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Reducing the operation and maintenance (O&M) cost is a necessity in current offshore wind farms so that the produced power can achieve a competitive price in the market. An offshore wind farm normally comprises a large number of turbines which demand frequent maintenance visits. In addition to making maintenance plans that avoid downtime and production losses, it is important to utilize the expensive resources, such as service vessels, in an efficient way. This article introduces the routing and scheduling problem of a maintenance fleet for offshore wind farms (RSPMFOWF), which is to determine the optimal assignments of turbines and routes to the vessels in terms of cost. Simultaneously considering the characteristics and limitations in this problem, we present the mathematical formulations for the RSPMFOWF. A computational case study is also carried out. The results provide both the optimized cost and detailed arrangements, which can be directly used in maintenance planning.

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Technological innovations and new areas of application introduce new challenges related to safety and control of risk in the maritime industry. Dynamic-positioning systems (DP systems) are increasingly used, contributing to a higher level of autonomy and complexity aboard maritime vessels. Currently, risk assessment and verification of DP systems are focused on technical reliability, and the main effort is centered on design and demonstration of redundancy in order to protect against component failures. In this article, we argue that factors, such as software requirement errors, human errors, including unsafe or too late decision-making, and inadequate coordination between decision makers, also should be considered in the risk assessments. Hence, we investigate the feasibility of using a systems approach to analyzing risk in DP-systems and present an adapted version of the system-theoretic process analysis (STPA). A case study where the STPA is applied to a DP system is conducted to assess whether this method significantly expands the current view on safety of DP systems. The results indicate that the reliability-centered approaches, such as the failure mode and effect analysis (FMEA), sea-trials and hardware-in-theloop (HIL) testing, are insufficient and that their view on safety is too narrow. The article shows that safety constraints can be violated in a number of manners other than component failures for DP systems, and hence, STPA complements the currently applied methods.

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