Installation engineering for inter-array cables of a Baltic Sea offshore wind farm

  • Client Confidential
  • Year 2021
  • Business unit Renewables

The handling and deployment of the numerous inter-array and export cables in an offshore wind farm are critical operations. Specific and detailed planning is required to ensure that the risk of cable damage is minimised.

With extended marine operations and boats on hire, it is also essential that the approach avoids undue conservatism.

Our client awarded a contract to Apollo in 2020 to perform the inter-array cable analyses for a Baltic Sea wind farm, located 15 to 40 kilometres east of the Danish coast. Support was provided into the operations phase to help resolve operational issues as they emerged.

The background

Our client approached us looking for an analysis of water depth and operational situation cable installation for cable installation.

The process

  • Apollo’s engineers applied their extensive experience of cable analyses in OrcaFlex software to perform the analysis.

What did the client think?

The support service did not stop with the analysis, and Apollo were instructed to perform a range of follow-up engineering studies, to help resolve emergent issues into the operational phase.

And for all you engineers who want more details:

The Problem

  • Cable installation operations are performed from specialist vessels working within defined operating envelopes for each water depth and operational situation.  The client required specialist hydrodynamic analysis of the numerous permutations of these variables, pulled together to practical summary envelopes that can be applied by the offshore crew.

The Solution

Apollo’s engineers applied their extensive experience of cable analyses in OrcaFlex software to cover the following:

  • Software model construction for 1st end pull-in, progressive lay, 2nd end pull in, abandonment and recovery cases, for all relevant water depths
  • Sensitivity analysis to establish the criticality of parameters such as current and J-tube arrangements, so focusing the programme onto key variables
  • Analyses of system response to wave loading and heading ranges, establishing limiting combinations in terms of cable properties (MBR, cable tension, compression, touchdown, quadrant crane wire, etc.)
  • Generation of operating envelopes and pull in tensions
  • Report

Also, diffraction analysis was performed for the deployment vessels, using the Aqwa software to generate their dynamic response properties. These are key OrcaFlex inputs.

During the operations phase, support was provided to resolve emergent technical challenges.

The Outcome

  • Offshore cables are sensitive, business-critical items that need careful, well-thought-out installation processes. Apollo brought their specialist expertise in OWF cables to develop efficient and practical operating envelopes. Having supported more than a dozen North Sea and Baltic Sea wind farms with similar services, the Apollo team was primed and ready to deliver an effective, efficient service.
  • A significant challenge was the trade-off between the vast numbers of simulations that can be performed, computation power and the project schedule. Apollo used techniques that had been proven from other OWF projects to reduce the simulation time to manageable levels, working with multi-core processors to run the tens of thousands of cases.
  • The Apollo team are experienced in offshore operations and understand what a workable set of operating guidance should look like.  Our approach is to convert the technical insight into practical control measures.  Significantly, the deliverables were accepted by third parties with minimal review cycles.

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