A coupled multibody and discrete element approach for roller compaction dynamics
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Författare
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Examensarbete för masterexamen
Modellbyggare
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Sammanfattning
This thesis presents a novel compaction simulation method, where a multibody dynamics model of a vibratory
roller is coupled to the discrete element method (DEM) for unbound granular materials. A multibody dynamics
solver is developed, and an analysis of the roller mechanical system is performed to construct a rigid body
model of the machine. Further, a method for bed initialisation is developed, and a uniaxial strain test is used
to calibrate the multisphere DEM material parameters. Then, compaction simulation is made possible by
implementation of a coupling server, that runs the DEM and multibody solvers simultaneously at different
timesteps. Such simulations are compared to full-scale experiments and compaction theory. The machine
response to beds of varying stiffness agrees with experience from compaction practice, and characteristic
behaviour, such as double jumps, is observed. The stresses in the bed agree with experiments if the particle
Young's modulus is kept low. However, the roller penetration of the bed is higher than in experiments due
to insufficient shear resistance in the DEM model. At the same time, no increase in bulk density is achieved.
Further analysis shows that the lack of shear resistance is likely related to the multisphere model of the particle
geometry, and the lack of compaction may be due to a particle size distribution that is too narrow. On the
other hand, such simplifications are necessary, because large computational costs impose limits on the particle
size distribution, particle discretisation, and domain size. The function of the solver coupling and machine
model is verified, but in order to enhance agreement with full-scale experiments, improvements are needed in
terms of both the particle modelling and computational performance capacity.
Beskrivning
Ämne/nyckelord
Compaction, discrete element method, multibody dynamics, vibratory roller, model coupling