Engineering Design Consultants

Rov Garage

 

Eadon Consulting were invited to provide a redesign of an existing garage for remote operated vehicles (ROVs).  The ROV garage acts as a lifting frame for transfer of the ROV from on board a ship into the water, as well as providing a mounting frame for all required ancillary equipment.  For further information about the technical aspects of the project click here.

Eadon Consulting had worked with this client to design the previous version of the ROV Garage and it was good to hear that they were keen for us to upgrade the design in line with new requirements.  The redesign was required to enable the Garage to be used with a heavier ROV (40% increase); limitations on design changes were that the client wished the geometry of the equipment mounting frame to be maintained, to reduce rework required for weight balancing of ancillary equipment, whilst also minimising weight of the garage.  In addition, they requested design changes to include integral forklift pockets and a fixed access ladder.  As the garage was for subsea application, all structural members were rolled channels of duplex steel and face to face contact between members was not accepted; this added an additional limitation to design options. 

Once I had a clear understanding of the client’s requirements, the next step was to create a finite element (FE) model of the existing garage frame, along with scoping level hand calculations, to be used to assess the suitability of various design options.  It was really interesting to use FE as design development tool rather than pure analysis, implementing approximate geometry changes quickly to enable fast-paced design optimisation.  As a first pass, I tried only applying minor structural adjustments to the geometry of the baseframe, to minimise redesign; however, the large increase in live load coupled with the requirements for forklift pockets resulted in large bending moments on the frame legs.  Since the geometrical spacing of these legs had to be maintained, a complete redesign of the garage baseframe was necessary and the mass of the baseframe increased.  To minimise overall mass of the garage frame, the FE model was used to optimise the rest of the garage and remove mass in areas of low stress.  The whole process of design development was quite difficult due to the very tight timescales limited by the client’s manufacturing end dates; however, it was also incredibly interesting and provided numerous engineering development opportunities.

An additional design challenge was the implementation of a fixed ladder, which had a knock-on effect of requiring additional harness points; these had to be attached into the garage bumper frame, which was of aluminium.  This provided an unexpected design challenge; due to the reduction in strength of aluminium once welded, the design of the harness points required some additional FE and thinking outside the box to achieve an optimal solution.

Once I was happy that the garage design met the client’s requirements and also complied with the code requirements, we moved into the detailed design phase.  I was assisted by my colleagues to finalise the 3D model in Solidworks and then create a full set of detailed 2D fabrication drawings to the client’s in-house drawing standards.  These were provided to the client, along with final calculations, FE model and a proof load test procedure.

The garage frame has since been fabricated; we have had very positive feedback in terms of ease of assembly of the frame.  We attended the client’s premises to observe the proof load test.  It was incredibly satisfying to see the fabricated garage and know that I had designed the structure.

Sarah Lee

 

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