Reaserch On Global And Fine Identification Theory For Hydraulic Structural Damage

The structural health monitoring and damage detection become increasinglyimportant as the scale of hydraulic structures increases and the working conditionsimprove. Firstly, research on optimal sensor placement (OSP) has become a veryimportant topic due to the need to obtain effective testing results from limited testresources. However, the existing methods for OSP are often difficult to meet theneeds of hydraulic structural health monitoring, because part of or most part of thehydraulic structures are always underwater and the test requirements are various.Secondly, modal parameter identification is the follow-up work of vibration signalmeasurement, and it is also the necessary means for damage detection. The noiseaffects the hydraulic structures under ambient excitation obviously, so the quality ofthe signal is difficult to guarantee. Because the accuracy of modal parameteridentification directly affects the accuracy of damage detection, it is very critical tofind an efficient method which is suitable for the modal parameter identification ofhydraulic structures under ambient excitation. Thirdly, early damage detection notonly improves safety and reliability of structures but also reduces maintenance cost.However, damage detection is difficult to implement in hydraulic structures underambient excitation because of the uncertainty of ambient excitation and the limitationof sensors.Based on the above three reasons, this study considers the global dynamiccharacteristics of hydraulic structures, uses the vibration responses of hydraulicstructures under ambient excitation, emploies the OSP technique and signalprocessing technique to ensure the accuracy of modal parameter identification,extracts the features which are sensitive to structural damage, and achieves theaccurate diagnosis for hydraulic structural damage. Without affecting the normaloperation of hydraulic structures, the entire methodology can solve the difficulties indamage detection of hydraulic structures, especially the underwater parts, and can fillup the lackness of existing theoretical methods. There are five innovative points in theglobal and fine identification theory for hydraulic structural damage: (1) The OSP methods of hydraulic structures for various dynamic testrequirements. In order to meet the various test requirements for hydraulic structuresunder ambient excitation, this study dissects the limitations of typical effectiveindependence (EfI) method, introduces the energy coefficient, distance coefficient andspatial correlation index to improve the EfI method comprehensively, and pioneersthe triaxial effective independence driving-point residue (EfI3-DPR3) methodsatisfying the test requirements under strong noise environment and the distancecoefficient-effective independence method and spatial correlation-effectiveindependence method which do not rely on the finite element mesh generation. Theeffectiveness and applicability are comprehensively verified in the health monitoringof the hydraulic structures, such as the hydropower house and dam.(2) The OSP methods for hydraulic structures based on novel particleswarm optimization (PSO) algorithms. To further improve the global optimizationeffectiveness of intelligent algorithm dealing with OSP problems of high dimensions,this study first proposes an integer-encoding multi-swarm particle swarm optimization(IMPSO) algorithm and a hybrid intelligence algorithm of clonal selection algorithm(CSA) and discrete particle swarm optimization (DPSO), optimizes the fitnessfunctions considering the modal observability and information independence, andthen assures the efficiency and reliability of intelligent algorithms when dealing withOSP problems of high dimensions.(3) The swarm intelligence modal parameter identification method based onnatural excitation technique (NExT) and order determination of singularentropy under ambient excitation. The method empolies the wavelet de-noisingtechnique to improve the quality of signals, uses NExT method to calculate theimpulse response function, ensures the order of singular entropy for the impulseresponse function, and finally obtains the structural modal frequency and dampingratio based on a novel mutation particle swarm optimization algorithm. The method isvery suitable for the modal parameter identification of hydraulic structures underambient excitation due to fewer parameters, high identification accuracy andinsensitivity to the noise.(4) The global damage identification method for hydraulic structural cracksbased on modal frequency. A new damage detection method, which employs a realencoding hybrid algorithm of clonal selection and particle swarm optimization tooptimize the modal frequency index, is proposed for guide wall structures. The proposed method only requires low modal frequency, thus making the methodsuitable for nondestructive dynamic damage detection of large hydraulic structuresunder ambient excitation. Taking a guide wall structure as an example, results showthat this method has advantages in the global searching performance and identificationaccuracy. The proposed method is effective and can be applied in many types of largehydraulic structures.(5) The global and fine identification theory for hydraulic structural damageby the OSP technique, modal identification method and strain modal testtechnique. This study proposes a new damage detection method that employs the realencoding multi-swarm particle swarm optimization algorithm and fitness functionsevolved from strain modes to find the optimal match between measured and simulatedmodal parameters and to determine the actual condition of structures. The proposedmethod merges the OSP technique with signal processing technique, requires lowfrequency modes and incomplete modes and does not require mass normalization ofparameters, thus making the method suitable for nondestructive dynamic damagedetection of large hydraulic structures under ambient excitation. The efficiency of theproposed method was analyzed by using different noise levels and sensor numbers.Results show that the proposed method is effective and can be applied in many typesof hydraulic structures.