We are often asked to install our A-Frames / hyperbaric recovery systems onto vessels with very short lead times. Generally, the practical aspects of installation are fairly simple only taking a day or two and not surprisingly our clients are therefore surprised when we ask for a number of weeks to complete preparatory integration engineering design.
The key integration engineering aspects are as follows:
Feasibility assessment;
Structural analysis (which entails Finite Element Analysis (FEA));
Motions analysis;
Stability analysis;
Development of detailed installation drawings; and
Development of an interface design report.
The most time consuming aspect is the conduct of the structural analysis. A 3-dimensional model of the vessels hull structure, including frames, transverse and longitudinal stiffeners and any small brackets is generated. The bases of the A-Frame/winch are then placed into the model with bolting connections as appropriate.
The complete model is then meshed using a fine mesh to ensure suitable accuracy and once the meshing is completed, the analysis is solved. Until recently, the solving of these calculations typically took 48 hours to solve per load case. Recently however we commenced using a Microsoft cloud based service called Azure for the conduct of the numerical analysis. Excitingly this now allows calculations to be solved in under 12 hours – essentially a fourfold increase in speed!
Generally there are at least 6 load cases which are required to be solved, which therefore results in a dramatic improvement in our ability to quickly conduct integration engineering.
Typically we conduct analysis at the highest design load in various weather, operational, roll and pitch combinations; we also conduct analysis at the load testing weight as generally the highest practical loads are experienced during the load testing when the water weights / water bags are used in conjunction with a load cell shackle to verify the overall system. As this is the key verification step, it is important to progressively ensure that the expected deflections are experienced and hence the overall system is as per expectation.