Marine current energy is an abundant renewable energy resource. Marine current turbines (MCTs) can convert the kinetic energy of marine currents into electrical energy. However, the variations in the marine currents are violent and complex. These characteristics will be reflected in the variation in the operating condition of MCTs, thus interfering with normal diagnosis for the high-resistance connection (HRC). The HRC can be caused by damaged connections between device components that are easily made due to the harsh marine environment. To diagnose HRC in MCT, an inequality indicator is proposed to quantify the current imbalance caused by HRC. The inequality indicator is defined based on the arithmetic–geometric mean inequality and can identify slight current imbalances in the early stages of HRC. The inequality indicator is robust to the variable operating conditions of the permanent magnet synchronous machine (PMSM) in the MCT. Experimental results show that the inequality indicator can be used to effectively diagnose HRC in the MCT with 100% accuracy. This research will help maintain the health condition of the MCTs and provide some ideas for diagnosis in MCTs. Moreover, the inequality indicator may provide a different approach to the analysis for other faults that can lead to a current imbalance.

The risk level of the Aids to Navigation (AtoNs) can reflect the ship navigation safety level in the channel to some extent. In order to appreciate the risk level of the aids to navigation (AtoNs) in a navigation channel and to provide some decision-making suggestions for the AtoNs Maintenance and Management Department, the risk assessment index system of the AtoNs was built considering the advanced experience of IALA. Under the Formal Safety Assessment frame, taking the advantages of the fuzzy comprehensive evaluation method, the fuzzy-FSA model of risk assessment for aids to navigation was established. The model was implemented for the assessment of aids to navigation in Shanghai area based on the aids to navigation three-dimensional simulation system. The real-time data were extracted from the existing information system of aids to navigation, and the real-time risk assessment for aids to navigation of the chosen channel was performed on platform of the three-dimensional simulation system, with the risk assessment software. Specifically, the deep-water channel of the Yangtze River estuary was taken as an example to illustrate the general assessment procedure. The method proposed presents practical significance and application prospect on the maintenance and management of the aids to navigation. http://www.transnav.eu the International Journal on Marine Navigation and Safety of Sea Transportation Volume 8 Number 2

Marine current turbine (MCT) blades are continuously exposed to seawater, making them extremely susceptible to marine biological attachment and causing MCT blade imbalance fault. It is challenging to extract attachment features with the instantaneous variable current speed. In fact, the collected signal is highly nonlinear and nonstationary, which involves different scales and dimensions affected by the instantaneous current speed. In this paper, improved multifractal detrended fluctuation analysis (MF-DFA) is adopted to analyze such signals. The original MF-DFA is easily affected by the order of the fitting polynomial and cannot achieve the desired adaptive effect. The paper combines grey relation analysis and ensemble empirical mode decomposition (EEMD) to adaptively select the detrended function. The proposed adaptive grey MF-DFA (AGMF-DFA) method is validated with data collected from a testbed composed of an MCT coupled to a 230W permanent magnet synchronous generator. The result shows that the proposed method is effective for the attachment degree classification under the instantaneous variable current speed.