The soft soil road surface is represented as a rectangular structured grid of deformable
springs in the vertical (z-axis) direction, as shown in the figure below. Using this
approach, each spring represents a small road patch for which the necessary information is
stored.
Typical parameters include the soil properties, the soil elevation (z coordinate) as well
as information regarding the compaction of the soil, as functions of x and y coordinates.
Moreover, the information stored for each road patch is set independently of the other
springs. In addition, the grid spacing is set automatically based on the minimum tire width
or track link dimension of the model. Figure 1. Road surface modeled as a regular grid of deformable springs
Soil Library
A soil library containing ready-to-use road data files for a variety of soils are located
in the installation
<Installation>\hwdesktop\hw\mdl\autoentities\properties\Tires\ALTAIR_SOFTSOIL.
Road Data File
All the necessary (and optional) parameters for the soft-soil model are provided in the
road data (.rdf) file. It can be used with tires, tracks, or both models. The soil
properties are structured into Common Soil Properties, Tire Soil Properties, Track Soil
Properties, and Advanced Track Soil Properties.
The Common Soil Properties contain information inherent to soil
characteristics used in both tire and track soil equations.
Parameter
Description
PHI
Angle of internal shearing resistance [Units: angle]
The Tire Soil Properties contain information used only for the tire
soft soil contact model.
Parameter
Description
KX0
Shear deformation module [Units: length]
KY0
Shear deformation module [Units: length]
C1
Parameter for wheel angle of maximum normal stress [-]
C2
Parameter for wheel angle of maximum normal stress [-]
Besides the common soil properties, the additional requirements to simulate the track soft
soil interaction are included in the Track Soil Properties.
Parameter
Description
R_CASE
The input report of the soft-soil model (0≤R_CASE≤2)
If R_CASE=0, the input is not reported
If R_CASE=1, the input is partially reported
If R_CASE=2, a full report is generated
WID_OR_MIN
Definition of Bekker parameter b (1≤WID_OR_MIN≤2)
If WID_OR_MIN=1, b is the width of the track (recommended value)
If WID_OR_MIN=2, b is the minimum dimension of the track link
In addition, the optional parameters for the track model are available in the
Advanced Track Soil Properties.
Parameter
Description
DELTA
The internal angle of soil-grouser friction.
If DELTA<0, then
DELTA=PHI*|DELTA|
CA
The cohesion between the soil and the grouser.
If CA<0, then CA=C*|CA|
R_JAN
r of modified Janosi
JMAX
jmax of modified Janosi
If JMAX<0, then JMAX=|JMAX|*(Link
length)
JULT
ju of modified Janosi
If JULT<0, then JULT=|JULT|*(Link
length)
AS
The plasticity factor of the shearing (0≤AS≤1)
AM
The plasticity factor of the grouser force (0≤AM≤1)
PHI_LONG
The internal angle of soil friction. This value is used for the interaction
between a link and the soil in the longitudinal direction.
PHI_LONG=PHI*PHI_LONG
DELTA_LONG
The internal angle of soil-link friction. This value is used for the
interaction between a link and the soil in the longitudinal direction.
DELTA_LONG=DELTA*DELTA_LONG
C_LONG
The cohesion of the soil particles. This value is used for the interaction
between a link and the soil in the longitudinal direction. C_LONG=C*C_LONG
CA_LONG
The cohesion between the soil and the grouser. This value is used for the
interaction between a link and the soil in the longitudinal direction.
CA_LONG=CA*CA_LONG
PHI_LAT
The internal angle of soil friction. This value is used for the interaction
between a link and the soil in the lateral direction. PHI_LAT=PHI*PHI_LAT
DELTA_LAT
The internal angle of soil-link friction. This value is used for the
interaction between a link and the soil in the lateral direction.
DELTA_LAT=DELTA*DELTA_LAT
C_LAT
The cohesion of the soil particles. This value is used for the interaction
between a link and the soil in lateral direction. C_LAT=C*C_LAT
CA_LAT
The cohesion between the soil and the grouser. This value is used for the
interaction between a link and the soil in the lateral direction.
CA_LAT=CA*CA_LAT
CJ1
Cohesion, c of the Janosi approach, for the longitudinal direction.
CJ1=C*CJ1
CJ2
Cohesion, c of the Janosi approach, for the lateral direction.
CJ2=C*CJ2
PHIJ1
Angle of internal friction, φ of Janosi, for the longitudinal direction.
PHIJ1=PHI*PHIJ1
PHIJ2
Angle of internal friction, φ of Janosi, for the lateral direction.
PHIJ2=PHI*PHIJ2
RJ1
r of the modified Janosi, for the longitudinal direction.
RJ1=R_JAN*RJ1
RJ2
r of the modified Janosi, for the lateral direction.
If RJ2≥0, then RJ2=R_JAN*RJ2
If RJ2<0, then RJ2= |RJ2|
Recommended value: RJ2=-1.
JMAX1
jmax of modified Janosi, for the longitudinal direction. JMAX1=
JMAX*JMAX1
JMAX2
jmax of modified Janosi, for the lateral direction. JMAX2=
JMAX*JMAX2
JULT1
ju of modified Janosi, for the longitudinal direction.
JULT1=JULT*JULT1
JULT2
ju of modified Janosi, for the lateral direction.
JULT2=JULT*JULT2
AS1
The plasticity factor of the shearing (0≤AS1≤1). The index 1 indicates the
longitudinal direction. AS1=AS*AS1
AS2
The plasticity factor of the shearing (0≤AS2≤1). The index 2 indicates the
lateral direction. AS2=AS*AS2
AM1
The plasticity factor of the grouser force (0≤AM1≤1). The index 1 indicates
the longitudinal direction. AM1=AM*AM1
AM2
The plasticity factor of the grouser force (0≤AM2≤1). The index 2 indicates
the lateral direction. AM2=AM*AM2
Property File Example
$----------------------------------------------------------------MDI_HEADER
[MDI_HEADER]
FILE_TYPE = 'rdf'
FILE_VERSION = 5.00
FILE_FORMAT = 'ASCII'
$---------------------------------------------------------------------UNITS
[UNITS]
LENGTH = 'm'
FORCE = 'newton'
ANGLE = 'radians'
MASS = 'kg'
TIME = 'sec'
$---------------------------------------------------------------------MODEL
[MODEL]
PROPERTY_FILE_FORMAT = 'USER'
FUNCTION_NAME = 'mbdtire::ROADSUB'
METHOD = '3D'
ROAD_TYPE = 'softsoil'
$---------------------------------------------------------------------PARAMETERS
[PARAMETERS]
MU = 1.0 $ Friction coefficient
LENGTH = 300.0 $ Range of soil region in x direction
WIDTH = 5.0 $ Range of soil region in y direction
NODES = 1 $ Number of integration points
MULTIPASS = 'TRUE'
$----------------------------------------------------------------COMMON_SOIL_PROPERTIES
[PROPERTIES]
PHI = 0.65 $ Angle of internal shearing resistance [angle]
C = 800.0 $ Soil apparent cohesion [force/length**2]
KC = 1370.0 $ Pressure-sinkage parameter [force/length**(n+1)]
KPHI = 8.14E5 $ Pressure-sinkage parameter [force/length**(n+2)]
SINKAGE_EXPONENT = 1.0 $ Sinkage exponent n [-]
SOIL_STIFFNESS = 8.14E6 $ Soil elastic stiffness [force/length**3]
SOIL_DAMPING = 500.0 $ Soil damping [force*time/length]
SOIL_DENSITY = 1600.0 $ Soil density [mass/length**3]
KX1 = 0.036 $ Shear deformation module [length]
KY1 = 0.013 $ Shear deformation module [length]
$--------------------------------------------------------------TIRE_SOIL_PROPERTIES
$-Properties used for the tire-soil interaction
$-
KX0 = 0.043 $ Shear deformation module [length/angle]
KY0 = 0.02 $ Shear deformation module [length/angle]
C1 = 0.4 $ Parameter for wheel angle of maximum normal stress [-]
C2 = 0.15 $ Parameter for wheel angle of maximum normal stress [-]
$--------------------------------------------------------------TRACK_SOIL_PROPERTIES
$-Properties used for the Track-soil interaction
$-
R_CASE = 0 $ Report of softsoil input - 0: None, 1: Minimal, 2: Full
WID_OR_MIN = 1 $ Definition of Bekker parameter b - 1: Width, 2: Minimum dimension of link
$--------------------------------------------------------------ADVANCED_TRACK_SOIL_PROPERTIES
$-Advanced Properties used for the Track-soil interaction (OPTIONAL)
DELTA = -0.5 $ Internal angle of soil-grouser friction
CA = -0.5 $ Cohesion between soil and grouser
R_JAN = 0.5 $ r of modified Janosi
JMAX = -0.8 $ jmax of modified Janosi
JULT = -1.5 $ ju of modified Janosi
AS = 0.5 $ Plasticity factor of shearing
AM = 0.5 $ Plasticity factor of grouser force
PHI_LONG = 1.0 $ The internal angle of soil friction.
DELTA_LONG = 1.0 $ The internal angle of soil-link friction.
C_LONG = 1.0 $ The cohesion of the soil particles.
CA_LONG = 1.0 $ The cohesion between the soil and the grouser.
PHI_LAT = 1.0 $ The internal angle of soil friction.
DELTA_LAT = 1.0 $ The internal angle of soil-link friction.
C_LAT = 1.0 $ The cohesion of the soil particles.
CA_LAT = 1.0 $ The cohesion between the soil and the grouser.
CJ1 = 1.0 $ Cohesion C of the Janosi approach, for the longitudinal direction
CJ2 = 1.0 $ Cohesion C of the Janosi approach, for the lateral direction
PHIJ1 = 1.0 $ Angle of internal friction, Φ, of Janosi, for the longitudinal direction
PHIJ2 = 1.0 $ Angle of internal friction, Φ, of Janosi, for the lateral direction
KJ1 = 1.0 $ k of Janosi, for the longitudinal direction
KJ2 = 1.0 $ k of Janosi, for the lateral direction
RJ1 = 1.0 $ r of the modified Janosi, for the longitudinal direction
RJ2 = 1.0 $ r of the modified Janosi, for the lateral direction
JMAX1 = 1.0 $ jmax of modified Janosi, for the longitudinal direction
JMAX2 = 1.0 $ jmax of modified Janosi, for the lateral direction
JULT1 = 1.0 $ ju of modified Janosi, for the longitudinal direction
JULT2 = 1.0 $ ju of modified Janosi, for the lateral direction
AS1 = 1.0 $ The plasticity factor of the shearing 0≤AS1≤1.
AS2 = 1.0 $ The plasticity factor of the shearing 0≤AS2≤1.
AM1 = 1.0 $ The plasticity factor of the grouser force 0≤AM1≤1.
AM2 = 1.0 $ The plasticity factor of the grouser force 0≤AM2≤1.
$----------------------------------------------------------------------GRAPHICS
[GRAPHICS]
ROAD_INCR = 0.050
CRG Road Data File
By default, a flat road model with the user-defined dimensions (length, width) is created
using the soft-soil tire model, see the figure below. Figure 2. Road Model with user-defined dimensions (length, width)
In order to represent complex terrain geometries, the soft soil road model enables the use
of curved regular grid (CGR) files. For this, the attribute CRG_FILE=’path to .crg file’
needs to be set in the PARAMETERS block of the road (.rdf) file.
$---------------------------------------------------------------------PARAMETERS
[PARAMETERS]
MU = 1.0 $ Friction coefficient
LENGTH = 300.0 $ Range of soil region in x direction
WIDTH = 6.0 $ Range of soil region in y direction
NODES = 1 $ Number of integration points
MULTIPASS = 'TRUE'
CRG_FILE = '<road_path>.crg'
Note: The obstacles defined in the soft soil road are still
superimposed on the existing road geometry. In a road containing a
.crg file, the parameters LENGTH and WIDTH are still used to define
the limit of the road. If the .crg surface is smaller than the
specified dimensions, a flat surface is created extending the .crg
surface to the road limits, instead if the .crg surface is bigger,
the road limits crops the .crg surface. If the specified
.crg file cannot be found, the simulation proceeds using a flat
road model.
Deformable Road
MotionView provides the ability to include soft-soil road
deformation in simulations using the soft-soil tire model. The deformable road graphic is
created in MotionView using the Road Tools and sent to MotionSolve to simulate the tire-soft-soil dynamics. The soft-soil road
deformation can be visualized in HyperView.
Figure 3. a) Soft-soil road graphics in MotionView; b) Soft-soil
road graphics deformed in HyperView
The Road Tool supports the creation of flat and Curved Regular Grid
(.crg) roads using the road property file
(.rdf). It is also possible to include the different obstacle types
available in the soft-soil tire model that deforms along with the road depending on the
obstacle material. Refer to Obstacles
for more information.
Note: The soft-soil deformation can be plastic or elastic depending on
the soil material and load applied on the soil by the tire. In case of an elastic
deformation where no plastic sinkage is present, the road graphics will not display any
deformation.
Road Positioning
The soft-soil road is positioned according to the road reference marker. In case of flat
surfaces and an obstacle, the road reference marker is positioned at the center of the road
in both the X and Y direction. For .crg surfaces, the road marker is positioned at the
beginning of the road. The figures below, highlight the different cases of road positioning
in the deformable road. Figure 4. Flat surfaces and an obstacle positioned with the road reference marker Figure 5. CRG surfaces positioned with the road reference marker on the deformable
road
Note: The .crg files have by definition the
length direction along positive X. The vehicle models built using MotionView vehicle libraries point along negative Global X direction.
When using the .crg surfaces with the vehicle library models, it is recommended to rotate
the road reference maker to align the vehicle direction with the road.
Add a Soft-Soil Deformable Road and Visualize the Results
Load the soft-soil road property file (.rdf) in the Road Tools
(see the Visualization - Road Tools topic for additional
information).
When loading the road property file, an .h3d file
and .mdl file are created at the selected path. The road graphics
are displayed in MotionView's modeling windows and a
graphic system containing the road graphics is defined in the model browser. Figure 6.
Add the soft-soil tire and road property files in the Tires entity or use the track
builder to create a track system with soft soil.
Run the analysis in MotionSolve.
MotionSolve reads the road .h3d created by
the Road Tools and generates an additional SSR (soft-soil road) file which has the
name <MotionSolve_result_xml_name>_softsoil_road.ssr during
run time. The softsoil_road.ssr contains the information about
the road graphic nodes deformed during the simulation.
Post-process the analysis in HyperView.
Once the
simulation in completed, open the model animation results in HyperView.
