Abstract
This article proposes a framework for the integration of tactical and operational optimisation models for maintenance scheduling and routing at offshore windfarms. A tactical model is formulated to find the optimal schedule for preventive maintenance over a medium-term planning horizon (one month). The schedule is produced assuming a weather forecast for the entire planning horizon, which in practice will be uncertain. However, for each day, an operational maintenance routing model is solved to obtain optimal vessel routes with a one-day planning horizon, assuming an updated weather forecast for that day. In the operational routing model, the turbines scheduled for preventive maintenance are provided by the tactical scheduling model, whereas the turbines requiring corrective maintenance are provided by information about failures and alarms updated on a daily basis. In the case that the solution generated by the routing model contains turbines that cannot be maintained, the monthly maintenance activities are rescheduled by solving the tactical scheduling model considering the delayed activities. As the routing problem is too time consuming to solve exactly, we propose efficient matheuristic solution methods incorporating Variable Neighbourhood Search and an exact method. Computational experiments have been carried out to assess the performance of the tactical-operational framework.