SEMI-active Inertance Based Devices For Structural Vibration Control

To optimally design the passive mass-and inerter-based devices such as tuned mass damper(TMD)and tuned viscous mass damper(TVMD),the natural frequency of the devices are tuned close to the fundamental frequency of the primary structure.Nevertheless,introducing a device that can adjust its natural frequency relative to the excitation’s current frequency can significantly increase the damping properties along a large band of frequency while detuning effect of the passive devices could be removed.In this study,two novel vibration control devices are proposed at which they are able to control their natural frequencies relying on the current frequency of the external excitation.This adjustable frequency can be achieved by calibration of the inertance(amplified mass)generated by devices.In this regard,the generated inertance can be controlled by adjusting the rotation of a small physical rotational mass(flywheel).In order to control the generated inertance,a special type of continuously variable transmission(CVT)core is redesigned and introduced in the proposed devices.In fact,the required inertance is attained when the CVT core is calibrated into a proper CVT-ratio,based on the current frequency of excitation.The function of variability in the frequency of devices is acquired by using a ball-screw system.In the first proposed device,known as a semi-active tuned viscous inertance damper(SATVID),a variable inerter is constructed by assembling the ball-screw and the CVT core while a narrow layer of viscous material is employed in addition to the flywheel.The device is configured in a way that the parallel layout of viscous damping and inertance is serially linked to a spring’s stiffness.Since an induced structure activates the device,the CVT core transfers the input rotation into an arbitrary output rotation.Later on,through the ideal rotating of the flywheel and the viscous oil,controllable inertial and damping forces are attained in opposite to the direction of the structure’s motion.Likewise,in the second proposed device,a parallel layout is configured to integrate the variable inerter,small damping due to CVT reaction and spring in a parallel manner.The layout is serially connected to an additional mass and device called semi-active tuned mass inertance damper(SATMID).The flywheel rotation can be controlled by using CVT core;therefore,an ideal variable inertance is produced along with its associated inertial force.In both SATVID and SATMID,their natural frequencies are controlled by using CVT core,while the seamless variability in frequency depends on the measured frequency of the excitation.To evaluate the devices’ performance and show the controllable dynamic characteristics of the devices,a single degree of freedom(SDOF)is equipped with SATVID/SATMID subjected to the harmonic ground excitation.Initially,the simulations are validated with the existing experimental tests,and later on,the proposed devices are compared with passive-controlled and uncontrolled structures in frequency-and time-domain.Results show an excellent mitigation level in an oscillation of the structure by using novel SATVID or SATMID,while this reduction occurs in an enlarged band of the excitation frequency.In the frequency range other than resonance frequency,both proposed semi-active devices are able to reduce the structural displacement by even more than 50% compared to passive devices.In addition,the detuning effect of passive devices are removed,and retuning can easily happen.Moreover,a simple control algorithm is designed to detect the current frequency of excitation and compute the required order of inertance;afterwards,the device is allowed to be appropriately and punctually tuned.Results verified the efficiency of the new proposed devices in vibration control of structures when induced by harmonic excitation with the frequency that could be changed during excitation.