AutoBush

The AutoBush is a bushing model that is designed to easily simulate bushings used in ground vehicles. The AutoBush entity reads bushing stiffness (force-displacement) and damping (force-velocity) data from a file written in the TeimOrbit format.

Some advantages of the AutoBush entity include the following:

Forces-deflection properties are stored in one ASCII format file, called the property file.
Multiple bushings may reference the same property file.
The property file format is compatible with other MBD codes, such as SIMPACK and ADAMS.
Bushing Coupling is supported as a user selected choice.

The AutoBush entity uses a Force_field XML statement in the MotionSolve deck, along with a subroutine to calculate the bushing forces and moments. The bushing property file is read by MotionSolve at the beginning of the simulation. MotionSolve uses Akima’s method to interpolate the force-deflection curves stored in the property file. For deflections outside the range in the property file, MotionSolve linearly extrapolates forces and/or moments.

Bushing Graphic

A bushing graphic appears when an AutoBush entity is added using the interface. The graphic includes a cylinder, and two large X-Y local coordinate frame indicators.

The height direction of the cylinder is along the bushing local Z axis. The radial directions of the cylinder are along the bushing local X and Y coordinate frames. The red axis indicator is aligned with the bushing local X axis, and the blue axis indicator is along the bushing local Y axis. Two different indicators are shown for the AutoBush entity. The red/blue indicator is displayed at +20 mm along the bushing local Z axis, and the blue/blue axis indicator is shown at -20 mm along the bushing local Z axis.

Coupling

The coupling method determines how the displacements in the bushing are computed.

Note: The coupling method does not matter for a linear rate bushing.

Method

Description

Rectangular

The displacement on each axis of the bushing is computed independently.

Cylindrical

Couple the X and Y displacements (translational and rotational). The radial deflection (r) is given by:

r = sqrt( x^2 + y^2 )

Fx = x/r*Gx( sign(x)*r )

Fy = y/r*Gy( sign(y)*r )

Where Gx and Gy are the force-deflection curves in the property file. The moments about the X and Y bushing axes are treated similarly.

Spherical

Couple the X, Y, and Z direction displacements (translational and rotational). The radial deflection (r) is given by:

r = sqrt( x^2 + y^2 + z^2 )

Fx = x/r*Gx( sign(x)*r )

Fy = y/z*Gy( sign(y)*r )

Fz = z/r*Gz( sign(z)*r )

Connecting an AutoBush

Connections define the two connecting bodies, the point where the forces act, and the marker that defines the bushing orientation. Bodies, Markers, and Points can be selected either graphically or through the Model Browser.

From the Connectivity tab, select the first body to connect.
The I marker of the Force_field statement in the solver deck lies on Body 1, is located at Point 1, and has the orientation of Marker.
- Click Body 1 and select a body from the modeling window.
- Double click Body 1 and select the required body from the dialog.
Similarly, select the second body to connect by clicking the Body 2 input collector.
The J marker of the Force_field statement in the solver deck lies on Body, is located at Point 1, and has the orientation of Marker.
Select a marker to orient the bushing in space.
- Click Marker and select a marker from the modeling window.
- Double click Marker and select the required marker from the dialog.
All three axes of the bushing are along the axes of the respective axes of the Marker (X-X,Y-Y,Z-Z).
Select a point to locate the bushing. The point defines the location where the bushing forces act. The I marker and the J (floating) marker of the Force_field statement are at Point 1.
- Click Point 1 and select a point from the modeling window.
- Double click Point 1 and select the required point from the dialog.
Click on the Property file browser icon to find the bushing property file. The file path is written to the solver deck and the file is read when the solver executes. The property file is written in the TeimOrbit format.
Check the Output box to write requests into the solver deck that request the force in the bushing, the displacement across the bushing, and the relative velocity across the bushing.

Tip: Click Edit File to edit and save the road tire file.

TeimOrbit Bushing File

A sample TeimOrbit Bushing File text file is shown below. The blocks have the following meaning:

HEADER: The header block describes the format of the file, if it was written from a pre-processor.
UNITS: The units block describes the data in the file.
DAMPING: The damping in the bushing. Linear damping is supported in this bushing model and is shown in the file below.
FX_CURVE, FYCURVE, etc.: The Displacement vs Force data for the degree of freedom identified in the block header. Enter the data in ascending order.

$-------------------------------------------------------------------HEADER
[HEADER]
 FILE_TYPE     =  'bus'
 FILE_VERSION  =  4.0
 FILE_FORMAT   =  'ASCII'
$------------------------------------------------------------------UNITS
[UNITS]
 LENGTH =  'mm'
 ANGLE  =  'degrees'
 FORCE  =  'newton'
 MASS   =  'kg'
 TIME   =  'second'
$-----------------------------------------------------------------DAMPING
[DAMPING]
 FX_DAMPING  =  0.5
 FY_DAMPING  =  0.5
 FZ_DAMPING  =  0.5
 TX_DAMPING  =  0.5
 TY_DAMPING  =  0.5
 TZ_DAMPING  =  0.5
$----------------------------------------------------------------FX_CURVE
[FX_CURVE]
{  x         fx}
-10.0  -45000.0
 -8.0  -36000.0
 -6.0  -27000.0
 -4.0  -18000.0
 -2.0   -9000.0
  0.0       0.0
  2.0    9000.0
  4.0   18000.0
  6.0   27000.0
  8.0   36000.0
 10.0   45000.0
$----------------------------------------------------------------FY_CURVE
[FY_CURVE]
{  y          fy}
-10.0  -45000.0
 -8.0  -36000.0
 -6.0  -27000.0
 -4.0  -18000.0
 -2.0   -9000.0
  0.0       0.0
  2.0    9000.0
  4.0   18000.0
  6.0   27000.0
  8.0   36000.0
 10.0   45000.0
$----------------------------------------------------------------FZ_CURVE
[FZ_CURVE]
{  z         fz}
-10.0  -45000.0
 -8.0  -36000.0
 -6.0  -27000.0
 -4.0  -18000.0
 -2.0   -9000.0
  0.0       0.0
  2.0    9000.0
  4.0   18000.0
  6.0   27000.0
  8.0   36000.0
 10.0   45000.0
$----------------------------------------------------------------TX_CURVE
[TX_CURVE]
{  ax          tx}
-45.0  -2025000.0
-36.0  -1620000.0
-27.0  -1215000.0
-18.0   -810000.0
 -9.0   -405000.0
  0.0         0.0
  9.0    405000.0
 18.0    810000.0
 27.0   1215000.0
 36.0   1620000.0
 45.0   2025000.0
$----------------------------------------------------------------TY_CURVE
[TY_CURVE]
{  ay          ty}
-45.0  -2025000.0
-36.0  -1620000.0
-27.0  -1215000.0
-18.0   -810000.0
 -9.0   -405000.0
  0.0         0.0
  9.0    405000.0
 18.0    810000.0
 27.0   1215000.0
 36.0   1620000.0
 45.0   2025000.0
$----------------------------------------------------------------TZ_CURVE
[TZ_CURVE]
{  az          tz}
-45.0  -2025000.0
-36.0  -1620000.0
-27.0  -1215000.0
-18.0   -810000.0
 -9.0   -405000.0
  0.0         0.0
  9.0    405000.0
 18.0    810000.0
 27.0   1215000.0
 36.0   1620000.0
 45.0   2025000.0