A Conversation with Assistant Professor Brenden Epps
Just a few months ago Brenden Epps was a postdoc at MIT. Now the first-time Assistant Professor at Thayer has returned to the Upper Valley Region—he visited in 2004 while hiking the Appalachian Trail—bringing a vast knowledge of fluid mechanics as it relates to wind and wave energy, which he is using to research aeroelastic modeling of offshore wind turbines. Epps took a few minutes to chat about his research and his experience since arriving in August.
What has your experience teaching at Thayer been like so far?
This fall I taught ENGS/PHYS 100, Methods in Applied Mathematics, which is targeted at first-year graduate students. I like to think of the class as "all the math you should know to be successful in graduate school," and try to emphasize the connections between different math topics as well as the connections between math and physics. One of my students summarized the class best by drawing a wrench and labeling it "math," drawing a nut and labeling it "physics," and saying that my class is about learning how to use the wrench to turn the nut.
Tell us about the underwater robots you built for MIT's Sea Grant College Program.
I am most proud of the software package I developed called OpenProp, which can be used for the design optimization and analysis of both marine propellers and wind turbines. The "Open" refers to the fact that we published the code open-source, and to date we have over 23,000 page views on the OpenProp website. In my research, I have used OpenProp to compare possible propeller designs and the resulting fuel efficiency gains for the U.S. Navy's all-electric ship. In addition to conventional marine propellers, I also investigated the forces and flow structures responsible for fish propulsion. The interesting part is how they kick their tails—what are the precise kinematics and how does that result in forward thrust? In my work, I quantified the vortex structures generated by the fish and the resulting thrust, which have since been verified and been used to compare different body kinematics for optimal propulsion.
I also looked at the canonical "free surface flows" problem of a sphere falling into a basin of water. When you cannonball into the water, you make a tremendous splash, and the resulting fluid dynamics and flow field are quite interesting. What's more interesting though is the case of no splash, which happens if you coat the sphere with a hydrophilic coating. The water remains attached to the surface of the sphere, and you end up seeing a vortex wake, much like that of the fish. In this case though, the vortices impart a tremendous drag on the sphere, actually slowing it down more than the case of the splash. It's important to understand how engineered structures interact with fluids and what the resulting forces are so that we can design efficient propulsion systems and design energy-harvesting turbine systems that maximize power production.
What are your research goals?
I would like to make offshore wind energy a reality. Building off my successes with OpenProp, one of my goals is to continue developing open-source computational engineering tools that can be used for the design and analysis of offshore floating wind turbines. In the offshore case, the fluid-structure interaction problems are quite complex, as the hydrodynamic (wave) forces, aerodynamic (wind) forces, structural loads, and controls systems inputs are all coupled, often non-linearly. I aim to use my strengths in computational modeling to tackle this complex problem. However, numerical models are only as good as the experiments they have been validated against.
Another goal of my work is to build and test scale-model prototypes in order to produce high-quality experimental data for code validation. I plan to use a combination of high-speed imaging, quantitative flow field characterization, and direct instrumentation and measurement of stresses in wind turbine blades in order to characterize the behavior of these turbine systems in unsteady wind and waves.
What attracted you to Thayer School?
Engineering problems don't fit nicely into different disciplines, so we shouldn't pretend that they do. I believe that the cross-pollination between mechanical engineers, chemical engineers, and so on makes Thayer stronger than schools with individual departments. I also appreciate having to explain my work in wind energy to really intelligent people who happen to have a very different knowledge base than I do. This helps me to become a better communicator, and it also sparks great conversation.