6

Sciences for Maneuver

The Panel on Mechanical Science and Engineering at the Army Research Laboratory (ARL) conducted its review of ARL’s vehicle intelligence (VI) programs—human–robot interaction, intelligence and control, and perception—at Adelphi, Maryland, on July 8-10, 2015; and ARL’s vehicle technology (VT) programs—platform mechanics, energy and propulsion, and logistics and sustainability—at Aberdeen, Maryland, on June 28-30, 2016. This chapter evaluates that work, recognizing that it represents only a portion of ARL’s overall Sciences for Maneuver Campaign.

VEHICLE INTELLIGENCE

Human–Robot Interaction

The human–robot interaction (HRI) research at ARL reviewed by ARLTAB in 2015 was of top quality. The researchers presented studies with rigorous design, evaluation, and analysis, and all used appropriate metrics in their evaluations. They have a thorough understanding of related research and have built collaborations with others at ARL across campaigns and have connected with the right faculty and laboratories in academia through the Robotics Collaborative Technology Alliance (RCTA). The research team has benefitted from an expansion in the postdoctoral program and early-career hiring, which has grown the capabilities and collaborations of the team.

Each individual project defines its own appropriate algorithmic or experimental metrics, but the researchers did not uniformly communicate the higher-level success criteria—that is, what makes their project successful in the context of the larger HRI effort. Such metrics need to be defined at a programmatic level and also be communicated well to the research team; some researchers could not identify the larger goals of the program.

The science in the HRI program is technically sound, and the work is published in top journals, including Human Factors. The work needs to have broad exposure, which is achieved through presentations at conferences and meetings. The utility of the work appears to be recognized within ARL—for example, elements from the tactile feedback project will be incorporated into the next warrior experiment.

The use of soldiers in experiments is commended. The move toward more realistic warfighting vignettes and more real-life simulations that instantiate threats and hostile elements would help to establish the value of a technology in achieving a desired capability.

Some researchers were embedded directly with the soldiers for a few weeks, and their experiences directly led to the formulation of research topics. This type of exchange is of great value for the research program. Also, some researchers are permanently stationed at U.S. Army installations, where they have regular contact with active-duty soldiers and are able to recruit soldiers as participants in research.

The research presented will be shifting from one-person/one-robot studies to multiperson/multirobot scenarios. This shift in focus is appropriate as the Army moves to the use of more complex teaming architectures. This new direction will bring a need for additional research in trust and in HRI, raising questions about how one verifies software and validates systems to build confidence in the joint human–robot system, considering complex, emergent behaviors. This use case also highlights the importance of providing the right information at the right time to the humans and to the robots, identified as a thrust of the HRI program.

Human–Robot Trust

In recognition of the changing role of people in a human–robot system, this topic investigates the relationship between trust and the design of vehicle autonomy. The goal is to look at design factors proactively in simulation concurrently with technology development, rather than retroactively; the design of human–robot interaction during early system development is important in order to create a robot system that will be used effectively and as intended. This project is commendable in that it is conducting evaluations and experimentation concurrently based on the applied robotics for installation and base operations system development at the U.S. Army Tank Automotive Research, Development and Engineering Center (TARDEC). The simulation models are based on real data from the system under development at TARDEC.

The milestones are clearly defined, appropriate, and feasible. This 6.2-funded work (early applied research) may lead to shorter-term application than the 6.1-funded work (basic research) described for most of the other HRI projects, though both may have longer-term implications. Trying to visualize what will be available in the way of automated vehicles in the longer term is challenging. This work seems to be a good stepping-stone to future interactions of humans with autonomous vehicles. Additionally, the close interaction with TARDEC on this project shows that the research is targeting a current Army need.

The researchers turned up more than 300 definitions of the simple-sounding word trust, a fundamental variable when working with people. They explained convincingly that trust is a critical factor to be considered when studying the interactions between humans and autonomous vehicles.

A three-factor model for trust, developed for the RCTA, served as the foundation of the researcher’s Ph.D. thesis on human–robot trust. The effort takes an analytic and empirical approach, deconstructing the factors involved in trust, into three categories: human, environmental, and robotic. One known factor that influences trust is system reliability. The effects of many other factors, including stress, workload, personality, trust propensity, and coping style, are still unknown. Quantifying this space is the basis and motivation for the project.

The equipment and tools that are being used are appropriate for this early investigation. The team is in collaboration with TARDEC as well as collaboration across ARL directorates, using the Control of Autonomous Robotic Vehicle Experiments (CARVE) and the Robotic Interactive Visualization Toolbox (RIVET) simulation tools. The trust theory was developed through the RCTA. The autonomous vehicle is under development by TARDEC, and current work uses computer-based simulation. The simulation is low fidelity—a reasonable first step for an early investigation. The simulation is based on data from the real system at TARDEC, and the simulation is updated as the actual system is developed further. Improvements in the simulation’s impact could be achieved with some affordable upgrades to the current desktop solution: for example, with wrap-around hardware.

There is some question about the effect of perception of risk on the experimental results, given the use of a simulated environment instead of a real one. Prior research in HRI has shown that the perception of risk, or lack thereof, influences the behavior of participants in studies with human subjects.

The work has been published in top journals, including Human Factors. Broad exposure of ARL’s work is necessary and is achieved through presentations at conferences and meetings.

The findings on how different people trust an autonomous system illustrate the complexity of the challenges faced by the new technologies. The project also demonstrates the effectiveness of the RCTA mechanism for conducting Army-relevant research in academic environments and the pathways that are created to hire researchers into ARL.

Multimodal Displays for Human–Robot Interaction

The motivation for the project is well-founded: Indeed, a soldier’s visual modality is overloaded. Additionally, constraints on auditory communication may pose a threat to soldier security and mission success. This project investigates the use of other modalities for communication with the soldier, including tactile and gesture. The project goal is to identify interaction modes (single or in combination) that are most effective for soldier-robot communication. The focus is on achieving external validity by synthesizing and translating theory-based predictions, meta-analysis, and experiments to determine whether results generalize to the field.

The project is commendable in that it conducted experiments with real soldiers in a realistic environment and context. The principal investigator is an outstanding practical researcher, and the effort is a clear success. The work was disseminated well at conferences and meetings; journal publications would be very valuable to the research community.

The experiments conducted would have been improved if they had explicitly included in the scenarios a robot as a critical element to provide meaningful information to the soldier, rather than focusing on the communication medium itself. Additionally, the information passed to the tactile belt could have been provided as easily from a human as from a robot, and so other scenarios involving human–human communication using the tactile belt could be performed.

The comparison of text messages, which remain on the screen, versus one-time tactile input, is questionable. It would be reasonable to allow the soldier to re-trigger the signal, which would provide a better comparison of the two methods in terms of the length of time for which the information is available.

Understanding how the technology supports the soldier in abnormal conditions is important, because there may be trade-offs in task performance and situation awareness. Additional insight into the effect of the tactile vest on the soldier’s behavior is expected if disruptive scenarios are incorporated into the experiments.

Overall, the project has developed a piece of technology that has the potential to improve soldier performance, particularly in terms of safely passing information in combat situations.

Human-Autonomy Sensor Fusion for Rapid Object Detection

The project conducts research on models of fusion between computer vision and neurophysiological responses. Recognition systems do not integrate humans explicitly; this project looks at an alternative architecture in which humans are peers to share the information with autonomous systems. The approach fuses human neurophysiological response to enable rapid real-time target detection. The objective of the work is to evaluate the hypothesis that joint human–autonomous system target recognition surpasses the target recognition capability of the autonomous system alone.

The project defined appropriate algorithmic and experimental metrics. The larger milestones and success criteria were less clear, although the project is part of a larger project with 40 researchers.

The project addresses challenging technical issues; neural classifiers are not yet fully understood. The push-button response (part of the human target recognition component) lags behind computer vision, and the neurophysiological recognition lag depends on human conditions. The goal is to produce overall better accuracy and efficiency with a human sensor and to demonstrate a path forward to relevant target tracking and engagement scenarios.

At this preliminary point, the results support the hypothesis that the human component improves object detection, but it is unclear whether the improvements are significant from a practical standpoint. While the research is young and the delta improvement is small in terms of making progress to a fielded, capable system, the payoff could be significant. One manuscript has been submitted for a journal publication and another was accepted and presented at the 2015 International Conference on Intelligent Robots and Systems. This project is currently limited to object detection, but it could be expanded to explore similar approaches for object classification.

Intelligence and Control

The intelligence and control (I&C) research theme is focused on enabling the teaming of autonomous systems with soldiers. The overarching goal is to develop an intelligent autonomous system of robots that can perform effectively in an uncertain environment by optimally using limited resources. The long-term goal as articulated by ARL is to minimize the human presence in the battlefield. The topics investigated in this research area are aimed at generating the technologies needed to meet the challenges posed by future military operations that could occur in military-relevant missions and in military-relevant environments. To meet the goals of the research theme, six research programs have been initiated:

• Control focuses on the low-level processes and closely couples sensing and action (actuation) of individual elements of the vehicle;
• Planning and guidance focus on the mid-level, vehicle-centric layer of the control architecture, with immediate path-planning objectives;
• Abstract reasoning focuses on the cognitive element of the architecture, with a special emphasis on human–robot teaming occurring at this level of the architecture;
• Teaming and coordination focus on the interaction of multiple homogeneous or heterogeneous entities to achieve a specified goal, including coordination and communication;
• Behaviors focus on actions of a vehicle built from a hierarchy of elemental tasks and capabilities to achieve one or more specified goals; and
• Learning and adaptation focus on employing key cognitive features of an intelligent vehicle to enable control of its actions and/or behavior to successfully achieve goals in dynamic and/or unrecognizable scenarios and environments.

Projects in the teaming and coordination and learning and adaptation project areas were not presented for review.

The focus of the I&C theme is developing software and algorithms that enable the vehicle to approach a higher level of cognition, enabling the teaming of autonomous systems and soldiers. The I&C theme has tight couplings with the RCTA program and the Micro Autonomous Systems Technologies (MAST) Collaborative Technology Alliance program, with some specific ARL focuses. The higher level cognition that the I&C theme focuses on is aimed at enabling autonomous assets to work in environments of relevance to the military—caves, subterranean spaces, jungles, undercanopies, megacities, and urban environments. Specific I&C research topics are targeted to leveraging state-of-the-art approaches and expanding them to address the uniqueness of the military environment and missions. To identify specific research projects that address the theme, the Army needs, which emphasize high-level capabilities, are deconstructed into specific project areas. The following projects were presented for review.

Abstract Reasoning: Spatial Reasoning in Uncertain Conditions

The focus of this research was on determining how to characterize information collected from field data represented as the collection of uncertain (or incomplete) information. The primary issues this research is trying to resolve are how to build an initial knowledge base and how to expand it autonomously when needed. The state of the art in this domain has been achieved by Microsoft (Bing), Google (Knowledge Graph), and IBM (Watson). The primary limitation of current approaches is that they are trying to extract all information prior to deployment (versus at query time). Overall, the principal investigator (PI) demonstrated broad understanding of the field and possesses the skills necessary to perform this research. The PI employs adequate tools and methods for this research and has several papers published, including in well-respected venues such as the Association for the Advancement of Artificial Intelligence.

Opportunities

This is an analytical study that is still a work in progress. It was not completely linked to specific military-relevant applications and did not involve any real-world experiments. Issues that might impact the success of the work include how to determine whether outcomes are reliable and correct; how to get algorithms and operations to run on the robot processor (along with the other processing components); and understanding key elements of the development path necessary to get to that point. Only limited results were presented. Estimates of the algorithm accuracy were not provided; more effort is required to provide evidence of feasibility. Experiments would also be helpful. Growing the PI’s team might help in addressing these challenges.

Planning and Guidance: Autonomous Mobile Robot Exploration with an Information-Gain Metric

This research applied an information-based approach to the mobile robot exploration problem, based on probabilistic and entropy concepts. Effective robot exploration is important for intelligence, surveillance, and reconnaissance efforts. It was shown that the developed algorithm could be used to more effectively detect improvised explosive devices (IEDs). Probabilities or weighted probabilities could also be used to reflect prior information. As such, the problem being addressed is particularly relevant to the mission of enhancing the warfighter’s capabilities via intelligent robotic teams. The algorithm

presented was compared to a baseline (non-information based) algorithm. The PI was well aware of the state of the art in this domain and is well qualified to pursue these important issues. The PI’s collaborative efforts, which led to a number of publications, are excellent.

Opportunities

While the information-based entropy algorithm was shown to outperform the baseline (greedy) algorithm, work needs to focus on describing the pros and cons of each algorithm, comparing the algorithms presented to other algorithms considered in the literature, examining the effect of local topology on the algorithm’s temporal and spatial performance, examining the effect of a priori probabilities and weightings on algorithm performance, its reflection of real-world concerns (e.g., uncertain communications, terminal hazards), and extending the work to include multiple robots.

Behaviors: Scene Consistent Visual Saliency

This research dealt with how to better define visual saliency in a dynamic environment. The project was first envisioned because ARL researchers were examining images from a moving robot and realized that present definitions of saliency did not give consistent metrics for saliency—for any given feature––as the moving camera passed a feature and dynamically changed its field of view. The goal was to define visual saliency in a manner that was independent of the view in a general way. As a step toward this, the research considered images obtained from a fixed camera as it panned, tilted, and zoomed to give different views. This was the first step toward defining a more general definition for a camera with a moving base. The approach began with a bottom-up method of determining saliency, in which one looks for whatever jumps out of the background. Later, this approach was merged with the top-down approach of looking for specific objects. Using a consistency metric, it was realized that consistency for the saliency of a given feature in the surroundings can be obtained only if various images (from different views) are merged into a composite mosaic that casts the set of pixels as a unified field of view. From this concept came a consistent definition of saliency of the visual image. The project is well thought out and has demonstrated that the new definition of saliency can give consistent answers for saliency over a range of camera angles and zoom parameters. The scientific quality of the work is excellent, and the researchers are qualified to do the work. The researchers understand the positioning of this work with respect to other work in the field and have published in appropriate journals and conference proceedings.

Opportunities

The approach represents a first step in addressing a larger problem. It does not work well when the focus is changing, so additional improvements in methodology are needed. This work could also be improved by use of a depth parameter via the stereoscopic effect (once the base is allowed to move). Researchers could then better understand how the work connects with other human–robot interaction work in ARL. The researchers need to identify how the work addresses an important need—that is, why is it necessary to measure saliency consistently and how good does saliency consistency need to be for images to be useful for the Army mission? An additional opportunity could include integrating eye-tracking devices to try to determine what a solider thinks is salient, inferring what the solider is trying to convey based on eye-gaze, and providing that information to the robot or informing the robot planning algorithms.

Control: Autonomous Self-Righting for a Generic Robot with Dynamic Maneuvers

In this research, the problem of self-righting a fallen robot was examined. This situation occurred when the robot fell despite all that had been done to prevent toppling, so the problem is an important one. A potential energy method was used to address the problem. The method is based on an approximation approach that was shown to be potentially useful for robot design, minimizing the number of states from which acceptable recovery is not feasible. The PI has provided metrics and validations to evaluate the accuracy of the approximation. The associated publications of the PI are also good, and a related patent has been filed.

Opportunities

The work could examine how well the energy approach taken by ARL works in practice and a more precise (albeit computationally more burdensome) measure of acceptable recovery (e.g., a measure that includes spatial/temporal constraints). Although the focus is on righting the robot from a static overturned position, a better understanding of the dynamics would come from a more general examination of a broader set of related issues, including stabilizing and destabilizing factors before overturn and the ability to right itself while falling and rolling before coming to rest.

Behaviors: Autonomous Navigation Analysis

This project had the objective of evaluating the performance of three different Army robots navigating from a fixed starting point to a number of predetermined global positioning system way points in an outdoor environment. The evaluation was at the system level—that is, the overall performance of the robots, including their sensors, controllers, and traction/power train systems, was included. The project was designed to expand on research that had been conducted indoors by Microsoft and apply it to the more Army-relevant situation occurring outdoors, in unfamiliar surroundings and with various obstacles that cause significant difficulties for the robots. The experiment was conducted at the Aberdeen Proving Ground facility, and the errors, difficulties, time, and success rates of the robots were evaluated. Further experiments are planned over the next year to enrich the comparison of system performances. The referenced work done by Microsoft was an appropriate starting point. The researchers were qualified to perform this research and they conducted the research as a team and used state-of-the-art facilities to conduct their analyses.

Opportunities

This project was not a sophisticated research effort, but it was a good start in evaluating the performance of a system. Future work could focus on developing methods to predict system-level failures and understanding what causes them. It could conduct more detailed experimentation and analysis to better grasp the effect of the various system components on the robot’s performance.

Abstract Reasoning: Robotic Dream—Episodic Memory Consolidation and Revision

This research focused on the development of a memory system that allowed a robot to retain knowledge from previous experiences. There was some uncertainty about how long this particular project has been pursued. It was listed as a 2004-2020 effort, but it was unclear whether the project was ending or

continuing through 2020. There was mention of a path forward, including transition to CTA partners, although this was not defined. It would be helpful if the objectives included more metrics-oriented information and were more clearly set forth.

Storing and processing only exciting events and precursors is an elegant and logical contribution, and there is also a process to code the events into a set of simple low-memory symbols. Memory access time savings also seem intuitive, and they are dramatic.

One PI indicated that no similar research was being done elsewhere, but this was belied by the numerous references cited in a recent journal paper of the PI, which had a sufficient scholarly section of related research. The PIs could continue to strive to publish work in mainstream journals in the field, such as those of the Association for Computing Machinery or the Institute of Electrical and Electronics Engineers.

Opportunities

Since this research has been in existence for a while, there needs to be a stronger linkage, at this point, to military-relevant scenarios.

Overall Accomplishments

The I&C team is developing and supporting a suite of forward-looking technologies, algorithms, tools, collaborations—all of which are important for the warfighter effort. ARL has brought together a number of different viewpoints and different skills from different disciplines to start thinking about these problems and tackling them in innovative ways. Collaboration with universities and other agencies and industry has been active and of high value, and ARL has invested in the research through the people it has hired. In general, PIs recognize related research and methods and leverage them to push forward improvements to address the uniqueness of military-relevant problems. While unifying demonstrations, milestones, objectives, and capabilities could better motivate the specifics being developed and elucidate how they will be integrated, the developments being pursued are for the most part essential.

Overall Challenges and Opportunities

The I&C team needs to move on to the next step—bringing the different research projects together synergistically to successfully address broader problems faced by the Army. The I&C team has a good start on this but needs to formalize the process for integrating and knitting together the various research pieces necessary to transition to the next step. Developing quantitative milestones for gauging progress and performance would help in this endeavor. By using milestones, research projects can be redirected where appropriate to better achieve the overall mission goals. It would also be good to see the process whereby desired future capabilities or goals are broken down into a sequence of achievable (realistic) short-term capabilities and goals.

There also needs to be a focus on the big picture: an understanding of where ARL is going and how the projects fit into the bigger picture. To quantify general progress and application-specific performance, more specific connections to the literature could be made in the course of baselining or benchmarking. All projects could make sure to reference the related literature (baselines, metrics, or benchmarks) and understand how they fit and compare. Through mentoring, guidance, and appropriate milestones, quicker progress might also be made toward integrating projects and more effectively contributing to solutions to

important problems. Mentoring can come from both internal and external experts. ARL’s open campus concept can be used to bring in external experts.

Challenges to I&C research focus on determining (1) how to deal with trade-offs in order to determine which research to continue; (2) how to effectively integrate outcomes from the individual projects and develop a methodology for this integration; (3) how to share the overarching systems perspective and relay that vision to the research projects; (4) how to identify and validate the process of getting from high-level capability or needs to research tasks (and evaluation or benchmarking of whether they comply with needs); (5) how to appropriately delineate between basic and early applied work; (6) how to balance and integrate top-down and bottom-up-driven processes; (7) how to compare the research against the standard baseline data sets (when available) and how to identify standard metrics for validating whether the research has achieved the stated goals of the proposed work; and (8) how to transition the research from work on simplified problems that facilitate analysis to actual scenarios that are germane to the Army’s unique problems and characteristics.

Perception

The ARL aspires to be the nation’s premier laboratory for land forces. The perception group at ARL has made significant headway toward achievement of this goal. It has succeeded in establishing relationships with top university laboratories, has attracted some outstanding personnel, especially new Ph.D.’s, and is undertaking interesting and relevant work on a par with academic departments. The ARL perception group is well aware of the current trends in the research community through participation in top, highly competitive conferences in the field. ARL’s open campus policy appears to be making a positive difference in the quality of the work.

The perception group did not articulate clearly the context within which it works and did not clearly differentiate its approach from the approaches in other areas. Research work on robotics perception needs to be linked to the power needed for the robot or the materials of which the robot is constructed. A systems approach is needed here. Therefore, based on the material presented, the following were inferred:

• The perception group, for the purposes of this evaluation, works in the context of three scenarios:
  • —Microautonomous systems and technology (MAST), where soldiers use microrobots to explore;
  • —Robotics collaborative technology alliance (RCTA), where soldiers use robot/human teams to penetrate the built environment; and
  • —Applied robotics for installations and base operations, where robots perform functions on bases, relieving the warfighters of these functions.
• Most of the perception group’s efforts are basic research in one of the three scenarios. The goal of each is as follows: Within the next 5 years, perform relevant basic science; 5 to 10 years from now, inspire concrete modules for the three integrated scenarios; and 10 to 15 years from now, apply these modules to support integrated experiments, which will subsequently enter the Army Research, Development and Engineering Center as processes to be matured by 2040.

The perception research was assessed according to its achievement of the above-inferred goals.

Autonomous Squad Member

This project attempts to detect changes in the tactical situation by observing the motion of individual soldiers. It is an interesting and important problem as the Army integrates robots into small unit operations. It was not made clear whether there is a roadmap from the broad concept to achievable steps in that direction. Is it going to be practically feasible to deploy a robot with sufficient capabilities in the next 10 to 15 years? Will the robot participate beyond being a team member? In 2040, a robot may have unique capabilities—will it then be a more active participant in activities?

Data-Driven Learning and Semantic Perception

The core of this work is using video analysis to categorize the actions a human is performing using machine learning with a hierarchy of action templates. This is good, focused work using state-of-the-art methods. Like similar methods, there are still questions about its broader applicability. It would be informative to learn how this work might relate to or affect other projects in the group.

Efficient Discovery and Labeling of Environments for Visual Classification and Autonomous Navigation

This project is also using machine learning methods to examine video data. In this case, the intent is to segment the scene into regions such as trafficable areas, vegetation, buildings, and sky. This is a good combination of theory and practical application and has great potential. The work could become a framework for developing and testing other new ideas and scenarios.

Dynamic Belief Fusion

Dempster-Shafer theory is a well-known framework for reasoning about uncertain events when, because the categories might overlap, the sum of probabilities need not add up to one. The method introduced here updates Dempster-Shafer for object detection. The results indicate that the new method outperforms existing methods, but the theoretical basis has not yet been fully explored.

Immersive Display of Robot Lidar Imagery

ARL has its own design for a lidar that has excellent performance, generating 256 × 128 pixel depth images. This project takes that three-dimensional (3D) data and displays it on an Oculus Rift head-mounted display for visualization. The project is building the tools needed to enable future research efforts.

Real-Time Optical Flow

The basis of optical flow—measuring the apparent motion of a scene as the observer or the object moves—has been established for many decades. Typical optical flow techniques break down with large changes in illumination (e.g., the sun going behind a cloud) or with cluttered scenes (e.g., trees blowing in the wind). The work shown here demonstrates a new approach, which is much less sensitive to the absolute brightness of the scene and is capable of differentiating the optical flow from humans moving in the scene from the flow caused by vegetation. While the parts of the algorithm are not novel, the combination of these subunits shows promise.

Overall Accomplishments

The perception group presented a broad spectrum of projects, including understanding group behavior, perception for mapping and navigation, and basic research on dimensional reduction and clustering. Many of these projects are of high quality and are informed by the goals and needs of today’s Army. The projects are well defined, and the researchers are aware of the state-of-the-art of computer vision. The group actively participates in important international conferences, which guarantees their awareness of the current and relevant activities in computer vision. Most of the work focuses on specific scenarios relevant to the Army. While it may not be as broad or groundbreaking as the best university research, the work is appropriate to the ARL context.

Through the MAST and RCTA collaborations, the perception group has access to many of the best computer vision researchers in the country, including those at University of Illinois; University of California, Berkeley; University of Southern California; John Hopkins University; and Carnegie Mellon University. Although these collaborative projects at the universities were not within the scope of this review, it seemed clear that they are a good chance to enhance the visibility and quality of the science at ARL. These collaborations need to be exploited to continue to strengthen the group.

The facilities, equipment, and approaches are well-targeted at the group’s goals. The laboratories appear to have created a good computing and experimental environment, and the test site at Fort Indian Town Gap provides realistic scenarios for testing against the three scenarios.

The researchers seemed to work smoothly together, with encouragement from their management to cross organizational boundaries both within ARL and with other national laboratories. At the same time, it was not apparent what mechanisms exist to encourage sharing information; a regular seminar series might be a good addition.

While the quality of the work overall is very good, there was no single project that stood out as especially promising and ready for accelerated deployment. The closest is the work on weakly supervised segmentation for mobility. This project is significant for several reasons: an interesting vision/science result was published at a major conference; it is an integrated end-to-end project that demonstrates the value of the research; and it is an external collaboration with a university. These are all indicators of the project’s scientific value and intrinsic contributions. The more projects that exhibit those characteristics, the stronger the perception effort will be.

It would have been helpful to present, in a concise form, a list of publications, awards, and other data that would help to convey the recognized accomplishments of the group.

Overall Challenges and Opportunities

Perception is a rapidly evolving area. The tool sets, the approaches, and the benchmarks on performance change yearly (sometimes monthly). It is also an area in which it is highly competitive to hire, placing a premium on providing the best resources, colleagues, and opportunities to attract the best people.

The ARL has done a very good job of building a strong perception group and giving them the opportunity to perform very credible single-investigator basic research. To move to the next level, ARL needs to think about a few audacious challenges that go beyond the extant state of the art—so-called grand challenges. These challenges would provide an exciting context for the group and would provide a point of focus for collaborative efforts. This is not to say that the work might not continue to be basic research. Semantic labeling of scenes, for example, would contribute both to the various integrated scenarios and to the international perception community.

More domain-specific challenges for teams, such as off-road mobility, would speak to the broader ARL mission. There are many other possibilities, but it is important for the perception group to aspire to one or more audacious projects that speak to Army needs.

Another opportunity would be to pursue some common platform/sandbox concepts that could be built upon. For example, the project related to weakly supervised segmentation deployed on a robot could be driven in a wide variety of directions. Its current application for driving is already interesting, but perhaps that could be expanded to become a platform for testing other segmentation methods (e.g., motion-based segmentation) and human body tracking for teaming. Again, this would become a point of cohesion for the group.

Most of the work presented focused on relatively traditional RGB vision.¹ However, there is no reason to limit the activities to vision. It may be relevant to consider multispectral sensing, range sensing, and contact sensors, such as temperature, force, and pressure.

VEHICLE TECHNOLOGIES

Platform Mechanics

The platform mechanics area focuses on fundamental research to enable highly maneuverable high-speed air and ground vehicle platforms and subsystems for the future Army, ranging from large combat/cargo vehicles to microscale devices. Specific research programs include fluids, structures and dynamics (rotor dynamics), actuation and mechanisms (adaptive wing span mechanisms), and platform configuration concepts (capability assessment and trade-off environment). The key campaign initiative (KCI) addresses small unmanned system airfoil research and rotorcraft aeroelasticity research within the discover and advance vertical takeoff and landing innovations, novel, concepts, and ideas (DAVINCI) program. The core campaign enabler addresses mechanics and dynamics of complex systems with research on dynamics of fluids and structures interactions, morphing structures, and immersive, interactive technology impacts and trade space exploration.

Koopman Decomposition of Periodically Excited Hopf Bifurcation Systems

This is excellent work, bringing modern ideas from nonlinear dynamics into the Army set of tools. The applications will give insights into a number of areas, such as dynamic stall. Publications are strong with a good paper in the Physical Review Journal. Another great area of application would be the fundamental nonlinearities of ground resonance. The researchers might consider this as a possibility. The approach could very well be adapted to include methodologies for the design of control laws for realistic systems. This does not imply that a turnkey control software needs to be developed. It does mean, however, that the theory could be advanced to a state where, for example, a Ph.D. controls engineer at a helicopter company would be able to utilize the ideas of this group in the design of nonlinear control systems.

This project is identified as one of the outstanding presentations that was given at this review. The investigators have taken advanced mathematical methodology in nonlinear systems theory and applied those tools to current, meaningful Army problems. By the use of nonlinear modal decomposition, they have been able to take complex experimental data and decompose them into the fundamental modes of interest, thereby giving insight into the physics of the underlying mechanisms.

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¹ RGB is an additive color model in which red, green, and blue light are mixed in various ways to reproduce a broad array of colors.

The fundamental mathematics used relies on the proof that for any nonlinear system there exists a mapping that represents its evolutions by an infinite-dimensional linear system. Although it is not possible to perform exact computations on the infinite dimensional system, the researchers have shown that the original system and its nonlinear modes can nevertheless be approximated by a finite number of linear systems. This holds great promise for realistic improvements in understanding and in design.

This methodology can be used to give insight into the fundamental behavior of nonlinear systems. It can also provide a low-order model of such systems to be used in control-system design. The method is broadly applicable and not limited to one particular type of nonlinear problem. The investigators have used dynamic stall as an exemplar system upon which to exercise the methodology, and this example has generated keen novel insights.

The researchers might consider also looking into Floquet instabilities. The Army’s need in their future vertical lift initiative to fly faster (and therefore to slow the rotors of aircraft) implies that these Floquet type of instabilities will become more and more important as one proceeds forward. Floquet instabilities usually are computed by periodic-coefficient equations that arise from linearization of a nonlinear set of equations about a periodic orbit. While classical Floquet theory typically neglects some of the nonlinear behavior, the present methodology might be able to properly account for nonlinear effects.

The researchers need to consider the possibility of applying the methodology to ground-resonance instabilities. These types of instabilities are so nonlinear that the military specifications (MIL specs) do not even call out a particular damping level for compliance. That would be meaningless for such a nonlinear system. Rather, the flight specifications declare that the limit cycle of the instability will be smaller than a certain amplitude of shaft wobble. This implies that the nonlinear methodologies studied here might be helpful. Ground resonance with one damper inoperative is also a crucial requirement for military aircraft. That condition gives the periodic coefficients of Floquet problems for which this approach could also help.

Other possible applications to periodic problems can exist even in the case of hover. For two-bladed systems, there are periodic coefficients even when there is no forward speed. Also, the interaction with wake dynamics (and the tendency of vortices to pair in hover) is another source of periodic nonlinearities that this nonlinear methodology could address. Again, the present approach could contribute. The researchers need to consider looking into how control system designers in the rotorcraft industry might be able to use the work of this group to design control systems for nonlinear flight systems.

Characterization of Coaxial Rotor Performance and Vibratory Loads

This work is long overdue. The effort could be both enhanced and accelerated to support the timely need for more fundamental coaxial-rotor methodologies required to support ongoing future of vertical lift activities. The project can do a better job in uncovering previous research that is directly applicable to the project, such as that available in the public literature on the Sikorsky XH-59 B ABC experimental aircraft and the Kamov family of coaxial rotors. This study of previous data seemed to be absent. The proposed plan for assessing the effect of rotor separation, rotor phasing, blade number, and so on is good.

While the work reported on the loads and vibration is applicable to the recent University of Texas, Austin, test efforts (and seemed to correlate well with computational fluid dynamics [CFD] work), it did not seem to explain the fundamental technical parameters applicable in the experiment such as rotor separation and hinge offset.

A more complete methodology could explore the results of stiff high-hinge offset rotors. Important parameters, such as rotor separation and upper and lower rotor phasing, were also absent from the presen-

tation and ought to be explicitly considered. Furthermore, there was no effort to discuss the appropriate frequency placement of the target rotors. This could be a crucial element.

Possibly, the researchers were only concerned with the aerodynamics of the subject model rotors and not the necessary aeromechanics and dynamics. An additional direction for future work would be consideration of different blade geometries for the upper and lower rotors. Finally, the work still needs to be expanded to cover an anticipated range of advance ratios up to speeds of 300 knots. Eventually, the interaction of the rotor with the aircraft tail at various speeds could be explored.

Experimental and Analytical Investigation of Continuous Trailing-Edge Flap Actuation Authority

This project aims to apply state-of-the-art CFD methodology (HELIOS) to prediction of coaxial rotor aeromechanics. Specifically, rotor-to-rotor interactions (lower rotor affected by upper rotor downwash) and wake-to-wake interactions are studied. Questions being addressed are these: Can one exploit dissimilar rotors for improved performance? Can one use on blade systems to reduce vibrations? How can one improve accuracy and efficiency of prediction of vibration and deflections?

This is extremely important work that analytically and experimentally explores the ability of embedded blade flaps to achieve rotor collective and cyclic control using electrically stimulated trailing-edge elements. The work appears to be very well done with good supporting background that demonstrates an understanding of existing literature. Agreement of experimental voltage and displacement is very good. One of the findings is that, although adequate displacement for full cyclic control is achievable, full collective authority over the entire range of flight conditions is not yet achievable; and a relatively slow moving separate rotor pitch control––located within the drive shaft––will replace the current complex, mechanical swashplate and drag producing pitch rods.

The work could easily be expanded in two important ways. Specifically, the researcher might include an element of controls thinking at this early stage in the work. Any lack of controls thinking will complicate the future applicability of the work. Incorporation of controls thinking is necessary if one is to include plans for sensor-embedded, sensor feedback and, more importantly, if one is to include redundancy management. Additionally, the effort, if feasible, might be extended to explore the system response bandwidth appropriate to incorporate a modicum of higher harmonic control into the logic. This will probably entail incorporating a different trailing-edge actuation surface stiffness into the end solution.

Multi-Fidelity Modeling of Active Rotor Concepts

This project is focused on the development and validation of comprehensive dynamics and CFD models of rotors with active trailing-edge flaps. There is collaboration among ARL, Army AeroFlight-Dynamics Directorate (AFDD), and Pennsylvania State University (in the form of a summer intern). The dynamics analyses utilized include RCAS (Rotorcraft Comprehensive Analysis System) and CAMRAD II,² and the CFD analysis is HELIOS.³ The quantities of interest include hover and high-speed performance, aeroelastic stability, active controls, loads and vibration, and acoustics. The project seems to be proceeding well.

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² CAMRAD II is an aeromechanical analysis of helicopters and rotorcraft that incorporates a combination of advanced technology, including multibody dynamics, nonlinear finite elements, structural dynamics, and rotorcraft aerodynamics.

³ The Helicopter Overset Simulations software (HELIOS) is a multidisciplinary computational suite being developed by DoD and the U.S. Army. It includes modular software components for near-field and far-field CFD, off-body adaption, domain connectivity, rotorcraft comprehensive analysis, mesh motion and deformation, and an exact fluid structure interface module.

A conference paper was written this past year, and RCAS simulations of the Boeing Smart Materials Actuated Rotor Technology (SMART) rotor testing at NASA Ames Research Center was initiated. Ongoing tasks are making a good effort to work with HELIOS developers to move to the incorporation of that capability this coming year. When completed, this project will result in a very-high-fidelity validated simulation of the SMART rotor system. A conference paper has been written based on the initial stages of this work, and this is a very positive development.

It is suggested that the scope of the project be limited to rotors with active flaps, as opposed to numerous other active devices. It is also suggested that a careful review of previous validation and simulation efforts on the SMART rotor be conducted. More emphasis needs to be placed on an array of theoretical/experimental models to develop improved physical understanding.

Bio-Inspired Air Vehicle with Arbitrary Wing

This is a fascinating project aimed at the design of a system level performance model for RoboRaven—a robotic flapping wing drone. RoboRaven is an intermediate size drone designed to be able to hit the sweet spot of both maneuverability and speed based on programmed wing configuration and actuation. The wings are driven separately, and wing kinematic models were developed. The aerodynamic model––which calculates thrust, lift, and power––is integrated with the motor and battery model to provide a system-level model. This model is then used to create a performance map. A vortex-ring formulation is used for the system model. This avoids approaches that are based on low-fidelity coefficients as well as approaches that are computationally expensive, such as detailed CFD analyses.

The system-level model allows for an interactive design environment where trade-offs can be explicitly considered, such as wing size and motor weight. In addition to the modeling, experimental innovation includes the design and fabrication of an onboard sensor suite so that inflight data can be gathered in real time in realistic flight, as opposed to collecting data from a fixed stand in a wind tunnel. This aspect is important for realistic model verification for a flapping wing robot, which will be crucial to the success of the project.

The overall goal is to be able to use the developed and validated system models to evolve a perfectly adapted winged robot design for given applications. Overall, this is an excellent project that combines detailed and system-level modeling, meta-modeling, experimental developments, and characterization.

Axial Propulsion with Flapping and Rotating Wings

This is a very interesting area of investigation. It is an old-school analysis of the performance of rotating and flapping wings, which yields deep insight into flapping propulsion and how to best design a flapping system. In this study of axial propulsion by the use of either flapping or rotating wings, the investigators are drilling down to first principles in order to determine the set of parameters and the design space for which either flapping or rotating wings are the best alternative. In this light, they are utilizing the classical ideas of momentum theory going back to the work of Glauert in the 1930s. Although these concepts may appear at first glance to be crude in their assumptions, as compared with modern-day CFD methods, they nonetheless form an important piece of insight into how thrust and power are obtained when one grabs air particles and accelerates them to make lift and simultaneously produce drag.

The work has opportunities to be even more productive if the researchers will pay a little more attention to the literature, starting with Hermann Glauert and ending with recent work at AFDD by Mahendra Bhagwat. The importance of wake rotation, wake contraction, and momentum assumptions has been keenly investigated by Bhagwat’s group in the past 5 years, building steadily on the work going back

to Glauert and improving on those original assumptions. A study of that literature could give even more insight into the study of flapping versus rotating wings.

It is important that the researchers pay attention to their overall goals and have the wisdom to know when the investigation has taken them as far as it can. Once a certain amount of insight is obtained, it will be time to use that insight to proceed to more advanced methods, such as vortex-lattice, vortex particles, or CFD. The project might look ahead to determine how it will know when it is time to make that transition.

Performance and Controllability of Overlapped Quadrotor Vertical Takeoff and Landing

The objectives of this project have been to develop comprehensive tools to gain insight into the performance and aeromechanics of novel quadrotor configurations with overlapping rotors. This configuration of overlapping quadrotors is motivated by recent progress by a small company in the United Kingdom. The present work also has a number of interactions with researchers at AFDD and University of Maryland. A conference paper was written based on the initial stages of this research.

The Army’s premier analysis tool, RCAS, is the platform being used to model the overlapping rotors. The thrust, power, torque, and required individual rotor rotation speed are being analyzed as the flight speed, turn rate, and center of gravity shift are varied. This project is focusing on the correct physics and applying rational methods. A conference paper was written based on the initial stages of the project, and the path forward seems appropriate. There may be opportunities to explore the vibration and load aspects of this unique configuration. The overlap of the rotors may cause impulsive changes in aerodynamic loading that lead to significant vibrations in forward flight. This possibility is something that the group could consider.

On-Demand Small Unmanned Aircraft Systems

The project title, “On-Demand Small Unmanned Aircraft Systems,” is somewhat confusing. The project really ought to be described as the aerodynamic performance effort necessary to support a soldier tool box for providing a multiple number of combinations of quadrotor aircraft for field use. Specifically, most quadrotors are designed based on the concepts of fixed-pitch propellers. Because these rotors have fixed pitch, they generally incorporate variable rotations per minute to affect thrust change.

The project researcher was correct in noting that little codified data is available to describe propellers in edgewise flow. Although the University of Illinois has a reasonable data base for model propellers at the appropriate Reynolds number, these data simply cover the pure hover case. Consequently, the intent to develop small-scale, low-Reynolds-number, edgewise data at higher speed makes sense.

Although the use of simple blade-element codes might appear simplistic, the approach is probably adequate for the intended use. Once these predictions are reasonably validated during wind tunnel and limited flight tests, a family of quad raptor propulsors can be eventually finalized, printed, and incorporated into the soldier tool box. The appropriate mission-level vehicle capability software package (payload, endurance, speed, range) needs to be outlined in a timely manner.

Design and Characterization of Stretchable Electronic Materials and Components as Soft Robotics Enablers

This is a very ambitious project aimed at creating stretchable electronics using micron-scale particles embedded in soft elastomers to enable soft robotics. A range of particle aspect ratios (spheres to rods) is

used to address various and interesting application spaces. The diagnostics developed in-house by the team is very unique and a definite plus for the program. Surface functionality and dispersion have not yet been considered, but their importance is recognized; studies of these effects are planned, in particular, as lower-length-scale particles will be examined.

By tuning the aspect ratio of the microfiber, the researchers have demonstrated the ability to achieve positive resistivity, negative resistivity, and also sharp resistivity changes with changes in strain. An impressive goal is the intention of demonstration of the ability to create a logic gate, which has interesting applications for simple, low-level control in soft robotic systems.

The researchers need to consider surface functionality and dispersion, as planned—which can go hand in hand with their present work—and will be key in order for the properties of these composites to be investigated. It might also be interesting to investigate the applicability of the group’s work in this space with roll-to-roll printing using graphene for flexible electronics. The researchers need to address durability and longevity of the electronics performance over time and use. Also, the researchers need to thoroughly consider the literature in the flexible electronics space, which has grown rapidly in recent years.

Neuromorphic Control, Theory, and Hardware

This project investigates a novel approach for the design of feedback control circuits based on neural networks. The focus is on low size, weight, and power; biologically realistic neuron models; and low-complexity interconnections. Stable, closed-loop behavior is demonstrated for a simple, inverted pendulum. An ambitious objective is to understand low-level neuron circuit design principles. A concrete deliverable over the next 2 years is the design and fabrication of a memristor-based microcontroller and its testing in a closed-loop hardware setup.

It would be of great scientific interest if the investigators could develop a deeper understanding of circuit design principles. Some questions that could be asked are as follows: What is the closed-loop behavior of interconnected neurons? Can one predict the behavior of networks with an increasing number of devices? Scientifically, it would also be of interest to situate this novel approach within the broad field of neural network dynamics, such as the 2005 paper by Vogels, Rajan, and Abbott.⁴

Autonomous Navigation and Work in Three Dimensions

This work incorporates a system involving a high degree of freedom propulsion core (array of propellers), mechanical manipulator, and novel end effector. The latter utilizes a unique concept to vacuum grasp a selected object. The system is intended to be robust and capable of operation over a wide range of forces. The work concentrates on the effector (grasper), which utilizes a novel approach to assure flexible engagement and offers a robust capability to avoid inappropriate disengagement. This capability was demonstrated by experiment, which validated the design analysis. However, the work did not include adequate control discussion of the vehicles autonomous positioning within the control space. Structural dynamics ought to be considered for the truss. Incorporation of the important control/ actuator bandwidth, proximity sensor, and system stability were not presented. Having said this, the effort looks very promising and is expected to incorporate a rigorous simulation, including the aircraft and robot manipulator, as soon as practicable. Development of a detailed stability model will also be

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⁴ T.P. Vogels, K. Rajan, and L.F. Abbott, Neural Network Dynamics, Annual Review of Neuroscience 28:357 -376, 2005.

extremely important and could include combined aircraft and robot control. Several current conference papers were cited that document the activity.

High-Fidelity Modeling of Dynamic Limbed Systems

This work is an innovative project focusing on design and controller development for legged locomotion mobility for robots. Legged robots could potentially enable faster locomotion, more agile movement, and the ability to handle disrupted environments. This project concentrates on leg design and the control, not on sensing or perception of environment, which is handled in other related projects. The test platform, entitled CANID, is a six-legged robot with a flexible spine. It has been demonstrated that the flexible spine leads to efficient robotic motion but also leads to complexity in control.

C-legs were implemented initially but also presented difficulties in modeling because they create uncertainty in terms of the unknown push-off point during motion. Thus, multiple other possibilities of leg geometries are being considered, with current focus on a five-bar leg with 2 degrees of freedom at the foot. Control algorithms have been developed––both with high-fidelity and lower-order modeling––the lower-order model will enable real-time control and is being validated against the high-fidelity model.

Many very interesting aspects of the legged robot are being considered, including how to design for both agility and speed, and a simultaneous ability to open a door, which are typically competitive goals. The ability to open a door adds weight in motors at each joint for dexterity, and that weight is counterproductive to attainment of speed. Control algorithms have been used in order to define the stable states in 9-dimensional space, and these are being used to enable the robot to move smoothly with changing gait and to address gaps in the landscape seamlessly. This is a very unique aspect of the work. The work, overall, is clearly defined, and this is an ambitious project with significant accomplishments and many areas of fundamental interest that remain to be explored.

Low Reynolds Number Dynamic Stall

With the Army’s focus on small, autonomous aircraft in the future, the scientific community will need data on the dynamic stall of airfoils at low Reynolds numbers. Otherwise, it will be impossible to design these small aircraft, whether they will have flapping wings, rotating wings, or fixed wings. There presently are very little data in this area.

The classical National Advisory Committee for Aeronautics airfoil charts have a few plots down to a Reynolds number of 25,000; but these are for only a few airfoils, and there are less data at lower Reynolds numbers. In addition, the data in this area are only static data and would not indicate how these low Reynolds number airfoils would behave dynamically, which is essential for design of the aircraft the Army has in mind.

The researchers on this project have thought the issue through and have arrived at a research plan to obtain the data and also to obtain insight into the flows. The facilities that the researchers have developed will enable them to proceed along a well-designed path toward the needed database. The particle-image velocimetry data already obtained are very impressive. These data can give insight into when a vortex is shed and where it goes after it is shed. This type of information is what one will need to formulate lower-order dynamic stall models in this Reynolds-number regime.

Although the work so far is excellent, it will all go for naught unless actual load measurements are obtained. Partial loads can, in theory, be obtained from the particle-image velocimetry data. In particular, an integration of circulation and vorticity––around a closed loop that encircles the airfoil––ought to be

able to give an approximation for the circulatory lift (although it cannot determine the complete lift, drag, and pitching moment). Nevertheless, the team needs to pursue this path, since it will give some preliminary data and will also give a benchmark against which to compare the load measurements that will follow.

The team’s plan of attack on how to obtain loads is very sound. The concept of balancing a free-floating airfoil with counter-weights goes back to the Wright brothers and is a very powerful method. This method is very creative and will probably be able to extract out the steady lift, drag, and pitching moment. It remains to be seen if the method will be successful for obtaining the unsteady loads, but it seems that the seeds for success are there. The research team needs to proceed at full speed on this work.

Energy and Propulsion

Energy and propulsion focuses on the exploitation of innovations in energy sources, storage, generation, conversion, transmission, distribution, and management to provide technologies and configurations to improve the operational effectiveness and efficiency of Army platforms to enable military power projection superiority. The principal activity in energy and propulsion are specific research and development (R&D) programs in the areas of fuel injection and combustion, turbine engine efficiency and sand tolerance, lightweight hybrid gears, and ARL-developed power electronics components. KCI consists of research on advanced power electronics conversion and control. CCE includes advanced switching and control for power electronics and high-power-density and energy-efficient drivetrain technologies. The KCI is directed at advancing tactical energy networks (intelligent distribution and control and the integration of generation, renewables, storage, and distribution). The CCEs focus on high-performance packaging and thermal management and DOD-specific diagnostics for high-pressure and high-temperature combustion vessels and high-speed chemiluminescence.

Hybrid Gears

The overall objective of this research effort is to enable weight reduction of power transmissions, thereby increasing power density. In order to accomplish this objective, experimental investigation of hybrid gears under adverse conditions is being conducted. This research effort is of high relevance and has been ongoing for a few years. In addition to the potential weight reduction, hybrid gears may also provide vibration and noise reduction.

The experimental programs being conducted are of high quality. However, in absence of a companion modeling effort, these programs get reduced to conducting tests rather than experiments. For example, previous testing with subscale gears does not provide a high-confidence path for pre-test predictions for tests conducted with full-size gears. A modeling effort would help in the identification of relevant dimensionless parameters for the phenomena of interest. It would also provide insights into how to use experiments to understand fundamental phenomena and predict the behavior of full-scale transmissions. Sustained resources for the modeling portion are now being deployed.

Tribology and Lubrication Science

The research program on tribology is outstanding in its approach and content. This field has traditionally been very empirical in its approach. It has been common to gather data for material pairs of interest in the laboratory environment and then use the data in design of the components and systems. This approach can result in expensive problems because the laboratory testing may not encompass all

the conditions for the system accurately. The research team has chosen to conduct experiments rather than tests. This approach is focused on getting answers to specific questions aimed at understanding the basic physics underlying the wear phenomena. This will make it possible to apply the knowledge to the conditions corresponding to the actual system operating conditions in the future. Experiments are logically planned with an analytical approach. Replacement of steel by lightweight Si₃N₄ could be beneficial.

The research program has two stated objectives: (1) achieve fundamental understanding of limiting failure mechanisms in power transfer interfaces to enable operation under adverse lubrication conditions and (2) increase power density and specific power in vehicle transmissions.

The research meets the first objective very well. Even though there is not a clear link to meeting the second objective, this is somewhat ground-breaking research. Its value will only be better understood once one has all the information and focus can be turned to utilizing it in the design process.

The hypothesis, as stated in the poster presented to the panel, is somewhat vague. In particular, the link between high-slide tribology experiments and specific gear or bearing applications needs improvement.

Plans to perform in situ diagnostics at high-sliding junctions are good. Application of more comprehensive experiments to characterize tribologically formed films would be good.

The team of researchers working on this program also demonstrate excellent effort in keeping abreast of the state of the art via attendance at conferences and other training opportunities. This approach needs to be continued to maintain relevance of the program and internal efforts. While the in-house activities do not have an extensive modeling component, there are excellent collaborative programs aimed at developing companion modeling capability. It will be very useful to include these collaborative activities in future reviews.

Effect of Semi-Molten Particulate on Tailored Thermal Barrier Coatings for Gas Turbine Engine

The overall objectives of this research effort is to enable uninhibited operation of gas turbine engines in harsh environments that may contain dust, sand, salt, ash, etc. The research effort is directed at understanding fundamental mechanisms of thermal barrier coating degradation caused by these contaminants. A balanced approach consisting of experiments and modeling (being pursued at partner institutions) is being executed. This problem is highly relevant to the gas turbine industry and goes well beyond just Army applications.

The experimental programs being conducted are of high quality. The experimental facilities are state of the art. Researchers need to pay close attention to ensuring that the configuration of the test coupons (geometry as well as film-cooling flow rates) are in the right parametric space and correctly simulate the fluid mechanics in gas turbine engine components. Another opportunity for improvement is to closely examine the concept of using average sand in the experiments. Such an approach may provide data that is not applicable to any specific conditions encountered by the engine. It may be a better idea to identify the range of parameters and conduct experiments that bracket the range.

Nonlinear Ultrasonics and Advanced Sensing Methods for High-Temperature Propulsion Materials

Overall, the quality of the work presented was excellent. The paramount goal of this work is to develop an in situ temperature-strain sensing capability at temperatures above 1250°C. Such conditions contribute to what is generally an austere sensing environment.

Ultrasonic frequency was selected to be sufficiently high so that the wavelength (speed of wave or frequency) is much smaller than the damage feature to be detected.

In this research, classic Fourier harmonic wave analysis concepts were used to examine a nonlinear quantity that is proportional to the ratio of the second harmonic wave amplitude and the first harmonic wave amplitude squared and also inversely proportional to the distance traveled by the wave.

This ratio is sensitive to microstructural damage accumulation. The researcher showed that this ratio increases with increasing fatigue cycles. It was also demonstrated that these ideas may be useful to detect thermomechanical fatigue damage precursors—for various materials (e.g., aluminum, titanium, and nickel based alloys).

The problem being addressed in this work—reliable damage detection for propulsion applications—is very important for current and future warfighting missions. The sensing methods under development can be used for damage detection, state assessment, and health monitoring. As such, they can eventually play a critical role in ensuring the safe operation of mission-critical propulsion systems.

Opportunities for this work include the following: (1) carefully comparing results with existing methods (e.g., eddy current and fluorescent penetrant inspection); (2) developing a benchmark (e.g., with a very precise type of damage) for rigorous comparison purposes—such a benchmark can be used to systematically compare alternative approaches; (3) examining relevant signal to noise ratio issues and possibilities for real-time/post processing; and (4) examining possibilities for use of such a sensor for future real-time control (e.g., reduce control system bandwidth when damage is detected).

JP-8 Desulfurization

In this work, the link to a pressing Army need is clear, and the approach is well chosen. The context to other non-ARL work on fuel desulfurization is good. The methodology is well chosen. The accomplishment of nearly 10 times improvement in organosulfur adsorption specific capacity since 2012 is commendable.

Opportunities for improvement exist in formulating the hypothesis, which is not well formed. The selection process for creating improved sorbents is ad hoc and could benefit from more rational design principles. A companion computational modeling effort could be beneficial here.

Transient Thermal Management of Electronic Components

Overall, the quality of the work was excellent. The paramount goal of this work is to better address traditional or classic thermal overdesign issues by using predictive knowledge of transients.

The work focused on examining fast transients (20 msec to 100 msec) for high-power applications. Multilevel encapsulated phase-change material (guided by classic low-pass filter modeling ideas) was used to appreciably dampen high-speed transients. Enhanced package design with greater than 40 percent peak temperature reduction was achieved for a benchmark case. The work was published, with one of the papers being highly cited.

The problem being addressed in this work, thermal management of electronic components, is very important for current and future warfighting missions. Thermal management methods can be used for controlling overall system performance, reducing design conservatism, and extending life. As such, this work can play a critical role for ensuring the safe operation of a mission-critical subsystem.

Opportunities for this work include the following: (1) gathering data from real devices and comparing it to simulation data, which can then be used to improve modeling capabilities; (2) partnering with Texas A&M University on the above and more precise modeling; and (3) showing how work can

be used to better control and significantly impact the performance of an overall warfighting system or critical subsystem, which can include using feedback to precisely control transients in the presence of uncertainty.

Solid-State Circuit Breaker

Overall, the quality of the work was excellent. The paramount goal of this work is to design and build a solid-state circuit breaker with a much longer life expectancy than state-of-the-art nonsolid-state breakers while delivering improved performance. The work focused on addressing 850 V and 100 A breakers using silicon carbide. With a footprint of the same size as a mechanical breaker, the silicon carbide breaker achieved a factor of 6,500 improvement in switching time, while trading off resistance by a factor of 23.25, which is 3 times more efficient than silicon.

Avalanche diodes were used to accommodate 4 times greater surge vis-à-vis silicon. It needs to be emphasized that the developed solid-state breaker is not available commercially. The design procedure is fast—taking approximately 10 minutes for a redesign—and the desired switching profile can be programed in, for example. The research results have been published.

The problem being addressed in this work—a longer lasting circuit breaker—is very important for current and future warfighting missions. A longer-lasting circuit breaker can be very useful for ensuring and controlling overall system performance and extending system life. As such, this work can play a critical role for ensuring the safe operation of mission-critical systems.

Opportunities for this research include the following: (1) carefully quantify performance vis-à-vis state of the art; (2) the possibility of developing a graphical user interface to permit users to input desired characteristics; (3) working toward automating the building process; and (4) showing how this breaker (or the next version of the breaker) can make a significant difference vis-à-vis other competing breakers within a critical warfighting system application.

Advanced Thermal and High-Voltage Electronics Packaging

Overall, the quality of the work was excellent. Current power electronics packages are generally oversized and have multicomponent reliability challenges. A critical goal here is achieving a greater power density. The state-of-the-art package is one with the following specifications: 150 W/(sq cm) power density, 10 kV operational voltage, and 150°C operational temperature. A 2-year goal for the research is as follows: 1 kW/(sq cm) power density, 30 kV operational voltage, and 200°C operational temperature.

An integrated power tower package has been developed—a new packaging approach that stacks devices between multipurpose mechanical/electrical/thermal copper interconnects. While commercial packages have a characteristic thermal resistance of 1 to 3 (°C/(W/(sq cm))), the researcher has achieved 0.2 and is aiming for 0.1. Modeling has shown that this goal requires that multiple methods be properly combined.

The researcher has shown that one can get close with a heat spreader (i.e., thermal ground plane). However, more is needed in order to achieve the objective. The researcher worked with WMRD to develop a substrate board using custom cold spray additive manufacturing powder to replace more standard direct-bond copper board that cannot operate at high voltages. The research achieved 500 W/(sq cm) and 30 kV with the above additive manufacturing approach. The research results have been published and have received best paper track and session awards.

The problem being addressed in this work—the design of thermally robust electronic packages—is very important for future warfighting missions. A more robust electronic package can be very useful for

ensuring and controlling overall system performance and extending system life. As such, this work can play a critical role for ensuring the safe operation of mission-critical systems.

Opportunities for this research include the following: (1) pursuing performance-based modeling (i.e., co-design co-simulation work) with faculty from the Naval Academy in order to more precisely and holistically optimize thermal, electrical, and mechanical design objectives; (2) collaborating among others with University of Maryland, Power America, NASA, and the Department of Energy on the above; and (3) establishing future longer-term benchmarks and goals.

Spray Combustion Studies

ARL has a commendable program on spray atomization and combustion. It covers both computational and experimental topics and is staffed by several competent early career researchers. The facilities are impressive. The program involves the investigation of diesel-engine spray combustion by studying pulsed, round, fuel jet injection into gas chambers—at pressures ranging up to 60 bar at this point. The combined computational and experimental effort aims at understanding spray dynamics, mostly in the context of combustion for propulsion. The scientific questions being addressed are well formed, and the findings to date were clearly stated and shown in the posters presented to the panel. The results are relevant to combustion science, with the computational and experimental collaborators on a clear path to generating useful insights. The team appears to be well connected with multiple consortia both within and outside DOD, both nationally and internationally, focusing on the study of fundamental combustion of diesel sprays. The team is to be commended for the tight integration of theory, computations, and experiments.

The team’s three-dimensional, unsteady computational model currently addresses the lower pressure conditions by considering both the gas and liquid to be incompressible and isothermal (with no coupling to energetics). Vaporization was not considered. The surface was tracked by the volume-of-fluid technique. Examples of their progress are given by several papers that include the results of collaborative research. See, for example, Ma et al. (2014),⁵ Bravo et al. (2016),⁶ and Bravo et al. (2016).⁷ The round jet was previously studied by Shinjo and Umemura (2010)⁸ for spatially developing instability and by Jarrahbashi and Sirignano (2014)⁹ and Jarrahbashi et al. (2016)¹⁰ for temporally developing instability. The ARL study can build upon these works in several ways. For example, a wider range of fuels and, therefore, of Ohnesorge numbers can be studied, and stronger coupling with experiments can be made.

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⁵ P.C. Ma, L. Bravo, and M. Ihme, “Supercritical and Transcritical Real-Fluid Mixing in Diesel Engine Applications,” pp. 99-108 in Center for Turbulence Research Proceedings of the Summer Program 2014, https://web.stanford.edu/group/ctr/Summer/SP14/05_Two-phase_flows/06_ma.pdf.

⁶ L. Bravo, S. Wijeyakulasuriya, E. Pomraning, P.K. Senecal, and C.B. Kweon, Large eddy simulation of high Reynolds number nonreacting and reacting JP-8 sprays in a constant pressure flow vessel with a detailed chemistry approach, Journal of Energy Resources Technology 138:032207-1, 2016.

⁷ L. Bravo, D. Kim, F. Ham, K.E. Matusik, D.J. Duke, A.L. Kastengren, A.B. Swantek, and C.F. Powell, “Numerical Investigation of Liquid Jet Breakup and Droplet Statistics with Comparison to X-ray Radiography,” AIAA Preprint, 52nd AIAA/ SAE/ASEE Joint Propulsion Conference, http://arc.aiaa.org/doi/abs/10.2514/6.2016-5096, 2016.

⁸ J. Shinjo and A. Umemura, Simulation of liquid jet primary break-up: dynamics of ligament and droplet formation, International Journal of Multiphase Flow 36:513-532, 2010.

⁹ D. Jarrahbashi and W.A. Sirignano, Vorticity dynamics for transient high-pressure liquid injection, invited paper, Physics of Fluids 26(10):101304, 2014.

¹⁰ D. Jarrahbashi, P.P. Pavel, W.A. Sirignano, and F. Hussain, Early spray development at high-density: Hole, ligament, and bridge formations, Journal of Fluid Mechanics 792:188-231, 2016.

The work appears to mostly focus on spray expansion and ignition in large chambers without considering the dynamical changes that would occur in an operating piston engine. In this regard, the researchers’ plans to extend their experimental diagnostics to include an observation port on an operating piston engine are well thought out and sound.

The team needs to seek different domains of physical behavior in the plot of Weber number versus Reynolds number. What is the path for the cascade through decreasing scales as the two-dimensional Kelvin-Helmholtz (K-H) waves become three-dimensional with eventual droplet formation? The various, smaller three-dimensional structures consisting of lobes, holes, bridges, ligaments, and droplets could be identified. Specifically, the team could study how the Ohnesorge number relates to the breakup mechanism.

The team needs to do post-processing to determine the vorticity field and to relate the vortex dynamics to the development of the liquid-gas interface dynamics, which could explain the physical mechanism for the break-up cascade. Then, post-processing analysis could be used to determine the major vorticity generation terms, especially for the streamwise vorticity and the hairpin vortices formations.

The team plans to develop, in the near future, a computational model that describes the injection of fuel at subcritical temperature into a gas at supercritical pressure. The team understands that this will require one to consider the use of a cubic equation of state, variable density, variable composition, heat and mass exchange between the two phases, an enthalpy departure function to correct for real-gas behavior, the energy of vaporization (which is distinct from the latent heat), and detailed phase equilibrium to account for both the original gas in solution and the fuel vapors in the gas. A review of the work done at the Air Force Research Laboratories (Edwards Air Force Base) by Talley, Chehroudi, and co-workers would greatly benefit this effort.

An issue for discussion and examination is the need to use large-eddy simulations (LES) for the liquid jet problem. The transitional turbulence generated by the liquid jet has two major, critical features. (1) Transitional turbulence is the cause of the hydrodynamic instability and leads to jet break-up process; therefore, it cannot be treated as a subgrid phenomenon. The team clearly understands this point. (2) The turbulence kinetic energy generated upstream in the orifice in the absence of cavitation has substantially smaller magnitude. Thus, the value of modeling the smaller scales is questioned. Note that the three papers from non-ARL work referenced above use direct numerical simulation without resolving turbulence generated in the orifice flow. The ARL team is not modeling the ambient turbulence that might be generated through air intake. However, if it did, the length scale would be larger than the liquid jet dimension—implying that LES will not help there.

The experimental work addresses interesting issues concerning the transient injection of fuels with vaporization, mixing, and chemical reactions. Higher pressure tests are included. While excellent high-pressure facilities are available at ARL, a potentially important collaboration with Argonne National Laboratory has been made to access testing with higher-resolution X-ray imaging, albeit limited to atmospheric conditions. The fuels include JP-8, diesel oil, and biofuels. Simultaneous diagnostics at high speeds are available. Ignition and ensuing, transient, combustion are studied. Comparisons with computations are made yielding qualitative agreement but with quantitative disagreement. The researchers agree that pursuit of higher resolution is critical. Investments have been made in forefront imaging to accomplish this goal.

Several improvements to the research can be made. The team could do the following:

1. Determine the three-dimensional, smaller-scale structures that form in the transition from two-dimensional (2D) K-H waves to the droplets;

2. Examine whether the path from 2D K-H waves to droplets depends on Ohnesorge number rather than just on Reynolds number and Weber number;
3. Attempt to identify whether fuel-rich “blobs”¹¹ exist and, if so, can a pattern be found related to the original K-H wavelength;
4. Determine if vortex structures are forming in the gas and study the role they play in the mixing and combustion processes (velocity measurements will be helpful here);
5. Use simple injector configurations (e.g., simple orifices) in the initial studies instead of commercial injectors to allow investigation of injector design effects;
6. Invest available resources to study of the atomization, mixing, and the locations within and outside the sprays where local ignition occurs, although it is doubtful that the proposed detailed chemical kinetics studies would impact the results, considering the complexity of fuel sprays combustion; and
7. Obtain more information on how high-speed chemiluminescence would yield information about ignition and the quality of the combustion process.

Logistics and Sustainability

The logistics and sustainability area focuses on empowering the Army with breakthrough technologies and capabilities to conduct expeditionary maneuvers with substantial reduction in operation and sustainment costs. Its goal is reduced-maintenance and longer fatigue life Army systems. Condition-based maintenance is driven by research in (1) material state awareness/self-healing, (2) digital nanomaterial architecture (additive manufacturing), and (3) material damage precursor development (failure correlation) forming the virtual risk-informed agile maneuver sustainment (VRAMS) program. This drive advances in condition-based maintenance to mission-informed material state-based awareness. This represents an advance from hardware-level concern to a focus on higher-level, mission-relevant operations. VRAMS has developed a 10-year plan that includes demonstration and transition to technology readiness level (TRL) 5. The 5-year plan is supported by uniquely integrated computational, modeling, test, and analysis facilities and environments.

The main research activities of the logistics and sustainability group are centered around the VRAMS program. VRAMS emphasizes early damage detection, focuses real-time integrity monitoring and state awareness, expedites operation adjustment, and automates planning and implementation of needed logistical modification. This is a laudable and very desirable goal for the Army. ARL is to be commended for tackling this holy grail of integrated material system behavior.

VRAMS is a paradigm change in design, operation, and sustainment for all structural platforms. The program has a grand and ambitious vision with huge industry-wide impact. It involves multidisciplinary research with a link to current emerging research topics on information, sensors, multifunctional materials, intelligent structures, multiscale, multi-physics computations, etc. It touches multiple research areas with vertical integration possibility.

Challenges for the logistics and sustainability area include the following: (1) Enormous efforts are required with focused steps to execute the program. Phase in approach is needed with clear near-term and long-term objectives and targeted milestones or metrics. (2) Because of the complexity and diversity of the program, integrated efforts in both technology and industry-academia collaboration are needed.

While the program has laudable high-level goals, its extreme breadth can also make progress difficult. ARL has reached out to collaborate with several universities and the Navy and could benefit greatly

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¹¹ A “blob” is some combination of liquid and fuel vapor.

by expanding that outreach to many other leaders in numerous programs with similar goals, including industry and the Air Force. Having identified that major challenge, a next logical step for ARL might be to harness the collective wisdom of the broader community as to proposed strategies for approaching such a major goal by asking one or more professional societies to convene a major conference and harnessing the brainpower of all sectors—industry, academia, and government—for such an undertaking.

Sustainable, long-term support would be critical to carry out this research. Strong interaction with Army Research Office program managers are needed to develop collaborative programs. For instance, VRAMS-focused programs as part of multidisciplinary university research initiatives might be sought to create additional infusion to the project. Open-campus programs can be utilized to address project needs. Joint efforts with academia and industries need to be further encouraged. A benchmark test-bed approach is needed to demonstrate technology development to align with DOD-targeted thrust areas. ARL, in the short term, needs to focus on those known parameters for a proof of concept, while continuing long-term studies on unknown parameters, such as damage precursors on selected materials (metals and composites) that are most critical to the rotorcraft industry. For instance, as an intermediate point, some explicit linkages need to be made between damage precursors and sensors, for specific materials, and damage mechanisms and goals need to be set in that context. Early interaction with airworthiness authorities is needed. Promotion of VRAMS concepts and results is needed at conferences, in journal publications, and at special VRAMS-focused technical sessions and meetings.

The approach initiated by ARL has several laudable elements, as discussed below. All projects need to define intermediate goals where specific materials (or classes) are identified and specific failure mechanisms are linked to clear structural changes. These structural changes then need to be linked with sensing and/or health monitoring technologies that can sense specific damage precursors. These mechanistic connections between explicit structural changes and failure mechanisms and sensing strategies can be strengthened significantly.

Materials Damage Precursor

The concept of very early detection of structural material damage to enable early action for safety and maintenance is a very desirable goal. Because it is so strongly related to material microstructure, participation by materials scientists in this program is essential. It is not clear that testing individual fibers adds significant insight into failure modes in fiber composites, nor is it clear what precursor structural changes are being tracked, how this can be sensed in a fielded application, or how these will relate to eventual failure. Further, phenomena occurring on the surface of a fiber is not indicative of fiber-matrix interfacial failure modes. Clear understandings of the envisioned failure mechanisms relating this to measurements would accelerate useful progress.

Elastodynamic Modeling of Metal Microstructure

The program approach is relating material behavior to microstructure, which is an important subset of this effort. There is significant knowledge both from theoretical work and experiments as to how stress affects the elastic stiffness tensor of crystals, and several models can be used to extend this to the behavior of polycrystalline aggregates. The program would benefit from more clearly defining how this work is differentiated from work now in the literature and presenting an explicit sensing strategy by which this information could be used in measuring stress in fielded applications. The effort would also benefit by including materials engineering talent and evaluating the extensive literature in that area.

Advanced Sensor Fusion

This program is a well-thought-out analytical integration of measurable and detectable damage and structural behavior. It provides a very tangible example of very advanced and powerful use of sensors with a clear path for in situ, in-mission use. The collaborations with airframe manufacturers and universities is particularly laudable. The research has captured an important challenge and has made a strong contribution.

Magnetostrictive Material Modeling for Structural Health Modeling

This project presents a novel method for local measurement of stress using the magnetic properties of a Fe-Ga alloy. The work is well thought out and uses an advanced process—magnetic pulse welding—to join the alloy to the prototype component without the use of heat. The program is clearly carried out carefully, intelligently, and with academic impact. It is not clear, however, what the strategy might be to incorporate this technology into fielded systems. Addressing this at a conceptual level would better tie this program to the broad VRAMS mission.

Reduced Logistical Burden by Part Reduction via Composite Drive Shafts

This program proposes the possibility of reducing weight and part count by replacing metal drive shafts. These shafts require flexible couplings with longer composite shafts having an elastomeric matrix to accommodate the motion carried by the couplings. The replacement of aluminum with composites can provide significant rotorcraft weight reduction, making it more capable. Because the primary goal of eliminating couplings requires demonstration of functionality of the composite shaft, it is not clear why the first part of the program deals with ballistic vulnerability and puts off the demonstration of functionality. This work can provide real benefits to the warfighter. Considering full drive shaft designs early in the design of the program can accelerate impact.

Topology Optimization for Additive Manufacturing

The researcher that presented this topic to the panel is commended for a very clear and insightful articulation of the work. The development of topology optimization is a very worthwhile and relevant effort and does lend itself to additive manufacturing. It was not fully clear what the novel aspects of this work are in the rapidly developing areas of topology optimization and additive manufacturing. This work would benefit by developing an extensive literature review in these areas. In addition, including additive manufacturing and materials expertise in this project would benefit the development of relationships among process, structure, property, and performance that are required to ultimately apply topology optimization through additive manufacturing in fielded applications.

Damage Precursor Detection and Identification in Composite Materials

The goal of linking damage propagation prediction with actual data is a very desirable goal and a challenge in composite materials. It is very well known that, in composite systems, compliance will increase with damage. It is not clear how this work adds clearly to that body of knowledge. Because it is so strongly related to material microstructure, participation by materials scientists in this program is essential.

OVERALL QUALITY OF THE WORK

Vehicle Intelligence

In each of the three pillars of the vehicle intelligence (VI) program—intelligence and control, perception, and human–robot interaction—the research quality was generally high. Research results are published in high-quality journals. Collaboration with other government agencies, industry, and universities continues to yield benefits. Internal personnel advancement, including hiring new, well-qualified Ph.D. researchers, strengthens the capability of the Sciences for Maneuver VI R&D program.

Each of the three pillars of the VI program has demonstrated significant progress in advancing its R&D objectives to support the warfighter in increasingly complex environments. The R&D activities in each pillar were consistent with its defined objectives. Opportunities in multiperson/multirobot scenario simulation, teaming of autonomous systems with soldiers in uncertain environments, multispectral sensing, range sensing, contact sensing, and immersive display of robot lidar imagery may allow ARL to take the lead in this research and offer greater benefit to the soldier.

The intelligence and control pillar employs innovative approaches in developing and supporting advanced technologies, algorithms, and tools in support of the warfighter effort. There are high-value collaborations with top universities, industry, and other government agencies. This pillar invests in advancing the effectiveness and efficiency of its research personnel.

The perception pillar benefits from high-quality collaborations with top universities that enable successful hiring of outstanding personnel at the Ph.D. level. Current trends and research vectors were observed. Research personnel participate in highly competitive technical conferences and publish in top research journals.

The human–robot interaction pillar’s R&D program is of high quality and based on rigorous design and appropriate metrics. It benefits from a substantial increase in external and internal collaborations. Through early retirements and expansion of the postdoctoral program, qualified Ph.D. personnel have been hired.

The VI R&D program is correctly constituted and resourced with the ARL workforce and facilities. In general, the VI team demonstrates good awareness of the scope and direction of R&D in each of the pillars. Cognizance of related activities in industry, government, and international R&D enable meaningful goal setting and tactical adjustments in specific program advancements.

Within VI R&D programs, research quality is generally of high quality. Based on rigorous design, useful evaluation and analysis, appropriate metrics, thorough understanding of related research, workforce interaction at critical open conferences, and publishing VI investigations in top journals, VI is well positioned to maintain and improve the quality of its research products.

Recently hired researchers within VI appear to be well qualified to conduct leading R&D in VI. These new additions to the VI workforce have been educated and trained by leading faculty in the three pillars at top-ranked U.S. academic institutions. At ARL, new personnel are exposed to effective mentoring. The VI principal investigators are well prepared and energetic.

VI collaborations with U.S. industry, government, and academia appear to be extensive and are very effective at advancing the VI R&D mission. These collaborations are important components driving VI awareness, leading to the establishment of meaningful goal setting and tactical program adjustments. Similarly, the collaborations feed the energy of the VI principal investigators.

Inclusion of U.S. soldiers in VI field experiments is commendable. Usage of more realistic vignettes and real-life simulations in experiments would be very beneficial. In particular, the use of realistic

warfighting vignettes, where researchers are in the field with soldiers, provides opportunities to test and evaluate research hypotheses more thoroughly, including the revelation of previous unknowns.

Within VI, the emerging shift from one-person/one-robot studies to multiperson/multirobot studies merits sustained attention. This shift exposes VI to more complex teaming architectures, a concomitant realistic field environment, and potential improvement of the validity and applicability of the research results.

Some strategic goals and tactical milestones for VI R&D programs could be made more apparent. To help quantify general progress and application-specific performance, more efforts need to be made in terms of baselining and benchmarking. A process whereby desired capabilities and goals are broken down into a sequence of achievable (realistic) short-term capabilities and goals would be beneficial. Unifying demonstrations, milestones, objectives, and capabilities could help to better motivate the specifics being developed and how they will be integrated.

Application of more systems integration principles across research projects and pillars would strengthen the overall impact of VI research products. Similarly, connectivity between individual principal investigators could be improved.

The VI program is well positioned to maintain and improve the quality of its research products. To move to the next level, VI needs to undertake carefully chosen, audacious, grand challenges that go beyond the extant state of the art. Resulting activity and research products would provide leadership in R&D. This would yield inherent advantages in framing VI problems to achieve solutions that benefit the Army.

Vehicle Technologies

In each of the foundational pillars and key enablers of the vehicle technology program—platform intelligence, energy and propulsion, platform mechanics, and logistics and intelligence—the research quality was generally high. Research results are published in high-quality journals. Collaboration with other government agencies, industry, and universities continues to yield benefits. Internal personnel advancement, including hiring new, well-qualified Ph.D. researchers, strengthens the capability of the sciences-for-maneuver R&D program.

In the platform mechanics area, the research was overall of an excellent quality. The steady improvement of the work over past years is quite evident and is to be commended. Each of the tasks was well thought out. The tasks have an appropriate amount of connectivity with other tasks in this area, and the researchers have a good understanding of how their work fits into the larger picture. Although the publications of the researchers at conferences and in journals continue to improve—as they have over the past few years—this area can still use more improvement. Hopefully, more travel funds and better mentoring will see an increased number of publications. Overall, the work is excellent and shows a solid improvement in the research quality, applicability, and dissemination of the research results.

The Koopman decomposition of periodically excited Hopf bifurcation research (nonlinear system theory) initiative is outstanding, with a potentially significant impact on Army understanding and exploitation of nonlinear mechanics, such as dynamic stall, Floquet instabilities, low-order modeling of control system design, and ground resonance instabilities.

The experimental and analytical research on continuous trailing-edge flap actuation authority is important, well executed, and advances the state of the art in understanding the rotor-to-rotor interactions and wake-to-wake interactions. The sound methodology of simulation, analysis, and experimental testing is to be commended.

The R&D work on stretchable electronic materials is outstanding. This work is a clear demonstration of ARL in-house research leadership. The demonstration of tuning the aspect ratio of microfibers is an advance in capability to achieve positive, negative, and also sharp resistivity changes with strain.

In general, platform mechanics research presentations were professional, logical, content-rich, and useful. Growth in knowledge content by researchers and staff is noted. Significant advances in the use of experimental and diagnostic facilities were observed (high-altitude test chamber, tribology upgrade, low-turbulence wind tunnel).

In the energy and propulsion area, clear advancement has occurred since the panel visit 2 years ago. The new facilities are producing publishable results. The early career researchers show greater maturity, knowledge, and subject command. In the high-pressure spray combustion domain, ARL is well positioned for a leadership role. Wider recognition of this group is needed over the coming years.

The ongoing hybrid gears research is excellent. This work has high potential to reduce system weight, vibration, and gear noise. A modeling effort that includes the development of primary dimensionless parameters is needed.

The research on the effect of semi-molten particulate on tailored thermal barrier coatings for gas engines is also to be commended. Progress obtained in collaboration with industry is advancing the understanding of thermal barrier coating degradation caused by dust, sand, salts, and ash.

Research and development of nonlinear ultrasonic and advanced sensing methods for high-temperature propulsion is excellent. With a goal of an in situ temperature-strain sensing capability at temperatures above 1250°C, the proposed ultrasonic frequency method is quite appropriate and useful.

The overall quality of the transient thermal management of electronic components is excellent. This work is critical to warfighting missions. Using multilevel encapsulated phase change material, this work focuses on examining fast transients for high-power applications.

A big picture demonstration showing how the energy and power work will be integrated would be helpful to the researchers and for future reviews. Such a demonstration can be used to pursue a very relevant and informative system-of-systems analysis that can be used to identify weak links, guide research, and steer collaborations. This team needs to discuss the limitations of approaches being taken in each of the research initiatives. Such a discussion will fundamentally enhance understanding for early career researchers.

In the logistics and sustainability area, while the program has laudable high-level goals, its extreme breadth can also make progress difficult. ARL has reached out to collaborate with several universities and the Navy and could benefit greatly by expanding that outreach to many other thought leaders in numerous programs with similar goals including industry and the Air Force. Having identified that major challenge, a next logical step for ARL might be to harness the collective wisdom of the broader community as to proposed strategies for approaching such a major goal by asking one or more professional societies to convene a major conference and harnessing the brainpower of all sectors—industry, academia, and government—for such an undertaking.

Several logistics and sustainability research programs are laudable—namely, materials damage precursor, elastodynamic modeling of metal microstructure, advanced sensor fusion, and topology optimization for additive manufacturing.