As the size of wind turbines increases, the design of blades, control systems, and supporting structures becomes more complex because stress and other factors that cause failure are on a bigger scale. This creates greater engineering challenges as well as those in sourcing, manufacture, logistics, installation and maintenance. New designs need to be quickly tested for fatigue and twisting under expected operating conditions on- or offshore.
Finite Element Analysis (FE) is used to test structural integrity of potential designs. Virtual and physical wind tunnel testing is also conducted. Tests on foundations, the interaction of components with each other as well as testing the entire fabrication in virtual operating situations is performed. This needs to be done fast so that designs can be certified and put to use quickly as possible.
It is neither economical nor practical to built and test many (if any) physical prototypes. Virtual testing of blade components reduces the need for expensive prototypes and minimizes development time and cost.
It is expensive and time consuming to make physical prototypes. Many industries including aerospace and automotive have reduced their reliance on their use. Instead they build digital 3D models to test their designs virtually. This means that thousands of tests can be done. Geophysical and meteorological data is incorporated into testing. Measuring stress on physical models is difficult and often inaccurate. Compared to a physical model a virtual one can be a more accurate representation of the final product and is easier to test run tests on. Another disadvantage of making physical prototypes is that they take a long time to produce. By the time they have been made the design may have moved on making the physical prototype redundant and inaccurate. Using digital models this way means that if physical prototypes are made it will happen later in the design process. This leads to fewer late change requirements and subsequent cost savings.
STRUCTeam, a UK-based structural and composite material engineering services company for advanced composite structures, has a list of customers including leading wind turbine developers. Working directly with clients, designers, fabricators, material suppliers and certification bodies, the company transforms carbon fibre and composite products from creative ideas to finished goods.
Customers' ideas are combined with those of the company which is able to add its own knowledge of what can be achieved with advanced composites. Understanding the nature of working with composites means that more innovative concepts can be developed. Knowing what will and will not work steers this creativity towards better technical and commercial outcomes.
STRUCTeam technical director Radek Michalik described some of the complexities of designing with carbon fibre and advanced composite materials as opposed to designing with light alloys such as aluminium: “At present, there are few standards for designing composite materials because they are relatively new and, unlike metals, their physical properties can vary almost infinitely. We need to optimise three interdependent and often contradictory requirements – design, engineering and production – in order to simplify and improve the development process.”
Wind farm developers request ever-larger turbines. Their size is challenging in design and engineering terms and new manufacturing techniques have to be well understood to ensure that designs can actually and practically be produced.
Working collaboratively within an integrated software environment, designers, analysts and manufacturing engineers produce products that can be thoroughly virtually tested throughout their digital development. Using software, designs of composite blades are optimised for better performance by changing the number and direction of plies – the rotation of the carbon fibre layers and their characteristic warp and weft. This reduces weight and introduces strength where it is needed with extra layers or specially designed engineering solutions. Software calculations of vibrations, nonlinear deformation and stress, fracture and failure, and other multiphysics effects including fluid-structure interactions and hail storms, can greatly improve turbine performance and reliability. These measures reduce the risk of catastrophic in-field failure that leads to turbine write-off. And it makes blades less expensive to manufacture, as there is less material being used or optimisation of blade profiles.
The material offers so many possible design options that considerable expertise and manufacturing experience are required to develop and successfully make optimised designs. “3D models realistically show how to make the best use of highly sophisticated composite materials and how to optimise their use” Michalik says. The material’s almost limitless possibilities of the fibre type, weave pattern, resin composition and final design can lead to errors if not fully understood. “We can visualise and tailor laminate patterns to add strength and/or stiffness to finished products at the digital visualisation stage. This provides us with more elegant and precise engineering solutions. It also reduces both cost and commercial and engineering risk because we are confident that our designs will always work.” Without this input, risk is increased as manufacturing and usage outcomes are not so predictable.
Automated System Improvement
Investments in automated production systems incur high capital costs for plant and other equipment and resources. By optimising and validating production systems in virtual environments, manufacturers can better judge if a proposed system will enable the company to achieve its goals. This also helps validate capital investment.
Software planning features help define and refine manufacturing processes within standards while reducing production cycle times and increasing throughput. By iterating development based on stakeholder feedback, issues can be detected early in the process. This helps eliminate manufacturing problems and delays. Information silos containing different versions of the "final" product data can cause errors to be introduced into processes. Combining data into a single environment, used by everyone involved, produces only one version of the design and its associated data which everyone involved uses. This eliminates miscommunication and the potential damage this type of error can incur. Feedback between stakeholders on technical, commercial or other planning issues is conducted within single data environment. This leads to collaboration between groups who often use the universal language of 3D.
Manufacturers often struggle with defects during production due to process complexity, lack of experience, or unresolved engineering issues. Defects introduced at the design stage or during manufacture can lead to hidden layering and processing errors. These may only show up through breakages or malfunction in use.
To improve, manufacturers need to better control the production process. A 3D digital, rules-based continuous process improvement methodology can be specifically tailored for error free complex composite parts development. Workflow software ensures complete traceability of all design, manufacturing and installation data and changes to it, ensuring that work proceeds within company and quality rules from inception to delivery. It can also help manufacturers decrease their development and operating costs, reduce engineering and manufacturing time, and increase product quality.
Lead image: composite blade design, courtesy Dassault Systèmes