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Delegates are invited to meet and discuss with the poster presenters in this topic directly after the session 'On- and off-shore installation technologies' taking place on Wednesday, 12 March 2014 at 11:15-12:45. The meet-the-authors will take place in the poster area.

Ainhoa Pujana TECNALIA, Spain
German Perez (1) F P Goren Aguirre (1) Jonathan Fernandez (2) Manel Guijon (3) Miguel Martin (4) Alberto Laidler (5)
(1) TECNALIA, Derio, Spain (2) Vicinay Marine Innovation, Bilbao, Spain (3) TAMOIN, Erandio, Spain (4) Astilleros de Murueta, Murueta, Spain (5) VELATIA, Zamudio, Spain

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Ainhoa Pujana received the M.Sc. degree in Industrial Engineering from Escuela Técnica Superior
de Ingenieria de Bilbao in 2003. She has been working in the area of electric machines since 2004,
five years in the company ANDIA GROUP ELECTRIC APPLICANCES, SAL, as technical director of small
rotating electric machines projects for special applications. In 2010 she joined to TECNALIA,
where she currently is a researcher in the Marine Energy Area, involved in activities related to
the design of electrical machines for offshore wind turbines and wave generators.
She has contributed to several conference proceedings in this field




Fixed offshore wind has been demonstrated to be a feasible and profitable technology, however floating offshore
wind is still in its development state. Most of the European and United States Energetic requirements will be
covered if this challenge is solved. NAUTILUS FLOATING SOLUTIONS consortium is working in a new floating
structure able to support a 5MW turbine.


In the near future floating offshore wind market will be an attractive investment and many companies will profit
of it. The constitution of Nautilus Floating Solutions SL, an industrial and technological consortium made up of
Astilleros de Murueta, Tamoin, Velatia and Vicinay Marine Innovation, four leading companies in advanced
technology with presence in international markets and the applied Research Centre, Tecnalia Research &
Innovation, has been created with the aim of becoming a key player in the development of floating platforms for
the off-shore wind power market.

A first step was the study of the three types of floating platforms, semisubmersible, spar and Tension Leg
Platform. Attending to different criteria such as economics, wind turbine effectiveness, water depth, type of
seabed and range of deployment, the semisubmersible technology was selected. This technology is more easy
to install and is less location sensitive than the other two, so the potential is also bigger.

The concept has been developed taking into account not only the technical aspects involved in such a design
but also the economic feasibility. In this sense, a set of requirements were defined in order to simplify the
logistics in the whole project development stages: from the manufacturing to the decommissioning including
the assembly, installation and O&M from a wind farm perspective.

This new technological and industrial development will undergo a pilot test in a testing channel in 2014 to
commence production of commercial units as of 2016, whereby it is expected to have a positive impact on
Basque Country industrial activity.

Main body of abstract

The aim of this paper is to describe the NAUTILUS semi-submersible floating platform concept design procedure
and the expected milestones.

Current floating wind turbine prototypes are up to 2,3 MW rated power. NAUTILUS consortium goal is to design a
floating platform for larger power offshore commercial turbine. The first approach is for a 5MW turbine with the
possibility to scale up the design to 10MW wind turbines. Furthermore, this platform must be easy construction
and commissioning. That means the platform should be built in a conventional shipyard and using standard and
minimum logistic means (cranes, AHV and tugboats). With this intention, Bilbao Port and its supply chain
industries are used as a guideline, but it would be same way in other similar European ports.

The first step of the design was assessing the future floating concept. A set of evaluation criteria were defined
together with a protocol to compare different ideas. These evaluation criteria cover all project phases: conceptual
design, construction, installation, operation, maintenance, decommissioning and economics. Both technical and
economical parameters are to be taken into consideration and they are scaled and their weight over the project
is evaluated.

The conceptual design procedure is based in the spiral design used in naval engineering procedures. In the
iterative process different technology areas must be taken into account, like hydrodynamics, aerodynamics and
structural calculations. NAUTILUS solution has just completed the first iteration of the design.

The first step is the functional requirements definition, based on the type of wind turbine selected. In our case,
NREL 5MW was selected in order to make the platform ‘technology agnostic’. Once defined the wind turbine
requirements in terms of size, weight, thrust, a first sizing is carried out. Centre of gravity and weight are the
primary inputs for the design process.

For this first sizing the floating structure must satisfy the functional requirements but they can be reduced to:
buoyancy must be equal to weight plus vertical loads from the mooring; dimensions and compartments must
comply with shipyard features and capabilities; natural periods and stability must meet minimum criteria. In the
case of NAUTLIUS solution, the selected shipyard and the turbine requirements lead to a four column
semisubmersible structure with a maximum breath of 40m and an approximate draft of 20m. A parametric tool
has been developed for the sizing and stability calculation.

The next step has been the structure calculation. Based on DNV rules, another parametric tool helps to the
structural calculation defining thickness, beam dimensions and framing… The tool carries out a weight
optimization in order to adjust the amount of steel needed.

A first hydrodynamic modeling and basic simulation based on 6 defined load cases -3 for operation and 3 for
survival- has been carried out. The results comply with the turbine functional requirements.

Once completed the previous steps, a further detailed hydrodynamic, aerodynamic and mooring design was
defined. Based on the location selected for the design –Basque Coast- a complete set of load cases were
defined. Those load cases will be used to launch dynamic simulations coupling aerolastic and
hydrodynamic codes. The simulation results will be validated with two tank testing campaigns, one at University
College Cork facilities in the framework of MARINET FP7 project –dec2013- and the other one at IHC Cantabria,
expected by mid 2014.


In the initial state of the design is essential to define the requirements and constrains of the project, with the
focus on cost reduction. Stability and sea keeping requirements will determinate whether turbine performance is
correct or not. On the other hand construction and logistics should be economically feasible.

Although commercial software can be used for all the aspects of the design, there’s still some uncertainty with
the codes and the coupling of the aerodynamic and hydrodynamic loads. The design process showed that in
addition to the use of commercial software, there´s a need to develop tools to support some of the calculations,
and to pre and post process the results of the simulations. Only with the basin tests the simulation models can
be validated, but even with a good tests setup it is difficult to simulate the combined effect of the wind and wave
loads on the structure.

The modeling, simulation and validation in the wave tank it is only the first step in the design process. Real
scale tests are mandatory to validate the technology. Thus, the objective of the consortium is to design and
validate a semisubmersible structure with the final aim of building and installing a floating 5MW turbine,
technically and economically feasible.

Cost reduction is one of the main tasks during the whole design process. With the requirements for the
manufacturing and the installation of the structure and the design procedure defined, it is expected to be
more cost competitive than fixed offshore wind in the range of 60 to 100m depths. This is the commitment
of the companies involved in NAUTILUS FLOATING SOLUTIONS.

Learning objectives
Design proccess of a floating structure for a 5MW wind turbine, with the focus on the economic feasibility from
the first stages of the design.

Tools developed for the sizing, sructre calculation and aerodynamic analysis.