artisynth.core.materials

Class ContactForceBehavior

java.lang.Object

artisynth.core.materials.MaterialBase

artisynth.core.materials.ContactForceBehavior

All Implemented Interfaces:

HasMaterialState, PostScannable, ScalableUnits, java.lang.Cloneable, CompositeProperty, HasProperties, Clonable, Scannable

Direct Known Subclasses:

AreaCompliantContact, ElasticContactBase

public abstract class ContactForceBehavior
extends MaterialBase

Field Summary

Fields

Modifier and Type	Field and Description
static int	TWO_WAY_CONTACT Deprecated. This flag is no longer set. Instead, for two-way contact, the contactArea argument of computeResponse(double[], double, artisynth.core.modelbase.ContactPoint, artisynth.core.modelbase.ContactPoint, maspack.matrix.Vector3d, double, int) is halved for vertex contacts, so that no further scaling is required.

Fields inherited from class artisynth.core.materials.MaterialBase

myProps

Constructor Summary

Constructors

Constructor and Description
ContactForceBehavior()

Method Summary

Modifier and Type	Method and Description
static double	computeContactArea(ContactPoint cpnt0, ContactPoint cpnt1, Vector3d normal) Deprecated. The contact area is now supplied directly to computeResponse(double[], double, artisynth.core.modelbase.ContactPoint, artisynth.core.modelbase.ContactPoint, maspack.matrix.Vector3d, double, int) via its contactArea argument, which should be used instead. Note that for two-way vertex contact, the value returned by this method is twice the effective area supplied by contactArea.
abstract void	computeResponse(double[] fres, double dist, ContactPoint cpnt0, ContactPoint cpnt1, Vector3d normal, double contactArea, int flags) Computes the force response for a given contact.
static java.lang.Class<?>[]	getSubClasses()
static void	registerSubclass(java.lang.Class<? extends FemMaterial> cls) Allow adding of classes (for use in control panels)

Methods inherited from class artisynth.core.materials.MaterialBase

advanceState, clone, createChangeEvent, createStateObject, getAllPropertyInfo, getProperty, getPropertyHost, getPropertyInfo, hasProperty, hasState, hasSymmetricTangent, isWritable, postscan, scaleDistance, scaleMass, scan, setPropertyHost, setPropertyInfo, symmetryOrStateChanged, updateMaterial, write, writeItems

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TWO_WAY_CONTACT

@Deprecated
public static final int TWO_WAY_CONTACT

Deprecated. This flag is no longer set. Instead, for two-way contact, the contactArea argument of computeResponse(double[], double, artisynth.core.modelbase.ContactPoint, artisynth.core.modelbase.ContactPoint, maspack.matrix.Vector3d, double, int) is halved for vertex contacts, so that no further scaling is required.

Flag formerly used to indicate that vertex penetrations are being calculated for both collidables, which means that the effective area should be divided by two in order to produce the same contact pressures as for one-way contact.

See Also:

Constant Field Values

Constructor Detail

ContactForceBehavior

public ContactForceBehavior()

Method Detail

registerSubclass

public static void registerSubclass(java.lang.Class<? extends FemMaterial> cls)

Allow adding of classes (for use in control panels)

Parameters:

cls - class to register

getSubClasses

public static java.lang.Class<?>[] getSubClasses()

computeResponse

public abstract void computeResponse(double[] fres,
                                     double dist,
                                     ContactPoint cpnt0,
                                     ContactPoint cpnt1,
                                     Vector3d normal,
                                     double contactArea,
                                     int flags)

Computes the force response for a given contact. The response consists of four values: force, compliance, damping, and step damping, which should be placed into the first four entries of fres. Entries that are not set default to 0. The force is defined as the restoring force

 force = f(dist)
 

computed in response to the interpenetration distance dist. Note that in general, dist will be negative, and a negative force will be expected in response. The compliance is the reciprocal of the derivative of f(dist) evaluated at dist. The damping is a positive damping parameter used to generate damping forces in response to motion in the contact direction. The step damping is an optional dimensionless factor that specifies a minimum damping proportional to the step size h, such that the effective damping d is given by

 d = max (damping, stepDamping*h/compliance)
 

This allows the damping time constant d*compliance to be kept at or above h/2, which is the minimum required for stable compliant contact, without the behavior needing to know h. Damping and step damping are applied only if the compliance is greater than 0.

Other information the can be used includes the two contact points associated the contact, and the contact normal, which is facing outward from the contact surface.

Parameters:

fres - returns the force, compliance, damping and step damping for a given contact distance.

dist - contact interpenetration distance. This value is usually negative, with greater negativity indicating greater interpenetration.

cpnt0 - first contact point

cpnt1 - second contact point

normal - contact normal, directed from cpnt0 to cpnt1

contactArea - area associated with the contact. For vertex penetration contacts, this is one third of the area of each face surrounding the penetrating vertex; for edge-edge contacts, it is one third of the area of each face adjacent to the first edge; in both cases, the area is projected onto the plane perpendicular to the normal. For contour region contacts, it is the area of the contact region divided by the number of contact points. For two-way contact (when vertex penetrations are computed for both collidables), the area of vertex contacts is halved, since the vertices of both collidables then cover the same contact patch.

flags - flags providing additional information to the calculation. No flags are currently defined.

computeContactArea

@Deprecated
public static double computeContactArea(ContactPoint cpnt0,
                                                    ContactPoint cpnt1,
                                                    Vector3d normal)

Deprecated. The contact area is now supplied directly to computeResponse(double[], double, artisynth.core.modelbase.ContactPoint, artisynth.core.modelbase.ContactPoint, maspack.matrix.Vector3d, double, int) via its contactArea argument, which should be used instead. Note that for two-way vertex contact, the value returned by this method is twice the effective area supplied by contactArea.

Compute the local contact area for a contact described by contact points cpnt0 and cpnt1 and a normal normal, using ContactPoint.computeContactArea(maspack.matrix.Vector3d).

Parameters:

cpnt0 - first contact point

cpnt1 - second contact point

normal - contact normal, directed from cpnt0 to cpnt1

Returns:

local contact area, or -1 if cpnt0 is not associated with a vertex or edge