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As they are getting increasingly longer, wind turbine blades need to be stiffer and lighter to avoid cracks from fatigue loading and to help lower foundation construction costs. Current development processes are mainly 2D-based and rely on heterogeneous suites of tools that are not compatible with the quality and stiffness requirements of designing larger blades. Moreover, these tools do not allow to take last-minute engineering changes into account for manufacturing instructions.. In this context, wind turbine manufacturers are looking for innovative development solutions – particularly for blade architecture, design, simulation and manufacturing – that will help them meet these requirements while achieving longer life spans without defects.
Composites Business Development, Dassault Systèmes
(Published on April 2011 – JEC Magazine #64)
Optimizing composite blade design
Defining the aerodynamic properties of blades is critical in delivering outer shapes avoiding significant cracks in the aerodynamic structure. Advanced capabilities are needed to generate very high shape quality, i.e. a powerful and complete set of modelling capabilities, free-form and section-based modelling capabilities, realistic and fast quality analysis tools, and shape optimization capabilities.
The surface design is then provided to mechanical engineers, who define the detailed design and basic ply guidelines for the blade. Various methods, including zone, grid and solid slicing, are available for the automatic creation of plies, with full associativity between surface and composite parameters. A rotor blade is generally composed of structural elements such as spar webs and a shell, which are designed as sandwich composites. It is important for the designer to tightly control the properties of composite blades over their lifespan through appropriate optimization of ply orientation, thickness and lay-up.
Designing the composite lay-up in line with the complete blade assembly makes it possible to streamline the design process, ensuring a higher level of accuracy and reducing the number of physical prototypes needed to finalize the design. Powerful design optimization tools also
include the ability to swap ply edges, optimize drop-offs, shape plies and reroute sets of plies along a preferred path.
Integrating advanced specialized applications into the composite design environment makes it possible to simulate ply behaviour at an early stage and to evaluate fibre deformation. Engineers can visualize the ply stacking and tweak the laminate structure to eliminate wrinkles and other issues like fibre defects, fibre misalignments, broken fibres or missing fibres before the design is sent to manufacturing.
It also becomes possible to generate conceptual solids to quickly integrate the composite part in the mock-up, enable concurrent engineering with mating parts, and even provide preliminary inputs for tooling to start working on the mould.
Integration with tooling solutions means the tooling designer can create the mould based on the precise output surface. Rotor blade moulds can consist of several complex systems such as an integrated heating system, a hydraulic closing device and a built-in vacuum system that can be designed within the same environment. The lay-up of the composite plies onto the mould tool is simulated to identify areas where the part geometry will cause fabric distortion. The engineer can then add darts or splices, or make other changes to the ply and receive immediate feedback on whether the changes have corrected the design problem.
Improved composite blade reliability and durabilityTo test the blade durability and reliability, the analysis department applies many different loading conditions that simulate various wind conditions. Based on the results, the analyst goes back to the designer and recommends changes to the plies. This is typically a repetitive process involving numerous iterations between the analyst and the designer to reach the adequate level of performance.
Integrating the design information with a finite-element analysis programme helps eliminate these lengthy iterations. Additionally, the ability to transfer accurate fibre angles and ply thicknesses directly from the design to the analysis environment improves simulation accuracy. Transferring updated design information from analysis seamlessly back to design enables designers and analysts to work closely together, ensures the analyzed model matches the final structure, and avoids specifying plies and structures that cannot be manufactured down the road.
Analysts need advanced, state-of-the-art solutions to simulate composite behaviour realistically, including delamination and damage. These complex, non-linear effects can be modelled using cohesive elements, CZONE technology for direct implementation of crush-based element force generation and failure in defined “crush zones”, and VCCT (Virtual Crack Closure Technique). Engineers
can use VCCT to identify the overall load at which a crack initiates and to predict the behaviour of the structure as the crack propagates. It also helps them understand the stability and loadcarrying capacity of the composite structure after failure. Not having the possibility to validate the detailed blade design early in the development process is highly detrimental as it may cause structural damage, surface defects, and thin cracks in bonding areas.
As quality assessment becomes more important for larger structures, integrated simulation solutions are there to demonstrate that the performance of the final blade complies with the blade design specifications and with blade manufacturing rules from both an internal (processes/requirements) and an external (regulation) standpoint.
Securing high-quality production and reducing manufacturing costs
Securing blade life spans of 20 years and beyond requires highly industrialized production planning and manufacturing processes. Process standardization is essential and requires an integrated planning solution to define standard manufacturing processes and resource libraries. Manufacturing processes can be optimized to minimize investment and production costs. Quality assurance (QA) planning and adequate QA measurements for critical manufacturing steps are integrated in the process plan. Optimizing the workflow and directly deriving the complete manufacturing documentation from the process plan are also important.
The process plan and work instructions can be generated automatically by taking advantage of the ply stacking and composite properties from the design model to deliver comprehensive process planning and documentation. The process plan contains the complete sequence of operations (one or several per ply or cut piece) to be performed in the shop floor. It is generated automatically from the design model, using customizable rules and can be used to feed the manufacturing execution system downstream.
For each operation, the generated work instruction contains textual information for the shop floor worker as well as graphical information (images, annotations) created from the 3D model.