# Ptdsff

Model ElementPtdsff defines a force between a point and a deformable surface.

Ptdsff

## Description

The deformable surface is defined using the Reference_DeformSurface element. A sphere of a specified radius is located at the origin of the I Marker. When the distance between the origin of the I Marker and the surface becomes less than the sphere radius, a repulsive contact force is generated.

## Attribute Summary

Name Property Modifiable by command? Designable?
id Int ()
label Str () Yes
dsurface Reference ("DeformableSurface") Yes Yes
i Reference ("Marker") Yes Yes
flip_normal Bool (False) Yes
radius Double () Yes FD Only
radius_x Double () Yes FD Only
radius_y Double () Yes FD Only
radius_z Double () Yes FD Only
force_model Enum ("UNDEFINED LINEAR POISSON HERTZIAN USERSUB") Yes
stiffness Double ()   FD Only
damping Double ()   FD Only
penalty Double () Yes FD Only
restitution_coefficient Double (0.0) Yes FD Only
active Bool () Yes

## Usage

Four implementations of PTDSFF are currently available.
#1: Linear contact force model
Ptdsff (i=objMarker, dsurface=objDeformableSurface, force_model= "LINEAR", optional_attributes)

#2: Nonlinear contact force using the POISSON model
Ptdsff (i=objMarker, dsurface=objDeformableSurface, force_model= "POISSON", optional_attributes)

#3: Nonlinear contact force implemented in a compiled DLL
Ptdsff (i=objMarker, dsurface=objDeformableSurface, force_model= "USERSUB", function=userString, routine=string, optional_attributes)

#4: Nonlinear contact force implemented in a Python function
Ptdsff (i=objMarker, dsurface=objDeformableSurface, force_model= "USERSUB", function=userString, routine= functionPointer, optional_attributes)

## Attributes

Linear contact force
i
Reference to an existing Marker object.
Specifies a Marker used to define a sphere geometry. The sphere is centered at the origin of the Marker and is attached to the parent body of the Marker. The sphere geometry is used for detecting contact with the deformable surface.
The i attribute is mandatory.
dsurface
Reference to an existing DeformableSurface object.
Specifies the deformable surface to be used for the contact.
The dsurface attribute is mandatory.
force_model
String
Specifies the force model. Must be set to "LINEAR" for a linear contact model.
The force_model attribute is mandatory.
stiffness
Double
Specifies the stiffness coefficient for the LINEAR contact force model.
The stiffness attribute is optional.
When not specified, it is set to zero.
damping
Double
Specifies the damping coefficient for the LINEAR contact force model.
The damping attribute is optional.
When not specified, it is set to zero.
Nonlinear contact force using the POISSON model
i
Reference to an existing Marker object.
Specifies a Marker used to define a sphere geometry. The sphere is centered at the origin of the Marker and is attached to the parent body of the Marker. The sphere geometry is used for detecting contact with the deformable surface.
The i attribute is mandatory.
dsurface
Reference to an existing DeformableSurface object.
Specifies the deformable surface to be used for the contact.
The dsurface attribute is mandatory.
force_model
String
Specifies the force model. Must be set to "POISSON" for a Poisson contact model.
The force_model attribute is mandatory.
penalty
Double
Specifies the penalty parameter for the POISSON contact force model.
The penalty attribute is optional. When not specified, penalty=0.
penalty ≥ 0
restitution_coef
Double
Specifies the restitution coefficient for the POISSON contact force model.
The restitution_coef attribute is optional. When not specified, restitution_coef =1.
0 ≤ restitution_coef ≤ 1.
Nonlinear contact force implemented in a compiled DLL
i
Reference to an existing Marker object.
Specifies a Marker used to define a sphere geometry. The sphere is centered at the origin of the Marker and is attached to the parent body of the Marker. The sphere geometry is used for detecting contact with the deformable surface.
The i attribute is mandatory.
dsurface
Reference to an existing DeformableSurface object.
Specifies the deformable surface to be used for the contact.
The dsurface attribute is mandatory.
force_model
String
Specifies the force model. Must be set to "POISSON" for a Poisson contact model.
The force_model 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 Ptdsff 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 Ptdsff. The second is the name of the function in the shared library that does the computation.
An example is: routine="/staff/Altair/engine.dllmyPtdsff".
• "/staff/Altair/ engine.dll is the DLL
• "myPtdsff" is the function within this DLL that performs the calculations
The attribute routine is optional.
When not specified, routine defaults to PTDSFSUB.
Nonlinear contact force implemented in a Python function
i
Reference to an existing Marker object.
Specifies a Marker used to define a sphere geometry. The sphere is centered at the origin of the Marker and is attached to the parent body of the Marker. The sphere geometry is used for detecting contact with the deformable surface.
The i attribute is mandatory.
dsurface
Reference to an existing DeformableSurface object.
Specifies the deformable surface to be used for the contact.
The dsurface attribute is mandatory.
force_model
String
Specifies the force model. Must be set to "POISSON" for a Poisson contact model.
The force_model 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 Variable is defined.
The function attribute is mandatory.
routine
Pointer to a callable function in Python.
An example is: routine=myPtdsff.
• myPtdsff 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 PTDSFSUB.
Optional attributes - Available to all variants
id
Integer
Specifies the element identification number. This number must be unique among all the Ptdsff 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 Ptdsff object.
This attribute is optional. When not specified, MotionSolve will create a label for you.
flip_normal
Boolean (True/False).
Specifies whether the normals are to be generated.
• True means that the element normals are generated using the right hand rule. Specifically, if one curls the fingers of the right hand in the order N1, N2, and N3 of a triangular element, then the thumb provides the direction of the normal vector.
• False means the converse: The normal vector points in the direction opposite to the right hand thumb.
This attribute is optional. When not specified, flip_normal = False.
Double
Specifies the radius of the spherical geometry centered at marker I.
This attribute is optional. When not specified, radius=0.
Double
Specifies the radius of the ellipsoid geometry centered at marker I, in the X direction of its orientation.
Double
Specifies the radius of the ellipsoid geometry centered at marker I, in the Y direction of its orientation.
Double
Specifies the radius of the ellipsoid geometry centered at marker I, in the Z direction of its orientation.
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

Express the XML example shown below using the Python interface.
<Reference_DeformSurface
id             = "1"
end_type       = "NATURAL"
num_marker_row = "7"
num_marker_col = "7">
30101490 30101500 30101510 30101520 30101530 30101540 30101540
30101420 30109781 30113791 30117801 30121811 30125821 30101480
30101350 30108711 30112721 30116731 30120741 30124751 30101410
30101120 30102061 30103071 30104081 30105091 30106101 30101130
30101140 30110571 30114581 30118591 30122601 30126611 30101200
30101210 30111641 30115651 30119661 30123671 30127681 30101270
30101280 30101290 30101300 30101310 30101320 30101330 30101340
</Reference_DeformSurface
<Force_PTdSF
id              = "1"
i_marker_id     = "30107850"
ref_dsurface_id = "1"
force_model     = "LINEAR"
stiffness       = "1000.0"
damping         = "0.1"
/>
# Create the I Marker
imrkr = Marker (label="ptdsff-i", body=p3030)

# Define the deformable surface points
mkrMatrix = [[m30101490, m30101500, m30101510, m30101520, m30101530, m30101540, m30101540],
[m30101420, m30109781, m30113791, m30117801, m30121811, m30125821, m30101480],
[m30101350, m30108711, m30112721, m30116731, m30120741, m30124751, m30101410],
[m30101120, m30102061, m30103071, m30104081, m30105091, m30106101, m30101130],
[m30101140, m30110571, m30114581, m30118591, m30122601, m30126611, m30101200],
[m30101210, m30111641, m30115651, m30119661, m30123671, m30127681, m30101270],
[m30101280, m30101290, m30101300, m30101310, m30101320, m30101330, m30101340]]

# Create the deformable surface object
ds = Dsurface (markers=mkrmatrix))

# Create the Ptdsff object
ptdsff1 = Ptdsff (i=imrkr, dsurface=ds, radius=10, force_model="LINEAR", stiffness=1000, damping=0.1)