Net structure with wake

Class containing a net object.

Collaboration diagram for Net structure with wake:

Author

Karl-Johan Reite

Review issues:

0163 — fhsim_aquaculture cannot build on fhsim_marine_elements 4 without a port, and the migration guide does not list what the port must change

Deprecated:

Kept in 4.x only because fhsim_aquaculture derives Netcage/NetCageWakeEffect from it (MARE-0117); it will be removed in fhsim_marine_elements 5.0. Use Net/NetStructure instead, with the net-hydrodynamics load laws (HydroModel) and its wake casting into the environment wake (CastWake, Wake casting). Setup logs a warning. See Deprecated.

Warning

FinalSetup samples the waked current to build its wake polynomials, so a wake source that sets its field in its own FinalSetup counts only when its object comes before this one in the input file (MARE-0157). Not fixed: the class is frozen for fhsim_aquaculture.

A variant of Net/NetStructure whose panels (NetElement3NWakeEffect) can reduce the current velocity by a velocity ratio, use a Reynolds-number-dependent twine drag coefficient, or use a screen model for the hydrodynamic force. The net definition file is read by the same code as for Net/NetStructure, so its General, ExternalNodeMap, NetElements and CableElements parameters are as listed there. Compared with Net/NetStructure:

• The knot drag coefficient (0.4) and the knot diameter (2 BarD) are fixed.
• The panel water velocity is the particle velocity at the panel centroid, with its current part (particle velocity minus wave part) multiplied by the velocity ratios.
• There is no line visualisation, and unset initial conditions are always set to 0.

Example configuration excerpt

<Lib
   LibName                             = "marine_elements"
   SimObject                           = "Net/NetStructureWakeEffect"
   Name                                = "Net"
   File                                = "Morenot520Simple.xml"
   NodesInputForce                     = "PWing1, SWing1"
   NodesOutputPosAndVel                = "PWing1, SWing1"
   WakeEffectBetweenTwinesInElementsOn = "true"
   UseActualElementSizeInWakeEffect    = "true"
   UseReynoldsDependentDragCoefficient = "true"
   UseScreenModelForHydrodynamicForce  = "false"
/>

Note

The simulation must include an Environment, e.g. Environment found in fhsim_environment, and a SeafloorForces shared resource must be available.

Input Ports

Name	Width	Description
<tag>Force	3	External force [N] added to the node of each tag in NodesInputForce. Registered when UseTagForExternalNodes is true.
ExternalForce<node>	3	As \<tag\>Force, named by zero-based node number. Registered when UseTagForExternalNodes is false.

Output Ports

Name	Width	Description
<tag>Force	3	The value of the matching \<tag\>Force input port [N]. Registered when UseTagForExternalNodes is true.
ExternalForce<node>	3	As \<tag\>Force, named by node number. Registered when UseTagForExternalNodes is false.
<tag>Pos	3	Position [m] of the node of each tag in NodesOutputPosAndVel. Registered when UseTagForExternalNodes is true.
ExternalPos<node>	3	As \<tag\>Pos, named by node number. Registered when UseTagForExternalNodes is false.
<tag>Vel	3	Velocity [m/s] of the node of each tag in NodesOutputPosAndVel. Registered when UseTagForExternalNodes is true.
ExternalVel<node>	3	As \<tag\>Vel, named by node number. Registered when UseTagForExternalNodes is false.
BottomContact	6	IIR-filtered bottom-contact buffer. The buffer is zeroed in the constructor and never written, so the port always outputs zeros.
NetTotalForceCheck	3	Meant as the total screen-model force on the net, but never computed: always zero.

Configuration parameters in the main input file

Name	Width	Description
File	1	Name of the net definition file (XML), looked up relative to the directory of the main input file, with the working directory as fallback. An absolute path still fails, a bug in FhSim's InputReader (fhsim_marine_elements_issue_0120). Either File or BinaryFile is required; File wins when both are given.
BinaryFile	1	Name of a protobuf net definition file. As for Net/NetStructure.
NodesInputForce	n	Comma-separated tags from ExternalNodeMap that get a force input port (Default: none).
NodesOutputPosAndVel	n	Comma-separated tags from ExternalNodeMap that get position and velocity output ports (Default: none).
UseTagForExternalNodes	1	Names the external node ports by tag (true) or by zero-based node number (false), as for Net/NetStructure (Default: true).
AddedDragPerMPS	1	Read, then overwritten with 0 by the net definition file's settings before it is used, so it has no effect (Default: 0).
NetDampingRatio	1	Damping ratio of the panels, as for Net/NetStructure (Default: 1).
WakeEffectBetweenElementsOn	1	Wake from other panels (the upstream side of a cage). When true, a wake polynomial is generated for each panel at start-up with a hard-coded distance of 51.625 m to the wall in front. The factor is applied only to panels flagged as in the shadowed region, and nothing sets that flag, so the option has no effect on the forces (Default: false).
WakeEffectBetweenTwinesInElementsOn	1	Wake between the twines inside a panel. When true, each panel's current velocity is multiplied by a dimensionless velocity ratio from a polynomial fitted at start-up to the current at its centroid (Default: false).
UseActualElementSizeInWakeEffect	1	When true, the wake polynomials use the panel's own size in mesh bars (the mean of its u and v extents). When false, they use NumBarsInWakeEffectCalc (Default: true).
NumBarsInWakeEffectCalc	1	Number of twine bars used in the wake polynomials when UseActualElementSizeInWakeEffect is false (Default: 100).
UseReynoldsDependentDragCoefficient	1	When true and the twine Reynolds number (twine diameter, kinematic viscosity 1.19e-6 m²/s) satisfies \(32 \le Re < 10000\), the twine normal drag coefficient comes from a seventh-order polynomial for a smooth cylinder (Kristiansen and Faltinsen 2012). Otherwise the Net/NetStructure twine drag model is used. The flag also sets the drag coefficient in the wake polynomials: the same polynomial in that range, otherwise 1.15 (Default: true).
UseScreenModelForHydrodynamicForce	1	When true, the panel twine drag is replaced by screen-model drag and lift forces, with net solidity \(S_n = 2,\mathrm{BarD}/\mathrm{BarL}\) and the coefficients of Kristiansen and Faltinsen (2012). Twine tension, mesh-opening forces, weight and damping are kept (Default: false).
UseDragCoeffFromMoeFore2021	1	Screen model only. Uses the drag and lift coefficients of Moe-Føre et al. (2021), with SnFromImageAnalysis as the solidity. Turned off when SnFromImageAnalysis is outside 0.185 to 0.364 (Default: false).
SnFromImageAnalysis	1	Net solidity [-] for UseDragCoeffFromMoeFore2021. The default lies outside the valid range, so the Moe-Føre formulas are used only when this is set (Default: 0.4).
RhoWater	1	Water density [kg/m³] in the screen-model drag and lift forces. The other forces use 1025 (Default: 1025).

Parameters of the net definition file

The General, ExternalNodeMap, NetElements and CableElements tags are read exactly as for Net/NetStructure; see its tables.

Initial conditions

There are two states per node after refinement, numbered from 1: state Pos_k belongs to zero-based node k - 1. Unset values are set to 0. The z axis points down.

Name	Width	Description
Pos_1...Pos_<N>	3	Position of each node [m].
Vel_1...Vel_<N>	3	Velocity of each node [m/s].

Full example file

This SimObject is referred to as Net/NetStructureWakeEffect