Operational strategies for offshore wind turbines to mitigate failure rate uncertainty on operational costs and revenue

Several operational strategies for offshore wind farms have been established and explored in order to improve understanding of operational costs with a focus on heavy lift vessel strategies. Additionally, an investigation into the uncertainty surrounding failure behaviour has been performed identifying the robustness of different strategies. Four operational strategies were considered: fix on fail, batch repair, annual charter and purchase. A range of failure rates have been explored identifying the key cost drivers and under which circumstances an operator would choose to adopt them. When failures are low, the fix on fail and batch strategies perform best and allow flexibility of operating strategy. When failures are high, purchase becomes optimal and is least sensitive to increasing failure rate. Late life failure distributions based on mechanical and electrical components behaviour have been explored. Increased operating costs because of wear-out failures have been quantified. An increase in minor failures principally increase lost revenue costs and can be mitigated by deploying increased maintenance resources. An increase in larger failures primarily increases vessel and repair costs. Adopting a purchase strategy can negate the vessel cost increase; however, significant cost increases are still observed. Maintenance actions requiring the use of heavy lift vessels, currently drive train components and blades are identified as critical for proactive maintenance to minimise overall maintenance costs

Analysis of offshore wind turbine operation & maintenance using a novel time domain meteo-ocean modeling approach

This paper presents a novel approach to repair modeling using a time domain Auto-Regressive model to represent meteo-ocean site conditions. The short term hourly correlations, medium term access windows of periods up to days and the annual distibution of site data are captured. In addition, seasonality is included. Correlation observed between wind and wave site can be incorporated if simultaneous data exists. Using this approach a time series for both significant wave height and mean wind speed is described. This allows MTTR to be implemented within the reliability simulation as a variable process, dependent on significant wave height. This approach automatically captures site characteristics including seasonality and allows for complex analysis using time dependent constaints such as working patterns to be implemented. A simple cost model for lost revenues determined by the concurrent simulated wind speed is also presented. A preliminary investigation of the influence of component reliability and access thresholds at various existing sites on availability is presented demonstrating the abiltiy of the modeling approach to offer new insights into offshore wind turbine operation and maintenance

Sequential importance sampling for multiway tables

We describe an algorithm for the sequential sampling of entries in multiway contingency tables with given constraints. The algorithm can be used for computations in exact conditional inference. To justify the algorithm, a theory relates sampling values at each step to properties of the associated toric ideal using computational commutative algebra. In particular, the property of interval cell counts at each step is related to exponents on lead indeterminates of a lexicographic Gr\"{o}bner basis. Also, the approximation of integer programming by linear programming for sampling is related to initial terms of a toric ideal. We apply the algorithm to examples of contingency tables which appear in the social and medical sciences. The numerical results demonstrate that the theory is applicable and that the algorithm performs well.Comment: Published at http://dx.doi.org/10.1214/009053605000000822 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Dimensional instability of cement bonded particleboard: Modelling CBPB as a composite of two materials

Copyright @ Springer Verlag. This is a post print version of the article. The official published version can be obtained from the link below.Previous papers have quantitatively indicated that the total movement of cement bonded particleboard (CBPB) is equal to the sum of the movement of its components. This paper examined the efficacy of the law of mixtures when applied to the movement of a wood-cement composite under internal swelling or shrinkage stresses. Abundant data generated in companion papers were first manipulated to develop the universal formulae for predicting the movement of components. In conjunction with previous numerical results from image analysis of the structure of CBPB, and the orientated elasticity and stress algorithms, the models for theoretically predicting mass and dimensional changes of CBPB were derived. Validation studies were conducted and these demonstrated an excellent agreement of the theoretical predictions with experimental data for both mass and dimensional changes of CBPB due to internal swelling or shrinkage stresses during adsorption and desorption. The success also implied that CBPB can be treated as a composite and its properties can be well derived by the law of mixtures even though CBPB is an unusual type of composite having a very high volume fraction of wood chips, but a very high mass fraction of cement paste

THE DECISION TO UNDERTAKE VOCATIONAL HIGHER EDUCATION IN SHIPPING AND LOGISTICS IN THE UK

This work investigates the decision to study shipping and logistics at advanced levels in the UK. Documented evidence reports and analyses the perceptions of students on vocational courses in shipping, transport and logistics and investigates why they chose their particular fields of study. A range of instruments are presented to analyse how students perceived that they had arrived at their study decisions, including national surveys of undergraduates in maritime business, postgraduates in shipping and logistics and professionals contemplating updating short courses. Qualitative, quantitative and mapping methods are presented along with perceptions of relevant professional outcome roles and other factors. Exploratory approaches to proposing and evaluating alternative approaches to teaching aimed at raising the student's perception of the nature of professional skills requirements were predicated by identifying and defining local student schemae and tailoring aids to their specific learning and teaching requirements. A cognitive mapping approach enabled comparisons of perceptions between postgraduates, whose individual beliefs, after being mapped and modelled as a directed network, were analysed, and differences between maps were quantified. Quantitative pairwise map comparisons included 54 individuals generating 1430 synchronal comparisons in one cohort and four diachronal cohort comparisons. These revealed that distance measures constrained by the numbers of transmitters or receivers, and the strength of relationships where appropriate, formed the best discriminators. Empirical and theoretical explanations of maps and attempts to compare particular subgroups and explain differences were often inconclusive. A unified social cognitive theory of career and academic interest, choice and performance generated useful propositions relating to how individuals manage issues of self-efFicacy, expected outcomes from decisions and their personal goals. Substantive work revealed problems of conflicting domains between students' verbatim statements, only weakly coincident with theoretical concepts. Conclusions that mapping is most powerful/when based on qualitative analysis of the richness and diversity of individual perceptions; infer that no simple standard decision process is operating and hence no single recruitment marketing device is apparent. In applying and disseminating findings, where possible, proposals were made to assist organisations promoting careers awareness and recruitment into relevant professions and university based vocational courses, published by relevant professional bodies