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========= |
\\ / F ield | OpenFOAM: The Open Source CFD Toolbox
\\ / O peration | Website: https://openfoam.org
\\ / A nd | Copyright (C) 2016-2026 OpenFOAM Foundation
\\/ M anipulation |
-------------------------------------------------------------------------------
License
This file is part of OpenFOAM.
OpenFOAM is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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for more details.
You should have received a copy of the GNU General Public License
along with OpenFOAM. If not, see <http://www.gnu.org/licenses/>.
Class
Foam::RBD::rigidBodyModel
Description
Basic rigid-body model representing a system of rigid-bodies connected by
1-6 DoF joints.
This class holds various body and joint state fields needed by the
kinematics and forward-dynamics algorithms presented in
reference:
\verbatim
Featherstone, R. (2008).
Rigid body dynamics algorithms.
Springer.
Chapter 4.
\endverbatim
SourceFiles
rigidBodyModel.C
kinematics.C
forwardDynamics.C
\*---------------------------------------------------------------------------*/
#ifndef RBD_rigidBodyModel_H
#define RBD_rigidBodyModel_H
#include "rigidBody.H"
#include "subBody.H"
#include "joint.H"
#include "compositeJoint.H"
#include "PtrList.H"
#include "HashTable.H"
namespace Foam
{
namespace RBD
{
// Forward declaration of friend functions and operators
class rigidBodyModel;
Ostream& operator<<(Ostream&, const rigidBodyModel&);
class rigidBodyModelState;
class restraint;
/*---------------------------------------------------------------------------*\
Class rigidBodyModel Declaration
\*---------------------------------------------------------------------------*/
class rigidBodyModel
{
// Private Member Functions
//- Initialise the model with the root-body
// which is a fixed massless bodyat the origin.
void initialiseRootBody();
//- Resize the state fields following the joining of a body
void resizeState();
//- Convert the body with given ID into a composite-body
void makeComposite(const label bodyID);
//- Add restraints to the motion
void addRestraints(const dictionary& dict);
protected:
// Protected data representing the model structure
//- List of the bodies.
// The 0'th body represents the fixed origin and is constructed
// automatically. The subsequent (moving) bodies are appended by the
// join member function.
PtrList<rigidBody> bodies_;
//- Bodies may be merged into existing bodies, the inertia of which is
// updated to represent the combined body which is more efficient than
// attaching them with fixed joints. These 'merged' bodies are held on
// this list.
PtrList<subBody> mergedBodies_;
//- Lookup-table of the IDs of the bodies
HashTable<label, word> bodyIndices_;
//- List of indices of the parent of each body
DynamicList<label> lambda_;
//- Each body it attached with a joint which are held on this list.
PtrList<joint> joints_;
//- Transform from the parent body frame to the joint frame.
DynamicList<spatialTransform> XT_;
//- The number of degrees of freedom of the model
// used to set the size of the of joint state fields q, qDot and qDdot.
label nDoF_;
//- True if any of the joints using quaternions
bool unitQuaternions_;
//- Motion restraints
PtrList<restraint> restraints_;
// Other protected member data
//- Acceleration due to gravity
vector g_;
// Mutable transforms maintained by kinematics and forward-dynamics
//- Transform from the parent body to the current body
mutable DynamicList<spatialTransform> Xlambda_;
//- Transform for external forces to the bodies reference frame
mutable DynamicList<spatialTransform> X0_;
// Mutable kinematic body state fields
//- The spatial velocity of the bodies
mutable DynamicList<spatialVector> v_;
//- The spatial acceleration of the bodies
mutable DynamicList<spatialVector> a_;
//- The velocity dependent spatial acceleration of the joints
mutable DynamicList<spatialVector> c_;
// Mutable state fields needed by the forward-dynamics algorithm
//- Velocity-product acceleration
//- Articulated body inertia
mutable DynamicList<spatialTensor> IA_;
//- Articulated body bias force
mutable DynamicList<spatialVector> pA_;
// Mutable joint state fields
//- Motion subspace for joints with 3 degrees of freedom
mutable DynamicList<compactSpatialTensor> S_;
//- Motion subspace for joints with 1 degrees of freedom
mutable DynamicList<spatialVector> S1_;
//- Sub-expression IA.S in the forward-dynamics algorithm
mutable DynamicList<compactSpatialTensor> U_;
//- Sub-expression IA.S1 in the forward-dynamics algorithm
mutable DynamicList<spatialVector> U1_;
//- Sub-expression (S^T.U)^-1 in the forward-dynamics algorithm
mutable DynamicList<tensor> Dinv_;
//- Sub-expression tau - S^T.pA in the forward-dynamics algorithm
mutable DynamicList<vector> u_;
// Protected Member Functions
//- Join the given body to the parent with ID parentID via the given
// joint with transform from the parent frame to the joint frame XT.
virtual label join_
(
const label parentID,
const spatialTransform& XT,
autoPtr<joint> jointPtr,
autoPtr<rigidBody> bodyPtr
);
public:
//- Runtime type information
TypeName("rigidBodyModel");
// Constructors
//- Null-constructor which adds the single root-body at the origin
rigidBodyModel();
//- Construct from dictionary
rigidBodyModel(const dictionary& dict);
//- Destructor
virtual ~rigidBodyModel();
// Member Functions
//- Return the number of bodies in the model (bodies().size())
inline label nBodies() const;
//- Return the list of the bodies in the model
inline const PtrList<rigidBody>& bodies() const;
//- List of indices of the parent of each body
inline const DynamicList<label>& lambda() const;
//- Return the list of joints in the model
inline const PtrList<joint>& joints() const;
//- Return the number of degrees of freedom of the model
// used to set the size of the of joint state fields q, qDot and qDdot.
inline label nDoF() const;
//- Return true if any of the joints using quaternions
inline bool unitQuaternions() const;
//- Return the acceleration due to gravity
inline const vector& g() const;
//- Allow the acceleration due to gravity to be set
// after model construction
inline vector& g();
//- Return the name of body with the given ID
inline const word& name(const label bodyID) const;
//- Return the names of the moving bodies
wordList movingBodyNames() const;
//- Return the inertia of body i
inline const rigidBodyInertia& I(const label i) const;
//- Return the spatial velocity of body i
inline const spatialVector& v(const label i) const;
//- Return the spatial acceleration of body i
inline const spatialVector& a(const label i) const;
//- Join the given body to the parent with ID parentID via the given
// joint with transform from the parent frame to the joint frame XT.
virtual label join
(
const label parentID,
const spatialTransform& XT,
autoPtr<joint> jointPtr,
autoPtr<rigidBody> bodyPtr
);
//- Join the given body to the parent with ID parentID via the given
// composite joint (specified as a list of co-located joints) with
// transform from the parent frame to the joint frame XT.
// Composite joins are useful to represent complex joints with degrees
// of freedom other than 1 or 3 which are directly supported.
label join
(
const label parentID,
const spatialTransform& XT,
autoPtr<joints::composite> cJoint,
autoPtr<rigidBody> bodyPtr
);
//- Merge the given body with transform X into the parent with ID
// parentID. The parent body assumes the properties of the combined
// body (inertia etc.) and the merged body is held on a
// separate list for reference.
label merge
(
const label parentID,
const spatialTransform& X,
autoPtr<rigidBody> bodyPtr
);
//- Return true if the body with given ID has been merged with a parent
inline bool merged(label bodyID) const;
//- Return the ID of the master body for a sub-body otherwise
// return the given body ID
inline label master(label bodyID) const;
//- Return the index of the merged body in the mergedBody list
// from the given body ID
inline label mergedBodyIndex(const label mergedBodyID) const;
//- Return the merged body ID for the given merged body index
// in the mergedBody list
inline label mergedBodyID(const label mergedBodyIndex) const;
//- Return the merged body for the given body ID
inline const subBody& mergedBody(label mergedBodyID) const;
//- Return the ID of the body with the given name
inline label bodyIndex(const word& name) const;
//- Return the current transform to the global frame for the given body
spatialTransform X0(const label bodyId) const;
// Find the corresponding point in the master body frame
inline vector masterPoint(const label bodyID, const vector& p) const;
//- Return the current position of the given point on the given body
inline vector p(const label bodyID, const vector& p) const;
//- Return the current direction of the given direction
// on the given body
inline vector d(const label bodyID, const vector& d) const;
//- Return the velocity of the given point on the given body
inline spatialVector v(const label bodyID, const vector& p) const;
//- Return the acceleration of the given point on the given body
inline spatialVector a(const label bodyID, const vector& p) const;
//- Apply the restraints and accumulate the internal joint forces
// into the tau field and external forces into the fx field
void applyRestraints
(
scalarField& tau,
Field<spatialVector>& fx,
const rigidBodyModelState& state
) const;
//- Calculate the joint acceleration qDdot from the joint state q,
// velocity qDot, internal force tau (in the joint frame) and
// external force fx (in the global frame) using the articulated body
// algorithm (Section 7.3 and Table 7.1)
void forwardDynamics
(
rigidBodyModelState& state,
const scalarField& tau,
const Field<spatialVector>& fx
) const;
//- Correct the velocity and acceleration of the bodies in the model
// from the given joint state fields following an integration step
// of the forwardDynamics
void forwardDynamicsCorrection(const rigidBodyModelState& state) const;
//- Write
virtual void write(Ostream&) const;
//- Read coefficients dictionary and update system parameters,
// restraints but not the current state
bool read(const dictionary& dict);
// Ostream Operator
friend Ostream& operator<<(Ostream&, const rigidBodyModel&);
};
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
} // End namespace RBD
} // End namespace Foam
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
#include "rigidBodyModelI.H"
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
#endif
// ************************************************************************* //
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