SimObject representing a continuous bottom ring. More...

#include <CFlexibleBottomRing.h>

Inheritance diagram for System::CFlexibleBottomRing:

Collaboration diagram for System::CFlexibleBottomRing:

Public Member Functions
	CFlexibleBottomRing (string simobjectname, ISimObjectCreator *creator)
	Reads parameters, registers states, input/output ports and shared resources. More...

virtual void	FinalSetup (const double T, const double const X, ISimObjectCreator const pCreator)

void	GetExternalForces (const double T, const double const X, double m_extlForce, int index)
	Returns the external forces at indexed element. More...

const double *	outNetConnectorPos (const double T, const double *const X, const int index)
	Output port. Returns the position of indexed net connection point. More...

const double *	outNetConnectorVel (const double T, const double *const X, const int index)
	Output port. Returns the velocity of indexed net connection point. More...

const double *	outChainConnectorPos (const double T, const double *const X, const int index)
	Output port. Returns the position of indexed chain connection point. More...

const double *	outChainConnectorVel (const double T, const double *const X, const int index)
	Output port. Returns the velocity of indexed chain connection point. More...

Public Member Functions inherited from System::CRing
	CRing (const string &simObjectName, ISimObjectCreator *const creator)
	reads parameters, registers states, output and intput ports.

void	OdeFcn (const double T, const double const X, double const XDot, const bool bIsMajorTimeStep)

void	InitialConditionSetup (const double T, const double const currentIC, double const updatedIC, ISimObjectCreator *const creator)

virtual void	GetExternalForces (const double T, const double const X, double m_extlForce, int index)
	get the external forces at element 'index'. Should be overridden by inheriting classes to get forces from their specific connectors More...

void	calculations (const double T, const double *const X)

virtual const double *	outConnectorPos (const double T, const double *const X, const int index)

virtual const double *	outConnectorVel (const double T, const double *const X, const int index)

Protected Attributes
int	m_numNetConnectors
	number of connectors to the net structure

int	m_numChainConnectors
	number of connectors to the bottom ring chains

int	m_ElementsPerNetConnector
	number of elements between net connector positions (must be an int; check perfomed in constructor)

int	m_ElementsPerChainConnector
	number of elements between chain connector positions (must be an int; check perfomed in constructor)

double	m_Cd_t
	Drag coefficient. Tangential drag.

double	m_Cd_n
	Drag coefficient. Normal drag.

double	m_Cm_diff
	Added mass coefficient for diffraction force.

ISignalPort **	m_aIINetForce
	Array of indices to net connector forces.

ISignalPort **	m_aIIChainForce
	Array of indices to chain connector forces.

double **	m_aadNetConnectorPos
	Local array for storing output positions.

double **	m_aadNetConnectorVel
	Local array for storing output velocities.

double **	m_aadChainConnectorPos
	Local array for storing output positions.

double **	m_aadChainConnectorVel
	Local array for storing output velocities.

CEnvironment *	m_Environment
	Pointer to DeepSeaGravityWaves, CEnvironment.

Protected Attributes inherited from System::CRing
int	m_numElements

double	m_totalLength

double	m_radius

double	m_weight

double	m_length

double	m_mass

double	m_Ixy

double	m_Iz

double	m_C_isAddMassHack

double	m_AddMassHack

double	m_alphaN

double	m_betaN

double	m_epsilonN

double	m_alphaM

double	m_betaM

double	m_epsilonM

double	m_alphaT

double	m_betaT

double	m_epsilonT

double	m_centrePosInit [3]
	Parameter for describing the initial position of the centre of the ring (not an IC since there is no corresponding state)

double	m_rho

double	m_surfacePosZ

double	m_rhoWater

double	m_Ct

double	m_Cn

double	m_bouyFactor

bool	m_additionalConnectors
	flag for additional connectors along cable

int	m_numConnectors
	number of additional connectors, if any

int	m_numInputsPerConnector
	number of force inputs per connector position (used for multiple attachments at same point)

int	m_ElementsPerConnector
	number of elements between connectors

ISignalPort **	m_aIIForce
	Array of indices to connector forces in input vector.

double	m_extlForce [3]
	Array for holding current value of external force at a given node.

double **	m_aadConnectorPos
	Local array for storing output positions.

double **	m_aadConnectorVel
	Local array for storing output velocities.

double	m_bending_epsilon [3]

element *	m_el

ICommonComputation *	m_calcDynamics

Eigen::Matrix< double, Eigen::Dynamic, 1 >	m_lambda

Eigen::Matrix< double, Eigen::Dynamic, 1 >	m_F_MDotV

double	m_forceA [3]

double	m_forceB [3]

int	m_shape

Eigen::Matrix< double, Eigen::Dynamic, 1 >	m_shapeMat
	0: circular; 1: square

Additional Inherited Members
Protected Types inherited from System::CRing
typedef Eigen::Matrix< double, 3, 3 >	mat3

typedef Eigen::Matrix< double, 3, 1 >	vec3

Detailed Description

Author: Brad Scofield

User Documentation:

Class modelling a flexible bottom ring using a cable model with bending/torsional stiffness. The cable is discretized as "6 degrees of freedom" rigid cylinders which are connected with axial and angular constraints. For high bending stiffness the cable will work as a truss/beam.

The constraints are regularized with a compliant variation of the Baumgarte method. In effect the cylinders can be thought of as connected with axial and angular springs like a traditional spring-mass-damper model, but without some of the numerical instability problems associated with high stiffness cables.

The behavior of the springs are defined with three parameters; \(\alpha\), \(\beta\) and \(\epsilon\). \(\beta\) controls the rate at which the constraint seeks towards equilibrium, \(\alpha\) is the damping factor, and \(\epsilon\) is the constraint compliance.

The effective spring stiffness is a combination of \(\beta\), \(\epsilon\), and the mathematical formulation of the constraint function.

For the axial spring the effective restoring force is: \( F = \beta^2/\epsilon*dL \) where \(dL\) is the distance between two successive cylinder endpoints.

For the angular spring the effective restoring moment is: \(M = \beta^2/\epsilon*sin(\theta/2)\) where theta is the difference in orientation angle between two successive cylinders. Note that the bending and the torsional stiffness can be set independently.

\(\alpha\) less than \(\beta\) means the system is underdamped, \(\alpha\) equal to \(\beta\) means critical damping, and \(\alpha\) larger than Beta means overdamped. The effective damping scales with \(\alpha/\epsilon\)

A fairly robust technique for adjusting the parameters when using an explicit integration scheme is as follows:

Choose a time step \(dt\) small enough to resolve the main macroscopic dynamics of the cable. The exact meaning of this is not precisely defined, but the important part is that the axial wave propagation speed which is responsible for the main numerical problems in spring-mass cable modeling need -not- be accounted for.
Set BetaN to \(1/dt\) or smaller, and then EpsilonN to the value which gives the desired global stiffness. A formula for determining effective Youngs-modulus is: \(E = \beta^2*L/(\epsilon*N*A)\), where \(L\) is the total cable length, \(N\) is the number of discrete cylinders in the cable, and \(A\) is the material cross-sectional area. For bending and torsional stiffness the expression is the same except \(A\) is replaced with \(2*I\) and \(2*J\) respectively.
Higher axial loads gives higher propagation rate of transversal waves. A smaller EpsilonM-value will suppress numerical instabilities from this cause. If the simulation crashes, reduce EpsilonM. As long as the BetaM-value is adjusted simultaneously, the total bending stiffness can be kept the same. If however BetaM becomes to small, the rate at which the cable 'self-aligns' will become too small, and the cable will tend to 'keep its shape'. In this case one may either accept this slightly non-physical consequence, keep the bending stiffness higher than the actual physical value, or reduce the time step and/or the element count.
Torsional parameters and \(\alpha\) values have only minor effect on stability, and can usually be set to taste. No \(\alpha\) or \(\beta\) value should however be set larger than \(1/dt\).

The bottom ring may be connected to a net structure through and a floating collar through connection points ("NetConnector" for net, "ChainConnector" for floating collar). Each of these connection points are assigned input ports ("NetForce\<i\>" or "ChainForce\<i\>") that take in forces in N, and output ports ("NetConnectorPos\<i\>/NetConnectorVel\<i\>" or "ChainConnectorPos\<i\>/ChainConnectorVel\<i\>").

Parameters

Parameter	Default		Comment
Length	-	total circumference of the ring [m]
numElements	-	number of rigid elements in the ring [#]
AlphaN	-	axial damping factor [s^-1]
BetaN	-	axial restoring factor [s^-1]
EpsilonN	-	axial compliance factor [kg^-1]
AlphaM	-	bending damping factor [s^-1]
BetaM	-	bending restoring factor [s^-1]
EpsilonM	-	bending compliance factor [kg^-1*m^-2]
AlphaT	-	torsional damping factor [s^-1]
BetaT	-	torsional restoring factor [s^-1]
EpsilonT	-	torsional compliance factor [kg^-1*m^-2]
Weight	-	weight of the ring [kg/m]
Radius	-	radius of the tube forming the bottom ring [m]
NumNetConnectors	0	Number of connection points between net structure and bottom ring [#]
NumChainConnectors	0	Number of connection points between floating collar and bottom ring [#]
CentrePosInit		Initial position of the centre of the ring in x,y,z [m,m,m]

Input ports

Tag	Size	Comment
ForceCables	3	Force transferred to the buoy from cables attached to the apex of the cone.

Output ports

Tag	Size	Comment
NetConnectorPos<i>	3	Position of the net connection point referred to by <i>.
NetConnectorVel<i>	3	Velocity of the net connection point referred to by <i>.
ChainConnectorPos<i>	3	Position of the chain connection point referred to by <i>.
ChainConnectorVel<i>	3	Velocity of the chain connection point referred to by <i>.

States

Tag	Size	Comment
NetForce<i>	3	Force input to ring at net connection point referred to by <i>.
ChainForce<i>	3	Force input to ring at chain connection point referred to by <i>.

Revision history:: 12.08.2011 BS: Initial version

Constructor & Destructor Documentation

◆ CFlexibleBottomRing()

System::CFlexibleBottomRing::CFlexibleBottomRing	(	string	simobjectname,
		ISimObjectCreator *	creator
	)

The constructor performs all initial setup for a flexible bottom ring simobject. Reading in parameters, setting up communication interface i.e. output ports, input ports, and states, plus additional 'one time only' resource setup.

Parameters

[in]	simobjectname	-> The name of the simobject
[in]	creator	-> Retrieve parameters. Register states, ports and shared resources

Member Function Documentation

◆ GetExternalForces()

void System::CFlexibleBottomRing::GetExternalForces	(	const double	T,
		const double *const	X,
		double *	m_extlForce,
		int	index
	)

virtual

Parameters

[in]	T	-> Current simulation time
[in]	X	-> Current simulation state
[out]	m_extlForce	-> External forces at element indexed by "index"
[in]	index	-> Element for which external forces will be provided

Reimplemented from System::CRing.

◆ outChainConnectorPos()

const double * System::CFlexibleBottomRing::outChainConnectorPos	(	const double	T,
		const double *const	X,
		const int	index
	)

See PortDefs.h

Parameters

[in]	T	-> Current simulation time
[in]	X	-> Current simulation state
[in]	index	-> Index of desired chain connection point position

Returns: -> Address of position of chain connection point indexed by "index"

◆ outChainConnectorVel()

const double * System::CFlexibleBottomRing::outChainConnectorVel	(	const double	T,
		const double *const	X,
		const int	index
	)

See PortDefs.h

Parameters

[in]	T	-> Current simulation time
[in]	X	-> Current simulation state
[in]	index	-> Index of desired chain connection point velocity

Returns: -> Address of velocity of chain connection point indexed by "index"

◆ outNetConnectorPos()

const double * System::CFlexibleBottomRing::outNetConnectorPos	(	const double	T,
		const double *const	X,
		const int	index
	)

See PortDefs.h

Parameters

[in]	T	-> Current simulation time
[in]	X	-> Current simulation state
[in]	index	-> Index of desired net connection point position

Returns: -> Address of position of net connection point indexed by "index"

◆ outNetConnectorVel()

const double * System::CFlexibleBottomRing::outNetConnectorVel	(	const double	T,
		const double *const	X,
		const int	index
	)

See PortDefs.h

Parameters

[in]	T	-> Current simulation time
[in]	X	-> Current simulation state
[in]	index	-> Index of desired net connection point velocity

Returns: -> Address of velocity of net connection point indexed by "index"

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

reloadrepos/fhsim_maritime/src/system/CFlexibleBottomRing.h

Public Member Functions

Protected Attributes

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

◆ CFlexibleBottomRing()

Member Function Documentation

◆ GetExternalForces()

◆ outChainConnectorPos()

◆ outChainConnectorVel()

◆ outNetConnectorPos()

◆ outNetConnectorVel()