Moorings & Foundations Richard Yemm

Transcription

1 Moorings & Foundations Richard Yemm 1

2 Relevant experience Pelamis 17 Pelamis, 6 machines, 5 different mooring designs, 4 different connection methods, catenary, synthetic line, dynamic cables, wet-mates, diverse range of vessels & equipment used etc Station-keeping mooring though dynamic influence significant of course In house analysis using Orcaflex & proprietary simulations, FEA etc In house design, procurement, offshore operations planning, risk assessment & execution Several team members experienced from Oil & Gas, worked very closely with Atkins both invaluable Quoceant Wave Energy Scotland Knowledge Capture projects good body of experience/information see Involved in a range of fixed and floating tidal projects Working with several wave technologies where mooring is reaction frame for PTO, as well as others more similar to Pelamis Case studies on our website 2

3 Characteristics & design drivers COST! Much more Capex & Opex sensitive than Oil & Gas Challenging locations rough, intermediate depth, tidal streams etc Short weather and/or tidal windows rapid, weather tolerant, abandonable work-scopes Variable seabed types with no, or thin and mobile, sediment layer Small footprint limits effectiveness of some conventional approaches Repetitive/modular like offshore wind foundations, opportunities for cost saving Unmanned installations need for recovery & redeployment through life for maintenance & repair Integration with electrical need to avoid complex multi-stage operations Consequence of failure (generally) lower than oil & gas installations, reduced FoS & redundancy possible? 3

4 Sector / development issues Most developers are small SMEs with limited access to expertise & capital Moorings & foundations often an afterthought rather than core to concept Many established practices and vessels etc are very expensive These can lead to siloed development and re-inventing the wheel etc Deployment sites often dictated or chosen based on existing or politically motivated choices rather than seabed type etc Pressure to reduce cost in development can lead to solutions suited to one-offs, but unsuitable for or expensive in volume Inexperience can lead to inappropriate and dangerous approaches & solutions codes and building experience base helping reduce this now Definitely strong benefits possible from working more closely with O&G supplychain, but some now thinking and approaches required 4

5 Sector SOTA Tidal Two main classes of machine fixed & floating with different mooring/foundation needs Main issues include high thrust loads and reaction torques, lack of sediment, turbulence, vibration, flotsam, fouling etc Additional issues with vortex induced vibration of lines and cables for floating Predominantly gravity based anchors used to date Drilled/grouted pile solution demonstrated Rock-anchor type solution in development Wave Again two main classes of machine fixed & floating with different mooring/foundation needs Subclasses in floating where the machine reacts against the mooring for PTO or relies on it only for station-keeping Main issues include highly dynamic loading and high extreme loads due to shallow-moderate depths, small footprint for array spacing Predominantly drag-embedment or gravity based anchors used to date, though some systems have been drilled/piled Various anchor types possible, strong benefits from sharing anchor points 5

6 Some existing anchor/foundation types Drag embedment Driven, suction or drilled/screwed piles Active embedment Gravity 6

7 Mooring line & connection options For floating systems a range of existing mooring line options are available: Chain catenary Wire rope Conventional synthetic lines High stretch (nylon) lines Experience so far is that footprint can be an issue for lighter/synthetic lines Connections are key to allow small vessels to be used and to enable offsite maintenance: MCT machine used surface piercing tower Fixed tidal turbines have generally used cup-cone systems Pelamis developed a bespoke mechanical/electrical connection Ball-grab (!), Rocksteady connectors etc Various wet-mate and deck-mate connector options All of these are key enabling technologies but need to be married and adapted to suit MRE applications. 7

8 Conclusions & opportunities Sector now has a sound experience base to understand what it needs Sector has a good understanding of applicability and limitations of many existing technologies However, it is likely that considerable un-tapped opportunities remain Perhaps more or most valuable is the proven fearless creativity and problem solving ability However, will need to realign requirements, drivers and metrics etc Biggest opportunities? More integrated approach to problem solving & knowledge sharing! Innovative multi-point hybrid foundations/anchors for floating systems Bespoke deployment vessels, techniques & equipment Optimising detection of, consequences of and response to partial failures THANK YOU! 8