Research And Optimization Of A Semi-active Dynamic Absorber With Variable Frequency And Variable Damping

Vibration widely exists in civil engineering and mechanical industry.The requirements of vibration absorbers are different with different environments.Therefore,it is an urgent problem to construct a dynamic vibration absorber with nonlinear characteristics that can meet a variety of working conditions.Based on shape memory alloy(SMA),smooth discontinuous(SD)vibrator and magnetorheological fluid(MRF),a semi-active vibration absorber with variable frequency and variable damping is constructed and optimized.The results show that the vibration absorber designed in this paper can be used for vibration reduction of variable cross-section beams,buildings and other working conditions.The main contents are as follows:In this paper,a two degree of freedom system with a linear vibration absorber is established.The working principle and the optimal design formula of the vibration absorber are studied through its dynamic equation,which provides a theoretical premise for the optimization of the vibration absorber.This paper introduces the constitutive models of SMA and MRF,and provides the theoretical basis for the analysis of SMA spring and MRF.Based on SMA,SD and MRF,a semi-active vibration absorber with variable frequency and damping is designed.The variable frequency and damping function of the absorber can be realized by changing the current intensity.By analyzing the related characteristics of SMA spring,then introducing it into SD oscillator system,the influences of temperature on the smooth parameters,restoring force and stiffness of the system are analyzed.Combined with the relationship between temperature and current,the natural frequency and stiffness of the system can be controlled by the current.The relationship between the damping provided by MRF and the current is discussed.A coupling system of variable cross-section beam bridge with the additional design absorber is established.The numerical results show that the vibration control of the absorber can be realized under different conditions by changing the current intensity.Aiming at the vibration absorber with nonlinear stiffness and damping proposed in this paper,based on the measurability and practicability of acceleration,a new force transfer rate for the evaluation of shock absorbers is proposed.The index is sensitive to the change of parameters and feasible,which is beneficial to the practical application of engineering.In order to reflect the adaptability of the designed absorber,the variable cross-section girder bridge is replaced by the building structure,a coupling system with the designed absorber is established,and the sensitivity of the new force transfer rate to the system parameters is studied.The feasibility of the new index is proved by comparing the energy method with the evaluation method proposed in this paper.The vibration absorber is optimized in two steps.The time history diagram,phase diagram,Poincaré section diagram and spectrum diagram are used to analyze the response of the main structure in the time-domain.The results show that the main structure achieves a single period state with small energy and stable or strong law of small amplitude in a wide range of external excitation frequency.Hence,the absorber can achieve wide-band damping performance by changing the current intensity,and the two-step optimization is effective.Finally,the research results show that the semi-active vibration absorber with variable frequency and variable damping designed in this paper can adapt to a variety of working conditions,such as variable cross-section beam bridge or building,just by changing the current intensity.After the two-step parameter optimization,the designed absorber can be adjusted less frequently over a wide frequency range to achieve a better damping effect,providing a new method for the optimal design of the shock absorber.