Engineers are increasingly turning to the already perfected designs found in nature to create lightweight and optimized products. And one software program—also inspired by nature– optimizes the CAD model for the job at hand
Jean Thilmany, Senior Editor
Want an example of efficient, environmentally friendly design? Look to nature.
When engineers take a biomimetic approach to their projects, they’re taking inspiration from how plants and animals, even the microbes around us, work. Nature has had eons to perfect its systems and shapes. Engineers haven’t. But they can crib from nature’s design methods and at least one form of CAD and analysis technology—itself based on biomimicry—can help.
Advances in additive manufacturing techniques mean the unusual geometries found in nature can be attempted and feasibly manufactured today.
For a modern-day example of biomimicry (that is, engineers drawing upon biology for their designs), look at the 500 Series Shinkasen Japanese bullet trains, which can reach speeds up to 200 miles per hour. This train was developed in 1992 to test technologies for future bullet trains. For the 500, designers wanted a fast train that ran quieter than earlier models.
Designer Eiji Nakatsu modeled the train’s nose after the beak of the kingfisher bird, which dives from air to water with very little splash thanks to its aerodynamic beak. The 500 is not only less noisy than earlier versions of the bullet train, it uses 15% less electricity and travels 10% faster, he says.
A few years ago, researchers in the University of California, Berkeley, Biomimetic Millisystems Lab created an adhesive based on the method geckos use to climb walls or hang from a tree branch from just one toe. They created the self-cleaning adhesive made from the long, slender polypropylene fibers that mimic the millions of hair-like structures called setae on the bottom of a gecko’s toes.
The adhesion is based on the geometry of the fibers: sliding the tape against a surface uncurls the fibers to engage the adhesive while sliding the tape in the opposite direction causes it to unstick, says Ronald Fearing, an electrical engineering professor at the school who led the research.
Because engineers could optimize the geometry of the polypropylene fibers using engineering analysis software, the adhesive can be made much stronger and stickier than a gecko’s feet. Also, the gecko adhesive, unlike conventional adhesive tapes, does not feel sticky to the touch, Fearing says.
Making things lighter, stronger and faster has long been the goal in engineering and biomimetics is one tool that can help. Automotive and aircraft companies—to name just a few—want to decrease the weight of their products as much as possible so they burn less fuel and are easier to handle.
Some of them—Airbus, Boeing, and Volvo among them—are using a topology optimization tool to cut excess material and weight. The tool is itself based on algorithms derived from a natural, biological process.
From the body to the aircraft
Engineers have been using the OptiStruct topology optimization program from Altair Engineering to optimize their CAD models for weight and strength. The program does this in the same way bones grow to be as light and strong as possible, says Janine Benyus. She’s co-founder of the Biomimicry Institute, of Missoula, Mont., which states its mission is to promote the transfer of ideas, designs, and strategies from biology to sustainable human systems design.
The OptiStruct program, developed by Jeff Brennan, is based on the way human bones grow. As a biomedical graduate student at the University of Michigan, Brennan investigated the theory that bone growth responds directly to external stimuli, he says.
He and his fellow researchers created a mathematical model to represent bone growth in the human body, theorizing the model could help point medical researchers toward ways to induce bone growth to treat conditions like osteoporosis. They found that bones grow in response to stress into an optimal structure through trial and error, says Brennan, now chief marketing officer at Altair.
And bones, of course, are not stiff and heavy. Rather, they’re porous, lightweight, but very strong. Many engineered structures could be designed in that same way, he says. Brennan applied the mathematical growth patterns seen in bone to static structures to bring to them that same type of lightweight, strong flexibility.
Brennan’s model is now the basis of the Altair topology optimization program. Engineers use topology optimization to discover the best way to distribute material throughout a structure, given their goals for that structure as well as their set of constraints.
Now companies in many different industries use the Altair software to analyze and optimize structures for strength, durability and noise, vibration and harshness (NVH) characteristics and to help improve on existing designs, Brennan says.
For instance, the software was instrumental in helping Airbus reduce the materials used for certain wing and airplane rib assemblies by up to 40 percent, Benyus says.
“It’s pure biomimicry in the sense that by studying bones and then mathematically describing what it is they do to make themselves lighter, we’ve been able to save all of this material, but you wouldn’t look at that plane and say, ‘That’s biomimicry,’” she says. “But there’s biomimicry inside, and I really think that these are some of the most powerful things, these algorithms.”
The software offers engineers a different way of thinking about the design process. They can use topology optimization to specify constraints and them simulate potential designs before they’ve created their initial CAD model, Brennan says. They can choose the best of the potential designs returned to them and then further optimize them and adjust to their own needs, he adds.
The designs suggested by the tool may require some additional redesign or tweaking so as to be manufactured using traditional processes. The tool may suggest unorthodox shapes that just can’t be made with the help of a CNC machine or with an extruder, for example.
Though 3D printing is changing that…
As additive manufacturing continues to evolve it gives engineering companies the capability to manufacture nontraditional designs. Because 3D printers build up materials layer after layer they can print objects with any type of geometry. With 3D printing, for instance, designs can be created in intricate or swirling shapes. It also means patient aids like a prosthetic limb or dental implant can be printed exactly to the wearer’s unique shape and specifications.
And the printers can now produce objects in a variety of materials. The introduction of engineering-grade metals to 3D printing, along with the already-existing array of engineering-grade thermoplastics, means manufacturers can build parts that are strong, yet lightweight, and that can be used directly in the final product.
Look, up in the air (the design of slime)
Airbus continues in its efforts to reduce the weight of the aircraft by using biomimicry and additive manufacturing.
Bastian Schäfer, an Airbus engineer, believes the capability to 3-D print airplane parts that range in size up to and including the plane’s very skeleton structure will revolutionize air travel. These lightweight additively produced parts will make planes that weigh much less than today’s models. A lighter plane uses less fuel and reduces the amount of greenhouse gases it emits. Planes with a smaller carbon footprint could be bigger and roomier, with improvements like larger and moldable seats, Schäfer said.
For him, the move to a 3-D-printed airliner begins with a printed partition his group unveiled two years ago and continues to perfect.
Schäfer is project manager on what his group calls the Bionic Partition Project. The project itself is under the purview of the Airbus Emerging Technologies and Concepts Group, led by Peter Sander.
Working under Schäfer, the group has created a 3-D printed partition to separate the seating area on the A320 from the galley. The partition weighs 45% less than the 7-feet-tall partitions now used on that model. It’s also substantially stronger, as the team replaced the component’s solid aluminum alloy parts with a number of slender, 3-D-printed metal pieces that connect to form a lattice of the same shape and size as the existing partition. The lattice is then covered in a thin material.
Partitions of this nature are large, weighty, and can be somewhat of a design challenge, Schäfer said. It needs to include a cutout wide and tall enough for a hospital stretcher to pass through and to be strong enough to anchor the two seats that fold down from the frame, which flight attendants sit in for takeoff and landing. And it must withstand impacts of up to 16 g-force. Oh, and it also must be less than 1-inch thick (to save space) and attach to the plane in only four places to decrease the weight of connecting hardware and to make for easy changeout.
With all that in mind, the team turned to nature. The partition’s internal, 3-D-printed structure mimics that of human bones, which, though light, have a high strength-to-weight ratio as they are dense at their stress points. Schäfer’s team designed a lattice structure comprised of metal pieces that are printed individually and then fit together to form the partition.
The Living, an Autodesk-owned design and prototyping studio in New York, also played a part in the project by creating the biological algorithm that would allow for the mimicking of human bones.
“Our algorithm was based on the growth of an organism called slime mold,” says David Benjamin, head of the group.
The mold grows and stretches its form to connect a set of points—or locations of food—with the minimum number of lines. It also has built-in redundancy; each point is connected with at least two lines so if one fails, the point is still connected to the network, or slime body, he says.
“The mold spores are efficient because they use the least amount of material to connect the dots. And they are redundant because when one of the paths is broken, the network can route around the problem and stay connected,” he said. “Although the size and material of the partition is different than that of slime mold, the logic is similar. And in our application, this approach worked very well.”
Schäfer has plans to further improve upon the partition’s existing design and build. He’d like to cut out a step in the manufacturing process by printing larger pieces of the structure at once, rather than printing the individual parts that are then fit together. Printer size now limits this capability.
The partition isn’t in production, but that will probably change within five years as Airbus furthers its move toward lighter planes, Schäfer says.
While no slime mold was injured in the making of the Airbus partition, the lowly organism will soon be helping the planes use less fuel—and emit fewer greenhouse gases—as they fly through the skies.
You may not want to thank the slime mold in person, but the engineers who use it—and well as many other natural designs—for inspiration—may just to do it for you.
Altair Engineering
www.altair.com
