David Henann develops theoretical models for granular flow

Granular materials, a classification that includes everything from sand and gravel to cereal and grains to pills and pharmaceuticals, is the second-largest class of materials, in terms of volume, handled in industry. In spite of this ubiquity, mathematical models that represent the behavior of flows of dense granular materials are lacking. When a granular material consists of particles of different sizes, it is even more difficult to predict, since grains tend to sort based on size during flow. A better understanding of their behavior could make any number of industrial processes more efficient and less costly.

Brown Assistant Professor of Engineering David Henann is confident he can provide just that.

The National Science Foundation, equally confident about his early modeling work, awarded him an NSF CAREER project grant in 2016. The grant allows further development of a theoretical model that describes the behavior of flowing granular materials—specifically, a continuum theory that simultaneously predicts flow and size-segregation to account for the effect of grain-size differences. His success could not only help streamline industrial processes, but also better predict the dynamics of future landslides or mudslides.

“We started with a model predicting how dense collections of same-sized grains flow,” said Henann. “This gave us good predictions in many flow geometries. Now that we have a set of equations that works well when the grains are the same size, we’re working to incorporate additional physics, accounting for the effect of grain size differences.

“This is the fun part. Our research approach is to take it grain-by-grain in a deliberate way. We do discrete simulations, systematically progressing through various parameters to build up our model. Then, we test the model against simple physical experiments. Currently, we have several undergraduates working to design and build experimental equipment.”

For this work, and for his earlier work with other amorphous materials, Henann was recently awarded the 2016 Pi Tau Sigma Gold Medal from the American Society of Mechanical Engineers. The award—given to only one individual per year—recognizes outstanding achievement in mechanical engineering within ten years following graduation with a bachelor’s degree in that field. The only other Brown professor to have received the award is James R. Rice; Henann is currently the James R. Rice Assistant Professor of Engineering. A former professor at Brown for more than 16 years, Rice is regarded by many as the most influential scholar in the field of applied mechanics during the past 60 years.

Interestingly, a month prior to being named to the Rice chair, Henann received the Brown School of Engineering Dedicated Faculty Award from the engineering honor society Tau Beta Pi. And Rice held that a good professor must excel both in research and in teaching.

Henann has a deep appreciation not only of Rice, but of the many professors and graduate students who came before him and established Brown as a leader in solid mechanics. In fact, Rice’s “groundbreaking contributions to the understanding of the mechanics of granular materials” paved the way, says Henann, for his own research.

Henann, who earned his undergraduate degree from SUNY Binghamton and his Ph.D. from MIT, has been at Brown four years. The common thread running through his lab work is modeling the behaviors of complex material. Most of the graduate students in his research group are working on research supported by the NSF award. Others are studying soft elastomeric materials, dielectric elastomers (rubbery polymeric materials of interest for soft actuators, such as artificial muscles, and energy harvesting devices), and foam rubbers (which could prove helpful in applications from padding materials to military uses).

An additional project, involving cavitation in soft materials, is being undertaken with fellow Assistant Professor Christian Franck. “Our skill sets are symbiotic,” Henann said. “We have a couple of joint projects in the works between our groups.”

Collaborations like these are a hallmark of Brown’s engineering experience where, with students and faculty unconstrained by disciplinary or departmental boundaries, innovative research flourishes.