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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Krish Thiagarajan University of Maine, United States
Co-authors:
Krish Thiagarajan (1) F P Anthony Viselli (1) Habib Dagher (1) Andrew Goupee (1) Richard Kimball (2)
(1) University of Maine, Orono, United States (2) Maine Maritime Academy, Castine, United States

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Poster
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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

Krish Thiagarajan joined the University of Maine in 2011, as the Correll Presidential Chair in Energy. Concurrently he is a Professor of Mechanical Engineering. His research spans design and analysis of energy generating systems located offshore in the deep oceans. In particular, his area of research is dynamics and global performance of floating offshore systems for oil and gas, as well as renewable energy production.

Abstract

Measurement and modeling of wind directionality for better design and operation of floating offshore wind turbines

Introduction

Environmental directionality is gaining importance in floating offshore wind turbine (FOWT) structure design. Often a non-collinear condition of major forces like waves and wind, can result in a more onerous operational, or fatigue loading condition for an FOWT. Understanding directionality can help in identifying severe load cases that can lead to robust design and reduce long-term costs. Better knowledge of the environment can lead to reduction of risk and needless conservatism. This paper highlights knowledge gained from analysis of field data from a small prototype FOWT and its application to the development of a novel experimental multidirectional wind generation facility.

Approach

Under funding from the US Department of Energy, UMaine completed an 18-month offshore deployment of VolturnUS 1:8, the first grid-connected offshore wind turbine in the country. Field data from the deployment is analyzed and the effects of wind – wave directionality on the platform stability and turbine power performance are quantified. The measured environmental and performance parameters are used to develop the mechanical and aerodynamic design of a unique rotating wind tunnel system for W2: wind wave testing facility. The design is refined to incorporate control of key parameters like directional spreading range, vertical profile, turbulence and flow uniformity.

Main body of abstract

Multi-directional environmental conditions are increasingly considered in floating offshore wind turbine (FOWT) structure design. These considerations can result in better assessment of off-axis loads on the turbine tower, better design of yaw control, and ultimately improving design and performance of an FOWT. In this paper, we provide an overview of the VolturnUS 1:8 semi-submersible, the first grid connected offshore wind turbine in the US. The turbine is a 1:8-geometric scale prototype of a 6 MW wind turbine supported atop a floating concrete semi-submersible. The scaled prototype includes the same geometry, concrete materials, construction techniques, towing operations, and anchoring methods of the full-scale system. The VolturnUS is instrumented with motion, acceleration, and tower and mooring load sensors. The environment is monitored with floating buoys as well as wave gages on the platform. The performance data collected during extreme storm events is used to develop case studies on floating wind turbine behavior in non-collinear wind and waves. Findings from the case studies are incorporated in the overall design of a unique multi-directional wind-wave ocean basin currently under construction at the University of Maine. The design and development of the rotating open-jet wind tunnel system, including its positioning arrangement, aerodynamic nozzle and collector design will be presented. The presentation will conclude with facility specifications, including a forecast of the range of control of key metocean parameters. Utilization of the facility in ongoing and future research will enable better FOWT design and improve the robustness of the emerging renewable energy industry.

Conclusion

Deployment of VolturnUS 1:8 has provided the authors with rich experience in designing and operating a floating offshore wind turbine (FOWT) in US waters. Using field data obtained from testing the first FOWT in the US, University of Maine has developed a multi-directional wind wave basin facility capable of modeling real environmental conditions. This facility will aid in developing and optimizing the next generation of floating wind turbines as their use become more widespread.


Learning objectives
Following this presentation the audience will:
• Understand the types of data received from offshore floating wind turbine testing
• Understand laboratory capabilities and the need to properly model floating offshore wind turbines
• Understand the behavior of floating wind turbines when subjected to directional wind and wave conditions offshore.