Study On Dynamic Characteristics Of Periodic Structure Double-layer Vibration Isolation System For Marine Auxiliary Machines

The existing auxiliary equipment of ships adopts the traditional double-layer vibration isolation mode to perform better vibration damping in mid-high frequency range,but the damping effect in the low frequency range is limited.With the new ship stealth performance requirements increase,vibration isolation equipment performance requirements greatly improved,especially in the low-frequency vibration isolation effect.The measures taken to improve the vibration isolation performance of the traditional double-layer vibration isolation system by improving the performance of the vibration isolator,optimizing the structure of the intermediate body and the base,and optimizing the arrangement of the vibration isolators are limited.It has been found in the long-term research that the elastic wave has frequency band gap characteristic when propagating in the periodic structure.In the absence of external energy access,the periodic structure can block the vibrations in the band gap frequency range.Based on the band gap characteristics of periodic structure,this paper designs an intermediate mass structure with good band gap performance in low frequency band and applies it to the double-layer vibration isolation system of marine auxiliary machinery.On the basis of the traditional double-layer vibration isolation system,combined with the periodic structure to further enhance its damping effect in the low frequency band in order to meet the requirements of new stealth performance.In this paper,R175-type diesel engine as the object,through the theoretical calculation R175 diesel engine design of traditional double-layer vibration isolation system.Based on the size and quality of the intermediate mass of the traditional two-layer vibration isolation system,the periodic intermediate mass structure of brick,straight square column and skew square column was established respectively by the method of periodic topology.The establishment of R175 diesel engine in ANSYS adopts the traditional double-layer vibration isolation method and the finite element model of double-layer vibration isolation system with periodic structure,in which the periodic structure adopts three forms of brick,straight square column and skew square column,and modal harmonic response analysis.The results of modal analysis show that the modal distribution of the three kinds of double-layer vibration isolation system with periodic structure is sparse.The modal analysis of the middle mass structure of traditional,brick-type,straight square column and skew square column is carried out.Through harmonic response analysis found: four structures in the 0-150 Hz range,the vibration isolation effect is basically the same;Within 200-700 Hz,the vibration isolation effect of the three-cycle double-layer vibration isolation system with intermediate structure is better than the traditional structure;Within 700-1000 Hz,the three periodic intermediate structures exhibit completely different vibration isolation characteristics: The brick-shaped periodic intermediate structure has the same vibration isolation effect in this frequency band as the traditional structure;The vibration isolation effect of the middle column of periodic column becomes worse and more resonance peaks appear;The vibration isolation effect of the middle structure of the skew square column period is obviously better than that of the traditional structure.In 140Hz-1000 Hz,the anti-vibration performance of the double-layer vibration isolation system with a skew square column intermediate structure is obviously better than the traditional structure,and there are two significant band gaps at 406-414 Hz and 790-819.5Hz,which accord with the periodic structure band gap characteristics Bragg scattering mechanism,can't achieve the "small size control of large wavelengths."A double-layer vibration isolation experimental system is established by reducing the number of cycles in the middle structure of the skew column.The vibration isolation system is analyzed through experiments,and the existence of the band gap characteristic of the periodic structure of the skew square column is verified.It also shows the correctness of the simulation method adopted in this paper.With the help of the local resonance theory of phonon crystal,the helical resonance element is added to the periodic structure of oblique square column based on the double layer vibration isolation system with oblique square column periodic structure.The harmonic response of the vibration isolation system is calculated by modal analysis.It is found that there are the same dense modes as the number of helical resonance elements,and the anti-resonance peak appears in the frequency domain of the dense modes.The lower the first order natural frequency of the spiral resonance element,the lower the dense mode frequency and the lower anti-resonance frequency of the system.Therefore,by designing the low frequency spiral resonance element structure,we add it to the periodic structure.It is a method to improve the low frequency vibration isolation effect of vibration isolation system.