Description

Added mass for hydrodynamic loads.

The added mass is an inertia added to the system due to accelerating bodies having to displace some volume of surrounding fluid. The additional system-wide mass matrix term is a block-sparse matrix with non-zero blocks corresponding to all bodies that interact with fluid. For each of these n bodies (not necessarily all bodies included in the Chrono system), a dense 6 x 6n block of hydrodynamic coefficients must be provided (see ChBodyAddedMassBlocks). The 6 x 6 blocks for each of these bodies is distributed at the appropriate location in the system mass matrix.

The coefficients of each body refer to the velocity of the origin of the body reference frame (the COM frame for a ChBody, the auxiliary reference frame for a ChBodyAuxRef) and to the body angular velocity, both expressed either in the inertial (absolute) axes or in the axes of the body reference frame (see AddedMassFrame). Coefficients computed about a different point must be shifted to the origin of the body reference frame before they are passed to this load (see ComputeShiftTransformation). Since Chrono uses the COM velocity in absolute axes and the angular velocity in the axes of the COM frame as velocity coordinates, the coefficients are transformed accordingly, using the current orientation of the bodies. The added mass is therefore constant in the selected axes and, in general, varies with the body orientation in the Chrono velocity coordinates. The velocity-dependent terms arising from the time variation of the added mass (e.g., the Munk moment) are not included, which is consistent with the small-rotation assumptions under which hydrodynamic coefficients are typically computed.

Note that, with a solver that needs the inverse of the total mass matrix (APGD or Barzilai-Borwein), that inverse is recomputed whenever a hydrodynamic body rotates, which requires the inversion of a dense system-size matrix.

#include <ChLoadHydrodynamics.h>

Inheritance diagram for chrono::ChLoadHydrodynamics:

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Collaboration diagram for chrono::ChLoadHydrodynamics:

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Public Types
enum	AddedMassFrame { AddedMassFrame::INERTIAL, AddedMassFrame::BODY }
	Axes in which the added mass coefficients are expressed (and in which they are constant). More...

Public Types inherited from chrono::ChPhysicsItem
enum	InitPhase { InitPhase::NONE = 0, InitPhase::STRUCTURE = 1, InitPhase::STATE = 2 }
	Initialization phases of a physics item. More...

Public Member Functions
	ChLoadHydrodynamics (const ChBodyAddedMassBlocks &body_blocks)

	ChLoadHydrodynamics (const ChLoadHydrodynamics &other)

virtual bool	SupportsCheckpoint () const override
	Return true: the internal state of this item is restored from a checkpoint (see ChPhysicsItem).

virtual ChLoadHydrodynamics *	Clone () const override
	"Virtual" copy constructor (covariant return type).

void	SetVerbose (bool verbose)
	Enable/disable verbose terminal output (default: false).

void	SetAddedMassFrame (AddedMassFrame frame)
	Set the axes in which the added mass coefficients are expressed (default: AddedMassFrame::INERTIAL).

AddedMassFrame	GetAddedMassFrame () const
	Get the axes in which the added mass coefficients are expressed.

void	SetBodyAddedMassBlocks (const std::vector< ChMatrixDynamic<>> &blocks)
	Modify the added mass blocks. More...

void	UpdateBodyAddedMassBlocks (const std::vector< ChMatrix66d > &blocks)
	Modify the added mass block. More...

virtual void	Setup () override
	Perform setup operations at the beginning of a step.

virtual void	Update (double time, UpdateFlags update_flags) override
	Perform any updates necessary at the current phase during the solution process. More...

virtual void	IntLoadResidual_Mv (const unsigned int off, ChVectorDynamic<> &R, const ChVectorDynamic<> &w, const double c) override
	Increment the given residual vector R with the term c * M * w (for the entire system). More...

virtual void	InjectKRMMatrices (ChSystemDescriptor &descriptor) override
	Register with the given system descriptor any ChMBlock objects associated with this item.

virtual void	LoadKRMMatrices (double Kfactor, double Rfactor, double Mfactor) override
	Compute and load current mass matrices in encapsulated ChMBlock objects. More...

Public Member Functions inherited from chrono::ChPhysicsItem
	ChPhysicsItem (const ChPhysicsItem &other)

ChSystem *	GetSystem () const
	Get the pointer to the parent ChSystem().

virtual void	SetSystem (ChSystem *m_system)
	Set the pointer to the parent ChSystem(). More...

virtual bool	IsActive () const
	Return true if the object is active and included in dynamics.

virtual bool	IsCollisionEnabled () const
	Tell if the object is subject to collision. More...

virtual void	AddCollisionModelsToSystem (ChCollisionSystem *coll_sys) const
	Add to the provided collision system any collision models managed by this physics item. More...

virtual void	RemoveCollisionModelsFromSystem (ChCollisionSystem *coll_sys) const
	Remove from the provided collision system any collision models managed by this physics item. More...

virtual void	SyncCollisionModels ()
	Synchronize the position and bounding box of any collision models managed by this physics item.

virtual ChAABB	GetTotalAABB () const
	Get the axis-aligned bounding box (AABB) of this object. More...

virtual ChVector3d	GetCenter () const
	Get a symbolic 'center' of the object. More...

bool	IsInitialized () const
	Return true if both initialization phases ran for this item.

void	InitializePhase (InitPhase phase)
	Run the specified initialization phase on this item (if not already done) and then on its children. More...

virtual void	ResetInitialization ()
	Mark this item (and its children, if any) as not initialized. More...

virtual void	SaveInternalState (ChCheckpointWriter &writer) const
	Save the internal state of this item. More...

virtual void	LoadInternalState (ChCheckpointReader &reader)
	Load the internal state of this item, as saved by SaveInternalState. More...

virtual void	ForceToRest ()
	Set zero speed (and zero accelerations) in state, without changing the position. More...

virtual unsigned int	GetNumCoordsPosLevel ()
	Get the number of coordinates at the position level. More...

virtual unsigned int	GetNumCoordsVelLevel ()
	Get the number of coordinates at the velocity level. More...

virtual unsigned int	GetNumConstraints ()
	Get the number of scalar constraints.

virtual unsigned int	GetNumConstraintsBilateral ()
	Get the number of bilateral scalar constraints.

virtual unsigned int	GetNumConstraintsUnilateral ()
	Get the number of unilateral scalar constraints.

unsigned int	GetOffset_x ()
	Get offset in the state vector (position part)

unsigned int	GetOffset_w ()
	Get offset in the state vector (speed part)

unsigned int	GetOffset_L ()
	Get offset in the Lagrange multipliers.

void	SetOffset_x (const unsigned int moff)
	Set offset in the state vector (position part) Note: only the ChSystem::Setup function should use this.

void	SetOffset_w (const unsigned int moff)
	Set offset in the state vector (speed part) Note: only the ChSystem::Setup function should use this.

void	SetOffset_L (const unsigned int moff)
	Set offset in the Lagrange multipliers Note: only the ChSystem::Setup function should use this.

virtual void	IntStateGather (const unsigned int off_x, ChState &x, const unsigned int off_v, ChStateDelta &v, double &T)
	From item's state to global state vectors y={x,v} pasting the states at the specified offsets. More...

virtual void	IntStateScatter (const unsigned int off_x, const ChState &x, const unsigned int off_v, const ChStateDelta &v, const double T, UpdateFlags update_flags)
	From global state vectors y={x,v} to item's state (and update) fetching the states at the specified offsets. More...

virtual void	IntStateGatherAcceleration (const unsigned int off_a, ChStateDelta &a)
	From item's state acceleration to global acceleration vector. More...

virtual void	IntStateScatterAcceleration (const unsigned int off_a, const ChStateDelta &a)
	From global acceleration vector to item's state acceleration. More...

virtual void	IntStateGatherReactions (const unsigned int off_L, ChVectorDynamic<> &L)
	From item's reaction forces to global reaction vector. More...

virtual void	IntStateScatterReactions (const unsigned int off_L, const ChVectorDynamic<> &L)
	From global reaction vector to item's reaction forces. More...

virtual void	IntStateOnEndStep (double T)
	Called at the end of a step, after the state has been updated. More...

virtual void	IntStateIncrement (const unsigned int off_x, ChState &x_new, const ChState &x, const unsigned int off_v, const ChStateDelta &Dv)
	Computes x_new = x + Dt , using vectors at specified offsets. More...

virtual void	IntStateGetIncrement (const unsigned int off_x, const ChState &x_new, const ChState &x, const unsigned int off_v, ChStateDelta &Dv)
	Computes Dt = x_new - x, using vectors at specified offsets. More...

virtual void	IntLoadResidual_F (const unsigned int off, ChVectorDynamic<> &R, const double c)
	Takes the F force term, scale and adds to R at given offset: R += c*F. More...

virtual void	IntLoadResidual_F_applied (const unsigned int off, ChVectorDynamic<> &R, const double c)
	Takes only the externally applied loads, scale and adds to R at given offset: R += c*F_applied Applied loads are loads set or accumulated by the user (e.g., accumulator loads, ChForce objects, node forces). More...

virtual void	IntLoadLumpedMass_Md (const unsigned int off, ChVectorDynamic<> &Md, double &err, const double c)
	Adds the lumped mass to a Md vector, representing a mass diagonal matrix. More...

virtual void	IntLoadResidual_CqL (const unsigned int off_L, ChVectorDynamic<> &R, const ChVectorDynamic<> &L, const double c)
	Takes the term Cq'L, scale and adds to R at given offset: R += cCq'*L. More...

virtual void	IntLoadConstraint_C (const unsigned int off, ChVectorDynamic<> &Qc, const double c, const double c_vel, bool do_clamp, double recovery_clamp)
	Takes the term C, scale and adds to Qc at given offset: Qc += c*C. More...

virtual void	IntLoadConstraint_Ct (const unsigned int off, ChVectorDynamic<> &Qc, const double c, const double c_vel)
	Takes the term Ct, scale and adds to Qc at given offset: Qc += c*Ct. More...

virtual void	IntToDescriptor (const unsigned int off_v, const ChStateDelta &v, const ChVectorDynamic<> &R, const unsigned int off_L, const ChVectorDynamic<> &L, const ChVectorDynamic<> &Qc)
	Prepare variables and constraints to accommodate a solution: More...

virtual void	IntFromDescriptor (const unsigned int off_v, ChStateDelta &v, const unsigned int off_L, ChVectorDynamic<> &L)
	After a solver solution, fetch values from variables and constraints into vectors: More...

virtual void	InjectVariables (ChSystemDescriptor &descriptor)
	Register with the given system descriptor any ChVariable objects associated with this item.

virtual void	InjectConstraints (ChSystemDescriptor &descriptor)
	Register with the given system descriptor any ChConstraint objects associated with this item.

virtual void	LoadConstraintJacobians ()
	Compute and load current Jacobians in encapsulated ChConstraint objects.

virtual void	VariablesFbReset ()
	Sets the 'fb' part (the known term) of the encapsulated ChVariables to zero.

virtual void	VariablesFbLoadForces (double factor=1)
	Adds the current forces (applied to item) into the encapsulated ChVariables, in the 'fb' part: qf+=forces*factor.

virtual void	VariablesQbLoadSpeed ()
	Initialize the 'qb' part of the ChVariables with the current value of speeds. More...

virtual void	VariablesFbIncrementMq ()
	Adds M*q (masses multiplied current 'qb') to Fb, ex. More...

virtual void	VariablesQbSetSpeed (double step=0)
	Fetches the item speed (ex. More...

virtual void	VariablesQbIncrementPosition (double step)
	Increment item positions by the 'qb' part of the ChVariables, multiplied by a 'step' factor. More...

virtual void	ConstraintsBiReset ()
	Sets to zero the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsBiLoad_C (double factor=1, double recovery_clamp=0.1, bool do_clamp=false)
	Adds the current C (constraint violation) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsBiLoad_Ct (double factor=1)
	Adds the current Ct (partial t-derivative, as in C_dt=0-> [Cq]*q_dt=-Ct) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsBiLoad_Qc (double factor=1)
	Adds the current Qc (the vector of C_dtdt=0 -> [Cq]*q_dtdt=Qc ) to the known term (b_i) of encapsulated ChConstraints.

virtual void	ConstraintsFbLoadForces (double factor=1)
	Adds the current link-forces, if any, (caused by springs, etc.) to the 'fb' vectors of the ChVariables referenced by encapsulated ChConstraints.

virtual void	ConstraintsFetch_react (double factor=1)
	Fetches the reactions from the lagrangian multiplier (l_i) of encapsulated ChConstraints. More...

virtual void	ArchiveOut (ChArchiveOut &archive_out) override
	Method to allow serialization of transient data to archives.

virtual void	ArchiveIn (ChArchiveIn &archive_in) override
	Method to allow deserialization of transient data from archives. More...

Public Member Functions inherited from chrono::ChObj
	ChObj (const ChObj &other)

int	GetIdentifier () const
	Get the unique integer identifier of this object. More...

void	SetTag (int tag)
	Set an object integer tag (default: -1). More...

int	GetTag () const
	Get the tag of this object.

void	SetName (const std::string &myname)
	Set the name of this object.

const std::string &	GetName () const
	Get the name of this object.

double	GetChTime () const
	Gets the simulation time of this object.

void	SetChTime (double m_time)
	Sets the simulation time of this object.

void	AddVisualModel (std::shared_ptr< ChVisualModel > model)
	Add an (optional) visualization model. More...

std::shared_ptr< ChVisualModel >	GetVisualModel () const
	Access the visualization model (if any). More...

void	AddVisualShape (std::shared_ptr< ChVisualShape > shape, const ChFrame<> &frame=ChFrame<>())
	Add the specified visual shape to the visualization model. More...

std::shared_ptr< ChVisualShape >	GetVisualShape (unsigned int i) const
	Access the specified visualization shape in the visualization model (if any). More...

virtual ChFrame	GetVisualModelFrame (unsigned int nclone=0) const
	Get the reference frame (expressed in and relative to the absolute frame) of the visual model. More...

virtual unsigned int	GetNumVisualModelClones () const
	Return the number of clones of the visual model associated with this object. More...

void	AddCamera (std::shared_ptr< ChCamera > camera)
	Attach a camera to this object. More...

std::vector< std::shared_ptr< ChCamera > >	GetCameras () const
	Get the set of cameras attached to this object.

void	UpdateVisualModel ()
	Utility function to update only the associated visual assets (if any).

virtual std::string &	ArchiveContainerName ()

Static Public Member Functions
static ChMatrix66d	ComputeShiftTransformation (const ChBody &body, const ChVector3d &point, AddedMassFrame frame)
	Compute the transformation that shifts added mass coefficients to the origin of the body reference frame. More...

static void	ShiftBlocks (std::vector< ChMatrixDynamic<>> &blocks, const std::vector< ChMatrix66d > &shifts)
	Shift added mass blocks with the given transformations (see ComputeShiftTransformation). More...

Protected Member Functions
bool	NeedsMassInverse () const
	Return true if the current solver needs the inverse of the total mass matrix.

void	OnBlocksModified ()
	Recompute the mass inverse right away if the blocks were modified and a mass inverse is in use.

void	ComputeMassInverse ()
	Assemble the total mass matrix (including added mass), invert it, and pass it to the system descriptor.

bool	BodiesRotated () const
	Return true if any hydrodynamic body rotated since the mass inverse was last computed.

ChMatrix66d	ComputeTransformation (const ChBodyAddedMassBlock &b) const
	Compute the transformation from Chrono velocity coordinates to the velocities the coefficients refer to. More...

void	ComputeAddedMassMatrix ()
	Compute the added mass matrix in Chrono velocity coordinates at the current body configuration. More...

Protected Member Functions inherited from chrono::ChPhysicsItem
virtual void	InitializeChildren (InitPhase phase)
	Run the specified initialization phase on the children of this item. More...

void	SetInitializationPending ()
	Notify the parent system that some items need initialization.

Protected Member Functions inherited from chrono::ChObj
int	GenerateUniqueIdentifier ()

Protected Attributes
bool	m_verbose

AddedMassFrame	m_frame
	axes in which the added mass coefficients are expressed

ChBodyAddedMassBlocks	m_body_blocks
	added mass blocks for hydrodynamic bodies

ChMatrixDynamic	m_M
	added mass matrix in Chrono velocity coordinates (in block order)

ChKRMBlock	m_KRM
	scaled added mass matrix (6*num_bodies square, in block order)

unsigned int	m_system_size
	system size for which the mass inverse was last computed

bool	m_blocks_modified
	added mass blocks changed since the mass inverse was last computed

std::vector< ChQuaterniond >	m_inverse_rotations
	body orientations for which the mass inverse was last computed

Protected Attributes inherited from chrono::ChPhysicsItem
ChSystem *	system
	parent system

unsigned int	offset_x
	offset in vector of state (position part)

unsigned int	offset_w
	offset in vector of state (speed part)

unsigned int	offset_L
	offset in vector of Lagrange multipliers

Protected Attributes inherited from chrono::ChObj
double	ChTime
	object simulation time

std::string	m_name
	object name

int	m_identifier
	object unique identifier

int	m_tag
	user-supplied tag

std::shared_ptr< ChVisualModelInstance >	vis_model_instance
	instantiated visualization model

std::vector< std::shared_ptr< ChCamera > >	cameras
	set of cameras

Member Enumeration Documentation

◆ AddedMassFrame

enum chrono::ChLoadHydrodynamics::AddedMassFrame

strong

Axes in which the added mass coefficients are expressed (and in which they are constant).

Enumerator
INERTIAL	inertial (absolute) axes, e.g. coefficients from a BEM code (default)
BODY	axes of the body reference frame, i.e. coefficients that rotate with the body

Member Function Documentation

◆ ComputeAddedMassMatrix()

void chrono::ChLoadHydrodynamics::ComputeAddedMassMatrix ( )

protected

Compute the added mass matrix in Chrono velocity coordinates at the current body configuration.

The block coupling bodies i and j is T_i^T * A_ij * T_j, where A_ij is the corresponding 6 x 6 block of coefficients.

◆ ComputeShiftTransformation()

ChMatrix66d chrono::ChLoadHydrodynamics::ComputeShiftTransformation	(	const ChBody &	body,
		const ChVector3d &	point,
		AddedMassFrame	frame
	)

static

Compute the transformation that shifts added mass coefficients to the origin of the body reference frame.

The coefficients A are given about a point fixed on the body, with the specified location in the body reference frame, and are expressed in the axes of the given frame convention. If S_i is the transformation for body i, the coefficients about the origins of the body reference frames are S_i^T * A_ij * S_j. With the inertial convention, S depends on the body orientation: the transformation computed at the current orientation applies exactly only at that orientation.

◆ ComputeTransformation()

ChMatrix66d chrono::ChLoadHydrodynamics::ComputeTransformation ( const ChBodyAddedMassBlock & b ) const

protected

Compute the transformation from Chrono velocity coordinates to the velocities the coefficients refer to.

For body i, the velocity of the origin of its reference frame and its angular velocity (in the axes given by the frame convention) are T_i * [v; w], where v is the COM velocity in absolute axes and w the angular velocity in the axes of the COM frame.

◆ IntLoadResidual_Mv()

void chrono::ChLoadHydrodynamics::IntLoadResidual_Mv	(	const unsigned int	off,
		ChVectorDynamic<> &	R,
		const ChVectorDynamic<> &	w,
		const double	c
	)

overridevirtual

Increment the given residual vector R with the term c * M * w (for the entire system).

Parameters

off	offset in R residual
R	updated residual R += cMv
w	w vector
c	scaling factor

Reimplemented from chrono::ChPhysicsItem.

◆ LoadKRMMatrices()

void chrono::ChLoadHydrodynamics::LoadKRMMatrices	(	double	Kfactor,
		double	Rfactor,
		double	Mfactor
	)

overridevirtual

Compute and load current mass matrices in encapsulated ChMBlock objects.

The resulting M block contains Mfactor * M (Kfactor and Rfactor are ignored here).

Reimplemented from chrono::ChPhysicsItem.

◆ SetBodyAddedMassBlocks()

void chrono::ChLoadHydrodynamics::SetBodyAddedMassBlocks ( const std::vector< ChMatrixDynamic<>> & blocks )

Modify the added mass blocks.

In this case, each given block is assumed to have size 6 x 6n and is expressed in the current frame convention. If any block changes, the inverse of the total mass matrix (if needed by the solver) is recomputed.

◆ ShiftBlocks()

void chrono::ChLoadHydrodynamics::ShiftBlocks	(	std::vector< ChMatrixDynamic<>> &	blocks,
		const std::vector< ChMatrix66d > &	shifts
	)

static

Shift added mass blocks with the given transformations (see ComputeShiftTransformation).

Each block, of size 6 x 6n, is replaced in place with the blocks S_i^T * A_ij * S_j.

◆ Update()

void chrono::ChLoadHydrodynamics::Update	(	double	time,
		UpdateFlags	update_flags
	)

overridevirtual

Perform any updates necessary at the current phase during the solution process.

This function is called at least once per step to update auxiliary data, internal states, etc. If a problem size is detected, resize the underlying KRM block.

Reimplemented from chrono::ChPhysicsItem.

◆ UpdateBodyAddedMassBlocks()

void chrono::ChLoadHydrodynamics::UpdateBodyAddedMassBlocks ( const std::vector< ChMatrix66d > & blocks )

Modify the added mass block.

In this case, each given block is assumed to have size 6 x 6, is expressed in the current frame convention, and overwrites the diagonal block of the added mass matrix. If any block changes, the inverse of the total mass matrix (if needed by the solver) is recomputed.

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

/builds/uwsbel/chrono/src/chrono/physics/ChLoadHydrodynamics.h
/builds/uwsbel/chrono/src/chrono/physics/ChLoadHydrodynamics.cpp

Description

Public Types

Public Member Functions

Static Public Member Functions

Protected Member Functions

Protected Attributes

Member Enumeration Documentation

◆ AddedMassFrame

Member Function Documentation

◆ ComputeAddedMassMatrix()

◆ ComputeShiftTransformation()

◆ ComputeTransformation()

◆ IntLoadResidual_Mv()

◆ LoadKRMMatrices()

◆ SetBodyAddedMassBlocks()

◆ ShiftBlocks()

◆ Update()

◆ UpdateBodyAddedMassBlocks()