Browsing by Author "Wang, Lin"
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Item Open Access Blade design optimisation for fixed-pitch fixed-speed wind turbines(Hindawi Publishing Corporation, 2012-07) Wang, Lin; Tang, Xinzi; Liu, XiongweiFixed-pitch fixed-speed (FPFS) wind turbines have some distinct advantages over other topologies for small wind turbines, particularly for low wind speed sites. The blade design of FPFS wind turbines is fundamentally different to fixed-pitch variable-speed wind turbine blade design. Theoretically, it is difficult to obtain a global mathematical solution for the blade design optimisation. Through case studies of a given baseline wind turbine and its blade airfoil, this paper aims to demonstrate a practical method for optimum blade design of FPFS small wind turbines. The optimum blade design is based on the aerodynamic characteristics of the airfoil, that is, the lift and drag coefficients, and the annual mean wind speed. The design parameters for the blade optimisation include design wind speed, design tip speed ratio, and design attack angle. A series of design case studies using various design parameters are investigated for the wind turbine blade design. The design outcomes are analyzed and compared to each other against power performance of the rotor and annual energy production. The design outcomes from the limited design cases demonstrate clearly which blade design provides the best performance. This approach can be used for any practice of FPFS wind turbine blade design and refurbishment.Item Open Access Comparative study of structural reliability assessment methods for offshore wind turbine jacket support structures(MDPI, 2020-01-26) Shittu, Abdulhakim Adeoye; Mehmanparast, Ali; Wang, Lin; Salonitis, Konstantinos; Kolios, AthanasiosOffshore wind turbines (OWTs) are deployed in harsh environments often characterized by highly stochastic loads and resistance properties, thus necessitating the need for structural reliability assessment (SRA) to account for such uncertainties systematically. In this work, the SRA of an OWT jacket-type support structure is conducted, applying two stochastic methods to predict the safety level of the structure considering various design constraints. The first method refers to a commercial finite element analysis (FEA) package (DesignXplorer© from ANSYS) which employs direct simulations and the six sigma analysis function applying Latin hypercube sampling (LHS) to predict the probability of failure. The second method develops a non-intrusive formulation which maps the response of the structure through a finite number of simulations to develop a response surface, and then employs first-order reliability methods (FORM) to evaluate the reliability index and, subsequently, the probability of failure. In this analysis, five design constraints were considered: stress, fatigue, deformation, buckling, and vibration. The two methods were applied to a baseline 10-MW OWT jacket-type support structure to identify critical components. The results revealed that, for the inherent stochastic conditions, the structural components can safely withstand such conditions, as the reliability index values were found acceptable when compared with allowable values from design standards. The reliability assessment results revealed that the fatigue performance is the design-driving criterion for structural components of OWT support structures. While there was good agreement in the safety index values predicted by both methods, a limitation of the direct simulation method is in its requirement for a prohibitively large number of simulations to estimate the very low probabilities of failure in the deformation and buckling constraint cases. This limitation can be overcome through the non-intrusive formulation presented in this work.Item Open Access Design implications towards inspection reduction of large scale structures(Elsevier, 2017-05-09) Ioannou, Anastasia; Wang, Lin; Brennan, Feargal P.Operational management is a key contributor in life cycle costs, especially for large scale assets which are in most times complex in structural hierarchy and with a large nominal service life. Decisions on the operational management may concern the number of inspections or maintenance strategies which may allow full utilization of structural capacity or sacrifice residual life in order to avoid an unscheduled intervention. Design of such assets is often governed by design standards which offer the designer the flexibility to take certain decisions that may affect the CAPEX to OPEX ratio such as that of building a more robust structure which may eliminate the need for costly inspection operations. This paper is investigating this approach, taking the example of offshore wind turbine support structures as the reference case, and examines the relevant provisions of the DNV-Os-J101 Standard with respect to the design implications that such a decision may have to the overall life-cycle cost of the structure. Assessment of the structural properties under different design conditions is evaluated through a combination of detailed cost model and an iterative optimization algorithm. The approach which is followed and documented, can be applicable to other complex structural systems for decision making through evaluation of service life costs. Paper presented at: Complex Systems Engineering and Development Proceedings of the 27th CIRP Design Conference Cranfield University, UK 10th – 12th May 2017.Item Open Access Effect of the number of blades and solidity on the performance of a vertical axis wind turbine(IOP Publishing: Conference Series / Institute of Physics (IoP), 2016-10-03) Delafin, Pierre-Luc; Nishino, Takafumi; Wang, Lin; Kolios, AthanasiosTwo, three and four bladed phgr-shape Vertical Axis Wind Turbines are simulated using a free-wake vortex model. Two versions of the three and four bladed turbines are considered, one having the same chord length as the two-bladed turbine and the other having the same solidity as the two-bladed turbine. Results of the two-bladed turbine are validated against published experimental data of power coefficient and instantaneous torque. The effect of solidity on the power coefficient is presented and the instantaneous torque, thrust and lateral force of the two-, three- and four-bladed turbines are compared for the same solidity. It is found that increasing the number of blades from two to three significantly reduces the torque, thrust and lateral force ripples. Adding a fourth blade further reduces the ripples except for the torque at low tip speed ratio. This work aims to help choosing the number of blades during the design phase of a vertical axis wind turbine.Item Open Access Evaluation of an offshore wind farm computational fluid dynamics model against operational site data(Elsevier, 2019-10-31) Richmond, Mark; Antoniadis, Antonis F.; Wang, Lin; Kolios, Athanasios; Al-Sanad, Shaikha A.; Parol, JafaraliModelling wind turbine wake effects at a range of wind speeds and directions with actuator disk (AD) models can provide insight but also be challenging. With any model it is important to quantify the level of error, but this can also present a challenge when comparing a steady-state model to measurement data with scatter. This paper models wind flow in a wind farm at a range of wind speeds and directions using an AD implementation. The results from these models are compared to data collected from the actual farm being modelled. An extensive comparison is conducted, constituted from 35 cases where two turbulence models, the standard k-ε and k-ω SST are evaluated. The steps taken in building the models as well as processes for comparing the AD computational fluid dynamics (CFD) results to real-world data using the regression models of ensemble bagging and Gaussian process are outlined. Turbine performance data and boundary conditions are determined using the site data. Modifications to an existing opensource AD code are shown so that the predetermined turbine performance can be implemented into the CFD model. Steady state solutions are obtained with the OpenFOAM CFD solver. Results are compared in terms of velocity deficit at the measurement locations. Using the standard k-ε model, a mean absolute error for all cases together of roughly 8% can be achieved, but this error changes for different directions and methods of evaluating it.Item Open Access Flexible multibody dynamics modelling of point-absorber wave energy converters(Elsevier, 2018-05-07) Wang, Lin; Kolios, Athanasios; Cui, Lin; Sheng, QihuAs an inexhaustible and environmentally-friendly energy resource, ocean wave power, which is extracted from ocean waves through WECs (wave energy converters), is highly valued by coastal countries. Compared to other types of WECs, point-absorber WECs, the main body of which can be fixed on a platform (e.g. ship), save on installation costs and therefore have concentrated significant interest among researchers and technology developers. In the development of point-absorber WECs, it is crucial to develop a reliable structural model to accurately predict the structural dynamic responses of WECs subjected to wave loadings. In this work, a FMBD (flexible multibody dynamics) model, which is a combination of MBD (multibody dynamics) and FEA (finite element analysis), has been developed for point-absorber WECs. The FMBD model has been applied to the structural modelling of the NOTC (National Ocean Technology Centre) 10 kW multiple-point-absorber WEC. The floater arm tip displacement and velocity obtained from the FMBD model are validated against the values obtained from an analytical model, which is also developed in this work. The results from the FMBD model show reasonable agreement with those from the analytical model, with a relative difference of 10.1% at the maximum value of the floater arm tip displacement. The FMBD model is further used to calculate the stress distributions, fatigue life, deformations, modal frequencies and modal shapes of the structure. The results indicate that WECs are prone to experience fatigue failure, with the shortest fatigue life (2 years) observed in the floater arm. The FMBD model developed in this work is demonstrated to be capable of accurately modelling point-absorber WECs, providing valuable information for designers to further optimise the structure and assess the reliability of WECs.Item Open Access Fluid structure interaction modelling of horizontal-axis wind turbine blades based on CFD and FEA(Elsevier, 2016-09-17) Wang, Lin; Quant, Robin; Kolios, AthanasiosThe increasing size and flexibility of large wind turbine blades introduces considerable aeroelastic effects, which are caused by FSI (fluid structure interaction). These effects might result in aeroelastic instability problems, such as edgewise instability and flutter, which can be devastating to the blades and the wind turbine. Therefore, accurate FSI modelling of wind turbine blades is crucial in the development of large wind turbines. In this study, an FSI model for wind turbine blades at full scale is established. The aerodynamic loads are calculated using a CFD (computational fluid dynamics) model implemented in ANSYS FLUENT, and the blade structural responses are determined using a FEA (finite element analysis) model implemented in ANSYS Static Structural module. The interface of CFD and FEA is based on a one-way coupling, in which aerodynamic loads calculated from CFD modelling are mapped to FEA modelling as load boundary conditions. Validated by a series of benchmark computational tests, the one-way FSI model was applied to the modelling of WindPACT 1.5 MW wind turbine blade, a representative large-scale horizontal-axis wind turbine blade. Five operational conditions are assessed, with the worst case found to be near the rated wind speed. Maximum tensile/compressive stresses and tip deflections in each case are found to be within material and structural limits, according to relevant design standards.Item Open Access Integrated structural optimisation of offshore wind turbine support structures based on finite element analysis and genetic algorithm(Elsevier, 2017-05-09) Gentils, Theo; Wang, Lin; Kolios, AthanasiosBy accounting for almost 25% of the capital cost of an OWT (offshore wind turbine), optimisation of support structures provides an efficient way to reduce the currently high cost of offshore wind energy. In this paper, a structural optimisation model for OWT support structures has been developed based on a coupled parametric FEA (Finite Element Analysis) and GA (Genetic Algorithm), minimising the mass of the support structure under multi-criteria constraints. Contrary to existing optimisation models for OWT support structures, the proposed model is an integrated structural optimisation model, which optimises the components of the support structure (i.e. tower, transition piece, grout and monopile) simultaneously. The outer diameters and section thicknesses along the support structure are chosen as design variables. A set of constraints based on multi-criteria design assessment is applied according to standard requirements, which includes vibration, stress, deformation, buckling, fatigue and design variable constraints. The model has been applied to the NREL (National Renewable Energy Laboratory) 5 MW OWT on an 00 (Offshore Code Comparison Collaboration) monopile. The results of the application of the integrated optimisation methodology show a 19.8% reduction in the global mass of the support structure while satisfying all the design constraints. It is demonstrated that the proposed structural optimisation model is capable of effectively and accurately determining the optimal design of OWT support structures, which significantly improves their design efficiency. (C) 2017 Elsevier Ltd. All rights reserved.Item Open Access Parametric FEA modelling of offshore wind turbine support structures: towards scaling-up and CAPEX reduction(Elsevier, 2017-05-26) Martinez-Luengo, Maria; Kolios, Athanasios; Wang, LinParametric Finite Element Analysis (FEA) modelling is a powerful design tool often used for offshore wind. It is so effective because key design parameters (KDPs) can be modified directly within the python code, to assess their effect on the structure’s integrity, saving time and resources. A parametric FEA model of offshore wind turbine (OWT) support structures (consisting of monopile (MP), soil-structure interaction, transition piece (TP), grouted connection (GC) and tower) has been developed and validated. Furthermore, the different KDPs that impact on the design and scaling-up of OWT support structures were identified. The aim of the analyses is determining how different geometry variations will affect the structural integrity of the unit and if these could contribute to the turbine’s scale-up by either modifying the structure’s modal properties, improving its structural integrity, or reducing capital expenditure (CAPEX). To do so, three design cases, assessing different KDPs, have been developed and presented. Case A investigated how the TP’s and GC’s length influences the structural integrity. Case B evaluated the effect of size and number of stoppers in the TP, keeping a constant volume of steel; and Case C assessed the structure’s response to scour development. It is expected that this paper will provide useful information in the conceptual design and scale-up of OWT support structures, helping in the understanding of how KDPs can affect not only the structure’s health, but also its CAPEX.Item Open Access Reliability assessment of point-absorber wave energy converters(Elsevier, 2018-06-04) Kolios, Athanasios; Di Maio, Loris Francesco; Wang, Lin; Cui, Lin; Sheng, QihuOcean wave energy is a clean and inexhaustible energy resource, capable of providing more than 2 TW of energy supply worldwide. Among all the technologies available to convert wave energy, the point-absorber is one of the most promising solutions today, due to its ease of both fabrication and installation. The floaters of point-absorber WECs (wave energy converters) are generally exposed to harsh marine environments with great uncertainties in environmental loads, which make their reliability assessment quite challenging. In this work, a reliability assessment framework, which combines parametric finite element analysis (FEA) modelling, response surface modelling and reliability analysis, has been developed specifically for the floater of point-absorber WECs. An analytical model of point-absorber WECs is also developed in this work to calculate wave loads and to validate the developed FEA model. After the validation through a series of simulations, the reliability assessment framework has been applied to the NOTC (National Ocean Technology Centre) 10 kW multiple-point-absorber WEC to assess the reliability of the floater, considering the fatigue limit state (FLS). Optimisation of key design components is also performed based on reliability assessment in order to achieve target reliability. The results show that for the considered conditions, the WEC floater is prone to experience fatigue failure before the end of their nominal service life. It is demonstrated that the reliability assessment framework developed in this work is capable of accurately assessing the reliability of WECs and optimising the structure on the basis of reliability.Item Open Access State of the art in the aeroelasticity of wind turbine blades: Aeroelastic modelling(Elsevier, 2016-06-22) Wang, Lin; Liu, Xiongwei; Kolios, AthanasiosWith the continuous increasing size and flexibility of large wind turbine blades, aeroelasticity has been becoming a significant subject for wind turbine blade design. There have been some examples of commercially developed wind turbines experiencing aeroelastic instability problems in the last decade, which spokes for the necessity of aeroelastic modelling of wind turbine blades. This paper presents the state-of-the-art aeroelastic modelling of wind turbine blades, provides a comprehensive review on the available models for aerodynamic, structural and cross-sectional analysis, discusses the advantages and disadvantages of these models, and outlines the current implementations in this field. This paper is written for both researchers new to this research field by summarising underlying theory whilst presenting a comprehensive review on the latest studies, and experts in this research field by providing a comprehensive list of relevant references in which the details of modelling approaches can be obtained.Item Open Access Structural health monitoring of offshore wind turbines: A review through the Statistical Pattern Recognition Paradigm(Elsevier, 2016-06-09) Martinez-Luengo, Maria; Kolios, Athanasios; Wang, LinOffshore Wind has become the most profitable renewable energy source due to the remarkable development it has experienced in Europe over the last decade. In this paper, a review of Structural Health Monitoring Systems (SHMS) for offshore wind turbines (OWT) has been carried out considering the topic as a Statistical Pattern Recognition problem. Therefore, each one of the stages of this paradigm has been reviewed focusing on OWT application. These stages are: Operational Evaluation; Data Acquisition, Normalization and Cleansing; Feature Extraction and Information Condensation; and Statistical Model Development. It is expected that optimizing each stage, SHMS can contribute to the development of efficient Condition-Based Maintenance Strategies. Optimizing this strategy will help reduce labor costs of OWTs׳ inspection, avoid unnecessary maintenance, identify design weaknesses before failure, improve the availability of power production while preventing wind turbines׳ overloading, therefore, maximizing the investments׳ return. In the forthcoming years, a growing interest in SHM technologies for OWT is expected, enhancing the potential of offshore wind farm deployments further offshore. Increasing efficiency in operational management will contribute towards achieving UK׳s 2020 and 2050 targets, through ultimately reducing the Levelised Cost of Energy (LCOE).Item Open Access Structural optimisation of vertical-axis wind turbine composite blades based on finite element analysis and genetic algorithm(Elsevier, 2016-06-02) Wang, Lin; Kolios, Athanasios; Nishino, Takafumi; Delafin, Pierre-Luc; Bird, TheodoreA wind turbine blade generally has complex structures including several layers of composite materials with shear webs, making its structure design very challenging. In this paper, a structural optimisation model for wind turbine composite blades has been developed based on a parametric FEA (finite element analysis) model and a GA (genetic algorithm) model. The optimisation model minimises the mass of composite blades with multi-criteria constraints. The number of unidirectional plies, the locations of the spar cap and the thicknesses of shear webs are taken as design variables. The optimisation model takes account of five constraints, i.e. stress constraint, deformation constraint, vibration constraint, buckling constraint, and manufacturing manoeuvrability and continuity of laminate layups constraint. The model has been applied to the blade structural optimisation of ELECTRA 30 kW wind turbine, which is a novel VAWT (vertical-axis wind turbine) combining sails and V-shape arm. The mass of the optimised blade is 228 kg, which is 17.4% lower than the initial design, indicating the blade mass can be significantly reduced by using the present optimisation model. It is demonstrated that the structural optimisation model presented in this paper is capable of effectively and accurately determining the optimal structural layups of composite blades.Item Open Access Viscoelastic solid-repellent coatings for extreme water saving and global sanitation(Nature Research, 2019-11-18) Wang, Jing; Wang, Lin; Sun, Nan; Tierney, Ross; Li, Hui; Corsetti, Margo; Williams, Leon; Wong, Pak Kin; Wong, Tak-SingWater scarcity threatens over half of the world’s population, yet over 141 billion litres of fresh water are used globally each day for toilet flushing. This is nearly six times the daily water consumption of the population in Africa. The toilet water footprint is so large primarily because large volumes of water are necessary for the removal of human faeces; human faeces is viscoelastic and sticky in nature, causing it to adhere to conventional surfaces. Here, we designed and fabricated the liquid-entrenched smooth surface (LESS)—a sprayable non-fouling coating that can reduce cleaning water consumption by ~90% compared with untreated surfaces due to its extreme repellency towards liquids, bacteria and viscoelastic solids. Importantly, LESS-coated surfaces can repel viscoelastic solids with dynamic viscosities spanning over nine orders of magnitude (that is, three orders of magnitude higher than has previously been reported for other repellent materials). With an estimated 1 billion or more toilets and urinals worldwide, incorporating LESS coating into sanitation systems will have significant implications for global sanitation and large-scale wastewater reduction for sustainable water management.