APPENDIX A: COLD REGIONS MOBILITY MODEL CRM-1.F
GENERAL
The program CRM-1.F is a FORTRAN code that calculates mobility parameters and factors that can be
used to determine go/no-go conditions, drawbar pull, drawbar coefficient, gross traction, total resistance
and slip due to traction on snow. For calculations on snow the required data are snow depth and density,
slope, RCI if there is a soft soil underlying the snow, and vehicle data (described below). If the analysis
involves only thawing or freezing soils, the model requires soil type, soil wetness (Table 2) and the frost or
thaw depth. To calculate the frost depth needed to support a vehicle, the vehicle weight or class is needed.
The code consists of a main program and the following subroutines:
For snow calculations:
vehdata
reads the vehicle data files for snow modeling
snow
reads the snow and terrain data (interactively)
pressure
calculates vehicle contact pressures
calculates ρf and the vehicle sinkage
density
rterrain
calculates the resistance due to the terrain
hard
determines the internal resistance coefficient
traction
calculates the gross traction
totalsnow
calculates the ratio of vehicle to wheel speed, net traction and drawbar coefficients.
For thawing and freezing soil:
soil
reads USCS soil type and soil wetness (interactively)
trmult
calculates traction multipliers for thawing soils
mrmult
calculates resistance multipliers for thawing soils
thaw
writes traction and resistance multipliers to the screen
freeze
models frozen soil bearing capacities for wet or dry soils.
VEHICLE DATA FILES
CRM-1.F reads vehicle data files developed specifically for the Cold Regions Mobility Model to deter-
mine the mobility parameters of a specified vehicle operating in snow. No vehicle data file is required for
the freezingthawing soils subroutines. The program reads two types of data files: wheeled and tracked
vehicle files. The data below are for the HMMWV, a wheeled vehicle.
The second line represents the type of vehicle. Wheeled vehicles are labeled as type 0, and tracked
vehicles are type 1. Line 3 lists the number of axles. The number of wheels per axle is in line 5; as indi-
cated, the HMMWV has two wheels for each axle. The axles are powered if the value for the axle power
is 1; if the value is 0, the axle is not powered. Line 7 is the radius of each wheel. Line 8 is the maximum
Line
Value
Data
FORTRAN format code
1
Vehicle name
HMMWV
2a4
2
Vehicle type
0
10i2
3
No. of axles
2
i2
4
Ground clearance, inches
15.75
f8.2
5
No. wheels per axle
2
2
10i2
6
Axle power
1
1
10i2
7
Radius of each wheel (in.)
16.90
16.90
10f7.2
8
Width of each wheel (in.)
12.60
13.00
10f7.2
9
Load on each axle divided
1625.00
2135.00
10f7.2
by the number of wheels (lb)
Tire contact area (in.2)
10
115.00
115.00
10f7.2
11
Unloaded section height
9.0
1.2
*
and loaded tire deflection (in.)
19
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