Body Constraint Reference

After creating a body contact constraint, you set up the properties according to the constraint type.

[contact constraint] Properties

Properties of this constraint type are listed here:

Bodies

A list of bodies to which the constraint applies. Only those bodies with the Body Motion Option set to Multi-Body Motion are available for this list.

Enabled

When On, puts the constraint into effect. The default is On.

Contact Method

The type of surface the body comes in contact with. Properties for the method are set in a sub-node under the constraint node. Presently, only the Half-plane method is available.

Contact Tolerance

The distance above the surface where contact is assumed. The default is 1.0E-4 m.

Half-plane Properties

Specifies the position and orientation of a half-plane contact surface. A body can slide down the half-plane and drop off the edge, or it can lift off from it. Collisions with the half-plane are not supported.

Origin: A point on the half-plane edge. The default is [0.0, 0.0, 0.0] m,m,m.
Direction: A vector normal to the half-plane edge, lying in the same plane as the half-plane. The default is [1.0, 0.0, 0.0] m.
Normal: A vector normal to the half-plane. The default is [0.0, 0.0, 1.0] m.
Coordinate System: Specifies which steady coordinate system is used. Time-dependent coordinate systems are not supported. The default is Laboratory.

Friction Settings Properties

Specifies the friction properties for the contact between the bodies and surfaces.

Dynamic Friction Coefficient: If the relative sliding velocity is above Velocity Tolerance, dynamic friction is in effect. Dynamic friction is modeled using the Coulomb friction model. The default is zero.
Static Friction Coefficient: If the relative sliding velocity is below Velocity Tolerance, static friction is in effect. The default is zero.
Tanh Coefficient: The Tanh Coefficient is used to smooth the discontinuity of the friction force for small relative sliding velocities. See Eqn. (4965). The default is 10.0 s/m.
Velocity Tolerance: The relative sliding velocity at which static friction gives way to dynamic friction. The default is 0.001 m/s.

[velocity driver] Properties

Properties of this constraint type are listed here:

Object 1: Specifies the first constrained object, which is coupled with Object 2 by the velocity constraint. A velocity dependence is created between these two objects. The object can be Environment or a 6-DOF body with the Body Motion Option set to Multi-Body Motion.
Object 2: Specifies the second constrained object. Same to Object 1, Object 2 can be Environment or a 6-DOF body with the Body Motion Option set to Multi-Body Motion.
Enabled: When Activated, the constraint is active.
Position 1: Specifies the position of a point on Object 1. The velocity driver constraint defines the relative velocity between this point and a second point defined on Object2. You specify the coordinate system for Position1 using the Coordinate System 1 property.
For example, to specify the center of mass of Body 1, you can define position [0,0,0] in the body coordinate system Laboratory->Body 1-Csys.
Position 2: Specifies the position of a point on Object 2. You specify the coordinate system for Position 2 using the Coordinate System 2 property.
Velocity: Specifies a relative velocity of Position 1 on Object 1 with respect to Position 2 on Object 2, ina Direction that you specify..
This velocity must be consistent with the initial velocity and angular velocity of all the participating bodies. To make sure the settings are consistent, you can use the InitialVelocityOfDfbiConstraint field function.
Direction: Specifies the direction in which the Velocity is defined, with respect to the specified Direction Coordinate System.
In the directions orthogonal to this specified direction, the bodies are free to move, unless other constraints restrict the motion.
Direction Coordinate System: Specifies the coordinate system used for the definition of Direction.
Coordinate System 1 (Expert): Specifies the coordinate system used for Position 1.
Coordinate System 2 (Expert): Specifies the coordinate system used for Position 2.

[distance driver] Properties

Object 1: Specifies the first constrained object, which is coupled with Object 2 by the distance constraint. A distance dependence is created between these two objects. The object can be Environment or a 6-DOF body with the Body Motion Option set to Multi-Body Motion.
Object 2: Specifies the second constrained object. As for Object 1, Object 2 can be Environment or a 6-DOF body with the Body Motion Option set to Multi-Body Motion.
Enabled: When Activated, the constraint is active.
Position 1: Specifies the position of a point on Object 1. The coordinate system for Position1 is given by the Coordinate System 1 property.
For example, to specify the center of mass of Body 1, you can define position [0,0,0] in the body coordinate system Laboratory->Body 1-Csys.
Position 2: Specifies the position of a point on Object 2. The coordinate system for Position2 is given by the Coordinate System 2 property.
Distance: Specifies the distance between the points at Position 1 and Position 2. By default, this property is initially filled with the expression ${InitialDistanceOfDfbiConstraint...}+${Time}*${InitialVelocityOfDfbiConstraint...}, where the dots (...) refer to the index of the constraint, e.g., "1", "2", etc.
In case that the distance specification is inconsistent to the initial distance, velocity and angular velocity settings of the bodies, you must set a Blending Time to blend the initial values into this user-specified Distance over some short period of time.
Coordinate System 1 (Expert): Specifies the coordinate system used for Position 1.
Coordinate System 2 (Expert): Specifies the coordinate system used for Position 2.
Blending Time (Expert): Specify a time window to blend the initial distance and velocity resulting from the body initial conditions into the user-specified distance and velocity, where velocity refers to the time derivative of the distance. At the end of the Blending Time, the distance and velocity both follow the user-specified values.
You use blending time when there is an inconsistency between body initial conditions (i.e., distance, velocities and angular velocities) and the user-specified distance definition. Without blending time, the case can not run until you remove the inconsistency. An example of using the blending time is introduced in Setting up Body Constraints.