Investigation On Flow-induced Vibration Characteristics Of Overflow Concrete Face Rockfill Dam Discharge Chute

The paper relies on the data about the characteristics of the fluctuating pressure in the model test to make a summary of the characteristics of the fluctuating pressure of overflow concrete-faced rockfill dam chute and engage in a simple design.It also studies the system mode in flow-induced vibration,stress and deformation in the key parts,distribution laws of chute bottom slab stress and deformation as well as the effects of set bolts.The main contents and findings are as below:(1)According to the pulse pressure characteristic data observed by the hydraulic model test of overflow CFRD,the paper analyses and summaries the pulse pressure characteristics of discharge chute flow and proposed the generalized design method.The result indicates that for the overflow CFRD discharge chute with multiple inbrication-type air slot,the pulse pressure and pulse pressure coefficient on the base plate descends along with the discharge chute and happens in the alternative form of wave peak and wave valley.The pulse energy mainly focuses on low frequency area and the type of spectrum density is mainly the broad-band noise spectrum with low-frequency narrow band and low-frequency advantage component.The pulse pressure coefficients are distributed between 0.002 and 0.046 and the advantageous frequency smaller than 1.5 Hz accounts for 90.9%.The pulse pressure spectrum density on the side wall is LF narrow-band noise spectrum,the pulse pressure coefficients are distributed between 0.002 and 0.007 and the advantageous frequency smaller than 1.0Hz accounts for 94.4%.According to the data processing method of generalized spectrum frequency domain signal by using pulse pressure triangle-level Gaussian model,the time domain load curve reflecting pulse pressure spectrum frequency domain signal can be built by utilizing MATLAB software.(2)Based on the distribution law of pulsating pressure in water flow in the overflow CFRD discharge chute and the time domain load construction method,the modal analysis method is used to study the influence of system frequency,dam material modulus and discharge plate thickness on its frequency under different discharge conditions.The results show that the natural frequency of the the overflow CFRD discharge chute under the action of the pulsating pressure is mainly determined by the flow velocity in the discharge chute.The greater the flow velocity is,the system frequency is reduced rapidly,and it is easy to overlap with the main frequency range of the pulsating pressure of the water flow,and the system resonance damage is easy to occur.In order to ensure the stability of the system leakage,the flow velocity of the discharge tank should be controlled not too large.Moreover,the anchor rate of the system is obviously slowed down.The elastic modulus of the dam material and the thickness of the discharge chute plate have a great influence on the system frequency.Increasing the modulus of the dam and increasing the thickness of the discharge chute plate are beneficial to avoid the vibration of the system.(3)Aiming at the dynamic stability analysis of the overflow CFRD discharge chute plate under water flow flow cavity,the time domain analysis method is used to set the stress and deformation of the critical parts of the front and rear bottom of the anchor.The results show that the imbricated overflow CFRD discharge chute connecting with the joints and the imbricated structure connecting with the plate corner are the weak links.During the gradual increase of the discharge velocity,it is easy to produce excessive deformation of the septum at the bottom of the bottom of the trough.The anchors reduce the relative deformation of the seepage of the bottom plate of the overflow CFRD discharge chute and the tensile stress at the corners of the stacking tiles,so that the discharge limit flow rate that makes the chute bottom cause dynamical instability failure is improved,which enhances the ability of the bottom plate of the chute to resist the action of the flow of water vibrates.(4)In order to obtain the economical and rational arrangement of the overflow CFRD discharge chute anchor,the dynamic response analysis of the verflow CFRD discharge chute anchor under the flow of water vibrates is carried out based on the time domain analysis method.The uniform design method is used to study the sensitivity of anchor design parameters(laying ?distance L,laying length L,diameter D).The results show that the dynamic response of the overflow CFRD discharge chute anchor and the response peak of the river along the dam foundation to the dam foundation are gradually reduced,and the effect of the flow of water vibrates on the bottom plate of the overflow CFRD discharge chute is the most obvious.There is a significant order in the influence of anchor design parameters((laying distance,laying length,diameter)on the choke flow vibration performance,that is,the laying distance of anchors have the greatest influence on the laying distance of the anchors,followed by the length of the anchors and the minimum diameter of the anchors.