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North American Shipbuilding (NAS) designs and builds offshore vessels for its parent company, Edison Chouest Offshore, (ECO) and affiliated companies.

NAS uses finite element analysis (FEA) software from Algor for building and repairing ships.

Jacob Cheramie, naval architect at NAS, said: ‘Algor FEA allows us to check our first principal calculations as well as investigate more detailed problems.’ For example, when a new anchor-handling tug supply vessel was built, a 1,000-tonne superstructure needed to be lifted by cranes for installation on the hull.

Engineers at NAS performed Algor linear static stress analyses of key components to ensure that the ship could withstand the forces generated during the lifting operation.

The FEA stress and displacement results verified NAS’s calculations, which allowed NAS to execute the crane-lift successfully.

NAS crane-lifted the 1,000-tonne superstructure for an anchor-handling tug supply ship.

Engineers at NAS used Algor FEA software to analyse key components to verify that the ship could withstand the lifting operation.

The Algor analyses were performed early on during the design of the ship.

The port side frame and a section of the hull were analysed because they contained the pad eyes and saddles where the cranes would pull upward on the superstructure.

This meant they would experience the greatest stresses.

A section of the port-side frame was modelled with a pad eye and saddle that bore a lifting force of 350,000 lbs (or 175 tons), representing 17.5 per cent of the total 1,000-tonne lift load.

The model geometry was created using Algor’s built-in modelling tools.

Plate elements were used to simulate the steel walls of the superstructure.

The Algor analysis results verified that the maximum stress in the model was below the stress limits allowed by the American Bureau of Shipping.

A section of the hull was modelled with two lifting forces of 350,000lbs applied at each of two pad eyes for a total lifting load of 700,000lbs (or 350 tons), representing 35 per cent of the total lift load.

FEA allowed the results to be studied in more detail; for example, Algor’s results evaluation capabilities allowed NAS engineers to examine colour-coded contour displays of displacement magnitude and von Mises stresses.

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