Detailed Description

template<typename T>
class drake::multibody::DeformableModel< T >

DeformableModel implements the interface in PhysicalModel and provides the functionalities to specify deformable bodies.

Unlike rigid bodies, the shape of deformable bodies can change in a simulation. Each deformable body is modeled as a volumetric mesh with persisting topology, changing vertex positions, and an approximated signed distance field. A finite element model is built for each registered deformable body that is used to evaluate the dynamics of the body.

Warning: This feature is considered to be experimental and may change or be removed at any time, without any deprecation notice ahead of time.

Template Parameters

T	The scalar type, which must be `double`.

#include <drake/multibody/plant/physical_model.h>

Public Member Functions
	DeformableModel (MultibodyPlant< T > *plant)
	Constructs a DeformableModel to be owned by the given MultibodyPlant. More...

int	num_bodies () const
	Returns the number of deformable bodies registered with this DeformableModel. More...

DeformableBodyId	RegisterDeformableBody (std::unique_ptr< geometry::GeometryInstance > geometry_instance, const fem::DeformableBodyConfig< T > &config, double resolution_hint)
	Registers a deformable body in `this` DeformableModel with the given GeometryInstance. More...

void	SetWallBoundaryCondition (DeformableBodyId id, const Vector3< T > &p_WQ, const Vector3< T > &n_W)
	Sets wall boundary conditions for the body with the given `id`. More...

MultibodyConstraintId	AddFixedConstraint (DeformableBodyId body_A_id, const RigidBody< T > &body_B, const math::RigidTransform< double > &X_BA, const geometry::Shape &shape, const math::RigidTransform< double > &X_BG)
	Defines a fixed constraint between a deformable body A and a rigid body B. More...

systems::DiscreteStateIndex	GetDiscreteStateIndex (DeformableBodyId id) const
	Returns the discrete state index of the deformable body identified by the given `id`. More...

void	AddExternalForce (std::unique_ptr< ForceDensityField< T >> external_force)
	Registers an external force density field that applies external force to all deformable bodies. More...

const std::vector< const ForceDensityField< T > * > &	GetExternalForces (DeformableBodyId id) const
	Returns the force density fields acting on the deformable body with the given `id`. More...

const fem::FemModel< T > &	GetFemModel (DeformableBodyId id) const
	Returns the FemModel for the body with `id`. More...

const VectorX< T > &	GetReferencePositions (DeformableBodyId id) const
	Returns the reference positions of the vertices of the deformable body identified by the given `id`. More...

DeformableBodyId	GetBodyId (DeformableBodyIndex index) const
	Returns the DeformableBodyId of the body with the given body index. More...

DeformableBodyIndex	GetBodyIndex (DeformableBodyId id) const
	(Internal) Returns the DeformableBodyIndex of the body with the given id. More...

geometry::GeometryId	GetGeometryId (DeformableBodyId id) const
	Returns the GeometryId of the geometry associated with the body with the given `id`. More...

DeformableBodyId	GetBodyId (geometry::GeometryId geometry_id) const
	Returns the DeformableBodyId associated with the given `geometry_id`. More...

bool	HasConstraint (DeformableBodyId id) const
	(Internal use only) Returns the true iff the deformable body with the given `id` has constraints associated with it. More...

const internal::DeformableRigidFixedConstraintSpec &	fixed_constraint_spec (MultibodyConstraintId id) const
	(Internal use only) Returns the fixed constraint specification corresponding to the given `id`. More...

const std::vector< MultibodyConstraintId > &	fixed_constraint_ids (DeformableBodyId id) const
	(Internal use only) Returns a reference to the all ids of fixed constraints registered with the deformable body with the given `id`. More...

const systems::OutputPort< T > &	vertex_positions_port () const
	Returns the output port of the vertex positions for all registered deformable bodies. More...

Does not allow copy, move, or assignment
	DeformableModel (const DeformableModel &)=delete

DeformableModel &	operator= (const DeformableModel &)=delete

	DeformableModel (DeformableModel &&)=delete

DeformableModel &	operator= (DeformableModel &&)=delete

Public Member Functions inherited from PhysicalModel< T >
	PhysicalModel ()=default

	~PhysicalModel () override=default

template<typename ScalarType >
std::unique_ptr< PhysicalModel< ScalarType > >	CloneToScalar () const
	Creates a clone of the concrete PhysicalModel object with the scalar type `ScalarType`. More...

bool	is_cloneable_to_double () const override
	Defaults to false. More...

bool	is_cloneable_to_autodiff () const override
	Defaults to false. More...

bool	is_cloneable_to_symbolic () const override
	Defaults to false. More...

void	DeclareSystemResources (MultibodyPlant< T > *plant)
	MultibodyPlant calls this from within Finalize() to declare additional system resources. More...

PhysicalModelPointerVariant< T >	ToPhysicalModelPointerVariant () const
	Returns (a const pointer to) the specific model variant of `this` PhysicalModel. More...

	PhysicalModel (const PhysicalModel &)=delete

PhysicalModel &	operator= (const PhysicalModel &)=delete

	PhysicalModel (PhysicalModel &&)=delete

PhysicalModel &	operator= (PhysicalModel &&)=delete

Additional Inherited Members
Protected Member Functions inherited from PhysicalModel< T >
virtual std::unique_ptr< PhysicalModel< double > >	CloneToDouble () const

virtual std::unique_ptr< PhysicalModel< AutoDiffXd > >	CloneToAutoDiffXd () const

virtual std::unique_ptr< PhysicalModel< symbolic::Expression > >	CloneToSymbolic () const

void	ThrowIfSystemResourcesDeclared (const char *source_method) const

void	ThrowIfSystemResourcesNotDeclared (const char *source_method) const

geometry::SceneGraph< T > &	mutable_scene_graph (MultibodyPlant< T > *plant)

Static Protected Member Functions inherited from PhysicalModel< T >
static systems::DiscreteStateIndex	DeclareDiscreteState (MultibodyPlant< T > *plant, const VectorX< T > &model_value)

static systems::LeafOutputPort< T > &	DeclareAbstractOutputPort (MultibodyPlant< T > *plant, std::string name, typename systems::LeafOutputPort< T >::AllocCallback alloc_function, typename systems::LeafOutputPort< T >::CalcCallback calc_function, std::set< systems::DependencyTicket > prerequisites_of_calc={ systems::System< T >::all_sources_ticket()})

static systems::LeafOutputPort< T > &	DeclareVectorOutputPort (MultibodyPlant< T > *plant, std::string name, const systems::BasicVector< T > &model_vector, typename systems::LeafOutputPort< T >::CalcVectorCallback vector_calc_function, std::set< systems::DependencyTicket > prerequisites_of_calc={ systems::System< T >::all_sources_ticket()})

Constructor & Destructor Documentation

◆ DeformableModel() [1/3]

DeformableModel ( const DeformableModel< T > & )

delete

◆ DeformableModel() [2/3]

DeformableModel ( DeformableModel< T > && )

delete

◆ DeformableModel() [3/3]

DeformableModel ( MultibodyPlant< T > * plant )

explicit

Constructs a DeformableModel to be owned by the given MultibodyPlant.

Precondition: plant != nullptr.; Finalize() has not been called on plant.

Member Function Documentation

◆ AddExternalForce()

void AddExternalForce ( std::unique_ptr< ForceDensityField< T >> external_force )

Registers an external force density field that applies external force to all deformable bodies.

Exceptions

std::exception if Finalize() has been called on the multibody plant owning this deformable model.

◆ AddFixedConstraint()

MultibodyConstraintId AddFixedConstraint	(	DeformableBodyId	body_A_id,
		const RigidBody< T > &	body_B,
		const math::RigidTransform< double > &	X_BA,
		const geometry::Shape &	shape,
		const math::RigidTransform< double > &	X_BG
	)

Defines a fixed constraint between a deformable body A and a rigid body B.

Such a fixed constraint is modeled as distance holonomic constraints:

p_PᵢQᵢ(q) = 0 for each constrained vertex Pᵢ

where Pᵢ is the i-th vertex of the deformable body under constraint and Qᵢ is a point rigidly affixed to the rigid body B. To specify the constraint, we put the reference mesh M of the deformable body A in B's body frame with the given pose X_BA and prescribe a shape G with pose X_BG in B's body frame. All vertices Pᵢ in M that are inside (or on the surface of) G are subject to the fixed constraints with Qᵢ being coincident with Pᵢ when M is in pose X_BA. p_PᵢQᵢ(q) denotes the relative position of point Qᵢ with respect to point Pᵢ as a function of the configuration of the model q. Imposing this constraint forces Pᵢ and Qᵢ to be coincident for each vertex i of the deformable body specified to be under constraint.

Parameters

[in]	body_A_id	The unique id of the deformable body under the fixed constraint.
[in]	body_B	The rigid body under constraint.
[in]	X_BA	The pose of deformable body A's reference mesh in B's body frame
[in]	shape	The prescribed geometry shape, attached to rigid body B, used to determine which vertices of the deformable body A is under constraint.
[in]	X_BG	The fixed pose of the geometry frame of the given `shape` in body B's frame.

Returns: the unique id of the newly added constraint.

Exceptions

std::exception	if no deformable body with the given `body_A_id` has been registered.
std::exception	unless `body_B` is registered with the same multibody plant owning this deformable model.
std::exception	if shape is not supported by QueryObject::ComputeSignedDistanceToPoint(). Currently, supported shapes include Box, Capsule, Cylinder, Ellipsoid, HalfSpace, and Sphere.
std::exception	if Finalize() has been called on the multibody plant owning this deformable model.
std::exception	if no constraint is added (i.e. no vertex of the deformable body is inside the given `shape` with the given poses).

◆ fixed_constraint_ids()

const std::vector<MultibodyConstraintId>& fixed_constraint_ids ( DeformableBodyId id ) const

(Internal use only) Returns a reference to the all ids of fixed constraints registered with the deformable body with the given id.

◆ fixed_constraint_spec()

const internal::DeformableRigidFixedConstraintSpec& fixed_constraint_spec ( MultibodyConstraintId id ) const

(Internal use only) Returns the fixed constraint specification corresponding to the given id.

Exceptions

if	`id` is not a valid identifier for a fixed constraint.

◆ GetBodyId() [1/2]

DeformableBodyId GetBodyId ( DeformableBodyIndex index ) const

Returns the DeformableBodyId of the body with the given body index.

Exceptions

std::exception if MultibodyPlant::Finalize() has not been called yet or if index is larger than or equal to the total number of registered deformable bodies.

◆ GetBodyId() [2/2]

DeformableBodyId GetBodyId ( geometry::GeometryId geometry_id ) const

Returns the DeformableBodyId associated with the given geometry_id.

Exceptions

std::exception if the given geometry_id does not correspond to a deformable body registered with this model.

◆ GetBodyIndex()

DeformableBodyIndex GetBodyIndex ( DeformableBodyId id ) const

(Internal) Returns the DeformableBodyIndex of the body with the given id.

This function is for internal bookkeeping use only. Most users should use DeformableBodyId instead.

Exceptions

std::exception if MultibodyPlant::Finalize() has not been called yet or if no body with the given id has been registered.

◆ GetDiscreteStateIndex()

systems::DiscreteStateIndex GetDiscreteStateIndex ( DeformableBodyId id ) const

Returns the discrete state index of the deformable body identified by the given id.

Exceptions

std::exception if MultibodyPlant::Finalize() has not been called yet. or if no deformable body with the given id has been registered in this model.

◆ GetExternalForces()

const std::vector<const ForceDensityField<T>*>& GetExternalForces ( DeformableBodyId id ) const

Returns the force density fields acting on the deformable body with the given id.

Exceptions

std::exception if MultibodyPlant::Finalize() has not been called yet. or if no deformable body with the given id has been registered in this model.

◆ GetFemModel()

const fem::FemModel<T>& GetFemModel ( DeformableBodyId id ) const

Returns the FemModel for the body with id.

Exceptions

exception if no deformable body with id is registered with this DeformableModel.

◆ GetGeometryId()

geometry::GeometryId GetGeometryId ( DeformableBodyId id ) const

Returns the GeometryId of the geometry associated with the body with the given id.

Exceptions

std::exception if no body with the given id has been registered.

◆ GetReferencePositions()

const VectorX<T>& GetReferencePositions ( DeformableBodyId id ) const

Returns the reference positions of the vertices of the deformable body identified by the given id.

The reference positions are represented as a VectorX with 3N values where N is the number of vertices. The x-, y-, and z-positions (measured and expressed in the world frame) of the j-th vertex are 3j, 3j + 1, and 3j + 2 in the VectorX.

Exceptions

std::exception if no deformable body with the given id has been registered in this model.

◆ HasConstraint()

bool HasConstraint ( DeformableBodyId id ) const

(Internal use only) Returns the true iff the deformable body with the given id has constraints associated with it.

◆ num_bodies()

int num_bodies ( ) const

Returns the number of deformable bodies registered with this DeformableModel.

◆ operator=() [1/2]

DeformableModel& operator= ( DeformableModel< T > && )

delete

◆ operator=() [2/2]

DeformableModel& operator= ( const DeformableModel< T > & )

delete

◆ RegisterDeformableBody()

DeformableBodyId RegisterDeformableBody	(	std::unique_ptr< geometry::GeometryInstance >	geometry_instance,
		const fem::DeformableBodyConfig< T > &	config,
		double	resolution_hint
	)

Registers a deformable body in this DeformableModel with the given GeometryInstance.

The body is represented in the world frame and simulated with FEM with linear elements and a first order quadrature rule that integrates linear functions exactly. See FemModel for details. Returns a unique identifier for the added geometry.

Parameters

[in]	geometry_instance	The geometry to be registered with the model.
[in]	config	The physical properties of deformable body.
[in]	resolution_hint	The parameter that guides the level of mesh refinement of the deformable geometry. It has length units (in meters) and roughly corresponds to a typical edge length in the resulting mesh for a primitive shape.

Precondition: resolution_hint > 0.

Exceptions

std::exception if Finalize() has been called on the multibody plant owning this deformable model.

◆ SetWallBoundaryCondition()

void SetWallBoundaryCondition	(	DeformableBodyId	id,
		const Vector3< T > &	p_WQ,
		const Vector3< T > &	n_W
	)

Sets wall boundary conditions for the body with the given id.

All vertices of the mesh of the deformable body whose reference positions are inside the prescribed open half space are put under zero displacement boundary conditions. The open half space is defined by a plane with outward normal n_W. A vertex V is considered to be subject to the boundary condition if n̂ ⋅ p_QV < 0 where Q is a point on the plane and n̂ is normalized n_W.

Parameters

[in]	id	The body to be put under boundary condition.
[in]	p_WQ	The position of a point Q on the plane in the world frame.
[in]	n_W	Outward normal to the half space expressed in the world frame.

Precondition: n_W.norm() > 1e-10.

Warning: Be aware of round-off errors in floating computations when placing a vertex very close to the plane defining the half space.

Exceptions

std::exception if Finalize() has been called on the multibody plant owning this deformable model or if no deformable body with the given id has been registered in this model.

◆ vertex_positions_port()

const systems::OutputPort<T>& vertex_positions_port ( ) const

Returns the output port of the vertex positions for all registered deformable bodies.

Exceptions

std::exception if MultibodyPlant::Finalize() has not been called yet.

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

drake/multibody/plant/deformable_model.h

Detailed Description

template<typename T> class drake::multibody::DeformableModel< T >

Public Member Functions

Additional Inherited Members

Constructor & Destructor Documentation

◆ DeformableModel() [1/3]

◆ DeformableModel() [2/3]

◆ DeformableModel() [3/3]

Member Function Documentation

◆ AddExternalForce()

◆ AddFixedConstraint()

◆ fixed_constraint_ids()

◆ fixed_constraint_spec()

◆ GetBodyId() [1/2]

◆ GetBodyId() [2/2]

◆ GetBodyIndex()

◆ GetDiscreteStateIndex()

◆ GetExternalForces()

◆ GetFemModel()

◆ GetGeometryId()

◆ GetReferencePositions()

◆ HasConstraint()

◆ num_bodies()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ RegisterDeformableBody()

◆ SetWallBoundaryCondition()

◆ vertex_positions_port()

template<typename T>
class drake::multibody::DeformableModel< T >