Professors J. Gregory McDaniel
and Karen Warkentin

Professor J. Gregory McDaniel’s research focuses on acoustics and vibrations—but it is by no means confined to that specialization. Professor McDaniel is able to look at seemingly disparate topics—from the “how’s” and “why’s” behind squealing brakes on automobiles to the early hatching of frog eggs that sense an oncoming predator. Grants from the National Science Foundation, the Office of Naval Research, and the Ford Motor Company enable Professor McDaniel to investigate ways of analyzing and improving acoustical damping in complex vibrating structures.

Q. Tell me about the classes you teach.

A. I’ve taught various undergraduate courses. I teach Statics and Dynamics courses and “Mechanics of Materials.” I also teach “Engineering Mathematics.” Last, but not least, I teach “Atmospheric Flight Mechanics,” which I have taught more than anything else.

Q. Tell me more about that course.

A. Some people call it a hybrid course because it combines material from different areas. We do problems that are viewed by some people, including me, as design problems. Students are asked to try many different aspects of controlling airplanes. They do a project with a “real” airplane on a computer that uses data from an actual airplane. They go through the dynamics of that plane, design an autopilot and write a report.

This semester we added a lab experience. In our lab, we have a radio-controlled, scale airplane on a pivot that “flies” and can be controlled. It’s as close to flying an airplane as you can get without being dangerous. You can move it with your hands and watch it do different maneuvers. It allows you to really explore airplane dynamics. We were the first aerospace program in the country to get one.

Q. Tell me about the research you’re involved in.

A. My Ford Project probably gets the most press. Some BU journalism students made a movie on this particular project. In the movie the students interviewed me and asked, “What do you think would happen if you eliminated brake squeal?” Then, they interviewed a local mechanic and asked him the same question. He said it would put him out of work!

We did another study about how brakes actually produce sound. Most people investigate why brakes vibrate in the first place but there is a difference between vibration and sound. Not everything that vibrates produces sound. We started looking at how the brake actually produces sound—not why or how it vibrates, but how that vibration is turned into sound. We found a strange coincidence: the brake rotor itself, the thickness and the geometry, is optimized to project sound. Once it vibrates, that vibration can turn into sound more efficiently than nearly anything else. Brakes are more efficient at creating sound than a Stradivarius violin.

I have also been working with faculty in the biology department, primarily Professor Karen Warkentin. Professor Warkentin discovered something profound and new in the rainforest: certain creatures can be born early to escape death. This is a philosophically profound concept and a new discovery for biology. In the rainforest, mother tree frogs lay their eggs over small bodies of water. When tadpoles hatch out of the eggs, they fall into the water. The eggs are clustered together in a “clutch,” and their predators include snakes and wasps. When the tree snake comes up, grabs one egg, shakes it, and tries to eat it, it’s connected by a sort of “glue” to the other eggs. The snake shakes it around for a while until it becomes disconnected. In the meantime, the shaking produces vibration, which the embryos seem to sense, causing them to get out of the eggs. They hatch early and fall into the water and try to survive.

Professor Warkentin narrowed it down with a series of very clever studies about vibration, and we figured out a way to artificially vibrate the clutches of eggs to make the frogs hatch prematurely.

To watch a brief movie on this phenomenon, click here (requires Quicktime: download free plugin here)

We are doing a study that combines engineering and biology in a way that’s truly multi-disciplinary. In fact, it’s so multi-disciplinary that we speak different languages to each other. It’s been a great experience, however. How these eggs sense and process vibration is a big mystery. How much knowledge can they store? What do they pay attention to. To make matters even more interesting, the clutch vibrates when rain falls on the leaf and when wind blows. They’re able to distinguish between vibrations. They assess the risk. People I tell about it, and I’ve told lots of acoustics and vibrations researchers, are absolutely fascinated by it—at least more fascinated than they are by brakes (laughs).

Q. How does this type of research benefit your classroom teaching?

A. Part of the art is to find the right moment to inject research into the class. In some cases, there is a very clear connection. I talk to seniors about mechanical vibrations, opening their eyes to complex vibrations. I’m able to talk about brake squeal in “Introduction to Engineering” in a context that’s very concrete.

It has been said that “knowledge is best taught by people who are in the midst of creating.” I think that describes my feeling. To generate curiosity in the students before you give them the answers mimics the research process. I wouldn’t do research on something if I knew the answer ahead of time. What drives me in research is a curiosity about the final answer. Similiarly, if you say to a class of students, “After two hours the answer will be on the board,” that won't generate curiosity. What I try to do in class is to re-create the research environment, where you keep wondering about the answer.

If an unaswered question drives you to do good research, then it’s going to drive students to engage in the material. By the time you get to a senior aerospace class, most students are pretty conscientious. The challenge then is to get them to come to their own inner peace with the material. I told my class, “I hope everyone grasps that you came in here knowing a fundamental level of dynamics of rigid bodies, and that you’re leaving the class with the ability not only to calculate and understand how an airplane moves through the air, but to develop a controller for it. I hope that you can appreciate the magnitude of the knowledge you’ve acquired.”