Cathelco Ltd Dynamic Lift Analysis

Company Profile

Cathelco is the world leader in Seawater Pipework Anti Fouling (AF) and Impressed Current Cathodic Protection Systems (ICCP). Cathelco have installations of Anti Fouling and Cathodic Protection systems on all types of vessels including container carriers, ferries, cruise ships, tankers, FPSOs (Floating Production Storage and Offloading vessels), tugs, frigates, destroyers, fast patrol craft, luxury yachts and offshore structures.

Cathelco AF and ICCP brand names are market leaders and are recommended by ship yards, naval architects and procurement departments across the world. The Cathelco portfolio includes C Shield, Minitek, Alutek, Jotun ICCP, Wilson Taylor, FA Hughes, MPSL and Morgan Berkeley.


Background

Cathelco required IDAC to carry out a dynamic analysis of an enclosure containing a Transformer Rectifier (TR) Unit. The enclosures are heated environmental shelters to protect the TR units that control the ICCP system on each of the platforms legs and super structure. The enclosures are to be installed on a platform off the coast of Scotland; they are part of the overhaul of the ICCP system that is also supplied by Cathelco.

The enclosures also act as the means to successfully transport the TR units around the platform during the installation phase of the project, hence the need for a complete dynamic FEA study.

All equipment being lifted must have design calculations carried out which take into account a Dynamic Amplification Factor (DAF) to cover all global dynamic load effects. Cathelco were required by their clients to validate the design of the enclosure before they were able to supply it.

Analysis

The SolidWorks geometry, as provided by Cathelco, was imported into ANSYS Workbench DesignModeler. The assembly, shown in the graphics to the right, consisted of 176 parts including various fasteners.

The geometry was modified in the following ways:

The TR Unit assembly was converted to a single part within the enclosure, which was subsequently treated as a rigid body, with mass and inertia properties only. The stresses within the TR Unit were not required for this project.

Fasteners such as bolts, nuts and washers were suppressed, as was the lifting eye geometry.

Other geometric details such as holes, which were not pertinent to the stress analysis, were removed in order to simplify the meshing procedure.

Geometry

FE Mesh

A finite element model was generated using 3D thick-shell and higher-order solid element types throughout the solid model. The bolted and welded connections were modelled as bonded contact between the mating surfaces.

A linear, three-dimensional structural analysis was carried out on the enclosure. Zero displacements were applied at each of the lifting eye locations using remote points with the reference directions for these displacements being inclined at 45 degrees to correspond with the geometry of the lifting sling.

From carrying out the Finite Element Analysis it was established that there were no significant areas beyond the yield stress and Ultimate Tensile Strength (UTS) of the material, in the model.

The graphics to the left show some of the results as contour plots (Yield Safety Factor & Displacement) obtained from the analysis. The plots show the exaggerated deformed shapes and the TR Unit has been removed to show only the enclosure.


Design Benefit

The FE Analysis has validated the enclosure design and therefore allowed IDAC’s customer to supply the enclosure to its clients. The main benefits that accrue to Cathelco from this analysis are the abilities to evaluate the design in accordance with the required design standard through computer simulation rather than by physical testing, which is time consuming and expensive in comparison to numerical modelling.