Force: Contact

Command ElementThe Force_Contact command can be used to modify the parameters of a Force_Contact model element.

Format

<Force_Contact 
         id                             = "integer"
         num_i_graphics                 = "integer"
         i_graphics_id                  = "integer [,integer,...,integer]"
         num_j_graphics                 = "integer"
         j_graphics_id                  = "integer [,integer,...,integer]"
         ignore_penetration_larger_than = "real"
         master_surface                 = { "I" | "J" | "I_and_J" | "AUTO" }         
         enable_sphere_to_mesh          = { "TRUE" | "FALSE" | "AUTO" } 
         contact_stability_2d           = "real"
     {
         penalty                        = "real"
         restitution_coeff              = "real"
         normal_trans_vel               = "real"
     |         
         stiffness                      = "real"
         damping                        = "real"
         exponent                       = "real"
         dmax                           = "real"
     | 
         i_elastic_modulus              = "real"
         j_elastic_modulus              = "real"
         i_layer_depth                  = "real"
         j_layer_depth                  = "real"     
     }         
         cff_type                       = " { Coulomb_On | Coulomb_Off | Dynamics_Only } "
         mu_static                      = "real"
         mu_dynamic                     = "real"
         stiction_trans_vel             = "real"
         friction_trans_vel             = "real"
/>

Attributes

id: Element identification number (integer>0). This number is unique among all Force_Contact elements and uniquely identifies the element.

Note: id is used only to identify the Force_Contact element to be modified. By itself id cannot be modified.
num_i_graphics: Modifies the number of Post_Graphic elements on body I or the first body that is to be considered in evaluating the contact force.; num_i_graphics > 0
i_graphics_id: Modifies the list of Post_Graphic element IDs on the first body to be considered for contact. The number of IDs in this list is specified by num_i_graphics.
Note: All the Post_Graphic entities must belong to the same body.
num_j_graphics: Modifies the number of Post_Graphic elements on body J or the second body that is to be considered in evaluating the contact force.; num_j_graphics > 0
j_graphics_id: Modifies the list of Post_Graphic element IDs on the second body to be considered for contact. The number of IDs in this list is specified by num_j_graphics.
Note: All the Post_Graphic entities must belong to the same body.
ignore_penetration_larger_than: Use this attribute to change the maximum penetration depth that MotionSolve will consider for evaluating contact forces. Any value above this threshold will be ignored.
master_surface: Use this attribute to change the selection of the master surface for the contact calculations.
enable_sphere_to_mesh: Use this attribute to change how MotionSolve treats spherical geometries. Set this to "TRUE" to use the analytical collision engine and "FALSE" to use the tessellated collision engine.
i_elastic_modulus (VOLUME): Modifies the elastic modulus of the geometries belonging to Body I for the volume force model.; i_elastic_modulus > 0
j_elastic_modulus (VOLUME): Modifies the elastic modulus of the geometries belonging to Body J for the Volume force model.; j_elastic_modulus > 0
i_layer_depth (VOLUME): Modifies the size of the layer depth for the geometries belonging to body I.
j_layer_depth (VOLUME): Specifies the size of the layer depth for the geometries belonging to body J.
penalty (POISSON): Modifies the penalty parameter that is used to calculate the spring force.; This attribute may only be modified when the cnf_type is set to POISSON in the Force_Contact element.; penalty≥0
restitution_coeff (POISSON): Modifies the coefficient of restitution (COR) between the contacting bodies.; This attribute may only be modified when the cnf_type is set to POISSON in the Force_Contact element.
normal_trans_vel (POISSON): Modifies the velocity limit between the two bodies at which full damping is applied in the contact force. If unset or set to 0, MotionSolve initializes it to 1.; This attribute may only be modified when the cnf_type is set to POISSON in the Force_Contact element.
stiffness (IMPACT): Modifies the stiffness parameter of the contact.; This attribute may only be modified when the cnf_type is set to IMPACT in the Force_Contact element.; stiffness ≥ 0
exponent (IMPACT): Modifies the exponent of the force deformation characteristic of the contact interface.; This attribute may only be modified when the cnf_type is set to IMPACT in the Force_Contact element.; exponent > 0
damping (IMPACT): Modifies the maximum damping coefficient.; This attribute may only be modified when the cnf_type is set to IMPACT in the Force_Contact element.; damping≥0
dmax (IMPACT): Modifies the penetration at which full damping is applied.; This attribute may only be modified when the cnf_type is set to IMPACT in the Force_Contact element.; dmax > 0
mu_static: Modifies the coefficient of friction when the relative slip velocity is equal to stiction_trans_vel.; This attribute may only be modified when the cff_type is set to COULOMB_ON in the Force_Contact element.; mu_static≥0
mu_dynamic: Modifies the coefficient of friction when the relative slip velocity is greater than friction_trans_vel.; This attribute may only be modified when the cff_type is set to COULOMB_ON or DYNAMICS_ONLY in the Force_Contact element.; mu_dynamic≥0
stiction_trans_vel: Modifies the slip velocity at which the static coefficient of friction, mu_static, is applied.; This attribute may only be modified when the cff_type is set to COULOMB_ON in the Force_Contact element.; stiction_trans_vel≥0
friction_trans_vel: Modifies the slip velocity at which the dynamic coefficient of friction, mu_dynamic, is applied.; This attribute may only be modified when the cff_type is set to COULOMB_ON or DYNAMICS_ONLY in the Force_Contact element.; friction_trans_vel≥0

Example

The following example illustrates how the <Force_Contact> command element may be used to change the parameters of the 3D rigid body contact in a MotionSolve model. In this example, to see the effect of damping in 3D contact, the model is simulated two times - once with damping turned on, and once with damping turned off. The SAVE/LOAD commands are used to combine the two simulations into one.

<Model
   …
   …
   <!- Definition of the contact force element in the model section with damping specified -->
   <Force_Contact
     id                  = "303001"
     num_i_graphics      = "1"
     i_graphics_id       = "90001"
     num_j_graphics      = "1"
     j_graphics_id       = "90002"
     cnf_type            = "Impact"
     stiffness           = "2000."
     exponent            = "1.2"
     damping             = "0"
     dmax                = "0.001"
     cff_type            = "Coulomb_Off"
    />
    …
    …
</Model>
<Command>
    …
    …
    <!- Save the model -->
    <Save
      model_file          = "model.xml"
    />
    <!- Simulate the model with damping turned on for 1 second -->
    <Simulate
      analysis_type       = "Transient"
      end_time            = "1."
      print_interval      = "0.01"   
    />
    <!- Load the saved model -->
    <Load_Model
      model_file          = "model.xml"
      result_file         = "damping_off.mrf"
      anima_file          = "damping_off.h3d"
    <!- Turn off damping -->
    <Force_Contact
      id                  = "303001"
      damping             = "0"
    />
    <!- Simulate the model with damping turned off for 1 second -->
    <Simulate
      analysis_type       = "Transient"
      end_time            = "1."
      print_interval      = "0.01"
    />
</Command>

Comments

Please refer to the help pages on the model element for more details on modeling 3D rigid to rigid contact in your model.