Journal of Terramechanics, Vol. 48, Issue 6 (Dec 2011)
Braham Breytenbach, Pieter Schalk Els, Optimal vehicle suspension
characteristics for increased structural fatigue life, Journal of
Terramechanics, Volume 48, Issue 6, December 2011, Pages 397-408, ISSN
0022-4898, 10.1016/j.jterra.2011.09.004.
(http://www.sciencedirect.com/science/article/pii/S0022489811000620)
Abstract: Heavy off-road vehicle suspension systems face unique
challenges. The ride comfort versus handling compromise in these
vehicles has been frequently investigated using mathematical
optimisation. Further challenges exist due to the large variations in
vehicle sprung mass. A passive suspension system can only provide
optimal isolation at a single payload. The designer of such a suspension
system must therefore make a compromise between designing for a
fully-laden or unladen payload state. This work deals with suspension
optimisation for vehicle structural life. The paper mainly addresses two
questions: (1) What are the suspension characteristics required to
ensure optimal isolation of the vehicle structure from road loads? and
(2) If such optimal suspension characteristics can be found, how
sensitive are they to changes in vehicle payload? The study aims to
answer these questions by examining a Land Rover Defender 110 as test
vehicle. An experimentally validated non-linear seven degree-of-freedom
mathematical model of the test vehicle is constructed for the use in
sensitivity studies. Mathematical optimisation is performed using the
model in order to find the suspension characteristics for optimal
structural life for the vehicle under consideration. Sensitivity studies
are conducted to determine the robustness of the optimal characteristics
and their sensitivity to vehicle payload variation. Recommendations are
made for suspension characteristic selection for optimal structural
life. Keywords: Off-road vehicles; Structural life; Mathematical
optimisation; Dynamic modelling
Seongpil Ryu, Youngjin Park, Moonsuk Suh, Ride quality analysis of a
tracked vehicle suspension with a preview control, Journal of
Terramechanics, Volume 48, Issue 6, December 2011, Pages 409-417, ISSN
0022-4898, 10.1016/j.jterra.2011.09.002.
(http://www.sciencedirect.com/science/article/pii/S0022489811000607)
Abstract: The feasibility of a preview control is examined for tracked
vehicle's suspension systems to improve the performance of tracked
vehicle systems. Numerical results are compared with LQ, robust H∞,
reference model tracking and hybrid preview control methods. The ride
quality analysis is performed based on the vertical acceleration at the
driver's position. On the simulations, it is proven that the hybrid
preview controller is the most efficient and practical method. Keywords:
Preview control; Active suspension; Tracked vehicle system; Ride quality
Christopher Brunskill, Nildeep Patel, Thibault P. Gouache, Gregory P.
Scott, Chakravarthini M. Saaj, Marcus Matthews, Liang Cui,
Characterisation of martian soil simulants for the ExoMars rover
testbed, Journal of Terramechanics, Volume 48, Issue 6, December 2011,
Pages 419-438, ISSN 0022-4898, 10.1016/j.jterra.2011.10.001.
(http://www.sciencedirect.com/science/article/pii/S0022489811000814)
Abstract: The European Space Agency (ESA) ExoMars mission involves
landing a rover on the surface of Mars on an exobiology mission to
extend the search for life. The locomotion capabilities of the ExoMars
rover will enable it to use its scientific instruments in a wide variety
of locations. Before it is sent to Mars, this locomotion system must be
tested and its performance limitations understood. To test the
locomotion performance of the ExoMars rover, three martian regolith
simulants were selected: a fine dust analogue, a fine Aeolian sand
analogue, and a coarse sand analogue. To predict the performance of the
ExoMars rover locomotion system in these three regolith simulants, it is
necessary to measure some fundamental macroscopic properties of the
materials: cohesion, friction angle, and various bearing capacity
constants. This paper presents the tests conducted to determine these
properties. During these tests, emphasis was placed on preparing the
regolith simulants at different levels of density in order to evaluate
its impact on the value of the parameters in particular. It was shown
that compaction can influence the Bekker coefficients of
pressure-sinkage. The shear properties are consistent with the critical
state model at normal stresses similar to those of the ExoMars rover in
all but one of the simulants, which showed behaviour more consistent
with transitional soil behaviour. It is necessary to give due
consideration to these variations to ensure a robust test regime is
developed when testing the tractive ability of the ExoMars mobility
system. Keywords: Mars; ExoMars; Rover; Mobility; Simulant; Soil
mechanics
M. Zehsaz, M.H. Sadeghi, M.M. Ettefagh, F. Shams, Tractor cabin's
passive suspension parameters optimization via experimental and
numerical methods, Journal of Terramechanics, Volume 48, Issue 6,
December 2011, Pages 439-450, ISSN 0022-4898,
10.1016/j.jterra.2011.09.005.
(http://www.sciencedirect.com/science/article/pii/S0022489811000632)
Abstract: Reduction of transmitted vibrations of tractor cabin which is
caused by road roughness is the major objective of this study;
consequently operator health can be achieved. This objective is carried
out via experimental measurements and finite element modeling. For this
purpose the vertical acceleration of the cabin as well as the rear axle
of the tractor is measured in different road conditions and forward
speeds. However, it should be mentioned that tests were carried out
according to the ISO 2631-1985 but no measurements were done on the
driver's seat. Then the finite element model of the cabin's tractor is
developed and the dynamic response of the cabin interior (with the
measured axle acceleration as input dynamic force) is obtained. At the
third step the suspension parameters are calculated by comparing the
accelerations obtained from the model and measurements. Finally the
suspension parameters are optimized according to ISO 2631-1985 via
iterative method. Keywords: Tractor cabin; Road roughness; Passive
suspension system; Optimization; Vibration
Mohammad A. Sadek, Ying Chen, Jude Liu, Simulating shear behavior of a
sandy soil under different soil conditions, Journal of Terramechanics,
Volume 48, Issue 6, December 2011, Pages 451-458, ISSN 0022-4898,
10.1016/j.jterra.2011.09.006.
(http://www.sciencedirect.com/science/article/pii/S0022489811000644)
Abstract: Understanding of soil shear behavior is very important in the
field of agricultural machinery and soil dynamics. In this study, a
discrete element model was developed using a simulation tool, Particle
Flow Code in Three Dimensions (PFC3D). The model simulates direct shear
tests of soil and predicts soil shear behavior, in terms of shear forces
and displacements. To determine and calibrate model parameters
(stiffness of particles, strength and stiffness of bond between
particles), laboratory direct shear tests were conducted to examine
effects of soil moisture content and bulk density on shear behaviors of
a sandy soil. Three soil moisture levels (0.02%, 13.0%, and 21.5%) and
four bulk density levels (0.99, 1.28, 1.36, and 1.50 Mg/m3) were
used in the tests. The test results showed that in general drier and
denser soil conditions produced higher shear forces. Based on the test
results, the bond strengths of the model particles were determined from
soil cohesion and internal friction angle. The model particle stiffness
was calibrated based on the yield forces from the tests. The calibrated
particle stiffness varied from 1.0 × 103 to
8.2 × 103 N/m, depending on soil moisture and density
levels. The bond stiffness calibrated was 1.0 × 107 Pa/m
for all soil conditions. Keywords: Sandy soil; Moisture; Bulk density;
Direct shear test; PFC<sup>3D</sup>; Stiffness; Calibration
Srđan M. Bošnjak, Comments on ''Design of aluminium boom and arm for an
excavator", Journal of Terramechanics, Volume 48, Issue 6, December
2011, Pages 459-462, ISSN 0022-4898, 10.1016/j.jterra.2011.09.001.
(http://www.sciencedirect.com/science/article/pii/S0022489811000590)
Abstract: This paper comments on the recently published work dealing
with the problem in the design of the backhoe excavator working device.
It also includes remarks on the inadequacy in the problem approach to
the device weight optimization and synthesis, and highlights mistakes in
the mathematical model. This work points out the demand for a much wider
approach to the optimization problem of the backhoe excavator working
device. Keywords: Backhoe excavator; Working device; Weight optimization