Research On The Vibration Transmissibility Of Impedance Layered Structure Modulated On Magnetorheological Fluid

As a class of novel smart materials,magnetorheological(MR)fluid has a promising potential in the field of vibration control due to its liquid–solid conversion can be instantly changed and controlled through the application of external magnetic field.At present,the vibration control structures do not have great structural variability and parameter adjustability in the vibration transmission,so it can only be investigated for a specific structural device with fixed parameters,which is difficult to explain and verify the essence and mechanism of vibration transfer phenomenon.Therefore,in order to reveal the dissipation and blocking mechanism of vibration transmission,it is of great theoretical significance and engineering value to investigate the vibration transmissibility of modulating structures.In this paper,the impedance modulating structure constructed by MR fluid is mainly researched.The impedance modulating characteristics of MR fluid is analyzed in the external magnetic field.The monolayer and periodic impedance structure modulated by MR fluid are constructed,and the vibration transmissibility of above two constructed structures are theoretically studied and experimentally verified.The specific workings are listed as follows:MR fluid is proposed as a smart medium which property is controllable,and its impedance modulating characteristics is analyzed.Based on the theory of equivalent medium,the impedance analysis model of MR fluid in absence and presence of magnetic field are established.The impedance curves of MR fluid in the above two different states are obtained by numerical calculation.The results demonstrate that the impedance of MR fluid is proportional to the material density in the absence of magnetic field state,while it increases with the increase of magnetic flux density when the external magnetic field is applied.Compared with the impedance in the absence of magnetic field state,the impedance of MR fluid modulated by external magnetic field is more designable.The vibration transmissibility of monolayer impedance structure is investigated,which is modulated by MR fluid.A monolayer impedance structure is constructed by using the monolayer arranged electromagnet outside MR fluid to control its impedance.Based on the theory of biphasic porous media,the governing equations of elastic waves in monolayer impedance structure is established.The Helmholtz decomposition theorem is adopted to solve the wave equation,and the mathematical expressions of the propagation velocity,attenuation coefficient and vibration level difference of elastic waves are obtained.The effect of impedance parameters on the propagation velocity and attenuation coefficient of elastic waves are analyzed to clarify the propagation law of elastic waves.Meanwhile,with the vibration level difference used as the evaluation index,the effect of the change of impedance parameters on the vibration transmissibility of monolayer impedance structure are investigated.The curves of vibration level difference with different impedance parameters are obtained by numerical calculation.The results indicate that the vibration level difference increases with the increase of magnetic flux density and the electromagnet thickness,but when the magnetic flux density and the electromagnet thickness reaches up to 40 m T and 20 mm,the vibration level difference no longer increases with the increase of above two parameters;In addition,the vibration level difference increases with the decrease of the distance between the electromagnet and the excitation source.The results provide a basis for the investigation of hierarchical impedance structure modulated by MR fluid.The vibration transmissibility of periodic impedance structure is investigated,which is modulated by MR fluid.A periodic impedance structure is constructed by using the periodic layered electromagnet arranged outside MR fluid to control its impedance.Based on the transfer function method,the transfer model of elastic waves in the periodic impedance structure is established.After that,the transfer model is solved by standing wave method and discrete method,then the mathematical expressions of the propagation velocity,attenuation coefficient and vibration level difference of elastic waves are obtained.The effect of structural parameters on the propagation velocity and attenuation coefficient of elastic waves are analyzed to clarify the propagation law of elastic waves.Meanwhile,with the vibration level difference used as the evaluation index,the effect of the change of structural parameters on the vibration transmissibility of periodic impedance structure are investigated.The curves of vibration level difference with different structural parameters are obtained by numerical calculation.The results indicate that the vibration level difference increases with the increase of magnetic flux density and the number of periodic layers,but when the magnetic flux density and the number of periodic layers reaches up to 30 m T and 4 layers,the vibration level difference changes less with the increase of above two parameters.In addition,the characteristic frequency points of the periodic impedance structure move to the low frequency area with the increase of the periodic distance,and the change of the periodic distance has different attenuation effects on the transmission of vibration in different frequency ranges.The results provide a theoretical guidance for the layered design of MR fluid impedance modulating structure.The experimental research on the vibration transmissibility of impedance modulating structure is completed.An impedance layered structure device modulated by MR fluid is designed and fabricated,and corresponding testing platform of vibration transmissibility is built.The experiments of the vibration transmission in the monolayer and periodic impedance structures are carried out.The effects of different parameters on the vibration transmissibility of the above impedance structures are obtained,and the experimental results are compared with the theoretical results.The results demonstrate that the experimental curves of the vibration level difference of monolayer and periodic impedance structures at different parameters are consistent with the theoretical curves.The maximal vibration level difference of monolayer impedance structure measured by experiment can reach up to 31.94 d B,and the relative error with theoretical calculation result is 6.4%;The maximal vibration level difference of periodic impedance structure measured by experiment can reach up to 40.07 d B,and the relative error with theoretical calculation result is 8.5%,which shows that the experimental test results are in good agreement with the theoretical prediction results,thus fully verifying the correctness of the theoretical prediction model.The experimental results provide a reference for the application design and parameter optimization of impedance modulating structure based on MR fluid.