Workability Analysis

ORCA Offshore can perform various levels of workability analysis for an offshore operation. A workability assessment combines the offshore environment, the marine spread dynamic behaviour and the operational procedure into one simulation model which will give insight in the environmental risk of the operation.

 

Offshore environment 

To assess the workability of a vessel it is not enough to look at wave heights only. The heading and period of the waves are also important parameters which determine together with the wave height if an operation can be performed. It is therefore important that the seastate wave height and wave periods are included in the environmental data. The following data can be used for this analysis:

  • Long term statistics in the form of monthly Hs-Tp scatter diagrams
  • Historical time traces with short term statistical data of wind, wave and swell based on 3 hour time steps

Vessel dynamic behaviour

The mesh representation of the vessel underwater hull will be generated in MOSES and using 3-D Diffraction a hydrodynamic database will be prepared. If the client provides RAO’s of the vessel they will be used to tune the MOSES model. The tuning will be limited to the fitting of the RAO peaks near or at the relevant wave frequencies. MOSES included non linear viscous damping will be scaled to match the RAO peaks and if required Morrison elements will be added to increase the amount of damping if needed. In case of a multibody analysis the other hulls will be modeled in similar fashion.

Operational Limits

Operational limits in terms of vessel motions, accelerations and velocities can be defined and included in the workability analysis. Also direct environmental limits can be included like wave height and directions and wave period.

Operational Analysis

With the vessel model a frequency domain motion analysis will be performed and limiting seastates will be calculated based on the set operational limits.

 

Workability Analysis

The workability analysis will be performed by combining the vessel operational seastate limits with the provided wave scatter diagrams. This will result in a workability numbers for each provided scatter diagram.

 

Down Time analysis

A down time analysis will use a time sequence tool where the environmental time traces are being used.

The schedule of the operation and the vessel specific operational limits will be run through a time sequence tool which will calculate the historical downtime based on weather time traces.

This procedure will be repeated for several years of data in order to get a statistical prediction of the weather risk of the operation. See for more information Down Time Analysis.

 

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