Class containing a fundamental cable element object. More...

#include <CableElBasics.h>

Inheritance diagram for CableElBasics:

Collaboration diagram for CableElBasics:

Public Member Functions
	CableElBasics ()
	The constructor.

	~CableElBasics ()
	The destructor.

virtual void	AddEndForces (const double adPosA[3], const double adVelA[3], const double adPosB[3], const double adVelB[3], const double adFluidVel[3], const double rhoWater, double adForceA[3], double adForceB[3])
	Calculates the end forces on the cable element.

virtual void	SetConstants ()
	Calculates parameters and sets physical constants.

virtual void	CalcMassAndWeight ()
	Calculates the mass and weight of the element in water.

virtual bool	CheckAndInitialize ()
	Does the initialization and checking to make sure that the element is ready for simulation.

double	GetDampingCoeff () const
	Returns the structural damping coefficient (negative value: -2dampRatioareasqrt(Erho)).

virtual void	UpdateLength (double newLength)
	Upates the length of the cable element, and its dependant properties.

double	GetLength ()

void	SetSurfaceElevation (double etaA, double etaB)

virtual double	SurfaceHalfSize () const
	The half-size the surface gate needs: the element's radius; larger with floats (NetCableElement).

void	SetWaveAcceleration (const double acceleration[3])

double	InertiaShare () const
	The inertia force factor of one end node: half of (1 + Ca) rho V f (environment::cylinder_hydro::InertiaForceFactor).

void	WaveExcitationPositionJacobian (const double posA[3], const double posB[3], const double acceleration[3], double dF_dpB[9]) const

void	DragVelocityJacobian (const double posA[3], const double posB[3], const double velA[3], const double velB[3], const double vFluid[3], double rhoWater, double dFA_dvA[9], double dFA_dvB[9], double dFB_dvA[9], double dFB_dvB[9]) const

void	DragPositionJacobian (const double posA[3], const double posB[3], const double velA[3], const double velB[3], const double vFluid[3], double rhoWater, double dFA_dpA[9], double dFA_dpB[9], double dFB_dpA[9], double dFB_dpB[9]) const

double	BlendedFluidDensity (const double posA[3], const double posB[3]) const

Public Attributes
unsigned long	m_iD
	The ID of the element.

std::string	m_cableName
	The name of the parent cable.

double	m_dL0
	The relaxed length of the element.

double	m_dD
	The diameter of the element.

double	m_dE
	The Young modulus of the element.

double	m_rho
	The density of the element material.

double	m_addedWeightInWater
	The weight in water added to the element.

double	m_tangentialFrictionCoeff
	The tangential drag coefficient of the cable element.

double	m_normalDragCoeff
	The normal drag coefficient of the cable element.

double	m_rhoWater
	The density of the surrounding fluid: the water density blended with the air density by the submerged fraction (CalcFoundation).

double	m_rhoWaterFull = 1025.0
	The water density the owner passed, unblended [kg/m³]; also that of the stiffness factor (CableElDynStiff, MARE-0357).

double	m_rhoAir = 1.2
	The air density, kg/m³; the owner sets the environment's (cable_air::EnvironmentAirDensity, owner ruling R65).

double	m_minLength
	The minimum length of the element.

double	m_maxTension
	The maximum tension in the element.

double	m_dampingRatio
	The relative damping ratio of the cable.

double	m_eA
	The linear stiffness of the element.

double	m_dA
	The cross sectional area of the cable.

double	m_weightInWater [2]
	The weight in water distributed to each node.

double	m_massInWater [2]
	The mass in water distributed to each node.

double	m_weightInWaterPerMeter [2]
	The weight in water distributed to each node, per meter cable.

double	m_massInWaterPerMeter [2]
	The mass in water distributed to each node, per meter cable.

Protected Member Functions
virtual bool	AppendagesNearTheSurface ()
	True when a float on the element is near the surface, so its weight must be recomputed every call; none here.

double	WetFractionAt (const double posA[3], const double posB[3], double submergence[2], double &axisVertical) const

void	AddWaveExcitationCable (double adForceA[3], double adForceB[3]) const
	Adds the rope's Froude-Krylov and added-mass wave excitation (owner rulings R67, R104). CalcFoundation must be run first.

void	CalcFoundation (const double adPosA[3], const double adVelA[3], const double adPosB[3], const double adVelB[3], const double adFluidVel[3], const double rhoWater)

virtual void	AddStructuralForces (double adForceA[3], double adForceB[3])=0

void	AddGravityBuoyancy (double adForceA[3], double adForceB[3], const double adPosA[3], const double adPosB[3])
	Adds the forces from gravity and buoyancy to the nodes. CalcFoundation must be run first.

void	AddHydroForcesCable (double adForceA[3], double adForceB[3])
	Calculates the hydrodynamic forces on the cable and the spheres and disks attached to it. CalcFoundation must be run first.

Protected Attributes
double	m_surfaceElevation [2] = {0.0, 0.0}
	η above the ends [m] (SetSurfaceElevation).

double	m_submergence [2] = {1e10, 1e10}
	z + η at the ends at the last CalcFoundation [m]; deep before the first.

double	m_axisVertical = 0.0
	The vertical component of the unit axis A→B at the last CalcFoundation.

double	m_wetFraction = 1.0
	The element's wet fraction at the last CalcFoundation (CylinderWetFraction).

double	m_waveAcceleration [3] = {0.0, 0.0, 0.0}
	The water particle acceleration at the element (SetWaveAcceleration) [m/s²].

double	ma_adDirection [3]
	Memory allocation to increase the computational efficiency.

double	ma_dDampingCoeff
	A intermediate damping calculation to increase the computational efficiency.

double	ma_adVel [3]
	The average hydrodynamic velocity of the element.

double	ma_dVelAmp
	The scalar average hydrodynamic velocity of the element.

double	ma_adVt [3]
	The average tangential hydrodynamic velocity of the element.

double	ma_dVtAmp
	The scalar average tangential hydrodynamic velocity of the element.

double	ma_adVn [3]
	The average normal hydrodynamic velocity of the element.

double	ma_dVnAmp
	The scalar average normal hydrodynamic velocity of the element.

double	ma_adVn_A [3]
	The hydrodynamic normal velocity of the end A: its own velocity against the water, the part normal to the element, saturated.

double	ma_adVn_B [3]
	The hydrodynamic normal velocity of the end B.

double	ma_dVnAmp_A
	The scalar hydrodynamic normal velocity of the end A (saturated with the vector).

double	ma_dVnAmp_B
	The scalar hydrodynamic normal velocity of the end B.

double	ma_adVt_A [3]
	The hydrodynamic axial velocity of the end A: its own velocity against the water, the part along the element, saturated.

double	ma_adVt_B [3]
	The hydrodynamic axial velocity of the end B.

double	ma_dVtAmp_A
	The speed of the hydrodynamic axial velocity of the end A (unsigned, saturated with the vector).

double	ma_dVtAmp_B
	The speed of the hydrodynamic axial velocity of the end B.

double	ma_dLength
	The actual distance between the ends.

double	ma_dCompressionSpeed
	The speed at which the distance between the two ends decreases.

Detailed Description

Author: Karl-Johan Reite

Member Function Documentation

◆ AddStructuralForces()

virtual void CableElBasics::AddStructuralForces	(	double	adForceA[3],
		double	adForceB[3]
	)

protectedpure virtual

Adds the forces from tension and internal damping to the nodes (CableElDynStiff: the axial law, CableAxialLaw.h). CalcFoundation must be run first.

Implemented in CableElDynStiff.

◆ AppendagesNearTheSurface()

virtual bool CableElBasics::AppendagesNearTheSurface ( )

inlineprotectedvirtual

Reimplemented in NetCableElement.

◆ BlendedFluidDensity()

double CableElBasics::BlendedFluidDensity	(	const double	posA[3],
		const double	posB[3]
	)		const

The fluid density of the element with its ends at posA and posB: the water density the owner passed last (m_rhoWaterFull) blended with the air density by the wet fraction against the surface elevations last set, as CalcFoundation blends it (owner rulings R65, R66). For an analytical Jacobian at a state other than the last CalcFoundation's (MARE-0319).

Parameters

posA	End A [m], NED.
posB	End B [m], NED.

Returns: f rhoWater + (1 - f) rhoAir [kg/m³].

◆ CalcFoundation()

void CableElBasics::CalcFoundation	(	const double	adPosA[3],
		const double	adVelA[3],
		const double	adPosB[3],
		const double	adVelB[3],
		const double	adFluidVel[3],
		const double	rhoWater
	)

protected

Calculates the member variables used for increased computational efficiency, and must be run before any further calculations.

◆ CalcMassAndWeight()

virtual void CableElBasics::CalcMassAndWeight ( )

virtual

Reimplemented in NetCableElement.

◆ CheckAndInitialize()

virtual bool CableElBasics::CheckAndInitialize ( )

virtual

Reimplemented in CableElDynStiff, and NetCableElement.

◆ DragPositionJacobian()

void CableElBasics::DragPositionJacobian	(	const double	posA[3],
		const double	posB[3],
		const double	velA[3],
		const double	velB[3],
		const double	vFluid[3],
		double	rhoWater,
		double	dFA_dpA[9],
		double	dFA_dpB[9],
		double	dFB_dpA[9],
		double	dFB_dpB[9]
	)		const

The 3x3 position blocks of the drag: the turning of the element's axis changes the axial and normal parts of each end's velocity. For an analytical Jacobian; the same omissions as DragVelocityJacobian. A displacement of end B is the opposite of one of end A.

Parameters

posA	End A [m], NED.
posB	End B [m], NED.
velA	Velocity of end A [m/s].
velB	Velocity of end B [m/s].
vFluid	The water velocity at the element [m/s].
rhoWater	The fluid density of the element [kg/m³], the air/water blend (MARE-0319).
dFA_dpA	Out: dF_A[j]/dpA[k] at [3 * j + k] [N/m]. The other three outputs follow the same naming.

◆ DragVelocityJacobian()

void CableElBasics::DragVelocityJacobian	(	const double	posA[3],
		const double	posB[3],
		const double	velA[3],
		const double	velB[3],
		const double	vFluid[3],
		double	rhoWater,
		double	dFA_dvA[9],
		double	dFA_dvB[9],
		double	dFB_dvA[9],
		double	dFB_dvB[9]
	)		const

The 3x3 velocity blocks of the drag (AddHydroForcesCable): each end node's axial and normal drag on its own velocity, so the blocks between the two ends are zero. For an analytical Jacobian. The position blocks are DragPositionJacobian's; the clip at kSaturationSpeed, the slope of the air/water blend and the spatial gradient of vFluid are left out.

Parameters

posA	End A [m], NED.
posB	End B [m], NED.
velA	Velocity of end A [m/s].
velB	Velocity of end B [m/s].
vFluid	The water velocity at the element [m/s].
rhoWater	The fluid density of the element [kg/m³], the air/water blend (MARE-0319).
dFA_dvA	Out: dF_A[j]/dvA[k] at [3 * j + k] [N s/m]. The other three outputs follow the same naming.

◆ InertiaShare()

double CableElBasics::InertiaShare ( ) const

The added-mass coefficient of the rope normal to its axis is environment::cylinder_hydro::kCylinderAddedMassCoefficient, Ca = 1 (the exact potential-flow value, Newman, Marine Hydrodynamics, 1977; DNV-RP-C205 (2021), Appendix A, Table A-1 gives the same). The element's inertia (rho_c + rho) A L (CalcMassAndWeight) carries the same Ca, in every direction.

◆ SetConstants()

virtual void CableElBasics::SetConstants ( )

virtual

Reimplemented in NetCableElement.

◆ SetSurfaceElevation()

void CableElBasics::SetSurfaceElevation	(	double	etaA,
		double	etaB
	)

inline

Sets the surface elevation η above the two ends for the next force evaluations (owner ruling R66).

The owner evaluates η at the ends, or passes 0 where the element is deeper, or higher, than the maximum wave elevation plus SurfaceHalfSize() (then the fraction is the same).

Parameters

etaA	η above end A [m], positive up.
etaB	η above end B [m].

◆ SetWaveAcceleration()

void CableElBasics::SetWaveAcceleration ( const double acceleration[3] )

inline

Sets the water particle acceleration at the element for the next force evaluations (owner rulings R67, R104); 0 by default, so an owner without waves adds nothing.

Parameters

acceleration The acceleration [m/s²], NED.

◆ SurfaceHalfSize()

virtual double CableElBasics::SurfaceHalfSize ( ) const

inlinevirtual

Reimplemented in NetCableElement.

◆ WaveExcitationPositionJacobian()

void CableElBasics::WaveExcitationPositionJacobian	(	const double	posA[3],
		const double	posB[3],
		const double	acceleration[3],
		double	dF_dpB[9]
	)		const

The derivative of the rope's wave excitation (AddWaveExcitationCable) in the position of end B through the turning of the element's axis (owner ruling R108), for an analytical Jacobian. The force is the same on both ends, and its derivative in end A is the negative. The wet fraction is the last CalcFoundation's, and the gradient of the wave field and of the wet fraction are left out, as the drag's current gradient is.

Parameters

posA	End A [m], NED.
posB	End B [m], NED.
acceleration	The water particle acceleration at the element [m/s²], NED.
dF_dpB	Out: dF[j]/dpB[k] at [3 * j + k] [N/m].

◆ WetFractionAt()

double CableElBasics::WetFractionAt	(	const double	posA[3],
		const double	posB[3],
		double	submergence[2],
		double &	axisVertical
	)		const

protected

The wet fraction of the element with its ends at posA and posB against the surface elevations last set (owner ruling R66, environment::body_submergence::CylinderWetFraction).

Parameters

posA	End A [m], NED.
posB	End B [m], NED.
submergence	Out: z + η at the two ends [m].
axisVertical	Out: the vertical component of the unit axis A→B.

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

webfhsim/reloadrepos/fhsim_marine_elements/src/cable/subroutines/CableElBasics.h

Public Member Functions

Public Attributes

Protected Member Functions

Protected Attributes

Detailed Description

Member Function Documentation

◆ AddStructuralForces()

◆ AppendagesNearTheSurface()

◆ BlendedFluidDensity()

◆ CalcFoundation()

◆ CalcMassAndWeight()

◆ CheckAndInitialize()

◆ DragPositionJacobian()

◆ DragVelocityJacobian()

◆ InertiaShare()

◆ SetConstants()

◆ SetSurfaceElevation()

◆ SetWaveAcceleration()

◆ SurfaceHalfSize()

◆ WaveExcitationPositionJacobian()

◆ WetFractionAt()