This work addresses the way in which a viscoelastic granular medium dissipates vibration energy over broad ranges of frequency, amplitude and direction of excitation. The viscoelastic properties (modulus and loss factor) of polymer particles are obtained experimentally both by deriving the master curve of the material and by measuring the stiffness of these spherical particles at different frequencies using a test rig designed for this purpose. Three dimensional Discrete Element Method (DEM) is used to develop a numerical model of the granular medium and is validated by comparison with experimental results. Despite the simplifications the model was found to be in good agreement with experiments under vertical and horizontal vibrations with different numbers of particles over a range of frequencies and amplitudes of excitation. The study is extended to investigate different phases that occur under vibrations of granular materials. The low amplitude vibrations when the particles are permanently in contact without rolling on each other is called solid phase. In this phase, most energy is dissipated internally in the material. A theoretical/numerical approach is considered for this phase and it is validated by experiment. At higher amplitude vibrations when the particles start to move and roll on each other (the convection phase) there is a trade-off between energy dissipation by friction and viscous/viscoelastic effects. Energy dissipation is relatively insensitive to the damping of individual particles. At extremely high amplitude vibrations particles spend more time out of contact with each other (the particles are separated from each other – gas region). It can be seen the particles with lower damping reach the gas region earlier because they are less sticky and more collisions can happen so although the damping for each individual particle it less, the total damping increases. ii The effect of parameters of particles on energy dissipation is also studied using sensitivity analysis. The benefit of doing this is to better understand how each parameter influences the total system damping.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:572397 |
| Date | January 2013 |
| Creators | Darabi, Babak |
| Contributors | Rongong, Jem |
| Publisher | University of Sheffield |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://etheses.whiterose.ac.uk/3929/ |
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