# Aerospace Engineering Research Works

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Item Terrapin Rocket Team's Technical Report to the 2023 Spaceport America Cup(2023) Daniel, Hailu; Bean, Andrew; Bregin, Ezra; Gill, Dasam; Roy, Nathan; M Jaffar, Mohamed Khalid; Alessandrini, Garret; Mallamaci, Michael; Goldberg, Adin; Zheng, Howard; Rizvi, SaimThis document presents the University of Maryland’s 10,000 ft SRAD Motor Category rocket, Karkinos. It is the third time that the team will be attending the Cup in person since 2018, and the current team has built on the lessons learned at the 2022 Cup. The design process for Karkinos is centered around manufacturability and reliability coupled with a rigorous testing process. This report also documents the design of our Air Brake system that actively trims the rocket’s altitude during flight. The CubeSat payload for this rocket will test the release of a vehicle from the rocket during drogue descent.Item Simulation of packet dropouts over wireless channels considering Rayleigh fading effects(2020) M Jaffar, Mohamed Khalid; Otte, MichaelThis document describes how we implement a Rayleigh fading model for use in a multi-robot communication simulation. The main objective of this work is to characterize communication losses in multi-agent settings that require high levels of collaboration.Item Feedback motion replanning during high-stakes scenario(2019) M Jaffar, Mohamed Khalid; Otte, MichaelThis paper proposes a novel algorithm for a quadrotor to replan its motion in the event of one, two or three rotor loss. Further, during the course of its replanned trajectory, the MAV avoids collision with static obstacles including the ground.Item Terrapin Rocket Team's Technical Report to the 2022 Spaceport America Cup(2022) Bregin, Ezra; Bean, Andrew; Daniel, Hailu; Roy, Nathan; M Jaffar, Mohamed Khalid; Alessandrini, Garret; Mallamaci, Michael; Goldberg, Adin; Zheng, Howard; Gill, DasamThis document presents University of Maryland’s 10,000 ft COTS Motor Category rocket, Terpulence II. This project is a return to high power rocketry fundamentals within the Terrapin Rocket Team. It is the first time that the team will be attending the Cup in person since 2018 and the first time any current team members will compete at Spaceport. The design process is targeted at building off of other successful projects and manufacturing a safe and reliable competition rocket. This reports also documents the design of a novel air brake system that increases the rocket performance to reach a desired apogee. The CubeSat payload for this rocket will test liquid fuel tank geometry to gauge if capillary action can replace ullage motors in micro-gravity environments.Item Magnetic Susceptibility Instrument for Magnetically Inhomogeneous Granular Mixtures(Review of Scientific Instruments, 2024) Charles T. PettWe introduce an instrument and novel method for characterizing the bulk magnetic susceptibility of granular mixtures by submerging an inductor coil in a bed of metallic beads and gauging changes in self-inductance. The resonance frequency of the coil was measured to determine its inductance and evaluate the magnetic permeability of ferrous mixtures relative to air. In air, our coil was accurate to within 0.1\% of the permeability of free space. The range of magnetic susceptibility values for magnetically inhomogeneous granular mixtures is poorly constrained, but our coil uniquely quantifies bulk effects that other surface meters are not designed to resolve. Compared to both a commercial Terraplus Inc. KT-10 meter and theoretical approximations, we report similar trends in susceptibility values measured as a function of mass of ferromagnetic material per volume.Item Control of a Heavy-Lift Robotic Manipulator with Pneumatic Artificial Muscles(MDPI, 2014-04-24) Robinson, Ryan M.; Kothera, Curt S.; Wereley, Norman M.Lightweight, compliant actuators are particularly desirable in robotic systems intended for interaction with humans. Pneumatic artificial muscles (PAMs) exhibit these characteristics and are capable of higher specific work than comparably-sized hydraulic actuators and electric motors. The objective of this work is to develop a control algorithm that can smoothly and accurately track the desired motions of a manipulator actuated by pneumatic artificial muscles. The manipulator is intended for lifting humans in nursing assistance or casualty extraction scenarios; hence, the control strategy must be capable of responding to large variations in payload over a large range of motion. The present work first investigates the feasibility of two output feedback controllers (proportional-integral-derivative and fuzzy logic), but due to the limitations of pure output feedback control, a model-based feedforward controller is developed and combined with output feedback to achieve improved closed-loop performance. The model upon which the controller is based incorporates the internal airflow dynamics, the physical parameters of the pneumatic muscles and the manipulator dynamics. Simulations were performed in order to validate the control algorithms, guide controller design and predict optimal gains. Using real-time interface software and hardware, the controllers were implemented and experimentally tested on the manipulator, demonstrating the improved capability.Item Massively Parallel Large Eddy Simulation of Rotating Turbomachinery for Variable Speed Gas Turbine Engine Operation †(MDPI, 2020-02-06) Jain, Nishan; Bravo, Luis; Kim, Dokyun; Murugan, Muthuvel; Ghoshal, Anindya; Ham, Frank; Flatau, AlisonGas turbine engines are required to operate at both design and off-design conditions that can lead to strongly unsteady flow-fields and aerodynamic losses severely impacting performance. Addressing this problem requires effective use of computational fluid dynamics tools and emerging models that resolve the large scale fields in detail while accurately modeling the under-resolved scale dynamics. The objective of the current study is to conduct massively parallel large eddy simulations (LES) of rotating turbomachinery that handle the near-wall dynamics using accurate wall models at relevant operating conditions. The finite volume compressible CharLES solver was employed to conduct the simulations over moving grids generated through Voronoi-based unstructured cells. A grid sensitivity analysis was carried out first to establish reliable parameters and assess the quality of the results. LES simulations were then conducted to understand the impact of blade tip clearance and operating conditions on the stage performance. Variations in tip clearance of 3% and 16% chord were considered in the analysis. Other design points included operation at 100% rotor speed and off-design conditions at 75% and 50% of the rotor speed. The simulation results showed that the adiabatic efficiency improves dramatically with reduction in tip gap due to the decrease in tip leakage flow and the resulting flow structures. The analysis also showed that the internal flow becomes highly unsteady, undergoing massive separation, as the rotor speed deviates from the design point. This study demonstrates the capability of the framework to simulate highly turbulent unsteady flows in a rotating turbomachinery environment. The results provide much needed insight and massive data to investigate novel design concepts for the US Army Future Vertical Lift program.Item Characterization and Analysis of Extensile Fluidic Artificial Muscles(MDPI, 2021-01-30) Garbulinski, Jacek; Balasankula, Sai C.; Wereley, Norman M.Extensile fluidic artificial muscles (EFAMs) are soft actuators known for their large ranges of extension, low weight, and blocked forces comparable to those of pneumatic cylinders. EFAMs have yet to be studied in a way that thoroughly focuses on their manufacturing, experimental characterization, and modeling. A fabrication method was developed for production of two EFAMs. The quasi-static axial force response of EFAMs to varying displacement was measured by testing two specimens under isobaric conditions over a pressure range of 103.4–517.1 kPa (15–75 psi) with 103.4 kPa (15 psi) increments. The muscles were characterized by a blocked force of 280 N and a maximum stroke of 98% at 517.1 kPa (75 psi). A force-balance model was used to analyze EFAM response. Prior work employing the force-balance approach used hyper-elastic constitutive models based on polynomial expressions. In this study, these models are validated for EFAMs, and new constitutive models are proposed that better represent the measured stress values of rubber as a function of strain. These constitutive models are compared in terms of accuracy when estimating pressure-dependent stress–strain relationships of the bladder material. The analysis demonstrates that the new hyper-elastic stress models have an error 5% smaller than models previously employed for EFAMs for the same number of coefficients. Finally, the analysis suggests that the new stress functions have smaller errors than the polynomial stress model with the same number of coefficients, guarantee material stability, and are more conservative about the stress values for strains outside of the testing range.Item Photogrammetric Measurement and Analysis of the Shape Profile of Pneumatic Artificial Muscles(MDPI, 2021-04-06) Chambers, Jonathan M.; Wereley, Norman M.Inaccuracies in modeling of the geometric shape of PAMs has long been cited as a probable source of error in modeling and design efforts. The geometric shape and volume of PAMs is commonly approximated using a cylindrical shape profile, even though its shape is non-cylindrical. Correction factors—based on qualitative observations of the PAM’s general shape—are often implemented to compensate for error in this cylindrical shape approximation. However, there is little evidence or consensus on the accuracy and form of these correction factors. Approximations of the shape profile are also used to calculate the internal volume of PAMs, as experimental measurements of the internal volume require intrusive testing methods and specialized equipment. This research presents a photogrammetric method for measuring the shape profile and internal volume of PAMs. A test setup, method of image data acquisition, and a preliminary analysis of the image data, is presented in this research. A 22.2 mm (7/8 in) diameter PAM is used to demonstrate the photogrammetric procedure and test its accuracy. Analysis of the tested PAM characterizes trends of the shape profile with respect to pressure and contraction. The common method of estimating the diameter—through the use of the cylindrical approximation and initial geometry of the PAM—is tested by comparison to the measured shape profile data. Finally, a simple method of calculating the internal volume using the measured shape profile data is developed. The presented method of acquiring photogrammetric measurements of PAM shape produces an accurate characterization of its shape profile, thereby mitigating uncertainty in PAM shape in analysis and other efforts.Item Formulation of Shell Elements Based on the Motion Formalism(MDPI, 2021-12-10) Bauchau, Olivier; Sonneville, ValentinThis paper presents a finite element implementation of plates and shells for the analysis of flexible multibody systems. The developments are set within the framework of the motion formalism that (1) uses configuration and motion to describe the kinematics of flexible multibody systems, (2) couples their displacement and rotation components by recognizing that configuration and motion are members of the Special Euclidean group, and (3) resolves all tensors components in local frames. The formulation based on the motion formalism (1) provides a theoretical framework that streamlines the formulation of shell elements, (2) leads to governing equations of motion that are objective, intrinsic, and present a reduced order of nonlinearity, (3) improves the efficiency of the solution process, (4) circumvents the shear locking phenomenon that plagues shell formulations based on classical kinematic descriptions, and (5) prevents the occurrence of singularities in the treatment of finite rotation. Numerical examples are presented to illustrate the advantageous features of the proposed formulation.Item Vibration Isolation Performance of an Adaptive Magnetorheological Elastomer-Based Dynamic Vibration Absorber(MDPI, 2022-06-12) Choi, Young; Wereley, Norman M.This study evaluates the vibration isolation performance of an adaptive magnetorheological elastomer (MRE)-based dynamic vibration absorber (MRE-DVA) for mitigating the high frequency vibrations (100–250 Hz) of target devices. A simple and effective MRE-DVA design was presented and its vibration isolation performance was experimentally measured. A cylindrical shaped MRE pad was configured to be operated in shear mode and also worked as a semi-actively tunable spring for achieving adaptive DVA. A complex stiffness analysis for the damper force cycle was conducted and it was experimentally observed that the controllable dynamic stiffness range of the MRE-DVA was greater than two over the tested frequency range. The transmissibility of a target system was measured and used as a performance index to evaluate its vibration isolation performance. It was also experimentally demonstrated that a better vibration isolation performance of the target device exposed to the high frequency vibrations could be achieved by using the adaptive MRE-DVA.Item Analysis of Pneumatic Artificial Muscles and the Inelastic Braid Assumption(MDPI, 2022-08-04) Chambers, Jonathan M.; Wereley, Norman M.Pneumatic artificial muscles (PAMs) are becoming an increasingly popular form of soft actuator due to their unique actuation characteristics. The creation of accurate PAM actuation models is important for their successful implementation. However, PAM studies often employ actuation models that use simplifying assumptions which make the models easier to formulate and use, but at the cost of reduced accuracy. One of the most commonly used assumptions, the inelastic braid assumption, suggests that the braid does not stretch, and therefore would not affect its geometry or actuation force. Although this assumption has often been cited as a likely source of model error, its use has persevered for decades due to researchers’ inability to directly measure the effects of braid elasticity. The recent development of a photogrammetric method to accurately measure PAM geometry now enables this analysis. This study seeks to assess the current default adoption of the inelastic braid assumption in PAM models by attempting to quantify the braid elasticity effects. This research finds that current models that use the inelastic braid assumption can underestimate PAM diameter by as much as 30%, and overestimate actuation force by as much as 70%. These results show that braid elasticity can have a substantial effect on the geometry and actuation force of PAMs, and demonstrates that the inelastic braid assumption may not be a suitable universal assumption for PAM modeling and analyses, especially when low-stiffness braid materials are used.Item Tunable Energy Absorbing Property of Bilayer Amorphous Glass Foam via Dry Powder Printing(MDPI, 2022-12-19) Park, Jungjin; Howard, John; Edery, Avi; DeMay, Matthew; Wereley, NormanThe research in this paper entails the design of material systems with tunable energy-absorbing properties. Hollow glass microspheres of different densities are layered using dry powder printing and subsequently sintered to form a cellular structure. The tunability of the bilayer foams is investigated using various combinations of hollow microspheres with different densities and different thickness ratios of the layers. The mechanical responses to quasi-static uniaxial compression of the bilayer foams are also investigated. These bilayer samples show different mechanical responses from uniform samples with a distinctive two-step stress–strain profile that includes a first and second plateau stress. The strain where the second plateau starts can be tuned by adjusting the thickness ratio of the two layers. The resulting tunable stress–strain profile demonstrates tunable energy absorption. The tunability is found to be more significant if the density values of each layer differ largely. For comparison, bilayer samples are fabricated using epoxy at the interface instead of a sintering process and a different mechanical response is shown from a sintered sample with the different stress–strain profile. Designing the layered foams allows tuning of the stress–strain profile, enabling desired energy-absorbing properties which are critical in diverse impact conditions.Item A lionfish-inspired predation strategy in planar structured environments(Institute of Physics, 2023-06-30) Thompson, Anthony A.; Peterson, Ashley N.; McHenry, Matthew J.; Paley, Derek A.This paper investigates a pursuit-evasion game with a single pursuer and evader in a bounded environment, inspired by observations of predation attempts by lionfish (Pterois sp.). The pursuer tracks the evader with a pure pursuit strategy while using an additional bioinspired tactic to trap the evader, i.e. minimize the evader’s escape routes. Specifically, the pursuer employs symmetric appendages inspired by the large pectoral fins of lionfish, but this expansion increases its drag and therefore its work to capture the evader. The evader employs a bioinspired randomly-directed escape strategy to avoid capture and collisions with the boundary. Here we investigate the trade-off between minimizing the work to capture the evader and minimizing the evader’s escape routes. By using the pursuer’s expected work to capture as a cost function, we determine when the pursuer should expand its appendages as a function of the relative distance to the evader and the evader’s proximity to the boundary. Visualizing the pursuer’s expected work to capture everywhere in the bounded domain, yields additional insights about optimal pursuit trajectories and illustrates the role of the boundary in predator-prey interactions.Item Biorthogonal decomposition of the disturbance flow field generated by particle impingement on a hypersonic boundary layer(Cambridge University Press, 2023-08-10) A. Al Hasnine, S.; Russo, V.; Tumin, A.; Brehm, C.The disturbance flow field in a hypersonic boundary layer excited by particle impingement was investigated with a focus on the first stage of the laminar-to-turbulent transition process, namely the receptivity process. A previously validated direct numerical simulation approach adopting disturbance flow tracking is used to simulate the particle-induced transition process. Particle impingement generates a highly complex disturbance flow field that can be characterised by a wide range of frequencies and wavenumbers. After providing some insight about the spectral characteristics of the disturbance flow field in the frequency and wavenumber domains, biorthogonal decomposition is employed to reveal the composition of the disturbance flow field consisting of different continuous and discrete eigenmodes that are triggered through particle impingement. The disturbance flow characteristics for different frequency and wavenumber pairs are discussed where large contributions in the disturbance flow spectrum are observed in the vicinity of the impingement location. A significant amount of the disturbance energy is diverted into the free stream leading to large coefficients of projection for the slow and fast acoustic branches while contributions to the entropy and vorticity branches are negligible. In addition to the continuous acoustic spectra, the first-, second- and other higher-order Mack modes are activated and provide large contributions to the disturbance flow field inside the boundary layer. Finally, it is demonstrated that the disturbance flow field in the vicinity of the impingement location can be reconstructed with a maximum relative error of 2.3 % by employing a theoretical biorthogonal eigenfunction system expansion and by considering contributions from fast and slow acoustic waves and at most four discrete modes only.Item Compressibility effects on Reynolds stress amplification and shock structure in shock–isotropic turbulence interactions(Cambridge University Press, 2023-02-27) Grube, Nathan E.; Martín, M. PinoRecent direct numerical simulation studies of canonical shock–isotropic turbulence interactions (SITIs) in the highly compressible regime exhibit streamwise Reynolds stress amplification that is significantly higher in some cases than in previous studies; an explanation is offered based on a relatively high Mach number combined with significant dilatational energy in the incident flow. Some cases exhibit a loss of amplification that is associated with a highly perturbed shock structure as the flow parameters approach the threshold between the wrinkled and broken shock regimes. The shock structure perturbations due to the highly compressible incident turbulence match those proposed by Donzis (Phys. Fluids, vol. 24, 2012, 126101) relatively well, but due to the presence of thermodynamic fluctuations in addition to velocity fluctuations in the incident flow, we propose a generalized parametrization based on the root-mean-square Mach number fluctuation in place of the turbulence Mach number. This is found to improve the collapse of the shock structure data, suggesting that the wrinkled–broken shock regime threshold determined previously for vortical turbulence (Donzis, Phys. Fluids, vol. 24, 2012, 126101; Larsson et al., J. Fluid Mech., vol. 717, 2013, pp. 293–321) can be applied to more general isotropic inflow fields using the proposed parametrization.Item Transitional hypersonic flow over slender cone/flare geometries(Cambridge University Press, 2022-09-30) Butler, Cameron S.; Laurence, Stuart J.Experiments are performed in a Mach-6 shock tunnel to examine the laminar-to-turbulent transition process associated with a sudden increase in surface angle on a slender body. A cone/flare geometry with a 5◦ frustum and compression angles ranging from 5◦ to 15◦ allow a range of mean flow configurations, spanning an attached shock-wave/boundary-layer interaction to a fully separated one; the unit Reynolds number of the flow is also varied to modify the state of incoming second-mode boundary-layer disturbances. Ultra-high-speed schlieren visualizations provide a global picture of the flow development, supplemented by high-frequency surface pressure measurements. For the 5◦ compression, the unsteady flow field is dominated by the second-mode waves, whose breakdown to turbulence is generally accelerated (compared with the straight-cone configuration) by encountering the angle change. As the compression angle is increased to induce separation, lower-frequency disturbances appear along the separated shear layer that exhibit much larger amplification rates than the incoming second-mode waves; the latter effectively freeze in amplitude downstream of the separation point before rapidly breaking down upon reattachment. The shear-layer disturbances become dominant at the largest compression angle tested. Radiation of disturbance energy to the external flow is consistently observed: this generally occurs along mean flow features (flare, separation or reattachment shocks) for the second-mode disturbances and spontaneously for the shear-layer waves. The combined application of spectral proper orthogonal decomposition and a global bispectral analysis allows the identification of important unsteady flow structures and the association of these with prominent nonlinear interactions in the various configurations.Item Physics of gust response mitigation in open-loop pitching manoeuvres(Cambridge University Press, 2022-07-01) Sedky, Girguis; Gementzopoulos, Antonios; Andreu-Angulo, Ignacio; Lagor, Francis D.; Jones, Anya R.This paper experimentally investigates the flow field development and unsteady loading of three force-mitigating pitch manoeuvres during a transverse gust encounter. The manoeuvres are constructed using varying levels of theoretical and simulation fidelity and implemented as open-loop kinematics in a water towing tank. It is found that pitch actuation during a gust encounter results in two important changes in flow topology: (i) early detachment of the leading-edge vortex (LEV) and (ii) formation of an LEV on the pressure side of the wing upon gust exit. Each of the pitch manoeuvres is found to mitigate a significant portion of the circulatory contribution of the lift force while only manoeuvres with accurate modelling of the added-mass force are found to adequately mitigate the total lift force. The penalty of aerodynamic lift mitigation using pitch manoeuvres was a twofold increase in the pitching moment transients experienced by the wing for all cases. By quantifying changes in the vertical gust momentum before and after the encounter, lift-mitigating manoeuvres were found to reduce the disturbance to the gust’s flow field, thereby reducing the momentum exchange between the gust and the wing.Item Amplitude and wavelength scaling of sinusoidal roughness effects in turbulent channel flow at fixed Reτ=720(Cambridge University Press, 2022-02-28) Ganju, Sparsh; Bailey, Sean C.C.; Brehm, ChristophDirect numerical simulations are performed for incompressible, turbulent channel flow over a smooth wall and different sinusoidal wall roughness configurations at a constant Reτ = 720. Sinusoidal walls are used to study the effects of well-defined geometric features of roughness-amplitude, a, and wavelength, λ, on the flow. The flow in the near-wall region is strongly influenced by both a and λ. Establishing appropriate scaling laws will aid in understanding the effects of roughness and identifying the relevant physical mechanisms. Using inner variables and the roughness function to scale the flow quantities provides support for Townsend’s hypothesis, but inner scaling is unable to capture the flow physics in the near-wall region. We provide modified scaling relations considering the dynamics of the shear layer and its interaction with the roughness. Although not a particularly surprising observation, this study provides clear evidence of the dependence of flow features on both a and λ. With these relations, we are able to collapse and/or align peaks for some flow quantities and, thus, capture the effects of surface roughness on turbulent flows even in the near-wall region. The shear-layer scaling supports the hypothesis that the physical mechanisms responsible for turbulent kinetic energy production in turbulent flows over rough walls are greatly influenced by the shear layer and its interaction with the roughness elements. Finally, a semiempirical model is developed to predict the contribution of pressure and skin friction drag on the roughness element based purely on its geometric parameters and the corresponding shear-layer velocity scale.Item A Path Dependent Approach for Characterizing the Legal Governance of Autonomous Systems(IEEE, 2022-11-10) Borson, Joseph E.; Xu, HuanAutonomous systems promise significant improvements in many fields. These systems will be subject to legal governance requirements. The literature has largely focused on “autonomous governance” as a framework that is broadly applicable to autonomous devices regardless of the type of system (e.g., aviation or motor vehicles) at issue. While there are regulatory principles applicable to autonomous systems generally, an “autonomy-focused” approach is an inadequate lens to consider the governance of these systems. Rather, because autonomous systems are improvements of currently regulated complex systems, the regulation of autonomous elements will occur within those systems’ preexisting regulatory framework. Accordingly, the nature of future autonomous regulation will likely depend on the preexisting features of that substantive system, rather than on an optimal approach divorced from that history, an attribute known in the social science literature as path dependency. In order to characterize diverse regulated systems with an eye toward assessing future autonomous developments, we develop a framework of regulatory approaches to identify specific features of the preexisting regulatory scheme for a given system. We then analyze that approach by examining three different regulatory regimes (aviation, motor vehicles, and medical devices), across two different continents, and consider how the same type of requirement, e.g., fail-safe systems, can lead to different types of regulations depending on the differing baseline framework.

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