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Researchers often explore metaheuristic algorithms for their studies. These algorithms possess unique features for solving optimization problems and are usually developed on the basis of real-world natural phenomena or animal and insect behavior. Numerous fields have benefited from metaheuristic algorithms for solving real-world optimization problems. As a renewable energy source, offshore wind energy is a rapidly developing subject of research, attracting considerable interest worldwide. However, designing offshore wind turbine systems can be challenging because of the large space of design parameters and different environmental conditions, and the optimization of offshore wind turbines can be extremely expensive. Nevertheless, advanced optimization methods can help to overcome these challenges. This study explores the use of metaheuristic algorithms in optimizing the design of wind turbines, including wind farm layout and wind turbine blades. Given that offshore wind energy relies more heavily on subsidies than fossil fuel-based energy sources, lowering the costs for future projects, particularly by developing new technologies and optimizing existing methods, is crucial. [ABSTRACT FROM AUTHOR]

Purpose: Predicting the dynamic response at unmeasured locations is of great interest in the study of structural dynamic systems to address limitations of number of available sensors and inaccessibility of measurements in enclosed or hazardous environments. Dynamic response at measured points on a structure can be expanded to predict response for unmeasured points through model-based expansion, but this approach requires a correlated (or calibrated) finite element model. To avoid finite element model dependency and the need for correlation, model-free dynamic response prediction techniques have been proposed for plate-type structures and cylindrical-shell structures. However, a limitation of those techniques is that only the 1D (one-dimensional) dynamic response along one direction of the 2D (two-dimensional structure) could be studied using the developed shape functions. Methods: In this work, we present a model-free method that overcomes these limitations in order to predict the 3D dynamic response for unmeasured locations for complicated three-dimensional structures. This work develops a new model-free method based on three-dimensional Chebyshev polynomial shape functions for predicting the 3D dynamic response of the three-dimensional utility structures. The method is based on orthogonal Chebyshev polynomials as shape functions to decompose the physical dynamic response of the measurement points into a set of polynomial dynamic response. The expansion is performed within the polynomial space from measurement points to the measurement points plus the unmeasured point. Then, the expanded polynomial space is mapped back to physical space to obtain the physical dynamic response at the unmeasured point. The advantage of the proposed method is that only the measured dynamic response data and geometric coordinates of the measurement points are needed. Namely, in this advantage, the external excitation applied to the structures and the boundary condition of the structures are not required to be quantified or known. Results and Conclusions: An accelerometer-based test and high-spatial-resolution 3D scanning laser Doppler vibrometer (SLDV) test on a wind turbine blade provide test data used to experimentally validate the application of the proposed method of predicting the three-dimensional dynamic response on the three-dimensional structures. Convergence studies are performed to evaluate the impact of the number of measurement points and the location of measurement points on the accuracy of the method. [ABSTRACT FROM AUTHOR]

The flammability levels, flame retardancy ratings, and reaction-to-fire (fire response) properties (under five radiant heat fluxes, i.e., 15, 25, 35, 50, and 75 kW m−2) for same real E-glass fiber-reinforced unsaturated polyester resin (UPR) composite wind turbine blade (WTB) samples were determined by experimental techniques like limiting oxygen index (LOI), vertical flame test (VFT), and cone calorimeter test (CCT). Based on typical CCT results (main test parameters), thermal and non-thermal hazard assessment index systems were selected, calculated, and compared to deduce corresponding hazard characteristics of the blade samples. The WTB shows a LOI value of 25.10% (combustible) and a non-rated (NR) UL (Underwriters Laboratories) 94 classification according to the after-flame time criterion. CCT analyses indicate that higher external heat fluxes correspond to increased peak heat release rate (PkHRR), total heat release (THR), and mass loss rate (MLR) values, and reduced ignition time (tig), flame duration (tfl), and overall flame (combustion) duration (FD) values. Meanwhile, CCT analyses indicate that higher external heat fluxes result in elevated specific extinction area (SEA), rate of smoke released (RSR), total smoke released (TSR), CO yield (COY), and CO production rate (COP) values, and relatively lower CO2 yield (CO2Y) and CO2 production rate (CO2P) values. These results reflect real WTB fires will pose severe situations with noticeable thermal and non-thermal hazards. Multiple physical and chemical evolution processes undergo in burning processes of such fires with higher PkHRR values through heat releases, transfers, exchanges, and feedback. Composite blade materials may be largely deformed and disintegrated in faster rates. Burning blade blocks may form spotting fires and cause secondary ground fires. Local air quality, visibility levels, working, and health conditions of related persons may be worsened. It is really urgent to develop mature, effective, novel, and even revolutionary fire protection and suppression technologies for such fires. [ABSTRACT FROM AUTHOR]

In order to solve the end-effector force control response speed hysteresis and mechanical vibration problems caused by parameter perturbations and other disturbances during the processing of wind turbine blades by polishing robots, this paper proposes a robot pneumatic end-effector polishing force control strategy based on adaptive sliding mode backstepping algorithm. Based on the establishment of the mathematical model of the end-effector pneumatic system, a smooth and continuous sliding mode control law is adopted to solve the design conflict between sliding mode control theory and backstepping method, and to suppress output chattering in sliding mode control. By utilizing the insensitivity of the sliding mode control to the system model, the influence of matching disturbances on the system is eliminated. The non-matching disturbances of the known model are accurately compensated by backstepping control, and parameter uncertainty is effectively handled by adaptive control. Simulation and experimental results show that this method can effectively solve the uncertainty of system parameters and has good disturbance suppression ability, significantly improving the surface quality of wind turbine blades. [ABSTRACT FROM AUTHOR]

This work concentrates on the design parameters of a turbine blade for a small-scale solar chimney plant. The pitch angle (θ), relative wind angles (ϕ and ψ), lift force (FL) and relative chord length (lcr) of the turbine blade are determined. Betz and Bernoulli's theories were used for estimating and optimizing the above blade parameters. The coefficients of power, drag, lift and thrust forces are estimated and analyzed. Two wind speeds were considered. One represented higher speed (10 m/s) and the other for lower speed (2 m/s). At 10 m/s, the required rotor diameter is drastically reduced for producing the same power output. At 2 m/s, θ, ϕ, ψ and FL were optimized and they are; θ = 18.4°, ϕ = 26.4°, ψ = 75.6° and FL = 0.0073 N for maintaining the maximum power (P) of 0.026 W. The required diameter for the rotor blade is estimated and is varied from 0.66 to 6.56 m for producing a power range of 1–100 W. At 10 m/s, the optimized parameters are; θ = 42.9°, ϕ = 50.94° and ψ = 20.39° and FL = 0.4082 N for reaching the maximum P of 2.538 W. The estimated results were validated with existing studies and observed a good match. [ABSTRACT FROM AUTHOR]

The core of the modern lightweight wind turbine blade may be a truss structure based on carbon-fiber rods connected to stiff ribs. A specialized robot manufactures these structures by spatially winding impregnated carbon fibers around pre-positioned ribs with cutouts for securing the fiber bundle. Quantity of the ribs, their positions, and positions of the rods can vary, making this type of blades well-suited for optimization. We present an optimization approach for designing the core of a lightweight wind turbine blade. Our approach involves dividing the task into two stages and utilizing multiple optimization algorithms at each stage. Proposed approach used the FUD, DAJA, and Evolution Strategy algorithms. To test the approach, an existing blade structure with known characteristics was used. Comparison of the resulting design with the original one reveals 53 percent smaller value of objective function. These results demonstrate the effectiveness of applying the proposed approach. New approach allows for the optimization of complex rod with ribs' structures that cannot be optimized using standard optimization method. This will hopefully result in a significant decrease of wind turbine production cost. [ABSTRACT FROM AUTHOR]

This study employed experimental methods to systematically investigate the bending behavior of composite materials at high temperatures. The biaxial warp-knitted fabric (BWKC) and quadaxial warp-knitted fabric (QWKC) were selected as reinforcement and the mixture solution of epoxy resin and curing agent were selected as matrix. The composite specimen was fabricated by vacuum assisted resin film (VARI). Taking into influence of temperature on the bending behavior of composites for wind turbine blades, further investigations have been conducted to analyze the influence of temperature on the mechanical properties of composites. The quasi-bending behavior of BWKC and QWKC in 0°–90°directions at different service temperatures (20℃, 45℃ and 70℃) were analyzed at macro-scale and micro-scale. Results show that the bending strength and modulus were decreased with the increase of temperature. The ultimate normalized strength of BWKC and QWKC composites were decreased by 20.36–23.56%. The behavior such as the stress–strain curves were also obtained. The relationships between bending behavior and temperatures are also obtained by nonlinear fitting with the experimental data, which could be used to predict the bending properties at different temperatures. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the co-pyrolysis properties of epoxy resin and polyurethane, which are the main components of retired wind turbine blades. Methods: Pyrolysis experiments were carried out using TG/MS and Py-GC/MS techniques to reveal possible synergistic effects in the co-pyrolysis process. The key pyrolysis conditions such as pyrolysis temperature, raw material mixing ratio and ramp rate were investigated. Results: At a lower pyrolysis temperature of 500 °C and a higher heating rate of 10 °C/ms, the mixed pyrolysis of waste epoxy resin with polyurethane significantly promoted the formation of pyrolysis oil while inhibiting the formation of small molecule gaseous products. The kinetic results also showed that the synergistic effect between epoxy resin and polyurethane significantly reduced the apparent activation energy of the pyrolysis reaction, thus reducing the temperature required for complete pyrolysis of the feedstock. Conclusion: Based on the experimental results, reasonable pathways and synergistic mechanisms for the co-pyrolysis of epoxy resin and polyurethane are proposed. The present work contributes to the conversion of waste epoxy resin and polyurethane components into high quality pyrolysis oil, thus realizing clean disposal and resource utilization of wind turbine blade waste. [ABSTRACT FROM AUTHOR]

Purpose: With the development of large-scale wind turbine, the blade has become longer and flexible. The flutter of blades has an important effect on blade failure. Methods: Inspired by birds, the V-stripe structure on the wings of typical birds has been extracted and used for blade to improve the flutter of blade. The width, depth-to-diameter ratio and spacing of V-stripe have been taken as the main parameters, and been optimized by orthogonal experiment based on numerical simulation. The optimized V-stripe has the following parameters. The width is 2 mm, the depth-to-diameter ratio is 3, and the spacing is 2 mm. Then, the V-strip structure with optimal parameters has been reconstructed on the web of wind turbine blade. The comparative study of deformation between the prototype blade and the bionic blade has been conducted by numerical simulation. Results: Compared with the prototype blade, when the bionic blade flutter occurs, the V-shaped stripe web is continuously subjected to pressure and tension, and the energy of the blade flutter is continuously dissipated, resulting in the flutter displacement and flutter speed of the wind turbine blade decreasing. Conclusion: Compared with prototype blade, the bionic blade with V-striped web has anti-flutter properties, and the flutter displacement and speed of wind turbine blade have been reduced. [ABSTRACT FROM AUTHOR]

This article aims to evaluate the performance of a blade prototype made of composite materials in terms of stiffness and mechanical strength. In this purpose, series of load levels will be applied to the blade in the direction of flapwise and edgewise loading to characterize strength and stiffness of the structure which is degrades as a function of the loading rate and the number of cycles. A test bench has been designed and built in the laboratory to test a blade of 712 mm in length for fatigue. The results of this experiment will be used to assess the structural integrity of the blades during their manufacturing process. [ABSTRACT FROM AUTHOR]

In most full-scale fatigue tests of wind turbine blades, only longitudinal strains are considered in the calculation of damage, while the effects of transverse and tangential strains are ignored, which will lead to varied damage inflicted on different parts of the blade. To analyze this problem, this paper conducted uniaxial and biaxial fatigue tests on a 52.5-meter wind turbine blade and recorded the strain response at each cross section. The test results show that transverse and tangential strains are greater than longitudinal strains in some cross sections of the blade. Then, a cross section of the blade was modeled and simulated using ABAQUS to analyze the strain relationships at other locations on the blade. The strain response at different locations on the blade was also examined, and the simulation results showed that both the transverse and longitudinal strain values for this cross section varied significantly. In addition, the multiaxial strain varies greatly with different loading methods. The strain pattern in the trailing edge panel region is very complex. Therefore, the damage calculation and life prediction of the blade should consider the effect of multiaxial strain, which provides a powerful reference for the subsequent improvement of the multiaxial fatigue damage calculation method and the design of the fatigue test program for large wind turbine blades. [ABSTRACT FROM AUTHOR]

Usually, only one surface or one side of 3D structures is measured in Scanning Laser Doppler Vibrometer (SLDV) tests due to test setup and instrumentation limitations. However, in this work, we demonstrate an approach to overcome these limitations while also using an SLDV that provides high spatial resolution measurement. In the case of a wind turbine blade, only one surface is typically measured. In most scenarios, only focusing on one surface of the blade is sufficient to characterize the dynamics of the global blade modes. However, as we show measurement of both surfaces offers valuable insights to explore both the global blade modes and the relative motions of the two surfaces of the blade. This work proposes and applies a new method of experimental modal testing on both surfaces of the wind turbine blade using a high spatial resolution 3D SLDV. The two surfaces of the wind turbine blade are scanned by the 3D SLDV respectively under the same global test coordinate system defined by several alignment objects. Then the two surfaces are stitched together to build the blade mode shapes of both surfaces. In the current testing, a total of over 1,500 points (4,500 response degrees of freedom for the 3D measurement) are scanned from both surfaces of the blade in a non-contact fashion to obtain the flap-wise, edge-wise, and torsional mode shapes of the blade. The orthogonality of the measured mode shapes, either one surface or both surfaces, is validated by the correlation tool, Modal Assurance Criterion (MAC). The effectiveness of the two-surface measurement is demonstrated by comparing the drive point Frequency Response Function and by correlating the mode shapes from the two surfaces. With the high spatial resolution 3D SLDV measurement, local panel modes of the wind turbine blade are observed from the mode shapes. Especially the panel breathing mode can only be revealed due to the two-surface measurement. This work also provides a useful reference for the wind turbine blade designers and researchers for design, structural analysis, and reliability study on the wind turbine blade. The two-surface measurement technique proposed in this work is demonstrated on a wind turbine blade, and it will also be applicable for other types of two-surface shell-type structures. [ABSTRACT FROM AUTHOR]

The utilization of wind power has increased almost exponentially during the last decade, leading to the growth in both the number and size of wind turbines. Modern turbine blades are typically made of fiberglass sandwiched around a balsa wood (BW) core. With an increase in the use of wind energy a collateral issue of what to do with the large and voluminous wind turbine blades (WTB) that reached end-of-life has arisen. Through previous research, we developed a recycling process that will keep these turbine blades out of the landfill by considering recycled wind turbine blades as a feedstock for second generation composite panels. The objective of this research is to further the research by understanding the effect that different compositions of wood and fiberglass have on the properties of these panels. Through testing, it was found that the addition of balsa wood increases the modulus of rupture (MOR) and the modulus of elasticity (MOE). The internal bonding (IB) strength values are well above that of typical particle board. All panels tested were visibly more resistant to water sorption than typical particle board. The thermal conductivity for all samples was within the typical range for particleboard. Fire test result indicates that the addition of balsa wood increases the heat and visible smoke release rate of composites. [ABSTRACT FROM AUTHOR]

The mode shapes of many beam-type structures, such as aircraft wings and wind turbine blades, involve a high degree of coupling between flap-wise and edge-wise bending deformations. In the case of wind turbine blades, the principal bending deformations (flap-wise deformation and edge-wise deformation) are typically easily recognized by visual observation. However, this visual approach is sometimes challenging for high-order mode shapes that have complex mode deformation. More importantly, visual observation cannot quantify the contribution of different deformation components for each mode. This work proposes a novel mode shape recognition algorithm, called Mode Shape Recognition Matrix (MSRM), for application to complicated spatial beam-type structures not only to identify the deformation components of the complex beam mode shapes, but more importantly, to quantify their respective relative contribution. In the application case studied for the MSRM method, a three-dimensional wind turbine blade is mapped into three-dimensional Chebyshev polynomial space. The blade mode shape is correlated to each polynomial shape function to find the contribution of each polynomial shape function for the mode shape. To validate the mode shape recognition performance, MSRM is applied on both numerical mode shapes from a fidelity blade finite element model and experimental mode shapes from a high spatial resolution 3D SLDV modal test. Both numerical and experimental studies demonstrate that MSRM can successfully recognize the quantitative contribution of flap-wise deformation and edge-wise deformation for each wind turbine blade mode shape. [ABSTRACT FROM AUTHOR]

The development of wind power industry is one of the important ways to solve current energy shortage and reduce carbon emissions. As the key component to capture wind energy, fiber-reinforced composite (FRC) wind turbine blades are subject to complex alternating loads in harsh environments. It is easy to produce various damages during long-term service, such as cracks, fiber spalling, and surface abrasion. Among them, crack is the most serious damage. FRC is a kind of composite material with obvious anisotropy, which is very sensitive to crack damage. The generation and propagation of cracks can easily lead to further failure of the whole blade, resulting in great economic losses and safety risks. How to deal with the damage of wind turbine blades in time has become a thorny problem in the wind power industry. In this paper, the current research status of the crack damage for the FRC wind turbine blade is comprehensively reviewed from the formation mechanism of crack and the detection and evaluation methods as well as the repair technologies. Finally, the development of related technologies has been prospected. [ABSTRACT FROM AUTHOR]

System identification is the main goal when performing modal testing of mechanical structures. In cases where only the structural responses are measured, the identification technique is addressed in the literature as operational modal analysis (OMA). Applications of OMA are found in structures where the excitation from the ambient can not be removed or it is the only possible one. Since the ambient forces can not be measured, the identification of the modal parameters is possible if some hypotheses about its random nature are made. In this paper, the modal identification of a small and flexible wind turbine blade is performed under the OMA framework. Although the tested structure was in laboratory condition, traditional experimental modal analysis was not possible due to the small size and high flexibility of the blade. Therefore, this paper demonstrates the importance of OMA in the modal identification of this type of structure (simultaneously light and flexible). An artificially generated wind was used instead as source of excitation, which presented good properties necessary for OMA (stationarity and broadband frequency). The stochastic subspace identification method was used to identify the modal parameters, leading to good identification in a prescribed frequency band of interest. A procedure to analyze and validate the experimental results is also given at the end. [ABSTRACT FROM AUTHOR]

Good structural performance and reliability are two key objectives in design of wind turbine blade. To improve the natural frequency of blades to avoid resonance effectively, but it also increases the weight and direct manufacturing cost of blades. To achieve the best trade-off between mass and first-order frequency of blades, this paper presents a method of structural optimization based on multi-objective genetic algorithm NSGA-II. A small wind turbine blade is taken as case study. The CFD computation is performed to obtain the aerodynamic load, and the FEM is applied to obtain structure responses. With the weight minimization and the first-order frequency maximization of the blade as two goals, the optimization model is constructed and the Pareto solution set of two goals is obtained. Compared with original scheme, the weight of the optimized blade is reduced by about 15%. On the premise of avoiding blade resonance, the solution with the weight as light as possible is selected as the design scheme. The delamination failure, buckling failure, strength failure, and other failure modes of the blade with thin airfoil are analyzed, and the results show that the delamination failure and buckling failure of the blade can be ignored temporarily. Time-varying wind speed and some mechanical parameters of composite materials are taken as random input variables. The reliabilities of the design scheme with multiple failure modes are evaluated, and the reliability sensitivity is analyzed by combining FEM, BP neural network method and Monte Carlo Simulation (MCS) method. The results show that wind speed and longitudinal elastic modulus of uniaxial fiberglass are critical influence factors for affecting reliabilities of the blade. Meanwhile, the results can also provide some references about the timing of shutting down wind turbines and the selection of composite materials. [ABSTRACT FROM AUTHOR]

A suitable material for wind turbine blades has promoted great interest in carbon-based thermoplastic polyurethane (TPU) composites as they are flexible, lightweight, and mechanically robust. However, these carbon-based fillers deteriorate the thermal and mechanical properties in the long run due to the high agglomeration of the nanoparticles. In addition to that, these fillers also increase the production cost because of the chemical treatment conducted on the fillers. Therefore, a new approach is essential for maintaining the mechanical and thermal properties without using expensive chemical treatment in a low-cost platform. In this work, we present low agglomeration with even distribution of reinforcing fillers in the TPU matrix and robust mechanical and thermal properties by incorporating TiO2 in the carbon-based TPU matrix (TiO2/MWCNT/TPU), without inclusion of costly chemical treatments. TiO2 improves morphology due to the low valency of Ti2+, which may decrease the particle size and thus, reduces agglomeration. Moreover, the enhanced morphology assists in sustaining the rigidity of its molecular structure at high temperatures. The composite also reveals excellent mechanical properties of high tensile stress (4.46 MPa), more extended elongation at break (49%), and high Young's Modulus (9.17 MPa). The thermal analysis using DMA and TGA revealed that the sample TiO2/MWCNT/TPU is a good heat insulator and has a high glass transition temperature compared to the neat TPU indicating its ability to sustain rigidity at high temperatures overall, this composite can perform in elevated weather conditions. [ABSTRACT FROM AUTHOR]

Purpose: The main goal of this work is to evaluate the environmental impact of a 63-m blade for wind generators. The embodied energy and the carbon footprint are used as supporting tools for material selection in the initial project stages. Methods: Real industrial data regarding the most used materials for wind turbine blade construction are used. Two eco-parameters, embodied energy and carbon footprint, were calculated from each selected material together with values of manufacture, transport, use, and final disposal. The blades must be built to have a mechanical strength high enough to withstand vibrations caused by manufacturing flaws, turbulence, or irregular loading. In this sense, Young's modulus, yield strength, and density were compared to the environmental footprint data to support the final material choice. This evaluation process of the possible materials to be used in the blade manufacture was carried out in the initial stages of the project. Results: Composite materials such as glass fiber-reinforced polymer (GFRP) and carbon fiber-reinforced polymer (CFRP), bonded together with an adhesive material, are used to build modern wind turbine blades. Those composites comprise a considerable number of different materials that can be mixed to reach adequate performance. Comparisons were made with 46 pre-selected materials, considering the mechanical behavior and environmental impacts. The final selected materials have better properties than the reference material. Finally, two materials with the desired mechanical properties and with a potential lower negative environmental impact than the reference material were selected. Conclusions: Replacing the reference resin—epoxy/E-glass fiber—with the epoxy resin with the lowest environmental impact—epoxy/S-glass fiber—will reduce the total value of the environmental load to 102 GJ of energy and 3.4 t of CO2. As important as the material selection in the early stages of product development is the end of life (EoL) choice. In this case, the glass fiber has an EoL potential of 370 GJ of energy and 460 t of CO2 in the remanufacturing option, against zero for the landfill. This work shows that carefully selected raw materials and EoL alternatives for WTB can significantly reduce the environmental impact of this component. [ABSTRACT FROM AUTHOR]

Energy conservation is one of the most challenging issues throughout the world. As consumers demand alternatives to fossil fuel, the use of alternative energy sources including wind energy is increasing. With an increase in the use of wind energy a collateral issue of what to do with the large and voluminous wind turbine blades (WTB) has arisen. Currently, there are no economically viable recycling pathways for damaged or end-of-life WTBs, which are made primarily of glass fiber composites. This research evaluates an economically viable composite fabrication system using mechanically recycled WTB (rWTB) material as a feedstock for thermoplastic composites. The WTB material was first mechanically milled and classified through a range of varying screen sizes. We then blended this with high density polyethylene (HDPE) thermoplastic resin and extruded it to a profiled composite. We determined the influence of refined particle size, resin content and coupling agents [maleic anhydride polyethylene (MAPE) and methacryloxypropyltriethoxysilane (Silane)] on the properties of recycled composites. We also obtained static bending, coefficient of linear thermal expansion (CLTE) and water sorption properties for all composites. Overall improvement of mechanical and physical properties of composites achieved by using MAPE as a coupling agent. Findings show that mechanical recycling of wind turbine blades is a feasible and promising way to fabricate a high-performance second-generation composite. [ABSTRACT FROM AUTHOR]

Most wind turbine blades are assembled piece-by-piece onto the hub of a monopile-type offshore wind turbine using jack-up crane vessels. Despite the stable foundation of the lifting cranes, the mating process exhibits substantial relative responses amidst blade root and hub. These relative motions are combined effects of wave-induced monopile motions and wind-induced blade root motions, which can cause impact loads at the blade root's guide pin in the course of alignment procedure. Environmental parameters including the wind-wave misalignments play an important role for the safety of the installation tasks and govern the impact scenarios. The present study investigates the effects of wind-wave misalignments on the blade root mating process on a monopile-type offshore wind turbine. The dynamic responses including the impact velocities between root and hub in selected wind-wave misalignment conditions are investigated using multibody simulations. Furthermore, based on a finite element study, different impact-induced failure modes at the blade root for sideways and head-on impact scenarios, developed due to wind-wave misalignment conditions, are investigated. Finally, based on extreme value analyses of critical responses, safe domain for the mating task under different wind-wave misalignments is compared. The results show that although misaligned wind-wave conditions develop substantial relative motions between root and hub, aligned wind-wave conditions induce largest impact velocities and develop critical failure modes at a relatively low threshold velocity of impact. [ABSTRACT FROM AUTHOR]

Due to the surface protection structure of wind turbine blades, coating plays a key role in ensuring the surface quality of blades and improving the working performance of wind turbine. In this paper, a simplified method of finite element simulation on blade coating of wind turbine is carried out by means of theoretical analysis and computer software simulation. The influence of particle erosion velocity, mass flow rate and particle diameter was made clear on the coating erosion. This will provide a theoretical reference for improving the cover technique of wind turbine blade coating and improving the coating reliability. [ABSTRACT FROM AUTHOR]

Failure analysis of a fractured high strength bolt used in a MW Class wind turbine blade connection system was conducted to clarify the failure cause and to determine the prevention method. Applying detailed mechanical characteristics and metallurgical investigations, the bolts failure cause can be attributed to bending fatigue. Evidenced by the nut polished markings, insufficient tightening was considered as the important reason for the bolt failure. The thread microstructure indicated that the fractured bolt thread was rolled rather than machined. However, rolling induced cracks locating on the thread crest and non-uniformly distributed decarburized layer on the bolt thread root existed. Thus, it can be concluded that the bolt failure was caused by the insufficient tightening and improper manufacturing procedure. [ABSTRACT FROM AUTHOR]

Full-scale fatigue test is an effective method for validating the fatigue performance of wind turbine blade. Its primary problem is how to design the test load. The conventional approach to determine test load requires a complicated and time-consuming process. Thus, a simplified method for directly converting load spectrum of blade into test load is proposed in this paper. Firstly, beam theory is used to obtain the relationship between stress, strain and bending moment of blade cross section. Based on the assumption of local stress concentration and linear relationship between stress and strain, M-N curves (applied moment vs. allowable number of cycles to failure) is defined. Secondly, based on Miner's linear cumulative damage theory and constant life diagram, the equivalent fatigue cumulative damage of load spectrum which is equal to the damage of full-scale fatigue test is obtained. Then, in the case of the selected test load ratio and cycles, the mean and amplitude of test load can be solved. Finally, the validity of the proposed method is verified by an illustrative example. The result indicates that the error of the calculated results between this method and the traditional method is close to 5 %, and it can be used for fatigue test and improve the efficiency of test load design. [ABSTRACT FROM AUTHOR]

In this study, we optimized thick airfoils for wind turbines using a genetic algorithm (GA) coupled with computational fluid dynamics (CFD) and geometric parameterization based on the Akima curve fitting method. Complex and separated flow fields around the airfoils of each design generation were obtained by performing Reynolds-averaged Navier-Stokes steady flow simulation based on the in-house code of an implicit high-resolution upwind relaxation scheme for finite volume formulation. Airfoils with 40 % and 35 % thickness values were selected as baseline airfoils. An airfoil becomes thicker toward the blade root area, thereby increasing blade stiffness and lowering its aerodynamic efficiency. We optimized the airfoils to simultaneously maximize aerodynamic efficiency and blade thickness. The design variables and objective function correspond to the airfoil coordinates and the lift-to-drag ratio at a high angle of attack with airfoil thickness constraints. We improved the lift-to-drag ratio by 30 %~40 % compared with the baseline airfoils by performing optimization using GA and CFD. The improved airfoils are expected to achieve a 5 %~11 % higher torque coefficient while minimizing the thrust coefficient near the blade root area. [ABSTRACT FROM AUTHOR]

The parameter sensitivities affecting the flutter speed of the NREL (National Renewable Energy Laboratory) 5-MW baseline HAWT (horizontal axis wind turbine) blades are analyzed. An aeroelastic model, which comprises an aerodynamic part to calculate the aerodynamic loads and a structural part to determine the structural dynamic responses, is established to describe the classical flutter of the blades. For the aerodynamic part, Theodorsen unsteady aerodynamics model is used. For the structural part, Lagrange’s equation is employed. The flutter speed is determined by introducing “V-g” method to the aeroelastic model, which converts the issue of classical flutter speed determination into an eigenvalue problem. Furthermore, the time domain aeroelastic response of the wind turbine blade section is obtained with employing Runge-Kutta method. The results show that four cases (i.e., reducing the blade torsional stiffness, moving the center of gravity or the elastic axis towards the trailing edge of the section, and placing the turbine in high air density area) will decrease the flutter speed. Therefore, the judicious selection of the four parameters (the torsional stiffness, the chordwise position of the center of gravity, the elastic axis position and air density) can increase the relative inflow speed at the blade section associated with the onset of flutter. [ABSTRACT FROM AUTHOR]

The flatback airfoil effect on the inboard region of a large wind turbine blade was investigated by numerical analysis. Complicated flow phenomena in wind turbine blade with flatback and non-flatback airfoil were captured by Reynolds-averaged Navier-Stokes flow simulation with shear stress transport turbulence model. Although both airfoil blades were designed using blade element momentum theory to produce identical shaft power, results of three-dimensional computational fluid dynamics (CFD) flow analysis indicated that at a specific location of the root area, the flatback airfoil improved the inboard force by approximately 6 % compared with the non-flatback airfoil. We were also able to confirm that by using the flatback airfoil, the overall shaft power throughout the blade increased by 1 %, thereby restraining the bending moment exerted by the thrust force on the hub by 0.5 %. Moreover, numerical analysis results indicated that the flatback airfoil blade reduced the size of the secondary vortex around the blade root area and its progress in the secondary direction in comparison with the non-flatback airfoil blade. The shape of the flatback airfoil on the trailing edge weakened the adverse pressure gradient migrating from the lower to the upper surface. Regardless of the flatback airfoils, the tip vortex core of the outboard region formed on the suction surface leading edge and strongly rolled up by the pressure surface boundary layers due to the large pressure difference between the suction and pressure surfaces in the blade tip region. This remarkable strong tip vortex developed downstream and raked up the boundary layer of the blade trailing edge with low energy. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study is to investigate the effect of piezoelectric actuator patch size and material on the active vibration control of wind turbine blades.Methods: This work builds on a recently developed numerical technique to reduce vibrations in wind turbine blades. Control action is achieved by bonding a piezoelectric actuator on the upper surface of the blade and a similar piezoelectric sensor on the blade’s lower surface. An approximate analytical method is used to solve the governing equations to obtain dynamic characteristics of the smart blade. Modal coordinates are used to obtain the model in state space form, then a linear quadratic regulator controller is used to provide active control.Results: The system is solved for different piezoelectric patch sizes and materials. Results show that increasing the values of piezoelectric stress/charge (e31) increases both the maximum blade displacement and required actuation force.Conclusions: Using piezoelectric patches with reduced (e31) can effectively decrease blade vibrations. [ABSTRACT FROM AUTHOR]

This paper reports the development of a vibration monitoring system for wind turbine blades. This system is used to estimate the deflection at the tip blade on a wind turbine tower. Technical accidents of wind turbine blades have become increasingly common. Thus, regular monitoring of the blades is very important to prevent breakdowns, especially in cases when the blades begin to vibrate excessively. The monitoring system developed in this study satisfies two main objectives for practicality. First, our system is easy to install on existing wind turbines. Second, blade deflection is measured in real time. Our system can be operated using a few strain gages attached at the blade root, and the deflection is calculated based on the monitored stress. Thus, direct measurement of deflection at the blade tip is unnecessary. An estimation algorithm for this purpose is adopted based on the experimental modal analysis. This paper focuses on the evaluation of the estimation algorithm to investigate the feasibility of our system. Basic experiments were conducted using a simple blade model of a 300 W scaled wind turbine under rotation. Signals from the strain gages were acquired by a sensor network and sent to a computer through a wireless connection. The results show that the estimation accuracy is acceptably high. Therefore, we conclude that our proposed system is practical. [ABSTRACT FROM AUTHOR]

Aiming at the Megawatt (MW) scale wind turbine, a dynamic analysis and simulation method is presented to research blade loads and dynamic characteristics. To consider blade flexible deformation, the whole blade was divided into a number of units. Each unit was treated as a rigid body, the flexible connection between two adjacent units is considered. A nacelle coordinate system, a rotating shaft coordinate system, and a blade coordinate system were employed to describe the wind turbine blade. In those coordinate systems, blade inertial load calculation model, centrifugal force load calculation model and gravity load calculation model are established. Combining load model with the whole model of wind turbines, the real-time dynamic simulation model of blade loads was established in Simulink circumstance and a numerical simulation was performed. Based on the simulation analysis, some research results were obtained. When the large instantaneous fluctuation of electromagnetic torque of generator happens, rotor speed does not appear to have large fluctuation due to the inertia of the wind rotor, but the blade vibration speed changes obviously. Gravity has a periodic variation in the process of blade rotation and has a large influence on the edgewise moment. The research results provide a helpful reference for the structure design, operation, and control of wind turbines. [ABSTRACT FROM AUTHOR]

The structural integrity of wind turbine blades can be adversely affected by their structural dynamics, temperature extremes, lightning strikes, ultraviolet radiation from sunlight and airborne particulate matter such as hailstones and sand. If subsurface delamination occurs and is undetected then this can lead to fibre breakage and catastrophic failures in composite blades. In this paper we introduce a microwave scanning technique that detects such delamination in practical blade assemblies. Using an open-ended waveguide sensor, the electromagnetic signal reflected from the composite is found to have a phase profile that can detect changes in the composite cross section. Glass fibre T-joints are scanned and the results used to detect thickness variations (e.g., the presence of the web) and delamination. Results are compared across the 18-20 GHz frequency band. The dielectric permittivity of the composite system is measured and is used to estimate the stand-off distance and operating frequency of the sensor. This is critical to the system's ability to detect damage. When the sensor is close to the surface of the structure (standoff distance ≈ 5 mm), delamination down to 0.2 mm in width could be detected. [ABSTRACT FROM AUTHOR]

The blade of a wind turbine is a critical component that can be damaged by extreme loads; thus, its structural safety is paramount. Further, because its manufacturing cost comprise a high proportion of overall wind power production cost, its weight should be optimized to save on production and material cost. Much research has been conducted on structural optimization of wind turbine blades; however, focus has only been on exterior design. In this study, we optimize the cross-sectional dimensions of a 5-MW wind turbine blade by performing 3-D fluid analysis of the blade and using the pressure distribution obtained as input loads to find the inner structural shape of its cross section. Subsequent 2-D and 3-D fluid structural analyses conducted to find the maximum stress on the overall blade and its cross sections confirm that the cross section of the blade is minimized and that it is structurally safe. [ABSTRACT FROM AUTHOR]

This paper presents the analysis of dynamic characteristics of horizontal axis wind turbine blade, where the mode coupling among axial extension, flap vibration (out-of-plane bending), lead/lag vibration (in-plane bending) and torsion is emphasized. By using the Bernoulli-Euler beam to describe the slender blade which is mounted on rigid hub and subjected to unsteady aerodynamic force, the governing equation and characteristic equation of the coupled vibration of the blade are obtained. Due to the combined influences of mode coupling, centrifugal effect, and the non-uniform distribution of mass and stiffness, the explicit solution of characteristic equation is impossible to obtain. An equivalent transformation based on Green's functions is taken for the characteristic equation, and then a system of integrodifferential equations is derived. The numerical difference methods are adopted to solve the integrodifferential equations to get natural frequencies and mode shapes. The influences of mode coupling, centrifugal effect, and rotational speed on natural frequencies and mode shapes are analyzed. Results show that: (1) the influence of bending-torsion coupling on natural frequency is tiny; (2) rotation has dramatic influence on bending frequency but little influence on torsion frequency; (3) the influence of bending-bending coupling on dynamic characteristics is notable at high rotational speed; (4) the effect of rotational speed on bending mode is tiny. [ABSTRACT FROM AUTHOR]

The challenge of wind turbine blade design is to balance the conflict between high capacity and heavy system loads introduced by the large scale rotor. To solve this problem, we present a multi-objective optimization method to maximize the Annual energy production (AEP) and minimize the blade mass. The well-known Blade element momentum (BEM) theory is employed to predict the aerodynamic performance and AEP of the blade. The blade is simplified as a thin Bernoulli beam. The cross section is modelled as a combination of composite layer, shear webs and spar caps typically. The strain of every cross section has been considered as a constraint to minimize the spar cap thickness for minimizing the blade mass. An improved genetic algorithm (NSGA-II) is applied to obtain the Pareto front set. Several solutions of the Pareto set are selected to compare with the reference blade (NREL 5MW blade). Performance of the rotors on design condition is simulated by STAR-CCM+ to verify the results of BEM theory. Optimal results show that the present blade, which is fully superior to the reference blade, can be selected from the Pareto set. The optimization design method can provide a superior blade with an increase by 2.48% of AEP and a reduction by 5.52% of the blade mass. It indicates the present optimization method is effective. Results of numerical simulations show that the spanwise flow would be increased obviously in tip region of the reference blade. The reason is that chord length variation in blade tip affects the flow and causes minor stall. The abrupt change of chord distribution in blade tip should be avoided to reduce the spanwise flow in initial blade design. [ABSTRACT FROM AUTHOR]

Iron pellets are often added in blades to maintain moment balance in the design process of a wind turbine. The balance weight will change the natural vibration characteristics of the wind turbine blade. Resonant frequencies may appear for this reason, so it is necessary to study the effects of balance weight on the dynamic characteristics of a blade. In this paper, the wind turbine blade, after the weight balance process, is modeled as an Euler-Bernoulli beam with lumped masses. A mathematical model for a rotating nonuniform blade with a lumped mass on an arbitrary section is established, while nonlinear partial differential equations governing the coupled extensional-bending-bending vibration are obtained by applying the Hamiltonian principle. The associated modal problem is obtained from the governing equations, and then the differential form of the modal problem is transformed to integral form based on Green's functions (structural influence functions). A direct numerical approach is applied to calculate natural frequencies and vibrating modes. The effects of the mass and position of the balance weight and the rotating speed on the natural frequencies and mode shapes of the blade are discussed. [ABSTRACT FROM AUTHOR]

A comprehensive fatigue analysis framework for composite wind turbine blades has been developed. It includes variable wind loads from wind field simulation and aerodynamic analysis, stress prediction by finite element analysis, and fatigue damage evaluation based on the resulting fatigue data. The variable wind load is represented by a joint distribution of mean wind speed and turbulence intensity. In order to simulate realistic wind loads applied on the blade while maintaining affordable computational time, the sectional surface pressure fields obtained from the potential flow aerodynamics model XFOIL are transformed to match the lift, drag, and moment coefficients obtained using AeroDyn. Thus, the modified pressure distribution includes the effect of dynamic stall, rotation, and wake effects on the blade aerodynamics. A high-fidelity finite element blade model, in which the design of composite materials can be easily tailored, has been parameterized for detailed stress analysis. The non-proportional multi-axial complex stress states are involved when calculating 10-min fatigue damage of section points through laminate thickness. The annual fatigue damage is calculated based on the 10-min fatigue damage and the joint distribution of 10-min mean wind speed and 10-min turbulence intensity. Consequently, the blade fatigue effect due to not only the mean wind speed and the atmospheric turbulence in the short term, but also the wind load variation in a large spatiotemporal range, can be investigated. The developed fatigue analysis framework can facilitate reliability analysis and reliability-based design optimization of composite wind turbine blades. [ABSTRACT FROM AUTHOR]

This paper introduces a new airfoil series to optimize the aerodynamic shape of wind turbine blades. It is verified that the CQU-A airfoil series exhibits high aerodynamic performance by using the wind tunnel experimental data and RFOIL. The geometry of a 2 MW wind turbine blade with new airfoil families is designed preliminarily based on the shape of Tjaereborg 2 MW rotor. A multi-objective optimized model combining the maximum power coefficient of the wind turbine with minimum area of the blade surface is proposed for the pitch regulated wind turbine. An optimized code is developed based on the corrected blade element momentum (BEM) theory and particle swarm optimization (PSO) algorithm. The optimization results show that, compared with that of the original rotor and the Tjaereborg rotor, not only the power coefficient and annual power production is improved, but also the area of the blade surface is reduced. The decreased area indicates that the mass of the optimized blades is reduced. It is beneficial for increasing the fatigue life and reducing cost of composite materials if the internal structure of the wind turbine blades is unchanged. Furthermore, the load of the blade root is effectively controlled by using this alternative optimization program. [ABSTRACT FROM AUTHOR]

Nowadays wind energy is widely used as a non-polluting cost-effective renewable energy resource. During the lifetime of a composite wind turbine which is about 20 years, the rotor blades are subjected to different cyclic loads such as aerodynamics, centrifugal and gravitational forces. These loading conditions, cause to fatigue failure of the blade at the adhesively bonded root joint, where the highest bending moments will occur and consequently, is the most critical zone of the blade. So it is important to estimate the fatigue life of the root joint. The cohesive zone model is one of the best methods for prediction of initiation and propagation of debonding at the root joint. The advantage of this method is the possibility of modeling the debonding without any requirement to the remeshing. However in order to use this approach, it is necessary to analyze the cyclic loading condition at the root joint. For this purpose after implementing a cohesive interface element in the Ansys finite element software, one blade of a horizontal axis wind turbine with 46 m rotor diameter was modelled in full scale. Then after applying loads on the blade under different condition of the blade in a full rotation, the critical condition of the blade is obtained based on the delamination index and also the load ratio on the root joint in fatigue cycles is calculated. These data are the inputs for fatigue damage growth analysis of the root joint by using CZM approach that will be investigated in future work. [ABSTRACT FROM AUTHOR]

Abstract: Lagwise dynamic characteristics of a wind turbine blade subjected to unsteady aerodynamic loads are studied in this paper. The partial differential equations governing the coupled longitudinal-transverse vibration of the blade with large bending deflection are obtained by applying Hamilton's principle. The modal problem of the coupled vibration is handled by using the method of numerical integration of Green's function. Influences of the rotating speed, the pitch angle, the setting angle, and the aerodynamic loads on natural frequencies are discussed. Results show that: (1) Lagwise natural frequencies ascend with the increase of rotating speed; effects of the rotating speed on low-frequencies are dramatic while these effects on high-frequencies become less. (2) Influences of the pitch angle on natural frequencies are little; in the range of the normal rotating speed, the first frequency ascends with the increase of the absolute value of the pitch angle, while it is contrary to the second and third frequencies. (3) Effects of the setting angle on natural frequencies depend on the rotating speed; influences are not significant at low speed, while they are dramatic on the first frequency at high speed. (4) Effects of the aerodynamic loads on natural frequencies are very little; frequencies derived from the model considering aerodynamic loads are smaller than those from the model neglecting aerodynamic loads; relative errors of the results corresponding to two models ascend with the increase of the absolute value of the setting angle. [Copyright &y& Elsevier]

The failure analysis of the high-strength bolt at root position of the wind turbine blade was conducted to find the cause of fracture. Detailed investigations using several characterization techniques such as stress calculation, chemical composition test, mechanical property test, metallurgical investigation, and fractography analysis were performed to identify the cause of the bolt failure. Based on the theoretical calculation and failure analysis, it could be concluded that the bolt failed by fatigue accelerated by stress concentration while under low temperature. Practical suggestions were also given to avoid similar failures. [ABSTRACT FROM AUTHOR]

The absolute nodal coordinate formulation (ANCF) has been used in the analysis of large deformation of flexible multibody systems that encompass belt drive, rotor blade, and cable applications. As demonstrated in the literature, the ANCF finite elements are ideal for isogeometric analysis. The purpose of this investigation is to establish a relationship between the B-splines, which are widely used in the geometric modeling, and the ANCF finite elements in order to construct continuum models of large-deformation geometries. This paper proposes a simplified approach to map the B-spline surfaces into ANCF thin plate elements. Matrix representation of the mapping process is established and examined through numerical examples successfully. The matrix representation of the mapping process is used because of its suitability of computer coding and to minimize the calculation time. The error estimation is carried out by analyzing the gap between the points of each ANCF element and the corresponding points of the portion of the B-spline surface. The Hausdorff distance is used to study the effect of the number of control points, the degree of interpolation, and the knot multiplicity on the mapped geometry. It is found that cubic interpolation is recommended for optimizing the accuracy of mapping the B-spline surface to ANCF thin plate elements. It is found that thin plate element in ANCF missing a number of basis functions which considered a source of error between the two surfaces, as well as it does not allow to converting the ANCF thin plate elements model to B-spline surface. In this investigation, an application example of modeling large-size wind turbine blade with uniform structure is illustrated. The use of the continuum plate elements in modeling flexible blades is more efficient because of the relative scale between the plate thickness and its length and width and the high flexibility of its structure. The numerical results are compared with the results of ANSYS code with a good agreement. The dynamic simulation for mapped surface model shows a numerical convergence, which ensures the ability of using the proposed approach for applications of dynamics for design and computer-aided design. [ABSTRACT FROM AUTHOR]

The wind turbine blade sustains various kinds of loadings during the operation and parking state. Due to the increasing size of the wind turbine blade, it is important to arrange the composite materials in a sufficient way to reach the optimal utilization of the material strength. Most of the composite blades are made of glass fibers composites while carbon fibers are also employed in recent years. Composite materials have the advantages of high specific strength and stress. This study develops a GUI interface to construct the blade model for the stress analysis using ANSYS. With the aid of visualization interface, the geometric model of the blade can be constructed by only a few data inputs. Based on the numerical stress analysis of the turbine blade, a simple iterative method was proposed to design the structure of the composite blade. [ABSTRACT FROM AUTHOR]

With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced the interest for aerodynamic control systems with build-in intelligence on the blades. The paper aims to provide a way for modeling the adaptive wind turbine blades and analyze its ability for vibration suppress. It consists of the modeling of the adaptive wind turbine blades with the wire of piezoelectric material embedded in blade matrix, and smart sandwich structure of wind turbine blade. By using this model, an active vibration method which effectively suppresses the vibrations of the smart blade is designed. [ABSTRACT FROM AUTHOR]

With the increasing size of wind turbine blades, the need for more sophisticated load control techniques has induced the interest for aerodynamic control systems with build-in intelligence on the blades. New structural concepts have emerged where multifunctional materials, exhibiting a strong coupling between its mechanical response and its electrical behaviour, which work as sensors and actuators, are embedded or bonded to composite laminates for high-performance structural applications. The paper aims to provide a way for modeling the adaptive wind turbine blades and analyze its ability for vibration suppress. This study provides a finite element model of the smart blade for wind turbines. Numerical analysis is performed using finite element method, which is used to calculate the time response of the model. The displacement response from the piezoelectric actuator and piezoelectric sensors is obtained to control the vibration. By using this model, an active vibration method which effectively suppresses the vibrations of the smart blade is designed. [ABSTRACT FROM AUTHOR]

Design optimization of the wind turbine of a NREL 1.5-MW HAWT blade was studied to minimize the fluctuation of the bending moment of the blade in turbulent wind. In order to analyze the unsteady aerodynamic load of a wind turbine, FAST code was used as the analysis code. To consider turbulent wind as the wind input model in FAST, TurbSim was used as a turbulent wind simulator. For effective geometrical representation of the aerodynamic shape of a wind turbine blade, the shape modeling function was used to represent the chord length and twist angle. The fluctuation of the out-of-plane bending moment at the blade root was minimized by maintaining the required power of the wind turbine. Through the redistribution of the section force in the radial direction between both the primary and tip regions, the magnitude of the fluctuation of the out-of-plane bending moment was reduced by about 20%, and the rated power of 1.5-MW was maintained. The local angles of attack for the optimized blade were near the point of the maximum lift-to-drag ratio in the primary and tip regions compared to the baseline blade. The fluctuating unsteady aerodynamic load in the optimized blade was reduced within the operating range of the wind speed. With the optimized blade shape, the wind turbine can be operated with decreased fluctuating aerodynamic loads and have a longer life in turbulent wind. [ABSTRACT FROM AUTHOR]

An extensively automated optimization procedure is presented for a horizontal axis wind turbine (HAWT) blade based on ultimate limit state analysis. Two composite materials named glass fiber reinforced plastic (GFRP) and carbon fiber reinforced plastic (CFRP) are applied with a multi-objective of blade cost and total mass. Laminate layer thickness, material type and orientation angle are tailored for the structural performance and subjected to three design constraints which are derived from analysis of ultimate strength, fatigue failure and critical deflection, respectively. Combining FEM analysis and an evolutionary algorithm, the proposed optimization process has dramatically reduced design cost and improved blade performance. [ABSTRACT FROM AUTHOR]

damage detection method for complicated beam-like structures is proposed based on the subsection strain energy method (SSEM), and its applicability condition is introduced. For a beam with the continuously varying flexural stiffness and an edge crack, the SSEM is used to detect the crack location effectively by numerical modal shapes. As a complicated beam, the glass fiber-reinforced composite model of a wind turbine blade is studied based on an experimental modal analysis. The SSEM is used to calculate the damage index from the measured modal parameters and locate the damage position in the blade model successfully. The results indicate that the SSEM based on the modal shapes can be used to detect the damages in complicated beams or beam-like structures for engineering applications. [ABSTRACT FROM AUTHOR]

With the background of offshore wind energy projects, this paper studies aerodynamic performance and geometric characteristics of large capacity wind turbine rotors (1 to 10 MW), and the main characteristic parameters such as the rated wind speed, blade tip speed, and rotor solidity. We show that the essential criterion of a high-performance wind turbine is a highest possible annual usable energy pattern factor and a smallest possible dimension, capturing the maximum wind energy and producing the maximum annual power. The influence of the above-mentioned three parameters on the pattern factor and rotor geometry of wind turbine operated in China’s offshore meteorological environment is investigated. The variation patterns of aerodynamic and geometric parameters are obtained, analyzed, and compared with each other. The present method for aerodynamic analysis and its results can form a basis for evaluating aerodynamic performance of large-scale offshore wind turbine rotors. [ABSTRACT FROM AUTHOR]

Detecting anomalies in wind turbine blades from aerial images taken by drones can reduce the costs of periodic inspections. Deep learning is useful for image recognition, but it requires large amounts of data to be collected on rare abnormalities. In this paper, we propose a method to distinguish normal and abnormal parts of a blade by combining one-class support vector machine, an unsupervised learning method, with deep features learned from a generic image dataset. The images taken by a drone are subsampled, projected to the feature space, and compressed by using principle component analysis (PCA) to make them learnable. Experiments show that features in the lower layers of deep nets are useful for detecting anomalies in blade images. [ABSTRACT FROM AUTHOR]