By Ali Trueworthy

I want to put things in the ocean that can generate electricity. In pursuit of that, I do research which works to answer the question, “How do we design things that go in the ocean and generate electricity?” This is different from, “What things can we design that go in the ocean and generate electricity?” If I can answer the how, the answer to the what will be much better.

Imagine you build houses in the arid Arizona climate. One day, someone asks you to build a house for a family in New England. Given that the structure and methods you use to build homes in the Southwest are unique to the geography and climate of the region, you realize that if you build the same kind of house in New England that you build for families in the Southwest, it probably won’t turn out well for your customer. You have been given a new set of design challenges. What might you do? Would you visit New England, note things about the weather and the houses that are already there? Or maybe, since you live in the 21st century, you would use what you know about construction combined with what you can learn on the internet about New England weather and New England home construction to make design choices.

Now, imagine you have been asked to build a house for a family to live in the ocean. That’s right, not on the ocean, but in the ocean; preferably where the waves are big, frequent and full of energy. Now, if you are thinking, “no problem, I know a guy who lives in a pineapple under the sea,” I point out that his property on Bikini Bottom is far from where the waves are big, frequent, and full of energy. The family you are working with wants to be where the action is! If step one is still to visit the location of the house, suddenly it’s not as easy as getting on a plane. Even if you were to get out to visit, there wouldn’t be other houses floating around for you to take note of. Once you go below the surface of the water, your senses can’t provide you with nearly as much knowledge. So, you have a lot of questions. The main one is, “How do I build a house for this family to live in the ocean?” You aren’t even thinking about what the house looks like yet, you are just thinking about step one: what should I do?

This is the question I try to answer for designers and developers of wave energy converters (WECs). I use what we know about the ocean and the ways people design complex systems, along with what we have learned from previous tests and models of WECs, to develop methods for how we should design them. If we want low-cost, clean energy from ocean waves, we must develop the design and assessment methodologies to help designers succeed in an environment in which there are very few models of success.

Tabeel Jacob is a mechanical engineering doctoral student focusing on thermal fluid sciences. He is advised by Brian Fronk, assistant professor of mechanical engineering.

By Tabeel Jacob

Have you ever heard of a “refrigerant?” It almost sounds like “refrigerator,” right? Well, if you thought they might be related, you’d be right! In fact, a wide range of our daily appliances and machinery – such as air conditioners, refrigerators, and automobiles – contain refrigerants. The refrigerants in these systems undergo a cycle of condensation and evaporation to absorb heat from the one location and release it at a different location. Doing so, provides the cooling effect that we humans have become quite reliant upon in the 21st century.

Refrigerants currently being used can be classified as Hydrofluorocarbons (HFCs). HFCs have favorable heat transfer properties. However, as numerous studies have confirmed that HFC emissions contribute to global warming, these refrigerants have fallen under scrutiny given their environmental impacts. To combat this, majority of the developing and developed countries, through international agreements, have agreed to reduce their use of HFC refrigerants by more than 80% over the next 30 years. Finding a viable alternative to HFC refrigerants is crucial for these plans to succeed.

An experimental facility designed and built by Tabeel to test the performance of new low global warming potential refrigerants.

In order to mitigate the impact of HFC while still being able operate daily heating and cooling equipment, mixtures of hydrofluoroolefins (HFOs) and hydrofluorocarbons (HFCs) have been proposed as a potential alternative to pure HFCs. These HFC/HFO mixtures have significantly lower global warming potential (GWP), the measure of a gas’s contribution to the heating of the atmosphere. A higher GWP indicates an increased amount of heat trapped by the gas in atmosphere. For example, R404A is a widely used refrigerant with a GWP of 3922. It is set to be replaced by R448A, an HFC/HFO mixture with a GWP of 1273. That’s less than one-third of the GWP of R404A! Unfortunately, there is currently not enough experimental data available on the heat transfer capabilities, specifically condensation, of these newer refrigerants. This data is necessary to accurately design critical components in our daily appliances.

Previous studies on similar mixtures have reported decreased condensation performance as compared to their pure components at similar operating conditions. This occurs because theunderlying heat transfer mechanisms during condensation of mixtures differ significantly than those of pure refrigerants. Therefore, the appliances designed to use HFC/HFO mixtures may require different components than those developed for pure refrigerants. Motivated by the need to better understand the phase change process of HFC/HFO refrigerants and the need to reduce the impact on the environment, the focus of my doctoral research is to investigate the condensation heat transfer performance of low GWP refrigerant mixtures. An experimental facility designed specifically for this application will be used to test the performance of these new refrigerants. The experimental data will be used to introduce equations that can be used to design critical components for heating, cooling and refrigeration applications. The results of the study will be shared with industry and academics in order to further facilitate the adoption of low GWP refrigerants.

By Suresh Ramasamy

A majority of mobile robots that operate in the world around us either use wheels or legs for locomotion. The reason for this is the inherent simplicity of operation in the case of wheels and easy access to environments of societal interests like buildings, stores, and warehouses in the case of legs. These modes of locomotion generally perform poorly in environments with either heterogeneous ground or deformable substrates like sand, mud, and soil. The diversity of locomotion methods employed successfully by different animals in these harsh environments suggest alternative modes of locomotion are critical for robots to operate efficiently in these environments.

A major stumbling block while studying robots which employ novel methods of locomotion is that most strong results are limited by a set of assumptions (such as the quasi-static assumption, which is essentially assuming all the forces on the robot are always in balance) or are applicable to only a particular robot morphology (like bipeds or quadrupeds). The lack of a universal framework impedes comparison of different approaches to locomotion and hinders discovering fundamental principles that apply to all locomoting systems. One approach to developing a unifying framework to analyze, design and control robotic locomotion is to determine the normal form or a small set of normal forms of the equations of motion, that can capture the mechanics of a very large class of locomoting systems. With this goal in mind, a normal form of the equations that describe mechanics of locomotion when the interaction with the environment is described by a nonholonomic constraint (In locomotion analysis, a constraint is holonomic if it relates the shape of the robot to the position of the robot. All other types of constraints are classied as nonholonomic constraints.) was presented in [1]. My long term research goal is to develop, understand and use these normal forms to create frameworks that simplify locomotion analysis and help identify optimal locomotion strategies for robotic systems that employ novel methods of actuation.

For robots operating in a fluid, the origin of the drag force it experiences lies in the need to displace the particles of the fluidout of the way of a moving object. At low velocities, the movement of the fluid is smooth and the faster the object moves, the greater is the amount of fluid it has to displace. This leads to a linear relationship between the velocity of the robot and the drag force it experiences. This causes the equations of motion to take the form presented in [1]. The motion of paramecia-like vehicles (which move by an interaction of a periodically vibrating boundary and the fluid) can also be described by equations that take the form presented in [1]. So the normal form presented in [1] is already representative of a large class of locomoting systems. My short term research goal is taking advantage of the structure introduced by the normal form introduced in [1] to develop a framework that identifies optimal gaits for locomoting systems.

References
[1] J.P. Ostrowski and J.W. Burdick. The geometric mechanics of undulatory robotic locomotion. Interna-
tional Journal of Robotics Research, 17(7):683{702, 1998.

Suresh Ramasamy is pursuing a dual doctoral degree in robotics and mechanical engineering at Oregon State University.