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 hangs from 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 warp's end (Pos1, Vel1) is the door's WarpPos, as on Trawl/TrawlDoor: the crowfoot is short beside the warp, and an end that followed the collecting point would follow the direction of the warp force it feeds, which is erratic while the warp is nearly slack (FISH-0106). The collecting point and ControlLineTension are solved at (T, X) from Force1 and ControlLineLength.

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, -0.2"
   LBPos                     = "-1.5, 0.3, 0.0"
   UBPos                     = "-1.5, 0.3, 0.0"
   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; Pos1 and Vel1 at WarpPos), and:

Name	Width	Description
ControlLineTension	1	Tension in the control line [N]; zero when it is slack.
CollectingPoint	3	Global position of the crowfoot's collecting point, where the warp force acts [m].

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