13
Jul

Anchoring your analysis

A mooring system connects floating structures to the shore or seabed. An anchor provides the holding point at the seabed and terminates the mooring system. Mooring lines can use synthetic fibre or elastomeric rope, wire, and chain, or any combination. Environmental factors from wind, currents, and waves determine the type of materials and layout to be used in a particular mooring system.

To design mooring systems, the tension in the mooring lines must be determined. This can be a complex and challenging task when considering the interaction of the mooring lines with the seabed, various material properties, and complex environmental loading effects. The goal is to calculate a cost effective and safe mooring configuration and reduce the risk of failures.

Mooring systems come in all shapes and sizes, from single leg moorings to four leg moorings, to aquaculture farm systems, which use significantly more complex mooring grid systems. Analysis of complex mooring systems is performed using numerical dynamic simulation tools.  By performing the analysis using simulation software, users can streamline their efforts and design and optimise mooring systems for all types of configurations.

ProteusDS simulation of a multi-cage aquaculture farm

ProteusDS simulation of a multi-cage aquaculture farm

 

Using ProteusDS, Dynamic Systems Analysis is able to analyse and visualise the mooring system. The positions and internal reaction forces of each of the lines in the system can be visualised for easy post processing. The vessel, platform, or system motions may be included in the dynamics, either by direct calculation or by use of an RAO database.

ProteusDS features a cubic-spline lumped mass cable model. The cable model can be used to simulate risers, pipes, beams, umbilicals, synthetic fibre or elastomeric ropes, and chains. ProteusDS performs time-domain analysis of mooring arrangements taking into account the effects of the wind, current, and wave loading.  It can be used for engineering assessment, planning, and operational analysis in advance of a mooring deployment.

 

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ProteusDS simulation of the ecoSPRAY mooring prior to deployment.

 

The benefits of the ProteusDS finite-element cable model are:

  • Cubic finite elements are more accurate than linear and significantly longer element lengths are possible.
  • Longer elements for a given mooring line can lead to substantial increases in simulation execution speed due to larger allowable numerical time steps and fewer calculations per line.
  • Torsional and bending effects allow accurate resolution of slack line and snap load events.
  • The torsional inertia of the line itself is neglected and an instantaneous twist response results, which mitigates high-frequency torsional dynamics noise from inducing small numerical integration time steps and slowing execution speed.

*to explore ProteusDS’ finite-element cable model in more detail, pleasure review our manual here

 

ProteusDS provides a visual interface where the user can easily setup and adjust the mooring and change the environmental conditions. ProteusDS will then calculate and display stresses and line tensions.

 

ProteusDS Simulation Toolbox and PostPDS simulation of a buoy surface mooring

ProteusDS Simulation Toolbox and PostPDS simulation of a buoy surface mooring

 

DSA has also introduced a unique module available to ProteusDS users called the ProteusDS Queuing Manager. This feature allows users to queue up multiple simulations to run either in sequence or concurrently.

ProteusDS simulation of the ecoSPRAY mooring prior to deployment.

ProteusDS simulation of the ecoSPRAY mooring prior to deployment.

 

 

This is a valuable tool for users looking to evaluate several mooring system designs or determine performance in various sea states.

These features make ProteusDS ideal for performing detailed dynamic design and analysis for many applications, including:

  • Single leg moorings for metocean, oceanography, science and R&D applications
  • Wave energy device moorings
  • Tidal energy device moorings
  • Analysis of fish farm moorings (open net cage aquaculture)
  • Analysis of shellfish farms
  • Multi-leg moorings for oil and gas applications
  • Moorings for navigation aids
  • In-shore barge moorings
  • Vessel moorings
  • Cable ferries
  • Floating breakwater

ProteusDS is currently available for annual lease or through consulting work with DSA. An evaluation version is also available.  If you’d like to learn more about DSA or ProteusDS, please visit our website: www.dsa-ltd.ca/proteusds