Shaken, not stirred: Design and application of particle dampers

01.03.2021

Niklas MeyerInstitute of Mechanics and Ocean Engineering -

Lightweight machine designs are becoming increasingly important these days to reduce energy consumption and natural resources. However, a smaller weight typically causes a decrease in stiffness and causing non-negligible vibration amplitudes. To reduce these vibrations active or passive damping techniques might be used. Both approaches are part of ongoing research at the Institute of Mechanics and Ocean Engineering at Hamburg University of Technology. To study these techniques the flexible robot FLEXOR, shown in Figure 1, is used. Large bending deformations occur in the robot’s links when the sliders are moving.

One sophisticated passive damping technique to reduce such vibrations is the use of particle dampers. Thereby containers attached to the vibrating structure are filled with granular material, as shown exemplarily in Figure 2. Due to the structural vibrations, momentum is transferred to the granular material which interacts with each other. As a result, energy is dissipated by impacts and frictional phenomena between the particles.

Particle dampers show a highly nonlinear dynamical behavior, starting at the micro-mechanical effects during single particle impacts and sliding contacts, continuing with the energy dissipation inside the particle container, and ending at the interaction within a structure. Thus, this complex dynamical behavior hinders their wide use in technical applications.

Especially, for low frequency applications only small energy dissipation rates are obtained so far, due to sticking of particles. We developed a new and much more efficient design of particle dampers for such applications. The design makes use of the rolling property of spheres inside particle containers with a flat base, as shown in Figure 2. Subjecting this particle container to a sinusoidal motion, two different motion modes of the particle bed are observed experimentally. For low driving amplitudes, the particle bed is showing a scattered behavior resulting in a low damper efficiency. For high driving amplitudes, a rolling state is observed. Here, the particle bed moves as one single particle block and collides inelastically with the container walls. This synchronous motion leads to a much higher efficiency.  An analytical description for the energy dissipation is derived for both motion modes, being in good agreement to experimental measurements. It is obtained that the optimal working point of such dampers is only depending on the filling ratio of the damper. Also, the optimal working point separates both observed motion modes. Finally, the analytical description for the energy dissipation is used for a damper optimization for the flexible robot shown in Figure 1. The optimization goal is the least vibration amplitude after a certain time for a given particle mass. The result is presented in the video below and compared to the undamped robot:

 

This research is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – project number SE1685-5/1 and is associated to the Schwerpunktprogramm "Calm, Smooth and Smart".

 

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