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Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, airfoil shape optimization of a wind turbine blade is performed using the ANSYS Fluent Adjoint Solver. The aim of this optimization process is to increase the wind turbine output power, and the objective function is to maximize the airfoil lift to drag ratio (CL/CD). This study is applied to the NREL phase VI wind turbine, therefore, the S809 airfoil is used as a reference profile. First, for the validation of the applied numerical model, steady-state simulations are carried out for the S809 airfoil at various angles of attack. Then, the optimization is performed with the airfoil set at a fixed angle of attack, 𝐴𝑂𝐴 = 6.1°, considering three Reynolds numbers, 𝑅𝑒 = 3 105, 4.8 105 and 106. Next, computations are performed for the fluid flow around the optimized airfoils at angles of attack ranging from 0° to 20°. The results show that (i) the lift to drag ratios of the optimized airfoils are significantly improved compared to the baseline S809 airfoil, (ii) this improvement is sensitive to the Reynolds number, and (iii) the CL/CD ratios are also improved for another angle of attack values. Thereafter, the optimized airfoils are used for the design of the NREL Phase VI blade and the aerodynamic performances of this new wind turbine are assessed using the open-source code QBlade. These latter results indicate that when the blades are designed with the optimized airfoils, the wind turbine aerodynamic performances increase significantly. Indeed, at a wind speed of 10 m/s, the power output of the wind turbine is improved by about 38% compared to that of the original turbine. [ABSTRACT FROM AUTHOR]

A compromise approach between aerodynamic performance and structural robustness is presented. The modeling of horizontal axis wind turbine blade GE1.5-XLE is studied regarding the applicability of three different solution methods computational fluid dynamics (CFD), one – way (unidirectional), and two – way (bidirectional) coupling fluid – structure interaction (FSI) at a shedding frequency of the vortex far from the natural frequency. The predicted results showed significant differences between the unidirectional coupling solution and experimental data. While, the bidirectional coupling method proposed accurate FSI and gave results closer to the experimental measurements than unidirectional simulation results. The bidirectional coupled approach appears to be more stable and accurate, where a large number of time steps should be used for uncoupled method to achieve the same level of precision. For the present case involving large blade strain, the difference between the prediction of rigid blade solution using CFD and FSI model increases considerably. However, it is concluded that for large blade strains, the FSI model is closer shown to be more adequate for accurate representation of the turbine performance. Moreover, when optimization is a key aspect, bidirectional simulations should be performed regardless of the higher computational cost. [ABSTRACT FROM AUTHOR]

The land needed to install wind turbines is shrinking as power generation from renewable energy sources increases significantly. A large number of studies are being conducted to maximize the power extraction from wind turbines in areas with low wind speeds. Wind turbine blades play a significant role in utilizing the maximum amount of energy from the wind. The aerodynamic performance of a wind turbine blade depends on the airfoil shape. The shape optimization of an asymmetric S2027 airfoil for a low wind speed region was investigated using the adjoint-based optimization technique. The primary objectives of this study were to maximize the lift coefficient, minimize the drag coefficient, and maximize the lift-to-drag ratio. The optimization is based on the adjoint method for Reynolds number variation in the range of 2 × 105 to 5 × 105 and an angle of attack variation from 0° to 12°. A two-dimensional Reynolds-Averaged Navier-Strokes Computational Fluid Dynamics model was created with all the operating parameters and used for optimization. The aerodynamic performance was validated experimentally. For each optimization function, approximately 16 shapes were obtained. The aerodynamic performance for each optimized shape was determined under different operating conditions. Different airfoil shapes with a specific chord, leading and trailing edges, and span arrangement was obtained. The drag coefficient was reduced by 2%-30%; the lift coefficient was improved by 2%-35%, and the lift-to-drag ratio was improved up to 40%. [ABSTRACT FROM AUTHOR]

The blade is a crucial part of large-scale wind turbine for converting wind energy into electricity. Increasing attentions have been paid to the blade health monitoring in recent years. This paper focuses on acoustic-based surface damage detection of the blade and presents a novel intelligent detection method of the whistle produced by the drain hold using the pattern recognition. In the algorithm, a developed preprocessing strategy with multiband adaptive spectral subtraction can well reduce the random wind noise from raw acoustic signal. Moreover, a correlated empirical mode decomposition method in combination with morphological filtering is proposed for extracting time–frequency ridge features of whistle event. Finally, an incremental support vector machine based on adaptive reserved set strategy is designed for recognizing the whistle event. Experimental results demonstrate that proposed method is feasible and effective in whistle detection of drain hole. • A novel acoustic-based whistle detection method of drain hole is proposed. • The whistle characteristics of drain hole for wind turbine blade is investigated. • An incremental AR-ISVM with correlated EMD is designed for recognizing the whistle. • Experiments validate effectiveness of proposed method in whistle detection. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This paper presents a pioneer study of identifying the wind turbine blade condition based on its vibration pattern. The study used variational mode decomposition (VMD) for signal pre-processing. VMD is an adaptive signal decomposition technique, which can non-recursively decompose a multi-component signal into a number of quasi-orthogonal intrinsic mode functions. This new tool is based on a solid mathematical foundation and can obtain a well-defined time–frequency representation. The main advantage of VMD is, there is no residual noise in the modes and it can avoid redundant modes. Thus, VMD provides a noise-free fault signal for classification. Initially, the obtained vibration data are pre-processed using VMD and then the descriptive statistical features like mean, standard deviation, sample variance, and kurtosis were extracted. After the feature extraction, the dominant features were selected using the C4.5 decision tree algorithm. In this study, multilayer perceptron (MLP) was used for fault classification (blade bend, blade crack, erosion, hub-blade loose connection, and pitch angle twist). Then a comparative study was made with MLP without VMD and MLP with VMD to suggest a better model. From the results, the maximum classification accuracy of 87% was obtained for MLP with VMD when compared to MLP without VMD (76.83%). [ABSTRACT FROM AUTHOR]

In order to solve the problem of insufficient exciting force of equipment for large full-scale wind turbine blade fatigue testing, the influence of gravity on the performance of excitation equipment and fatigue damage evaluation of the different positions of wind turbine blades are analyzed. With the multi-excitation loading in the horizontal direction, the actuator force of the excitation equipment does not need to overcome the gravity of the dynamic mass, w'hich directly outputs the exciting force of the system vibration. The excitation efficiency of the equipment is 77% higher than that of the vertical load. The gravity moment of the horizontal loading mode is perpendicular to the loading direction. That is, the mean load in the flapwise direction is zero. The weight of excitation equipment could replace the tuning mass on the condition that the self-weight of equipment is reduced by the multi-excitation mode, which helps the excitation equipment play the comprehensive function of excitation equipment and tuning mass. At the same time, the gravity moment in the edgewise direction will be decreased by 17.0%-22.5% under the multi-excitation horizontal loading mode. In the vertical loading mode, the gravity moment is the mean load, which only increases fatigue damage accumulation by 15.6%. By comparing the role of gravity in the excitation equipment and fatigue damage evaluation, the multi-excitation horizontal loading mode has more advantage to performance the exciting force than the contribution of gravity to the fatigue damage accumulation in the vertical loading mode. Through the fatigue testing of multi-excitation horizontal loading, the potential of excitation equipment is explored, and the problem of insufficient exciting force in large fullscale wind turbine blade fatigue testing will be solved. [ABSTRACT FROM AUTHOR]

Abstract The blades of offshore wind turbines accumulate structural damage such as fatigue due to aerodynamic loading by various wind speeds during their service time, leading to premature structural failures. This paper investigates the fatigue damage by the blade element momentum theory (BEMT) method and the cost of operation and maintenance by the integrating models. Three prediction models have been proposed for lifetime performance assessment and management of wind turbine blade, i.e. fatigue prediction model (FPM), the reliable stochastic model (SRM) and cost benefit model (CBM). The fatigue model is discussed to reproduce the fatigue damage evolution in composite blades subjected to aerodynamic loadings by cyclical winds. The lifetime probability of fatigue failure of the composite blades is estimated by stochastic deterioration modelling such as gamma process. On the basis of the cost model, an optimised maintenance policy is determined to make optimal maintenance decision for the composite blades. A numerical example is employed to investigate the effectiveness of predicting fatigue damage and estimating the probability of fatigue failure to determine an opportunistic maintenance policy. The results from the numerical study show that the stochastic gamma process together with the fatigue models can provide a useful tool for remaining useful life predictions and optimum maintenance strategies of the composite blades of offshore wind turbines. [ABSTRACT FROM AUTHOR]

Fatigue design optimization of composite material structures is limited by the classical approaches used, derived from knowledge based on metal fatigue. Other approaches exist to describe damage mechanisms of composites but they cannot always be applied at the structure scale because of their complexity. However, assumptions can be made in the case of beam structures to reduce the structural investigation at the section scale. With these assumptions this paper proposes to compare a progressive fatigue damage model written at the ply scale to the normative approach for the assessment of wind turbine blade section design. It is shown that the normative approach is very conservative and the progressive fatigue damage model provides very useful information to understand damage propagation at the structure scale. [ABSTRACT FROM AUTHOR]

A wind turbine blade shell made of glass fiber reinforced polymer (GFRP) composite materials was mechanically processed into slender elements referred to as “Needles”. The Needles were used to replace 5% and 10% of the coarse aggregate, by volume, in concrete mixtures that were tested to investigate a number of important properties of fresh and hardened concrete. It was found that the Needles did not affect the stability and workability of fresh concrete negatively. Although the incorporation of the Needles did not have a notable effect on compressive, tensile, and flexural strength of concrete, it resulted in a significant increase in energy absorption capacity (toughness) from 1.2 J in control specimens up to 33.3 J in those with 10% Needle replacement. A polymer burn-off test revealed that, due to the directions in which the shell was cut, in most of the Needles glass fibers were perpendicular to the Needle axis, and therefore to the tensile stress carried by the Needles. Although the Needles with transversely-aligned fibers improve the mechanical performance of concrete, if the cutting directions of wind blades can be optimized so that in the majority of the Needles the fibers are primarily aligned longitudinally, improvements are expected to be more significant. [ABSTRACT FROM AUTHOR]

This work presents the numerical and experimental analysis to obtain dynamic parameters of a twisted type blade, that composes the wind turbine VERNE555 of Brazilian company ENERSUD, based in Rio de Janeiro. The experimental analysis performed the characterization of the modal parameters (frequencies and modal shape) of a wind turbine of 2.73 m length. The experimental tests present three boundary condition configurations for the wind blade. Numerical modelling is performed using a Timoshenko beam element of six degrees of freedom per node, and conducted using the ANSYS finite element tool. In this way, we aim to evaluate the numerical and experimental results through a comparative analysis. [ABSTRACT FROM AUTHOR]

Wind energy is one of the important renewable energy resources available in nature. It is one of the major resources for production of energy because of its dependability due to the development of the technology and relatively low cost. Wind energy is converted into electrical energy using rotating blades. Due to environmental conditions and large structure, the blades are subjected to various vibration forces that may cause damage to the blades. This leads to a liability in energy production and turbine shutdown. The downtime can be reduced when the blades are diagnosed continuously using structural health condition monitoring. These are considered as a pattern recognition problem which consists of three phases namely, feature extraction, feature selection, and feature classification. In this study, statistical features were extracted from vibration signals, feature selection was carried out using a J48 decision tree algorithm and feature classification was performed using best-first tree algorithm and functional trees algorithm. The better algorithm is suggested for fault diagnosis of wind turbine blade. [ABSTRACT FROM AUTHOR]

A procedure based on MATLAB is presented and utilized for the structural optimization design of Horizontal-Axis Wind Turbine (HAWT) blades. Wind turbines matured towards a lowered cost-of-energy and have grown in rotor size therefore stretched the role of composite materials that offered the solution to more flexible, lighter and stronger blades. The structural aspects of a 82 meter long blade in an upwind, horizontal-axis wind turbine were developed in this paper. The promising generic blade structural designs were used to initialize a detailed structural optimization in which spar cap, panels and trailing edge reinforcements are sized such that the blades meet the intent of design standards. In this study, the optimization formulations include non-linear failure constraints. This present study has important significance for the structural design and optimization of wind turbine blades. [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]

This paper aims to optimize the distribution of chord and twist angle of small wind turbine blade in order to maximize its Annual Energy Production (AEP). A horizontal-axis wind turbine (HAWT) blade is optimized using a calculation code based on the Blade Element Momentum (BEM) theory. A difficult task in the implementation of the BEM theory is the correct representation of the lift and drag coefficients at post-stall regime. In this research, the method based on the Viterna equations was used for extrapolating airfoil data into the post-stall regime and the results were compared with various mathematical models. Results showed the high capability of this method to predict the performance of wind turbines. Evaluation of the efficiency of wind turbine blade designed with the proposed model shows that the optimum design parameters gave rise to an increase of 8.51% in the AEP rate as compared with the corresponding manufactured operating parameters. [ABSTRACT FROM AUTHOR]

Materials used in the development and construction of the blades are essential for the proper functioning of wind turbines. The challenges of engineers are related to the optimum combination of the following structural properties: optimum rigidity - specific gravity; lifetime to fatigue and flexibility; low cost of materials and processing to achieve the desired aerodynamic shape. The purpose of this paper is identification of risk areas of wind turbine blades and composite structural optimization of their structure in areas exposed to combined loading, using finite element analysis. Optimizing structural composites depending on risk areas is a difficult issue because it must take into account the aerodynamic profile, proper positioning of the center of gravity and dynamic and elastic center of blade so that during operation, will not develop the inertial masses to affect the functioning and integrity of the blades. In the first stage of the research, the blade structure with a length of 1.5 m and profile NACA 2412 was modeled from composite fiber reinforced polymer, with 7, 9, 11, 13, 15 layers of fiber glass fabric and mat with epoxy resin as matrix. Once static analysis, the risk areas where determined taking into account the maximum values of normal and tangential stresses. In the next stage, structural optimization and verification was performed, the state of stress and strain being compared to stress obtained initially. There were also determined the optimum package of composite taking into account the reduction of blade mass. It was found that increasing the number of layers in risk areas and their reduction to the blade tip leads to increasing resistance to static and dynamic loads. Orientation of layers can improve the static and dynamic behavior. The study aims to applying the finite element method in designing composites used in wind turbine blades structure, reducing the cost of production and improving the structure. [ABSTRACT FROM AUTHOR]

A Blade-Element Momentum (BEM) based software was used to design a 300 kW, variable speed Horizontal Axis Wind Turbine (HAWT). Chord lengths, blade twist angles and rotational speeds were allowed to change independently so as to achieve a maximum energy output, while design constraints were also being met. Computational Fluid Dynamic (CFD) was use to validated the BEM calculation. According to low wind area, the rated wind speed was set quite low at 10 m/s. The optimal design of wind turbine reaches 50.5% efficiency at the design tip speed ratio of 7.5. The wind turbine can maintain 50.5% efficiency level over wind speeds range of 4-9 m/s by changing the rotating speeds from 16-36 RPM. Beyond the rated wind speed, the turbine can regulate its power by changing the rotating speed to decrease its efficiency and maintain the power output at 300 kW. Results from CFD agree well with the BEM calculation. It verifies that the optimum designed blade from the BEM was reliable. [ABSTRACT FROM AUTHOR]

A Blade-Element Momentum (BEM) based software was used to design a 300 kW, variable speed Horizontal Axis Wind Turbine (HAWT). Chord lengths, blade twist angles and rotational speeds were allowed to change independently so as to achieve a maximum energy output, while design constraints were also being met. Computational Fluid Dynamic (CFD) was use to validated the BEM calculation. According to low wind area, the rated wind speed was set quite low at 10 m/s. The optimal design of wind turbine reaches 50.5% efficiency at the design tip speed ratio of 7.5. The wind turbine can maintain 50.5% efficiency level over wind speeds range of 4-9 m/s by changing the rotating speeds from 16-36 RPM. Beyond the rated wind speed, the turbine can regulate its power by changing the rotating speed to decrease its efficiency and maintain the power output at 300 kW. Results from CFD agree well with the BEM calculation. It verifies that the optimum designed blade from the BEM was reliable. [ABSTRACT FROM AUTHOR]

The main objective of this research work is to introduce a new material for wind turbine blades. Al 2024 is selected for the suitability analysis. Finite element Method or Finite Element Analysis is a approximation techniques used for the analysis of complex objects and geometries. Wind power or wind energy is considered as a clean source of energy which produces no environmental harm during operation. The total wind power generation potential of India at a height of 50 m is 50000 MW. In recent years Indian Government has focused on this renewable source of energy. The main part of this research is to identify natural frequencies and natural vibration modes of the Al 2024 wind turbine blade. Wind Turbine blade design is a complex procedure. For the design of wind turbine blade Solid Edge software is used and the model is imported in ANSYS 14.0 for modal analysis. For the suitability analysis of Al 2024 we have done structural and Modal analysis. The results of the analysis are used to verify a structure's fitness for use. The analysis results were verified with experimental result available in literature. [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]

Static aeroelastic is investigated in a wind turbine blade. Imposed to different loadings, the very long and flexible structures of blades experience some changes in its preliminary geometry. This results in variations of aerodynamic loadings. An iterative approach is developed to study the interactions between structure and aerodynamics evaluating variations in induced stresses in presence of aeroelasticity phenomenon for a specific wind turbine blade. A 3D finite element model of the blade is constructed. Aerodynamic loading is applied to the model and deflected shape is extracted. Then, aerodynamic loadings are updated in accordance with the new geometry of the deflected blade. This process is repeated till the convergence is met. Different operational conditions consisting of stand-by, start-up, power production and normal shut-down events are investigated. It is revealed that stress components vary significantly in the event of power production at the rated wind speed; while it is less pronounced for the events of normal shut-down and stand-by. [ABSTRACT FROM AUTHOR]

Abstract: Blade lengths of 30, 50, 70 and 90m were designed to quantify the effect of geometric scaling on bend-twist coupling. The blades were implemented with off-axis carbon fibers in the spar flanges to promote coupling while biaxial glass fibers were used to provide torsional stiffness and buckling resistance. Theoretical scaling laws were compared to nonlinear finite element simulations, both of which concluded that there was no dependence of bend- twist coupling on geometric up-scaling. At the maximum load, all blades achieved a tip twist between 6 and 7° towards feather. This resulted in load reductions of roughly 10-11%, showing that load alleviation from bend-twist coupling was also independent of scaling effects. The reduction in loads showed potential for blade mass reduction. [Copyright &y& Elsevier]

The fatigue load of a turbine blade has become more important because the size of commercial wind turbines has increased dramatically in the past 30 years. The reduction of the fatigue load can result in an increase in operational efficiency. This paper numerically investigates the load reduction of large wind turbine blades using active aerodynamic load control devices, namely trailing edge flaps. The PD and LQG controllers are used to determine the trailing edge flap angle; the difference between the root bending moment and its mean value during turbulent wind conditions is used as the error signal of the controllers. By numerically analyzing the effect of the trailing edge flaps on the wind turbines, a reduction of 30-50% in the standard deviation of the root bending moment was achieved. This result implies a reduction in the fatigue damage on the wind turbines, which allows the turbine blade lengths to be increased without exceeding the designed fatigue damage limit. [ABSTRACT FROM AUTHOR]

Abstract: The structural aspects of a 70 meter long blade in an upwind, horizontal-axis wind turbine were developed in this paper for use in a high wind speed location. A hybrid composite structure using glass and carbon fiber plies was created yielding a light-weight design with a low tip deflection. The blade was subjected to FEA studies to demonstrate its ability to withstand the extreme loading conditions as defined in the international offshore wind standard. The results confirmed the design to have acceptable performance with regard to tip deflection, maximum and minimum strains, and critical buckling load. Detailed descriptions of the structural components and ply layups are presented along with the resulting maximum and minimum strains and deflections. In addition, optimization techniques were introduced to provide insight for future studies with the blade. [Copyright &y& Elsevier]

Abstract: According to theoretical calculating result of stress, four different lay-up structures of 1.2MW horizontal axis wind turbine blade, which can effectively endure various loads, are designed primarily. Based on composite laminate theory and finite element method, through analyzing their stress-strain, the optimal lay-up schema is confirmed. The verified analysis of stiffness and strength were performed under extreme load conditions. Numerical analysis results show that the designed blade structure was safe, and the value of stress and strain was low. [Copyright &y& Elsevier]

Abstract: In this paper, the resin transfer molding (RTM) and compression molding manufacturing processes were used to fabricate composite wind turbine blades by stacking pieces of glass-fiber fabric, expandable polystyrene (EPS) foam and inserting parts in an interior pressure mold. The blade preform is a composite foam-filled sandwich structure, where the interior is an EPS foam layer while the exterior is coated with a main fiber layer, root reinforcing fiber layer and the parts are inserted. The inserted parts that were investigated were the I-beam, LED, conductor, root connection joint and repair patch. The reinforcing fiber layer was designed to provide maximum bending stiffness in the flexure to resist the stress concentration of the composite wind turbine blade. This research will also be used to develop adhesive bonding repair techniques for life extension of the damaged components in a wind turbine blade. A number of composite wind turbine blade constructions were fabricated to demonstrate the feasibility and applications of the proposed manufacturing method. [Copyright &y& Elsevier]

Abstract: In this paper, the progressive failure process of composite sandwich wind turbine blades subjected to wind load is studied via both theoretical and experimental approaches. In the theoretical study, the wind pressure acted on the wind blade surface is estimated in an aerodynamic analysis. The stresses in the wind blade are determined using the finite element code ANSYS in which the skin and the core of the blade are modeled using shell and solid elements, respectively. A phenomenological failure criterion is adopted to predict the first-ply failure strength of the blade. After the occurrence of the initial failure, the material properties at the failure locations are modified following a material degradation rule. The updated stiffness matrix of the blade is then obtained with the consideration of the changes of the material properties and configuration of the blade. An incremental load approach together with a sequential stiffness adjustment technique is used to trace the load-displacement curve and thus determine the ultimate strength of the blade. In the experimental investigation, a composite sandwich wind blade was fabricated for strength testing. In the test, the Whiffle-tree approach was used to simulate the wind load on the blade. The measured ultimate load of the wind blade was then used to validate the accuracy of the proposed method for failure analysis of composite sandwich wind blades. [Copyright &y& Elsevier]

Abstract: Monitoring technique for detection of early damage in the wind turbine blade has been investigated using PVDF film sensor and strain gages. The trailing edge component with shear web was prepared by sectioning the full-scale blade with a box spa. Several PVDF film sensors with dimension of 10x10x0.054 mm3 and strain gages were installed on shear web and skin of the component and the behaviour of these sensors were examined under opening and closing loads. From the test, optimal location for detecting the occurrence of damage with static loading was investigated and sensitivity of the PVDF sensors location to the damage was examined. With increasing the applied load, several pop-ins happened up to final failure. The outputs of the PVDF film sensors under quasi-static loads showed the relatively insignificant magnitude and peaks corresponding to pop-ins. So, it is found that PVDF film sensors mounted on the trailing edge component give an early response remarkably to the damage occurrence irrespective to the closing and opening loads. Therefore, it can be said the PVDF film sensors may be significantly useful in detecting the instance of damage occurrence in the trailing edge component. Further, it can be recommended that the relatively good location of the PVDF sensor to detect the damage in the trailing edge component be the locations free to the geometrical constraint, like the center of spar web and the blade skin remote from the joint between the spa cap and the shear web. [Copyright &y& Elsevier]

Abstract: Monitoring technique for detection of early damage in the wind turbine blade has been investigated using PVDF film sensor and strain gages. The trailing edge component with shear web was prepared by sectioning the full-scale blade with a box spa. Several PVDF film sensors with dimension of 10x10x0.054 mm3 and strain gages were installed on shear web and skin of the component and the behaviour of these sensors were examined under opening and closing loads. From the test, optimal location for detecting the occurrence of damage with static loading was investigated and sensitivity of the PVDF sensors location to the damage was examined. With increasing the applied load, several pop-ins happened up to final failure. The outputs of the PVDF film sensors under quasi-static loads showed the relatively insignificant magnitude and peaks corresponding to pop-ins. So, it is found that PVDF film sensors mounted on the trailing edge component give an early response remarkably to the damage occurrence irrespective to the closing and opening loads. Therefore, it can be said the PVDF film sensors may be significantly useful in detecting the instance of damage occurrence in the trailing edge component. Further, it can be recommended that the relatively good location of the PVDF sensor to detect the damage in the trailing edge component be the locations free to the geometrical constraint, like the center of spar web and the blade skin remote from the joint between the spa cap and the shear web. [Copyright &y& Elsevier]

Wind power does not generate pollution and is a clean source. The dynamic problems associated with wind turbine blades are formulated using the differential quadrature method. The Euler–Bernoulli beam paradigm is used to characterize wind turbine blades. The differential quadrature technique is utilized to transform partial differential equations, which presents the dynamic behaviour of wind turbine blades, into a discrete eigenvalue problem. The effects of the number of sample points on the accuracy of the calculated natural frequencies are studied. Numerical results show that the rotational speed impacts significantly the first frequency of the wind turbine blade. The pitch angle could not markedly affect wind turbine blade frequencies. [ABSTRACT FROM AUTHOR]