19. Simulate a surface mooring with Cable

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

19.1. Tutorial overview

This tutorial covers:

• Running a simulation from exported results
• Applying waves to a surface mooring

19.2. Setting up the simulation

• Load the simulation files from the tutorial Simulate a surface mooring with QuasiStaticCable. If the tutorial has not been completed, the input files can be downloaded here.

These files will be used as a starting point to simulate a surface mooring with the Cable DObject. The QuasiStaticCable surface mooring in the input files will need to be converted to a Cable DObject.

• Convert the QuasiStaticCable SURFACE_MOORING to a Cable DObject. The tutorial Convert a QuasiStaticCable to Cable outlines the required steps to convert a QuasiStaticCable to a Cable.
• Select the Cable DObject and review the input file.

The Cable is anchored to the seabed using $NodeNStatic 1. Additional detailed file output related to anchors is indicated using $NodeNAnchor 1. The Cable has multiple material properties using different DCableSegment Features. An instrument is also modeled with ExtMass Features attached along the mooring.

The $SubmergenceProbe property in the cable input file will tell the ProteusDS solver to calculate the submergence below the water surface for a given arc length location on a cable. This property can be used to determine if a surface buoy goes beneath the surface, or the level of submergence for a subsurface mooring floater. The submergence output is found in the submergenceProbe.dat file in the results folder for the specific Cable DObject.

• A submergence probe at an arclength of 0 has already been added to the SURFACE_MOORING input file.

19.3. Adjust integrator and run settling simulation

• In the simulation input file, set EndTime 200 and IntervalOutput 0.1.
• The integrator properties should be adjusted to the adaptive 4th/5th Runge-Kutta integration scheme, as shown in the integrator library feature below.

// Integrator parameters
$IntegratorType 1
$MinimumTimeStep 1E-15
$MaximumTimeStep 1
$InitialTimeStep 0.0001
$TruncationError 0.0001

• Run the simulation.

The surface mooring should come to a steady orientation in current.

19.4. Adding waves

To gain an understanding of the mooring’s ability to remain at the surface under wave conditions, waves will be added to the simulation.

• Export the previous simulation. Open the exported simulation in PST.
• Set $WaveType 1 to use AIRY waves (regular).
• Press Ctrl-R to automatically add the required properties for the AIRY wave type.
• Set WaveHeight 5.
• Set WavePeriod 10.

The wave section of the environment input file should look like the following:

// Wave
$WaveType 1
$WaveReferenceCurrentSpeed 0
$WaveReferenceCurrentHeading 0
$WaveHeight 5
$WaveHeading 0
$WavePeriod 10

• Run the simulation and view the results in PostPDS.