deflected tire width. The contact area, line 10, is the hard surface contact area for a single tire on each
axle. The unloaded section height is determined by the height of the tire without any load placed on it to
cause a deflection. The loaded tire deflection is determined by calculating the deflection of the tire when
a load is placed on it. Note that lines 8, 10 and 11 are functions of the tire inflation pressure.
For the tracked vehicles the data files are set up a little differently. The example below is for the M113.
Line
Value
Data
FORTRAN format code
1
Vehicle name
M113
2a4
2
Vehicle type
1
10i2
3
No. of track sets
1
i2
4
Width of the track (in.)
15.00
10f7.2
5
Length of the track (in.)
105.00
10f7.2
6
Gross vehicle weight (lb)
23401.00
f8.2
7
Ground clearance (in.)
16.93
f8.2
8
Entry angle (degrees)
21.00
10f7.2
The third line gives the number of track sets for the vehicle (the SUSV, a two-unit articulated vehicle has
two track sets). The number of tracks per set is set to 2 in the program. The entry angle, although re-
quired, is not used; an average value of 26 for all tracked vehicles is specified in CRM-1.
TERRAIN INPUT
Terrain data are input interactively through a series of menus. For a soils analysis the codes in Table
A1 and Table 2 (wetness definitions) are used. Table A2 contains the input data and associated output for
a freezingthawing soils analysis. Sample input data and the resulting output are shown in Table A3 and
A4 for thawing and freezing soils, respectively. For snow analysis the input data and corresponding
output are in Table A5. Table A6 is a set of results for an analysis of oversnow mobility of the M113 and
HMMWV (using the vehicle parameters stated in describing the vehicle data files), comparing each of
the underlying surfaces and snow types.
Table A2. Input and output of CRM-1 (Soils).
Table A1. Codes for different soil and
Input
Output
terrain surface types used in CRM-1.
Thawing Soils
These are the same surface codes
used in CAMMS and NRMM.
Soil type (Table A1)
Traction multiplier
yields
Wetness (dry, moist, or wet)
Resistance multiplier
1
SW
11
OL
Wheeled or tracked vehicle
2
SP
12
OH
Thaw depth (cm)
3
SM
13
WATER
4
SC
14
PAVEMENT
Freezing Soils
5
SMSC
15
ROCK
6
CL
16
GW
Wet or dry ground, plus
7
ML
17
GP
Frost depth (cm)
yields
Max. vehicle weight and class supported
8
CLML
18
GM
Vehicle class
yields
Min. frost depth required
9
CH
19
GC
Vehicle weight (lb)
yields
Min. frost depth required
10
MH
20
PT (peat)
Frost depth and vehicle
yields
Go/no-go
20
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