Research On Hydraulic Beat Mechanism And Dynamic Health Monitoring Method Of Flood Discharge Structures

The height, discharge, flood-discharge power of hydraulic engineering in China isin a leading position of the world. With the influence by high velocity flow, water-airtwo-phase flow and waterflow-structure coupling, the flow pulsating pressure is verylikely to result in structural vibration or even fatigue destruction of flood dischargestructures. It is an important guidance for design and safe operation of flood dischargestructures to research flow-induced vibration mechanism, time-frequency analysismethod for vibration responses, filtering method, working state identification methodand dynamic health monitoring method. The following three main areas are studied:Firstly, research on hydraulic beat mechanism of flood discharge structures. Thecharacteristics of the flow pulsating pressure on the flood discharge structures aresummarized, and then time-domain analysis, spectrum analysis, time-frequencyanalysis method are utilized to study the structural vibration responses induced byimpact load, harmonic load, wind-band random load and white noise load,respectively. Based on the prototype tests, flow-induced vibration model and finiteelement analysis, the relationship among flow discharge excitation, hydraulicstructures’ dynamic characteristics, and vibration response has been studied. Then thehydraulic beat phenomena of flood discharge structures has been put forward andexplained.(1) Series model tests of flow-induced vibration have been built, andcorrelation analysis, spectrum analysis, and the time-frequency analysis method areapplied to study the vibration testing data. According to vibration characteristics ofdifferent models induced by flow load, this random resonance responses phenomenonhas been researched, and a new concept “hydraulic beat” has been put farward.(2)The flow-induced vibration responses from each measuring point arranged on Ertandam have been analyzed. It can be concluded that the hydraulic beat phenomena, andeven beat vibration will occur in the closely frequency structures like high arch dam.(3) Based on the hydraulic beat theory and prototype tests for Ertan, Shuhe, Binglinghydropower station, the formation mechanism of hydraulic beat and flow-inducedvibration for flood discharge structures have been summarized.Secondly, study on the methods for filtering and working state identification offlood discharge structures based on time-frequency analysis. There are two difficultproblems for modal parameters identification under ambient loading: the first one isthat the excitation load must satisfy the characteristics of white noise, and the second is that the identification range is restricted in time domain or frequency domain.Aimed at these issues, the methods for filtering and working state identification basedon time-frequency analysis are provided.(1) The time-frequency analysis methodbased on HHT is utilized to extract the resonant response, which is closely related tothe structural modal parameters. Then resonant responses are used to working stateidentification of flood discharge structures, and the adverse effect caused by forcedvibration response will be avoided.(2) According to the characteristics of IMFsdecomposed from white noise, the calculation method of noise standard deviation ineach IMF is studied, and the filtering method based on EMD and Wavelet-threshold isimproved.(3) The methods based on time-frequency analysis studied in the paper areapplied to the operational modal parameter identification of Ertan arch dam andYingxiuwan hydropower station sluice respectively. The results show that thesemethods have good applicability in vibration responses analysis of flood dischargestructures.Thirdly, the dynamic health monitoring method for flood discharge structures. Inview of some shortcomings existed in health monitoring method, dynamic damageindexes and data fusion decision method are researched in this paper.(1) The dynamicdamage indexes based on vibration waveform, standard deviation, time series model,normalized change ratio of frequency, time-frequency analysis, coordinate modalcriterion, mode shapes and frequencies, mode curvature have been summarized, theindex system of dynamic health monitoring has been established for flood dischargestructures.(2) Due to some issues in the combination rule of D-S evidence theory, animproved method based on Jousselme distance and evidence reliability is put forward.The results of damage model test under flood discharge excitation demonstrates thatthe accurate decision can be obtained based on few evidences, the errors originatedfrom sensor and noise are avoided, and the influence by the wrong evidence iseffectively reduced. The method mentioned in this paper is suitable for damagelocation of dynamic health monitoring.(3) According to working characteristics ofguide walls, and the analysis results for stability, sensitivity, anti-noise of HHTmonitoring indexes, a new monitoring method for guide wall has been put forward.