Structural optimisation of composite wind turbine blade structures with variations of internal geometry configuration

Wind turbine blades are prone to icing under extreme working conditions, which will reduce the efficiency of wind power generation and seriously affect the service life of wind power system. Therefore, the anti-icing problem of wind turbine blades has become one of the hot topics in wind power technology research. It is of great practical significance to develop anti-icing/deicing technology for wind turbine blades for the safe and effective operation of wind power. In this paper, the numerical simulation optimization design for composite material wind turbine blades anti-/deicing component was studied, and the orthogonal optimization method was employed to optimize the parameters of the wind turbine blade to prevent ice formation. The optimization group parameter group is obtained. Through the wind turbine blade temperature distribution simulation, the correctness of the optimization results of the composite material anti-/deicing component was analyzed. The purpose of this paper is to optimize the heat transfer of anti-/deicing component for composite material wind turbine blade, and lay a theoretical and technical foundation for effectively solving the problem of wind turbine blade icing, which proposing a new composite wind turbine blade anti-/deicing scheme.

Application of videometric technique to deformation measurement for large-scale composite wind turbine blade

The present study investigates the structural behavior of glass and basalt fiber (BF)-reinforced epoxy composites for wind turbine blades using FEA and acoustic emission (AE)-based non-destructive testing. In addition, it focuses on improving failure mode identification and classification to enhance the structural efficiency of composite structures. FEA was used to evaluate variations in internal structural geometry parameters as well as the Von Mises stress distribution across the blades’ pressure and suction sides from root to tip. It focuses on crucial aspects such as stress distribution, damage behavior, and deformations, which are essential considerations for optimizing the design and ensuring the durability of wind turbine blades. Furthermore, the mechanical properties of fiber-reinforced plastic composites have been investigated experimentally. The results showed that glass fiber composite structures produced higher structural properties than BF composites utilized for producing wind blades. A signal-based AE technique is employed to detect and classify failure modes, including matrix cracking, fiber–matrix debonding, and fiber delamination (crack propagation), which are subsequently validated using scanning electron microscopy.

Wind turbine blades are the key components that allow the extraction of energy from the wind; these blades are often subjected to accidental impacts which usually occurs on moving blades with maintenance tools, hail, or flying birds, resulting in a significant degradation of the structural integrity of the blade. In this paper, a numerical simulation is adopted using finite element method (FEM) with ABAQUS software to investigate the mechanical behavior of a GRP composite wind turbine blade under low-velocity impact in operating conditions. On the other hand, damage modeling was formulated based on Hashin criteria for intra-laminar damage to detect failure modes in large wind turbine blade, the sensitive zones, and the size of damaged areas. To investigate this situation, a comparative evaluation was carried out considering many impact scenarios and the main parameters such as the impactor geometry, velocity, and weight. The results are then examined and analyzed, which show that major damage appeared at the tip of the blade and on trailing edge. Furthermore, the impactor geometry affects the type of damage, the weight affects the size of the damaged area, while the impact velocity influences the mechanical response of the composite wind turbine blade.

Abstract. The increasing demand for renewable energy has led to the development of several wind energy projects. A rising concern is the aging of these structures that must keep their serviceability and integrity for a long lifetime. That is why recent studies have focused on monitoring systems for data extraction based on accelerometers, fiber optic sensors, and piezoelectric sensors among many other sensing technologies. One of the most promising approaches is the use of fiber-Bragg-grating-based systems taking advantage of their proven benefits such as electromagnetic immunity, low size and weight, and ability to embed numerous sensors in a single optical fiber line. However, most of the reported studies have addressed the operational assessment of the acquisition systems without further deepening the exploitation of the acquired data for structural health monitoring purposes. This work aims to data exploitation of strain measurements acquired by simulated fiber Bragg gratings (FBG) for damage identification in wind turbine blades made of composite materials. A FEM model of a 2.5-meter-long wind turbine blade with 40 virtual FBGs strain sensors was used to obtain strain data under normal operational conditions. Then, strain measurements were calculated after defining several damages to the blade. Once the data were obtained, different data processing techniques following the pattern recognition paradigm were tested comparing their performance in terms of accuracy. The results will contribute to designing real-time automatic damage identification systems using FBGs strain sensors for composite wind turbine blades.

Fibre Reinforced Plastics (FRPs) have been used in many practical structural applications due to their excellent strength and weight characteristics as well as the ability for their properties to be tailored to the requirements of a given application. Thus, designing with FRPs can be extremely challenging, particularly when the number of design variables contained in the design space is large. For example, to determine the ply orientations and the material properties optimally is typically difficult without a considered approach. Optimization of composite structures with respect to the ply angles is necessary to realize the full potential of fibre-reinforced materials. Evaluating the fitness of each candidate in the design space, and selecting the most efficient can be very time consuming and costly. Structures composed of composite materials often contain components which may be modelled as rectangular plates or cylindrical shells, for example. Modelling of components such as plates can be useful as it is a means of simplifying elements of structures, and this can save time and thus cost. Variations in manufacturing processes and user environment may affect the quality and performance of a product. It is usually beneficial to account for such variances or tolerances in the design process, and in fact, sometimes it may be crucial, particularly when the effect is of consequence. The work conducted within this project focused on methodologies for optimally designing fibre-reinforced laminated composite structures with the effects of manufacturing tolerances included. For this study it is assumed that the probability of any tolerance value occurring within the tolerance band, compared with any other, is equal, and thus the techniques are aimed at designing for the worst-case scenario. This thesis thus discusses four new procedures for the optimization of composite structures with the effects of manufacturing uncertainties included.

Simulation of buckling-driven progressive damage in composite wind turbine blade under extreme wind loads

Composite wind turbine blades may experience interlaminar damage, including adhesive failure, cracking, and interlaminar fracture failure, from manufacturing or external fatigue load. Among these, the adhesive failure of adhesive joints is critical. Therefore, it is important to identify the failure mechanism in the adhesive joints between the spar cap–shear web and trailing edge of composite blades. We calculated fracture toughness through Mode I, Mode II, and Mixed-mode tests for quantitative analysis of adhesive joints. Then, to select a modeling method for realizing the damage generated in the blade, the method was verified from the specimen level. A damage model was constructed, considering contact conditions of the spar cap–shear web and trailing edge for an NREL 5MW wind turbine blade. Finally, a damage model based on cohesive zone modeling was used to analyze the progressive failure behavior of debonding at adhesive joints according to the external force applied to the blade.

Simulation and testing to develop an Intelligent Blade for wind turbines is presented in this paper. The concept blade has an integrated sensor system for structural health monitoring that will continuously monitor the condition of the blade, warn of initiating damage, and provide instant information that can be used to regulate loading in the blade to reduce or prevent fatigue damage. This can decrease maintenance costs, improve the reliability of wind power, and may make wind energy more affordable. Modeling and simulation of wave propagation in a plate was performed and different configurations of active and passive piezoceramic sensor systems were evaluated and shown to be capable of measuring propagating strain waves and identifying damage. A preliminary experiment to determine the damage detection capability of the sensors was done during a static test of a wind turbine blade. The stress wave propagation characteristics of the blade were monitored as the load level on the blade was increased until blade failure occurred. The effects of the blade stress and curvature on wave propagation need further study, but the results indicate that the technique has the potential for the detection of evolving damage in composite wind turbine blades.

Currently, wind turbine blades are manufactured from a combination of glass and/or carbon fiber composite materials with a thermoset resin such as epoxy, which requires energy-intensive and expensive heating processes to cure. Newly developed in-situ polymerizing thermoplastic resin systems for composite wind turbine blades polymerize at room temperature, eliminating the heating process and significantly reducing the blade manufacturing cycle time and embodied energy, which in turn reduces costs. Thermoplastic materials can also be thermally welded, eliminating the need for adhesive bonds between blade components and increasing the overall strength and reliability of the blades. As well, thermoplastic materials enable end-oflife blade recycling by reheating and decomposing the materials, which is a limitation of existing blade technology. This paper presents a manufacturing demonstration for a 9-m-long thermoplastic composite wind turbine blade. This blade was constructed in the Composites Manufacturing Education and Technology facility at the National Wind Technology Center at the National Renewable Energy Laboratory (NREL) using a vacuumassisted resin transfer molding process. Johns Manville fiberglass and an Arkema thermoplastic resin called Elium were used. Additional materials included Armacellrecycled polyethylene terephthalate foam from Creative Foam and low-cost carbonfiber pultruded spar caps (manufactured in collaboration with NREL, Oak Ridge National Laboratory, Huntsman, Strongwell, and Chomarat). This paper highlights the development of the thermoplastic resin formulations, including an additive designed to control the peak exothermic temperatures. Infusion and cure times of less than 3 hours are also demonstrated, highlighting the efficiency and energy savings associated with manufacturing thermoplastic composite blades.

Local buckling is one of the key driving forces of trailing edge failure in composite wind turbine blades. This study demonstrated a significant stiffness increase by adding a minor amount of foam material to the trailing edge region of a wind turbine blade. The proposed ‘place smart, load hard’ concept is based on the understanding of the local buckling in the critical trailing edge regions and to place additional foam there, where the blade is prone to buckle. The effective placing of foam inserts is numerically demonstrated for different load scenarios and its superiority compared to an experimentally validated blade model without foam inserts. The proposed strengthening method can be used for both building new blades and retrofitting old blades with local buckling issues in the trailing edge regions.

An effect assessment and prediction method of ultrasonic de-icing for composite wind turbine blades

Structural integrity of offshore wind turbine blade under extreme gust and normal operating conditions

Genetic Algorithms (GAs) are a powerful technique for search and optimization problems, and are particularly useful in the optimization of composite structures. The search space for an optimal composite structure is generally discontinuous and strongly multimodal, with the possibility for many local sub-optimal solutions or even singular extrema. These facts severely limit gradient-type approaches to optimization, bringing this broad class of problems under scrutiny for application of GAs. Examples described here of the successful use of parallel GAs to design composite structures by the authors include energy-absorbing laminated beams [1], airfoils with tailored bending-twisting coupling [2], and flywheel structures [3]. Optimal design of laminated composite beams was performed using a GA with a specialized finite element model to design material stacking sequences to maximize the mechanical energy absorbed before fracture. An initial GA approach to the optimal design of a specialized, idealized composite airfoil is now being refined for a practical application. The optimum stacking sequence to produce a desired twisting response while minimizing weight, maximizing in-plane stiffness and maintaining acceptable stress levels is determined. The GA has also been used to maximize the Specific Energy Density (SED) of composite flywheels. SED is defined as the amount of rotational energy stored per unit mass. Optimization of SED was achieved by allowing the GA to search for various flywheel shapes and allowing the GA to pick material sequences along the radius of the flywheel.KeywordsAutomated DesignGenetic AlgorithmsComposite MaterialLaminated StructureOptimization

Some interesting studies are made in this paper on the life management of a composite wind turbine blade. It presents the details of finite element modeling and validation, blade response under service loading conditions, power coefficient evaluation for the optimum design parameters of the blade configuration, development of failure envelope and fatigue life estimations. Finite element analysis results are found to be in good agreement with existing test results on a typical composite blade configuration. The failure envelope generated from the present modified failure criterion correlates well with the test results on different composite materials. The procedure adopted in this paper can be utilized for optimum design of large size composite wind turbine blades.