Force: PTdCV

Model ElementThe Force: PTdCV element defines a contact force between a deformable curve and point.

Description

The deformable curve is defined using the Reference_DeformCurve element. The point is represented as an ellipsoid defined using the i_marker as the center with arbitrary radius about each axis. The deformable curve is represented as a solid bar of an arbitrary start and end radius along the deformable curve as the center line. A negative radius for the start and end radius can be used to represent a pipe. The repulsive contact force is applied when this ellipsoid and solid bar or pipe come in to contact. Two types of contact force models are supported: Linear and Poisson.

Format

<Force_PTdCV
      id                    = "integer"    
    [ label                 = "string" ]      
      i_marker_id           = "integer"    
      radius_pt_x           = "real"
      radius_pt_y           = "real"
      radius_pt_z           = "real"      
      ref_dcurve_id         = "integer"
      radius_cv_start       = "real"
      radius_cv_end         = "real"
   { 
      force_model           = "LINEAR"      
      [ stiffness           = "real" ]
      [ damping             = "real" ]   
    | 
      force_model           = "POISSON"      
      [ penalty             = "real" ]
      [ restitution_coef    = "real" ]
    |     
   }
/> 

Attributes

id
Element identification number (integer>0). This number is unique among all Force_PTdCV elements.
label
The name of the Force_PTdCV element.
i_marker_id
Specifies a Reference_Marker used to define a ellipsoid geometry. The ellipsoid is centered at the origin of the Reference_Marker and is attached to the parent body of the Reference_Marker. The radius of this ellipsoid is specified by the radius_pt_x, radius_pt_y, and radius_pt_z attributes. This ellipsoid geometry is used for detecting contact with the deformable curve.
radius_pt_x
Radius of the ellipsoid geometry along the x axis of the I marker centered at the origin of the I marker.
Default = 0.0.
radius_pt_y
Radius of the ellipsoid geometry along the y axis of the I marker centered at the origin of the I marker.
Default = 0.0.
radius_pt_z
Radius of the ellipsoid geometry along the z axis of the I marker centered at the origin of the I marker.
Default = 0.0.
ref_curve_id
Specifies the Reference_DeformCurve used to define the Force_PTdCV element.
radius_cv_start
Radius at the start of the deformable curve. Use a negative radius to define a pipe.
Default = 0.0.
radius_cv_end
Radius at the end of the deformable curve. Use a negative radius to define a pipe.
Default = 0.0.
force_model
Select from LINEAR or POISSON.
stiffness
Stiffness coefficient for the contact force model. Only used when the force_model is set to LINEAR. The stiffness must be positive.
Default = 0.0
damping
Damping coefficient for the contact force model. Only used when the force_model is set to LINEAR. The damping must be positive.
Default = 0.0
penalty
Specifies the stiffness coefficient that is to be used for calculating the spring force. A large value for penalty permits only a small penetration between the two contacting geometries; a small value permits a larger penetration. Hertzian contact theory may be used to estimate the local stiffness. See The Roark's Formulas for Stress and Strain for more information on calculating Hertzian contact stiffness parameters. Only used when the force_model is set to POISSON. The penalty must be positive.
Default = 0.0
restitution_coef
Defines the coefficient of restitution (COR) between the contacting bodies. A value of zero specifies perfectly plastic contact meaning that the two bodies coalesce after contact. A value of one specifies perfectly elastic contact. No energy is lost in the collision and the relative velocity of separation equals the relative velocity of approach. Only used when the force_model is set to POISSON. The restitution_coef must lie between 0.0 and 1.0.
Default = 1.0

Example 1

<Reference_DeformCurve
     id                  = "1"
     label               = "DCurve/1"
     end_type_left       = "NATURAL"
     end_type_right      = "NATURAL"
     u_span              = "1."
     tension             = "0."
     is_u_closed         = "FALSE"
     num_marker_id       = "7"
30101120 30102061 30103071 30104081 30105091 30106101 30101130
/>

<Force_PTdCV
     id                  = "1"
     i_marker_id         = "30107060"
     ref_dcurve_id       = "1"
     radius_pt_x         = "10."
     radius_pt_y         = "10."
     radius_pt_z         = "10."
     radius_cv_start     = "5."
     radius_cv_end       = "5."
     force_model         = "LINEAR"
     stiffness           = "100."
     damping             = "0.01"
/>

<Post_Graphic
     id                  = "1"
     label               = "Deformable Curve"
     type                = "DeformCurve"
     curve_id            = "1"
     nseg                = "100"
/>

Comments

  1. The Force_PTdCV element can have only one unique contact point at any time during the simulation.
  2. To correctly model a Force_PTdCV element, you must ensure that the point which is referenced by the i_marker_id stays within the length defined by the normal projection of the deformable curve throughout the simulation. MotionSolve calculates a (u) value for the point's current position with respect to the deformable curve. This (u) value must always stay within range of the defined u_span. For example:

    - u_span/2 ≤ u ≤ + u_span/2

    If the current u value goes out of this range, MotionSolve will not calculate a force for that element. However, this may lead to incorrect results. You are encouraged to check the results for correctness in such a situation. For more information, please refer to the Reference: Deformable Curve model element.

  3. Unlike the Constraint_PTdCV element, the Force_PTdCV element permits lift-off. As long as the point remains within the "u" range, the normal distance between the point and the deformable curve is allowed to be greater than the radius value specified to define the point and curve.