Franck Vernerey

ME Course Column: Mechanics of Snow

Anonymous — Thu, 17 Mar 2022 15:45:29 +0000

ME Course Column: Mechanics of Snow Anonymous (not verified) Thu, 03/17/2022 - 09:45

Rachel Leuthauser

The ME Course Column is a recurring publication about the unique classes and labs that mechanical engineers can take while at the University of Colorado Boulder. Follow the series to understand the core curriculum, discover elective course options and learn the broad applications of mechanical engineering skills.

Most mechanical engineers will work with materials such as metals, polymers, ceramics and composites during their careers. However, a course taught by Department of Mechanical Engineering Professors Francois Barthelat and Franck Vernerey asks students to draw inspiration from another material – snow.

“I am a backcountry skier and as such, you have to learn a lot about avalanches and take courses for safety,” Vernerey said. “You realize there is so much mechanics involved with snow.”

Above: Professors Francois Barthelat and Franck Vernerey
Header image: Barthelat and Vernerey guide students through a slide test.

MCEN 4228/5228: Mechanics of Snow motivates students to look at their environment and the materials around them in an analytical way. The idea behind the course is to teach students the science behind certain phenomena by looking at the fundamentals of snow and ice from the atomic level to the mechanics of the snowpack.

“Snow in itself is an interesting material to study, you do not necessarily think of looking at snow in the context of mechanics of materials, but there is a lot to learn from this approach,” Barthelat said. “This is a great a way to expose students to state-of-the-art experimental and modeling techniques that people use in engineering.”

While studying the properties of natural versus artificial snow, the mechanics of sliding on skis and snowboards, or the conditions that trigger avalanches, students also master theoretical tools such as fracture mechanics and heat transfer. They also learn about the relationship between molecular structures, thermodynamics, and micromechanics, including viscoelasticity.

The professors explained that applying these critical engineering concepts to snow helps students better understand the information. It allows them to see that these concepts are real and happening in our environment.

“We often teach mechanics of materials and students are not always connected to the course because they have not worked with the materials before,” Vernerey said. “They learn the equations but may have difficulties connecting them to the real world. This course allows them to better connect because they already have an idea about the material. They are much more motivated to learn.”

Mechanical engineering students conduct slide tests on a snowboard.

Students in Mechanics of Snow conducted their own research out in the elements on March 10, after Boulder received about four inches of snow. They measured the densities of the fresh and old snow, assessed their compressive strength and calculated the snow’s coefficients of friction on skis and snowboards.

The class will take one more field trip outside to conduct strength and fracture tests on the snow before completing final projects to wrap up the semester. Some students are looking at avalanche conditions, while others are studying the impact mechanics of snowballs or snow construction such as igloos and walls.

“A big takeaway from this course is that students will be exposed to a vast number of topics in engineering and physics,” Barthelat said. “If they need these in their professional life later on, they know that the concepts exist and where to find more information.”

Mechanics of Snow is a technical elective open to upper-level undergraduate and graduate mechanical engineering students.

View all the Mechanical Engineering Technical Elective Courses

MCEN 4228/5228: Mechanics of Snow motivates students to look at natural materials in an analytical way. The idea behind the course is to teach students the science behind certain phenomena by looking at the fundamentals of snow and ice from the atomic level to the mechanics of the snowpack.

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The physics of fire ant rafts could help engineers design swarming robots

Anonymous — Wed, 02 Mar 2022 21:49:16 +0000

The physics of fire ant rafts could help engineers design swarming robots Anonymous (not verified) Wed, 03/02/2022 - 14:49

A new study led by Professor Franck Vernerey lays out the simple physics-based rules that govern how these ant rafts morph over time: shrinking, expanding or growing long protrusions like an elephant’s trunk. The team’s findings could one day help researchers design robots that work together in swarms or next-generation materials in which molecules migrate to fix damaged spots.

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Video: Emergent behavior in fire ants

Anonymous — Thu, 06 Jan 2022 16:51:00 +0000

Video: Emergent behavior in fire ants Anonymous (not verified) Thu, 01/06/2022 - 09:51

Rachel Leuthauser , Cody Johnston

Great discoveries lie at the edge of chaos, and nature provides perhaps the best inspiration for finding order in anarchy. Fish school, birds flock, fireflies sync and ants colonize. This type of collective behavior that forms complex and adaptive systems is what scientists refer to as emergence.

Studying emergent behavior has long fascinated engineers, and researchers at the University of Colorado Boulder have uncovered a distinct behavior in colonies of fire ants cooperating in flood situations. PhD candidates Robert Wagner, Kristen Such, Ethan Hobbs and Professor Franck Vernerey studied how the ants spontaneously form tether-like protrusions that help them navigate and escape flooded environments.

They found the dynamic shape that the fire ants take on is sustained by competing mechanisms of structural contraction and outward expansion. The researchers hope their work will inspire future studies by providing swarm roboticists and engineers with ant-inspired rules that could help achieve complex functional tasks.

Their research was recently published in the Journal of the Royal Society – titled "Treadmilling and dynamic protrusions in fire ant rafts." Check out the video below to watch how the ants form their own interconnected, floating raft.

[video:https://www.youtube.com/watch?v=IrLc-uDv7GU]

Studying emergent behavior has long fascinated engineers, and researchers at the University of Colorado Boulder just uncovered a distinct behavior in colonies of fire ants cooperating in flood situations.

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Researchers scale up tiny actuator inspired by muscle

Anonymous — Thu, 12 Nov 2020 17:38:38 +0000

Researchers scale up tiny actuator inspired by muscle Anonymous (not verified) Thu, 11/12/2020 - 10:38

Oksana Schuppan

Researchers at CU Boulder are collaborating to develop a new kind of biocompatible actuator that contracts and relaxes in only one dimension, like muscles. Their research may one day enable soft machines to fully integrate with our bodies to deliver drugs, target tumors, or repair aging or dysfunctional tissue.

Assistant Professor Carson Bruns (left) and Professor Franck Vernerey (right).

Professor Franck Vernerey of the Paul M. Rady Department of Mechanical Engineering and Assistant Professor Carson Bruns of the Paul M. Rady Department of Mechanical Engineering and ATLAS Institute received $477,000 from the National Science Foundation to begin this three-year project in January 2021.

“We are investigating an emerging class of materials known as slide ring polymers that resemble beads on a string,” said Vernerey. “When the network is subjected to a controlled stimulus, the bead-like molecules can slide around, which allows for a new way to actuate the material.”

Naturally occurring molecular machines in the body perform vital cell functions, such as gene replication, protein synthesis or transportation of intracellular cargo. Artificial molecular machines—inspired by those in nature—were recognized by the 2016 Nobel Prize, awarded to early pioneers in this area. Now, Bruns and Vernerey aim to scale up these tiny machines from nanoscale to macroscale using networks.

Instead of one molecule, a network incorporates numerous molecules, linked and working together, as occurs naturally in muscle. The process of starting small and scaling up allows the manmade material to copy how nature organizes molecular machines. To ensure the best results, Vernerey will also create a multiscale model to generate predictions that will help determine exactly how to tweak the molecular structure for the most effective scaling.

“The part that Franck’s group is doing is the first of its kind for these materials,” said Bruns. “It keeps my group from having to go into the lab and make hundreds of networked molecular machines until we find the property that we’re most interested in.”

Likewise, Vernerey said there would be no models without Bruns. “We make for a very cool integration,” said Vernerey.

A schematic showing a slide ring network relaxing (left) and contracting (right). The bead-like molecules slide around, allowing for a new way to actuate the material.

Hydrogels currently are the main available actuator based on molecular interactions, which change shape based on temperature, pH or pulses of electricity. However, these actuators are limited in that they cannot change shape in only one dimension. When a soft material experiences a change in volume instead of just length, its movements are slower, harder to control and a less efficient use of energy.

“Imagine the actuator is a sponge soaked in water, and it takes a long time for the water to leave,” said Vernerey. “The larger the actuator, the longer you have to push out. This means when you want to scale it up, this approach becomes unrealistically slow. The only way to make things fast is to contract without volume change.”

Natural muscle, the inspiration for this project, does this quickly in the body. Each molecular machine pulls on polymer ropes in a microscopic tug-of-war, and the movements collectively result in the muscle shortening to contract and fully extending to relax.

“Another consideration is that our materials can be made to be self-healing, and they are biodegradable, both properties of muscle,” said Bruns.

Bruns said their materials are made of non-toxic, food-grade products. This is significant, because most other actuators—especially those that rely on electricity—are not safe to use inside the body.

“While we hope there will be applications, we are equally interested in better understanding these systems,” said Bruns. To this end, Bruns and Vernerey are also developing interactive lessons in this area for high-school and undergraduate students.

“If you tell a student in high school, I’m just building a polymer, they might not be that excited,” said Vernerey. “But this project has great applications which will help them to be excited about the physics.”

Whether their findings help in tissue engineering or in developing soft micro-robots to mimic and guide cells, among other applications, Bruns and Vernerey said they are excited to be on the frontier of nanotechnology, gaining a better understanding of molecular machines and networks.

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