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In addition to designing and building
tuned mass dampers (TMDs)
using the more commonly used suspension
elements, i.e, metal springs and viscous dampers as well as viscoelastic materials,
DEICON has extended the use of its patent-pending
‘Computer Controlled Air
Isolation Technology’
developed originally for vibration isolation, to the realization of 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 air suspended tuned mass dampers. It should be noted that in addition to its utility as a tuned
damper, DEICON's air suspended tuned device can be used as a dynamic absorber.
The schematic of DEICON’s patent-pending ‘Air Suspended Tuned Mass Damper’ is shown in Figure 1(a).
Such a device 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(b).
Figure 1 Air-suspended tuned mass damper (a) and air-suspended
tuned mass damper installed on a structure (b)
The sensors installed on the air suspended tuned device are used to measure the net
motion 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 of
the tuned device.
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It should be noted that DEICON's computer controlled air suspended tuned
mass damper is quite different form active tuned mass dampers
discussed in the literature. Active tuned mass dampers use a full
authority actuator (electromagnetic or hydraulic) in parallel to, or
in place of, the spring in a traditional tuned device. The actuator
which puts out most or all of the vibration control force, mainly uses
the mass as an inertia to push/pull against, dynamically. In DEICON's technology,
no full-authority actuator is used. We still use the air spring as the spring
and only take advantage
its adjustability to adjust its parameters (stiffness and damping).
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Vibration treatment systems that use controls for adjusting their parameters are
normally categorized as semi-active systems. Since semi-actively controlled systems
only use a small amount of energy to modify their parameters, their needed energy
is by far less than systems under fully active control which constantly use energy to
impart forcing/actuation, via an actuator, to the structure.
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Design Possibilities
Figure 2 depicts two different designs, amongst many possible ones, for computer
controlled air suspended tuned mass dampers. In the design shown in Figure 2(a),
in addition to the 4 small air springs supporting the mass of the tuned damper 4
other air springs are used to allow for adjusting the stiffness of the tuned device
without over-extending the air springs. Also shown in Figure 2(a) is a part of the
underdamped, all-steel (I-beam) structure the tuned damper is used for adding
damping to. Figure 2(b) shows a large, computer controlled air suspended tuned
mass damper, designed for damping the vibration of a massive floor. The computer
controlled air suspended tuned mass damper is appended to the vibrating
structure, i.e., the floor, via its 4 posts.
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(a)
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(b)
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Figure 2 Two air-suspended tuned mass damper designs
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Another commonly used configuration for tuned dampers is ‘pendulum type”.
The image of a 1 ton pendulum type tuned mass damper undergoing testing/evaluation
is presented in Figure 3(b). Figure 3(a) shows the schematic of such damper.
If need be the lateral motion of the mass of tuned mass dampers, in
designs similar to the ones shown in Figure 2, can be constrained using a set of
laterally mounted air springs. In addition to constraining the lateral motion of
the tuned damper, these lateral air springs assist in adjusting the stiffness in
the main vibration direction. In pendulum type designs, shown in Figure 3, lateral
motion is automatically constrained through the mechanics of the design.
Figure 3 An image (a) and the schematic (b) of a
pendulum type tuned mass damper
Fine-tuning, Re-tuning,
and Self-tuning
As stated earlier, initial fine-tuning and occasional re-tuning of traditional
tuned mass dampers involves modifying the hardware and could be quite challenging,
especially for the large ones. On the other hand, fine-tuning and re-tuning of air
suspended tuned mass dampers can readily be accomplished thru the software,
using their active and semi-active stiffness control features, without physically
modifying the hardware. Moreover, self-tuning capabilities can be incorporated
into the supervisor controller of air suspended tuned mass dampers so that
they are constantly being fine-tuned, automatically.
Although originally developed for floor vibration control, DEICON TMDs can be
used in other structural damping applications with similar dynamics as those of floor systems.
Other Advantages
- Contrary to traditional TMDs that use two individual elements, i.e., spring and a
damper, to make up their suspension, DEICON's air suspended TMD uses only an air spring
(acting both as the resilient and dissipative elements) in its suspension. This results in
fewer part counts, more reliability, and lower cost.
- Friction-free, immediate response of its air suspension is another
advantages of DEICON's computer controlled air suspended tuned damper.
Since air springs have no sliding seals,
there is no breakaway friction (as in mechanical viscous dampers) making these
TMDs respond to the slightest of perturbation on the vibration structure.
- In DEICON's air suspended TMDs, vibration energy of the structure is dissipated
by releasing some compressed air from the
air suspension, not via heat dissipation (as is in viscous dampers) to the surrounding. Thus
the size of suspension in DEICON's air suspended TMDs are smaller and the cost of them lower than
the equivalent, spring+viscous damper suspension in the more traditional TMD.
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