SEMI-ACTIVE AIR SUSPENDED TUNED MASS DAMPER
DEICON has extended the use of its ‘Computer Controlled Air Isolation Technology’ developed originally for vibration isolation, to realize semi-active (adjustable) tuned mass dampers. That is, air springs equipped with damping and stiffness adjustability are used as both the resilient element and energy dissipating (damping) element in DEICON’s Semi-active Air-Suspended Tuned Mass Dampers.
In addition to its utility as a tuned damper, DEICON’s air suspended tuned device can be used as a dynamic absorber.
Figure 1 Air-suspended tuned mass damper (black) installed on a structure (red)
The schematic of DEICON’s patented ‘Semi-active Air-Suspended Tuned Mass Damper appended to a vibrating structure (depicted as a one degree of freedom spring-mass-dashpot system M1-K1-C1) is presented schematically in Figure 1.
The sensors installed on the air suspended tuned device are used to measure the deflection of the air spring. The dashed lines in Figure 1 show the sensory information feeding the controller and the control signal feeding the servo-valve which in turn manipulates the flow of air in and out of the air spring. Depending on the makeup of the control scheme, the controller residing in a small computer (micro-controller) regulates the pressure or height, realizes damping and adjusts the stiffness (and thus the tuning frequency) of the tuned device.
DEICON’s Semi-active Air-Suspended Tuned Mass Damper is different form of active tuned mass dampers which use full authority actuators (electromagnetic or hydraulic) in parallel to, or in place of, the suspension of the tuned mass dampers. In DEICON’s semi-active tuned damping technology, no full-authority actuator is used. We still use the air spring as the spring and only take advantage of its adjustability to adjust its parameters (stiffness and damping).
The ability of DEICON’s Semi-active Air-Suspended Tuned Mass Damper in adjusting its tuning frequency and its internal damping is demonstrated by four sets of frequency response functions (FRFs) presented in Figure 2. Each set is comprised of 3 FRFs of the semi-active TMD, with different levels of internal damping, tuned to tuned to four different frequencies of 2.8, 3.9, 4.8, and 5.9 Hz. The damping and tuning frequency adjustments are done thru software with no change in hardware.
Figure 2 Frequency response functions of the semi-active TMD, with different levels of internal damping, tuned to four different frequencies
TUNING, RE-TUNING, & SELF-TUNING
As stated earlier, initial fine-tuning and occasional re-tuning of traditionally tuned mass dampers involves modifying the hardware and could be quite challenging, especially in large tuned mass dampers. On the other hand, tuning, fine-tuning and re-tuning of Semi-active Air-Suspended Tuned Mass Dampers can readily be done thru software without physically modifying the hardware. Moreover, self-tuning capabilities can be incorporated into the controller of air suspended tuned mass dampers so that they continuously and automatically fine-tune themselves to the target frequency.
DEFCON’s Semi-active Air-Suspended Tuned Mass Damper can be used in a variety of structural damping applications including, but not limited to, floor systems, pedestrian bridges, and towers.