5
Mechanical Sciences

INTRODUCTION

The mechanical sciences competency focuses on the science of novel mechanics, mechanisms, and control to enable manned/unmanned ground and air vehicle concepts. Within the competency are two “core competencies,” which include the platform design and control core competency and the vehicle propulsion sciences core competency. The platform design and control core competency focuses on basic and applied research to establish interdisciplinary scientific foundations to enable maneuverable, adaptive, tactical platforms through advances in theoretical mechanics, machine-enabled and conceptual design, and non-classical mechanical systems and actuators. The vehicle propulsion sciences core competency focuses on fundamental research to understand and exploit energy conversion and power transfer mechanisms to enable extended reach, endurance, and readiness of Army platforms.¹ On July 25–27, 2023, the Panel on Assessment of Mechanical Sciences received presentations on the mechanical sciences competency and its core competencies at the Aberdeen Proving Ground, Aberdeen, Maryland. Below is a summary of its findings.

TECHNICAL QUALITY OF THE CORE-COMPETENCY RESEARCH

Platform Design and Control

Accomplishments and Advancements

The research under platform design and control shows a clear emphasis on scientific quality. Several aspects of intramural projects are particularly noteworthy and are discussed below. The research portfolio with respect to its fit within the broader scientific community is particularly impressive and demonstrates a good understanding of the underlying science and research conducted elsewhere. Many of the projects highlighted efforts that align with, and are at par with ongoing investigations in that community to expand the state-of-the-art capabilities. Overall, the intramural projects and extramural projects in platform design and control contain a diversity in research that can be seen in many university departments. The extramural Army Research Laboratory (ARL) research is a prime example of understanding the community. The extramural ARL program managers are actually setting the standard for which the broader scientific community is following in fields like embodied intelligence, particulate physics within a fluid, and flow separation as a critical aspect of aerodynamics. Some of their sponsored research thrusts are serving to drive related projects at the Office of Naval Research, Air Force Office of Scientific Research, and Defense Advanced Research Projects Agency (DARPA).

The intramural research enhances the extramural research by choosing topics that align with the broader community. Certainly, topics like machine learning (ML) and multi-functional materials are

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¹ Core competency descriptions in this passage come from U.S. Army Combat Capabilities Development Command (DEVCOM) Army Research Laboratory (ARL), 2022, “Foundational Research Competencies and Core Competencies,” March.

receiving extensive attention within that community so these intramural research efforts are adding to the growing literature. The research focus of functionally graded materials and structures and developing formal methods to design, analyze, and evaluate such materials and structures may also advance the platform design and control research portfolio.

The portfolio of the platform design and control core competency is tracking toward meeting the core competency objectives and there were no areas of major risk identified where such objectives would be in threat of not being reached. There is confidence that the research is meeting its goals. Some additional elements, such as including data science and multi-disciplinary optimization, may potentially facilitate the research to meet its objectives faster (discussed below).

Please see the section “Feedback for Individual Projects” below for more information on achievements and identified opportunities at the project level.

Research Portfolio Opportunities

The assessment criteria ask for commentary on the soundness of the core competency’s research methods and methodologies (e.g., the reasoning; the use of theory, modeling and simulation, analysis, and experimentation). The projects within platform design and control core competency followed best practices for research. Each project uses the scientific method (e.g., state a hypothesis and formulate a plan to test the hypothesis). Each project also notes an objective for advancement in some area or technology and then formulates a plan to meet that objective. The associated methodologies are sound and aligned to advance knowledge. The projects advancing the small, unmanned aerial system (UAS) are noted as using a methodology that synergistically takes advantage of multiple resources. These projects are using a software for modeling flight dynamics and then using wind tunnels to generate controlled-environment data to update those flight dynamics and finally using flight-testing to generate mission-realistic data to finalize those flight dynamics. The projects are an excellent example of combining theory, numerics, and experiments in a coupled fashion to meet their objectives.

Evaluating options for technologies underlying the research is encouraged. Many research projects use morphing mechanisms; however, it is not always clear that the choice of morphing is optimal for the given objectives. Many research projects use ML; however, it is not always clear that the algorithm being used is ideal given the process and statistics of the training data. Many research projects use reduced-order modeling; however, it is not always clear that the choice of reduction and representation provide best fits given the dynamics.

The assessment criteria also ask for commentary on where improved direction, increased focus, new connections with other research lines, or other changes could better and more quickly address the competency objectives. The strong fundamentals in the current research presents many opportunities to rapidly advance toward the competency objectives. No cautionary issues in which fundamentals need altering were found. Instead, what was noted was that the maturation of the research could lead to new avenues of collaboration by incorporating tools from other disciplines. Most especially, the field of system engineering is an area that may benefit most projects in the portfolio. Adopting a systems approach may help highlight interactions at the beginning stage of a project and thus ensure a more rapid maturation. Any project that includes controls in the forward path should consider its technologies from the perspective of systems engineering. Often closed-loop properties are not obtained using an open-loop approximation with a controller. Similarly, multi-functional materials often have small effects like lags and hysteresis that do not greatly affect the open-loop performance but are exacerbated by a feedback controller. Any projects related to aeroelasticity or morphing would be ideal candidates to introduce system engineering at an early stage.

The portfolio contains many efforts considering multi-functional materials for which energy is noted; however, actuation force and rate are initially the focus for achieving performance. Introducing a greater focus on energy at an early stage may assist the researchers with material selection and may be critical for future efforts.

The emphasis on ML is present in the majority of research projects; however, the project teams rarely had expertise in ML. Augmenting the teams with data science is critical to ensuring which methods, if any, from ML provide the best path to meeting competency objectives. In general, a continual refocus on both efforts and objectives on a yearly basis is suggested. Lessons learned within the competency could be augmented with lessons published by the greater research community to understand which directions are most promising. An emphasis on lifelong learning through staying cognizant of literature and attendance at conferences and short courses may be critical to maintaining the efficacy of the portfolio.

The assessment criteria also ask for commentary on the overall balance of the competency’s research portfolio (e.g., core competencies, partnerships, supporting extramural partners) to address the cumulative competency goals. The platform design and control core competency portfolio shows reasonable balance given its objectives. The extramural efforts dominate in scope and size over the intramural efforts, which is expected and not a sign of any imbalance. The reliance on extramural researchers allows for rapid and cost-effective re-balancing of skills. The main aspect identified relating to balance is the potential benefit of embracing some open-source methodologies. Efforts into modeling will benefit from inherent structuring as both reusable and modular so the resulting codes can be easily augmented to a wider variety of future problems. In addition, any modularity facilitates the incorporation of systems engineering into the software use. Some existing open-source software, for multidisciplinary design, analysis, and optimization (MDAO) could provide foundational codes to accelerate the projects in the research portfolio.

The research criteria also ask for commentary on promising new areas of research or novel research approaches the competency should pursue. The portfolio is already focused on research enabling next-generation technologies but some synergistic topics could be included. The concept of soft actuators is an appropriate choice for some of the morphing projects in the portfolio. The field of soft actuation is extensive and rapidly evolving and so the researchers need to continually evaluate their choice of actuation. Advances in direct current (DC)-motor-drive tendons, fluidic rubber, and fin rays are some choices that have characteristics appropriate to the projects along with being more mature for implementation.

Both analysis and design are noted in projects for aeroelasticity and small air and hypersonic vehicles, and so some advances in multi-disciplinary optimization are relevant. Open-source software that couple optimization and analysis codes in a seamless manner would allow researchers to spend less time on coding and more time on studying the physics of the problem.

The inclusion of the surrounding environment, such as air quality, sand type, and rock shapes, is currently a small aspect of the portfolio but one that is of growing importance. In this context, novel methods for multi-physics of granular materials may be highly beneficial to the research projects by introducing advances in discrete-element modeling coupled with computational fluid dynamics (CFD) and multi-body dynamics.

Opportunities Identified for Individual Projects

Individual intramural and extramural projects are highlighted below as evidence of the high quality intramural and extramural research efforts at ARL, and also to pinpoint opportunities for these projects.

• “From Image Generation to Morphological Design.” This project makes a strong impression due to its use of advanced techniques in artificial intelligence. In particular, the use of text-based tools and image-based tools being employed by ARL is an intriguing area also being pursued by computational organizations. The ability to generate initial designs using these tools is evidence of merit in the scientific quality. This effort matches ongoing work at leading institutions, although industry is probably leading more than academia or government. This project would team well with ongoing research in the computer science community.

• “Soft Actuators for Future Army Active Structure.” The research into soft actuators is well aligned with ongoing efforts in the broader community. This project is evaluating materials that will generate high force with high efficiency by considering tradeoffs with power and speed. The choice of soft actuators cannot realistically be cutting edge because the materials community is moving more rapidly than can be followed; however, the application to use a reasonably new actuator is advanced at a level that would be expected at a leading institution.
• “Kinematics of Bodies in Motion Using Geometric Algebra.” The field of mathematical representation for dynamics is not receiving much attention in the research community but it remains important. The ability to formulate dynamics using constructs such as bi-vectors is an achievement for the research along with determining the computational cost of this formulation compared to Euler-angle or quaternion formulations. The work is exploring a unique approach that, if it can be shown to be practically useful, may lead to unexpected capabilities.
• “Controls Laws for Phugoid Mode Tuning in Small UAS.” This project for following the surface of power lines presents some interesting aspects. The modeling of the surface as being a higher-order representation instead of simply a sinusoidal approximation is an impactful step toward accurate performance. The control strategy is particularly intriguing by using the natural resonance of the phugoid mode to efficiently generate the desired flight path. The results are at a level seen in industry for rapid development of flight capability; however, the project is well positioned to increase the maturity of the results and provide rigorous metrics of optimality by including more academic inputs.
• “Impact Alleviation for Small UAS.” The quality of the research into impact alleviation is shown in the experimental successes. This project covers flight dynamics and mechanism design and flight-testing as a coordinated approach to platform design. The resulting vehicle is able to recover from an impact and maintain flight in a manner that exceeds current off-the-shelf capabilities of aircraft. The flight capability is novel and more rigorous testing and analysis will greatly enhance the viability of the technology.
• “Aeroelastic Analysis for Reconfigurable Aerial Bodies.” An interesting aspect of the research into aeroelasticity is decoupling the structural dynamics from unsteady aerodynamics to dramatically reduce computational cost. The scientific quality in this project arises from the initial successes at parametrizing each of the decoupled models to efficiently represent a design space of the fully coupled system. The approach has some novel aspects that could be beneficial for rapid generation of flutter analysis or control designs; however, it should be noted that the field is generally moving more toward coupled approaches that utilize faster computational engines to achieve higher accuracy for next-generation systems.
• “A Surrogate-Based Modeling Framework for Nonlinear Static Aeroelasticity and Structural Design.” The use of surrogate modeling is adapted to system design for the decoupled approach to aeroelasticity. The research shows good results in using multiple types of modeling to represent the design space and indicate improved designs. The use of surrogate modeling provides a reasonable approximation; however, leading institutions are using higher-fidelity methods for exploring design spaces.

Vehicle Propulsion Sciences

Accomplishments and Advancements

The ARL portfolio of research in this core competency was demonstrative of the very high quality research conducted by ARL, both within its intramural activities and through its extramural collaborations. The work was considered to be at par with leading institutions nationally and

internationally. On many projects ARL appears to be at the leading edge of technology development. This is encouraging as some of the issues being addressed, such as compression ignition operation at high altitude conditions with low cetane fuels, are not being faced by others outside of the Department of Defense. The sections below identify opportunities for ARL based on the assessment criteria questions and notes areas where the portfolio is strong. The last section looks at opportunities specific to individual projects.

Research Portfolio Opportunities

While the scientists at ARL, for the most part, had an understanding of research conducted elsewhere, there were areas identified where a better understanding of recent academic research concerning sand-coating interaction studies and greater connections to industry concerning combustion and ignition could help advance the scientific efforts within this core competency and avoid duplicative efforts.

The ARL activity centered on sand-coating interactions from the presentation “Influence of Chemistry and Surface Roughness of Various Thermal Barrier Coating on the Wettability of Molten Sand” and the poster session was comprised of (1) fundamental research, consisting of heating microscope and furnace tests, as well as modeling, and (2) more applied research, such as testing with the sand burner rig and failure analysis of flight tested thermal environmental barrier coatings (TEBCs). From the information presented, ARL excels in the applied research domain. Few organizations, whether in industry, government or academia, have the capability to capture sand erosion, melting, and deposition on coatings via a sand burner rig with high temperature and particle flow. Furthermore, extramural teaming is very strong within this area of research with a mix of academic, government, and engine manufacturers, leading to unique opportunities to evaluate and synthesize data from flight-failed components to more basic academic research. ARL researchers appear to be positively leveraging academic partnerships to advance expertise in fundamental sand-coating interactions.

In flight scenarios, sand typically melts into a molten glass that can adhere and interact with the underlying coating, as also reported by the ARL researcher team. Because sand-coating interactions are highly dependent on sand composition and form, the current standard practice in the research community is to perform furnace tests using a homogenized sand glass (i.e., sand that is melted and quenched to form a glass) instead of crystalline sand in furnace-type tests. The intramural ARL team appears to be utilizing sand in its crystalline (unmelted) form for all experiments. The synthetic sand being used is a mixture of minerals, whereas a melted sand composition is homogenized due to being amorphous (glass) devoid of crystalline phases. The amount of synthetic sand applied to coating materials in ARL furnace studies is also significantly higher than the loadings used in the research community. Because the sand is not in its amorphous state, making direct comparisons or conclusions with results obtained outside of ARL may be more challenging, especially when evaluating some of the novel coating compositions ARL is proposing to test. Because a common synthetic sand composition is being used, the ARL team needs to be mindful of previous studies that have investigated the interactions between the same synthetic sand mixture and similar coating compositions.² Evaluating sand wettability on coating surfaces via high-temperature

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² See the following studies: V. Wiesner, B. Harder, and N. Bansal, 2018, “High-Temperature Interactions of Desert Sand CMAS Glass with Yttrium Disilicate Environmental Barrier Coating Material,” Ceramics International 44(18), https://doi.org/10.1016/j.ceramint.2018.09.058; J. Sleeper, A. Garg, V. Wiesner, and N. Bansal, 2019, “Thermochemical Interactions Between CMAS and Ca₂Y₈(SiO₄)₆O₂ Apatite Environmental Barrier Coating Material,” Journal of the European Ceramic Society 39(16), https://doi.org/10.1016/j.jeurceramsoc.2019.08.040; V. Wiesner, D. Scales, N. Johnson, B. Harder, A. Garg, and N. Bansal, 2020, “Calcium–Magnesium Aluminosilicate (CMAS) Interactions with Ytterbium Silicate Environmental Barrier Coating Material at Elevated Temperatures,” Ceramics International 46(10), https://doi.org/10.1016/j.ceramint.2020.03.249; M. Xinqing, K. Rivellini, P. Ruggiero, and G. Wildridge, 2023, “Novel Thermal Barrier Coatings with Phase Composite Structures for Extreme Environment Applications: Concept, Process, Evaluation and Performance,” Coatings 13(1), https://doi.org/10.3390/coatings13010210.

heating microscope experiments is a relatively new approach first reported in 2016.³ Researchers⁴ have made progress in pioneering the method, and ARL researchers should be aware of literature in this area to avoid duplication of work and also ensure this unique capability is effectively leveraged to understand these complex sand-coating interactions.

In some of the projects, ARL may advance its research and identify duplicative efforts through a better understanding of the products and experimental approaches used for product design, development, and manufacturing within industry. For example, although the operating conditions are somewhat different, it might be useful for the “Characteristics of Energy-Assisted Compression Ignition” team to review the research on the Mazda Skyactiv-X gasoline compression ignition engine. There are some commonalities with the ARL work. This spark plug controlled compression ignition engine produces high combustion efficiency while using gasoline—a lower cetane fuel than diesel. At many speed/load points, a spark is not needed, while at others a spark is needed. Another commercial area worth studying are the compression ignition engines being developed by ClearFlame Engine Technologies, where they are working with ethanol compression ignition. It may be helpful for the researchers working on the 6.1 presentation “High Throughput Alloy Design and Process Optimization for Aviation Propulsion” to look at the Magmasoft, a casting simulation computer aided engineering tool in widespread use throughout the automotive world.

The assessment criteria also ask for comments on opportunities, if found, within the competency where improved direction, increased focus, connections with other research lines, or other changes could better and more quickly address the competency objectives. As previously mentioned, enhancing ARL’s connections to current research and development efforts in industry may result in the acceleration of scientific research for projects specified above. In addition, opportunities for ARL to contribute to advance development of thermal barrier coatings (TBCs) and TEBCs based on their capabilities and expertise are ripe.⁵ Current efforts related to evaluating and characterizing TEBCs from fielded engine turbine blades offer a unique opportunity for ARL to advance understanding of actual failure due to ingestion of sand, which is commonly referred to by its compositional constituents of calcium-magnesium-aluminosilicate (CMAS). Direct understanding of CMAS failure modes from flight components will enable the unique opportunity to devise a highly accelerated test plan with the in-house burner rig to replicate and validate similar conditions. For example, use of sand burner rig testing can already be tailored for different CMAS loadings. ARL researchers could build on their strong work to further optimize loading conditions in the burner rig tests and map back to failures observed in the field for different components. Additionally, the forensic evaluation of CMAS-failed field components could benefit from leveraging a Six Sigma approach.

Increased focus at the more fundamental level of understanding CMAS interactions with coatings would benefit the overall program. For example, because the amount, composition, and phase (i.e., crystalline or amorphous) of CMAS applied to TEBC compositions in furnace testing directly influences the reaction products that form, the CMAS loadings used in furnace tests at ARL need to be carefully considered. ARL researchers may utilize their unique knowledge from field-tested parts to replicate loadings from field conditions. They may also consult with their academic partners, as well as others commonly referenced in literature, to inform studies going forward.

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³ W. Song, Y. Lavallée, K. Hess, U. Kueppers, C. Cimarelli, and D. Dingwell, 2016, “Volcanic Ash Melting Under Conditions Relevant to Ash Turbine Interactions,” Nature Communications 7, https://doi.org/10.1038/ncomms10795.

⁴ B. Zhang, W. Song, and H. Guo, 2018, “Wetting, Infiltration and Interaction Behavior of CMAS Towards Columnar YSZ Coatings Deposited by Plasma Spray Physical Vapor,” Journal of the European Ceramic Society 38.

⁵ This discussion is relevant to the following presentations shown during the assessment: “Investigation of Particle Entrainment Glassification of Thermal Barrier Coatings (TBCs) in Gas Turbine Engine Hot Section Components;” “Forensic Investigation of TEBCs on Fielded Engine Turbine Blades;” “Influence of Chemistry and Surface Roughness of Various Thermal Barrier Coating on the Wettability of Molten Sand;” and “Dynamic Wetting of Non-Newtonian Droplets at High Temperatures.”

Additionally, characterizing CMAS wetting on coating surfaces via heating microscope is a promising area of research in which ARL is poised to make a positively impact. Initial studies appear to be utilizing CMAS in its crystalline state (i.e., unmelted synthetic sand composition) for wetting experiments. In addition to crystalline CMAS, performing wetting studies with a CMAS glass would enable the team to accurately assess whether CMAS phase impacts the wetting behavior of CMAS on coatings, especially given that CMAS is typically detected in its glassy or amorphous state in hot-section turbine engine components. The activity in developing computational methods to model the dynamic wetting and infiltration of non-Newtonian droplets representative of CMAS at high temperatures ties well with the experimental wetting work. At this stage, the model only captures mechanical forces, ignoring the critical thermochemical interactions that occur between CMAS and a coating that can dominate infiltration behavior.

There appears to be a balanced focus in the areas of UAS, hypersonic missiles, helicopter transmissions, and large compression ignition engine drones within the ARL research portfolio. However, there does not appear to be much work on Army ground combat vehicles. Perhaps these studies are within another competency, but if not, some studies of technologies to increase the mobility of Army ground combat vehicles may be worthwhile, including how to move more quickly and/or to increase their capabilities to travel over varying terrains. Additionally, the work on examining solutions to the operation of ground-based diesel engines using fuels with a range of cetane numbers would be a natural extension of the existing studies on flight vehicles. Finally, consideration of fuels with a range of octane numbers for vehicles with spark ignition engines could also be considered.

The assessment criteria ask for commentary on the soundness of the competency’s research methods and methodologies (e.g., the reasoning; the use of theory, modeling and simulation, analysis, and experimentation). The review of presented work found that overall, the ARL core competency is making appropriate use of research methods. In a few projects more experimental and modeling efforts, including those that provide a quantitative analysis could be incorporated and in other projects, a focus on metrics or a better utilization of data could be added. Suggestions for individual projects on how to improve their methods and methodologies are in the section directly below on “Opportunities Identified for Individual Projects.”

Opportunities Identified for Individual Projects

This section identifies opportunities for individual projects to help raise the scientific quality of the overall portfolio.

• “Component Technologies and Analysis Tools for Electrified Compact Turbomachinery.” This project focuses on the aeroelasticity problem for a radial-flow turbocharger with two interesting features of the system. First, the rotating machinery with an applied magnetic field also serves as an electric generator. Second, a bearing-less design is sought; that is, a magnetic bearing is employed. The one-dimensional aerodynamic theory known as “piston theory” is applied to address the aeroelasticity evaluation. It is suggested that some validation of the use of piston theory is needed; either multidimensional CFD or an experiment is desirable. Outside of this suggestion, the team is encouraged to continue its key research approaches, which have resulted in the (1) development of a reduced order model for improved fluid response approximation, fusing structural and aerodynamic models to estimate the aeroelastic instability as a function of operating conditions; (2) creation of a new dynamic mode decomposition for aeroelastic stability analyses; (3) development of a multi-physics modeling framework for a bearing-less motor, validated and improved using prototype experiments; and (4) determination that bearing-less motors can be used beyond the state-of-art power-speed limit.
• “Impacts of Spray Atomization and Flame Kernel on Ignition Performance.” While this project reflects leading edge research, a few points need clarification. First, the results

showing average droplet size decreasing with increasing equivalence ratio is not a fundamental relation. Here, it appears to be the consequence of increasing fuel mass flux (and thereby equivalence ratio) by increasing velocity through the fuel injectors rather than increasing the number of injectors. With higher relative velocity between the liquid-fuel jet and the surrounding gas, smaller droplets result from atomization. The conclusion that smaller droplets result in higher combustion efficiency appears to be based on speed of vaporization only. A well-designed spray will distribute the liquid throughout the oxidizing gas. Larger droplets can penetrate further than smaller droplets and thereby produce a more uniform equivalence ratio. The researchers will need to consider droplet-size distribution, not just average size. In addition, the equivalence ratio will need to be examined as a function of spatial position; as more than a global view is needed.

• “Dynamic Modeling of Transmissions for Machine Learning-based Fault Detection.” There is great confidence that this 6.2 project will develop a model for the helicopter engine being studied. The transmission test rig was impressive. However, model validation may be difficult due to an inability to “seed” failure modes in a highly accelerated lifetime test. The presenters had explained that seeding just one failure mode on a given subcomponent would cost $160,000/rebuild and require a 9-month turnaround time. To overcome this issue, flight recorders capturing the acoustic signatures of helicopter transmissions in the field could be used.

  Alternatively, if the goal is to just establish out the soundness of the approach, another powertrain component could be selected, perhaps one that could be rebuilt at the Army’s Anniston Depot rebuild facility. For this, a simpler gearbox, such as a single gear pair or simple idler setup, can be adapted as a mule to test and down-select measurement systems (e.g., acoustic emission sensors, accelerometers at various locations, strain gauges, microphones, and chip detectors or counters) based on their ability to detect damage (pits or cracks) at earlier stages. Intentionally inducing gear or bearing damages to a simpler gearbox would be much straightforward as its assembly could be done in house. Alternatively, long-term tests on instrumented gearbox can be performed as such damage is initiated naturally. A model of such a reduced system would also be more computationally efficient, such that its ability in simulating the signatures caused by damage can be validated thoroughly. That way, the model can be used to generate data for ML more effectively. The current helicopter transmission and its large-scale dynamic model might not be suitable for developing a ML based fault detection method. While the focus appears to be on helicopter gearboxes, the same modeling and measurement methodologies can be generalized with some concentrated effort to any transmission diagnostics problem. While ARL’s transmission test facility, the Vehicle Innovative Powertrain Experimental Research [VIPER] testbed provides a unique capability to demonstrate that the developed diagnostics schemes are indeed effective, a smaller scale, fully instrumented gearbox and accompanying computational model might be more suitable for not only generalizing the gearbox diagnostics problem but also generating the volume of data required for the ML algorithms.

• “Diagnostics of High-Pressure Fuel Pumps Using Acoustic Emission.” The poster described an interesting study that relates intensity of acoustic emissions to certain physical happenings in the fuel-pump. The poster noted that “Army vehicles operate with lower viscosity fuels than the civilian vehicles,” and so the work focuses on fuel pumps for “diesel” engines that use aviation fuel rather than traditional diesel fuel. The fuel pumps presumably operate with high-compression-ratio reciprocating engines. From reviewing the work, a question emerged as to why the frequency of the emissions is not used in developing relationships. It can be noted that this study might also produce findings that can useful in reducing noise emissions, which could have both civilian and military impacts.

COMPETENCY PORTFOLIO OF SCIENTIFIC EXPERTISE

The research teams supporting the platform design and control core competency were uniformly impressive. The extramural researchers are subject-matter experts and leaders in their respective fields; similarly, the intramural researchers have solid backgrounds in their areas and are qualified in the foundations.

As previously mentioned, an emphasis on ML is present in the majority of research projects; however, the project teams rarely had expertise in ML. Augmenting the teams with data science is critical to ensuring which methods, if any, from ML provide the best path to meeting competency objectives. Furthermore, if not already in development, ARL could develop a rigorous mentoring program for the early- and mid-career intramural researchers and facilitate learning in areas outside their foundations, like ML and statistics, which will be needed to reach the competency goals.

The intramural research teams supporting the vehicle propulsion sciences core competency were, without exception, well qualified for the work they were undertaking. All of the presenters were smart, well educated, and highly motivated. ARL’s extramural work with leading universities and national laboratories ensure that ARL is working at the theoretical “state of the art.” At the level of 6.2 Applied Research, the effort focused on CMAS degradation of TEBCs is an example of an intramural team with strong scientific expertise and communication across experimentalists and computational researchers. Additionally, the team leverages external partners with scientific expertise and relevant technical experience from universities, engine manufacturers, and government.

Many of the projects (combustion, TBCs, and electrified turbochargers) exhibit a balance of efforts from ARL partners including universities, Department of Energy laboratories (Argonne and Sandia), the Air Force Research Laboratory, and occasional commercial entities. These team members bring to the table expertise not existing within ARL and substantially supplement the efforts toward achieving project goals.

ARL needs to continue its existing recruitment methods and its work with leading universities and national laboratories. ARL could also consider whether the addition of engineers and technicians assessing failures and making repairs in the field would be helpful. Such added expertise would allow for collection of data on key failure modes and direction of priority research in the future.

COMPETENCY FACILITIES AND RESOURCES

The facilities supporting the platform design and control core competency are a tremendous resource. The laboratories contain significant equipment and expertise that the researchers are effectively using. The projects on small UAS are particularly noted as integrating facilities that combine structures and aerodynamics and control for efficient design and analysis. The aircraft being considered are of a size and airspeed for which the on-site wind tunnel is appropriate. The wind tunnel has exceptional instrumentation including a range of balances and a particle image velocimetry for flow visualization. In every case, the choice of software and laboratory were directly related and showed understanding of both numerical computation and experimental testing as relates to characteristics of the flight regime for the particular vehicles being studied.

The projects on morphing can consider incorporating facilities, such as vibration testing and inflight deformation analysis, as the research progresses from numerical to experimental. Additive manufacturing (AM) might be leveraged to advance studies on embodied intelligence. Machines such as the Carbon M1 3D printer and volumetric additive manufacturing (VAM) allow printing of structures with which multi-functional materials will interact.

As noted, some existing open-source software—for example, MDAO software, could provide foundational codes to accelerate the projects in the research portfolio. While the research topics are appropriate and aligned with competency goals, some of the tools employed toward those goals could be

improved. The platform community is using advanced numerical resources such as high-fidelity coupled approaches that are open-source and feasible to use.

The staff expertise appears well matched with facilities and resources for the vehicle propulsion sciences core competency. Within the area of characterizing sand-coating interactions, the sand burner rig and heating microscope are examples of the unique, standout capabilities at ARL. The high altitude facility used for the combustion experiments to simulate various flight altitudes (pressures and velocities) is a great tool not available at most institutions. Within the United States, perhaps only a handful of sites can claim similar facilities and the ARL capability is an appropriate size for the engine testing performed; the ARL team is making good use of this capability.

In the case of working with Argonne (described above), it is clear that a lot of coordination and approvals were required to access an X-ray beam line (from the Advanced Photon Source) and perform spray atomization studies with combustion in a critical national facility, with a value on the order of multi-billions of dollars, and adjacent experimental equipment undoubtedly also of high value. Argonne has thus provided ARL with a unique capability. Continued utilization of this facility could prove to be very supportive of future ARL objectives.

The transmission test facility (VIPER) is very impressive. It provides a unique, state-of-the-art capability for ARL to be able to test full-scale helicopter transmission at the configurations representative of in situ operating conditions. This facility could be employed for both 6.1 and 6.2 type projects. For a 6.1 type research project, additional emphasis will need to be given to instrumentation; data transfer, collection, and analyses systems; and methodologies as well accessories to allow different operating and environmental conditions. In its current form, the facility lacks in instrumentation aspects. Limited accelerometer-based vibration measurements on the housing were mentioned during the assessment. Investing in a wide array of state-of-the-art instrumentation will provide an in-depth baseline characterization of the transmission behavior without any defects or damage so that the signatures added to this behavior by certain defects can be identified confidently and repeatedly.

In regard to the use of VIPER for 6.2 projects, solid examples were provided showing results from endurance experiments on fully ceramic bearings. The facility would be very effective for quantifying various component-level performance improvements. For instance, gears having different tooth modification schemes could be tested to determine the noise and vibration improvements they might offer. Long-cycle testing of these component refinements is also possible with this facility to assess fatigue life consequences.

As previously mentioned, ARL now has a Pankl electrified turbocharger designed with these computer-aided engineering (CAE) tools mounted on an engine. While Pankl is a great supplier with some unique experience to support the electrified turbocharger projects, there have been examples where they put on hold its commercial work when there is a pressing Formula 1 race car need. Additionally, much of the work they are doing may be proprietary to Pankl. Moving forward it may be important to assess Pankl’s willingness and ability to share its technology. Looking at the offerings of other supplies (e.g., Borg Warner, Honeywell, or Cummins) may also be helpful.

OVERALL SCIENTIFIC QUALITY OF THE COMPETENCY

This section provides a broad summary of trends identified in the research portfolio as they relate to the assessment criteria. It then summarizes the broader findings within each core competency.

Comparison to Other Research Institutions

ARL compares favorably to, and often surpasses, other leading research institutions. ARL distinguishes itself by addressing some of the most pressing challenges facing the U.S. Army through a blend of unique leading edge research and external collaborations. The key attributes that position it among the leading engineering research institutions are:

• Multidisciplinary Experience: It recognizes that innovation thrives in an environment that values different views and experiences. Its staff includes experts from diverse engineering disciplines, enabling it to tackle complex problems from multiple perspectives and therefore drive innovation.
• State-of-the-Art Facilities: An important part of its success is the excellence of its facilities. Its laboratories are equipped with some of the latest equipment and instrumentation. These provide its researchers with the tools necessary to explore the frontiers of science and technology.
• Innovative Research Initiatives: Whether developing new materials, structures, mechanisms, controls, or propulsion components, ARL is leading efforts to translate innovative ideas into proven technologies.
• External Partnerships: ARL actively engages with industry, academia, and other government laboratories. However, controls on discussing the results of even unclassified research findings may slow progress and technology transfer.

Understanding of Underlying Research Conducted Elsewhere

The mechanical sciences competency not only understands but actively seeks to collaborate with similar research being conducted at other institutions. An element of most ARL research involves conducting literature reviews of research performed elsewhere. By supporting research at leading universities, ARL has early access to recent advances, methodologies, and expertise. While many projects exhibited an understanding of research conducted elsewhere, this was not the case for every project in the vehicle propulsion sciences core competency. ARL could increase attendance at relevant technical conferences, perform more surveys of industry, and increase its connections with government laboratories to improve understanding of underlying research conducted elsewhere.

Soundness of the Methodologies

The research methodologies used in ARL research are well planned, ensuring sound and reliable results. Almost every project begins with a literature search to ensure that the effort builds on existing knowledge and identifies what needs further exploration. This establishes the research objective and enables an initial hypothesis to be formulated. These steps provide a structured framework of milestones and metrics for each study, ensuring a focused and targeted investigation. Almost without exception, each project includes both theoretical and experimental efforts, which ensures that hypotheses are tested and modified when necessary. Quantitative data are subject to validation procedures, utilizing AI and ML. This is intended to insure that data accurately represent the phenomenon under investigation. However, more experience with the use of these tools would enhance their utility. Still, there are areas that could be improved, and the chapter writings have attempted to diagnose these areas in both the platform design and control and vehicle propulsion sciences.

The research methodologies also undergo external review contributing to the overall robustness of the studies. However, more frequent internal peer reviews would take greater advantage of the diverse backgrounds and perspectives of the laboratory staff.

Risks of Not Meeting Objectives

ARL research utilizes the scientific method, which minimizes risk and ensures a high likelihood of meeting its objectives. Project objectives are well defined and achievable. Collaborations with established research institutions and universities are an important part of many projects. Partnering with

organizations that have a record in related research provides a solid foundation and reduces the risk of missteps.

Engaging with key stakeholders is integral to the true success of any research project. The previous practice of assigning active duty personnel to the laboratory was a good way to minimize risk in these areas. The creation of seminars on the future of warfighting can increase understanding of the importance of meeting research objectives. By combining these risk reduction strategies, ARL research is positioned to achieve its objectives with a high level of confidence. As a result, it holds significant promise for advancing the technological advantages of the U.S. Army.

Balance in the Research Portfolio

ARL has integrated its internal competency with external partnerships to achieve its goals. It has established a strong internal core competency with diverse expertise. To maximize this competency, it should encourage a collaborative, multidisciplinary environment where experts from different fields have the opportunity to contribute to each other’s research.

Recognizing the need for specialized knowledge and other perspectives, ARL has formed strategic partnerships with other institutions. These external partnerships not only serve as a source of knowledge and experience, but also as a way to increase capability. Therefore, establishing regular communications between internal staff and external partners is crucial. To ensure this occurs, it would be useful to set up regular in-person or virtual meetings. By combining its own internal competency with external partnerships, ARL is enhancing innovation.

Opportunities to Speed Achievement of Objectives

Some additional strategies that may help ARL to achieve its research objectives more quickly include:

• Introduce regular cross-project reviews, allowing laboratory staff to share insights, address bottlenecks, and strategize on ways to expedite progress. Our minds work by analogy. For example, electricity “flows” against “resistance” driven by voltage “pressure,” like water in a pipe. Encouraging dialogue between engineering disciplines will bring diverse perspectives to a problem, potentially accelerating problem solving and creating innovative solutions.
• Expand the use of AI and ML to expedite data processing and pattern recognition. This will allow researchers to quickly recognize trends and refine research strategies, thereby reducing the time required to achieve research objectives.
• Run multiple experiments in parallel, reducing the time required for data collection and analysis.
• Implement an evaluation system to track progress against predefined milestones and metrics.
• Adapt an agile project management approach that enables researchers to make rapid changes based on emerging challenges and prioritize tasks based on their effect on research objectives.
• Undertake a comprehensive assessment of resource allocation, including personnel, budgets, and facilities. Redirect resources to research areas based on the expertise of personnel and a project’s importance and rate of progress.
• Regularly assess the effectiveness of implemented changes and adjust strategies to ensure continuous improvement.

A Discussion of Each Core Competency

This section offers more details on the evaluation of each core competency to complement the broader summary above.

The platform design and control core competency presented very high quality research and several projects were at par with leading institutions. The research portfolio demonstrates a strong understanding of the underlying science and research conducted elsewhere. Many of the projects highlighted efforts that align with ongoing investigations in that community to expand the state-of-the-art capabilities. The extramural program managers are setting the standard for which the broader scientific community is following in fields like embodied intelligence, particulate physics within a fluid, and flow separation as a critical aspect of aerodynamics. The research teams supporting the core competency were uniformly impressive. The extramural researchers are subject-matter experts and leaders in their respective fields; similarly, the intramural researchers have solid backgrounds in their areas and are qualified in their foundational scientific areas.

Similarly, the vehicle propulsion sciences core competency portfolio was at par with leading institutions nationally and internationally. There do not appear to be risks to the overall portfolio. Without exception, the intramural team at ARL was well qualified for the work they were undertaking and all of the presenters were smart, well educated, and highly motivated. ARL’s extramural work with leading universities and national laboratories ensure that ARL is working at the theoretical “state of the art.” While the scientists at ARL, for the most part, had an understanding of research conducted elsewhere, there were areas identified above where a better understanding of recent academic research concerning sand-coating interaction studies and greater connections to industry concerning combustion and ignition could help advance the scientific efforts within this core competency and avoid duplicative efforts.

While the projects within the platform design and control core competency have strong research methods and follows best practices for research, it is not always clear that the choice of morphing is optimal for the given objectives. Many research projects use ML; however, it is not always clear that the algorithm being used is ideal given the process and statistics of the training data. Many research projects use reduced-order modeling; however, it is not always clear that the choice of reduction and representation provide best fits given the dynamics. Thus, evaluating options for technologies underlying the research is encouraged. Similarly, the projects within the vehicle propulsion sciences platform had, for the most part, strong research methods, but there were some areas in individual projects that could be improved. In a few projects more experimental and modeling efforts, including those that provide a quantitative analysis could be incorporated and in other projects, a focus on metrics or a better utilization of data could be added. These projects were identified within the chapter.

The laboratories supporting both core competencies contain significant equipment that the researchers are effectively using. In particular, the vehicle propulsion sciences core competency contains unique capabilities such as the sand burner rig and heating microscope, which make ARL stand out. For the platform design and control core competency, projects on morphing may consider incorporating facilities, such as vibration testing and in-flight deformation analysis, as the research progresses from numerical to experimental. AM might be leveraged to advance studies on embodied intelligence with machines like Carbon M1 3D printing and VAM, which will allow printing of structures with which multi-functional materials will interact.