# Gforce

Model ElementGforce defines a general force and torque acting between two markers.

Gforce

## Description

The force and torque vectors are defined by their three components with respect to a third marker. The components may be defined using MotionSolve expressions or a user-defined subroutine. They may be a function of any system state and time.

## Attribute Summary

Name Property Modifiable by command? Designable?
id Int ()
label Str () Yes
i Reference (Marker) Yes Yes
jfloat Reference (Marker) Yes Yes
rm Reference (Marker) Yes Yes
fx Function () Yes Yes
fy Function () Yes Yes
fz Function () Yes Yes
tx Function () Yes Yes
ty Function () Yes Yes
tz Function () Yes Yes
function Function ("GFOSUB") Yes
routine Routine ()
active Bool () Yes

## Usage

Gforce is available in three flavors.
1. Force and Torque defined in a MotionSolve expression.
Gforce (i=objMarker, j=objMarker, fx=expressionString, fy=expressionString, fz=expressionString,
tx=expressionString, ty=expressionString, tz=expressionString, optional_attributes)
2. Force and Torque defined in a compiled DLL.
Gforce (i=objMarker, j=objMarker, function=userString, routine=string, optional_attributes)
3. Force and Torque Python/Matlab script.
Gforce (i=objMarker, j=objMarker, function=userString, routine=functionPointer, optional_attributes)

## Attributes

Force and Torque defined in a MotionSolve expression.
i
Reference to an existing Marker object.
Specifies the marker at which the force and torque are applied. This is designated as the point of application of the force.
The i attribute is mandatory.
j
Reference to an existing floating Marker object.
Specifies the marker at which the reaction force and torque are applied. This is designated as the point of reaction of the force.
The j attribute is mandatory.
fx
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the force acting along the x-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The fx attribute is mandatory.
fy
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the force acting along the y-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The fy attribute is mandatory.
fz
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the force acting along the z-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The fz attribute is mandatory.
tx
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the torque acting about the x-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The tx attribute is mandatory.
ty
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the torque acting about the y-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The ty attribute is mandatory.
tz
String defining a valid MotionSolve expression.
Specifies the MotionSolve expression that defines the torque acting about the z-axis of the reference coordinate system (see rm below). Any valid run-time MotionSolve expression can be provided as input.
The tz attribute is mandatory.
Force and Torque defined in a compiled DLL
i
Reference to an existing Marker object.
Specifies the marker at which the force/torque is applied. This is designated as the point of application of the force.
The i attribute is mandatory.
j
Reference to an existing floating Marker object.
Specifies the marker at which the reaction force/torque is applied. This is designated as the point of reaction of the force.
The j attribute is mandatory.
function
String defining a valid user function MotionSolve expression.
The list of parameters that are passed from the data file to the user-defined subroutine where the Gforce is defined.
The function attribute is mandatory.
routine
String
Specifies an alternative name for the user subroutine. The name consists of two pieces of information, separated by "::". The first is the pathname to the shared library containing the function that computes the response of the user-defined Vforce. The second is the name of the function in the shared library that does the computation.
An example is: routine="/staff/Altair/engine.dll::myGforce"
• "/staff/Altair/engine.dll is the dll
• "myGforce" is the function within this DLL that performs the calculations
The attribute routine is optional.
When not specified, routine defaults to GFOSUB.
Force and Torque defined in a Python function
i
Reference to an existing Marker object.
Specifies the marker at which the torque is applied. This is designated as the point of application of the force.
The i attribute is mandatory.
j
Reference to an existing floating Marker object.
Specifies the marker at which the reaction torque is applied. This is designated as the point of reaction of the force.
The j attribute is mandatory.
function
String defining a valid user function MotionSolve expression.
The list of parameters that are passed from the data file to the user-defined subroutine where the Vtorque is defined.
The function attribute is mandatory.
routine
Pointer to a callable function in Python.
An example is: routine=myGforce
• myGforce is a Python function or method that can be called from wherever the model resides.
The attribute routine is optional.
When not specified, routine defaults to GFOSUB.
Optional attributes - Available to all variants
id
Integer
Specifies the element identification number. This number must be unique among all the Gforce objects in the model.
This attribute is optional. MotionSolve will automatically create an ID when one is not specified.
Range of values: id > 0
label
String
Specifies the name of the Gforce object.
This attribute is optional. When not specified, MotionSolve will create a label for you.
rm
Reference to an existing Marker object.
Specifies the marker in whose coordinate system the torque components are computed. rm can be on any body, including Ground
The rm attribute is optional.
When not specified, rm defaults to the global coordinate system.
active
Bool
Select one from True or False.
• True indicates that the element is active in the model and it affects the behavior of the system
• False indicates that the element is inactive in the model and it does not affect the behavior of the system. It is almost as if the entity was removed from the model, of course with the exception that can be turned "ON" when desirable.
The attribute active is optional. When not specified, active defaults to True.

## Example

1. Gforce defined via expressions.
gfo1 = gforce (label="nonlinear bushing", i=m1801, jfloat=m1901, rm=m1903,
fx="-1e3*DX(1801,1903,1903)",
fy="-1e3*DY(1801,1903,1903)",
fz="-1e3*DZ(1801,1903,1903)",
tx="-5e3*AX(1801,1903) - 2*WX(1801,1903,1903)**,
ty="-5e3*AY(1801,1903) - 2*WY(1801,1903,1903)**3"
tz="-5e3*AZ(1801,1903) - 2*WZ(1801,1903,1903)**3" )
2. Gforce defined in a Python function.
# Define the user subroutine first
def myGfosub (id, time, par, npar, dflag, iflag):
i = par[0]
j = par[1]
k = par[2]
kt= par[3]
ct= par[4]

# Get the state of the bushing
dx = DX(i,j,j)
dy = DY(i,j,j)
dz = DZ(I,j,j)

ax = AX(i,j)
ay = AY(i,j)
az = AZ(i,j)

wx = WX(i,j,j)
wy = WY(i,j,j)
wz = WZ(i,j,j)

# Compute force & torque
fx = -k*dx
fy = -k*dy
fz = -k*dz
tx = -kt*ax - ct*(wx**3)
ty = -kt*ay - ct*(wy**3)
tz = -kt*az - ct*(wz**3)

return [fx, fy, fz, tx, ty, tz]

# Define a bushing with nonlinear damping
gfo2 = Gforce (label="nonlinear bushing", i=m1801, jfloat=m1901, rm=m1903,
function="user(1801,1903,1000.0,5000.0, 2.0)", routine=myGfosub )