Trawl door with warp control

Trawl door whose warp hangs from a crowfoot with a control line, which rolls the door.

Collaboration diagram for Trawl door with warp control:

Author

Karl-Johan Reite

Date

13.11.2013 KJR: Initial version (fhsim_marine). 2026: ported to FhSim 3.

A Trawl/TrawlDoor whose warp is not fastened at WarpPos but at the collecting point of a two-line crowfoot (CrowfootMath): a base line of length WarpBaseLineLength from WarpPos and a control line from ControlLinePos, whose length is the input ControlLineLength. The collecting point is where the two lines balance the warp force; if one line is slack, the other points along the warp. The warp force acts at the collecting point, which gives the door the same force and moment as the two line tensions at their fastening points. Shortening the control line moves the collecting point towards ControlLinePos, and so changes the door's roll.

The collecting point depends on the warp force, and the warp's end position (Pos1) on the collecting point. To break that loop, Pos1 and Vel1 use the collecting point solved once per step, in PreOdeFcn, from Force1 and ControlLineLength at the start of the step (WarpPos before the first step). The force in OdeFcn and the ControlLineTension output are solved at their own (T, X).

Example configuration excerpt

<Lib LibName                 = "fishery"
   SimObject                 = "Trawl/TrawlDoorWarpControl"
   Name                      = "PDoor"
   Mass                      = "4400"
   Area                      = "8"
   AR                        = "3"
   MaxLiftCoeff              = "1.6"
   DragCoeffAtMaxLift        = "0.5"
   IsPort                    = "1"
   WarpPos                   = "0.25, -0.3, 0.5"
   LBPos                     = "0, 0, 0"
   UBPos                     = "-1.5, 0.0, -0.2"
   COG                       = "0, 0, 0.7"
   Curvature                 = "3.0"
   ControlLinePos            = "-0.3, 0.1, -1.0"
   WarpBaseLineLength        = "1.0"
/>

Input Ports

As Trawl/TrawlDoor (Force1 is the warp force, applied at the collecting point), and:

Name	Width	Description
ControlLineLength	1	Length of the control line [m].

Output Ports

As Trawl/TrawlDoor (with Roll), except that Pos1 and Vel1 are the global position and velocity of the collecting point solved at the start of the step, and:

Name	Width	Description
ControlLineTension	1	Tension in the control line [N]; zero when it is slack.

Configuration parameters

As Trawl/TrawlDoor, and:

Name	Width	Description
ControlLinePos	3	Fastening position of the control line in the body frame, as WarpPos. Mirrored in y when IsPort.
WarpBaseLineLength	1	Length of the base line from WarpPos to the collecting point [m] (Default: 0.5).

Initial conditions

As Trawl/TrawlDoor.

Full example file

The demos TrawlDoorControl.xml, TrawlDoorControl2.xml, TrawlDoorControlMovie.xml and flume2.xml in data/trawl/demos/trawldoorcontrol/.

This SimObject is referred to as Trawl/TrawlDoorWarpControl