A trawl door with an additional, controlled foil.

Collaboration diagram for Trawl door with foil:

Author: Karl-Johan Reite

Date: 09.01.2014 KJR: Initial version.

This simObject represents a trawl door with an additional, controlled foil. It is meant for testing proposed control concepts. The foil geometry (cord, span) and its lift and drag coefficients for several angles of attack are configuration parameters; its angle of attack relative to the door, its exposed area ratio and its position in the door coordinate system are input ports.

The trawl door is simulated in six degrees of freedom. This model includes a fairly complex model of the hydrodynamic forces and the fastening points of the warp and the bridles. It is based on unit quaternions for translation between different coordinate systems, to avoid the singularity problem of Euler angles.

Example file input:

<Lib LibName                = "fishery"
    SimObject               = "Trawl/TrawlDoorAddedFoil"
    Name                    = "door"
        />

Configuration parameters

Name	Width	Description
FoilHydro_Aoa	<HydroSpecWidth>	The foil angle of attack relative to the water flow: at least two angles, strictly increasing. Coefficients are interpolated linearly between them; an angle outside the table holds the coefficients of the nearest end.
FoilHydro_CL	<HydroSpecWidth>	The foil lift coefficient for the specified angles of attack in FoilHydro_Aoa.
FoilHydro_CD	<HydroSpecWidth>	The foil drag coefficient for the specified angles of attack in FoilHydro_Aoa.
FoilHydro_IsVertical	1	Is the foil vertical (in relation to the trawl door)? Must be 1: a horizontal foil is not implemented and is reported as a parameter error.
FoilHydro_Cord	1	The foil cord.
FoilHydro_Span	1	The foil span.
FoilHingeOffset	1	The distance along the chord from the foil hinge to its pressure centre, used for the hinge moment. Default 0.1 * FoilHydro_Cord.

Input Ports

Name	Width	Description
FoilRelativeAoa	1	The foil angle of attack relative to the door.
FoilRelativeAoaRate	1	The rate of change of FoilRelativeAoa (rad/s), which drives the foil energy. Connect it to the derivative of the FoilRelativeAoa signal, or to 0 for a foil that does not move.
FoilExposedAreaRatio	1	The ratio of the foils area which is exposed.
FoilRelPosition	3	The position of the foil in the trawl door coordinate system.

Output Ports

Name	Width	Description
FoilEnergyConsumed	1	The energy consumed by controlling the foil, the FoilEnergy state (J).

The foil energy integrates the positive power of the hinge moment, d/dt FoilEnergy = max(M_h * FoilRelativeAoaRate\, 0), with M_h = N * FoilHingeOffset and N the hydrodynamic force normal to the foil chord, N = L cos(a) + D sin(a) for the foil lift L, drag D and angle a to the flow. Power the load delivers back is not recovered, and changing FoilExposedAreaRatio costs nothing.

Initial conditions

Position, orientation, and FoilEnergy (1, the energy consumed by the foil; initial value 0).

This SimObject is referred to as Trawl/TrawlDoorAddedFoil