Objective and Intellectual Merits: In an age where multidisciplinary interactions have become ubiquitous in science and engineering, the interaction of a flowing fluid and a deformable structure or solid is one of the richest sources of mathematical challenges and fundamental physical phenomena with important applications to engineering and technology. Examples of mathematical challenges are the chaotic, high dimensional modeling of turbulence that continues to defy rationale predictions from first principles to the many distinct and complex limit cycle oscillations that emerge from dynamic stabilities that arise due to fluid-structure interaction. The physical phenomena of interest range from blood flows in arteries, to airflow over an oscillating tongue that can lead to clinical dangerous and potentially fatal oscillations, to flow over flexible long span bridges and tall buildings, to flow over and around flight vehicles over a wide range of scales from micro air vehicles to modern passenger airliners, to fluid-structural systems whose limit cycles may be a source of energy harvesting.
The methods that have been proposed to better understand and exploit these phenomena include theoretical models of high sophistication including the continuum models of the fluid and the structure. While analytical solutions continue to be sought and found, computational models that tax the resources of the most powerful computers also play an important role as do scale model experiments based upon a sound fundamental analysis and understanding of the first principles of the relevant continuum models. Indeed it is by exploiting the complementary strengths of each approach, theoretical modeling, computational modeling and experimental scale models that the deepest and richest insights can be obtained.
Such a collaborative approach is proposed here. Professor Balakrishnan will lead the theoretical modeling effort, Professor Hodges will be primarily responsible for the computational models and Professor Dowell will be the lead for the experimental scale model effort. Taken together this will be a powerful and highly experienced team It is expected that each investigator and the members of their research teams will learn much about the multidisciplinary dynamics of fluid-structure interaction, and also from each other!
There are many physical phenomena that might be chosen to focus our research program. Based upon our experience and after consultation among the principals, two have been chosen for this research project, i.e. long span wing-like structures in a flowing fluid which are found in novel flight vehicle designs and long span bridges and flapping ?flags? which are studies as models of the human tongue and also have been proposed as energy harvesting devices from the natural wind.
Broader Impact: This proposal brings together senior investigators from three major research institutions covering a wide range of intellectual experience from modern mathematics to rigorously based computational models to multidisciplinary experiments to address fluid-structure interaction phenomena. This research will also provide an opportunity for graduate students and post-doctoral visitors to participate and learn in this rich environment.
High-altitude, long-endurance (HALE) aircraft have applications in many fields including national defense, weather forecasting, and traffic control. For extended uninterrupted flight, they need to be energy efficient and able to harvest energy. We found that the configuration of HALE aircraft can be altered with near zero energy cost. This can be accomplished by passively "morphing" the configuration, using only the flight controls (e.g., flaps and engine thrust). For example, we showed that a solar-powered flying wing can maximize solar energy absorbency by passively morphing into a "Z-shape" configuration so that solar panels installed on the wing are at an angle to achieve maximum exposure to the sun at different times of the day; see Figs. 1 – 2. The process of passive morphing is done with near zero energy cost, making use of the aircraft flaps and engine thrusts to provide the forces needed to change the configuration of the aircraft. This is in contrast to active morphing (by means of actuators at the hinges), which makes the aircraft heavier and requires electronic equipment to be placed on board, which uses a lot of energy to morph the wings. HALE aircraft must be very light and therefore highly flexible. Thus, to increase flutter speed typically requires stiffening the structure, which leads to added weight and higher energy consumption to fly the aircraft. We found that engines can be placed in such a way as to increase the speed at which the aircraft experiences flutter, a dangerous kind of instability, without increasing its weight. Thus, by optimizing engine placement, one can design a lighter weight aircraft with the same stability; see Figs. 3 – 4. These changes in design feature lighter and more stable aircraft, which consume a lot less energy. Another aspect of this approach proved that use of multiple lighter engines not only increase the safety of the aircraft but also increase the stability of the aircraft up to four times; see Figs. 5 – 6. Our methodology can provide benefits for example to national security, weather forecast, biomedical science, and conservation of national energy resources.
