6-DOF trawl door

Simulation of a trawl door in six degrees of freedom.

Collaboration diagram for 6-DOF trawl door:

Author

Karl-Johan Reite

Date

21.04.2008 KJR: Initial version.

Review issues:

0018 — Example.xml: a Door output at t=0 depends on process memory layout

Simulation of a trawl door 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 also based on unit quaternions for translation between different coordinate systems, to avoid the singularity problem of Euler angles.

Note

Unlike many other simObjects, the parameter Mesh does not take the extension .mesh. The parameter must therefore be set as e.g. "fhSphere" instead of "fhSphere.mesh"

For the time being, the parameter Mesh needs to b set as "fhSpere", in the input file. The trawldoor will be visualized as a white elliptical sphere.

Example configuration excerpt

<Lib LibName                 = "fishery"
   SimObject                 = "Trawl/TrawlDoor"
   Name                      = "Door"
   Mass                      = "3400"
   Area                      = "8"
   AR                        = "3"
   MaxLiftCoeff              = "1.6"
   DragCoeffAtMaxLift        = "0.5"
   IsPort                    = "1"
   WarpPos                   = "0.25, -0.3, -0.2"
   LBPos                     = "-1.5, 0.3,  2.0"
   UBPos                     = "-1.5, 0.3, -2.0"
   COG                       = "0, 0, 0.7"
   Mesh                      = "fhSphere"
   Curvature                 = "3.0"
   VisualizationScale        = "1"
/>

Input Ports

Name	Width	Description
Force1	3	Force from the warp, applied at WarpPos (global frame).
Force2	3	Force from the upper bridle, applied at UBPos (global frame).
Force3	3	Force from the lower bridle, applied at LBPos (global frame).

Output Ports

Name	Width	Description
Pos1	3	Global position of the warp fastening point (WarpPos).
Pos2	3	Global position of the upper bridle fastening point (UBPos).
Pos3	3	Global position of the lower bridle fastening point (LBPos).
Vel1	3	Global velocity of the warp fastening point.
Vel2	3	Global velocity of the upper bridle fastening point.
Vel3	3	Global velocity of the lower bridle fastening point.
Roll	1	Door roll angle in rad (added by this class): asin of the vertical (NED z) component of the door's local y-axis, negated when IsPort is true so port and starboard doors report the same sense.
Pitch	1	Door pitch angle in rad (added by this class): asin of the vertical (NED z) component of the door's local x-axis, negated when IsPort is true.
AngleOfAttack	1	Hydrodynamic angle of attack of the door in rad (added by this class).

Configuration parameters

Name	Width	Description
Mass	1	Mass of trawl door.
Density	1	Density of trawl door (Default: 7900).
Area	1	Area of trawl door.
Curvature	1	Description here.
IsPort	1	Description here.
Rho	1	Density of sea water (Default: 1025).
AR	1	Description here (Default: 1.4).
MaxLiftCoeff	1	Description here (Default: 1.9).
DragCoeffAtMaxLift	1	Description here (Default: 0.84).
WarpPos	3	Description here.
LBPos	3	Description here.
UBPos	3	Description here.
COG	3	Description here.
VisualizationScale	1	Description here (Default: 1).
LengthScale	1	Description here.
BreadthScale	1	Description here.
CurvatureScale	1	Description here.
Mesh	1	Description here (Default: fhSphere.mesh).

Initial conditions

Name	Width	Description
Pos	3	Position (Default: "0,0,0").
Quater	4	Quaternion (Default: "1,0,0,0").
LocalVel	3	Local velocity (Default: "0,0,0").
Omega	3	Description here (Default: "0,0,0").

Full example file

<Contents>
   <OBJECTS>
      <Lib
         LibName                   = "environment"
         SimObject                 = "Environment"
         Name                      = "Env"
         Waves.NumWaves            = "0"
         Bathymetry.Depth          = "190"
         Current.Model             = "Constant"
         Current.Vector            = "2.5,0,0"
      />
      <Lib
         LibName                   = "fishery"
         SimObject                 = "Trawl/TrawlDoor"
         Name                      = "Door"
         Density                   = "7900"
         Mass                      = "3400"
         Area                      = "8"
         Curvature                 = "3.0"
         IsPort                    = "1"
         Rho                       = "1025"
         AR                        = "3"
         MaxLiftCoeff              = "1.6"
         DragCoeffAtMaxLift        = "0.5"
         WarpPos                   = "0.25, -0.3, -0.2"
         LBPos                     = "-1.5, 0.3,  2.0"
         UBPos                     = "-1.5, 0.3, -2.0"
         COG                       = "0, 0, 0.7"
         VisualizationScale        = "0.01"
         Mesh                      = "trawl_doors/traaldoer"
      />
   </OBJECTS>
 
   <INTERCONNECTIONS>
      <Connection
         Door.Force1    = "0,0,0"
         Door.Force2    = "0,0,0"
         Door.Force3    = "0,0,0"
      />
   </INTERCONNECTIONS>
 
   <INITIALIZATION>
      <InitialCondition
         Door.Pos    = "0,0,20"
         Door.Quater = "0,0,0,1"
      />
   </INITIALIZATION>
 
   <SIMULATION>
      <Timing TStart="0" TEnd="30"/>
      <Integrator Method="RK45_i" NumCores="1" LogStates="1" UseRSSNorm="0">
        <StepControl StepMax="0.002" StepMin="0.00000001" AbsTol="1e-3" RelTol="1e-3"/>
      </Integrator>
      <!-- TODO migrate_v3: FileOutput="objects:all" -> configure via <OBSERVERS> section -->
   </SIMULATION>
</Contents>

This SimObject is referred to as Trawl/TrawlDoor