Tuned Mass Dampers Based On Symmetrical Combined Air Springs

Semi-active tuned mass damper(SATMD)is a kind of small power consumption,good effect of shock absorption technology,most of the research is variable damping,this paper is a variable stiffness type.This variable stiffness SATMD's elastic component uses a symmetrical combined air springs(SCAS).This SCAS is made of two identical pistons air springs which are mirror symmetrically connected.By studying the piston SCAS,the stiffness is symmetrical about the equilibrium position and exhibits a hardening phenomenon,and its stiffness and stiffness nonlinearity are related to the initial global volume,the initial internal pressure,the piston area and the variable index n in the Gas State Equation.In this paper,the dynamic characteristics of TMD based on SCAS are studied.It is found that the performance of SCAS-TMD can be the same as that of single linear TMD by selecting the parameters of SCAS under the harmonic excitation.However,due to the non-linear stiffness TMD is sensitive to the excitation characteristics,even it may fail completely under a complex excitation.But the problem can be solved by improving the linearity of the SCAS stiffness.The feasibility of SCAS-TMD variable stiffness is studied by shaking table experiment.We used cystiform air spring with no auxiliary reservoir for the experiment,the air spring dynamic stiffness linearity is relatively good.We found the static stiffness of the SCAS based on the air spring is almost linear by static loading experiment.The effect of the initial working pressure on the static stiffness is almost linear and the stiffness-pressure formula is obtained.In this paper,we studied a simplified model,in which the stiffness of the main structure is zero.And the TMD's relative amplitude,phase and the amplitude,average power of the harmonic excitation are observed by keeping the vibration frequency and amplitude of the main structure constant.The results show that the TMD's relative phase lags ? / 2 when the relative amplitude of TMD reaches the maximum.And the amplitude and the average power of the excitation is also the maximum,indicating that TMD is in the best state.However,the dynamic stiffness obtained by the static stiffness-pressure formula is generally higher than the equivalent linear model's value.Therefore,the formula is modified based on the assumption that the nonlinearity of the dynamic stiffness is weak.And the accuracy of the new formula is so high.Shaking table experiments show that SCAS-TMD is feasible as variable stiffness SATMD.Stiffness control can adopt frequency tracking method,phase control method,relative amplitude method maximization method and so on.