Rearch On Vibration Mechanism And Reduction Methods For Structures And Surrounding Ground Under Excitations Generated By High Dam Flood Discharge

In the past several years,China's hydropower industry developed rapidly and a large number of high dams are either put into operation or under construction.Most of these projects are characterized by the common features of “high head,large flow rate,huge flood discharge power,narrow river valleys and complex geological conditions”,which makes the vibration problem induced by flood discharge is quite serious.The traditional researches mainly focus on the vibration safety of hydraulic structure itself.As more and more large-scale water conservancy and hydropower projects are put into operation,the flow-induced vibrations of dam foundation and surrounding ground and its environmental effects has gradually aroused the attention of the researchers.The flow-induced vibrations of hydraulic structures and surrounding ground are generated by a same and indivisible physical process.Firstly,the hydraulic structure vibrates under the flow excitation,and then the vibration transferred from the structures to the dam foundation and then to the surrounding field.In the dynamic coupling system consists of flow excitations,hydraulic structures,dam foundation and surrounding ground,all the probable vibrations of surrounding field are directly generated by the hydraulic structure oscillations.Moreover,the ground vibration,which has an adverse effect on industrial production,personal safety and common life of the residents,can be regarded as the dynamic response of the aforementioned coupled system.In this paper,the vibration mechanism and vibration reduction measures for the hydraulic structures and surrounding ground are mainly studied.The research progress on the vibration problems induced by flood discharge at home and abroad is firstly summarized.Then,the theoretical analysis and model test methods that are frequently applied for the vibration and fluctuation problems which respectively involved in the hydraulic structure and ground vibrations are introduced.Furthermore,the improved dynamic analysis approach and the vibration reducing measure for non-classical damping system are proposed;the vibration mechanism of the subsidiary structure installed on the primary structure is detailedly studied;the optimal operation scheme for damping vibration is proposed based on the hydroelastic model test of Wudongde project;and the application of the dynamic vibration absorber to reduce the structural vibration under flow-induced ground excitation is researched.The following research results are obtained:(1)Study on the characteristics and reduction measures for structural vibration induced by high dam flood discharge.Due to the non-orthogonal damping matrix,the complex modal decomposition method is firstly applied to decouple the multi-support structural dynamic equation.Then,considering the coupled damping term in the dynamic equation,the calculation formulae of the traditional complex multiple-support response spectrum(CMSRS)method are re-deduced.The improved CMSRS formulae describe the correlations between the modal responses under different decoupled excitations more comprehensively than the traditional formulae.Therefore,the improved formulae can calculate the dynamic response of the complex non-classical damping system more accurately,and the vibration reduction effect of the coupled damper is further studied.(2)Study on the mechanism of high dam flood discharge induced accompanying vibration of the subsidiary structures equipped on dam.Firstly,the special phenomenon that the gate vibration of the Jinping arch dam decrease with increasing opening ratio is investigated based on the prototype test data.A simplified theoretical model to analyze the dynamic response of the subsidiary structure which is installed on the primary structure is proposed on the basis of the traditional passive vibration absorber theory and the dry/wet mode numerical analysis of related structures.In the aforementioned theoretical model,the more complex load and damping conditions are considered and the research object is transformed from primary structure to subsidiary structure.The analysis results indicate that during the flood discharge process,the accompanying vibration of crest orifice gate on Jinping high arch dam is caused due to the mid-level outlet gate vibration.Moreover,the reason for the reduction of crest gate vibration with the increase of its opening ratio is clarified.(3)Study on characteristics of ground vibration induced by high dam flood discharge and the optimal operation scheme for ground vibration reduction.According to the hydraulics and structural dynamics similarity conditions as well as the physical dimensions of arch dam and plunge pool in Wudongde project,the hydroelastic model is designed and constructed.The effects of different operation schemes on the vibrations of bottom and slope bedrock are investigated based on the physical model test.Comprehensively analyzing the test results and considering the different discharge levels,the optimal operation scheme of Wudongde arch dam is proposed to reduce the flow-induced structure and ground vibrations.(4)Study on structural amplification effect on high dam flood discharge induced ground vibration and damping measures for structure vibration under ground excitation.According to theoretical analysis,a general characteristic of the ground vibration induced by high dam flood discharge is drawn that the dominant frequency ranges over several narrow frequency bands,which is verified by prototype test data.Nonlinear base isolation is used to reduce the structure vibration under ground excitation and the low-frequency resonance problem does not need to be considered due to the aforementioned excitation characteristics,which significantly facilitate the isolation design.Considering the nonlinearity of the base isolation,the probability analysis approach is improved to calculate its dynamic response.Moreover,the effectiveness of proposed approach is verified by numerical examples.In summary,the hydraulic structure and ground vibrations induced by high dam flood discharge are the different stages of the same physical process.The foundation and ground vibration is always directly caused by the vibration of hydraulic structures.In order to research the vibration mechanism and reduction method of the ground vibration,the hydraulic structure vibration should be detailedly analyzed in advance.Moreover,both the vibration attenuation of the hydraulic structure and surrounding ground can effectively reduce(or even avoid)the adverse environmental vibration.The mechanism and reduction measures for the vibrations of hydraulic structures and surrounding ground studied in the present paper are beneficial for the further study of the vibration problem generated by flood discharge,and provide a scientific basis for the reasonable choice for the reduction measures of structure and ground vibrations.Therefore,the researches involved in this paper have an important practical significance.