Computes the forces corresponding to sliding friction. More...

#include <SlidingFrictionInteraction.h>

Inheritance diagram for SlidingFrictionInteraction:

Public Types
typedef SlidingFrictionSpecies	SpeciesType
	An alias name for SlidingFrictionSpecies data type. More...

Public Member Functions
	SlidingFrictionInteraction (BaseInteractable P, BaseInteractable I, Mdouble timeStamp)
	Constructor. More...

	SlidingFrictionInteraction (const SlidingFrictionInteraction &p)
	Copy constructor. More...

virtual	~SlidingFrictionInteraction ()
	Destructor. More...

void	computeFrictionForce ()
	Computes the tangential force generated due to compression in the sliding spring. Does take into account if the interaction is between particle-particle or particle-wall. More...

void	read (std::istream &is)
	Interaction read function, which accepts an std::istream as input. More...

void	write (std::ostream &os) const
	Interaction write function, which accepts an std::ostream as input. More...

void	integrate (Mdouble timeStep)
	Increments the amount of compression in sliding spring. More...

Mdouble	getElasticEnergy () const
	Returns the amount of elastic energy stored in sliding spring. More...

Mdouble	getTangentialOverlap () const
	Returns the amount of tangential overlap which is needed by BaseInteraction::writeToFstat(). More...

std::string	getBaseName () const
	Returns the type/name of interaction (sliding friction interaction) More...

void	setSlidingSpring (const Vec3D slidingSpring)

Vec3D	getSlidingSpring () const

const Vec3D	getTangentialForce () const
	Returns the sliding friction force vector. More...

const SlidingFrictionSpecies *	getSpecies () const
	Returns a const pointer of type SlidingFrictionSpecies*. More...

void	reverseHistory ()
	A useful feature if one wants to return to the initial state of the spring. However, reverse history decrements the current state to the state corresponding to previous time step. Decrements the value of slidingSpring_. More...

void	rotateHistory (Matrix3D &rotationMatrix)
	When periodic particles are used, some interactions need certain history properties rotated (e.g. tangential springs). This is the function for that. More...

void	moveSlidingSpring (const Vec3D displacement)

Public Member Functions inherited from BaseInteraction
	BaseInteraction (BaseInteractable P, BaseInteractable I, Mdouble timeStamp)
	A constructor takes the BaseInteractable objects which are interacting (come into contact) and time the interaction starts. More...

	BaseInteraction (const BaseInteraction &p)
	Copy constructor. More...

	BaseInteraction ()
	Empty constructor. More...

virtual	~BaseInteraction ()
	The default destructor. More...

virtual void	actionsOnErase ()
	If an interaction needs to do something before it gets erased, add it here. E.g. Liquid bridges rupture at the end of their lifetime, and the liquid bridge volume has to be redistributed. The reason this action is not done in the destructor is that this action should not be taken when erasing ghost interactions. More...

virtual void	computeForce ()
	Virtual function that contains the force law between the two objects interacting. More...

void	writeToFStat (std::ostream &os) const
	Writes forces data to the FStat file. More...

virtual std::string	getName () const
	Virtual function which allows interactions to be named. More...

void	setDistance (Mdouble distance)
	Sets the interaction distance between the two interacting objects. More...

void	setNormal (Vec3D normal)
	Sets the normal vector between the two interacting objects. More...

void	setOverlap (Mdouble overlap)
	Set the overlap between the two interacting object. More...

void	setContactPoint (Vec3D contactPoint)
	Set the location of the contact point between the two interacting objects. More...

void	setTimeStamp (Mdouble timeStamp)
	Updates the time step of the interacting. Note, timesteps used to find completed interactions. More...

void	setSpecies (BaseSpecies *species)
	Set the Species of the interaction; note this can either be a Species or MixedSpecies. More...

void	setP (BaseInteractable *P)
	Sets the first object involved in the interaction (normally a particle). More...

void	setI (BaseInteractable *I)
	Sets the second object involved in the interaction (often particle or wall). More...

void	setHandler (InteractionHandler *handler)
	Sets the pointer to the interaction hander which is storing this interaction. More...

InteractionHandler *	getHandler () const
	Gets a point to the interaction handlers to which this interaction belongs. More...

const Vec3D &	getForce () const
	Gets the current force (vector) between the two interacting objects. More...

const Vec3D &	getTorque () const
	Gets the current torque (vector) between the two interacting objects. More...

const Vec3D &	getNormal () const
	Gets the normal vector between the two interacting objects. More...

const Vec3D &	getContactPoint () const
	Gets constant reference to contact point (vector). More...

Mdouble	getOverlap () const
	Returns a Mdouble with the current overlap between the two interacting objects. More...

Mdouble	getContactRadius () const
	Returns a Mdouble with the current contact between the two interacting objects. More...

void	removeFromHandler ()
	Removes this interaction from its interaction hander. More...

void	copySwitchPointer (const BaseInteractable original, BaseInteractable ghost) const
	This copies the interactions of the original particle and replaces the original with the ghost copy. More...

void	gatherContactStatistics ()

BaseInteractable *	getP ()
	Returns a pointer to first object involved in the interaction (normally a particle). More...

BaseInteractable *	getI ()

const BaseInteractable *	getP () const

const BaseInteractable *	getI () const
	Returns a constant pointer to the second object involved in the interaction. More...

Mdouble	getTimeStamp () const
	Returns an Mdouble which is the time stamp of the interaction. More...

Mdouble	getDistance () const
	Returns an Mdouble which is the norm (length) of distance vector. More...

const Vec3D &	getRelativeVelocity () const
	Returns a constant reference to a vector of relative velocity. More...

Mdouble	getNormalRelativeVelocity () const
	Returns a double which is the norm (length) of the relative velocity vector. More...

Mdouble	getAbsoluteNormalForce () const
	Returns the absolute value of the norm (length) of the Normal force vector. More...

virtual BaseInteraction *	copy () const =0
	Makes a copy of the interaction and returns a pointer to the copy. More...

unsigned int	getMultiContactIdentifier () const

void	setMultiContactIdentifier (unsigned int multiContactIdentifier_)

virtual void	actionsAfterTimeStep ()

virtual unsigned	getNumberOfFieldsVTK () const

virtual std::string	getTypeVTK (unsigned i) const

virtual std::string	getNameVTK (unsigned i) const

virtual std::vector< Mdouble >	getFieldVTK (unsigned i) const

void	setForce (Vec3D force)
	set total force (this is used by the normal force, tangential forces are added use addForce) More...

Public Member Functions inherited from BaseObject
	BaseObject ()
	Default constructor. More...

	BaseObject (const BaseObject &p)
	Copy constructor, copies all the objects BaseObject contains. More...

virtual	~BaseObject ()
	virtual destructor More...

virtual void	moveInHandler (const unsigned int index)
	Except that it is virtual, it does the same thing as setIndex() does. More...

void	setIndex (const unsigned int index)
	Allows one to assign an index to an object in the handler/container. More...

void	setId (const unsigned int id)
	Assigns a unique identifier to each object in the handler (container) which remains constant even after the object is deleted from the container/handler. More...

unsigned int	getIndex () const
	Returns the index of the object in the handler. More...

unsigned int	getId () const
	Returns the unique identifier of any particular object. More...

Private Attributes
Vec3D	slidingSpring_
	Stores the amount of sliding spring ( $\delta$ ) compression from the expression $f_t=-k\delta-\nurelVel$ . Set in the member function integrate(), used in computeFrictionForce(). More...

Vec3D	slidingSpringVelocity_
	Stores the rate at which the sliding spring compressed or relaxed. Set in the member function computeFrictionForce() and used in integrate(). More...

Vec3D	tangentialForce_
	Computes the tangential force such that $\|f_t\|=\mu*\|f_n\|$ . Set and computed in computeFrictionForce(). More...

Additional Inherited Members
Protected Member Functions inherited from BaseInteraction
Mdouble	getEffectiveRadius () const
	Returns a Mdouble to the effective radius of the interaction. (Not corrected for the overlap) More...

Mdouble	getEffectiveMass () const
	Returns a Mdouble to the effective radius of the interaction. (Not corrected for the overlap) More...

Mdouble	getEffectiveCorrectedRadius ()
	Returns a Mdouble to the effective radius corrected for the overlaps of the particles. More...

void	addForce (Vec3D force)
	add an force increment to the total force. More...

void	addTorque (Vec3D torque)

void	setTorque (Vec3D torque)
	set the total force (this is used by the normal force, tangential torques are added use addTorque) More...

void	setRelativeVelocity (Vec3D relativeVelocity)
	set the relative velocity of the current of the interactions. More...

void	setNormalRelativeVelocity (Mdouble normalRelativeVelocit)
	set the normal component of the relative velocity. More...

void	setAbsoluteNormalForce (Mdouble absoluteNormalForce)
	the absolute values of the norm (length) of the normal force More...

const BaseSpecies *	getBaseSpecies () const
	Return a constant point to BaseSpecies of the interaction. More...

virtual Mdouble	getElasticEnergyAtEquilibrium (Mdouble adhesiveForce) const

Detailed Description

Computes the forces corresponding to sliding friction.

Definition at line 39 of file SlidingFrictionInteraction.h.

Member Typedef Documentation

typedef SlidingFrictionSpecies SlidingFrictionInteraction::SpeciesType

An alias name for SlidingFrictionSpecies data type.

Definition at line 45 of file SlidingFrictionInteraction.h.

Constructor & Destructor Documentation

SlidingFrictionInteraction::SlidingFrictionInteraction	(	BaseInteractable *	P,
		BaseInteractable *	I,
		Mdouble	timeStamp
	)

Constructor.

Parameters

[in]	P
[in]	I
[in]	timeStamp

Definition at line 39 of file SlidingFrictionInteraction.cc.

References Vec3D::setZero(), and slidingSpring_.

     : BaseInteraction(P, I, timeStamp)
 {
     slidingSpring_.setZero();
 #ifdef DEBUG_CONSTRUCTOR
     std::cout<<"SlidingFrictionInteraction::SlidingFrictionInteraction() finished"<<std::endl;
 #endif
 }

SlidingFrictionInteraction::SlidingFrictionInteraction ( const SlidingFrictionInteraction & p )

Copy constructor.

Parameters

[in] p

Definition at line 50 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

     : BaseInteraction(p)
 {
     slidingSpring_=p.slidingSpring_;
 #ifdef DEBUG_CONSTRUCTOR
     std::cout<<"SlidingFrictionInteraction::SlidingFrictionInteraction(const SlidingFrictionInteraction& p) finished"<<std::endl;
 #endif
 }

SlidingFrictionInteraction::~SlidingFrictionInteraction ( )

virtual

Destructor.

Definition at line 61 of file SlidingFrictionInteraction.cc.

 {
 #ifdef DEBUG_DESTRUCTOR
     std::cout<<"SlidingFrictionInteraction::~SlidingFrictionInteraction() finished"<<std::endl;
 #endif
 }

Member Function Documentation

void SlidingFrictionInteraction::computeFrictionForce ( )

Computes the tangential force generated due to compression in the sliding spring. Does take into account if the interaction is between particle-particle or particle-wall.

Definition at line 87 of file SlidingFrictionInteraction.cc.

Referenced by FrictionInteraction::computeFrictionForce().

 {
     //If tangential forces are absent
     if (getAbsoluteNormalForce() == 0.0) return;
 
     const SlidingFrictionSpecies* species = getSpecies();//dynamic_cast
     
     if (species->getSlidingFrictionCoefficient() != 0.0)
     {
         //Compute the tangential component of relativeVelocity_
         // relativeVelocity = [v_p + (r_p-c) x w_p] - [v_i + (r_i-c) x w_i]
         // tangentialRelativeVelocity = relativeVelocity - (relativeVelocity . n) n
         Vec3D tangentialRelativeVelocity = getRelativeVelocity() - getNormal() * getNormalRelativeVelocity();
 
         if (species->getSlidingStiffness() != 0.0)
         {
             //used to Integrate the spring
             if (dynamic_cast<BaseParticle*>(getI())==0)  //if particle-wall
                 slidingSpringVelocity_= tangentialRelativeVelocity;
             else //if particle-particle
                 slidingSpringVelocity_= (tangentialRelativeVelocity - Vec3D::dot(slidingSpring_, getP()->getVelocity() - getI()->getVelocity()) * getNormal() / getDistance());
             // v_s = v_t - [xi . (v_p-v_i)/|r_pi|] n
 
             //integrate(getHandler()->timeStep_);
             // xi = xi' + dt v_s
             slidingSpring_ += slidingSpringVelocity_ * getHandler()->getDPMBase()->getTimeStep();
             // Stefan does [EJECE-12/2008] sth. like xi = xi' - (xi . n) n + dt*v_t
 
             //Calculate test force acting on P including viscous force
             tangentialForce_ = - species->getSlidingStiffness() * slidingSpring_ - species->getSlidingDissipation() * tangentialRelativeVelocity;
 
             //tangential forces are modelled by a spring-damper of elasticity kt and viscosity dispt (sticking),
             //but the force is limited by Coulomb friction (sliding):
             Mdouble tangentialForceSquared = tangentialForce_.getLengthSquared();
             if (tangentialForceSquared <= mathsFunc::square(species->getSlidingFrictionCoefficientStatic() * getAbsoluteNormalForce()))
             {
                 //if sticking (|ft|<=mu*|fn|), apply the force
                 addForce(tangentialForce_);
             }
             else
             {
                 //if sliding, resize the tangential force such that |ft|=mu*|fn|
                 tangentialForce_ *= species->getSlidingFrictionCoefficient() * getAbsoluteNormalForce() / std::sqrt(tangentialForceSquared);
                 addForce(tangentialForce_);
                 //resize the tangential spring accordingly such ft=-k*delta-nu*relVel
                 slidingSpring_ = -(tangentialForce_ + species->getSlidingDissipation() * tangentialRelativeVelocity) / species->getSlidingStiffness();
             }
         }
         else //if no spring stiffness is set
         {
 //            if (species->getSlidingDissipation()==0.0)
 //            {
 //                std::cerr << "SlidingFrictionInteraction::getForce(): warning:  both sliding stiffness and dissipation are zero" << std::endl;
 //            }
             Mdouble tangentialRelativeVelocitySquared = tangentialRelativeVelocity.getLengthSquared();
             if (tangentialRelativeVelocitySquared * mathsFunc::square(species->getSlidingDissipation()) <= mathsFunc::square(species->getSlidingFrictionCoefficientStatic() * getAbsoluteNormalForce()))
                 tangentialForce_=-species->getSlidingDissipation() * tangentialRelativeVelocity;
             else //if sliding, set force to Coulomb limit
                 tangentialForce_=-(species->getSlidingFrictionCoefficient() * getAbsoluteNormalForce() / std::sqrt(tangentialRelativeVelocitySquared)) * tangentialRelativeVelocity;
 
             addForce(tangentialForce_);
         }
     }
 //    else
 //    {
 //        std::cerr << "SlidingFrictionInteraction::getForce(): warning: sliding friction is zero" << std::endl;
 //    }
 }

std::string SlidingFrictionInteraction::getBaseName ( ) const

Returns the type/name of interaction (sliding friction interaction)

Returns: std::string

Definition at line 194 of file SlidingFrictionInteraction.cc.

 {
     return "SlidingFriction";
 }

Mdouble SlidingFrictionInteraction::getElasticEnergy ( ) const

virtual

Returns the amount of elastic energy stored in sliding spring.

Returns: Mdouble

Reimplemented from BaseInteraction.

Definition at line 165 of file SlidingFrictionInteraction.cc.

References Vec3D::getLengthSquared(), SlidingFrictionSpecies::getSlidingStiffness(), getSpecies(), and slidingSpring_.

Referenced by FrictionInteraction::getElasticEnergy().

 {
     return 0.5 * getSpecies()->getSlidingStiffness() * slidingSpring_.getLengthSquared();
 }

Vec3D SlidingFrictionInteraction::getSlidingSpring ( ) const

Definition at line 204 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

 {
     return slidingSpring_;
 }

const SlidingFrictionSpecies * SlidingFrictionInteraction::getSpecies ( ) const

Returns a const pointer of type SlidingFrictionSpecies*.

Returns: const SlidingFrictionSpecies*

Definition at line 187 of file SlidingFrictionInteraction.cc.

References BaseInteraction::getBaseSpecies().

Referenced by computeFrictionForce(), and getElasticEnergy().

 {
     return dynamic_cast<const SlidingFrictionSpecies*>(getBaseSpecies());
 }

const Vec3D SlidingFrictionInteraction::getTangentialForce ( ) const

virtual

Returns the sliding friction force vector.

Returns: const Vec3D

Reimplemented from BaseInteraction.

Definition at line 180 of file SlidingFrictionInteraction.cc.

References tangentialForce_.

 {
     return tangentialForce_;
 }

Mdouble SlidingFrictionInteraction::getTangentialOverlap ( ) const

virtual

Returns the amount of tangential overlap which is needed by BaseInteraction::writeToFstat().

Returns: Mdouble

Todo:: TWnow this should be positive

Reimplemented from BaseInteraction.

Definition at line 172 of file SlidingFrictionInteraction.cc.

References Vec3D::getLength(), and slidingSpring_.

 {
     return -slidingSpring_.getLength();
 }

void SlidingFrictionInteraction::integrate ( Mdouble timeStep )

virtual

Increments the amount of compression in sliding spring.

Parameters

[in] timeStep the dt

Reimplemented from BaseInteraction.

Definition at line 158 of file SlidingFrictionInteraction.cc.

References slidingSpring_, and slidingSpringVelocity_.

Referenced by FrictionInteraction::integrate().

 {
     slidingSpring_ += slidingSpringVelocity_ * timeStep;
 }

void SlidingFrictionInteraction::moveSlidingSpring ( const Vec3D displacement )

Definition at line 226 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

 {
     slidingSpring_ += displacement;
 }

void SlidingFrictionInteraction::read ( std::istream & is )

virtual

Interaction read function, which accepts an std::istream as input.

Parameters

[in,out] is

Reimplemented from BaseInteraction.

Definition at line 78 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

Referenced by FrictionInteraction::read().

 {
     //BaseInteraction::read(is);
     std::string dummy;
     is >> dummy >> slidingSpring_;
 }

void SlidingFrictionInteraction::reverseHistory ( )

virtual

A useful feature if one wants to return to the initial state of the spring. However, reverse history decrements the current state to the state corresponding to previous time step. Decrements the value of slidingSpring_.

Reimplemented from BaseInteraction.

Definition at line 212 of file SlidingFrictionInteraction.cc.

References slidingSpring_, slidingSpringVelocity_, and tangentialForce_.

Referenced by FrictionInteraction::reverseHistory().

 {
     slidingSpring_=-slidingSpring_;
     slidingSpringVelocity_=-slidingSpringVelocity_;
     tangentialForce_=-tangentialForce_;
 }

void SlidingFrictionInteraction::rotateHistory ( Matrix3D & rotationMatrix )

virtual

When periodic particles are used, some interactions need certain history properties rotated (e.g. tangential springs). This is the function for that.

Todo:: some of these might be unneccesary

Reimplemented from BaseInteraction.

Definition at line 219 of file SlidingFrictionInteraction.cc.

References slidingSpring_, slidingSpringVelocity_, and tangentialForce_.

Referenced by FrictionInteraction::rotateHistory().

 {
     slidingSpring_=rotationMatrix*slidingSpring_;
     slidingSpringVelocity_=rotationMatrix*slidingSpringVelocity_;
     tangentialForce_=rotationMatrix*tangentialForce_;
 }

void SlidingFrictionInteraction::setSlidingSpring ( const Vec3D slidingSpring )

Definition at line 199 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

 {
     slidingSpring_ = slidingSpring;
 }

void SlidingFrictionInteraction::write ( std::ostream & os ) const

virtual

Interaction write function, which accepts an std::ostream as input.

Parameters

[in,out] os

Reimplemented from BaseInteraction.

Definition at line 70 of file SlidingFrictionInteraction.cc.

References slidingSpring_.

Referenced by FrictionInteraction::write().

 {
     //BaseInteraction::write(os);
     os << " slidingSpring " << slidingSpring_;
 }

Member Data Documentation

Vec3D SlidingFrictionInteraction::slidingSpring_

private

Stores the amount of sliding spring ( $\delta$ ) compression from the expression $f_t=-k*\delta-\nu*relVel$ . Set in the member function integrate(), used in computeFrictionForce().

Definition at line 117 of file SlidingFrictionInteraction.h.

Referenced by computeFrictionForce(), getElasticEnergy(), getSlidingSpring(), getTangentialOverlap(), integrate(), moveSlidingSpring(), read(), reverseHistory(), rotateHistory(), setSlidingSpring(), SlidingFrictionInteraction(), and write().