SUSTAINABLE CAD
CAD offers tools that significantly improve the ability to apply sustainable design practices. Software is available that assists all elements of sustainable design, from manufacturing material selection and usage to product life cycle assessment. A powerful example of sustainable design with CAD is developing a digital prototype of a product as a 3-D solid model. Digital prototyping was described in the Prototyping section earlier in this chapter. Digital prototyping can support sustainable design by leading to lower costs, reduced material consumption, and optimized use of energy. CAD allows the design process to occur in significantly less time, using fewer engineers and technicians and reducing physical prototypes, which are expensive and time-consuming to create and test. The following information describes how Utility Scale Solar, Inc. uses CAD technology to optimize the cost and material used in solar energy production.
Manufactures solar tracking equipment for large-scale solar power plants (see Figure). Solar tracking equipment, such as the USS Megahelion™ MH144 heliostat, accurately follows the sun as it moves across the sky to position solar reflecting surfaces, or solar panel arrays, for the best collection of solar energy. Solar collection units are very large, about three stories tall, and each solar power plant includes thousands of units. Therefore, reducing the weight and increasing the efficiency of solar tracking equipment can provide significant material and energy savings.
The patent-pending Megahelion drive and heliostat products are resistant to wind, dust, dirt, weight, and weather, which are common issues affecting the performance of solar tracking machinery. The Megahelion uses fewer moving parts, stronger components, and a system that distributes forces over a larger surface area than conventional drives, resulting in a fluid motion with fewer breakdowns and much lower ownership and operating costs. Unlike traditional drives that use gears or conventional hydraulics, the Megahelion™ drive uses flexible hydraulic cells to position the drive shaft.
USS relies heavily on modern CAD technology for digital prototyping. USS uses Autodesk Inventor and Algor® software for design, dynamic simulation, and finite element analysis (FEA). USS also uses Autodesk Vault Manufacturing software to manage CAD data and Autodesk Showcase® software to prepare images and 3-D visualizations for sales and marketing. According to Jonathan Blitz, USS’s chief technical officer, “The software has significantly streamlined what we are doing and made it much easier to visualize and communicate our designs. The ability to then subject these designs to realistic forces and loads has given us the confidence to remove the mass and streamline the components without sacrificing structural integrity.”
An example of CAD optimization at USS is the redesign of an endcap for the Megahelion solar tracker. The figure shows the original endcap design’s 3-D solid model and FEA analysis. The original component weighs 650 pounds, is overdesigned, and uses a cylindrical drum with a flat endcap. The objective was to redesign the part to distribute loads more effectively, enabling a reduction in material use and mass.
The focus of the endcap redesign was changing to a hemispherical shape that would bear weight, and wind loads more efficiently and naturally than a flat end plate. The figure shows a digital prototype of an early, nonoptimized redesign. USS used Autodesk Inventor 3-D solid modelling and stress analysis tools to simulate and test design options, including varying the hemisphere’s depth, the shell’s thickness, and the number of reinforcing ribs. Autodesk Inventor parametric optimization capabilities allowed USS engineers to optimize the design for reduced mass and automatically validate the design against project requirements.
After analysis, USS determined a more optimal design with a wall thickness of .5 in., an endcap depth of 6 in., and six ribs (see Figure). The simulation results show that stress and safety factors are within the specifications set by the design team. Compared to the original endcap design in Figure, the redesigned endcap uses less material in low-stress areas, shows less dramatic stress concentrations, and distributes the load more evenly and efficiently. The mass of the new design is 481 pounds, making it 26% lighter than the original part. USS now has an accurate concept of a product that should perform better, require less material and energy to produce and handle, and cost less to manufacture and transport.
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