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

#include <HuntCrossleyContact.h>

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)

Guts &	updRep ()

const Guts &	getRep () const

Public Member Functions inherited from SimTK::Subsystem
	Subsystem ()

	Subsystem (const Subsystem &)

Subsystem &	operator= (const Subsystem &)

	~Subsystem ()

const String &	getName () const

const String &	getVersion () const

QIndex	allocateQ (State &, const Vector &qInit) const

UIndex	allocateU (State &, const Vector &uInit) const

ZIndex	allocateZ (State &, const Vector &zInit) const

DiscreteVariableIndex	allocateDiscreteVariable (State &, Stage invalidates, AbstractValue *v) const

DiscreteVariableIndex	allocateAutoUpdateDiscreteVariable (State &, Stage invalidates, AbstractValue *v, Stage updateDependsOn) const

CacheEntryIndex	allocateCacheEntry (const State &, 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 &, int nqerr) const

UErrIndex	allocateUErr (const State &, int nuerr) const

UDotErrIndex	allocateUDotErr (const State &, int nudoterr) const

EventTriggerByStageIndex	allocateEventTriggersByStage (const State &, Stage, int ntriggers) const

const Vector &	getQ (const State &) const

const Vector &	getU (const State &) const

const Vector &	getZ (const State &) const

const Vector &	getQDot (const State &) const

const Vector &	getUDot (const State &) const

const Vector &	getZDot (const State &) const

const Vector &	getQDotDot (const State &) const

const Vector &	getQErr (const State &) const

const Vector &	getUErr (const State &) const

const Vector &	getUDotErr (const State &) const

const Vector &	getMultipliers (const State &) const

const Vector &	getEventTriggersByStage (const State &, Stage) const

Vector &	updQ (State &) const

Vector &	updU (State &) const

Vector &	updZ (State &) 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

Vector &	updQDot (const State &) const

Vector &	updUDot (const State &) const

Vector &	updZDot (const State &) const

Vector &	updQDotDot (const State &) const

Vector &	updQErr (const State &) const

Vector &	updUErr (const State &) const

Vector &	updUDotErr (const State &) const

Vector &	updMultipliers (const State &) const

Vector &	updEventTriggersByStage (const State &, Stage) const

Stage	getStage (const State &) const

const AbstractValue &	getDiscreteVariable (const State &s, DiscreteVariableIndex dx) const

Real	getDiscreteVarLastUpdateTime (const State &s, DiscreteVariableIndex dx) const

CacheEntryIndex	getDiscreteVarUpdateIndex (const State &s, DiscreteVariableIndex dx) const

const AbstractValue &	getDiscreteVarUpdateValue (const State &s, DiscreteVariableIndex dx) const

AbstractValue &	updDiscreteVarUpdateValue (const State &s, DiscreteVariableIndex dx) const

bool	isDiscreteVarUpdateValueRealized (const State &s, DiscreteVariableIndex dx) const

void	markDiscreteVarUpdateValueRealized (const State &s, DiscreteVariableIndex dx) const

AbstractValue &	updDiscreteVariable (State &, DiscreteVariableIndex) const

const AbstractValue &	getCacheEntry (const State &, CacheEntryIndex) const

AbstractValue &	updCacheEntry (const State &, CacheEntryIndex) const

bool	isCacheValueRealized (const State &, CacheEntryIndex) const

void	markCacheValueRealized (const State &, CacheEntryIndex) const

void	markCacheValueNotRealized (const State &, CacheEntryIndex) const

SystemQIndex	getQStart (const State &) const

int	getNQ (const State &) const

SystemUIndex	getUStart (const State &) const

int	getNU (const State &) const

SystemZIndex	getZStart (const State &) const

int	getNZ (const State &) const

SystemQErrIndex	getQErrStart (const State &) const

int	getNQErr (const State &) const

SystemUErrIndex	getUErrStart (const State &) const

int	getNUErr (const State &) const

SystemUDotErrIndex	getUDotErrStart (const State &) const

int	getNUDotErr (const State &) const

SystemMultiplierIndex	getMultipliersStart (const State &) const

int	getNMultipliers (const State &) const

SystemEventTriggerByStageIndex	getEventTriggerStartByStage (const State &, Stage) const

int	getNEventTriggersByStage (const State &, Stage) const

bool	isInSystem () const

bool	isInSameSystem (const Subsystem &otherSubsystem) const

const System &	getSystem () const

System &	updSystem ()

SubsystemIndex	getMySubsystemIndex () const

bool	isOwnerHandle () const

bool	isEmptyHandle () const

bool	isSameSubsystem (const Subsystem &otherSubsystem) const

bool	subsystemTopologyHasBeenRealized () const

void	invalidateSubsystemTopologyCache () const

MeasureIndex	adoptMeasure (AbstractMeasure &)

AbstractMeasure	getMeasure (MeasureIndex) const

template<class T >
Measure_< T >	getMeasure_ (MeasureIndex mx) const

const Subsystem::Guts &	getSubsystemGuts () const

Subsystem::Guts &	updSubsystemGuts ()

void	adoptSubsystemGuts (Subsystem::Guts *g)

void	setSystem (System &, SubsystemIndex)

	Subsystem (Subsystem::Guts *g)

bool	hasGuts () const

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:

HuntCrossleyContact.h

Public Member Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation