Study On Dynamic Characteristics Of Semi-active Periodic Vibration Isolation System For Power Machine

Power machine is widely used in vehicle engineering,aerospace,ship engineering and other fields.The vibration and noise generated during operation is harmful for the equipment safety and external environment.Vibration isolation is one of important means to reduce the vibration and noise.A vibration isolation system through good design can improve the comfort,for vehicle driver and passenger,and the service life,for the vehicle.Passive vibration isolation technology is usually used in the vibration isolation system due to its simplity of adopted structure.However,its utility of vibration isolation is limited.In contrast,semi-active vibration isolation technology can control wide-band vibration effectively,especially for low-frequency vibration.In addition,a periodic structure appropriately designed can reduce vibration effectively in a specific frequency band because of its good capacity to attenuate elastic wave(band gap characteristics).Therefore,in this paper,a new technology combining semi-active vibration isolation system with a periodic structure was proposed,accounting for their aforementioned merits.Profound studies were then conducted on nonlinear dynamic characteristics and control strategy of the proposed system,and influence law of the main parameters of the system.The results obtained can provide theoretical basis and guidance to apply the semi-active periodic vibration isolation technology in the field of the vibration isolation of power machine.In this paper,the mechanical properties of magneto-rheological(MR)damper were tested,and its forward and reverse mechanical models were established using MATLAB.The dynamic equations for one-stage and two-stage semi-active vibration isolation systems of power machine were established based on improved Bingham model.Analytical and experimental methods were applied to study the main resonance characteristics of force transfer and displacement transfer in vibration isolation system,and explore the response characteristics of the semi-active vibration isolation system.The results obtained clarified the influence law of main parameters,such as damping coefficient,control force and zero force velocity of MR damper,on the main resonance characteristics of the vibration isolation system.Numerical simulation and experiment were also carried out to study the vibration isolation characteristics of the two-stage periodic vibration isolation system of power machine,and to clarify the influence of forms of the periodic structure on the performance of vibration isolation.A semi-active periodic vibration isolation technology of power machine was proposed accouting for the excellent performance of vibration isolation in low frequency resulting from the semi-active control technology,and the advantages of band gap characteristics in medium and high frequencies from the periodic vibration isolation technology.Simulation and analysis were then performed on the performance of vibration isolation of the designed system,using ADAMS / Simulink,and the optimal control strategy of such system was determined.The main research contents and work are as follows:(1)Mechanical model of MR damper.The dynamic characteristics of MR damper were tested,via a testing machine of material performance,in order to reveal the influence of control current and excitation characteristics on the dynamic characteristics of MR damper.Based on the test results,various kinds of forward mechanical models were constructed for MR damper.The calculation accuracy and applicability of each kind of model were validated through performing error analysis on model-predicted and experimental results and generalization verification.An inverse mechanical model were constructed for MR damper,using BP neural network technology.The weight and threshold of the inverse mechanical model were optimized,via genetic algorithm,to determine the nonlinear relationship of current and output force with response.The control model was determined for the MR damper,based on the BP network forward and GA-BP reverse mechanical models.(2)Study of nonlinear dynamic characteristics of one-stage semi-active vibration isolation system.Improved Bingham model was used to describe the mechanical characteristics of MR damper,and dynamic equation of one-stage vibration isolation system considering the influence of foundation mass was established.The main resonance characteristics of the vibration isolation system were studied,under different excitation conditions,through the average method.These characteristics included force transmissibility of the vibration isolation system due to excitation of mechanical force,and displacement transmissibility of the vibration isolation system due to excitation of displacement of the foundation.The obtained theoritical solution was compared with the numerical result.Meanwhile,experiments were carried out on a one-stage semi-active vibration isolation system to explore the influence of control current and excitation parameters on the vibration transmission of the vibration isolation system.The results showed that the analytical and numerical results are in good agreements.In addition,increasing the mass of foundation can reduce the natural frequency of system and efficiency of vibration reduction in vibration isolation area,and increasing the damper control force and zero force speed can improve the performance of vibration isolation.The increase of damping coefficient can improve the efficiency of vibration isolation in the resonance area but reduce it in the vibration isolation area.(3)Study of nonlinear dynamic characteristics of two-stage semi-active vibration isolation system.The dynamic equations of semi-active two-stage vibration isolation system excited by single machine and double machines were established,based on the improved Bingham model,yielding analytical solution of the main resonance of the vibration isolation system.In view of force transmissibility that was regarded as the key factor to evaluate the system performence,the influence of characterics parameters of MR damper on the vibration isolation system was studied.It was also studied that optimal control strategy affected the efficiency of vibration isolation of a two-stage semi-active vibration isolation system.The results showed that the increases of damping coefficient and zero force velocity can effectively reduce the rate of force transmission of first vibration mode and promote the vibration isolation of the system in the main resonance region.For the resonance regions of divese vibration modes,the influence law of control force on the vibration isolation effect of the system varies with each other.The damping coefficient and control force affect the force transmission more serious than the zero force velocity.In the resonance frequency band,the force transmitted from engine to foundation diminishes obviously if the optimal control strategy is adopted,and the efficiency of vibration isolation in the whole frequency band of the vibration isolation system is also improved.(4)Study of dynamic characteristics of two-stage periodic vibration isolation system.The periodic topological method was utilized to deisgn the intermediate structure with the same mass(three periodic structures of brick,square and inclined columns,and one frame structure),for two-stage vibration isolation system.Simualtaion and analysis of dynamic characteristics were performed on a diesel engine with two-stage periodic vibration isolation system in order to study the influence of periodic structure of intermediate mass on the performance of vibration isolate of the system.The tests of relevant vibration isolation were conducted via a testing system of two-stage periodic vibration isolation comprising periodic structure of inclined square column with a reduced cycle number.In the two-stage vibration isolation system,a local resonance element structure was designed to further improve the efficiency of vibration isolation of the periodic structure.The results showed that the larger the structural rigidity,the higher the first natural frequency of the vibration isolation system,resulting in moe scatted modal frequencies under various vibration modes and avoiding the influence from the disturbance frequency and its frequency multiplication.It is almost the same,under the low frequency range,in the efficiency of vibration isolation for four kinds of two-stage periodic systems.However,it is better in the periodic systems than the frame structure,under the medium and high frequencies greater than 200 Hz.The best one results from the inclined square column periodic structure.Moreover,such system has a better low-frequency band gap after the local resonance structure is introduced,and then the efficiency of vibration isolation in the high-frequency band is also improved.(5)Study of dynamic characteristics of two-stage semi-active periodic vibration isolation system.ADAMS/Simulink was used to perform joint-control simulation of the performance of vibration isolation of two-stage semi-active periodic vibration isolation system of power machine with inclined square column periodic structure.In-deep studies were conducted,for the vertical motion of the system,to explore the influence of three different control strategies,such as switch control,PID control and fuzzy PID control,on force transmissibility characteristics of the system.The results showed that it can reduce the force transmissibility of the vibration isolation system significantly in the low frequency if the semi-active control was applied in the two-stage periodic vibration isolation system.In particular,the fuzzy adaptive PID control can make the efficiency of vibration isolation best,and lower force transmissibility obviously,with good adaptability.