JACKET SUB-STRUCTURES FOROFFSHORE WINDFARMS

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JACKET SUBSTRUCTURES FOROFFSHORE WIND FARMSDESIGNED FOR YOUR SITE AND YOUR TURBINE

As offshore wind projects move intodeeper waters and the turbinesincrease in size and weight, thejacket structure will be increasinglycompetitive as compared withtoday's favoured monopile andgravity base foundations.

Jacket design experience

Our expertise in jacket design isbased on 30 years of Oil & Gasexperience from the hostile NorthSea. During the past 15 years we havealso been involved in more than 35detailed design projects ofsubstructures for offshore windfarms, which have already beenbuilt or will be built over the nextfew years. The total number ofsubstructures is more than 2,500 –mostly monopile foundations.Within this design portfolio we haveexperience in offshore wind jacketdesigns from three completeddetailed designs, one currentlyongoing detailed design and twoongoing FEED designs and differentconcept and FEED studies for mostof the 5-8 MW turbines available onthe market. By combining our jacket designexperience from Oil & Gas with ourmarket leading experience in designof substructures for the offshorewind market, we are able to supportthe offshore wind business tosuccessfully develop in the future.

Load exchange with wind turbinemanufacturers

In Ramboll we are experienced inworking together with all the keywind turbine manufacturers. In adetailed design we perform loadexchange with the wind turbine

manufacturer in order to optimisethe structural design of both thesubstructure and the wind turbinetower.

Design expertise

Our offshore design experienceenables us to offer all servicesnecessary to capture all relevantdesign effects, includinginstallation/handling analyses andsea transportation analyses.Our in-house expertise in jacketdesign comprises primary andsecondary structures as well asgeotechnical and electricalengineering. This means that weapply all design works in-house withour own staff, which eliminatestime, cost and interfaces betweenthe individual disciplines. WithinRamboll the offshore wind businessemploys close to 100 people in ourfour offices in Copenhagen, Esbjerg,London and Hamburg.

Project-specific design

Ramboll is an independentconsultant and we are therefore notconnected with any design solution.This means that we have fullflexibility to design the best suitedsubstructure for the client and theproject.

Transition piece design

The transition piece is a highlycomplex and important part of thesubstructure design connecting thewind turbine tower to the jacketand is therefore designed usingadvanced FE software.The layout of the transition piece isdesigned to best fit the givenproject. Possible project specificspecifications may include a door inthe transition piece wall or theaddition of hatches to give access

to otherwise inaccessible locationsin order to ease inspection of thetransition piece. Several optimisation rounds areperformed to ensure that the bestcompromise between weight andmanufacturing cost for thetransition piece is reached.

Pile-jacket connection design

For piled jacket designs, the setupconsists either of pre-piled or post-piled solutions based on the bestsuited concept for the givenproject. In both cases the pile-jacketconnection will include a groutedconnection with shear keys. Thedesign of the grouted connectionmay utilize detailed FE analyses. Pile swaging, which is a conceptwithout grouting for the pile-jacketconnection, may alternatively beadopted for a post-piled jacket.An alternative to foundation piles isthe suction bucket foundations,which can be welded to the bottomof the jacket avoiding a grouted orswaged connection.

Suction buckets

We are experienced in designingjackets supported by suctionbuckets and have designed the firststructure of this type installed in theworld.

Contact

Klaus Jacob JensenDirectorRamboll Energy - Wind & TowersD/M: +45 5161 8617kjj@ramboll.com

DESIGN

Primary structures

Some of the design options that canbe investigated are:• 3-legged vs. 4-legged jackets• Pre-piled vs. post-piled vs. suction

bucket foundations• Welded joints vs. cast joints• Transition Piece layout

Secondary structures

Detailed design of secondarystructures on a jacket substructurecomprises the following items:• J-tubes and J-tube supports• External and internal platforms• Boat landing• Ladders and resting platforms• Cathodic protection system

HSEQ - Health & Safety, Environmentand Quality

The primary and secondary structuresare modelled using 3D softwareproviding the required overview ofthe entire substructure layout thusminimising the risk of clashes in themanufacturing phase. Furthermore,the 3D model is the basis for designrisk assessment workshops, includingall parties in the project.

Design software

When designing offshoresubstructures we apply a combinationof our own developed ROSAPprogram package and commercialdesign tools, such as FE and CADtools. In ROSAP we have the option ofdesigning the substructure accordingto selected design standards, such asDNV, Eurocodes and DIN.