Crow foot

Crow foot with at most tree lines attached to a common collecting point.

Collaboration diagram for Crow foot:

Author

Karl-Johan Reite

Date

21.11.2013 KJR: Initial version.

Review issues:

0014 — Crowfoot header describes a state-based solution the code does not implement, and Example.xml passes three dead attributes

A run-time selected number of lines (1, 2 or 3) are attached to each other in a collection point. These lines are specified in terms of their length and fastening position. In addition, external forces acting on the collection point is specified. All positions and forces must be given in the global coordinate system.

This class finds the stable position of the collecting point, based on the forces acting on the point. This is done based on a direct solution that disregards dynamics. To avoid an algebraic loop between the output position and the input force, the external force is passed through a three-channel, three-tap FIR filter that is fed once per accepted integrator step (AcceptedStep), and the geometry is solved from the filtered force in OdeFcn. The filter is seeded in InitialConditionSetup with the centroid of the line fastening positions. The velocity of the collecting point is a backward difference of the solved position across accepted integrator steps, so it lags the position by one step and is zero until the second accepted step. The simObject has no states. If one or two lines are stretched, the solution is found using geometric considerations. If three lines are active, the solution is found based on the method described in "Reliable computation of the points of intersection of n spheres in R^n" by I.D. Coope (Received 7 August 2000).

Example configuration excerpt

<Lib
   LibName                   = "fishery"
   SimObject                 = "Trawl/Crowfoot"
   Name                      = "CF"
   NumLines                  = "3"
/>

Input Ports

Name	Width	Description
ExternalForce	3	External force acting on the collection point.
LinePos1...LinePos<NumLines>	3	Fastening position of each line.
LineLength1...LineLength<NumLines>	1	Length of each line.

Output Ports

Name	Width	Description
LineForce1...LineForce<NumLines>	3	The fore on each line.
LineTension1...LineTension<NumLines>	1	The tension of each line.
ExternalPos	3	Position of the collecting point (global frame).
ExternalVel	3	Velocity of the collecting point (global frame), backward-differenced across accepted integrator steps.

Configuration parameters

Name	Width	Description
NumLines	1	The number of lines.

Initial conditions

This simObject does not have any initial conditions.

Full example file

<Contents>
  <OBJECTS>
    <Lib 
      LibName                   = "fishery"
      SimObject                 = "Trawl/Crowfoot"
      Name                      = "CF"
      NumLines                  = "3"
    />
  </OBJECTS>
  
   <INTERCONNECTIONS>
    <Connection
       CF.ExternalForce    = "0,0,0"
       CF.LinePos1         = "0,0,0"
       CF.LinePos2         = "0,1,5"
       CF.LinePos3         = "0,2,5"
       CF.LineLength1      = "4"
       CF.LineLength2      = "4"
       CF.LineLength3      = "4"
    />
  </INTERCONNECTIONS>
 
  <INITIALIZATION>
    <InitialCondition
    />
  </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/Crowfoot