Adams Basic Package > Adams View > Adams View > Building Models > Contacts > Creating/Modifying Contact Forces

Creating/Modifying Contact Forces

To create or modify a contact force:

1. Select Forces Tab → Special Forces Container → click Create a Contact icon .
The Create/Modify Contact dialog box appears.
2. Enter values in the dialog box as explained in the table below, and then select OK.
 
Tip:  
You can change the direction of the force on some geometry (for example, circle, curve, plane, and sphere) by selecting the Change Direction tool .
To:
Do the following:
Define type and geometry
To define the geometry/flexible body that comes into contact:
1. Set Type to the type of geometry to come into contact. In case of flexible bodies, you must either select the Flex Body To Flex Body or Flex Body to Solid options. Flexible bodies can participate in the contact only for Adams Solver C++. In case of flex edge contacts, select Flex Edge To Flex Edge or Flex Edge To Curve or Flex Edge To Plane.
The text boxes change depending on the type of contact force you selected.
2. In the text boxes, enter the name of the geometry or flexible body objects. For solids and curves, you can enter more than one geometry, but the geometry must belong to the same part. You can select the objects from the screen or Database Navigator or type it directly in the text box. If you type the geometry object name directly in the text box, you must press Enter to register the value. In case of "Flex Body to Solid" type of contacts, the rigid body should always be the J geometry. Similarly in case of Flex Edge to Curve or Plane type of contacts, Curve or Plane should always be J geometries.
If you want to change the direction of the force, in the Direction pull-down menu, select the geometry on which you want to change the force, and then select the Change Direction tool . This is disabled in case of "Flex Body to Flex Body" and "Flex Body to Solid" contacts but is available in all the Flex Edge contacts.
Turn on the force display for both normal and friction forces and set its color
Select Force Display, and then from the option menu, select a color for the force display.
Note: If you are using an External Adams Solver, you must set the output files to XML to view the force display. See Solver Settings - Output dialog box help
Refine the normal force between two sets of rigid geometries that are in contact
Select Augmented Lagrangian.
When you select Augmented Lagrangian, Adams View uses iterative refinement to ensure that penetration between the geometries is minimal. It also ensures that the normal force magnitude is relatively insensitive to the penalty or stiffness used to model the local material compliance effects.
Note: Augmented Lagrangian is only available when defining a Restitution-based contact.
Define a restitution-based contact
To define the normal force as restitution-based:
1. Set Normal Force to Restitution.
2. Enter a penalty value to define the local stiffness properties between the contacting material.
A large penalty value ensures that the penetration of one geometry into another will be small. Large values, however, will cause numerical integration difficulties. A value of 1E6 is appropriate for systems modeled in Kg-mm-sec. For more information on how to specify this value, see the Extended Definition for the CONTACT statement in the Adams Solver online help.
3. Enter the coefficient of restitution, which models the energy loss during contact.
4. A value of zero specifies a perfectly plastic contact between the two colliding bodies.
5. A value of one specifies a perfectly elastic contact. There is no energy loss.
The coefficient of restitution is a function of the two materials that are coming into contact. For information on material types versus commonly used values of the coefficient of restitution, see the table for the CONTACT statement in the Adams Solver online help. Restitution based contacts is not available when flexible bodies are participating in the contact.
Define an impact contact
To define the normal force as based on an impact using the IMPACT function:
1. Set Normal Force to Impact.
2. Enter values for the following:
■Stiffness - Specifies a material stiffness that is to be used to calculate the normal force for the impact model.
In general, the higher the stiffness, the more rigid or hard the bodies in contact are.
Note: When changing the length units in Adams View, stiffnesses in contacts are scaled by (length conversion factor**exponent). When changing the force unit, stiffness is only scaled by the force conversion factor.
■Force Exponent - Adams Solver models normal force as a nonlinear springdamper. If the damping penetration, above, is the instantaneous penetration between the contacting geometry, Adams Solver calculates the contribution of the material stiffness to the instantaneous normal forces as:
STIFFNESS * (PENALTY)**EXPONENT
For more information, see the IMPACT function in the Adams Solver online help.
■Damping - Enter a value to define the damping properties of the contacting material. A good rule of thumb is that the damping coefficient is about one percent of the stiffness coefficient.
■Penetration Depth - Enter a value to define the penetration at which Adams Solver turns on full damping. Adams Solver uses a cubic STEP function to increase the damping coefficient from zero, at zero penetration, to full damping when the penetration reaches the damping penetration. A reasonable value for this parameter is 0.01 mm. For more information, refer to the IMPACT function in the Adams Solver online help.
Define your own contact model
1. Set Normal Force to User Defined.
2. Enter parameters to the user-defined subroutine. You can also specify an alternative library and name for the user subroutine in the Routine text box. Learn about ROUTINE Argument.
Model the friction effects at the contact locations using the Coulomb friction model
Note: The friction model models dynamic friction but not stiction.
For more on friction in contacts, see Contact Friction Force Calculation. In addition, read the information for the CONTACT statement in the Adams Solver online help.
1. Set Friction Force to Coulomb.
2. Set Coulomb Friction to On, Off, or Dynamics Only to define whether friction effects are to be included.
3. In the Static Coefficient text box, specify the coefficient of friction at a contact point when the slip velocity is smaller than the value for Stiction Transition Vel. For information on material types versus commonly used values of the coefficient of static friction, see Material Contact Properties Table.
Excessively large values of Static Coefficient can cause integration difficulties.
Range: Static Coefficient 0
4. In the Dynamic Coefficient text box, specify the coefficient of friction at a contact point when the slip velocity is larger than the value for Friction Transition Vel. For information on material types versus commonly used values of the coefficient of the dynamic coefficient of friction, see Material Contact Properties Table.
Excessively large values of Dynamic Coefficient can cause integration difficulties.
Range: 0 Dynamic Coefficient Static Coefficient
5. In the Stiction Transition Vel. text box, enter the static transition velocity. Learn more about this value.
6. In the Friction Transition Vel. text box, enter the friction transition velocity.
Adams Solver gradually transitions the coefficient of friction from the value for Static Coefficent to the value for Dynamic Coefficient as the slip velocity at the contact point increases. When the slip velocity is equal to the value specified for Friction Transition Vel., the effective coefficient of friction is set to Dynamic Coefficient.
Note: Small values for this option cause the integrator difficulties. You should specify this value as:
Friction Transition Vel. 5* ERROR
where ERROR is the integration error used for the solution. Its default value is 1E-3.
Range: Friction Transition Vel. Stiction Transition Vel. > 0
Model the friction effects at the contact locations using your own model
1. Set Friction Force to User Defined.
2. Enter parameters to a user-defined subroutine, CNFSUB, and enter the name of the routine.
3. In the Stiction Transition Vel. text box, enter the static transition velocity.
Adams Solver gradually transitions the coefficient of friction from the value in Dynamic Coefficient to the value in Static Coefficent as the slip velocity at the contact point decreases. When the slip velocity is equal to the value you specify for Stiction Transition Vel., the effective coefficient of friction is set to the value in Static Coefficient.
Range: 0 < Stiction Transition Vel. Friction Transition Vel
Note: A small value for Static Transition Vel. causes numerical integrator difficulties. A general rule for specifying this value is:
Stiction Transition Vel. ERROR
where ERROR is the accuracy requested of the integrator. Its default value is 1E-3. See Solver Settings - Dynamics.