Force: DCVSF

Model ElementThe Force: DCVSF element defines a contact force between a deformable curve and deformable surface.

Description

The deformable surface is defined using the Reference_DeformSurface element. 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 deformable curve and the surface becomes less than the curve radius, a repulsive contact force is applied. Two types of contact force models are supported: Linear and Poisson.

Format

<Force_DCVSF
      id                    = "integer"    
    [ label                 = "string" ]      
      dcurve_id             = "integer"    
      radius_start          = "real"   
      radius_end            = "real"   
      dsurface_id           = "integer"
   { 
      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_DCVSF elements.
label
The name of the Force_DCVSF elements.
dcurve_id
Specifies the Reference_DeformCurve used to define the Force_DCVCV element.
radius_start
Radius at the start of the deformable curve. Use a negative radius to define a pipe.
Default = 0.0.
radius_end
Radius at the end of the deformable curve. Use a negative radius to define a pipe.
Default = 0.0.
dsurface_id
Specifies the deformable surface used to define the Force_DCVSF element.
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                  = "2"
     label               = "DCurve/2"
     end_type_left       = "NATURAL"
     end_type_right      = "NATURAL"
     u_span              = "1."
     tension             = "0."
     is_u_closed         = "TRUE"
     num_marker_id       = "17"
1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 1
/>
<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
/>
<Force_DCVSF
     id                  = "2"
     dcurve_id           = "2"
     dsurface_id         = "1"
     radius_start        = "5."
     radius_end          = "5."
     force_model         = "LINEAR"
     stiffness           = "100."
     damping             = "0.01"
/>

<Post_Graphic
     id                  = "500000"
     type                = "DeformSurface"
     surface_id          = "1"
     nseg_u              = "30"
     nseg_v              = "30" 
/>
<Post_Graphic
     id                  = "200"
     label               = "Deformable Curve"
     type                = "DeformCurve"
     curve_id            = "2"
     nseg                = "100"
/>

Comments

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


    If the current u or v 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 Surface and Reference: Deformable Curve model element.

  3. Unlike the Constraint_CVSF element, the Force_DCVSF element permits lift-off. As long as the point remains within the "u" and "v" range, the normal distance between the deformable curve and the deformable surface is allowed to be greater than the value specified in the attribute radius.