Gse

Model Element

Class Name

Gse

Description

Gse is an abstract modeling element that defines a generic dynamic system. The dynamic system is characterized by a vector of inputs u, a vector of dynamic states x, and a vector of outputs y. The state vector x is defined through a set of differential equations. The output vector y is defined by a set of algebraic equations. The image below illustrates the concept of a dynamic system.

gse_api_img1

Attribute Summary

Name	Property	Modifiable by command?
id	Int ()
label	Str ()	✓
no	Int ()
ns	Int ()
x	Reference ("Array")	✓
y	Reference ("Array")	✓
u	Reference ("Array")	✓
ic	Reference ("Array")	✓
static_hold	Bool ()	✓
implicit	Bool ()
function	Function ("GESSUB")	✓
routine	Function ()
active	Bool ()	✓

Usage

# Defined in a compiled user-written subroutine

Gse (no=int, function=userString, routine=string optional_attributes)

# Defined in a Python function

Gse (no=int, function=userString, routine=functionPointer optional_attributes)

Attribute Description

Defined in a compiled user-written subroutine

Integer

An integer that specifies the number of outputs in the GSE.

no > 0

This attribute is mandatory.

function

String

Specifies the list of parameters that are passed from the data file to the user defined subroutines GSESUB, GSEXX, GSEXU, GSEYX and GSEYU. You must write GSESUB. The others, GSEXX, GSEXU, GSEYX and GSEYU, are optional. When these are not written, MotionSolve will generate the partial derivatives automatically via finite differencing.

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∷myGse”

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

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

The attribute routine is optional. When not specified, routine defaults to GSESUB.

Defined in a Python function

Integer

An integer that specifies the number of outputs in the GSE.

no > 0

This attribute is mandatory.

function

String

The function attribute is mandatory

routine

Pointer to a callable function in Python

An example is: routine=myGse

•	myGse is a Python function or method that can be called from wherever the model resides.

The attribute routine is optional. When not specified it defaults to GSESUB.

Optional attributes – available to all variants

Integer

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

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

Reference to an Array object of type U

Specifies the ARRAY used to store the input u of this GSE. You can use the ARYVAL() function with this ID to access the states in a MotionSolve expression. You can also use this ID in SYSFNC and SYSARY to access the input values from a user subroutine.

This attribute is optional.

Reference to an Array object of type Y

Specifies the ARRAY used to store the output, y, of this GSE. You can use the ARYVAL() function with the ID of this array to access the states in a MotionSolve expression. You can also use this ID in SYSFNC and SYSARY to access the output values from a user subroutine.

This attribute is optional.

Reference to an Array object of type X

Specifies the ARRAY used to store the states x of this GSE. You can use the ARYVAL() function with the ID of this Array to access the states in a MotionSolve expression. You can also use this ID in SYSFNC and SYSARY to access the state values from a user subroutine.

This attribute is mandatory.

Specifies the Array used to store the initial values of the states, x of this GSE. You can use the ARYVAL() function with the id of this Array to access the states in a MotionSolve expression. You can also use this ID in SYSFNC and SYSARY to access the initial state values from a user subroutine.

static_hold

Boolean

Specifies whether the value of the dynamic state is kept fixed or not during static equilibrium and quasi static solutions.

•	True implies that the value of the dynamic state is kept constant during static and quasi-static solutions.

•	False implies that the value of the dynamic state is allowed to change during static equilibrium or quasi-static solutions.

This attribute is optional. When not specified it defaults to False.

implicit

Boolean

A Boolean that specifies whether the differential equations defining the states are implicit or explicit.

•	True implies that the differential equations are implicitly and the equations define the residue of the differential equations.

•	False implies that the differential equations are explicitly defined and the equations define the time derivative of the states.

This attribute is optional. When not specified, implicit defaults to 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.	See Properties, for an explanation about what properties are, why they are used and how you can extend these.

2.	For a more detailed explanation about Gse, see the Comments in the XML syntax section.

Examples

1.	Use a GSE to define the LuGre model of friction.

################################################################################

# Model definition #

################################################################################

def sliding_block (out_name):

m = Model (output=out_name)

# Model units, Gravity and Integrator settings

units = Units (mass="KILOGRAM", length="METER", time="SECOND", force="NEWTON")

grav = Accgrav (jgrav=-9.800)

gstiff = Integrator (error=1e-5)

# Points and Vectors that will be reused

p0 = Point (10,0,0)

ux = Vector (1,0,0)

uy = Vector (0,1,0)

uz = Vector (0,0,1)

# Ground part and global coordinate system

grnd = Part (ground=True)

oxyz = Marker (body=grnd, label="Global CS")

# Block

blk = Part (mass=1, ip=[4.9e-4,4.9e-4,4.9e-4], label="Block")

blk.cm = Marker (body=blk, qp=p0, zp=p0+uz, xp=p0+ux, label="Block CM")

# Translational joint between Block and Ground along global X-axis

im = Marker (body=blk, qp=p0, zp=p0+ux, xp=p0+uz, label="Joint Marker on Ground")

jm = Marker (body=grnd, qp=p0, zp=p0+ux, xp=p0+uz, label="Joint Marker on Ground")

jnt = Joint (type="TRANSLATIONAL", i = im, j = jm, label="Trans Joint")

# An external force trying to move the block

sfojm = Marker (body=grnd, qp=p0, zp=p0+ux, xp=p0+uz, label="Sforce reaction")

sf = Sforce (type="TRANSLATION", actiononly=True, i=im, j=sfojm,

label="Actuation Force", function = "3*sin(2*pi*time)")

# Friction in the joint

m.lugre = LuGre(joint=jnt)

# Some requests of interest

m.r1 = Request (type="DISPLACEMENT", i=im, j=jm, rm=jm, comment="Joint displacement")

m.r2 = Request (type="FORCE", i=im, j=jm, rm=jm, comment="Joint forces")

m.r3 = Request (type="VELOCITY", i=im, j=jm, rm=jm, comment="Joint velocity")

so = Output (reqsave=True)

# Return the model you just defined

return m

###############################################################################

m = sliding_block("lugre1")

m.simulate (type="DYNAMICS", end=4, dtout=.01)

# Change the static friction coefficient and continue simulation

m.lugre.mus=0.5

m.simulate (type="DYNAMICS", end=8, dtout=.01)