chrono::fea::ChElementSpring Class Reference

## Description

Simple finite element with two nodes and a spring/damper between the two nodes.

This element is mass-less, so if used in dynamic analysis, the two nodes must be set with non-zero point mass.

#include <ChElementSpring.h>

Inheritance diagram for chrono::fea::ChElementSpring:
Collaboration diagram for chrono::fea::ChElementSpring:

## Public Member Functions

virtual int GetNnodes () override
Gets the number of nodes used by this element.

virtual int GetNdofs () override
Gets the number of coordinates in the field used by the referenced nodes. More...

virtual int GetNodeNdofs (int n) override
Get the number of coordinates from the n-th node that are used by this element. More...

virtual std::shared_ptr< ChNodeFEAbaseGetNodeN (int n) override
Access the nth node.

virtual void SetNodes (std::shared_ptr< ChNodeFEAxyz > nodeA, std::shared_ptr< ChNodeFEAxyz > nodeB)

virtual void GetStateBlock (ChMatrixDynamic<> &mD) override
Fills the D vector (column matrix) with the current field values at the nodes of the element, with proper ordering. More...

virtual void ComputeKRMmatricesGlobal (ChMatrix<> &H, double Kfactor, double Rfactor=0, double Mfactor=0) override
Sets H as the global stiffness matrix K, scaled by Kfactor. More...

virtual void ComputeInternalForces (ChMatrixDynamic<> &Fi) override
Computes the internal forces (ex. More...

virtual void SetupInitial (ChSystem *system) override
Setup. More...

virtual void SetSpringK (double ms)
Set the stiffness of the spring that connects the two nodes (N/m)

virtual double GetSpringK ()

virtual void SetDamperR (double md)
Set the damping of the damper that connects the two nodes (Ns/M)

virtual double GetDamperR ()

Public Member Functions inherited from chrono::fea::ChElementGeneric
ChKblockGenericKstiffness ()
Access the proxy to stiffness, for sparse solver.

virtual void EleIntLoadResidual_F (ChVectorDynamic<> &R, const double c) override
(This is a default (a bit unoptimal) book keeping so that in children classes you can avoid implementing this EleIntLoadResidual_F function, unless you need faster code)

virtual void EleIntLoadResidual_Mv (ChVectorDynamic<> &R, const ChVectorDynamic<> &w, const double c) override
(This is a default (VERY UNOPTIMAL) book keeping so that in children classes you can avoid implementing this EleIntLoadResidual_Mv function, unless you need faster code.)

virtual void ComputeMmatrixGlobal (ChMatrix<> &M) override
Returns the global mass matrix. More...

virtual void InjectKRMmatrices (ChSystemDescriptor &mdescriptor) override
Tell to a system descriptor that there are item(s) of type ChKblock in this object (for further passing it to a solver)

virtual void KRMmatricesLoad (double Kfactor, double Rfactor, double Mfactor) override
Adds the current stiffness K and damping R and mass M matrices in encapsulated ChKblock item(s), if any. More...

virtual void VariablesFbLoadInternalForces (double factor=1.) override
Adds the internal forces, expressed as nodal forces, into the encapsulated ChVariables, in the 'fb' part: qf+=forces*factor (This is a default (a bit unoptimal) book keeping so that in children classes you can avoid implementing this VariablesFbLoadInternalForces function, unless you need faster code)

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

Public Member Functions inherited from chrono::fea::ChElementBase
virtual void ComputeNodalMass ()
Compute element's nodal masses.

virtual void Update ()
Update: this is called at least at each time step. More...

virtual void EleDoIntegration ()
This is optionally implemented if there is some internal state that requires integration. More...

## Protected Attributes

std::vector< std::shared_ptr< ChNodeFEAxyz > > nodes

double spring_k

double damper_r

Protected Attributes inherited from chrono::fea::ChElementGeneric
ChKblockGeneric Kmatr

## Member Function Documentation

 virtual void chrono::fea::ChElementSpring::ComputeInternalForces ( ChMatrixDynamic<> & Fi )
overridevirtual

Computes the internal forces (ex.

the actual position of nodes is not in relaxed reference position) and set values in the Fi vector.

Implements chrono::fea::ChElementBase.

 virtual void chrono::fea::ChElementSpring::ComputeKRMmatricesGlobal ( ChMatrix<> & H, double Kfactor, double Rfactor = 0, double Mfactor = 0 )
overridevirtual

Sets H as the global stiffness matrix K, scaled by Kfactor.

Optionally, also superimposes global damping matrix R, scaled by Rfactor, and global mass matrix M multiplied by Mfactor. (For the spring matrix there is no need to corotate local matrices: we already know a closed form expression.)

Implements chrono::fea::ChElementBase.

 virtual int chrono::fea::ChElementSpring::GetNdofs ( )
overridevirtual

Gets the number of coordinates in the field used by the referenced nodes.

This is for example the size (n.of rows/columns) of the local stiffness matrix.

Implements chrono::fea::ChElementBase.

 virtual int chrono::fea::ChElementSpring::GetNodeNdofs ( int n )
overridevirtual

Get the number of coordinates from the n-th node that are used by this element.

Note that this may be different from the value returned by GetNodeN(n)->Get_ndof_w();

Implements chrono::fea::ChElementBase.

 virtual void chrono::fea::ChElementSpring::GetStateBlock ( ChMatrixDynamic<> & mD )
overridevirtual

Fills the D vector (column matrix) with the current field values at the nodes of the element, with proper ordering.

If the D vector has not the size of this->GetNdofs(), it will be resized.

Implements chrono::fea::ChElementBase.

 virtual void chrono::fea::ChElementSpring::SetupInitial ( ChSystem * system )
overridevirtual

Setup.

Precompute mass and matrices that do not change during the simulation, such as the local tangent stiffness Kl of each element, if needed, etc. (**Not needed for the spring element because global K is computed on-the-fly in ComputeAddKRmatricesGlobal() )

Reimplemented from chrono::fea::ChElementBase.