Browsing by Author "Collu, Maurizio"

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    Analysis of the effect of a series of back twist blade configurations for an active pitch-to-stall floating offshore wind turbine
    (American Society of Mechanical Engineers, 2020-04-08) Ward, Dawn; Collu, Maurizio; Sumner, Joy
    For a turbine mounted on a floating platform, extreme induced loads can be increased by up to 1.6 times those experienced by a turbine situated on a fixed base. If these loads cannot be reduced, towers must be strengthened which will result in increased costs and weight. These tower loads would be additionally exasperated for a pitch-to-feather controlled turbine by a phenomenon generally referred to as “negative damping,” if it were not avoided. Preventing negative damping from occurring on a pitch-to-feather controlled floating platform negatively affects rotor speed control and regulated power performance. However, minimizing the blade bending moment response can result in a reduction in the tower fore-aft moment response, which can increase the tower life. A variable-speed, variable pitch-to-stall (VSVP-S) floating semi-submersible wind turbine, which does not suffer from the negative damping and hence provides a more regulated power output, is presented. This incorporates a back twist blade profile such that the blade twist, starting at the root, initially twists toward stall and, at some pre-determined “initiation” point, changes direction to twist back toward feather until the tip. Wind frequency weighting was applied to the tower axial fatigue life trends of different blade profiles and a preferred blade back twist profile was identified. This had a back twist angle of −3 deg and started at 87.5% along the blade length and achieved a 5.1% increase in the tower fatigue life.
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    Can a wind turbine learn to operate itself? Evaluation of the potential of a heuristic, data-driven self-optimizing control system for a 5MW offshore wind turbine
    (Elsevier, 2017-12-15) Gueorguiev Iordanov, Stefan; Collu, Maurizio; Cao, Yi
    Larger and more expensive offshore wind turbines, subject to more complex loads, operating in larger wind farms, could substantially benefit from more advanced control strategies. Nonetheless, the wind industry is reluctant to adopt such advanced, more efficient solutions, since this is perceived linked to a lower reliability. Here, a relatively simple self-optimizing control strategy, capable to “learn” (data-driven) which is the optimum control strategy depending on the objective defined, is presented. It is proved that it “re-discovers”, model-free, the optimum strategy adopted by commercial wind turbine in region 2. This methodology has the potential to achieve advanced control performance without compromising its simplicity and reliability.
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    A comparison on the dynamics of a floating vertical axis wind turbine on three different floating support structures
    (Elsevier, 2014) Collu, Maurizio; Borg, Michael
    To increase the competitiveness of offshore wind energy in the global energy market, it is necessary to identify optimal offshore wind turbine configurations to deliver the lowest cost of energy. For deep waters where floating wind turbines are the feasible support structure option, the vertical axis wind turbine concept might prove to be one of these optimal configurations. This paper carries out a preliminary investigation into the dynamics of a vertical axis wind turbine coupled with three generic floating support structures originally intended for horizontal axis wind turbines. The modifications to the original characteristics of the support structures were kept to a minimum to illustrate the use of floating horizontal axis wind turbine platforms for floating vertical axis wind turbines Issues regarding the adequacy of the mooring systems are outlined and an overview of platform responses in a number of varying met-ocean conditions is presented and discussed.
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    Critical review of floating support structures for offshore wind farm deployment
    (2018-10-31) Leimeister, Mareike; Kolios, Athanasios; Collu, Maurizio
    Floating structures enable offshore wind power deployment at numerous deep water sites with promising wind potential where bottom-fixed systems are no longer feasible. However, the large diversity in existing floater concepts slows down the development and maturing processes of floating offshore wind turbines. Thus, in this work, different floating support structures are assessed with respect to their suitability for offshore wind farm deployment. A survey is conducted to examine the capacities of selected floater types, grouped into ten categories, with respect to ten specified criteria focusing on wind farm deployment. By this means, a multi-criteria decision analysis (MCDA) is carried out, using the technique for order preference by similarity to ideal solution (TOPSIS). With the individual scores of the different systems, considering the weighting of each criterion, suitable concepts are identified and potential hybrid designs, combining advantages of different solutions, are suggested.
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    Dataset for European Installed Offshore Wind Turbines (until year end 2017)
    (Cranfield University, 2018-06-11 09:18) Cevasco, Debora; Collu, Maurizio
    Introduction and aimThis dataset is aimed to list and collect the main characteristics of the European Offshore Wind Farms (to end of 2017). Firstly, this work wants to update and extend the one started by Zhang et al. [1, who gathered the main information and identified the drivetrain types for some of offshore EU wind turbines’ installed, until the end of 2011.Secondly, the wind turbines belonging to the population studied by Carroll et al. [2, [3 (in their reliability database), are identified and analysed more in details.Dataset organisationThe dataset is organised in an Excel worksheet, consisting of:sheet 1 - “Legend”Acronyms and colour coded legend are explained. Additionally the following acronyms are used in the Excel work and throughout this introduction:- WT(s) = Wind Turbine(s)- WF(s) = Wind Farm(s)sheet 2 - "EU WFs”Data from Zhang et al. [1 have been verified and updated by accessing the main information of the wind farms (see link in reference in the section). In particular, for each project, the following information are reported: - WF name, capacity and country - number of WTs - WTs manufacturer/type - type of control, gearbox, generator, and converter - year when WF was online - average distance from shore - current status of the WFsheet 3 - "EU WFs (Fully-Grid Connected)”The fully-grid connected, and still in operation, wind farms are selected out of the ones listed in sheet 1. In the main table (Range(“A1:N83”)), the WTs are identified in the four drivetrain types (and type D sub-types), defined by Perez et al. [4 (N2:N83). A table reporting the acronyms for the “if” cycle on the WT characteristics (speed, gearbox and generator) is reported in cells Range(“AH2:AL11”).Based on this latter, cells in Range(“Q1:AD84”) contain “if” cycles for identifying the share of each drivetrain type on the total installed capacity. The results are plotted in a pie chart, gathering type A and B. Finally, the table in Range(“AS1:CA86”) wants to verify how much of the actual installed (fully-grid connected) capacity is accounted in this dataset. WindEurope report on offshore wind energy statistics, to the end of 2017 [5, is used as a reference, and the sharing to the total capacity of the several manufacturers and of the top 5 countries and is checked.sheet 4 - “Strath. Stats (population info)”For a deeper understanding of the population analysed by Carroll et al. [2, the WTs with the following characteristics have been outlined (by the use of “if” cycles on the main table of sheet 2): - at least 3 year old structure (in 2016) - geared WTs with an induction machine (either SGIG, WRIG or DFIG)Among these, structures between 3 and 5 years old and above 5 years old are distinguished as done by the reference.References[1 Z. Zhang, A. Matveev, S. Øvrebø, R. Nilssen, and A. Nysveen, “State of the art in generator technology for offshore wind energy conversion systems,” in 2011 IEEE International Electric Machines & Drives Conference (IEMDC), 2011, pp. 1131–1136.[2 J. Carroll, A. McDonald, and D. McMillan, “Failure rate, repair time and unscheduled O&M cost analysis of offshore wind turbines,” Wind Energy, vol. 19, pp. 1107–1119, 2016.[3 J. Carroll, A. McDonald, I. Dinwoodie, D. McMillan, M. Revie, and I. Lazakis, “Availability, operation and maintenance costs of offshore wind turbines with different drive train configuration,” Wind Energy, vol. 20, no. July 2016, pp. 361–378, 2017.[4 J. M. Pinar Pérez, F. P. García Márquez, A. Tobias, and M. Papaelias, “Wind turbine reliability analysis,” Renew. Sustain. Energy Rev., vol. 23, pp. 463–472, 2013.[5 WindEurope, “Offshore wind in Europe: Key trends and statistics 2017,” 2018. The links below were used to extract the majority of the information about the wind farms and their wind turbines, respectively.https://www.4coffshore.com/windfarms/https://en.wind-turbine-models.com/turbinesMoreover, for these latter, a .zip folder with additional open access information (collected from various sources) is uploaded.
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    Design, construction and testing of an ascending micropenetrometer to measure soil crust resistance
    (Cranfield University, 2014-02) Lorentz, Andrew; Brennan, Feargal; Collu, Maurizio; Ritz, K.
    The increasing world population is putting pressure on global food production. Agriculture must meet these growing demands by increasing crop yields. One phenomenon which prevents seedling emergence and damages crop yield is soil crusting. Understanding of soil crusting and the factors which influence it is fundamental to ensuring good crop production. An instrument which will test soil crust strength in a novel way, mimicking seedling growth, may lead to pre-emptive agricultural soil management which could increase crop production. This work details the process of design, construction and testing of an ascending penetrometer to measure soil crust strength. The full design process is discussed from concept generation and evaluation, using experimental methods and a multi-criteria decision making tool, through to final design configuration, specification, manufacture and testing. Traditionally, soil penetrometers measure soil strength by forcing a probe from the surface of the soil into the bulk soil below. To more accurately measure the direct impedance a seedling would experience a device should measure impedance from the bulk soil upwards and into the soil crust, mimicking what a growing seedling would experience. Results prove that the manufactured ascending penetrometer with a force resolution of 0.01N and displacement resolution of 0.0004mm is capable of detecting differences in soil crusts. At these resolutions and accuracy to 0.1N and 0.1mm excellent repeatability was achieved. The machine is therefore a useful and realistic tool for quantitatively comparing soil crusts in soil. It is hoped that being able to compare soil crust strength will lead to improved soil management techniques.
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    Dynamics of marine vehicles with aerodynamic surfaces
    (Cranfield University, 2008-11) Collu, Maurizio; Patel, M. H.; Trarieux, F.
    An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap which can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high speed marine vehicle equipped with aerodynamic surfaces (called an AAMV, 'Aerodynamically Alleviated Marine Vehicle') is one such concept. The development of this type of vehicle requires a mathematical framework to characterize its dynamics taking account of both aerodynamic and hydrodynamic forces. This thesis presents the development of unified and consistent equations of equilibrium and equations of motion to predict the dynamic performance of such AAMV configurations. An overview of the models of dynamics developed for Wing In Ground effect 'WIGe' vehicles and high speed marine vehicles (planing craft) is given first. Starting from these models, a generic AAMV configuration is proposed and a kinematics framework is developed. Then, taking into account the aerodynamic, hydrostatic and hydrodynamic forces acting on the AAMV, equations of equilibrium are derived and solved. This is followed by deriving and solving the full equations of motion, using a small perturbation assumption. A static stability criterion, specific for the AAMV configuration, has been developed. This mathematical framework and its results are implemented in MATLAB and validated against theoretical and experimental data. The resultant capability for analysing novel AAMV configurations is presented through two parametric analysis. The analysis demonstrate that these models offer a powerful AAMV design tool.
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    High Speed Marine Vehicles With Aerodynamic Surfaces: Development of a Dynamic Model for a Novel Configuration.
    (2008-05-06T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    A research programme on high speed marine vehicles fitted with aerodynamic surfaces started in Cranfield University in 2005. One of the configurations analyzed is a high speed prismatic planing hull with one or more aerodynamic surfaces; it is called a hybrid vehicle (HV). Two mathematical models have been developed for the dynamic behavior which is a combination of the very different behaviors of aircraft and ships. The first model estimates the equilibrium attitude of the HV at a certain speed. A parametric analysis for the influence of the configuration on the performance of the HV has been conducted (1). With the second model, the authors propose a set of ordinary differential equations of motion, derived in the frame of small-disturbance stability theory which has been used to investigate the longitudinal dynamic stability of the HV (2). Ref. (1) and (2) present a complete description of the mathematical models, while this article summarizes the methodology adopted to develop these dynamic models and gives a brief summary of the results. (1) COLLU, M., PATEL, M. H., TRARIEUX, F., A Mathematical Model to analyze the Static Stability of Hybrid (Aero- hydrodynamically supported) vehicles., 8th Symposium on High Speed Marine Vehicles 2008 (HSMV08), Naples, Italy, 2008. (2) COLLU, M., PATEL, M. H., TRARIEUX, F., A Unified Mathematical Model for High Speed Hybrid (Air and Water- borne) Vehicles., 2nd International Conference on Marine Research and Transportation, 2007.
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    Longitudinal dynamics of wing in ground effect craft in waves
    (2017-06) Adhynugraha, Muhammad Ilham; Collu, Maurizio; Brennan, Feargal
    An assessment of the longitudinal motion of a hybrid configuration called the aerodynamically alleviated marine vehicle (AAMV) with the presence of waves, is demonstrated in the thesis. The development of this type of vehicle requires a mathematical framework to characterise its dynamics with the influence of external forces due to the waves’ motion. An overview of the effect of waves towards the models of dynamics developed for wing in ground effect (WIGE) craft and high-speed marine vehicles (planing craft) is carried out. However, the overview only leads to a finding that the longitudinal stability of a lifting surface over wavy ground effect is not entirely established. Taking this fact into account, the analysis of the model is proposed for a WIGE craft configuration. A simplification is adopted considering heave motion only in the modelling of oscillation. The simplification is made to thoroughly capture the effect of oscillation toward dynamic stability of the vehicle. To support the model verification, a numerical simulation followed by a semi-empirical design method was adopted to produce aerodynamic data, both in two-dimensional and three-dimensional domains, respectively. The results show that the combination of underpinning parameters, i.e. ride height, frequency and amplitude of oscillation, remarkably influence the aerodynamics. The characteristics in aerodynamics affect the production of stability derivatives and eventually stability behaviour of the chosen configuration. Some patterns in the results are identified but there also some data that show the peculiarity. Thus further investigation is needed.
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    The longitudinal static stability of an aerodynamically alleviated marine vehicle, a mathematical model
    (Royal Society, 2010-04-08T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    An assessment of the relative speeds and payload capacities of airborne and waterborne vehicles highlights a gap that can be usefully filled by a new vehicle concept, utilizing both hydrodynamic and aerodynamic forces. A high- speed marine vehicle equipped with aerodynamic surfaces is one such concept. In 1904, Bryan & Williams (Bryan & Williams 1904 Proc. R. Soc. Lond. 73, 100-116 (doi: 10.1098/rspl.1904.0017)) published an article on the longitudinal dynamics of aerial gliders, and this approach remains the foundation of all the mathematical models studying the dynamics of airborne vehicles. In 1932, Perring & Glauert (Perring & Glauert 1932 Reports and Memoranda no. 1493) presented a mathematical approach to study the dynamics of seaplanes experiencing the planing effect. From this work, planing theory has developed. The authors propose a unified mathematical model to study the longitudinal stability of a high-speed planing marine vehicle with aerodynamic surfaces. A kinematics framework is developed. Then, taking into account the aerodynamic, hydrostatic and hydrodynamic forces, the full equations of motion, using a small perturbation assumption, are derived and solved specifically for this concept. This technique reveals a new static stability criterion that can be used to characterize the longitudinal stability of high-speed planing vehicles with aerodynamic surfaces.
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    A Mathematical Model to Analyze the Static Stability of Hybrid (Aero- Hydrodynamically Supported) Vehicles.
    (2008-05-21T00:00:00Z) Collu, Maurizio; Patel, Minoo H.; Trarieux, Florent
    Among the new concepts developed for high speed marine vehicles over the last two decades, the "aerodynamic alleviation" approach consists in using an aerodynamic surface to "alleviate" the weight sustained by the hydrodynamic lift. Such vehicle experiences aerodynamic and hydrodynamic forces of the same order of magnitude, therefore the dynamic models developed for airborne and waterborne vehicles are not suitable. Considering a vehicle having a high-speed prismatic planing hull and one or more aerodynamic surfaces, the authors propose two mathematical methods. The first one calculates the equilibrium attitude of the vehicle at a given speed and its numerical implementation has been used to undertake a parametric analysis of the influence of some configuration characteristics on performances. The second method analyzes the static stability of the HV. Starting from the dynamic analysis previously proposed by the authors, the characteristic polynomial of the HV dynamics is derived and a static stability criterion is proposed.
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    Modelling and analysis of the techno-economic and social impacts of an algal oil
    (Cranfield University, 2015-03) Madugu, Fatima Usman; Collu, Maurizio; Brennan, Feargal
    The economic viability for a microalgae production facility for the production of algal oil and bioproducts remains challenging and unanswered. Important aspects not investigated in assessment of the economic viability of algal oil are the social benefits, such as employment, local earnings and outputs created from such facilities. A model that is able to include both techno-economic and social benefits can help provide answers on the future of these technologies. The development of this type of model requires a combination of techno-economic and social impact theory. This thesis presents an integrated model that estimates the social (employment earnings, and output) and techno-economic impacts generated from a microalgae production facility. A process and system configuration of the algal production chain is selected first. The construction costs of the equipment are then calculated, followed by overall capital cost calculation. Then, the operating costs are estimated by multiplying the resources and energy usage rate by a unit price. Employment, earnings, and output generated from constructing and operating the facility is then calculated using output from the capital and operating cost with input – output multipliers to measure the impact of the series of effects generated by expenditure. The model as far as the author knows, is the first techno-economic model that addresses the social impact. A parametric analysis is carried out using two different methods to determine the viability of an algal oil production facility. Taking the economic costs and the operating parameters from the socio- techno-economic model, some key parameters are changed across a range of values, and their influence on the final cost of algal oil and job impact are analysed. The results shows highest cost contributor to the algal oil cost comes from capital costs. Productivity rate and lipid content have the highest impact both on the final algal oil costs, and the social impact outputs. Improvement would need to be made both in biology and system units.
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    O&M cost-based FMECA: Identification and ranking of the most critical components for 2-4 MW geared offshore wind turbines
    (IOP, 2018-10-10) Cevasco, Debora; Collu, Maurizio; Lin, Z.
    To date, the focus of the research on offshore wind turbines (WTs) has been mainly on how to minimise their capital cost, but Operation and Maintenance (O&M) can represent up to a third of the lifetime costs of an offshore wind farm. The cost for the assets repair/replacement and for the logistics of the maintenance operations are two of the biggest contributors to O&M expenses. While the first is going to rise with the employment of bigger structures, the latter can significantly increase dependently on the reliability of the components, and thus the necessity to performed unscheduled maintenance operations. Using the reliability data for a population of offshore WTs (representing the configurations most employed offshore), first, the share of the components failures to the O&M cost, together with an estimation of their dependency on some O&M parameters has been derived. Then, by following a cost-based Failure Modes Effects and Criticality Analysis (FMECA), and ranking the components through O&M cost priority number, the most critical components for O&M unplanned operations are identified.
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    Offshore floating vertical axis wind turbines, dynamics modelling state of the art. Part II: Mooring line and structural dynamics
    (Elsevier, 2014-08-04) Borg, Michael; Collu, Maurizio; Kolios, Athanasios
    The need to exploit enhanced wind resources far offshore as well as in deep waters requires the use of floating support structures to become economically viable. The conventional three-bladed horizontal axis wind turbine may not continue to be the optimal design for floating applications. Therefore it is important to assess alternative concepts in this context that may be more suitable. Vertical axis wind turbines (VAWTs) are a promising concept, and it is important to first understand the coupled and relatively complex dynamics of floating VAWTs to assess their technical feasibility. As part of this task, a series of articles have been developed to present a comprehensive literature review covering the various areas of engineering expertise required to understand the coupled dynamics involved in floating VAWTs. This second article focuses on the modelling of mooring systems and structural behaviour of floating VAWTs, discussing various mathematical models and their suitability within the context of developing a model of coupled dynamics for. Emphasis is placed on computational aspects of model selection and development as computational efficiency is an important aspect during preliminary design stages. This paper has been written both for researchers new to this research area, outlining underlying theory whilst providing a comprehensive review of the latest work, and for experts in this area, providing a comprehensive list of the relevant references where the details of modelling approaches may be found.
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    Offshore multi-purpose platforms for a Blue Growth: a technological, environmental and socio-economic review
    (Elsevier, 2020-05-15) Abhinav, K. A.; Collu, Maurizio; Benjamins, Steven; Cai, Huiwen; Hughes, Adam; Jiang, Bo; Jude, Simon; Leithead, William; Lin, Cui; Liu, Hongda; Recalde-Camacho, Luis; Serpetti, Natalia; Sung, Ke; Wilson, Ben; Yue, Hong; Zhou, Binzhen
    “Blue Growth” and “Blue Economy” is defined by the World Bank as: “the sustainable use of ocean resources for economic growth, improved livelihoods and jobs, while preserving the health of ocean ecosystem”. Multi-purpose platforms (MPPs) can be defined as offshore platforms serving the needs of multiple offshore industries (energy and aquaculture), aim at exploiting the synergies and managing the tensions arising when closely co-locating systems from these industries. Despite a number of previous projects aimed at assessing, from a multidisciplinary point of view, the feasibility of multipurpose platforms, it is here shown that the state-of-the-art has focused mainly on single-purpose devices, and adopting a single discipline (either economic, or social, or technological, or environmental) approach. Therefore, the aim of the present study is to provide a multidisciplinary state of the art review on, whenever possible, multi-purpose platforms, complementing it with single-purpose and/or single discipline literature reviews when not possible. Synoptic tables are provided, giving an overview of the multi-purpose platform concepts investigated, the numerical approaches adopted, and a comprehensive snapshot classifying the references discussed by industry (offshore renewables, aquaculture, both) and by aspect (technological, environmental, socio-economic). The majority of the multi-purpose platform concepts proposed are integrating only multiple offshore renewable energy devices (e.g. hybrid wind-wave), with only few integrating also aquaculture systems. MPPs have significant potential in economizing CAPEX and operational costs for the offshore energy and aquaculture industry by means of concerted spatial planning and sharing of infrastructure
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    On mooring line tension and fatigue prediction for offshore vertical axis wind turbines: A comparison of lumped mass and quasi-static approaches
    (SAGE, 2018-03-20) Cevasco, Debora; Collu, Maurizio; Rizzo, C. M.; Hall, M.
    Despite several potential advantages, relatively few studies and design support tools have been developed for floating vertical axis wind turbines. Due to the substantial aerodynamics differences, the analyses of vertical axis wind turbine on floating structures cannot be easily extended from what have been already done for horizontal axis wind turbines. Therefore, the main aim of the present work is to compare the dynamic response of the floating offshore wind turbine system adopting two different mooring dynamics approaches. Two versions of the in-house aero-hydro-mooring coupled model of dynamics for floating vertical axis wind turbine (FloVAWT) have been used, employing a mooring quasi-static model, which solves the equations using an energetic approach, and a modified version of floating vertical axis wind turbine, which instead couples with the lumped mass mooring line model MoorDyn. The results, in terms of mooring line tension, fatigue and response in frequency have been obtained and analysed, based on a 5 MW Darrieus type rotor supported by the OC4-DeepCwind semisubmersible.
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    Operational modal analysis of a spar-type floating platform using frequency domain decomposition method
    (MDPI, 2016-10-26) Ruzzo, Carlo; Failla, Giuseppe; Collu, Maurizio; Nava, Vincenzo; Fiamma, Vincenzo; Arena, Felice
    System identification of offshore floating platforms is usually performed by testing small-scale models in wave tanks, where controlled conditions, such as still water for free decay tests, regular and irregular wave loading can be represented. However, this approach may result in constraints on model dimensions, testing time, and costs of the experimental activity. For such reasons, intermediate-scale field modelling of offshore floating structures may become an interesting as well as cost-effective alternative in a near future. Clearly, since the open sea is not a controlled environment, traditional system identification may become challenging and less precise. In this paper, a new approach based on Frequency Domain Decomposition (FDD) method for Operational Modal Analysis is proposed and validated against numerical simulations in ANSYS AQWA v.16.0 on a simple spar-type structure. The results obtained match well with numerical predictions, showing that this new approach, opportunely coupled with more traditional wave tanks techniques, proves to be very promising to perform field-site identification of the model structures.
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    Output-only identification of rigid body motions of floating structures: a case study
    (Elsevier, 2017-09-12) Ruzzo, C.; Failla, G.; Collu, Maurizio; Nava, V.; Fiamma, V.; Arena, Felice
    In order to identify rigid body motions of floating offshore structures, output-only techniques are very useful for developing low-cost intermediate-scale experimental activities directly into the sea, instead of wave tanks. A crucial parameter, however, is the length of the response records used as input for the identification process, since short records may result in significant loss of accuracy, while long ones may be incompatible with the assumption of stationarity of the sea state. This work presents a sensitivity study conducted on a numerical model of a spar structure, identified by means of Enhanced Frequency Domain Decomposition method. An overview on the efficiency of the method is given for various lengths of response record, along with practical indications on the minimum values acceptable.
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    Progress on the experimental set-up for the testing of a floating offshore wind turbine scaled model in a field site
    (Sage, 2016-07-20) Ruzzo, Carlo; Fiamma, Vincenzo; Nava, Vincenzo; Collu, Maurizio; Failla, Giuseppe; Arena, Felice
    This document describes design and realization of a small-scale field experiment on a 1:30 model of spar floating support structure for offshore wind turbines. The aim of the experiment is to investigate the dynamic behaviour of the floating wind turbine under extreme wave and parked rotor conditions. The experiment has been going on in the Natural Ocean Engineering Laboratory of Reggio Calabria (Italy). In this article, all the stages of the experimental activity are presented, and some results are shown in terms of motions and response amplitude operators. Finally, a comparison with corresponding results obtained using ANSYS AQWA software package is shown, and conclusions are drawn. The presented experimental set-up seems promising to test offshore floating structures for marine renewable energy at a relatively large scale in the Natural Ocean Engineering Laboratory field site.
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    Reducing tower fatigue through blade back twist and active pitch-to-stall control strategy for a semi-submersible floating offshore wind turbine
    (MDPI, 2019-05-18) Ward, Dawn; Collu, Maurizio; Sumner, Joy
    The necessity of producing more electricity from renewable sources has been driven predominantly by the need to prevent irreversible climate chance. Currently, industry is looking towards floating offshore wind turbine solutions to form part of their future renewable portfolio. However, wind turbine loads are often increased when mounted on a floating rather than fixed platform. Negative damping must also be avoided to prevent tower oscillations. By presenting a turbine actively pitching-to-stall, the impact on the tower fore–aft bending moment of a blade with back twist towards feather as it approaches the tip was explored, utilizing the time domain FAST v8 simulation tool. The turbine was coupled to a floating semisubmersible platform, as this type of floater suffers from increased fore–aft oscillations of the tower, and therefore could benefit from this alternative control approach. Correlation between the responses of the blade’s flapwise bending moment and the tower base’s fore–aft moment was observed with this back-twisted pitch-to-stall blade. Negative damping was also avoided by utilizing a pitch-to-stall control strategy. At 13 and 18 m/s mean turbulent winds, a 20% and 5.8% increase in the tower axial fatigue life was achieved, respectively. Overall, it was shown that the proposed approach seems to be effective in diminishing detrimental oscillations of the power output and in enhancing the tower axial fatigue life.