September 25, 2017

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WESEP: Wind Energy Science, Engineering, and Policy

Manufacturing, Construction, and Supply Chain

Thrust Goal and Connection to Project Objectives

The primary goal of this thrust is to study phenomena associated with the production and deployment of wind turbines in an environment in which demand for wind turbine components outpaces supply, associated costs must be reduced to compete with traditional energy sources, and scale-up issues are created by increasing wind turbine size. The rate at which wind energy penetration levels can be increased depends on wind turbine and related component manufacturing resources and their production levels, and so this work directly addresses RO1. Wind turbine costs are directly tied to current wind turbine production practices and construction techniques, and so this work also impacts RO2.

Background and Need for Research

Four of the nine major issues identified in a recent DOE wind energy workshop are related to the manufacture and deployment of wind turbines. Research problems in wind turbine design, manufacturing, and materials are tightly coupled. Attaining the DOE 20% wind scenario will require wind turbine component production volumes on unprecedented scales. However, the manufacture of most wind turbine systems and their components is currently a labor-intensive process, affecting the production capacity, cost, and quality of components. Blade design and optimization of composite materials used in wind turbine blades directly impact the manufacturing processes and the capital cost of wind turbines. Research on new manufacturing methods and processes is warranted to reduce costs and increase growth. For example, the composites layup process for turbine blades accounts for the largest percentage of production labor of any process, has high variability in cycle time, and requires costly finishing processes. Research at the interface of materials and automation has the potential to significantly increase productivity and quality while reducing cost. The quality of wind resources at higher altitudes is driving wind turbine designs to greater heights in order to expand penetration limits. A major limiting factor is the weight of a nacelle (which includes the shafts, gearbox, generator, and controller) that is on the order of 50 to 70 tons. Major weight reductions and innovative construction methods can also facilitate taller towers. Components of taller towers and longer blades will exceed the current transportation constraints for both rail and highway systems. These problems cannot be overcome without advances in design, manufacturing, and construction technology. As we work to improve designs and associated manufacturing processes, we will also devise a plan to overcome the transportation constraints.

Dissertation Project Examples

Nacelle weight and cost reduction: As the size of rotors continues to increase, major advances will be required to achieve the necessary weight reductions. The weight and cost of a wind turbine is proportional to the cube of the diameter of the rotor. Reducing cost and weight will involve an interdisciplinary focus on issues in component design, materials, and manufacturing. Two major components of the nacelle, the gearbox and generator, account for much of the weight. Housings for the gearbox and generator are made of ductile cast iron due legacy design practices. In the automotive industry, weight reductions of 20-70% have been achieved using magnesium alloys. However, the use of these alloys is not scalable to nacelle housings. Given their improved stiffness to weight ratio, steel castings hold promise in achieving significant weight reductions on the order of 10%. With the current trend of increasing size and height of wind turbines, research on component designs using steel castings is warranted. Studies are needed on design and process optimization, selection of steel alloy, and market acceptance using finite element analysis (FEA).

Wave prediction in composite fabric layups: Turbine blades are typically manufactured using fiberglass composite material. Plies of glass fiber fabric are manually arranged in an open mold and then infused with epoxy resin. The edges of the blade can have many plies in order to provide sufficient load-bearing capacity in different regions of the blade. An important characteristic of the cured composite is the uniformity of plies. Wrinkles in the fabric that occur during the layup of plies can cause waves in the cured blade that significantly reduce its strength and can be a point of crack initiation.

Predicting the potential regions where wrinkles could occur based on mold design and material properties would be an invaluable capability in the design and manufacture of blades. Much of the previous work in predicting wrinkles has focused on a relatively small number of plies. Methods of analysis have included geometric modeling of the fabric as well as FEA. Students working in this area will need an understanding of aerodynamic design and loading, FEA, geometric modeling, design of experiments, composite materials, and composite manufacturing. Research would focus on theoretical models of fabric behavior based on mold geometry with validation through empirical studies.

Transportation infrastructure planning: The current transportation infrastructure was not designed to support the transport of large scale products such as blades, nacelles, and towers. A fragmented set of regulations exist due to individual states that define a constrained set of routes for trucks. The wind industry has pushed superload permits to astronomical numbers. Four to five are needed for each load — last year, 22,000 were needed for 5,000 wind turbines. Transportation preplanning is critical to delivery. There are many obstacles, including overhead objects, height requirements, and weight limits. Students will study optimization methods for the routing of shipments given current transportation infrastructure constraints. Transportation planning for the future of wind energy will examine the infrastructure necessary to support larger scale wind energy deployment using simulation models to predict infrastructure performance and identify critical infrastructure needs.

Design of taller towers and their foundations: Today, steel towers are fabricated in a factory, transported to the site as three cylinders, and erected in the field. The 80m height of these towers is limited by the transportation system. Given that taller towers will provide a cost-effective means to increase wind energy production in less turbulent and increased wind velocity conditions, increasing the tower height will significantly boost our nation’s wind energy production. Potential options to increase the tower height include manufacturing the tower in more pieces with additional fabrication on site, using a combination of concrete and steel, utilizing higher strength steel, concrete or other advanced materials that can facilitate towers of smaller diameters, or a combination of different techniques, all of which require collaborative research between material scientists, structural engineers, construction engineers and supply chain experts. As tower height increases, their foundations should also be designed cost-effectively, which is not done in current practice.

Key Faculty

  • John Jackman, Associate Professor – Industrial and Manufacturing Systems Engineering (Lead)
  • Michael Kessler, Associate Professor – Materials Science and Engineering, Mechanical Engineering
  • Frank Peters, Associate Professor – Industrial and Manufacturing Systems Engineering
  • Sri Sritharan, Professor – Civil, Construction, and Environmental Engineering
  • Judy Vance, Joseph C. and Elizabeth A. Anderlik Professor of Engineering – Mechanical Engineering