RT&L FOCUS AREA(S): Autonomy TECHNOLOGY AREA(S): Air Platform OBJECTIVE: Design, develop, and demonstrate a rapid aero-structural assessment framework for finding the optimal three dimensional solution of the design trades associated with adaptation, material performance, mass, and energy cost. DESCRIPTION: Army air vehicles are designed as a compromise among the optimal configurations for the various expected missions in which they will perform. Most air vehicles cannot structurally adapt to various mission segments, unlike biological analogs, such as insects or birds [Reich; Lentink; Rosen]. Ideally, platforms could adapt to achieve the optimal configuration for each segment of the mission, e.g. configurations in which the vehicle has high maneuverability and endurance, and is collapsible/foldable for storage. Fluid dynamics simulations and experiments demonstrate that vehicle shape changes enable improvements in aerodynamic performance; however, these efforts typically do not consider structural complexity, cost, and material stiffness/strength with the associated trades [Faber; Vocke; Vale]. The goal is to create an assessment framework for platform adaptation that incorporates the given structural and aerodynamic conditions for an Army relevant problem. An example mission could be a small UAS that is capable of deploying from a collapsed configuration, dashing, and then loitering on station all the while adapting itself to perform optimally in each segment. The tool is expected to inform the required material properties of the morphing structure, for example: specific stiffness, strength, and activation energies. The work will also need to include consideration of the fluid structure interaction (FSI) [Barcelos; Gursul], which typically requires large amounts of computational power and is not viable for optimization without the use of novel uncoupling schemes [Scholten; White]. An effort will need to be made to reduce the computational time by use of similar parallelization or uncoupling schemes to explore the design space and optimize on a complex three dimensional structure. The framework will need to show that it can assess a FSI problem and return the best solution and trades with an aerodynamic and structural accuracy of at least 90% compared to other computational methods. Use of unlicensed or free-license software by the framework is desirable as it adds to the potential parallelization by not requiring multiple licenses to be purchased and maintained. The framework will need to focus on the assessment of adaptation in terms of the potential benefit to mission performance. Instead of static boundary conditions representing one state, the framework would need to accept two or more potential mission states (e.g. dashing, loitering, etc.) for which an internally consistent best structural solution can be found. Finally, the mission performance improvement would need to be weighed against the design trades associated with the weight and energy required for adaptation. The framework would likely determine the requirements of stimulus sensitive materials [Mabe; Jayasankar] and actuation across various Army relevant vehicle size scales and applications. At a minimum, the framework should be demonstrated against three different Army use cases and compared with a baseline representing a non-adapting configuration that is a compromise of the optimal configurations for each mission or mission segment. If successful, this effort would enable new tools for the Future Vertical Lift Army modernization priority by computing design trades and solutions for penetration through congested environments via extended maneuverability and range with respect to existing platforms. PHASE I: Design, develop, and validate an assessment framework that demonstrates the ability to rapidly simulate the design space of and perform trades on performance, mass, and other characteristics associated with a relevant Army aero-structure and mission. As an example, teams might consider a Class 1-2 UAS capable of adapting shape from a stowed configuration to perform a mission at low altitude within a congested environment. It is expected that teams will consult with the government in order to determine an appropriately bounded problem. Individual simulations should handle relatively large deformations associated with low-mass solutions. The framework should utilize computational techniques which reduce the typical computational time (100-1000x) associated with three dimensional coupled fluid structure interactions, such as parallelization. The goal of phase 1 is to demonstrate an ability to interrogate the trade space associated with bounds on a FSI problem to find the optimal design. The simulation should have an accuracy compared to slower analyses of at least 90%. Further, define the complete proof-of-concept optimization and trade space framework that will be developed in Phase 2, including a technically viable path for including potential adaptations. Adaptation technologies include stimulus sensitive materials, actuators, etc., which are internally consistent within the structure for different mission segments (dash, maneuver, endurance, etc.) but provide increased aerodynamic performance, for example, by modifying camber or span to increase lift. Typically there will be a point in design where mission segments need to be sufficiently numerous or different in order for adaptation to be viable, which should be computable in Phase 2. PHASE II: Design, develop, and validate an assessment framework that demonstrates the ability to rapidly simulate the design space of and perform trades on performance, mass, and energy associated with structural adaptation cost. In addition to the accuracy requirements of the Phase 1 effort, the framework should be able to identify which potential structural adaptations are viable for given mission requirements defined as structural and aerodynamic bounds. Assessment across mission requirements will need to be consistent internally for structural performance computation. The framework should also address user competency and likelihood of accurate solution generation. PHASE III DUAL USE APPLICATIONS: Currently, the Army relies on researcher experience to experimentally assess vehicle designs and determine the viability of the concept. Maturity of the rapid optimization and trade space framework will allow Army engineers to determine the trade space associated with various basic science technologies developed in academia, industry, and research institutions. A vehicle that is able to adapt itself can respond optimally to Soldier needs; this tool will be able to accept mission requirements and provide technical trades and solutions. For example, a mission space may require a UAS to be Soldier- or air vehicle-borne, penetrate a congested space, and then loiter on station for an extended time. The end state of the framework would provide a tool for rapid assessment of the technology required to construct a vehicle that is fully collapsible, is able to shorten its planform to maneuver through forests or trees undetected, and then lengthen its planform to loiter at extended duration. REFERENCES: Reich G and Sanders B, Introduction to Morphing Aircraft Research. Journal of Aircraft 2007, 44(4): 1049-1059. Lentink D et al., How Swifts Control Their Glide Performance With Morphing Wings. Nature 2007, 446(7139): 1082-1085. Rosen M and Hedenstrom A, Gliding Flight in a JackDaw: A Wind Tunnel Study. Journal of Experimental Biology 2001, 204(6): 1153-1166. Faber JA, Arrieta AF, and Studart AR, Bioinspired Spring Origami. Science 2018, 359(6382): 1386-1391. Vocke III RD et al., Development and Testing of a Span-Extending Morphing Wing. Journal of Intelligent Material Systems and Structures 2011, 22(9): 879-890. Vale J et al., Aero-Structural Optimization and Performance Evaluation of a Morphing Wing with Variable Span and Camber. Journal of Intelligent Material Systems and Structures 2011; 22(10): 1057-1073. Barcelos M, Bavestrello H, and Maute K, A Schur-Newton-Krylov Solver For Steady-State Aeroelastic Analysis and Design Sensitivity Analysis. Computer Methods in Applied Mechanics and Engineering 2006, 195(17-18): 2050-2069. Gursul I, Cleaver D, and Wang Z, Control of Low Reynolds Number Flows by Means of Fluid-Structure Interactions. Progress in Aerospace Sciences 2014, 64: 17-55. Scholten W and Hartl DJ, An Uncoupled Method for Fluid-Structure Interaction Analysis with Application to Aerostructural Design. AIAA Scitech Forum 2020, 1635. White T et al., Uncoupled Method for Massively Parallelizable 3D Fluid-Structure Interaction Analysis and Design. AIAA Aviation Forum 2020. Mabe J, Variable Area Jet Nozzle for Noise Reduction Using Shape Memory Alloy Actuators. Journal of Acoustical Society of America 2008, 123(5): 3871. Jayasankar et al., Smart Aerodynamic Surface for a Typical Military Aircraft Using Shape Memory Elements. Journal of Aircraft 2011, 48(6): 1968-1977. KEYWORDS: Unmanned aerial system, UAS, fluid structure interaction, optimization, morphing vehicle, adaptive structure
