Forecasting for day-ahead offshore maintenance scheduling under uncertainty

Offshore wind farm maintenance operations are complex and dangerous, and as such are subject to strict safety constraints. In addition, crew and vessels must be scheduled in advance for both planned and reactive maintenance operations. Meteorological forecasts on many time-scales are used to inform scheduling decisions, but are imperfect. Short-term maintenance scheduling is therefore a problem of decision-making under uncertainty. This paper proposes a probabilistic approach to the short-term scheduling problem based on a cost-loss model for individual maintenance missions, and probabilistic forecasts of appropriate access windows. This approach is found to increase the utilisation of possible access windows compared to using deterministic decision rules. The impact of forecasting on the availability and operational costs of oshore wind is then examined using a Monte Carlo-based cost model. This has quantified the impact on availability and revenue performance under a range of site conditions

Wave height forecasting to improve off-shore access and maintenance scheduling

This paper presents research into modelling and predicting wave heights based on historical data. Wave height is one of the key criteria for allowing access to off-shore wind turbines for maintenance. Better tools for predicting wave height will allow more accurate identification of suitable “weather windows” in which access vessels can be dispatched to site. This in turn improves the ability to schedule maintenance, reducing costs related to vessel dispatch and recall due to unexpected wave patterns. The paper outlines the data available for wave height modelling. Through data mining, different modelling approaches are identified and compared. The advantages and disadvantages of each approach, and their accuracies for a given site implementation, are discussed

Data driven case study of a wind turbine main-bearing failure

This paper presents a data driven case study of two outer-race spalling faults in double-row spherical roller main-bearings, with the purpose of identifying key features and relevant measurements associated with this failure mode in wind turbine main-bearings. Supervisory data is analysed for one fault case and vibration data for the other. The aim of this work is to inform practitioners and assist in improving fault detection systems for this component

Nonconcave entropies in multifractals and the thermodynamic formalism

We discuss a subtlety involved in the calculation of multifractal spectra when these are expressed as Legendre-Fenchel transforms of functions analogous to free energy functions. We show that the Legendre-Fenchel transform of a free energy function yields the correct multifractal spectrum only when the latter is wholly concave. If the spectrum has no definite concavity, then the transform yields the concave envelope of the spectrum rather than the spectrum itself. Some mathematical and physical examples are given to illustrate this result, which lies at the root of the nonequivalence of the microcanonical and canonical ensembles. On a more positive note, we also show that the impossibility of expressing nonconcave multifractal spectra through Legendre-Fenchel transforms of free energies can be circumvented with the help of a generalized free energy function, which relates to a recently introduced generalized canonical ensemble. Analogies with the calculation of rate functions in large deviation theory are finally discussed.Comment: 9 pages, revtex4, 3 figures. Changes in v2: sections added on applications plus many new references; contains an addendum not contained in published versio

Quantification of the influence of climate on predicted and observed cost of energy for offshore wind

This paper analyses the degree to which lifetime production and availability figures are subject to variation due to inherent inter annual climate variations. This is achieved by performing operational simulations based on different measurement periods chosen from 10 years of historic wind and wave data in the North Sea, establishing the financial implications this has for the industry. The investigation is carried out using a robust Monte Carlo simulation climate and lifetime operational expenditure model. Significant variations are observed with regards to availability, power production and OPEX costs with OPEX costs varying by 15% above and below the average value when a single year is used for the simulation input. It has also been demonstrated that results with similar availability predictions can have divergent power production and OPEX results. This is explained by the correlations between wind speed, wave height, accessibility and power production. The best practice to minimize uncertainty in cost projections from short term measurement campaigns has been identified

Data for: Factors Influencing Adoption of Pet Dogs and Eventual Owner Satisfaction

Dogs can be adopted from shelters, breeders, family, friends, local pet shops, or online resources. Personal likes, experience and deep-rooted interests to satisfy emotional needs such as companionship, affection, empathy and security are some of the underlying motivations for acquiring a pet companion. In this study, we sought to learn what key characteristics influence the adopters' decision to select pet dogs, and how satisfied they were with the result. The welfare effect caused by negatively mis-matched relations impacts both the “small inter-species social group” and, the community at large as emotional and financial burdens often ensue leading to pet surrender and even euthanasia. Pet professionals servicing the relationship are by extension also negatively impacted. In our qualitative study respondents (n=1225) completed an online questionnaire with responses representing 1704 dog/owner pairs. Of the characteristics explored we found, 44% of participants placed a strong emphasis on looks; 47% on trainability; 52% on the age of the dog; 53% on compatibility with other pets, and 54% a on the dogs’ breed. Close to half of the respondents, 49% spent between one week and six months thinking about acquiring a dog before taking action. Personality/behavior and age were two characteristics that stood out in our study. And while personality/behavior is a difficult characteristic to assess, it was a key factor for over a third of respondents. Most notably we found those who judged their dog’s future behavior by its behavior at the time of adoption reported a negative effect on owner satisfaction. Our findings further establish the need to guide new owners as they make decisions early in the acquisition process so they may better plan and manage expectations, reduce “buyers remorse”, prevent the development of unwanted behavioral challenges and thus improve the human animal bond