Research On Equivalent Load Identification And Vibration Reduction Of Centrifugal Water Pump

With the rapid development of the marine industry,the low-noise ship is the future trend.Since various types of mechanical and electrical equipments in auxiliary system are the main vibration sources,it is of crucial significance to perform the investigation on the control of vibration and noise of mechanical and electrical equipments.One of the key technology for equipment vibration and noise reduction is to obtain the accurate excitation source characteristics.It is often difficult to directly measure the dynamic loads due to the limitation with the practical structure and installing conditions of equipments.For the evaluation method of typical excitation force in mechanical and electrical equipments,the assessment error is relatively large.Then,the effective way to obtain the excitations is load identification technology,i.e.,determining the external load of the system according to test responses and vibration characteristics.As for the centrifugal pump group,the optimization of electromagnetic,fluid and rotator excitations is another key technology for the vibration and noise reduction for equipments.Although a lot of research has been performed on the excitation mechanism of motor,centrifugal pump and rotator systems,as well as their optimization,little work has been done to investigate the quantitative relationship between the excitation source and vibration response with the context of vibration transmission path.In this dissertation,the research was conducted from the pump excitation force identification,transmission path and the excitation source optimizations,so as to reveal the nature of pump vibration,and to give suitable improvements easy for engineering achievement.The detailed work is on the following aspects:Three factors,i.e.,the identification method,the response measuring point selection and noise interference,have an important influence on the accuracy of frequency-domain load identification.And the influence relationship of the three factors was studied by the simulation and experiment.Composite condition number was used to determine the merits of the response of the measuring point in the load identification,to get the best and worst response combinations.For the combination,singular value decomposition,Tikhonov regularization method and iterative inversion method were used to identify a single point excitation and two excitations of the plate structure under different noise interferences.And then,the application scopes of three identification methods were analyzed.For the complex internal excitation source,the real load is difficult to be directly identified.In this context,with the transfer path characteristics of the excitation source,the concept of equivalent excitations was put forward,i.e.,the pump vibration responses caused by the equivalent excitations agreed with those caused by the real excitation source.The finite element model of the centrifugal pump group was established.Then the accuracy of the model was verified by the correlation between the test modes and simulation modes.After that,the positions of equivalent excitations were selected and the excitation forces were identified in frequency bands.Provided that the equivalent excitations were input,the pump transmission path was optimized and the optimal results were estimated.The air-gap magnetic density of motor was got by the multi-section equivalent calculation in the two-dimensional finite element method.By Maxwell stress method,the radial and tangential electromagnetic forces were solved.The result shows that the influence of tangential force on the pump vibration can be ignored.Through the comparison of the simulation and measurement of the pump foot vibration response,the correctness of the electromagnetic force is validated.As the high-frequency radial force was unusual large,considering the motor running behavior,optimization program,that the ratio and shape of the groove was modified to reduce the vibration of the electromagnetic excitation force,was put forward.CFD software was used to calculate the three-dimensional steady and non-steady-state value for the full passage of the centrifugal pump.Combined with the results of load identification,noise source characteristics and influencing factors of the fluid were analyzed.It was pointed out that the fluid pressure pulsation in the volute tongue region is the main fluid excitation source.The improvements for appropriate engineering applications were put forward to reduce the pressure pulsation.After the transmission path,electromagnetic and fluid excitations of the pump were optimized,experiments were carried out.Satisfactory results have been obtained.The correctness of the identification through equivalent excitations,as well as the accuracy and effectiveness of the optimization for electromagnetic and fluid excitations,was validated.