The document is a master thesis project that investigates the mobility of tracked forestry machines on Nordic forest soil, comparing their performance with wheeled vehicles. It examines ground pressure, performance parameters, rut depth, and environmental impacts while utilizing empirical models and field test data. The results indicate that tracked vehicles perform better on soft soil due to lower ground pressure and higher tractive force, but existing rut depth models require further validation against new data.

1. 12/20/2013
Predicting the mobility of
tracked forestry machines
operating on Nordic forest
soil
Natchammai Revathi Palaniappan, A. Pirnazarov, U. Sellgren, B. Löfgren
Forest Machine Technology Academy, KTH
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Agenda
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Background
Purpose
Division of the project task
Delimitations
Terminologies
Field test data
Comparative study of tracked and wheeled forest machines
Conclusion
Future Work
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3. 12/20/2013
Background
• Performed as a Master thesis project at KTH
• Cut-To-Length Method
• Two machine solution (harvester and forwarder)
• Development of machines gentler to the
ground
• Trial and error method
• Expensive due to changing demands
• Track soil interaction model
• Complex and difficult to model
• Development of empirical models by WES
• Aimed at preserving the productivity of the
soil
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Purpose
• To contribute to the existing knowledge in the field of tracksoil interaction.
• Study the vehicle performance
• Understand the effects on the environment
• Tracked vehicles vs. wheeled vehicles
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5. 12/20/2013
Division of the project task
1. Calculate ground pressure, performance parameters, rut
depth for tracked and wheeled vehicles. Compare results.
2. Study the field test data and theoretical model results to
find out how efficiently the measured data match with the
real data.
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Delimitations
• Entire focus is on soft soil – Uplands Sandy Loam, Rubicon
Sandy Loam and North Gower Clayey Loam
• Limited to the use of three types of rigid steel tracks (ECO,
EVO and MAGNUM)
• The roots present in the soil bed are not considered for the
analysis.
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Terminologies
• Rutting
• Ruts are formed due to repeated heavy vehicle passes along the
same path.
• Rutted area becomes too wet due to water logging.
• Soil compaction
• Physical degradation of the soil.
• Porosity, permeability and biological activity is reduced.
• Risk of soil erosion.
• Ground bearing capacity
• Ability of the soil to carry the pressure exerted on it without
undergoing shear.
• Mobility
• Quality or capability of the machine which permits them to move
from place to place.
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Field test data analysis
• Performed in Tierp, Sweden in 2011
• Komatsu 860.3
• Three types of tracks – Eco, Evo and Magnum
• Soil composition
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• Ground pressure measurement
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• Soil penetration test
• Cone penetrometer
• Straight and S-curved trails
Komatsu 860.3, Eco-Magnum, S curve (loaded)
1.50
1.00
1st pass
0.50
10th pass
0.00
0
5
10
15
Penetration depth, cm
20
Penetration resistance, MPa
Penetrartion resistance, MPa
Komatsu 860.3, Eco-Magnum, straight
(loaded)
1.400
1.200
1.000
0.800
0.600
0.400
0.200
0.000
Curve
Straight
0
5
10
15
20
25
30
Penetration depth, cm
35
40
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• Rut depth measurement
• Increases with the increase in load and number of passes.
• Large differences in the rut between S curve and straight path
Komatsu 860.3, Eco-tracks
18.00
16.00
Rut depth, cm
14.00
12.00
10.00
Straight, loaded
8.00
Straight, unloaded
6.00
Slalom, loaded
4.00
Slalom, unloaded
2.00
0.00
Pass 1
Pass 2
Pass 3
Pass 4
Pass 5
Pass 8
Pass 10
Number of passes
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Comparative study of tracked
and wheeled forest machines
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Ground pressure
WES mobility models
Performance parameters
Rut depth analysis
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Ground Pressure Models, Tracks
• Ground pressure
• Reasonably low values
for Nominal Ground
pressure (NGP)
• Almost all the models
show a lower ground
pressure for the tracked
vehicles.
Magnum
Maclaurin
Evo
Littleton
Rowland
Eco
NGP
0
200
400
600
800
Ground pressure, kPa
Ground Pressure Models, Tires
Maclaurin
Larminie, Coarse grained
Larminie, Fine grained
Rowland, Conventional
Tires
Rowland, Cross country
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NGP
0
100 200 300 400 500 600 700 800
Ground Pressure, kPa
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• WES Mobility model
• Mobility index (MI) and Vehicle Cone Index (VCI)
• VCI – minimum strength of the soil in the critical layer which permits
the vehicle to make a specific number of passes.
• A low VCI value for the tracked vehicles indicate that they can
traverse on the low strength soils better than the wheeled vehicles.
Mobility Index and Vehicle Cone Index
Tires
Magnum
VCI 50 passes
VCI 1pass
EVO
MI
ECO
14
0
2000
4000
6000
8000
kPa
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• Performance parameters
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Based on Bekker’s pressure sinkage model
Shear displacement
Tractive effort
Drawbar pull
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• Shear displacement
SHEAR DISPLACEMENT DUE TO TRACKS
SHEAR DISPLACEMENT DUE TO Tires ON USL
1.4
0.4
slip-10%
slip-20%
slip-40%
slip-60%
slip-80%
1.2
0.3
shear displacement,m
shear displacement,m
1
slip-10%
slip-20%
slip-40%
slip-60%
slip-80%
0.35
0.8
0.6
0.25
0.2
0.15
0.4
0.1
0.2
0.05
0
0
0
0.5
1
distance from the front of the contact area,m
Tracks
1.5
0
0.1
0.2
0.3
0.4
theta, radians
Tires
0.5
0.6
0.7
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• Tractive force
• Tractive force – Force at the contact between tires/tracks and road.
• Traction-Maximum amount of force the tire can apply against the
ground.
ECO tracks, Thrust vs Slip
200
150
USL
100
RSL
NGCL
50
0
10
20
40
60
80
Slip, %
Tires, Thrust vs Slip
Tractive force, kN
Tractive effort, kN
250
50
45
40
35
30
25
20
15
10
5
0
USL
RSL
NGCL
10
20
40
60
17
80
Slip, %
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• Drawbar Pull
• Pulling ability of the vehicle.
• Drawbar pull at 20 % slip is usually used as a major performance
parameter for comparison because the operating efficiency at a slip
of 20 % is generally satisfactory.
Drawbar pull on Rubicon Sandy Loam
80
Slip, %
60
Tires
40
Magnum
Evo
20
Eco
10
0
20
40
60
Drawbar pull, kN
80
100
120
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• Rut depth analysis
• Willoughby and Turnage
• Single pass rut depth models
• Multi-pass rut depth models
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• Willoughby and Turnage model
WES sinkage model, Evo tracks
0.05
evo-loaded-measured
evo-loaded-predicted
evo-unloaded-measured
evo-unloaded-predicted
0.045
0.04
sinkage,m
0.035
0.03
0.025
0.02
0.015
0.01
0.005
0
1
2
3
4
5
6
Number of passes
7
8
9
10
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WES Sinkage model, tires
0.14
tire-loaded-measured
tire-loaded-predicted
tire-unloaded-measured
tire-unloaded-predicted
0.12
sinkage,m
0.1
0.08
0.06
0.04
0.02
0
1
2
3
4
5
6
Number of passes
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8
9
10
Predicted values follow the profile of the measured values
better in the case of tracked vehicles than wheeled vehicles.
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• Single pass rut depth models (Straight Loaded)
First wheel pass-Straight loaded
0.09
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
0.08
0.07
Rut depth, m
0.06
0.05
0.04
0.03
0.02
0.01
0
1
2
3
1,2,3,4 - Eco, Evo, Magnum, Tires
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• Single pass rut depth models (Straight unloaded)
First wheel pass-Straight unloaded
0.07
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
0.06
Rut depth, m
0.05
0.04
0.03
0.02
0.01
0
1
2
3
1,2,3,4 - Eco, Evo, Magnum, Tires
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• Single pass rut depth models (S-curve loaded)
First wheel pass-S-curve loaded
0.09
0.08
0.07
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
Rut depth, m
0.06
0.05
0.04
0.03
0.02
0.01
0
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1
2
3
1,2,3,4 - Eco, Evo, Magnum, Tires
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• Single pass rut depth models (S-curve unloaded)
First wheel pass-S-curve unloaded
0.07
0.06
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
Rut depth, m
0.05
0.04
0.03
0.02
0.01
0
1
2
1,2,3,4 - Eco, Evo, Tires
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Tires
Tracks
regression analysis for Saarilahti(1997) model
0.055
regression analysis for Saarilahti(1997) model
0.08
0.05
0.07
0.045
Rut depth in m
Rut depth in m
0.06
0.05
0.04
0.04
0.035
0.03
0.03
0.02
0.025
0.01
0
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Nci
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Source
Source
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36
0.02
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Model
Model
7
7.5
8
8.5
Nci
9
Original
a
b
10
Tracks
a
Original
a
9.5
Estimated
b
Tires
bEstimateda
Tracks
0.8060
b
b
Tires 0.366
b
Antilla (1998)
(-0.001)
0.248
(-0.0061)
Antilla (1998)
Saarilahti (1997)
(-0.001)
0.108
0.248
0.76
(-0.0061)
1.553
0.8060
1.27
(-0.0187)
1.003
0.366
1.74
Saarilahti & Antilla(1999)
Saarilahti (1997)
0.023
0.108
0.256
0.76
(-0.0082)
1.553
1.08
1.27
(-0.025)
1.003
0.491
1.74
a
(-0.0187)
a
Rantala (2001)
0.989
1.23
2.08
1.27
1.344
1.741
Saarilahti & Antilla(1999)
0.023
0.256
(-0.0082)
1.08
(-0.025)
0.491
Rantala (2001)
0.989
1.23
2.08
1.27
1.344
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1.741
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• Multi-pass rut depth models
1
• After Abebe’s model
• (Multi-pass coefficient)MPC should lie within 2-3
zn
z1 n a
magnum loaded-slalom
magnum loaded-slalom
0.13
0.13
0.12
0.12
0.11
0.11
0.1
Rut depth
Rut depth
0.1
0.09
0.08
0.09
0.08
0.07
0.07
0.06
0.06
0.05
0.04
0.05
0
5
10
15
20
25
Number of wheel passes
30
35
40
0.04
1
2
3
4
5
6
7
Number of vehicle passes
8
9
10
• For vehicle pass of 1, 2,3…, the wheel pass is 4,8,12…
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Conclusion
• Ground pressure
• Tracks seem to have a lower ground pressure compared to tires
• WES mobility index
• MI and VCI values for tracks are very much lesser than the values
for tires.
• Performance parameters
• Thrust force and drawbar pull is higher for the tracked vehicles in
comparison to the wheeled vehicles which indicate that the
tracked vehicles operate much better on these types of soils than
the wheeled vehicles.
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• Rut depth
• The existing models were developed for specific vehicle
conditions and soil conditions. Though the rut depth test data
didn’t match very well with the existing models, they didn’t
deviate so much either.
• Rut depth values can be related to the WES models.
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Future work
• FEM analysis could be done to see how much the track sinks
and how the pressure will be distributed beneath the tracks.
• In depth analysis on the position and size of the grouser could
be made.
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31. 12/20/2013
Thank you
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