Force: DCVCV

Model ElementThe Force: DCVCV element defines a contact force between two deformable curves.

Description

The deformable curve is defined using the Reference_DeformCurve element. 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. When the distance between the two curves becomes less than the sum of the local radius, a repulsive contact force is applied. Two types of contact force models are supported: Linear and Poisson.

Format

<Force_DCVCV
      id                    = "integer"    
    [ label                 = "string" ]      
      i_dcurve_id           = "integer"    
      j_dcurve_id           = "integer"    
      radius_i_start        = "real"
      radius_i_end          = "real"
      radius_j_start        = "real"
      radius_j_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_DCVCV elements.
label
The name of the Force_DCVCV elements.
i_dcurve_id
Specifies the first Reference_DeformCurve used to define the Force_DCVCV element.
j_dcurve_id
Specifies the second Reference_DeformCurve used to define the Force_DCVCV element.
radius_i_start
Start radius of the first curve. Use a negative radius to define a pipe.
Default = 0.0.
radius_i_end
End radius of the first curve. Use a negative radius to define a pipe.
Default = 0.0
radius_j_start
Start radius of the second curve. Use a negative radius to define a pipe.
Default = 0.0.
radius_j_end
End radius of the second 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
</Reference_DeformCurve>
<Reference_DeformCurve
     id                  = "2"
     label               = "DCurve/2"
     end_type_left       = "NATURAL"
     end_type_right      = "NATURAL"
     u_span              = "1."
     tension             = "0."
     is_u_closed         = "FALSE"
     num_marker_id       = "5">
1 2 3 4 5
</Reference_DeformCurve>

<Force_DCVCV
     id                  = "1"
     i_dcurve_id         = "1"
     j_dcurve_id         = "2"
     radius_i_start      = "5."
     radius_i_end        = "5."
     radius_j_start      = "10."
     radius_j_end        = "10."
     force_model         = "LINEAR"
     stiffness           = "100."
     damping             = "0.01"
/>

<Post_Graphic
     id                  = "100"
     label               = "Deformable Curve"
     type                = "DeformCurve"
     curve_id            = "1"
     nseg                = "100"
/>
<Post_Graphic
     id                  = "200"
     label               = "Deformable Curve"
     type                = "DeformCurve"
     curve_id            = "2"
     nseg                = "100"
/>

Comments

  1. The Force_DCVCV element can have only one unique contact point at any time during the simulation.
  2. To correctly model a Force_DCVCV element, you must ensure that the contact point stays within 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_CVCV element, the Force_DCVCV element permits lift-off. As long as the point remains within the "u" range, the normal distance between the two deformable curves is allowed to be greater than the sum of the value specified in the attribute radius.