Indiana University-Purdue University Indianapolis (IUPUI) / In this thesis, an explicit time integration code which integrates multibody dynamics
and the discrete element method is used for modelling the excavation and moving
operation of cohesive soft soil (such as mud and snow) by bulldozers. A soft cohesive
soil material model (that includes normal and tangential inter-particle force models)
is used that can account for soil compressibility, plasticity, fracture, friction, viscosity
and gain in cohesive strength due to compression. In addition, a time relaxation
sub-model for the soil plastic deformation and cohesive strength is added in order to
account for loss in soil cohesive strength and reduced bulk density due to tension or
removal of the compression. This is essential in earth moving applications since the
soil that is dug typically becomes loose soil that has lower shear strength and lower
bulk density (larger volume) than compacted soil. If the model does not account for
loss of soil shear strength then the dug soil pile in front of the blade of a bulldozer
will have an artificially high shear strength. A penalty technique is used to impose
joint and normal contact constraints. An asperity-based friction model is used to
model contact and joint friction. A Cartesian Eulerian grid contact search algorithm
is used to allow fast contact detection between particles. A recursive bounding box
contact search algorithm is used to allow fast contact detection between the particles
and polygonal contact surfaces.
A multibody dynamics bulldozer model is created which includes the chassis/body,
C-frame, blade, wheels and hydraulic actuators. The components are modelled as
rigid bodies and are connected using revolute and prismatic joints. Rotary actuators
along with PD (Proportional-Derivative) controllers are used to drive the wheels.
Linear actuators along with PD controllers are used to drive the hydraulic actuators.
Polygonal contact surfaces are defined for the tires and blade to model the interaction
between the soil and the bulldozer. Simulations of a bulldozer performing typical
shallow digging operations in a cohesive soil are presented. The simulation of a rear
wheel drive bulldozer shows that, it has a limited digging capacity compared to the
4-wheel drive bulldozer. The effect of the relaxation parameter can be easily observed
from the variation in the Bulldozer's velocity. The higher the relaxation parameter,
the higher is the bulldozer's velocity while it is crossing over the soil patch. For the
low penetration depth run the bulldozer takes less time compared to high penetration
depth. Also higher magnitudes of torques at front and rear wheels can be observed
in case of high penetration depth. The model is used to predict the wheel torque,
wheel speed, vehicle speed and actuator forces during shallow digging operations on
three types of soils and at two blade penetration depths. The model presented can
be used to predict the motion, loads and required actuators forces and to improve
the design of the various bulldozer components such as the blade, tires, engine and
hydraulic actuators.
| Identifer | oai:union.ndltd.org:IUPUI/oai:scholarworks.iupui.edu:1805/6441 |
| Date | 29 April 2015 |
| Creators | Sane, Akshay Gajanan |
| Contributors | Wasfy, Tamer, El-Mounayri, Hazim, Nematollahi, Khosrow |
| Source Sets | Indiana University-Purdue University Indianapolis |
| Detected Language | English |
| Type | Thesis |
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