Twin Rotor Damper (2009)

Videos of experiments on active control of structural vibrations. The model of a vibratory system consists of a ballasted plate suspended from a steel frame by cables. By adjusting their lengths, the natural frequency of the system is set. The active damper consists of two counter-rotating rods with a mass attached to each free end. These rotors are driven by two motors in master/slave mode. For the control of the master, system states are used which are computed from measured displacements.
The main purpose of the presented tests is to prove the practicability of a proposed damper concept. The tests include uncontrolled and controlled vibrations due to an initial displacement as well as due to impulse excitations. In the experiments, the uncontrolled vibrations exhibit a viscous damping ratio of 0.16 % which is increased to an equivalent viscous damping ratio of 5.6 % by the active damper. It is important to note that the performance of the damper depends on the amplitude of the vibrations or the initial displacement; in that case, the initial displacement is 2 cm. However, when the initial displacement is decreased to 1 cm, an equivalent viscous damping ratio of about 9 % can be observed. The ratio of the active mass to the system’s vibratory mass is slightly less than 0.5%.
With realistic frequencies and displacements, the model can represent a footbridge that is excited to vibrate laterally by pedestrians. Various other applications of the damper such as the vibration control of high-rise buildings or towers are conceivable. As an extension of the experiments, it is possible to supplement the model with a force-generating mechanism to study the performance of the active damper when the model is subjected to continuous excitations.



Mechanical System and Model Parameters


Test Setup

Videos Description Beschreibung

The control device is deactivated. The model is given an initial displacement and released from this initial position. The resulting free vibrations exhibit low damping.


Foto 2 AVI

The control device is activated. The damper moves to an initial position. The model is released with the same initial displacement as before. The control automatically initiates, and the active damper substantially increases the damping. When the vibration amplitudes are sufficiently small, the damper returns to its initial position and stops. 


Foto 3 AVI

Same test as before. When the damper has stopped, the model is again excited to vibrate by an impulse. The control process repeats.



Comparison of uncontrolled and controlled test in a split screen.



Controlled test as before. When the vibration amplitudes are relatively small, the mode of operation is switched to pivoting. In this way, it is possible to damp also small vibrations.