Processing and modeling techniques moving wind energy forward
By Don Rosato

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Note: This is the third article of a four-part series covering wind energy (1) trends, (2) material advances, (3) process technologies and (4) applications.

INDUSTRY PULSE

What is a key emerging plastic processing or design technology in wind energy?
  • 1. Fraunhofer IWES 5-year BladeMaker project
  • 2. Standardization to define wind blade manufacturing processes and resource libraries
  • 3. Robotic solutions to simplify automation of composite production lines
  • 4. VABS software realistic modeling of wind-turbine blades

Wind intercepted by the turbine is proportional to the square of its blade length. However, the maximum blade length of a turbine is limited by both the strength and stiffness of its material. The industry is looking to material advances in resin and fiber as well as processing technologies to enable development of longer, lighter turbine blades. Turbine blade manufacturing automation is a key wind-energy processing trend.

Rotor blades currently account for about 25 percent of the total cost of a wind turbine due to the high level of manual labor involved. Turbine blades are still made almost completely by hand. Significant cost reductions can be achieved through changing from small-series production to large-scale industrial production. Automating the process will make the blades more cost-effective, quicker to manufacture and of a higher quality.

Fraunhofer IWES (Institute for Wind Energy and Energy System Technology) is leading 18 industrial and research partners in a five-year BladeMaker project to automate blade manufacturing as fully as possible to slash costs while increasing quality. The team is aiming to slash more than 10 percent from the cost of turbine blade manufacture. The five-year project has €8 million funding from the German government.

Wind blade pilot line.

To achieve BladeMaker project goals, blade design, materials and manufacturing processes will be taken into consideration. The team will analyze the work procedures and technologies of rotor-blade production and assess the potential for automation. Then, any promising automated manufacturing processes will be investigated and simulated. Finally, the team will build a demonstration model and the BladeMaker blade will be designed and optimized for automated production. In the long term, IWES plans to set up a BladeMaker demonstration plant in Germany, with the aim of becoming a national and international center for the research and development of rotor-blade production.

Another key trend in wind energy is composite turbine-blade modeling. 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. Defining aerodynamic properties of blades is critical in delivering outer shapes avoiding significant cracks in the aerodynamic structure. Advanced capabilities are needed to generate high shape quality — for example, a powerful and complete set of modeling capabilities, free-form and section-based modeling capabilities, realistic and fast quality analysis tools, and shape optimization capabilities.

Blade lifespans of 20 years and beyond require highly industrialized production planning and manufacturing processes. Process standardization is essential and requires integrated planning to define standard manufacturing processes and resource libraries. Quality assurance planning and measurements for critical manufacturing steps are integrated in the process plan. Designing the composite lay-up in line with the complete blade assembly makes it possible to streamline the design process. This ensures higher accuracy and reduces the number of physical prototypes needed to finalize the design. Powerful design-optimization tools include the ability to swap ply edges, optimize drop-offs, shape plies and reroute sets of plies along a preferred path.

Wind blade load strength modeling.

To test the blade durability/reliability, many different loading conditions that simulate various wind conditions are applied. Rotor-blade manufacturing continues to be a labor-intensive process, but the strong drive to lower power-generation cost is making it increasingly urgent to automate production. Both the process plan and work instructions generated are model-based, and can thus be updated easily after a change is made on the design side. To lay the fabrics on the mold accurately, best-in-class nesting, cutting and laser projection solutions are fully integrated in the design environment to optimize ply lay-up for the composite model.

Simulation and off-line programming of automated tape-laying and automated fiber-placement machines can be performed through partnerships with leading machine-tool manufacturers. By using design data directly, design changes are automatically reflected in both 3-D simulation and the generated machine programs. Robotic solutions also simplify automation of composite production lines, as well as simulation and programming of water jet or ultrasonic cutting, gluing/painting or stitching robots.

Nondestructive testing (NDT) is another important technology in composite manufacturing. NDT can detect internal defects that are not visible externally but may have a huge impact on the work piece integrity. NDT can be performed by a machine or a robot, simulated and programmed upfront. For large blades over 60 meters long, wind-blade manufacturers need to manage large tools, and it is all the more critical to check whether there is a deviation between the produced physical part and the design intent. This can be done using measuring devices — coordinate-measuring machines (CMMs), laser trackers — with programming and simulating solutions that generate a report to compare the "as built" against the "as designed."

Composite wind-blade design optimization is a critical focus point. As wind turbine manufacturers seek additional ways to reduce costs and improve performance, attention has turned to improving modeling techniques as a way to reliably predict wind turbine behavior prior to expensive prototyping and testing. In particular, better designed wind-turbine blades are more effective, and they create significant savings for the tower and drive train, major components in the overall wind energy system.

Variational Asymptotical Beam Sectional Analysis (VABS) software, has recently gained the attention of the wind industry for its unique capabilities in realistic modeling of wind-turbine blades. VABS is an efficient high-fidelity, cross-sectional analysis program and a unique tool capable of realistic modeling of initially curved and twisted anisotropic beams.

Blades on wind turbines and helicopters have arbitrary sectional topology and materials. The program offers users a powerful, general-purpose, cross-sectional analysis tool to calculate sectional properties, including structural properties — tension center/neutral axis, centroid, elastic axis and shear center, shear correction factors, extensional, torsional, coupling, bending, shearing and stiffness along with principal bending axes pitch angle, modulus weighted radius of gyration. Inertia properties calculated by the program include center of mass and gravity, mass per unit span, mass moments of inertia, principal inertia axes pitch angle and mass weighted radius of gyration.

Using VABS for efficient, high-fidelity design and analysis allows saving 2-3 orders of magnitude in computing time relative to 3-D Finite Element Analysis (FEA) and without a loss of accuracy. In one example, a cantilevered beam with airfoil under thermal loading, predictions from VABS have excellent agreement with results from a highly regarded 3-D FEA code. However, the 3-D FEA took 3 hours, 5 minutes, and 23 seconds to finish the calculation, while the VABS analysis was completed in 37 seconds.

The images present the 3-D mesh in the FEA program (top) in its global view (white) and a close-up of its edge. The 2-D mesh (bottom) was generated in the VABS program.

AnalySwift's VABS 3.6 release can handle larger models than previous versions. A realistic blade meshed with 200,000 degrees of freedom using a typical laptop takes less than 20 seconds for constitutive modeling.

Dr. Donald V. "Don" Rosato serves as president of PlastiSource, Inc. a prototype manufacturing, technology development and marketing advisory firm located in Concord, Mass., and is the author of the Vol 1 & 2 "Plastics Technology Handbook".