CENER presented this January at the EERA DeepWind conference its latest solutions specifically designed to remove barriers for industrial floating wind development

The solutions impact the industry at different design stages, from early concept design to mature demonstrative projects. CENER presented results on pressure distribution on the floater in the time domain, control solutions for multi-wind turbine floaters, and the latest update of SiL water tank test for SPM floaters. In addition, spectacular CFD simulation results for X-Rotor were showed and a parametric tool for early design stages of turbine floaters or substations.

The EERA DeepWind, international event that aims to present the best ongoing research and innovation related to deep sea offshore wind farms, was hold in Trondheim Norway from January 17 to 19. CENER showed its commitment with floating wind presenting results of its ongoing projects targeted to easy floating technology optimization. CENER proudly presented these five projects, which were selected by EERA DeepWind’s technical committee, to share our experience.

1. Software in the Loop tank test for Single Point Mooring floaters and long yaw misalignment

Floating wind demonstration projects have an expensive “learning lesson ticket”, above 25M€ for a full scale. Water tank laboratory test has consolidated as an important milestone in the development of wind floaters. These lab tests provide the validation of floater properties, the fully coupled digital models and floater controller, and insights about the actual behaviour of the mooring – floater – turbine solution.

Water tank test laboratories were initially designed for Oil&Gas, naval and other marine infrastructure, where the wind was not so relevant. CENER developed in 2011 a revolutionary method to consider wind thrust during tank testing, known now as Software in the Loop (SiL), that was improved to multi-directional forces in 2016 and has now been improved to consider the misalignments between waves and wind, making possible testing weathervanning cases, especially important for Single Point Mooring floaters.

Oscar Pires, Senior Engineer, in charge of the test, said “The results have been highly satisfactory both, for the single point mooring floater and CENER. The floater has proved its capability to orient itself towards the wind and CENER has validated its SiL methodology to test weathervanning”.

2. Software OF2

Wind industry floater designers are facing another important challenge: structural floater design and its corresponding optimisation. To make this possible, the pressure distribution all around floater surface and internal face are mandatory. CENER has solved this problem obtaining the pressure distribution in time domain for fatigue and extreme load cases creating OF2.

CENER’s OF2 is a software which simulates the behaviour of FOWTs considering  aerodynamics, aeroelasticity and wind turbine controller, with OpenFAST, while the hydrodynamics are computed with OpenFOAM in an time cost efficient approach. Therefore, OF2 is the merge of two well-known tools, OpenFAST – OpenFOAM.

OF2, as aeroelastic tool, is capable to simulate any case from the standards like normal operation, start up, shut down, but also the extreme meteoceanic conditions windstorms, typhoons, killing waves, …, with a detailed simulation of hydrodynamic effects like wave splash, wind-waves-current misalignment, floater motions, green waters, …

Guillen Campaña, Research Engineer, presented the results obtained with OF2 for simulation of a complicated operating condition, making possible to obtain time domain pressure distribution on the DeltaWind floater coupled with a 10MW Innwind wind turbine.

The obtained pressure distribution over time on a column of the floater can be employed as an input for detailed structural analysis and provide valuable insights for its design optimisation and its implications on the lifetime of the asset.

3. SCAPO

As wind floater designers mature their solutions, they must optimize their floater to specific project constrains (budget, local infrastructure, turbine sizes, …). The optimization must be quick and fit in the limited time of bidding processes.

SCAPO is precisely designed to support those early design decisions for wind farm promoters and floater developers. The output of SCAPO is a systematic and comprehensive assessment of the design space, quantifying the required amount of steel, main dimensions, weights, stability, and natural periods as function of the design parameters. The analysis can be completed in just minutes on a standard personal computer.

The tool can assess different floater designs and configurations by parametrizing key geometric aspects. Jesús Artal, Research Engineer, presented an example of application of SCAPO. The tool visualizes the interplay of various design parameters and their influence on critical aspects of conceptual design, stability, hydrostatic stiffness, natural periods, CAPEX, and more.

4. COCO (Coordinator Controller for Multi-Rotor)

Among the most groundbreaking floating systems are Multi-Wind Turbines (FOMWT), where two or more full wind turbines are placed on the same floating platform. This harnesses existing commercial wind turbines at their current rated power to rapidly evolve towards higher power generation assets, thus facilitating economies of scale.

There exist already several industrial designs, at various development stages, consisting of two or more turbines. Commercial FOMWT are also commonly combined with single point mooring lines, which allows the system to weathervane and align the rotors with the wind. This design combination requires the turbines dynamic coordination to ensure safety and to obtain optimal and reliable asset performance, in terms of power production, fatigue and extreme loads.

An uncontrolled differential thrust may provoke a large or stochastic platform rotation in yaw. In addition, wind turbines could be led to operating conditions which they are not designed for, putting the overall system integrity into risk, due to high structural loads or stability issues. A coordinated control, being aware of all subcomponents, is being developed by AAA and Dr. Irene Eguinoa, Head of Control Engineering, presented the first results in DeepWind.

At current stage of development, the COordinated COntroller, COCO, commands the individual wind turbine controllers hierarchically, guaranteeing the dynamic stability and integrity of the asset. It also reduces the platform yaw drift, and the time wind turbines stay in potentially dangerous conditions.

5. X-Rotor concept assesment

In addition to previous works, Dr. Beatriz Mendez, Head of CFD simulations, presented the results of simulations of X-Rotor (European research project, TRL 2). The disruptive XROTOR concept is a hybrid horizontal and vertical axis wind turbine. The horizontal axis wind turbines (secondary rotors, 5 meters diameter) attached at the end of the primary rotor’s lower blades have a high level of energy extraction from the wind, up to 2,7MW each, due to the rotational speed caused by the primary rotor rotation around the vertical axis.

The understanding of the XROTOR aerodynamics was a great challenge. Relative movements between the rotors and interactions between the secondary blades and the primary rotor wake, make the characterization of the unsteady phenomena that appear very complicated. For this case study, CENER simulated the XROTOR concept using Computational Fluid Dynamics (CFD) and sliding meshes technique to communicate the rotating parts to the static parts.

The main output of CENER’s work is the power production, thrust load and aerodynamic forces as well as the flow field study to analyse the complex phenomena that appears. This information is used by project partners to validate and calibrate engineering models more effective for rotor simulation and design purposes.