Simbody  3.5
SimTK::HuntCrossleyContact Class Reference

This is a concrete subsystem that handles simple, frictionless contact situations with a model due to Hunt & Crossley: K. More...

+ Inheritance diagram for SimTK::HuntCrossleyContact:

Public Member Functions

 HuntCrossleyContact ()
 
 HuntCrossleyContact (MultibodySystem &)
 
int addSphere (MobilizedBodyIndex body, const Vec3 &center, const Real &radius, const Real &stiffness, const Real &dissipation)
 
int addHalfSpace (MobilizedBodyIndex body, const UnitVec3 &normal, const Real &height, const Real &stiffness, const Real &dissipation)
 
 SimTK_PIMPL_DOWNCAST (HuntCrossleyContact, ForceSubsystem)
 
- Public Member Functions inherited from SimTK::ForceSubsystem
 ForceSubsystem ()
 
 SimTK_PIMPL_DOWNCAST (ForceSubsystem, Subsystem)
 
GutsupdRep ()
 
const GutsgetRep () const
 
- Public Member Functions inherited from SimTK::Subsystem
 Subsystem ()
 Default constructor creates and empty handle with a null Subsystem::Guts pointer. More...
 
 Subsystem (const Subsystem &)
 Copy constructor clones the Subsystem::Guts object if there is one and makes this the owner handle of the new clone. More...
 
Subsystemoperator= (const Subsystem &)
 Copy assignment deletes the Subsystem::Guts object if there is one and then behaves like the copy constructor. More...
 
 ~Subsystem ()
 Destructor deletes the referenced Subsystem::Guts object if this is the owner handle of that object, otherwise does nothing. More...
 
QIndex allocateQ (State &s, const Vector &qInit) const
 
UIndex allocateU (State &s, const Vector &uInit) const
 
ZIndex allocateZ (State &s, const Vector &zInit) const
 
DiscreteVariableIndex allocateDiscreteVariable (State &s, Stage g, AbstractValue *v) const
 
DiscreteVariableIndex allocateAutoUpdateDiscreteVariable (State &s, Stage invalidates, AbstractValue *v, Stage updateDependsOn) const
 
CacheEntryIndex allocateCacheEntry (const State &s, Stage dependsOn, Stage computedBy, AbstractValue *v) const
 
CacheEntryIndex allocateCacheEntry (const State &state, Stage g, AbstractValue *v) const
 
CacheEntryIndex allocateLazyCacheEntry (const State &state, Stage earliest, AbstractValue *v) const
 
QErrIndex allocateQErr (const State &s, int nqerr) const
 
UErrIndex allocateUErr (const State &s, int nuerr) const
 
UDotErrIndex allocateUDotErr (const State &s, int nudoterr) const
 
EventTriggerByStageIndex allocateEventTriggersByStage (const State &s, Stage g, int ntriggers) const
 
const VectorgetQ (const State &s) const
 
const VectorgetU (const State &s) const
 
const VectorgetZ (const State &s) const
 
const VectorgetUWeights (const State &s) const
 
const VectorgetZWeights (const State &s) const
 
VectorupdQ (State &s) const
 
VectorupdU (State &s) const
 
VectorupdZ (State &s) const
 
const VectorgetQDot (const State &s) const
 
const VectorgetUDot (const State &s) const
 
const VectorgetZDot (const State &s) const
 
const VectorgetQDotDot (const State &s) const
 
VectorupdQDot (const State &s) const
 
VectorupdUDot (const State &s) const
 
VectorupdZDot (const State &s) const
 
VectorupdQDotDot (const State &s) const
 
const VectorgetQErr (const State &s) const
 
const VectorgetUErr (const State &s) const
 
const VectorgetQErrWeights (const State &s) const
 
const VectorgetUErrWeights (const State &s) const
 
const VectorgetUDotErr (const State &s) const
 
const VectorgetMultipliers (const State &s) const
 
const VectorgetEventTriggersByStage (const State &s, Stage g) const
 
VectorupdQErr (const State &s) const
 
VectorupdUErr (const State &s) const
 
VectorupdUDotErr (const State &s) const
 
VectorupdMultipliers (const State &s) const
 
VectorupdEventTriggersByStage (const State &s, Stage g) const
 
SystemQIndex getQStart (const State &s) const
 
int getNQ (const State &s) const
 
SystemUIndex getUStart (const State &s) const
 
int getNU (const State &s) const
 
SystemZIndex getZStart (const State &s) const
 
int getNZ (const State &s) const
 
SystemQErrIndex getQErrStart (const State &s) const
 
int getNQErr (const State &s) const
 
SystemUErrIndex getUErrStart (const State &s) const
 
int getNUErr (const State &s) const
 
SystemUDotErrIndex getUDotErrStart (const State &s) const
 
int getNUDotErr (const State &s) const
 
SystemMultiplierIndex getMultipliersStart (const State &s) const
 
int getNMultipliers (const State &s) const
 
SystemEventTriggerByStageIndex getEventTriggerStartByStage (const State &s, Stage g) const
 
int getNEventTriggersByStage (const State &s, Stage g) const
 
void setQ (State &s, const Vector &q) const
 
void setU (State &s, const Vector &u) const
 
void setZ (State &s, const Vector &z) const
 
Stage getStage (const State &s) const
 
void advanceToStage (const State &s, Stage g) const
 
const AbstractValuegetDiscreteVariable (const State &s, DiscreteVariableIndex index) const
 
AbstractValueupdDiscreteVariable (State &s, DiscreteVariableIndex index) const
 
const AbstractValuegetCacheEntry (const State &s, CacheEntryIndex index) const
 
AbstractValueupdCacheEntry (const State &s, CacheEntryIndex index) const
 
Real getDiscreteVarLastUpdateTime (const State &s, DiscreteVariableIndex dx) const
 
CacheEntryIndex getDiscreteVarUpdateIndex (const State &s, DiscreteVariableIndex dx) const
 
const AbstractValuegetDiscreteVarUpdateValue (const State &s, DiscreteVariableIndex dx) const
 
AbstractValueupdDiscreteVarUpdateValue (const State &s, DiscreteVariableIndex dx) const
 
bool isDiscreteVarUpdateValueRealized (const State &s, DiscreteVariableIndex dx) const
 
void markDiscreteVarUpdateValueRealized (const State &s, DiscreteVariableIndex dx) const
 
bool isCacheValueRealized (const State &s, CacheEntryIndex cx) const
 
void markCacheValueRealized (const State &s, CacheEntryIndex cx) const
 
void markCacheValueNotRealized (const State &s, CacheEntryIndex cx) const
 
const StringgetName () const
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
const StringgetVersion () const
 Obtain the Subsystem version string if one was given on construction. More...
 
bool isInSystem () const
 Return true if this Subsystem is contained in a System. More...
 
bool isInSameSystem (const Subsystem &otherSubsystem) const
 Return true if this Subsystem is contained in the same System as contains the given otherSubsystem. More...
 
const SystemgetSystem () const
 Return a const reference to the System that contains this Subsystem. More...
 
SystemupdSystem ()
 Return a writable reference to the System that contains this Subsystem. More...
 
void setSystem (System &system, SubsystemIndex subx)
 Inform this Subsystem of the System that contains it, as well as the SubsystemIndex which the System has assigned to it. More...
 
SubsystemIndex getMySubsystemIndex () const
 Return the SubsystemIndex within the containing System. More...
 
bool isEmptyHandle () const
 Return true if this handle has a null Subsystem::Guts pointer. More...
 
bool isSameSubsystem (const Subsystem &otherSubsystem) const
 Determine if this Subsystem handle refers to the same Subsystem::Guts object as handle otherSubsystem. More...
 
bool isOwnerHandle () const
 Is this Subsystem handle the owner of the Subsystem::Guts object it points to? This is true if the handle is empty or if its Guts object points back to this handle. More...
 
bool subsystemTopologyHasBeenRealized () const
 Returns true if this Subsystem's realizeTopology() method has been called since the last topological change or call to invalidateSubsystemTopologyCache(). More...
 
void invalidateSubsystemTopologyCache () const
 Always call this method when a topological change is made to this Subsystem to indicate that any Stage::Topology cache values may need recomputation. More...
 
MeasureIndex adoptMeasure (AbstractMeasure &)
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
AbstractMeasure getMeasure (MeasureIndex) const
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
template<class T >
Measure_< T > getMeasure_ (MeasureIndex mx) const
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
const Subsystem::GutsgetSubsystemGuts () const
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
Subsystem::GutsupdSubsystemGuts ()
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
void adoptSubsystemGuts (Subsystem::Guts *g)
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
 Subsystem (Subsystem::Guts *g)
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 
bool hasGuts () const
 Obtain the Subsystem name if one was given on construction of the concrete Subsystem. More...
 

Detailed Description

This is a concrete subsystem that handles simple, frictionless contact situations with a model due to Hunt & Crossley: K.

H. Hunt and F. R. E. Crossley, "Coefficient of Restitution Interpreted as Damping in Vibroimpact," ASME Journal of Applied Mechanics, pp. 440-445, June 1975. This is a continuous model based on Hertz elastic contact theory, which correctly reproduces the empirically observed dependence on velocity of coefficient of restitution, where e=(1-cv) for (small) impact velocity v and a material property c with units 1/v. Note that c can be measured right off the coefficient of restitution-vs.-velocity curves: it is the absolute value of the slope at low velocities.

Given a collision between two spheres, or a sphere and a plane, we can generate a contact force from this equation f = kx^n(1 + 3/2 cv) where k is a stiffness constant incorporating material properties and geometry (to be defined below), x is penetration depth and v = dx/dt is penetration rate (positive during penetration and negative during rebound). Exponent n depends on the surface geometry. For Hertz contact where the geometry can be approximated by sphere (or sphere-plane) interactions, which is all we are currently handling here, n=3/2.

Stiffness k is defined in terms of the relative radius of curvature R and effective plane-strain modulus E, each of which is a combination of the description of the two individual contacting elements. TODO: derivation of the following results should be in the SimTK Engr J; you'll have to take my word for it now:

R1*R2 E2^(2/3) R = ——-, E = (s1 * E1^(2/3))^(3/2), s1= ——————- R1 + R2 E1^(2/3) + E2^(2/3)

c = c1*s1 + c2*(1-s1) k = (4/3) sqrt(R) E f = k x^(3/2) (1 + 3/2 c xdot) pe = 2/5 k x^(5/2) Also, we can calculate the contact patch radius a as a = sqrt(R*x)

In the above, E1 and E2 are the *plane strain* moduli. If you have instead Young's modulus Y1 and Poisson's ratio p1, then E1=Y1/(1-p1^2). The interface to this subsystem asks for E1 (pressure/strain) and c1 (1/velocity), and E2,c2 only.

Constructor & Destructor Documentation

SimTK::HuntCrossleyContact::HuntCrossleyContact ( )
SimTK::HuntCrossleyContact::HuntCrossleyContact ( MultibodySystem )
explicit

Member Function Documentation

int SimTK::HuntCrossleyContact::addSphere ( MobilizedBodyIndex  body,
const Vec3 center,
const Real radius,
const Real stiffness,
const Real dissipation 
)
int SimTK::HuntCrossleyContact::addHalfSpace ( MobilizedBodyIndex  body,
const UnitVec3 normal,
const Real height,
const Real stiffness,
const Real dissipation 
)
SimTK::HuntCrossleyContact::SimTK_PIMPL_DOWNCAST ( HuntCrossleyContact  ,
ForceSubsystem   
)

The documentation for this class was generated from the following file: