47. Constant tension winch

The identification tag for this tutorial is PDS-ABW. Pregenerated input files for this tutorial are found in the folder named PDS-ABW in the provided tutorial input files.

47.1. Tutorial overview

This tutorial covers:

  • Functionality of the constant tension winch
  • Connection a cable to a barge with a constant tension winch

47.2. Functionality of a constant tension winch

Note

  • The DCableConstantTensionWinch DObject was created to simulate a heave compensation winch that is commonly used with tugboats or other applications that require a winch to maintain a constant tension.
  • The winch functions similarly to the $Node0PayoutMode pretensioning winch, however the constant tension winch allows for more physically realistic constraints to be applied.
  • The property $SlipTension sets the desired tension set point. The property $DeadbandPercentage sets the percentage on either side of the slip tension that will act as the deadband range where the winch will not take action.
  • For example, if a slip tension of 100 kN is set and a 10% deadband percentage is used. If the tension is within the range of 90 kN to 110 kN, the winch will not respond.
  • If the cable tension is below or above the deadband range, the winch will either pay in or pay out to try and achieve the desired slip tension.
  • If the cable tension is outside of the deadband range, the winch acceleration will be set based on the following formula:

\(WinchAcceleration = \frac{CableTension - SlipTension}{WinchInertia}\)

\(WinchInertia = \frac{WinchLoadRating}{MaxPayInAccel}\)

  • The winch speed will be based on the winch speed at the previous time step and the current acceleration of the winch.
  • It should be noted that when the winch is paying in, the max speed of the winch is limited based on the following formula:
\(MaxWinchPayInSpeed = \frac{WinchPower}{WinchLoadRating}\)

47.3. Setup of a cable connected to a RigidBody with a constant tension winch

  • Create a new cable with the following properties:
// Boundary constraints
$Node0Static 1
$NodeNStatic 0

// Mechanical
$CableSegment Chain40mm 10
  • Set the cable node 0 position to (0,0,10) m and node N position to (10,0,0) m. Leave the cable length as the default straight line value of 14.14 m.
  • Create the Chain40mm cable segment using the following properties:
// Axial Rigidity
$AxialRigidityMode 0
$EA 1.317E+08

// Fluid loading
$FluidDiameter 4.000E-02
$CDc 2.2
$CDt 1.5
$CAc 1.0

// Mechanical
$EI1 0
$EI2 0
$GJ 0
$Diameter 7.263E-02
$Density 7800
$AxialDampingMode 1
$AxialReferenceDampingRatio 0.5
$BCID 0
$TCID 0
$CE 1

// Strain Limit
$ElongationLimitMode 0
  • Create a new RigidBody with $Kinematic 1 set and a starting position of (10,0,0) m. The RigidBody will not move in the simulation, so it can be left with default mass properties.
  • Create a new ConstantTensionWinch DObject. Provide the winch with the following properties:
// Uncategorized properties
$Mode 1
$SlipTension 3500
$WinchPower 10000
$WinchLoadRating 10000
$MaxPayinAccel 0.1
$DeadbandPercentage 10
$MaxBrakingAccel 0.1
$Tsample 0.01
$Nfilter 1

47.4. Connection a cable to a RigidBody with a constant tension winch

Note

  • Similar to the $Node0PayoutMode pretensioning winch, the constant tension winch controller only controls the pay in and pay out of the cable at one end. It has no control over the location of the cable end or any other connections the cable may have.
  • Connect the cable to the RigidBody using a point connection.
  • Connect the ConstantTensionWinch DObject to the cable. Be sure to choose node N in the ConstantTensionWinchCable connection properties.

Note

  • The ConstantTensionWinch requires the following .dat file:
<state>
0
</state>

47.5. Run the simulation and check the results

  • Set the water depth to 10 m and run the simulation for 30 seconds. Check the final cable tensions to determine whether the slip tension of 3500 N +/- 10% was reached in the cable.
  • Use the WinchData.dat results file in the constant tension winch results folder to view the winch acceleration, speed and winch load. Check that the starting acceleration matches what you would expect using the equations from this tutorial. In order to do this you must determine the difference between the node N cable tension and the slip tension.