Research On Vibration Reduction Performance Of Adjustable Periodic Composite Structure

Traditional vibration reduction measures have shown great limitations in the face of complex and variable low-frequency vibration environment.Therefore,it is particularly important to develop new vibration reduction measures.The periodic structure with selective transmission of elastic waves provides a new direction for the development of new low-frequency vibration reduction measures.When the elastic wave propagates in a periodic structure and the frequency is within the band gap,the elastic wave propagation is prohibited.This unique characteristic of the periodic structure shows great potential applications in vibration and noise reduction.How to obtain the low band gap,increase the band gap width,and realize the band gap tunability are the keys to the application of periodic structures in the field of vibration and noise reduction.This paper takes the common structures in civil engineering as the research object,designs and studies the band gap characteristics of different periodic structures based on the basic theory and research methods of periodic structures.By changing the geometric parameters and material parameters of the periodic structure,we analyze effects of the external bias fields such as prestress and magnetic fieldson the band gap,achieve the adjustable band gap,and obtain the band gap with the lower initial frequency(<100 Hz).The analysis methods and conclusions in this paper can provide a reference for the design of new damping technology in civil engineering.The main research works are:(1)A periodic circular tunnel structure is designed.The bending wave propagation characteristics of the periodic circular tunnel structure are studied,the effects of the stiffness of the elastic foundation and material parameters on the band gap structure are discussed,and the regulation effect of the prestressed external field on the band gap characteristics is analyzed.The calculation results show that adjusting the axial prestress can change the effective bending stiffness of the structure,and then realize the regulation of the band gap width and frequency of the structure.As the axial tensile stress increases,the width of the band gap decreases,but the frequency increases.The reverse will occur when axial compressive stress is applied.In addition to the band gap generated by the periodicity of structure and material,the application of a periodic external field to a periodic circular tunnel structure can also generate and regulate the band gap.As the periodic prestress increases,the first band gap width decreases,the second band gap is increasing.(2)Based on the traditional vibration isolation barrier,an intelligent periodic vibration isolation barrier with piezoelectric effect is designed.The shear wave propagation characteristics of intelligent periodic isolation barriers are studied,the influence of geometric parameters and material parameters of the isolation barriers on the band gap are analyzed.The regulation effect of the prestressed external field on the band gap characteristics is discussed.It is found that the prestress has a clear regulation effect on the band gap.As the tensile stress increases,the band gap increases;as the compressive stress increases,the band gap decreases.Although compressive stress has an enhanced effect on vibration isolation performance,its effect is not obvious,and its influence is mainly reflected in the regulation of the band gap frequency.(3)The propagation characteristics of bending waves in a periodic steel-hybrid composite beam structure are constructed and studied.The effects of positive and negative external capacitor shunt circuits on the band gap structure and its vibration damping performance are discussed.It is found that the regulation effect of the shunt circuit is attributed to the regulation of the equivalent elastic modulus.The external positive capacitor has limited adjustable band gap due to the small range of adjustable equivalent elastic modulus.The external negative capacitor has a large adjustable equivalent elastic modulus and can be changed between positive and negative values.The effect on the regulation of the band gap is obvious,and the band gap with a larger control range can be obtained.When the equivalent bending stiffness of the composite beam is positive,the vibration damping performance decreases as the equivalent bending stiffness increases,otherwise,if the equivalent bending stiffness is negative,the vibration damping performance decreases as the equivalent bending stiffness decreases.(4)The propagation characteristics of Lamb waves in a double-clad slab structure are designed and studied.The influence of physical parameters on the band gap is discussed,the regulation effect of the bias magnetic field on the band gap characteristics is analyzed.It is found that the Lamb wave has multi-mode characteristics.When the Lamb wave propagates in the structure,a unique low-frequency mode band gap appears,which is of great significance for lowfrequency vibration reduction.The applied magnetic field can cause the shear modulus of the magnetorheological elastomer to change,so that the position and width of the band gap can be adjusted.With the increase of the magnetic field intensity,the band gap position shows an upward trend,however,the band gap width changes little.The influence of the external magnetic field on the band gap is mainly reflected in the regulation of the band gap position.