1. Research concept on self- maintenance offshore wind turbines © Elsam A/S References 1. G.J.W. van Bussel, Chr. Schöntag, Operation and Maintenance Aspects of Large Offshore Wind farms, Proceedings of the 1997 European Wind Energy Conference, Dublin, Ireland, October 1997. 2. Y. Umeda, T. Tomiyama, H. Yoshikawa, and Y. Shimomura: “Using Functional Maintenance to Improve Fault Tolerance,” IEEE Expert, Intelligent Systems & Their Applications, Vol. 9, No. 3, (June 1994), pp. 25-31. The reconfiguration approach is based on the Self Maintenance Machine (SMM) [2] concept applied already to other fields such as the photocopy industry. The aim is to make use of the existing functional redundancies to keep the wind turbine operational, even at a reduced capacity if necessary. HornsRev-Denmark SUMMARY The objective of on-going research at TU Delft is to develop a design methodology to increase the availability for offshore wind farms, by means of an intelligent maintenance system capable of responding to faults by reconfiguring the system or subsystems, without increasing service visits. Within the wind farm, there are different levels at which this reconfiguration concept can be applied. The possible solutions can range from using information from adjacent wind turbines to setting up different operational modes. OFFSHORE sites differ from onshore sites especially because of their exposure to extreme weather conditions, remote location, and of their difficult to impossible accessibility in certain periods of the year. These differences give rise to a significantly lower availability and hence lower energy production. This creates the need of a new approach to handle shutdowns due to faults. Acknowledgements This work is part of the project PhD@Sea, which is substantially funded under the BSIK programme of the Dutch Government and supported by the consortium We@Sea, http://www.we-at-sea.org.http://www.we-at-sea.org EXPECTED RESULT OF ONGOING RESEARCH A design methodology based on the re-configuration concept to achieve self-maintained wind turbines is a very interesting and promising approach to reduce stoppage rate, failure events, maintenance visits, and to maintain energy output possibly at reduced rate until the next scheduled maintenance. INTELLIGENT MAINTENANCE Repair Execution Operation Under Extreme Conditions Functional Redundancy Control Type Repair Methods Sensors + Actuators Intelligent monitoring FBS Function- Behavior- State Model Knowledge Base Functional Redundancy Designer Object Model Knowledge About Physical Laws Model Based Reasoner  Functional Model  Entity Model  Parameter Model  Repair Model FAULT DIAGNOSIS E. Echavarria, T. Tomiyama, G.J.W. van Bussel. Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. Faculty of Aerospace Engineering, Kluijverweg 1 2629 HS Delft, The Netherlands.  Non-stop operation.  Reduced number of failure events.  Maintained energy output.  Reduced maintenance visits. Design for Re-Configuration Intelligent Maintenance and Operation Support Offshore Maintenance Problems Failure Modes RECONFIGURATION The re-configuration concept intends to deal mainly with these offshore challenges, aiming to increase wind farms availability by using a design for re-configuration and intelligent maintenance: AVAILABILITY ANALYSIS – MONTE CARLO SIMULATION Availability highly depends on maintenance strategies. Increasing availability of offshore wind farms is about balancing and optimizing parameters such as: For instance, the crew has a time window at the site to perform a maintenance procedure, which is defined by the parameters mentioned above. If this procedure takes longer than the time window, fixed times such as traveling and setting up times will be again required. Even in some cases, the wind turbine will not be available until next maintenance visit is possible. Equally important are the vessel speed and vessel capability of traveling with high waves in order to increase this time window. Monte-Carlo simulations ran at TU Delft with the CONTOFAX [1] code show that the combination of these parameters can make a difference in availability levels for offshore wind farms of about 10%.  Site accessibility  Duration of crew shifts and number of crewmembers per shift  Duration of the maintenance procedures, in hours  Traveling time for the crew to reach the site from the base- station. Wind turbine topology Functional Redundancy Designer Proven technology Failure of components Mean Time between Failure Down time due to failures Failure modes Using the Functional Redundancy Designer, which contains all the knowledge of the system, a fault diagnosis is performed and a repair method is selected.