•Conduct a techno-economic life-extension analysis for classification and certification.•Coupled structural integrity assessment accounting for corrosion crack growth.•Economic analysis accounting ...for the likelihood of estimated return.•Life extension using unsupervised machine learning K-means clustering algorithm.
The objective of the present study is to conduct a techno-economic life-extension analysis for fixed offshore wind turbines for the purpose of classification and certification. The early installed offshore wind turbines are approaching the end of their design service lives. The life extension of these structures is under serious consideration as the support structures are still in a condition for further use. Hence, it is technically possible and economically beneficial to investigate roadmaps for potential life-extension decisions. The methodology developed to analyse the life-extension projects merges a structural integrity assessment of a monopile structure with a corrosion-induced crack development with an economic analysis of the return on assets accounting for the likelihood of obtaining the estimated return. The methodology commences with preprocessing the structural health monitoring data using a Gaussian kernel for denoising, followed by a time-domain crack growth analysis accounting for retardation performed on a cycle-by-cycle basis. The corrosion-related failure mechanisms are growing concerns for currently operating monopile offshore wind turbines. The present study introduces a novel nonlinear corrosion model to address the emergent issue, which is developed considering the spatial and temporal changes in the environmental and operational parameters and the reinforcing effect of fracture on the corrosion. The failure assessment diagram identifies the threshold based on the maintenance cost calculated with a confidence level. The economic analysis combines revenue estimates and operational expenditures, considering the life-extension duration and appropriate discount rate. The results of the life-extension assessment, presented through a risk-return diagram, are used to classify the life-extension projects using unsupervised machine learning k-means clustering algorithm.
•Risk-based maintenance planning for offshore wind farm is investigated.•The optimal number of turbines is estimated based on the minimum LCE.•The event tree is employed to assess the life cycle ...cost.•A novel framework for inspection and maintenance is developed here
A risk-based maintenance planning for offshore wind farm installations is developed. Initially, the optimal number of monopile offshore wind turbines to be installed in an offshore wind farm is estimated, targeting a minimum levelised cost of energy. To this end, a sufficient number of design combinations for monopile support structure is generated by the design of experiment technique and then analysed based on the fatigue limit state. Following the fatigue reliability analysis performed for the monopile designs, an analytical relation between manufacturing cost and the structural safety regarding fatigue is developed to be used in the life-cycle cost analysis. The offshore wind farm is considered here as a system consisting of correlated components. The system reliability is estimated by using Ditlevsen bounding technique, which uses a time-variant correlation matrix of offshore wind turbines. The event tree method is employed to assess the expected cost of failure to be included in the capital investment as the structural risk premium, and the total expected cost to be included in the operational cost. Furthermore, different inspection policies are studied, and the most cost-effective inspection and maintenance policy is found for each studied wind farm. The present study also develops a novel framework for inspection and maintenance planning that maximises the benefits of performing inspections for a multi-unit system. Finally, the developed framework is applied to an offshore wind farm with sixty installations, and the detailed description of the planned inspections are discussed.
•Spectral fatigue damage prediction of a tripod offshore wind turbine support structure is conducted.•The power spectral density of the hot spot stress is estimated.•The prediction of fatigue damage ...is evaluated in several spectral fatigue damage models.•The rainflow cycle counting method is assumed to be the “reference” data.•The model that best fits the fatigue damage is identified with the Akaike’s Information Criterion.
This work deals with the evaluation of the spectral fatigue damage prediction of a tripod offshore wind turbine support structure subjected to combined stochastic wave and wind – induced loads. The stochastic loadings are defined using the sea states based on a scatter diagram related to the North Atlantic. Further, the power spectral density of the hot spot stress is estimated accordingly. The prediction of fatigue damage is evaluated in several spectral fatigue damage models including the Rayleigh, Wirsching–Light, Tunna, α0.75, Tovo and Benasciutti, Zhao–Baker, Rice and Dirlik models. Critical hot spot locations, which experience the most fatigue damage, are analysed based on the finite element method and the S–N fatigue damage approach. The time-domain solution based on the rainflow cycle counting method is assumed to be the “real” data and the model that best fits the fatigue damage of the wind turbine support structure is identified with the Akaike’s Information Criterion.
•A risk-based life-cycle assessment of a monopile supporting offshore wind turbine structure is performed.•The design of the structure is based on the optimised levelised cost of energy.•The support ...structures are evaluated by using the finite element method.•The cost related to the life-cycle phases are categorised as capital, operational and decommissioning cost.•The optimal inspection interval and the sensitivity of the parameters influencing the risk life-cycle assessment are studied.
The objective of the present study is to perform a risk-based life-cycle assessment of monopile offshore wind turbine support structures. The design of the structure is based on the optimised levelised cost of energy so that the offshore wind energy can compete with the other energy resources. Both optimal design solutions for a monopile support structure and the optimal inspection planning are addressed here. The structural assessment of the monopile support structures is carried out using the finite element method accounting for the pile-soil interactions. The risk-based assessment is performed for the design solutions aiming to achieve the minimum of the levelised cost of energy and the total expected cost conditional to the implemented inspection strategy and the structural risk. Furthermore, the optimal inspection interval is investigated. Finally, the sensitivity of the parameters influencing the risk life-cycle assessment is also studied. The present study analyses a multi-dimensional framework, which integrates structural configuration of the support structure, manufacturing, detailed structural risk assessment, inspection and repair planning, and economic conditions into a coupled dynamic system accounting for the feedback loops resulted from the introduction of the probabilistic structural state to the life cost expenditure such as CAPEX, OPEX, and DECEX.
•The ultimate strength of a tubular structure subjected to a bending moment is analysed.•Three specimens are designed for the experimental test.•The moment-curvature and the stress-strain ...relationship of the tested specimens are studied.•The tested specimens are also evaluated based on the finite element method.•The results of the finite element analysis and the experiments are compared and discussed.
The objective of the present work is to analyse the ultimate strength of a tubular structure subjected to a bending moment. The tubular monopile structures are experimentally tested as well as the nonlinear finite element analysis is performed. Three specimens are designed for the experimental test by taking into consideration the typical ranges of the monopile support structures used in offshore wind turbines. The moment-curvature and the stress-strain relationship of the tested specimens are studied. The tested specimens are also evaluated numerically based on the finite element method employing a nonlinear FE analysis. The finite element analysis accounts for the nonlinearities associated with the geometry and material. The geometrical imperfections are introduced to the structure together with the initial stress arisen in the process of fabrication. The results obtained from the finite element analysis and the experimental tests are compared to each other and discussed.
The objective of this work is to study the uncertainties involved in the modelling of the soil-pile interaction concerning their influence on the prediction of the dynamic structural response of ...monopile offshore wind turbine support structures. Two main issues are identified and addressed: the adequacy of the method used to deal with the soil-pile interactions and the adequacy of the soil properties reflecting the behaviour of the soil. The present study develops an approach that defines the penetrated pile length depending on the soil profile. Also, a parameter is defined to avoid the excessive usage of steel for the penetrated pile structure. The uncertainties are included in the probabilistic free vibration analysis and the contribution of each random variable to the scatter of the response is estimated by performing a sensitivity analysis. The results indicate that the uncertainty involved in the modelling of the soil profile has a significant effect on the coefficient of variance of the natural frequency, which is a serious issue to be considered in the fatigue life assessment of offshore wind turbine support structures.
The primary objective of the present literature review is to provide a constructive and systematical discussion based on the relevant development, unsolved issues, gaps, and misconceptions in the ...literature regarding the fields of study that are building blocks of artificial intelligence-aided life extension assessment for offshore wind turbine support structures. The present review aims to set up the needed guidelines to develop a multi-disciplinary framework for life extension management and certification of the support structures for offshore wind turbines using artificial intelligence. The main focus of the literature review centres around the intelligent risk-based life extension management of offshore wind turbine support structures. In this regard, big data analytics, advanced signal processing techniques, supervised and unsupervised machine learning methods are discussed within the structural health monitoring and condition-based maintenance planning, the development of digital twins. Furthermore, the present review discusses the critical failure mechanisms affecting the structural condition, such as high-cycle fatigue, low-cycle fatigue, fracture, ultimate strength, and corrosion, considering deterministic and probabilistic approaches.
The present study aims to assess the ultimate strength of a jacket offshore wind turbine support structures at different water depths. The progressive collapse analysis is carried out based on the ...finite element method accounting for the nonlinearities regarding material and geometry. A two-step analysis is carried out, in which at first, the axial dead loads are applied in a linear quasi-static analysis and then the resulting pre-stressed jacket support structure is analysed by a nonlinear finite element analysis in order to identify the ultimate strength. The present study employs a global strength approach so as to assess the ultimate strength of the jacket support structures consisting of several supporting modules with different stiffness. The moment-curvature relationships are presented for the jacket support structures at water depths of 40, 60 and 80 m. The effects of the thickness and leg inclination on the ultimate strength are investigated.
•A fatigue damage assessment of a fixed offshore wind turbine support structure is performed.•The operational mode of the wind turbine 3 loading conditions are identified.•For each loading condition ...4 critical regions located in different zones of the supporting structure are studied.•The stress transfer function is obtained by carrying out dynamic finite element analysis.•An up-to-date rainflow cycle counting method is adopted to count the total number of cycles.
The objective of this work is to carry out a fatigue damage assessment of a fixed offshore wind turbine support structure due to combined wave and wind – induced loading. Considering the operational mode of the wind turbine 3 loading conditions are identified and for each loading condition 4 critical regions located in different zones of the supporting structure are studied. The stress transfer function is obtained by carrying out dynamic finite element analysis in the frequency domain. A wave scatter diagram of the North Atlantic is used in order to account for the environmental effects. The stress transfer function is formulated such that a sufficient number of frequencies can be used in the Inverse Fast Fourier Transform with random phase angles in order to obtain the stress time histories. An up-to-date rainflow cycle counting method is adopted to count the total number of cycles related to stress range bins. The S–N approach is employed to estimate fatigue damage.
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