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NorMoor JIP – on safe mooring-line design

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Siril Okkenhaug Siril Okkenhaug
Principal Engineer

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Challenge

There is a need to establish a consistent design analysis procedure for time-domain mooring calculations. Why?

  • Mooring standards are interpreted and applied in different ways.
  • The inherent reliability implied by the safety format is not known.

Solution

Analysis methodology and calibrated safety factors for mooring lines in ULS (intact), ALS (damaged) and FLS (fatigue) as a function of the target probability of failure. Calibration based on time-domain analyses for a range of environments and mooring systems: Haltenbanken, GOM and Brazilian environments

  • Small and large MODUs, turret and spread moored FPSOs and large production semis
  • Chain and wire systems and polyester systems
  • Water depths: 150, 350 and 1,500 m

Benefits

We have shown that the results and deliveries from Phases 1 and 2 (ULS and ALS) can give the industry more cost-effective mooring systems without jeopardizing the safety level:

  • The reliability levels implicit in existing standards are documented
  • Today’s safety factors can be reduced for time-domain analyses
  • Safety factors and analysis methodology are interlinked - detailed guidance will be given for both the time domain and frequency domain

For FLS: We believe there is a further potential for cost optimization by improving the FLS code check through Phase 3.