Vibration Test And Stress Analysis Of Large Surface Radial Steel Gate During Water Discharge

The radial steel gate is widely used in water conservancy and hydropower projects because of its convenient opening and closing,labor-saving and other characteristics.Because the radial gate is a welded steel structure with steel plate as raw material,it is prone to generate vibration under the excitation of fluctuating water pressure when discharging water.Larger vibration will endanger the safety and stability during operation of the radial gate.Therefore,it is necessary to study dynamic characteristics and flow-induced vibration of radial gate.Taking the radial working gate of spillway of Houziyan Hydropower Station as the research object,the flow dynamic response,dynamic characteristics and hydrodynamic pressure distribution of the gate structure are studied by combining field observation test with numerical simulation.By arranging strain gauges and acceleration sensors at corresponding measuring points of the gate,the time-domain signals of strain and acceleration during opening and closing of the gate at different openings under two test water levels are recorded,Processing and analyzing the original recorded signal of the test,obtain the data of moving average stress,dynamic stress,vibration acceleration and vibration displacement at each measuring point of the gate under various conditions,get the variation rule of vibration parameters with gate opening;finite volume method hydraulic model for flow field of gate and surrounding spillway by using FLUENT to get the distribution rule of hydrodynamic pressure on the panel,the flow velocity field around the gate and the water pressure field when the gate is discharged with different openings;the three-dimensional finite element model of gate structure is established based on ABAQUS,the structural stress distribution of the gate at different openings is analyzed,by considering different constraints to simulate the two states of gate closed and open,the corresponding free vibration frequency and mode shape are calculated,and the free vibration characteristics in the two states are compared.The research results have made a judgment for the structural strength and vibration safety of the gate in operation,pointed out the unfavorable opening condition of the gate vibration,and put forward suggestions for the structural optimization and operation regulations of the gate.The amplitude and dominant frequency of dynamic stress measured by test can provide basic data for fatigue checking of subsequent gates.The main research conclusions are as follows:(1)The stress values of the main components of the gate obtained by test and finite element simulation under various working conditions are less than the allowable stress,and the stress margin of most measuring points is large,It is found that the stress concentration is easy to occur at the joint of gate panel and longitudinal beam,the connection of main beam flange and arm,and the stress value is large.It is suggested that position should be strengthen in the design.(2)The test results show that the dynamic stresse at each measuring point of the gate are not significantly different,but gradually increase with gate opening.The maximum value of 6.26MPa meets the requirement of safe operation of the gate when it is discharged at large opening.Time signal processing of vibration acceleration finds that the mean rms value of vibration acceleration at the position of beam and arm of gate is larger when discharging water at 6m and 11m openings.It is suggested that the gate should not stay at this opening for long time while in operation.Power spectrum analysis of vibration acceleration finds that the dominant frequency of main beam and arm of gate is within 30Hz basically and decreases gradually with the increase of gate opening,it related to the dynamic pressure excitation of the gate under different opening degrees.Vibration of the gate under two test levels is small vibration according to the standard of vibration displacement.(3)The frequency of each order of the gate under the opening and closing conditions is not significantly different,and the vibration modes are basically similar.The first 10 order frequencies are all within 20Hz,which is located in the high energy area of water dynamic pressure and contribute possibility of resonance with the water.Most of the low order vibration modes are manifested as bending and torsion of the gate arm,the arm lack of contact support between the arms,which indicates that the rigidity of the gate arm is relatively weak and needs to be optimized and strengthened.The vibration prone parts of the gate are the arm and the gate leaf top.(4)The average pressure of dynamic water on the gate panel decreases with the increase of opening,which is less than the pressure when the gate is fully closed under the same head.Because the water flow speed at the bottom of the gate is faster,the pressure head is converted to the velocity head,and the average pressure at the bottom of the panel is very small.When the panel is discharged at each opening,the maximum dynamic water pressure on the panel basically appears at the height range of 2-3m from the bottom.