• Period | 2015 - 2018
  • Country |
  • Market | Offshore energy
  • Project Manager | Amir M Kaynia
  • Client | The Research Council of Norway
R&D program|

REDWIN - reduce wind energy cost

REDucing cost in offshore WINd by integrated structural and geotechnical design is a R&D Project supported by The Norwegian Research Council ENERGIX program.
REDucing cost
in offshore WINd

Generating PDF file

The primary objective of REDWIN is to contribute to reduction of costs in design of offshore wind turbines (OWT) by developing soil-foundation models that will account for key geotechnical issues such as stiffness, damping, drainage, degradation and long term behaviour, and integrate them in the OWT structural model for more optimal analysis and design.

The resulting tool will shorten the design process and will allow the designers to adopt accurate, advanced, and benchmarked foundation design tools already in the preliminary study phase. By using these methods, the uncertainties in the analyses will be significantly reduced, and unreasonably, conservative and expensive OWT design will be avoided. Some elements of this research include:

- Development of models for foundation stiffness and damping calibrated against full-scale prototype data - Library of soil-interaction models, 3DSoil, for shallow (e.g. caisson) Foundations   and deep (monopile) foundations - Implementation of 3DSoil in integrated aero-hydro-elastic analysis tool 3DFloat   (developed by project partner IFE) - Benchmarking and improving existing simplified foundation and   soil-structure-interaction models using results of this research

REDWIN started in 2015 and is scheduled to be completed in 2018.


Offshore wind has grown to be a significant renewable energy source during the last decade. However, there is a general consensus among the operators that for the offshore wind energy to be long-term sustainable, the cost of wind farms has to be reduced. Cost reduction can be achieved in several ways. To this end, optimal foundation solutions and steel tonnage are two aspects with significant potential.

While considerable research and development has been made on structural aspects of Offshore Wind Turbines (OWT) and their integrated analyses with wind and waves, conservative approaches and assumptions are often applied to geotechnical and foundation issues. Moreover, integration of suitable and validated foundation models in operational OWT design are lacking.

The coupling between load, structure, and foundation will influence OWT behaviour. It is therefore believed that considerable savings in OWT construction can be made through integrated analysis of soil-structure interaction (SSI) including a profoundly increased accuracy in modelling of the foundation behaviour. While several attempts have been made in this direction, (e.g. Zaaijer 2006, Damgaard et al. 2014), there is dire need for more research to include key soil response issues including damping, stiffness, drainage, degradation and long term behaviour. These issues not only impact design of the foundation, but they also have important influence on the behaviour of the structure.

The goal of this research project is to develop new engineering tools for accurate treatment of the soil and foundation behaviour and enable direct integrated OWT analyses. Such tools and methods may reduce uncertainty and provide a rational basis for design. This will lay the basis for more optimal design for OWT foundation and thereby reduce the price of renewable energy.

OWTs are designed and constructed in a number of different ways according to wind and wave conditions, sea currents, depths and soil conditions. It is time-consuming to establish a complete, comprehensive wind farm under varying conditions. Advanced computational tools are therefore needed in order to optimize design and engineering.

Today, the geotechnical engineers working on the foundations and the structural engineers working on the construction operate within separate professional fields. There are no comprehensive tools that can combine the two areas, enabling them to jointly arrive at the best solutions.

As a consequence, both expert groups often need to repeat their calculations several times before they can arrive at a solution that satisfies all needs. The engineering phases often take longer than scheduled,necessary, with no guarantees that the resulting solutions are the best possible. Since foundations represent 25- 30 per cent of total construction costs, there is a great potential for savings.  

REDWIN brings together experts from the two engineering fields, in order to jointly develop better methods.  The aim is to design new models describing soils and foundations that will be integrated with the computational tools used by structural engineers today. This will contribute to optimized engineering and design, resulting in less expensive offshore wind energy.

Period |

Project coordination and management

The consortium assembles research organizations (NGI, IFE), university (NTNU), and private organizations (Equinor, Vattenfall, and Dr. Tech. Olav Olsen). Each partner is keenly interested in contributing to the project, and has the competence to contribute to the new developments.

In addition, research collaboration with several external universities, research institutes, and R&D centres (Danish Technical University, University of Western Australia, Perth, University of Ålborg, University College Dublin, Rambøll Denmark and NOWITECH). These wellestablished institutions within OWT research have been targeted and responded positively. The role of the external partners are elaborated below.

The project will be conducted under the leadership of NGI. The project will in addition involve a range of other highly competent key specialists in each of the partner organizations. See organization chart below.

Research partners

NGI (Norwegian Geotechnical Institute) is a national centre for geo-related research, With a long experience in R&D in geotechnics and geosciences. NGI has a wide experience wth WT design, installation and monitoring through numerous projects. NGI will carry out the majority of the R&D work related to OWT soil and foundation modelling, soilstructure-interaction, model validation, signal processing and data analysis.

IFE (Institute for Energy Technology) has driven the development of the integrated model 3DFloat, which is considered to be a state of the art model. IFE is leading the activity on integrated analysis within the FME NOWITECH project. 3DFloat has advanced models for sea environment description, sea loads and structure. In the present project, IFE will be involved in implementation and testing of integrated soil-structure-interaction models. 

NTNU (Norwegian University of Science and Technology): The research group at NTNU on the topic of foundation for offshore wind turbines presently consist of five PhD candidates and one full professor. The research is founded by a joint academia-industrial initiative in the field Renewable Energy at the faculty. NTNU host the PhD student funded by the project, as well as the PhD student (Kristoffer Skau) provided in-kind by NGI. 

OO (Dr. Techn. Olav Olsen) is a structural engineering company that has been involved in numerous R&D projects within OWT through in-house and industry initiatives. OO will be involved in research activities related to OWT redesign and cost analysis using the new foundation models.

Industrial partners

The two industrial partners Equinor and Vattenfall represent significant international industry organizations within the offshore wind energy. Their extensive knowledge and insight will be valuable for project decision-making. The experiences of Equinor and Vattenfall stem from many relevant areas including offshore wind R&D and offshore wind farm ownership.

Equinor and its offshore wind energy R&D team in Bergen have high-level knowledge and will take active part in the project. The offshore wind energy team of Vattenfall has wide knowledge in OWT ownership, management, and research.

The partners were chosen based one the knowledge needs to address an important missing element in OWT design. NGI has a long and broad experience within the field of soil/foundation. IFE has top expertise within wind turbine technology and fluid dynamics. NTNU has focused research on OWT and provides PhD education in the project. Olav Olsen is a structural engineering firm with valuable experience in practical design in offshore wind.

Finally, Equinor and Vattenfall represent a significant international industry organizations within offshore wind. Collaboration with the various international R&D centres (see below) will ensure use of most recent international development in the project.

External partners

The project will collaborate with the following institutions on the following topics stated for each of them:

  1. Danish Technical University, DTU - Centrifuge data on monopiles
  2. University of Western Australia, Perth - Centrifuge data on monopod
  3. University of Ålborg - Full scale OWT data in Fredrikshavn
  4. University College Dublin - member of OWT project PISA - Access to data on pile testing.
  5. Rambøll Denmark - Permanent deformation of OWT Foundations
  6. The project will be carried out in close collaboration with NOWITECH. The project parties IFE, NTNU, Equinor and Vattenfall are all central partners in NOWITECH and will Ensure knowledge exchange between the two projects and that complementary research is performed in them.

It is intended that the Technical Advisory Group (TAG) will include one member from each of these institutions. TAG will meet once a year to review the progress of the project and give advice on the subject.

Main outputs from the REDWIN project

  • REDWIN foundation models
  • Publication list


REDWIN foundation models

One of the main outputs of the REDWIN project is a library of new soil-foundation models for shallow (e.g. bucket foundations) and deep foundations (e.g. monopiles) for time-domain dynamic analysis of offshore wind turbines (OWTs), that can be implemented in integrated analysis tools through standardized interfaces. The input to the foundation models are simple and intuitive nonlinear load-displacement curves that represent the foundation (pile or caisson) and soil response. The new models overcome several of the limitations inherent in existing foundation design tools and allow designers to adopt accurate, advanced, and validated foundation models in all phases of OWT design.

Foundation models 700

The new foundation models are freely available for use in research and engineering projects, and can be obtained by sending an email to: redwinmodels@ngi.no. Please include your name, organization, requested model (model 1, 2 or 3), and intended use of the model(s).

Below you will also find a report that presents an overview of the development and main features of the new soil-foundation models, outlines the required input to the models and how to obtain this input, and describes how the models can be implemented in software for integrated analyses of OWTs. The details regarding the mathematical formulation of the foundation models have been published in a series of journal papers (see list of publications below) and are therefore not included in this report.

Link to the REDWIN foundation models report.




Publication list

Carswell, W., Johansson, J., Løvholt, F., Arwade, S. R., Madshus, C., DeGroot, D. J., & Myers, A. T. (2015). Foundation damping and the dynamics of offshore wind turbine monopiles. Renewable Energy, 80, 724-736. doi:10.1016/j.renene.2015.02.058
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Kaynia, A. M. Seismic considerations in design of offshore wind turbines. Soil Dynamics and Earthquake Engineering. doi:10.1016/j.soildyn.2018.04.038

Krathe, V. L., & Kaynia, A. M. (2017). Implementation of a non‐linear foundation model for soil‐structure interaction analysis of offshore wind turbines in FAST. Wind Energy, 20(4), 695-712. doi:10.1002/we.2031

Markou, A.A., & Kaynia, A.M. (2018). Nonlinear soil‐pile interaction for offshore wind turbines. Wind Energy, 21(7), 558-574. doi:10.1002/we.2178 
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Nygaard, T. A., De Vaal, J., Pierella, F., Oggiano, L., & Stenbro, R. (2016). Development, Verification and Validation of 3DFloat; Aero-servo-hydro-elastic Computations of Offshore Structures. Energy Procedia, 94, 425-433. doi:https://doi.org/10.1016/j.egypro.2016.09.210

Page, A. M. Schafhirt, S., Eiksund, G.R., Skau, K.S., Jostad, H.P. & Sturm, H. (2016). Alternative Numerical Pile Foundation Models for Integrated Analyses of Monopile-based Offshore Wind Turbines. In Proceedings of the Twenty-sixth International Offshore and Polar Engineering Conference - ISOPE 2016 (pp 11-119). International Society of Offshore & Polar Engineers.
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Page, A. M., Grimstad, G., Eiksund, G. R., & Jostad, H. P. (2018). A macro-element pile foundation model for integrated analyses of monopile-based offshore wind turbines. Ocean Engineering, 167, 23-35. doi:10.1016/j.oceaneng.2018.08.019
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Page, Ana M., Skau, K.S., Jostad, H.P. & Eiksund, G.R. (2017). A New Foundation Model for Integrated Analyses of Monopile-based Offshore Wind Turbines. Energy Procedia, 137, 100-107. doi:10.1016/j.egypro.2017.10.337.

Schafhirt, S., Page, A., Eiksund, G. R., & Muskulus, M. (2016). Influence of Soil Parameters on the Fatigue Lifetime of Offshore Wind Turbines with Monopile Support Structure. Energy Procedia, 94, 347-356. doi:10.1016/j.egypro.2016.09.194

Skau, K. S., Chen, Y. & Jostad, H.P. (2017). A numerical study of capacity and stiffness of circular skirted foundations in clay subjected to combined static and cyclic general loading. Geotechnique, 68(3): 205-220. doi:10.1680/jgeot.16.P.092.

Skau, K. S., Grimstad, G., Page, A. M., Eiksund, G. R., & Jostad, H. P. (2018). A macro-element for integrated time domain analyses representing bucket foundations for offshore wind turbines. Marine Structures, 59, 158-178. doi:10.1016/j.marstruc.2018.01.011.

Skau, K.S., Kaynia, A. M., Page, A. M., Løvholt, F., Norén-Cosgriff, K., Sturm, H., Jostad, H.P., Nygard, T.A. et al. (2017). REDWIN – Reducing cost in offshore wind by integrated structural and geotechnical design : REDWIN – Kostnadsreduksjon i havvind gjennom integrert struktur- og geotekniskdesign. I Fjellsprengningsteknikk - bergmekanikk - geoteknikk. Oslo 2017. Foredrag 38. 17s.

Aasen, S., Page, A.M., Skau, K.S. & Nygaard, T.A. (2017). Effect of foundation modelling on the fatigue lifetime of a monopile-based offshore wind turbine. Wind Energy Science, 2(2): 361-376. doi:10.5194/wes-2-361-2017.

Skau, K.S. et al. (2018) REDWIN – REDucing cost in offshore WINd by integrated structural and geotechnical design. Journal of Physics: Conference Series 1104 012029


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