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Research Programs from BAA - Mechanical Sciences
Research supported in the Mechanical Sciences Division of the ARO is concerned with a broad spectrum of fundamental investigations in the disciplines of fluid dynamics, solid mechanics, complex dynamics and systems, and propulsion and energetics. Though many creative and imaginative studies concentrate on a particular subdiscipline, increasingly, new contributions arise from interdisciplinary approaches such as the coupling between aerodynamics and structures, complex dynamics and systems, combustion and fluid dynamics, or solid mechanics and structures as in the structural reliability areas. Additionally, several common themes run through much of these four subdisciplines, for example, active controls and computational mechanics. Research in such areas is addressed within the context of the application rather than as a separate subject of study. Fluid dynamics research is primarily concerned with investigations in the areas of rotorcraft wakes, unsteady aerodynamics of dynamic stall and unsteady separation, and fundamental studies of microadaptive flow control. Solid mechanics include a wide array of research areas such as high-strain rate phenomena, penetration mechanics, heterogeneous material behavior, and reliability of structures. The complex dynamics and systems area is focused on investigations in vehicle structural dynamics, and simulation and air vehicle dynamics including rotor aeromechanics. Research in the propulsion and energetics area is concentrated on processes characteristic of reciprocating (diesel) and gas turbine engines and the combustion dynamics of propellants used for gun and missile propulsion. The following narratives describe the details of the scope and emphasis in each of these subdisciplinary areas.
1.1 Fluid Dynamics
Fluid dynamics plays a critical role in many Army operational capabilities. Significant challenges exist for accurate and efficient prediction of flow physics critical for improved performance and future advanced capability. Army platforms are often dominated by flows with high degrees of unsteadiness, turbulence, numerous and widely separated spatio-temporal scales, and geometrical complexity of solid or flexible boundaries. In order to gain the necessary physical insight to enable future capabilities spanning Army vehicles, munitions, medical devices, and logistics, the Fluid Dynamics program seeks to support basic research investigations of fundamental and novel flow physics. In view of the nonlinear and high-dimensional character of the governing equations, revolutionary advances in fluid dynamics research tools are also of great interest; advanced experimental methods, sophisticated computational techniques and breakthrough theoretical advances will be critical for gaining the required fundamental understanding.
1.1.1 Dynamics of Unsteady and Separated Flows
Operating conditions for many Army platforms are characterized by flows featuring unsteadiness, nonlinear interactions, turbulence, three-dimensionality and flow separation. All efforts in this thrust area will require novel and aggressive strategies for examination of the interplay between disparate spatio-temporal scales, inclusion of physically significant sources of three-dimensionality, and characterization of the role of flow instabilities and nonlinear interactions across a range of appropriate Mach and Reynolds numbers. Historical management of physical complexity has often resulted in scientific approaches that result in the elimination of potentially critical flow physics. Research efforts that are capable of gaining deep understanding of highly complicated flows are likely to allow critical physics to be exploited, leading to significant performance gains for Army systems. As an example, shortcomings in understanding the details of unsteady flow separation, reverse flow phenomena, and dynamic stall continue to limit the capabilities of Army rotorcraft vehicle platforms. While much progress has been made towards unraveling these details, it has become apparent that revolutionary advances are unlikely if the full complexity of the physics is not considered.
1.1.2 Nonlinear Flow Interactions and Turbulence.
As mentioned above, many Army relevant flows are governed by strong nonlinearities and turbulent behaviors. Historically, many analysis tools developed for linear dynamics have been applied to gain understanding of flow behaviors. While local insights can be gained through applications of these methods, the ability to provide global understanding of the evolution of flows requires new approaches that are capable of dealing directly with inherent nonlinearities. Turbulent dynamics may also benefit from new approaches based in dynamical systems theory to push modeling frameworks beyond the notions based on Reynolds averaging and stochastic dynamics and to determine if a useful underlying deterministic structure exists. Modeling flows near walls is a continuing challenge to accurate numerical prediction of complex flows that may benefit from novel non-intrusive diagnostics to inform creative numerical and theoretical constructs capable of efficiently producing a high degree of fidelity near physical boundaries.
1.1.3 Flow Stability and Control
Many of the previously described flows are susceptible to initially small amplitude, but dynamically significant, instabilities that can ultimately lead to fundamental changes in global flow behaviors. Thorough understanding and prediction of these instabilities and their growth is crucial not only to maintaining robustness in the face of disturbances, but also to gain advanced control over the evolution of flows through their exploitation. Research breakthroughs in global and local stability characteristics and their subsequent manipulation are of interest. Theoretical, computational, and experimental examinations of canonical problems to enable focused studies of interactions between instability mechanisms and global flow characteristics are highly encouraged, especially those that seek nonlinear descriptions. Flow control efforts should seek to exploit understanding of these mechanisms to permit the flow evolution to be prescribed. Flow control investigations should also seek to understand not only the impact of control actuation on the flow, but should also consider strategies for closed-loop feedback control and appropriate scaling laws that lead to the potential for such strategies to transition into new capabilities in real-world flows.
Technical Point of Contact: Dr. Matthew Munson, e-mail: email@example.com,(919) 549-4284.
1.2 Solid Mechanics
The goal of the Solid Mechanics Program is to investigate and understand behavior of complex material systems under a broad range of loading regimes in various environments, to develop analytical and computational methods to characterize material models and to serve as physically-based tools for the quantitative prediction, control, and optimization of Army relevant material systems subjected to extreme battlefield environments. Army systems are frequently limited by material strength and failure resistance. Solid mechanics research plays a crucial role in the development of new materials, prediction of strength, toughness and potential damage development and failure of Army relevant material systems, structures and individual protective equipment under extreme loading conditions such as impact or blast, and prolonged normal operating conditions. Research in analytical, computational and experimental solid mechanics forms the foundation of optimization tools to enhance performance while minimizing equipment weight, and its theories provide a strong link between the underlying mechanical behavior of solids and the resulting design and functionality of actual systems resulting in reduced development cost by minimizing the need for expensive field testing, and it leads to novel ideas and concepts for revolutionary capabilities.
The below outlined research thrusts are broad and serve as a guideline of potential research project development. The goal of the program is to support basic research in solid mechanics addressing fundamental issues the subject is facing today and developing new concepts and methods with high potential for future applications for the Army.
1.2.1 Mechanical Behavior of Complex Material Systems
Modern Army structural service conditions and design requirements continually demand development of new materials and extensions of applicability limits and reliability of classical materials. Detailed understanding of material behavior and its capability during service is crucial for future applications. To utilize materials' capabilities close to their limiting capacity helps to reduce structural weight, increase service cycle, and reduce costs of the equipment. The understanding of the mechanics of material behavior in its intrinsic details during materials' transitions into states of damage and fracture initiation due to extreme loading, high rate loading, high temperature variations, repetitive loading, is important for setting appropriate limitations for material applications and for design and development of new materials with specific capabilities for particular applications. The specific component the subject of solid mechanics brings to that task is development of models of material behavior that are based on essential physical processes taking place on different scales and establishing essential quantitative relationships characterizing various processes taking place.
The common goal of the model development is to establish the critical relationships in the form useful for quantitative evaluation of the described processes during material service as a structural component. A material model should give a capability to evaluate and identify the specific internal material processes playing most significant role in a particular service environment and loading conditions. While current modeling techniques based on computational simulations of multiple micro- or nano- events are capable to include in the consideration a large number of these events and internal material components interactions, it is important for a model to have capability of quantitative determination of the significance of these events on the final material characteristics and to characterize as they may depend on the loading regimes, temperature, and other environmental factors.
The range of material groups of special interest is broad. They include various heterogeneous material systems like composite materials, various compositions of reinforced classical materials, materials undergoing special treatments and phase transformations.
1.2.2 Methods for Material and Structural Analysis
Development of analytical, computational and experimental methods capable to utilize material models in the analysis of extreme situations leading to damage and failure development.
Experimental methods aimed to investigate and validate material models play critical role in understanding material behavior on all scales. Development of new experimental techniques is essential for solid mechanics development. In particular, when the experiment is set to enhance the understanding of the physical processes taking place during deformation and failure, leading to development of new understanding and observation of a new physical processes, validating the new material models, helping to visualize the stress fields in complex situations where current analytical or computational methods cannot be successfully used or need validation.
Computational methods play a critical role in solid mechanics and its applications. Development of new computational methods and techniques addressing limitations of the currently widely used methods is of great importance in the field of solid mechanics. As material compositions and structures become more complex, and material models trend to be based on more detailed analysis of the material components interactions, and microstructural changes on multiple scales, demand for a reliable computational capabilities increases. Despite the rapid growth of the new methods and computational initiatives, and extensions of the established methods, a high demand remains for computational methods which are precise, high fidelity, efficient, capable to function in error controlled environment, validated by comparison with the benchmark analytical solutions, and capable to address and resolve computational challenges raised due to high stress/strain gradients or geometrical irregularities.
The advancement of analytical methods and development of analytical solutions to key characteristic problems in solid mechanics is extremely important as a fundamental development of the subject. Usually, analytical solutions serve as benchmark solutions for future development of material theories, understanding of the mechanical events and for verification of the validity and accuracy of the numerical methods used for similar problems before it could be reliably used for more complicated problems.
Technical Point of Contact: Dr. Asher Rubinstein, e-mail: firstname.lastname@example.org, (919) 549-4244
1.3 Complex Dynamics and Systems
The Complex Dynamics and Systems Program emphasizes fundamental understanding of the dynamics, both physical and information theoretic, of nonlinear and nonconservative systems as well as innovative scientific approaches for engineering and exploiting nonlinear and nonequilibrium physical and information theoretic dynamics for a broad range of future capabilities (e.g. novel energetic and entropic transduction, agile motion, and force generation). A common theme amongst all programmatic thrust areas is that systems of interest are "open" in the thermodynamic sense (or, similarly, dissipative dynamical systems). The program seeks to understand how information, momentum, energy, and entropy is directed, flows, and transforms in nonlinear systems due to interactions with the system's surroundings or within the system itself. Research efforts are not solely limited to descriptive understanding, however. Central to the mission of the program is the additional emphasis on pushing beyond descriptive understanding toward engineering and exploiting time-varying interactions, fluctuations, inertial dynamics, phase space structures, modal interplay and other nonlinearity in novel ways to enable the generation of useful work, agile motion, and engineered energetic and entropic transformations. Further information on the current scientific thrust areas are detailed in the paragraphs that follow
1.3.1 Dynamics of Nonlinear and Nonconservative Systems
Classical dynamics has produced limited fundamental insight and theoretical methods concerning strongly nonlinear, high-dimensional, dissipative, and time-varying systems. For over a century, qualitative geometric approaches in low-dimensions have dominated research in dynamics, dissipative processes are mostly relegated to phenomenological models, and reduced-order-modeling of high-dimensional dynamics are often premised on empirical and statistical model fitting and are incapable of capturing the effects of slowly growing instabilities and memory. Experimental efforts have similarly faded. There is prescient need for a return to fundamental investigations and new theoretical and experimental frameworks for high-dimensional nonlinear and nonconservative systems. At the same time, however, a number of exciting and new research problems are emerging. Research in this thrust concentrates on (but is not limited to):
- Spatially Extended and High-Dimensional Dynamics Far-from-Equilibrium – Develop novel theoretical and experimental methods for understanding the physical and information dynamics of driven dissipative continuous systems and novel reduced-order-modeling methodologies capable of retaining time-dependent and global nonlinearities. Novel research pertaining to the analysis and fundamental physics of time-varying nonlinear systems and transient dynamics is a high-priority. Programmatic interests also include unifying advances in nonequilibrium statistical mechanics with Statistical Energy Analysis (SEA), developing new methods for vibratory regimes outside the scope of overly-simplistic SEA assumptions (e.g. non-trivial modal overlap, mid-frequency range problems, and non-Gaussian stochastic processes), and novel research in experimental structural dynamics. This thrust also has special interest in pioneering research on creating and controlling nontraditional nonequilibrium critical phenomena and critical dynamics.
- Nonsmooth Dynamics and Interactions – Nonsmooth dynamics, for even a single degree-of-freedom, are extremely counter-intuitive and poorly understood yet they arise in many Army-relevant contexts spanning wave propagation in interconnected structures, autonomous system dynamics (e.g. locomotion and jumping), suddenly applied loads, etc. Novel and fundamental investigations concerning the experimental and theoretical physics for a variety of nonsmooth dynamical systems are of interest. Programmatic interests herein extend to the emerging field of experimental and theoretical terradynamics, especially in the domain of low-inertia systems and novel, non-wheeled and biomechanical propulsion mechanisms where Bekker's theories and assumptions are invalid.
- Formalisms for Engineering Complexity and Resilience – Developing an engineering science of complexity and resilience to understand complex engineered systems as well as enabling the next generation of engineering systems capable of exhibiting hallmark features of complex systems (e.g engineering robustness, fragility, propensity for self-organization) requires new mathematical methods, uncertainty propagation techniques, and clever leveraging of many recent advances and insight from complex systems science. Proposals taking a fundamental and rigorous scientific approach are encouraged.
1.3.2 Passive Dynamics and Underactuation
This scientific thrust seeks to develop deeper understanding through supporting theory and experiment of the role of embodiment and dynamics on a physical system's capability to process information and transform energy and entropy. Generally, this thrust strongly leverages advances in, and approaches from, sensory biomechanics, neuromechanics, underactuated systems theory, and mechanical locomotion dynamics to understand the motion of both articulated and continuum dynamical systems operating in highly-dynamic environments. The scientific principles sought, however, are not limited to biological movement and manipulation. Proposals are strongly encouraged that view morphology in an abstract sense. For example, understanding morphology as a system's symmetry, its confinement (e.g. chemical reactions), or its coupling topology.
1.3.3 Force Generation, Work and Power in Nonequilibrium Dynamical Systems
This thrust pioneers novel and innovative approaches, grounded in nonequilibrium and dissipative dynamical systems theory, for novel thermodynamic "engines" and new ways of generating forces, producing useful work and power, and transforming information to energy (e.g. Szilard engines) in both artificial and biological systems. Recently, advances in physics suggest nontraditional work cycles featuring non-ergodic intermediate steps (where processes cannot relax or are prohibited from reaching equilibrium) can potentially exceed Carnot efficiency bounds. However, more research is needed to explore this novel regime, connect ideas with modern concepts in information dynamics, as well as to perform experiments. Other major interests include enabling novel synthetic emulation capabilities by exploring universal features in biological "prime movers" (e.g. molecular motors, actin, dynein) as well as principles underlying biological force generation, dissipation, and load transfer via the nonlinear dynamics of muscles.
1.3.4. Strategic Program Challenges
Strategic program challenges focus on questions relevant to the programmatic scientific focus areas deemed beyond the scope of single investigator awards. The challenges emphasize high-risk, high-reward exploratory research to create breakthroughs, push science in truly novel directions, or to support mathematical abstractions and precise physical foundations for emerging technologies deemed likely to be of significant future Army and DoD impact. Potential investigator teams are encouraged to contact the program manager for further information concerning any Strategic Program Challenge topic.
For each topic, proposed efforts should be limited to 48 months and $1.5 million. There is no formal limit on the number of investigators, but white papers should clearly indicate significant, complementary, and meaningful intellectual commitment by each proposed team member. Potential individual investigators interested in a particular aspect of any topic are welcome to discuss single investigator proposals with the program manager. Related single investigator efforts will be considered, with support at a commensurate level.
Topic 1: Energetic Versatility of Muscles: Principles and Emulation
Discern, through both theory and experiment, the fundamental physical principles underlying the energetic versatility of muscles in dynamic operating conditions (e.g. force generation, shock absorption, energy dissipation, power conversion and distribution etc.). Of complementary interest are novel experimental approaches with sustained in-vitro electromechanical coupling as well as compelling new ideas to leverage biophysical principles to potentially engineer new classes of soft active matter exhibiting muscle-like energetic versatility.
Topic 2: Controlling Hyperelastic Matter
Bring together soft condensed matter physics, continuum mechanics, neuromechanics, and under-actuated systems theory to generate novel frameworks for directing complex spatial motions and wave propagation capabilities within soft continua with nonlinear material properties. Theoretical principles are expected to be integrated with novel experimental platforms, possibly leveraging advances in printed programmable matter. New interests relevant to this topic include coupling advances in printing bionic programmable matter with new understanding of scaling and regeneration of self-organized patterns to push towards new capabilities to engineering biological plasticity.
Topic 3: Theory of Morphological Energetics
Develop a formal abstraction of the principles underlying the efficiency of information processing, control, and energetic transformation on the intricate coupling with, and exploitation of, a physical system's shape (either articulated or amorphous), topological structure (functional morphology), and nonlinear dynamics (including transient and non-smooth dynamics). Emphasize the less-considered dynamics of energy and entropy transformations in the context of the challenge objective and present generality of the results across a broad range of data sets and experimental test beds.
Topic 4: Control and Creation of Critical Dynamics
Steer statistical physics towards a science of the artificial. The goal is to develop an experimentally tested theoretical framework for controlling and creating new types of critical dynamics, phase transitions, and universality classes by bringing together theory and physical principles in statistical dynamics with control and dynamical systems theory. Questions of interest for this challenge include: Can we develop the concept of an active universality class? Can we dynamically stabilize, through feedback, nonequilibrium states of matter that have no equilibrium counterparts? Can renormalization group theory be unified with control theory through geometry? What is the role of information dynamics in the control of critical dynamics? Proposed efforts should have a strong experimental component to test theoretical abstractions.
Technical Point of Contact: Dr Samuel Stanton, e-mail: email@example.com, (919) 549-4225
1.4 Propulsion and Energetics
Propulsion and Energetics Research supports the Army's need for higher performance propulsion systems. Future systems must provide reduced logistics burden (lower fuel/propellant usage), enhanced insensitivity to inadvertent ignition, and longer life than today's systems. Fundamental to this area are the extraction of stored chemical energy and the conversion of that energy into useful work for vehicle and projectile propulsion. In view of the high temperature and pressure environments encountered in these combustion systems, it is important to advance current understanding of fundamental processes as well as to advance the ability to make accurate, detailed measurements for the understanding of the dominant physical processes and the validation of predictive models. Thus, research in this area is characterized by a focus on high pressure, ignition and combustion processes and on the peculiarities of behavior in systems of Army interest.
Research on combustion phenomena relevant to engines is focused on intermittent reacting flows encountered in diesel combustion chambers and on continuous combustion characteristics of small, gas turbine combustors. Optimizing engine performance, through understanding and control of in-cylinder combustion dynamics, while retaining high power density, is a major objective. This focus leads to emphasis on fuel injection processes, jet break-up, atomization and spray dynamics, ignition, and subsequent heterogeneous flame propagation that will elucidate the underlying physics of these processes. Research on heterogeneous flames requires supporting study into kinetic and fluid dynamic models, turbulent flame structure, soot formation and destruction, flame extinction, surface reactions, multiphase heat transfer, and other factors that are critical to an understanding of engine performance and efficiency. An additional consideration is the high pressure/temperature environment encountered in advanced engines, which influences liquid behavior and combustion processes at near-critical and super-critical conditions. Fundamental research is needed in many areas, including low temperature physical and chemical rate processes, and combustion instability effects at low temperatures. New characterization methods to investigate kinetics and flame phenomena at high pressure are needed. New computational and theoretical methods to be able to model complex reacting systems are also needed. With advances in sensing, modeling, and control architectures, it is becoming possible to further optimize the performance of combustion systems. Providing the foundations for such active control is also a goal of the program.
1.4.2 Propellant Combustion Processes
Research on propellant combustion processes isfocused on understanding the dynamics of the planned and inadvertent ignition and subsequent combustion of energetic materials used for propulsion in gun and missile systems and in ordinance. The program is also addressing the characterization of advanced energetic materials, e.g., those based on nanoscale structures and/or ingredients. Basic research is needed in several areas, including: condesnsed phase reactions, flame spreading over unburned surfaces (particularly in narrow channels); surface reaction zone structure of burning propellants; chemical kinetics and burning mechanisms; propellant flame structures; characterization of physical and chemical properties of propellants and their pyrolysis products; and coupling effects among the ignition, combustion, and mechanical deformation/fracture processes. The use of advanced combustion diagnostic techniques for reaction front measurements, flame structure characterization, and determination of reaction mechanisms is highly encouraged. Especially of interest are novel methods which can well characterize the ignition and burning behavior of a material utilizing only minute quantities of that material. Complementary model development and numerical solution of these same ignition and combustion processes are also essential. There is also need to understand the unplanned or accidental ignition of energetic materials due to stimuli such as electrostatic discharge, impact, friction, rapid straining, etc. This requires, for example, research on the processes of energy absorption and energy partitioning in the materials, the effect of mechanical damage on the ignition events, and other topics relating to the safety of energetic materials.
Technical Point of Contact: Dr. Ralph A. Anthenien, firstname.lastname@example.org, (919) 549-4317