Particle dampers for passive vibration attenuation in flexible multibody systems
In order to save resources, lightweight designs are becoming increasingly important these days. Especially in machines performing large working motions, this might yield significant energy savings. However, a smaller weight typically causes a decrease in stiffness and non-negligible vibration amplitudes.
An additional active vibration damping is usually very difficult, since large working motions and undesired elastic vibrations occur simultaneously and affect each other. Therefore, it is desirable to use a passive vibration damping approach. These passive approaches are also often more cost-efficient and yield inherently stable systems. For the usage in flexible multibody systems, particle dampers shall be used. These are robust to environmental conditions and are as effective as other damping approaches.
In particle dampers granular material is filled in a container attached to a vibrating structure or filled in holes embedded in the vibrating structure. Due to the structural vibrations, momentum is transferred to the granular material which interacts with each other. Thereby energy is dissipated by impacts and frictional phenomena between the particles.
So far, the design of particle dampers is made by trial and error, because there is no systematic design guideline. For the development of such a guideline, particle dampers are investigated simulative with the discrete element method and experimentally.
Experimental & numerical analysis
Fort the analysis of particle dampers 2 different setups are used.
The setup I contains of a beam, which is supported by two ropes. The particle damper, which has the shape of a box, is placed in the middle of the beam. The beam is exited by a shaker at its one end. For the determination of the velocity-profile of the beam a laser scanning vibrometer is used. Therefore, a wide frequency spectrum can be analyzed.
For the numerical investigations, the beam is discretized with the finite element method. The particle movement is determined with a self-written discrete element code. By coupling of both methods, the damping of the system is determined.
As well from the experimental data, as from the simulation data the frequency response for different beam points is determined. By this data the eigenfrequency and damping values are obtained and compared with each other.
With the setup II the energy dissipation of particle damper alone is investigated, i.e. without an underlying structure. The concept of the testbed is a particle box with a free-free boundary condition and excited by a controlled harmonic force via a shaker. The excitation force is controlled such, that the frequency and acceleration magnitude of the box stays constant.
Via the measured velocity of the box and the measured force of the shaker, the complex power is determined . By the complex power, the energy dissipation and the loss factor can be calculated. Next, a comparison of experiment and simulation.
Application of the two methods to a lightweight manipulator:
Shaken, not stirred: Design and application of particle dampers
Spp 1897 - Calm, Smooth, and Smart
This topic covers a wide range of mechanics and numerics and offers much space for student works. Please contact us, if you are interested to contribute to this topic within the scope of a project work or a Bachelor-/Masterthesis.
Current topics are:
Experimental and numerical investigations.
Development and implementation of new functions for the discrete element code (in Matlab)