Except for aerodynamics forces, all vehicle excitation forces are generated at the tyre-road interface.
Considering low speed applications, such as terramechanics where the aerodynamics force
are negligible, the road-tyre interaction is of extreme importance. Crucial variables which govern the
forces generated at the tyre-road interface are tyre side-slip angle, tyre longitudinal slip ratio and
terrain pro le. Solutions to measure these variables exist for smooth hard roads but the solutions
experience challenges on rough and o -road terrain.
Digital Image Correlation is concerned with tracking the changes of a scene in a sequence of
images or in images obtained from multiple viewpoints. These methods are frequently used in micro
and nano-scale mechanical testing due to its ease of implementation and use as well as its non-contact
approach. As a result these techniques are being implemented in many elds from material testing,
physics, lm animations and engineering. The aim of this thesis is to investigate the applications
of Digital Image Correlation in vehicle dynamics using cost e cient o -the-shelf digital cameras and
lenses. The following three vehicle dynamic problems are investigated: The measurement of the
vehicle side-slip angle, longitudinal slip-ratio of a pneumatic tyre and high delity terrain pro ling.
The vehicle side-slip angle can be used as a measure of the vehicle stability and therefore be
used to improve the e ectiveness of vehicle stability controllers. The tyre side-slip angle is also
a vital measurement in characterising the lateral force characteristics of pneumatic tyres. A planar
measuring method using Digital Image Correlation is shown to accurately measure the side-slip angle.
The method is expanded by developing two additional algorithms which can measure all translational
and rotational velocities. These methods are validated on both smooth surfaces and rough o -road
terrain.
A method is also implemented whereby the longitudinal slip ratio of a tyre can be measured using
a single camera. Therefore, doing away with the conventional method of using three independent measurement systems. Features in the contact patch, encompassing both the tyre and the road, are
tracked in a sequence of images. The features are classi ed into features lying on the tyre, road
and outliers using a clustering algorithm. This enables the system to determine the tyre and road
velocities from which the slip ratio is determined.
High delity terrain pro ling is performed using a calibrated stereographic rig to obtain a three
dimensional point cloud of the scene which is being viewed. The point cloud generated at one sample
contains a grid of points encompassing a large area with points spaced both laterally and longitudinally.
Overlapping point clouds are generated and joined using various registration techniques. The joined
point clouds are sub-sampled to obtain a regularised grid of point containing a single point cloud of
non overlapping points.
The proposed techniques create new possibilities in the eld of vehicle dynamics. Enabling the
side-slip angle to be measured in rough of road conditions while providing additional measurements.
The longitudinal slip ratio which is measured directly at the contact patch could pave the way for
better understanding the mechanism of the longitudinal tyre force generation. The inexpensive road
pro ling systems enables multiple sensors to be used in terramechanics tests to determine the impact
of a vehicle on the environment. The thesis presents the mere tip of the ice berg concerning digital
image correlation used in vehicle dynamics with many more possibilities waiting to be discovered. / Thesis (PhD)--University of Pretoria, 2015. / tm2015 / Mechanical and Aeronautical Engineering / PhD / Unrestricted
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:up/oai:repository.up.ac.za:2263/45956 |
| Date | January 2015 |
| Creators | Botha, Theunis R. |
| Contributors | Els, P.S. (Pieter Schalk) |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | © 2015 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
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