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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
• 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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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 track-soil interaction.
• Study the vehicle performance
• Understand the effects on the environment
• Tracked vehicles vs. wheeled vehicles
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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. 7
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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
0.00
0.50
1.00
1.50
0 5 10 15 20
Pe
ne
trar
tio
n r
esis
tan
ce, M
Pa
Penetration depth, cm
Komatsu 860.3, Eco-Magnum, straight (loaded)
1st pass
10th pass
0.000
0.200
0.400
0.600
0.800
1.000
1.200
1.400
0 5 10 15 20 25 30 35 40
Pe
ne
trat
ion
res
ista
nce
, MP
a
Penetration depth, cm
Komatsu 860.3, Eco-Magnum, S curve (loaded)
Curve
Straight
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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
0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
16.00
18.00
Pass 1 Pass 2 Pass 3 Pass 4 Pass 5 Pass 8 Pass 10
Ru
t d
ep
th, c
m
Number of passes
Komatsu 860.3, Eco-tracks
Straight, loaded
Straight, unloaded
Slalom, loaded
Slalom, unloaded
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Comparative study of tracked and wheeled forest machines
• Ground pressure
• WES mobility models
• Performance parameters
• Rut depth analysis
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• Ground pressure
• Reasonably low values for Nominal Ground pressure (NGP)
• Almost all the models show a lower ground pressure for the tracked vehicles.
0 200 400 600 800
Eco
Evo
Magnum
Ground pressure, kPa
Ground Pressure Models, Tracks
Maclaurin
Littleton
Rowland
NGP
0 100 200 300 400 500 600 700 800
NGP
Rowland, Cross country
Rowland, Conventional
Larminie, Fine grained
Larminie, Coarse grained
Maclaurin
Ground Pressure, kPa
Ground Pressure Models, Tires
Tires
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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.
0 2000 4000 6000 8000
ECO
EVO
Magnum
Tires
kPa
Mobility Index and Vehicle Cone Index
VCI 50 passes
VCI 1pass
MI
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• Performance parameters
• Based on Bekker’s pressure sinkage model
• Shear displacement
• Tractive effort
• Drawbar pull
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• Shear displacement
0 0.5 1 1.50
0.2
0.4
0.6
0.8
1
1.2
1.4
distance from the front of the contact area,m
shear
dis
pla
cem
ent,
m
SHEAR DISPLACEMENT DUE TO TRACKS
slip-10%
slip-20%
slip-40%
slip-60%
slip-80%
0 0.1 0.2 0.3 0.4 0.5 0.6 0.70
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
theta, radians
shear
dis
pla
cem
ent,
m
SHEAR DISPLACEMENT DUE TO Tires ON USL
slip-10%
slip-20%
slip-40%
slip-60%
slip-80%
Tracks Tires 16
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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.
0
50
100
150
200
250
10 20 40 60 80
Trac
tive
eff
ort
, kN
Slip, %
ECO tracks, Thrust vs Slip
USL
RSL
NGCL
0
5
10
15
20
25
30
35
40
45
50
10 20 40 60 80
Trac
tive
forc
e, k
N
Slip, %
Tires, Thrust vs Slip
USL
RSL
NGCL 17
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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.
0 20 40 60 80 100 120
10
20
40
60
80
Drawbar pull, kN
Slip
, %
Drawbar pull on Rubicon Sandy Loam
Tires
Magnum
Evo
Eco
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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
1 2 3 4 5 6 7 8 9 100
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
0.045
0.05
Number of passes
sin
kage,m
WES sinkage model, Evo tracks
evo-loaded-measured
evo-loaded-predicted
evo-unloaded-measured
evo-unloaded-predicted
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Predicted values follow the profile of the measured values better in the case of tracked vehicles than wheeled vehicles.
1 2 3 4 5 6 7 8 9 100
0.02
0.04
0.06
0.08
0.1
0.12
0.14
Number of passes
sin
kage,m
WES Sinkage model, tires
tire-loaded-measured
tire-loaded-predicted
tire-unloaded-measured
tire-unloaded-predicted
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• Single pass rut depth models (Straight Loaded)
22 1 2 3 40
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09First wheel pass-Straight loaded
1,2,3,4 - Eco, Evo, Magnum, Tires
Rut
depth
, m
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
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• Single pass rut depth models (Straight unloaded)
23 1 2 3 40
0.01
0.02
0.03
0.04
0.05
0.06
0.07First wheel pass-Straight unloaded
1,2,3,4 - Eco, Evo, Magnum, Tires
Rut
depth
, m
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
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• Single pass rut depth models (S-curve loaded)
24 1 2 3 4
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09First wheel pass-S-curve loaded
1,2,3,4 - Eco, Evo, Magnum, Tires
Rut
depth
, m
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
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• Single pass rut depth models (S-curve unloaded)
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1 2 30
0.01
0.02
0.03
0.04
0.05
0.06
0.07First wheel pass-S-curve unloaded
1,2,3,4 - Eco, Evo, Tires
Rut
depth
, m
Antilla(1998)
Saarilahti(1997)
Saarilahti & Antilla(1999)
Rantala(2001)
Test data
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22 24 26 28 30 32 34 36 380
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08regression analysis for Saarilahti(1997) model
Nci
Rut
depth
in m
7 7.5 8 8.5 9 9.5 100.02
0.025
0.03
0.035
0.04
0.045
0.05
0.055regression analysis for Saarilahti(1997) model
Nci
Rut
depth
in m
a b
a b a b
Antilla (1998) (-0.001) 0.248 (-0.0061) 0.8060 (-0.0187) 0.366
Saarilahti (1997) 0.108 0.76 1.553 1.27 1.003 1.74
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 1.741
OriginalSource Model
Tracks
Estimated
Tires
a b
a b a b
Antilla (1998) (-0.001) 0.248 (-0.0061) 0.8060 (-0.0187) 0.366
Saarilahti (1997) 0.108 0.76 1.553 1.27 1.003 1.74
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 1.741
OriginalSource Model
Tracks
Estimated
Tires
Tracks Tires
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• Multi-pass rut depth models
• After Abebe’s model
• (Multi-pass coefficient)MPC should lie within 2-3
• For vehicle pass of 1, 2,3…, the wheel pass is 4,8,12…
1
1a
nzz n
0 5 10 15 20 25 30 35 400.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13magnum loaded-slalom
Number of wheel passes
Rut
depth
1 2 3 4 5 6 7 8 9 100.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
0.12
0.13magnum loaded-slalom
Number of vehicle passes
Rut
depth
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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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Thank you
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