Study On Frequency Model And Oscillation Modes Of Self-resonating Water Jet Under Confining Pressure

With the increasing demand of mineral resources and the decreasing of land mineral resources,deep-sea mineral resources exploitation has become a major development demand of the country.As the key technology in deep-sea resources exploration and development equipment,jet technology plays an important role in the tuberculosis collection system,among which,the self-resonating jet has strong oscillation characteristics and cavitation effect,and can significantly improve the erosion effect under high confining pressure.However,under the condition of deep-sea high-confining pressure,the frequency property of the self-resonating jet are difficult to predict,high frequency oscillation and erosion behavior have not been studied in depth.The relationship between the existing theoretical model and the actual jet dynamics is not strong,which can not guide the actual impact erosion behavior of the jet,which strictly restrict the application of the self-resonating jet under confining pressure.In order to solve the key problems in the research on the frequency property and erosion behavior of self-resonating jet under confining pressure,in this paper,the acoustic natural frequencies of the device are carried out theoretically firstly,and theoretical models are established based on different modeling methods.Through the impinging experiment under high confining pressure,the full spectrum structure of self-resonating jet is obtained,and the influencing factors and variation rules of self-excited frequency of jet are revealed.Finally,the frequency model of the actual jet is established,and the high-frequency oscillation modes of jet are analyzed.Based on the erosion experiment of self-oscillating jet under high confining pressure,the jet's erosion patterns are explored,and the influencing factors and changing rules of jet erosion behavior as cavitation number and impinging distance varies are further revealed.The main research contents are as follows,(1)In order to solve the problem that the theorectical model is too simplified,the theoretical model of the system device is studied.Firstly,the acoustic natural frequency of the device are analyzed theoretically.Based on the resonance characteristics of the device structure,the mathematical models of the pipe network structure and the nozzle resonator are established by using different modeling methods,respectively,and the broadband property and frequency range of the device are verified.(2)In order to solve the problem of disconnection between the theoretical model and the dynamic characteristics of the actual jet,the frequency spectrum of the actual jet are studied.The full spectrum structure of the jet is obtained through the jet impinging test under confining pressure and based on the signal analysis method.The frequency property of the self-resonating waterjet includes low-frequency pulsation and high-frequency oscillation,which are induced by fluid disturbance in pipe network and vortex-induced-vibration at nozzle outlet,respectively.The influencing factors and application conditions of these two types of oscillation are quite different.The full frequency spectrum provides a theoretical support for further study of the frequency property of the self-resonating jet under confining pressure.(3)On the basis of obtaining the full frequency spectrum of the self-resonating jet,the high-frequency oscillation characteristics of the jet are mainly studied.Through the analysis of the theoretical formula of the jet oscillating frequencies and the related factors,the important role of the Strouhal number in the calculation of the jet oscillating frequency is determined.According to the "triad resonance"theory,the fundamental frequency and the according Strouhal number of the jet are determined.By studying the influence factors and variation rules of Strouhal number,the relationship between the Strouhal number and the cavitation number is obtained.Based on the fluid similarity theory,an estimation model of the self-excited frequency of the actual jet is established,which lays a theoretical foundation for the oscillation mode analysis of the self-resonating jet.(4)Based on the estimation model of the self-excited frequency,the jet oscillation modes are studied,and the feasibility of high frequency oscillation mode modulation is explored.Firstly,according to the resonance characteristics and theoretical model of the jet device,the nozzle structure is designed to produce specific acoustic harmonics.The working parameters of the jet are modified to make the jet oscillation frequencies match with different acoustic harmonics of the device to produce a variety of oscillation modes.The mechanism and oscillation effect of subharmonic resonance and fundamental resonance are mainly analyzed,the feasibility of effective modulation of jet oscillation mode is explored.(5)On the premise that the oscillation modes of self-resonating jet can be modulated,the erosion behavior of self-resonating jet is studied based on the erosion experiments,and the variation law of the jet's erosion effect with environmental parameters is obtained.Three erosion modes of self-resonating jet are defined,and the evolution law and generation mechanism of different erosion modes are studied.On this basis,the influence of nozzle downstream boundary structure and target tilt angle on jet erosion behavior under confining pressure is studied,and the influence law of various factors is obtained,which provides experimental reference for cavitation erosion of self-resonating jet under confining pressure.