Sforce

Model Element

Class Name

Sforce

Description

Sforce defines a force or torque acting between two Markers. The force or torque is characterized by a magnitude and a direction. The direction is pre-defined dependent on TYPE and ACTIONONLY. For details see the Comments in the XML syntax section. The magnitude may be defined using a function expression, a user-defined subroutine, a Python script or a MATLAB script. The magnitude can be a function of any system state and time.

Attribute Summary

Name	Property	Modifiable by command?
id	Int ()
label	Str ()
i	Reference (Marker)	✓
j	Reference (Marker)	✓
type	Enum ("TRANSLATION ROTATION")
actiononly	Bool ()	✓
function	Function ("SFOSUB")	✓
routine	Routine ()
active	Bool ()	✓

Declaration

#1. Force or torque magnitude defined in a MotionSolve expression

Sforce (i=objMarker, j=objMarker, type=string, function=expressionString, routine=string, optional_attributes)

#2. Force or torque magnitude defined in a compiled DLL

Sforce (i=objMarker, j=objMarker, type=string, function=userString, routine=string, optional_attributes)

#3. Force or torque magnitude defined in a Python/Matlab script

Sforce (i=objMarker, j=objMarker, type=string, function=userString, routine=functionPointer, optional_attributes)

Attribute Description

Force or torque magnitude defined in a MotionSolve expression

Reference to an existing Marker object

Specifies the marker at which the force and moment is applied. This is designated as the point of application of the force.

The i attribute is mandatory.

Reference to an existing Marker object

Specifies the marker at which the reaction force and moment is applied. This is designated as the point of reaction of the force.

The j attribute is mandatory.

type

String

Specifies the type of Sforce being defined. Select from "TRANSLATION" and "ROTATION".

•	"TRANSLATION": The element applies a force between the two markers. No torque is applied.

•	"ROTATION": The element applies a torque between the two markers. No force is applied.

function

String defining a valid MotionSolve expression

Specifies the MotionSolve expression that defines the VARIABLE. Any valid run-time MotionSolve expression can be provided as input.

A constant magnitude Sforce can be specified as a constant expression.

The function attribute is mandatory.

Force or torque magnitude defined in a compiled DLL

Reference to an existing Marker object

Specifies the marker at which the force and moment is applied. This is designated as the point of application of the force.

The i attribute is mandatory.

Reference to an existing Marker object

Specifies the marker at which the reaction force and moment is applied. This is designated as the point of reaction of the force.

The j attribute is mandatory.

type

String

Specifies the type of Sforce being defined. Select from "TRANSLATION" and "ROTATION".

•	"TRANSLATION": The element applies a force between the two markers. No torque is applied.

•	"ROTATION": The element applies a torque between the two markers. No force is applied.

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 Sforce 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 Variable. The second is the name of the function in the shared library that does the computation.

An example is: routine=”/staff/Altair/engine.dll∷mySforce”

•	”/staff/Altair/ engine.dll is the dll

•	“mySforce” is the function within this DLL that performs the calculations

The attribute routine is optional.

When not specified, routine defaults to SFOSUB.

Force or torque magnitude defined in a Python function

Reference to an existing Marker object

Specifies the marker at which the force and moment is applied. This is designated as the point of application of the force.

The i attribute is mandatory.

Reference to an existing Marker object

Specifies the marker at which the reaction force and moment is applied. This is designated as the point of reaction of the force.

The j attribute is mandatory.

type

String

Specifies the type of Sforce being defined. Select from "TRANSLATION" and "ROTATION".

•	"TRANSLATION": The element applies a force between the two markers. No torque is applied.

•	"ROTATION": The element applies a torque between the two markers. No force is applied.

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 Sforce is defined.

The function attribute is mandatory.

routine

Pointer to a callable function in Python

An example is: routine=mySforce

•	mySforce 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 SFOSUB.

Optional attributes – Available to all variants

Integer

Specifies the element identification number. This number must be unique among all the Variable 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 Variable object.

This attribute is optional. When not specified, MotionSolve will create a label for you.

actiononly

Boolean. Select from "True" and "False".

•	"True": The element applies a force/torque on the I marker but no reaction on the J marker.

•	"False": The element applies a force/torque on the I marker and also a reaction force/torque on the J marker

Default value is FALSE.

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

Comments

1.	The table below summarizes the direction of the force or torque that is applied by an Sforce.

sforce_api_table

2.	See Properties, for an explanation about what properties are, why they are used and how you can extend these.

3.	For a more detailed explanation about Sforce, see the Comments in the XML syntax section.

Example

1.	Model the example below using the Python interface.

#<Force_Scalar_TwoBody

# id = "7"

# type = "TORQUE"

# i_marker_id = "71"

# j_marker_id = "81"

# val_expression = "(SQRT(JOINT(7,2,0,71)**2 + JOINT(7,3,0,71)**2) + 1167)*

# STEP(0.044*WZ(71,72,72),-0.01,0.3,0.01,-0.3) * 0.44"

#/>

# Normal force: Fn

Fn = "sqrt (joint(7,2,0,71)**2 + joint(7,3,0,71)**2) + 1167)”

# Coefficient of friction: Mu

Mu = “step (0.044*wz(71,72,72),-0.01,0.3,0.01,-0.3)"

# Friction Torque = Pin_Radius * Fn * Mu

pinRad = “0.44”

fricTorque = pinRad + “ * “ + Fn + “ * ” + Mu

# Sforce

sf07 = Sforce (id=7, label="sfo7", i=m71, j=m81, type="ROTATION", function=fricTorque)