration response and the gate-closing vibration would increase the pulsation of panel water pressure and the flow discharge.In addition,there is a negative correlation between the upstream panel pressure and the gate seals pressure with the flow discharge through the sluice,while there is a positive correlation between the downstream panel pressure,the gate top pressure and bottom pressure with the flow discharge.The lift coefficient on the gate bottom is related to the water depth upstream,plane gate opening ratio and the service gate opening ratio.The influence of opening ratio of plane gate and service gate on the coefficient is stronger than that of upstream water depth.The numerical simulation results of holding force are in agreement with the model test results,which can meet the requirements of engineering accuracy.It is shown that the numerical simulation model of holding force in this paper,considering the influence of gate-closing vibration,can provide technical support for capacity estimation of the hoist in design period.