Balakumar Balachandran - US grants

This grant provides funding for exploring the development of a novel fiber optic acoustic system for high-frequency bandwidth measurements. The novelty of the sensor system will be derived from the inclusion of extrinsic sensing capabilities based on a Fabry-Perot cavity, an integrated optical circuit based phase modulator, a high-speed photo detector, and a digital demodulation scheme based on a new multi-step phase stepping algorithm. The Fabry-Perot cavity will be located between the fiber tip and the diaphragm structure of the sensor, and the Mach-Zehnder interferometer in the phase modulator will be path matched with the Fabry-Perot arrangement to act as a read-out interferometer. Both experimental efforts and analytical efforts will be pursued for developing the sensor and understanding the sensor mechanics.

A potential risk involved in the development of this sensor system is that it may not be amenable to multiplexing as the other fiber-optic sensors. If successful, the development of this sensor system will have a tremendous impact on integrated active control systems for sound and vibration transmission problems where currently multiplexable sensors for high-frequency bandwidth applications are not readily available. Furthermore, if the sensor system is adapted, it can be used for high-frequency bandwidth pressure measurements in underwater flows. The sensor system may also have applications in the automotive industry such as ignition chambers

This Small Grant for Exploratory Research (SGER) project is to explore the development of a unified mechanics model for prediction of chatter during high-speed milling; in particular, for systems with flexible tools and flexible workpieces. The developed model will include time-delay effects and loss of contact effects, and it will allow for features such as partial engagement of a tool with the workpiece. Stability information will be obtained by using tools from the nonlinear dynamics area. This model will be analytically and numerically studied to determine stability charts in terms of parameters such as spindle speed and axial depth of cut and the sensitivity of these charts to feed rate and feed direction will be examined. Experiments will be conducted to validate the model predictions.

A potential risk involved in the development of the model is due to the lack of readily available cutting force data for high-speed milling operations. If successful, the development of this model will have a tremendous impact on simulating workpiece-tool interactions, selecting machining parameters, and redesigning tools for important industrial problems such as the machining of T-shaped stiffeners and return flanges with long end mills and the machining of difficult-to-machine materials.

Over the last two decades, atomic force microscopy (AFM) has been used to measure the topography of a wide range of nanoscale samples, including semiconductor surface features, biomolecules, carbon nanostructures, and organic monolayers. Despite the tremendous progress, gentle characterization of nanoscale biological and other delicate structures remains a challenge since they are susceptible to tip damage. The University of Maryland at College Park has teamed up with Asylum Research to address this challenge. This is addressed by developing a nonlinear dynamics based tapping mode atomic force microscopy scheme, where the cantilever is to be excited away from its fundamental resonance and operated close to a period-doubling bifurcation point. In order to realize and demonstrate this scheme, multi-scale simulations are to be used to determine the tip-sample interaction forces and experiments are to be conducted with delicate materials including DNA, soft protein molecules (bacteriorhodpsin, actin & myosin), and squamous cancer cells.

From a fundamental standpoint, the proposed study can help understand qualitative changes associated with mechanical systems with soft contacts and non-smoothness. From an application standpoint, the extension of AFM capabilities to characterize a wider range of soft materials can help realize commercial benefits in the areas of healthcare, drug design, pathology, tissue engineering, biotechnology, and other high-impact emerging technologies that are intimately related to the well-being of human beings and where mischaracterization can have severe consequences, even including death. Further development of simulation methodologies will also help reduce costs associated with extensive experimentation. Finally, the application of nanoscale science to specific problems in a systematic manner will be useful in the education of the next-generation of students, which is essential to ensure the nation?s competitiveness in nanotechnology in the next few decades.

Over the last two decades, stochastic resonance, a nonlinear phenomenon in which the addition of noise to a stochastic system leads to a coherently amplified response, has been explored to explain the dynamics of systems ranging from the Earth?s climate to sensory neurons in a monkey?s ear. Although considerable work has been carried out in the context of physical and biological systems, the use of noise for the benefit of nonlinear mechanical and structural systems, in particular, their transduction properties, has not been widely explored. This is to be addressed here by developing a fundamental understanding of the phenomenon of stochastic resonance in coupled, nonlinear mechanical and structural systems, and use this understanding to develop novel mechanical and structural design methodologies that incorporate the advantages of stochastic resonance for enhancement of the mechanical transduction capabilities and signal detection capabilities of these systems. It is expected that this understanding will help use noise in a constructive manner in the design of nonlinear systems.

From a fundamental standpoint, as stochastic resonance is relevant to physical systems (periodic recurrences of ice ages, ring lasers, Schmitt triggers, optical devices, magnetic systems), chemical systems, and biological systems (sensory neurons), the findings of this study are expected to be important for a wide range of nonlinear systems including many outside mechanical and structural systems. For example, certain aspects of the study will carry implications for frontier research areas such as quantum metrology and quantum computation. From an application standpoint, the extension of the advantages of stochastic resonance in resonator arrays to the micro-scale and nano-scale can produce commercial benefits in the areas of sensing technologies and nanodevices. Finally, the application of stochastic resonance in nano-scale science to specific problems in a systematic manner is expected to be important for the education of future generations of students.

Extreme waves occur as an emergent phenomenon in many natural systems. These unusually large concentrations of energy coalesce from smaller adjacent perturbations. This energy focusing effect, which has been observed in ocean waves, fiber optic systems, and microwave systems, is not well understood and has not been investigated through massively parallel computations. With this in mind, the overall goal of this multi-disciplinary team of researchers is to pioneer an integrated approach to computationally model extreme waves through Eulerian and Lagrangian formulations, use CUDA based large-scale computations as a means to obtain an enhanced understanding of energy focusing associated with the natural and complex phenomenon of extreme waves, and exploit the insights and knowledge gained for forecasting such conditions for the first time. The proposed four-year effort is to be carried out by a team comprised of researchers from mechanical engineering, applied mathematics and scientific computation, atmospheric and ocean sciences, and astrophysics. This team will pursue a novel integrated approach to create a computational platform, advance GPU-based simulations, and use computational thinking to derive fundamental insights into the complexity of extreme wave conditions. This understanding can help in facilitating energy focusing and taking advantage of it for energy harnessing. Specific outcomes are expected to include different computational models tailored for studies of full field extreme waves, including Lagrangian based N-particle computational models and grid based Navier-Stokes formulations. Instability tests based on the breeding method, which have been developed for atmospheric and ocean modeling studies, will be used for the first time to identify characteristics of instability growth in ocean wave interactions and forecast them.

The proposed work has multiple global economic, security, and scientific applications and shares many of the values of the Cyber-Enabled Discovery and Innovation program. A large number of broader impacts are conceivable given the wide ranging and multi-disciplinary influences of wave energy concentration. The potential to create sub-specialties and entirely new fields of energy transport optimization demonstrate the important science these emergent phenomena can reveal. The identification of precursors and modeling of extreme wave events can afford wide ranging benefits to many fronts including commercial shipping, naval missions, offshore energy harnessing, fiber optic communications, and galaxy formation and other astrophysical phenomena. Apart from integration of research findings into the undergraduate and graduate course offerings across departments, a new cross-disciplinary undergraduate elective on computational dynamics will be created and offered to enable discovery based learning. Along with a post-doctoral scholar, three graduate students will directly get a unique opportunity to work on convergence research and develop computational thinking through a robust cross-disciplinary education. Local high-school students are also expected to benefit through simulation based research practicum to be pursued at the University of Maryland. Art-in-science displays on solitons and other wave phenomena will be used to stimulate and nurture the interests of K-12 students who visit campus for different events including the annually held Maryland Day on campus.

Flapping flight is known to be the single most successful mode of animal locomotion that is exhibited by over 1000 species of bats, more than 9000 living species of flighted birds, and somewhere between millions and tens of millions of flying insects. Inspired by animal flight mechanics, proven capabilities of the Fast Multipole Methods to study vortex interactions in fluid-structure interaction problems, and advances in General Purpose computation on Graphics Processing Units, an interdisciplinary team of applied mathematicians, mechanical engineers, and computer scientists from Mechanical Engineering and Computer Science has been assembled to pursue a three-year data intensive program to further our understanding of flapping flight. The overall goal of the proposed effort is to conduct creative computational studies informed by data from experimental studies to advance computational algorithms for understanding complex fluid-structure interactions associated with flexible structures as well as to discover biological clues related to flapping flight. These clues can help answer fundamental questions, to address which, advanced computational modeling and simulation are needed in concert with experimental observations of flapping wing insects. Computational studies coupled with parallel computing are required to investigate and interrogate the system in ways that nature does not permit. From simple parameter sweeps to flow field analyses, computational studies can educate the analyst in ways that experimental studies alone cannot. The specific goals of this work range from using experimental studies as a guide for computational modeling and simulation to leveraging advanced computing for carrying complex fluid-structure interaction simulations and applying advanced computational architectures and algorithms to accelerate these simulations.

A salient broader impact of the proposed efforts will be the advancement of tools associated with the fourth pillar, data intensive investigations into multidisciplinary, complex, and subtle systems. By demonstrating how the power of experimental data and computational analyses can be harnessed to a degree not attempted before, the efforts are expected to pave the path for transformative investigations into important and diverse fluid-structure problems such as flows interacting with small-scale micro-air-vehicles, blood flow through arteries, and flows through biological organs. Beyond data mining in the natural sciences, this work will usher in a new generation of engineers and scientists trained to use the tools presented by the fourth pillar, data intensive investigation. The cross-disciplinary research will provide exceptional learning opportunities for all involved including a postdoctoral researcher and two graduate students across programs and contribute to the nation's talent pool. Furthermore, computational modeling and sciences curriculum across departments will be enriched by the research findings of the proposed efforts and lead to exciting new additions in undergraduate and graduate courses such as computational dynamics and Fast Multipole Methods. Art-in-science displays featuring captivating fluid-structure interactions and flapping flight will be used to stimulate and nurture the interests of K-12 students who visit campus for different events including the annually held Maryland Day that draws nearly 75,000 visitors each spring semester to campus.

Random fluctuations, which are called noise, occur naturally in many systems, and in many biological and chemical systems, noise is utilized to engender a large change in the system response. However, the use of noise to beneficially influence the response of an engineering system has received only limited attention. As the operating environments of engineering systems become extreme, both at the small scales as well as the large scales, the influence of nonlinearities, uncertainties, and noise gain increased importance. The study, and possible exploitation, of these usually ignored elements may allow for breakthrough advances in design and control of systems and help extend the frontiers of engineering and science. Through support of this award, fundamental studies will be pursued to develop a knowledge base for the use of combined deterministic and noise inputs to realize desired response changes in nonlinear systems. A salient impact is expected to be the advancement of our understanding of noise based schemes for control of nonlinear systems and extension of the application realm of these schemes from simple systems to complex systems. By experimentally demonstrating the feasibility of these schemes, it is expected that one can construct schemes for practical applications where slender, rotating structures are used, such as drilling and mining operations and subtractive manufacturing operations such as milling operations. This work will usher in a new generation of researchers trained to use tools suited for nonlinear systems with noise.

Building on prior efforts on noise-influenced responses of nonlinear oscillators and investigations into whirling motions of rotary systems carried out at the University of Maryland, a research team will pursue the common goal of understanding how mechanical and structural system responses may be altered by exercising partial control with noise. The group will conduct original experiments to explore the applicability of partial control schemes developed for Hénon maps and Duffing oscillators to an experimental prototype of a bi-stable Duffing oscillator. Informed by the experimental findings, analytical and numerical studies will be initiated with modified Jeffcott rotor systems to construct appropriate partial control algorithms and these findings will be extended to control the dynamics of slender, rotating structures. The findings are expected to open the doors to the combined use of noise and deterministic inputs for control of nonlinear mechanical systems that exhibit escape dynamics and steer responses of rotary systems away from states such as whirling motions, which can be detrimental to a system.

Locomotion on soft soil is important for many navigation and exploration operations, including explorations for coastal, petroleum, and fresh water resources, extraterrestrial terrain navigation, mapping operations for mine and radiation detection, and search and rescue operations. In general, motions on soft or loose soil require high energy expenditures compared to motions on packed surfaces. Through support of this award, fundamental research will be pursued to gain further understanding of locomotive interactions with different granular media. This research will draw upon knowledge from various areas, including soil modeling, numerical simulations, vehicle dynamics, and data mining. A salient impact is expected to be the advancement of our understanding of vehicle maneuverability in granular media and related strategies for energy efficiency. The cross-disciplinary research will provide exceptional learning opportunities for the researchers involved and also usher in new generation of researchers trained in computational modeling and sciences.

Guided by the team's prior efforts in computational and experimental dynamics, nonlinear phenomena, and fluid-structure interactions, this research effort will be pursued with a focus on understanding granular media interactions associated with wheeled and legged locomotion on soft soils. Original experiments will be conducted by using photo-elastic granules to examine inter-granular force chain development in response to local surface disturbances generated by external loading. These experiments are expected to generate data for simulations of granular interactions based on discrete element models. These simulations will leverage GPU computing. Continuum, geomechanical-hydrodynamic simulations will be used to associate observed force chains with specific soil types. The research effort will help answer basic questions such as the following: i) Can force chains be used to predict slipping in soft-soil interactions? ii) Does an optimum gait speed exist at which soil slipping is minimized? iii) Can spheres, combined with complex friction models, accurately simulate interactions of sand grains and other non-spherically shaped bodies in a statistically averaged sense? and iv) Can one apply statistical distributions such as the Tracy-Widom distribution to interactions with granular media? The findings are expected to provide a unique means for interrogating granular reactions to locomotive interactions in a way not tractable through experimentation alone. The outcomes are expected to be useful for developing efficient propulsion strategies for robot platforms that span a range of different sizes, weights, speeds, and energy consumption targets.

This grant will provide 40 attendees, several of whom are from under-represented groups, the opportunity to participate in the Fifth International Colloquium on Nonlinear Dynamics and Control of Deep Drilling Systems, in College Park, Maryland, 1-3 June 2020, where they will attend technical presentations and participate in a panel session on the future of deep drilling. The lecture sets will focus on the following emerging topics in deep drilling systems: modeling of drill strings through analysis, experiments, and computations, nonlinear dynamics of drill strings, and the control of drill strings. The participants will address challenges arising in the context of stick-slip dynamics, nonlinear modeling of directional drilling, state-dependent delay effects, and control schemes based on partial differential systems. Discussions will be undertaken on the problems faced in the field and developments that can be pursued to address them, as well as current and future directions associated with horizontal drilling and deep water drilling. The colloquium will serve as an opportunity to expose graduate students, post-doctoral researchers, and junior faculty to complex problems involving nonlinear dynamics and nonlinear control, as well as approaches and methodologies used in the deep drilling systems industry.

This colloquium could provide ways in which modeling, nonlinear dynamics, and nonlinear control can be used to tackle challenges faced in practice, beyond the considered application of deep drilling systems. Examples of other areas include those that involve flexible rotors and other distributed parameter systems, and manufacturing. In addition to 30 technical experts, 10 students, post-doctoral researchers, and junior faculty members, in particular, minorities and underrepresented groups, will be invited to participate in this colloquium to introduce them to the field as well as encourage their participation in future efforts. This colloquium is expected to be an exceptional learning experience for them. Furthermore, this colloquium can serve as a template for future colloquia and workshops involving academia and industry.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Wind energy became the largest renewable energy generated in the US in 2019, and this energy is projected to be a signification portion of all generated electrical energy in the nation within a decade. The introduction of large wind turbines has been considered to be an important direction, as they can result in an increase in generated power. However, wind turbines may not be the best solution for all wind speeds and locations such as building roof-tops. As an alternative, a set of piezoelectric harvesters, which can be used with small foot-prints and at low wind speeds will be studied. These harvesters represent an example of an oscillatory system, in which the coupling between the structural members is dominated by fluid forces that are generated during motions through an air flow. Other oscillatory systems with similar fluid (aerodynamic) coupling include rotating blades in turbine generators, compressors, and turbo fans. Through support of this Grant Opportunity for Academic Liaison with Industry (GOALI) award, fundamental studies will be pursued to develop and extend the knowledge base on aerodynamically coupled oscillators. A salient impact is expected to be the advancement of our understanding of the nonlinear behavior of systems involving fluid-structural-electromechanical interactions. Through experimental demonstrations of the feasibility of these systems, it is expected that one can design and build piezoelectric energy harvesters for use in building systems and tethered unmanned vehicle systems. This work will usher in a new generation of researchers trained to use multi-disciplinary tools suited for study of nonlinear dynamics of energy harnessing systems.

Building on prior efforts on nonlinear oscillators, aeroelasticity, experimental fluid mechanics, and active materials, a team of researchers from academia and industry will pursue the common goal of developing a fundamental understanding of aerodynamically coupled piezoelastic oscillators. The group will conduct original wind tunnel experiments to understand flow induced oscillations of thin airfoil oscillator arrays and bluff body oscillator arrays and study the energy distribution in the system responses across a variety of flows. Informed by experimental findings and guided by industry experience, modeling and simulation efforts will be undertaken to uncover nonlinear phenomena and nonlinear instabilities including Hopf instabilities. On the fundamental side, one of the outcomes will be an enhanced understanding of the behavior of the coupled oscillators with aerodynamic coupling, the nature of this coupling for different flows and oscillator configurations, and the associated nonlinear fluid-structure interactions. On the application side, this work will result in performance characterization tools for energy harnessing arrays based on streamlined and bluff body oscillators.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.