This is the base class from which all Force element handle classes derive. More...

Inheritance diagram for SimTK::Force:

Classes
class	ConstantForce
	A constant force applied to a body station. More...

class	ConstantTorque
	A constant torque to a body. More...

class	Custom
	This class is used to define new force elements. More...

class	DiscreteForces
	Arbitrary discrete body forces and mobility (generalized) forces. Useful for applying external forces or forces that are updated at discrete times due to the occurrence of events. More...

class	GlobalDamper
	A general energy "drain" on the system. More...

class	Gravity
	This force element represents a uniform gravitational field applied to a set of bodies. More...

class	LinearBushing
	This force element represents a bushing acting to connect a frame F fixed on one body (B1) to a frame M fixed on a second body (B2), by a massless, compliant element with linear stiffness and damping properties. More...

class	MobilityConstantForce
	A constant generalized force f (a scalar) applied to a mobility. More...

class	MobilityDiscreteForce
	A discrete mobility (generalized) force f applied to a particular mobility that is specified at construction. Useful for applying external forces or forces that are updated at discrete times due to the occurrence of events. More...

class	MobilityLinearDamper
	A linear damper that acts along or around a mobility coordinate to apply a generalized force there. More...

class	MobilityLinearSpring
	A linear spring that acts along or around a mobility coordinate to apply a generalized force there. More...

class	MobilityLinearStop
	Model a compliant stop element that acts to keep a mobilizer coordinate q within specified bounds. More...

class	Thermostat
	This is a feedback-controlled force that uses Nose'-Hoover chains to maintain a particular temperature Tb, as though the system were immersed in an infinite heat bath at that temperature. More...

class	TwoPointConstantForce
	A constant force f (a signed scalar) which acts along the line between two points, specified as a station on each of two bodies. More...

class	TwoPointLinearDamper
	A force which resists changes in the distance between two points, acting along the line between those points. More...

class	TwoPointLinearSpring
	A linear spring between two points, specified as a station on each of two bodies. More...

class	UniformGravity
	A uniform gravitational force applied to every body in the system. See Force::Gravity for a more flexible option. More...

Public Member Functions
Enabling and disabling
These methods determine whether this force element is active in a given State. When disabled, the Force element is completely ignored and will not be updated during realization. Normally force elements are enabled when defined unless explicitly disabled; you can reverse that using the setDisabledByDefault() method below.
void	disable (State &) const
	Disable this force element, effectively removing it from the System for computational purposes (it is still using its ForceIndex, however). More...

void	enable (State &) const
	Enable this force element if it was previously disabled. More...

bool	isDisabled (const State &) const
	Test whether this force element is currently disabled in the supplied State. More...

void	setDisabledByDefault (bool shouldBeDisabled)
	Normally force elements are enabled when defined and can be disabled later. More...

bool	isDisabledByDefault () const
	Test whether this force element is disabled by default in which case it must be explicitly enabled before it will take effect. More...

Advanced methods
Don't use these unless you're sure you know what you're doing. They aren't normally necessary but can be handy sometimes, especially when debugging newly-developed force elements.
void	calcForceContribution (const State &state, Vector_< SpatialVec > &bodyForces, Vector_< Vec3 > &particleForces, Vector &mobilityForces) const
	Calculate the force that would be applied by this force element if the given state were realized to Dynamics stage. More...

Real	calcPotentialEnergyContribution (const State &state) const
	Calculate the potential energy contribution that is made by this force element at the given state. More...

Bookkeeping
These methods are not normally needed. They provide bookkeeping information such as access to the parent force subsystem and the force index assigned to this force element.
	Force ()
	Default constructor for Force handle base class does nothing. More...

	operator ForceIndex () const
	Implicit conversion to ForceIndex when needed. More...

const GeneralForceSubsystem &	getForceSubsystem () const
	Get the GeneralForceSubsystem of which this Force is an element. More...

ForceIndex	getForceIndex () const
	Get the index of this force element within its parent force subsystem. More...

Public Member Functions inherited from SimTK::PIMPLHandle< Force, ForceImpl, true >
bool	isEmptyHandle () const
	Returns true if this handle is empty, that is, does not refer to any implementation object. More...

bool	isOwnerHandle () const
	Returns true if this handle is the owner of the implementation object to which it refers. More...

bool	isSameHandle (const Force &other) const
	Determine whether the supplied handle is the same object as "this" PIMPLHandle. More...

void	disown (Force &newOwner)
	Give up ownership of the implementation to an empty handle. More...

PIMPLHandle &	referenceAssign (const Force &source)
	"Copy" assignment but with shallow (pointer) semantics. More...

PIMPLHandle &	copyAssign (const Force &source)
	This is real copy assignment, with ordinary C++ object ("value") semantics. More...

void	clearHandle ()
	Make this an empty handle, deleting the implementation object if this handle is the owner of it. More...

const ForceImpl &	getImpl () const
	Get a const reference to the implementation associated with this Handle. More...

ForceImpl &	updImpl ()
	Get a writable reference to the implementation associated with this Handle. More...

int	getImplHandleCount () const
	Return the number of handles the implementation believes are referencing it. More...

Protected Member Functions
	Force (ForceImpl *r)
	Use this in a derived Force handle class constructor to supply the concrete implementation object to be stored in the handle base. More...

Protected Member Functions inherited from SimTK::PIMPLHandle< Force, ForceImpl, true >
	PIMPLHandle ()
	The default constructor makes this an empty handle. More...

	PIMPLHandle (ForceImpl *p)
	This provides consruction of a handle referencing an existing implementation object. More...

	PIMPLHandle (const PIMPLHandle &source)
	The copy constructor makes either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer semantics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...

	~PIMPLHandle ()
	Note that the destructor is non-virtual. More...

PIMPLHandle &	operator= (const PIMPLHandle &source)
	Copy assignment makes the current handle either a deep (value) or shallow (reference) copy of the supplied source PIMPL object, based on whether this is a "pointer sematics" (PTR=true) or "object (value) semantics" (PTR=false, default) class. More...

void	setImpl (ForceImpl *p)
	Set the implementation for this empty handle. More...

bool	hasSameImplementation (const Force &other) const
	Determine whether the supplied handle is a reference to the same implementation object as is referenced by "this" PIMPLHandle. More...

Additional Inherited Members
Public Types inherited from SimTK::PIMPLHandle< Force, ForceImpl, true >
typedef PIMPLHandle< Force, ForceImpl, PTR >	HandleBase

typedef HandleBase	ParentHandle

Detailed Description

This is the base class from which all Force element handle classes derive.

A Force object applies forces to some or all of the bodies, particles, and mobilities in a System. There are subclasses for various standard types of forces, or you can create your own forces by deriving from Force::Custom.

Constructor & Destructor Documentation

SimTK::Force::Force ( )

inline

Default constructor for Force handle base class does nothing.

SimTK::Force::Force ( ForceImpl * r )

inlineexplicitprotected

Use this in a derived Force handle class constructor to supply the concrete implementation object to be stored in the handle base.

Member Function Documentation

void SimTK::Force::disable ( State & ) const

Disable this force element, effectively removing it from the System for computational purposes (it is still using its ForceIndex, however).

This is an Instance-stage change.

void SimTK::Force::enable ( State & ) const

Enable this force element if it was previously disabled.

This is an Instance-stage change. Nothing happens if the force element was already enabled.

bool SimTK::Force::isDisabled ( const State & ) const

Test whether this force element is currently disabled in the supplied State.

If it is disabled you cannot depend on any computations it normally performs being available.

void SimTK::Force::setDisabledByDefault ( bool shouldBeDisabled )

Normally force elements are enabled when defined and can be disabled later.

If you want to define this force element but have it be off by default, use this method. Note that this is a Topology-stage (construction) change; you will have to call realizeTopology() before using the containing System after a change to this setting has been made.

bool SimTK::Force::isDisabledByDefault ( ) const

Test whether this force element is disabled by default in which case it must be explicitly enabled before it will take effect.

See also: enable()

void SimTK::Force::calcForceContribution	(	const State &	state,
		Vector_< SpatialVec > &	bodyForces,
		Vector_< Vec3 > &	particleForces,
		Vector &	mobilityForces
	)		const

Calculate the force that would be applied by this force element if the given state were realized to Dynamics stage.

This sizes the given arrays if necessary, zeroes them, and then calls the force element's calcForce() method which adds its force contributions if any to the appropriate array elements for bodies, particles, and mobilities. Note that in general we have no idea what elements of the system are affected by a force element, and in fact that can change based on state and time (consider contact forces, for example). A disabled force element will return all zeroes without invoking calcForce(), since that method may depend on earlier computations which may not have been performed in that case.

Parameters

[in]	state	The State containing information to be used by the force element to calculate the current force. This must have already been realized to a high enough stage for the force element to get what it needs; if you don't know then realize it to Stage::Velocity.
[out]	bodyForces	This is a Vector of spatial forces, one per mobilized body in the matter subsystem associated with this force element. This Vector is indexed by MobilizedBodyIndex so it has a 0th entry corresponding to Ground. A spatial force contains two Vec3's; index with [0] to get the moment vector, with [1] to get the force vector. This argument is resized if necessary to match the number of mobilized bodies and any unused entry will be set to zero on return.
[out]	particleForces	This is a Vector of force vectors, one per particle in the matter subsystem associated with this force element. This vector is indexed by ParticleIndex; the 0th entry is the 1st particle, not Ground. This argument is resized if necessary to match the number of particles and any unused entry will be set to zero on return. (As of March 2010 Simbody treats particles as mobilized bodies so this is unused.)
[out]	mobilityForces	This is a Vector of scalar generalized forces, one per mobility in the matter subsystem associated with this force element. This is the same as the number of generalized speeds u that collectively represent all the mobilities of the mobilizers. To determine the per-mobilizer correspondence, you must call methods of MobilizedBody; there is no hint here.

Note: This method must zero out the passed in arrays, and in most cases almost all returned entries will be zero, so this is not the most efficent way to calculate forces; use it sparingly.

Real SimTK::Force::calcPotentialEnergyContribution ( const State & state ) const

Calculate the potential energy contribution that is made by this force element at the given state.

This calls the force element's calcPotentialEnergy() method. A disabled force element will return zero without invoking calcPotentialEnergy().

Parameters

[in] state The State containing information to be used by the force element to calculate the current potential energy. This must have already been realized to a high enough stage for the force element to get what it needs; if you don't know then realize it to Stage::Position.

Returns: The potential energy contribution of this force element at this state value.

SimTK::Force::operator ForceIndex ( ) const

inline

Implicit conversion to ForceIndex when needed.

This will throw an exception if the force element has not yet been adopted by a force subsystem.

const GeneralForceSubsystem& SimTK::Force::getForceSubsystem ( ) const

Get the GeneralForceSubsystem of which this Force is an element.

This will throw an exception if the force element has not yet been adopted by a force subsystem.

ForceIndex SimTK::Force::getForceIndex ( ) const

Get the index of this force element within its parent force subsystem.

The returned index will be invalid if the force element has not yet been adopted by any subsystem (test with the index.isValid() method).

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

Force.h

Classes

Public Member Functions

Protected Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation