Dynamical Properties And Semi-active Control Of Dual-chamber Solid And Liquid Mixture Vibration Isolator

The solid and liquid mixture(SALiM)isolator is a kind of passive isolation device especially designed for low-band vibration isolation of heavy machines.The SALiM isolator consists of three main parts: compressible vessel,oil and certain number of elastic elements.The elastic element acts as elastic component of the isolator.The SALiM isolator can obtain satisfactory stiffness property by properly designed the material,structure and quantity of the elastic element.The SALiM isolator covers good capacity,low-stiffness property and negligible damping,which make it suitable for vibration isolation in high band.The SALiM isolator can function as a signal degree of freedom vibration system as well as an elastic component in multiple degree of freedom of system,which make it promising in the field of low-band vibration isolation of heavy machines.The SALiM isolator is good passive isolation device.Its stiffness and damping are almost constant,which makes it hard to deal with many harsh situations including wide-band excitation and external shocks.This article proposes a new design named as dual-chamber SALiM isolator based on the present work.The novel isolator adds an incompressible vessel(named as additional chamber)and a linking oil tube to the SALiM isolator(simply as main chamber).Just like the main chamber,the additional chamber is filled with the mixture of oil and elastic elements.So the dual-chamber isolator has lower stiffness.The linking oil tube serves as the damping component,the dissipation capacity of which can be simply designed by change its equivalent aperture.This article tries to investigate the stiffness and damping properties of the novel isolator by combining theoretical,numerical and experimental means.The dual-chamber SALiM isolator can be turned into a semi-active system by replacing the ball valve with an active valve group.Then,the isolator will get a variable stiffness and damping properties.At last,semi-active tests were carried out based on two newly designed control laws to verify the practicability of the semi-active isolation device.The primary coverage contributions of this paper are presented below.(1).the stiffness and damping model.The relation between the geometry deformation of the elastic elements and the oil pressure in each chamber,and the relation between the flow rate and pressure drop in the linking tube were established.The equations of motion of the vibrating system including a dual-chamber can be obtained by combining the above two relations.For simplicity,the nonlinearity caught by the elastic element was neglected and the fluid damping was replaced with the equivalent linear viscous damping.Then the nonlinear system was simplified into a linear one.In relating field,the dynamic stiffness and loss factor were derived based on the complex stiffness model,which can be obtained by converting the equation of motion to frequency domain using Fourier Transform method.In this article,the two degree of freedom of equation of motion was simplified into a single degree of freedom of equation of motion,based on which the equivalent stiffness and damping model can be obtained.(2).the stiffness and damping properties.The combination of theoretical derivation,numerical simulation and experimental test was adapted to investigate the stiffness and damping properties of the novel isolator.In the relating field,most researchers pay attention to the influence of the geometry parameters of the linking tube on the system’s stiffness and damping properties.Besides the above regularly discussed issue.Some new topic are introduced in this paper.(1)The boundary features of the equivalent stiffness and damping.The influence of various parameters including frequency,amplitude on the boundary features were discussed.The improvement methods for the dual chamber SALiM isolator were introduced based on the related conclusions.(2)The influence of the equivalent stiffness of the main chamber on the isolator’s stiffness and damping.The stiffness of a SALiM isolator can be easily designed by adjusting the quantity of elastic elements in the corresponding chamber.During the dynamic test,the quantity of the elastic elements of the main chamber was changed to analyze the effect of the equivalent stiffness of the main chamber on the system’s dynamic behaviors.(3)The dynamic test of the isolator was implemented both with sprung mass and without sprung mass.At first,the test without the sprung mass was carried out by a MTS system.The restoring force and displacement signals were recorded.And during the test,the excitation amplitude were changed to investigate the vibrating level on the system’s dynamic properties.The test of vibrating system including sprung mass was carried out with a vibration exciter and data acquisition equipment.Two liquid pressure sensors were added to the two chambers to record the real-time pressure signals,based on which the relation between the pressure drop and the flow rate in the linking tube can be derived.The acceleration signal and force signal were also recorded to identify the values of stiffness and damping at certain frequency point.The identification results were compared with the results obtained from the MTS system.In the relating field,people investigated the flowing capacity by recording the pressure drop in the linking tube when the flow rate is set to be constant,which is obvious not consistent with the piratical situation where the fluid oscillate in the linking tube.So the research results in this article is more convincing because all the analysis signals were obtained in vibration test.(3).the expansion of the dual-chamber SALiM isolator.The novel isolator can obtain various properties by designing the material and quantity of the elastic elements in the two chambers.Three kind isolators with different functions were introduced.The first one is a normal isolator which can capture a variable stiffness and damping property by replacing the linking tube with an active valve.The second one is an isolator with negative stiffness.When the phase difference between the oil column and the sprung mass is smaller than 90 degrees,the isolator will have a stiffness-softening property.To certain degree,the equivalent stiffness of the isolator can be negative.In quasi-zerostiffness band,the isolator get ideal isolation,which makes it resemble a dynamic absorber.So in many situations,the novel isolator has the potential to replace the traditional dynamic absorbers.The third one is an isolator with displacement limitation capacity.The main chamber is filled with a kind of soft elements with limited deformation.The additional chamber is filled with certain number of rigid elements.When the vibrating level is relatively low,only the elements in the main chamber function.The isolator shows small stiffness and negligible damping.When the vibrating level is sufficiently big,the elements in the additional chamber will take part in the isolation process,pushing the oil liquid back and forth in the linking tube.The isolator then has relatively big stiffness and damping,which helps to restrain the excessive displacement.(4).the variable stiffness and variable damping control.The semi-active control issue consists of following parts: the mechanism of variable stiffness,the method for aperture control,the data acquisition and control system and the semi-active control laws.For the dual-chamber system,the isolator’s stiffness can be changed by adjusting the flow aperture of the linking tube.To control the aperture timely,an active valve group was designed based on the principle of the digital valve.Some semi-active control laws including linear optical control,energy storage control,frequency estimation based control,reference model based control were verified by simulation analysis and semi-active isolation test.The test results showed that,compared to passive isolators,the semi-active isolator can fourthly improve the isolation performance.