Scholarly Works, Aerospace and Ocean Engineering

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  • Microstructures and Corrosion Properties of Wire Arc Additive Manufactured Copper–Nickel Alloys
    Song, Jie; Jimenez, Xavier A.; To, Albert C.; Fu, Yao (MDPI, 2024-02-14)
    The 70/30 copper–nickel alloy is used mainly in critical parts with more demanding conditions in marine settings. There is a need for innovative methods that offer fast production and cost-effectiveness in order to supplement current copper–nickel alloy manufacturing processes. In this study, we employ wire arc additive manufacturing (WAAM) to fabricate the 70/30 copper–nickel alloy. The as-built microstructure is characterized by columnar grains with prominent dendrites and chemical segregation in the inter-dendritic area. The aspect ratio of the columnar grain increases with increasing travel speed (TS) at the same wire feed speed (WFS). This is in contrast with the equiaxed grain structure, with a more random orientation, of the conventional sample. The sample built with a WFS of 8 m/min, TS of 1000 mm/min, and a track distance of 3.85 mm exhibits superior corrosion properties in the 3.5 wt% NaCl solution when compared with the conventional sample, as evidenced by a higher film resistance and breakdown potential, along with a lower passive current density of the WAAM sample. The corrosion morphology reveals the critical roles played by the nickel element that is unevenly distributed between the dendrite core and inter-dendritic area.
  • Spatiotemporal Optimization for Vertical Path Planning of an Ocean Current Turbine
    Hasankhan, Arezoo; Tang, Yufei; VanZwieten, James; Sultan, Cornel (IEEE, 2022-07-29)
    This article presents a novel spatiotemporal optimization approach for vertical path planning (i.e., waypoint optimization) to maximize the net output power of an ocean current turbine (OCT) under uncertain ocean velocities. To determine the net power, OCT power generation from hydrokinetic energy and the power consumption for controlling the depth are modeled. The stochastic behavior of ocean velocities is a function of spatial and temporal parameters, which is modeled through a Gaussian process (GP) approach. Two different algorithms, including model predictive control (MPC) as a model-based method and reinforcement learning (RL) as a learning-based method, are applied to solve the formulated spatiotemporal optimization problem with constraints. Comparative studies show that the MPC- and RL-based methods are computationally feasible to address vertical path planning, which are evaluated with a baseline A∗ approach. Analysis of the robustness is further carried out under the inaccurate ocean velocity predictions. Results verify the efficiency of the presented methods in finding the optimal path to maximize the total power of an OCT system, where the total harnessed energy after 200 h shows over an 18% increase compared to the case without optimization.
  • Numerical and Experimental Investigation of the Dynamics of a U-Shaped Sloshing Tank to Increase the Performance of Wave Energy Converters
    Fontana, Marco; Giorgi, Giuseppe; Accardi, Massimiliano; Giorcelli, Ermanno; Brizzolara, Stefano; Sirigu, Sergej Antonello (MDPI, 2023-12-11)
    In this investigation, a comprehensive study was conducted on a U-shaped sloshing tank, based on reversing the classical treatment of such devices as motion stabilizers and using them instead to improve the performance of wave energy converters. The modeling encompasses a comparative analysis between a linear model and Computational Fluid Dynamics (CFD) simulations. The validation of the CFD methodology was rigorously executed via a series of experimental tests, subsequently enhancing the linear model. The refined linear model demonstrates a notable alignment with rigorously verified results, thus establishing itself as a reliable tool for advanced research, indicating promise for various applications. Furthermore, this novelty is addressed by simulating the integration of a U-tank device with a pitch-based wave energy converter, displaying a broadening of the operational bandwidth and a substantial performance improvement, raising the pitch motion of the floater to about 850% in correspondence with the new secondary peak over extended periods, effectively addressing previously identified limitations. This achievement contributes to the system’s practical relevance in marine energy conversion.
  • Development of an OpenFOAM Solver for Hydroacoustic Simulations: An Application for Acoustic Fish Deterrence
    George, Edwin; Palmore, John A., Jr.; Alexander, William Nathan; Politano, Marcela; Smith, David; Woodley, Christa (2023-11-20)
  • Performance assessment of energy-preserving, adaptive time-step variational integrators
    Sharma, Harsh; Borggaard, Jeffrey T.; Patil, Mayuresh; Woolsey, Craig A. (Elsevier, 2022-11)
    A fixed time-step variational integrator cannot preserve momentum, energy, and symplectic form simultaneously for nonintegrable systems. This barrier can be overcome by treating time as a discrete dynamic variable and deriving adaptive time-step variational integrators that conserve the energy in addition to being symplectic and momentum-preserving. Their utility, however, is still an open question due to the numerical difficulties associated with solving the discrete governing equations. In this work, we investigate the numerical performance of energy-preserving, adaptive time-step variational integrators. First, we compare the time adaptation and energy performance of the energy-preserving adaptive algorithm with the adaptive variational integrator for Kepler's two-body problem. Second, we apply tools from Lagrangian backward error analysis to investigate numerical stability of the energy-preserving adaptive algorithm. Finally, we consider a simple mechanical system example to illustrate the backward stability of this energy-preserving, adaptive time-step variational integrator.
  • In the wind: Invasive species travel along predictable atmospheric pathways
    Pretorius, Ilze; Schou, Wayne C.; Richardson, Brian; Ross, Shane D.; Withers, Toni M.; Schmale, David G. III; Strand, Tara M. (Wiley, 2023-04)
    Invasive species such as insects, pathogens, and weeds reaching new environments by traveling with the wind, represent unquantified and difficult-to-manage biosecurity threats to human, animal, and plant health in managed and natural ecosystems. Despite the importance of these invasion events, their complexity is reflected by the lack of tools to predict them. Here, we provide the first known evidence showing that the long-distance aerial dispersal of invasive insects and wildfire smoke, a potential carrier of invasive species, is driven by atmospheric pathways known as Lagrangian coherent structures (LCS). An aerobiological modeling system combining LCS modeling with species biology and atmospheric survival has the potential to transform the understanding and prediction of atmospheric invasions. The proposed modeling system run in forecast or hindcast modes can inform high-risk invasion events and invasion source locations, making it possible to locate them early, improving the chances of eradication success.
  • Sizing optimization and experimental characterization of a variable stiffness shape memory polymer filled honeycomb composite
    Squibb, Carson; Philen, Michael K. (IOP Publishing, 2023-04)
    Variable stiffness structures and materials have been considered for many applications, including active vibration control and shape morphing. With regards to shape morphing, variable stiffness materials and composites have been considered for reconfigurable skin materials in aerospace vehicles. Of the many concepts that have been developed for such applications, shape memory polymers (SMPs) are one such promising materials for shape morphing. SMPs exhibit both high modulus ratios and recoverable strains but suffer from a low overall modulus and often require reinforcements, such as honeycomb. This work investigates the design space of such honeycomb reinforced SMPs as variable stiffness materials. Unit cell finite element models are developed for the material, and parametric studies are completed for varying honeycomb cell geometries. A multiobjective, constrained Pareto front optimization is completed for two honeycomb material models and in two loading directions using selected sizing design variables. Pareto fronts are established, and cell geometries are selected and fabricated to experimentally verify the optimized model predictions. The results both predict and demonstrate the advantages of using honeycomb reinforcements for SMPs. Effective in-plane moduli as high as 45 GPa are predicted while achieving a change in modulus of 450X. Compared to existing reinforcement strategies for shape memory polymers, these composites exhibit favorable combinations of both high stiffness and high changes in stiffness with a high degree of tailorability through the honeycomb cell geometry and predicted performances that meet and exceed the state of the art.
  • In-Flight Performance of the ICON EUV Spectrograph
    Korpela, Eric J.; Sirk, Martin M.; Edelstein, Jerry; McPhate, Jason B.; Tuminello, Richard M.; Stephan, Andrew W.; England, Scott L.; Immel, Thomas J. (Springer, 2023-04)
    We present in-flight performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (17 degrees x12 degrees) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the OII emission lines at 61.6 nmand 83.4 nm. In flight calibration and performance measurement has shown that the instrument has met all of the science performance requirements. We discuss the observed and expected changes in the instrument performance due to microchannel plate charge depletion, and how these changes were tracked over the first two years of flight. This paper shows raw data products from this instrument. A parallel paper (Stephan et al. in Space Sci. Rev. 218:63, 2022) in this volume discusses the use of these raw products to determine O+ density profiles versus altitude.
  • Reducing the Ionospheric Contamination Effects on the Column O/N-2 Ratio and Its Application to the Identification of Non-Migrating Tides
    Krier, Christopher S.; England, Scott L.; Meier, R. R.; Frey, Harald U. (American Geophysical Union, 2023-04)
    Prior investigations have attempted to characterize the longitudinal variability of the column number density ratio of atomic oxygen to molecular nitrogen (SO/N-2) in the context of non-migrating tides. The retrieval of thermospheric SO/N-2 from far ultra-violet (FUV) emissions assumes production is due to photoelectron impact excitation on O and N-2. Consequently, efforts to characterize the tidal variability in SO/N-2 have been limited by ionospheric contamination from O+ + e radiative recombination at afternoon local times (LT) around the equatorial ionization anomaly. The retrieval of SO/N-2 from FUV observations by the Ionospheric Connection Explorer (ICON) provides an opportunity to address this limitation. In this work, we derive modified SO/N-2 datasets to delineate the response of thermospheric composition to non-migrating tides as a function of LT in the absence of ionospheric contamination. We assess estimates of the ionospheric contribution to 135.6 nm emission intensities based on either Global Ionospheric Specification (GIS) electron density, International Reference Ionosphere (IRI) model output, or observations from the Extreme Ultra-Violet imager (EUV) onboard ICON during March and September equinox conditions in 2020. Our approach accounts for any biases between the ionospheric and airglow datasets. We found that the ICON-FUV data set, corrected for ionospheric contamination based on GIS, uncovered a previously obscured diurnal eastward wavenumber 2 tide in a longitudinal wavenumber 3 pattern at March equinox in 2020. This finding demonstrates not only the necessity of correcting for ionospheric contamination of the FUV signals but also the utility of using GIS for the correction.
  • In Flight Performance of the Far Ultraviolet Instrument (FUV) on ICON
    Frey, H. U.; Mende, S. B.; Meier, R. R.; Kamaci, U.; Urco, J. M.; Kamalabadi, F.; England, Scott L.; Immel, T. J. (Springer, 2023-04)
    The NASA Ionospheric Connection Explorer (ICON) was launched in October 2019 and has been observing the upper atmosphere and ionosphere to understand the sources of their strong variability, to understand the energy and momentum transfer, and to determine how the solar wind and magnetospheric effects modify the internally-driven atmosphere-space system. The Far Ultraviolet Instrument (FUV) supports these goals by observing the ultraviolet airglow in day and night, determining the atmospheric and ionospheric composition and density distribution. Based on the combination of ground calibration and flight data, this paper describes how major instrument parameters have been verified or refined since launch, how science data are collected, and how the instrument has performed over the first 3 years of the science mission. It also provides a brief summary of science results obtained so far.
  • Wall-pressure fluctuations in an axisymmetric boundary layer under strong adverse pressure gradient
    Balantrapu, N. Agastya; Alexander, W. Nathan; Devenport, William (Cambridge University Press, 2023-04)
    Measurements of fluctuating wall pressure in a high-Reynolds-number flow over a body of revolution are described. With a strong axial pressure gradient and moderate lateral curvature, this non-equilibrium flow is relevant to marine applications as well as short-haul urban transportation. The wall-pressure spectrum and its scaling are discussed, along with its relation to the space-time structure. As the flow decelerates downstream, the root-mean-square level of the pressure drops together with the wall shear stress (t(w)) and is consistently approximately 7t(w). While the associated dimensional spectra see a broadband reduction of over 15 dB per Hz, they appear to attain a single functional form, collapsing to within 2 dB when normalized with the wall-wake scaling where t(w) is the pressure scale and U-e/d is the frequency scale. Here, d is the boundary layer thickness and U-e is the local free-stream velocity. The general success of the wall-wake scaling, including in the viscous f(-5) region, suggests that the large-scale motions in the outer layer play a predominant role in the near-wall turbulence and wall pressure. On investigating further, we find that the instantaneous wall-pressure fluctuations are characterized by a quasi-periodic feature that appears to convect downstream at speeds consistent with the outer peak in the turbulence stresses. The conditional structure of this feature, estimated through peak detection in the time series, resembles that of a roller, supporting the embedded shear layer hypothesis (Schatzman & Thomas, J. Fluid Mech., vol. 815, 2017, pp. 592-642; Balantrapu et al., J. Fluid Mech., vol. 929, 2021, A9). Therefore, the outer-region shear-layer-type motions may be important when devising strategies for flow control, drag and noise reduction for decelerating boundary layers.
  • Feasibility Investigation of Attitude Control with Shape Memory Alloy Actuator on a Tethered Wing
    Zhu, Yufei; Tsuruta, Ryohei; Gupta, Rikin; Nam, Taewoo (MDPI, 2023-07-29)
    This study is aimed at assessing the feasibility of employing an innovative, smart-material-based control effector for an inflatable wing. A shape memory alloy (SMA) actuator is primarily investigated as a control effector in this work for its advantages of a simple actuation mechanism and a high force-to-weight ratio. This paper presents the design, control strategy and simulation results of the SMA actuator used as a stability augmentation system for a small-scale prototype kite. Stable flight of the kite is achieved during open wind tunnel tests using the SMA actuator. Based on experimental and simulation analyses, it is evident that the current SMA actuator is better for low-frequency actuations rather than stability augmentation purposes, as its performance is sensitive to practical conditions. The study also discusses potential improvements and applications of the SMA actuator.
  • Forecasting Equatorial Ionospheric Convective Instability With ICON Satellite Measurements
    Hysell, D. L.; Kirchman, A.; Harding, B. J.; Heelis, R. A.; England, Scott L. (American Geophysical Union, 2023-05)
    Measurements from the Ionospheric Connections Explorer satellite (ICON) form the basis of direct numerical forecast simulations of plasma convective instability in the postsunset equatorial F region ionosphere. ICON data are selected and used to initialize and force the simulations and then to test the results one orbit later when the satellite revisits the same longitude. Data from the IVM plasma density and drifts instrument and the MIGHTI red-line thermospheric winds instrument are used to force the simulation. Data from IVM are also used to test for irregularities (electrically polarized plasma depletions). Fourteen datasets from late March 2022, were examined. The simulations correctly predicted the occurrence or non-occurrence of irregularities 12 times while producing one false positive and one false negative. This demonstrates that the important telltales of instability are present in the ICON state variables and that the important mechanisms for irregularity formation are captured by the simulation code. Possible refinements to the forecast strategy are discussed.
  • A phase field model to simulate crack initiation from pitting site in isotropic and anisotropic elastoplastic material
    Song, Jie; Matthew, Christian; Sangoi, Kevin; Fu, Yao (IOP Publishing, 2023)
    A multiphysics phase field framework for coupled electrochemical and elastoplastic behaviors is presented, where the evolution of complex solid-electrolyte is described by the variation of the phase field variable with time. The solid-electrolyte interface kinetics nonlinearly depends on the thermodynamic driving force and can be accelerated by mechanical straining according to the film rupture-dissolution mechanism. A number of examples in two- and three- dimensions are demonstrated based on the finite element-based MOOSE framework. The model successfully captures the pit-to-crack transition under simultaneous electrochemical and mechanical effects. The crack initiation and growth has been demonstrated to depend on a variety of materials properties. The coupled corrosion and crystal plasticity framework also predict the crack initiation away from the perpendicular to the loading direction.
  • Combined Analysis of Hydrogen and Oxygen 102.6 nm Emission at Mars
    Chaffin, Michael S.; Deighan, Justin; Jain, Sonal; Holsclaw, Greg; AlMazmi, Hoor; Chirakkil, Krishnaprasad; Correira, John; England, Scott L.; Evans, J. Scott; Fillingim, Matt; Lillis, Rob; Lootah, Fatma; Raghuram, Susarla; Eparvier, Frank; Thiemann, Ed; Curry, Shannon; AlMatroushi, Hessa (American Geophysical Union, 2022-08)
    Water is lost from the Mars upper atmosphere to space as hydrogen and oxygen, both of which can be observed in scattered ultraviolet sunlight at 102.6 nm. We present Emirates Mars Mission Emirates Mars Ultraviolet Spectrometer (EMM/EMUS) insertion orbit observations of this airglow, resolving the independent altitude contributions of H and O for the first time. We present the first airglow modeling of the complete H and O 102.6 nm system and the first 3D azimuthally symmetric modeling of the O emission, retrieving temperatures and densities typical of northern spring. Our model reproduces the emission well above 200 km, but does not incorporate partial frequency redistribution needed to reproduce the observed O brightness at lower altitudes and on the disk. These results support future EMM/EMUS science orbit retrievals of H loss and the use of 102.6 nm observations to constrain planetary atmospheres across the solar system.
  • The Effect of a Linear Free Surface Boundary Condition on the Steady-State Wave-Making of Shallowly Submerged Underwater Vehicles
    Lambert, William; Brizzolara, Stefano; Woolsey, Craig A. (MDPI, 2023-05-05)
    Near-surface simulation methods for shallowly submerged underwater vehicles are necessary for the population of a variety of free-surface-affected, coefficient-based maneuvering and seakeeping models. Simulations vary in complexity and computational costs, often sacrificing accuracy for simplicity and speed. One particular simplifying assumption, the linearization of the free surface boundary conditions, is explored in this study by comparing the steady-state wave-making characteristics of a shallowly submerged prolate spheroid using two different simulation methods at several submergence depths and forward speeds. Hydrodynamic responses are compared between a time-domain boundary element method that makes use of a linearized free surface boundary condition and an inviscid, volume of fluid Reynolds-Averaged Navier–Stokes computational fluid dynamics code that imposes no explicit free surface boundary condition. Differences of up to 22.6%, 32.5%, and 33.3% are found in the prediction of steady state surge force, heave force, and pitch moment, respectively. The largest differences between the two simulation methods arise for motions occurring at small submergences and large wave-making velocities where linear free-surface assumptions become less valid. Nonlinearities that occur in such cases are revealed through physical artifacts such as wave steepening, wave breaking, and high-energy waves. A further examination of near-surface viscous forces reveals that the viscous drag on the vessel is depth dependent due to the changing velocity profile around the body.
  • Deconfusing Detections in Directly Imaged Multiplanet Systems
    Pogorelyuk, Leonid; Fitzgerald, Riley; Vlahakis, Sophia; Morgan, Rhonda; Cahoy, Kerri (IOP Publishing, 2022-10)
    High-contrast images from future space-based telescopes may contain several planets from multiplanet systems and potentially a few planet-like speckles. When taken several months apart, the short-period planets and speckles will appear to move significantly, to the point that it might not be clear which point source (detection) in the image belongs to which object. In this work, we develop a tool, the deconfuser, to test quickly all the plausible partitions of detections by planets based on orbital mechanics. We then apply the deconfuser to a large set of simulated observations to estimate "confusion" rates, i.e., how often there are multiple distinct orbit combinations that describe the data well. We find that in the absence of missed and false detections, four observations are sufficient to avoid confusion, except for systems with high inclinations (above 75 degrees). In future work, the deconfuser will be integrated into mission simulation tools, such as EXOSIMS, to assess the risk of confusion in missions such as the IR/O/UV large telescope recommended by the Astro2020 decadal survey.
  • Morphology of Extreme and Far Ultraviolet Martian Airglow Emissions Observed by the EMUS Instrument on Board the Emirates Mars Mission
    Jain, Sonal K.; Deighan, Justin; Chaffin, Mike; Holsclaw, Greg; Lillis, Rob; Fillingim, Matt; Evans, J. Scott; Correira, John; AlMatroushi, Hessa; Lootah, Fatma; England, Scott L.; AlMazmi, Hoor; Thiemann, Ed; Chamberlin, Phil; Eparvier, Frank (American Geophysical Union, 2022-10)
    We present the first continuous observations of the extreme and far ultraviolet (EUV and FUV) dayglow emissions measured by Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission. We found excellent agreement between the previous observations from the Hopkins Ultraviolet Telescope and recent observations by EMUS both in shape and magnitude. We presented the average disk brightness of major EUV and FUV emissions for about 10 months of data from April 2021 to February 2022. The solar activity was mild/minimum during the first half of the period presented in this study, but we noticed significant day-to-day variations in the major dayglow emissions independent of solar activity, indicating possible coupling from the lower atmosphere via waves/tides. The solar activity increased significantly during the second half of the study period. Our analysis showed that all major EUV and FUV emissions are highly correlated with solar forcing as well as seasonal changes.
  • Dose rate effects in radiation-induced changes to phenyl-based polymeric scintillators
    Papageorgakis, C.; Al-Sheikhly, M.; Belloni, A.; Edberg, T. K.; Eno, S. C.; Feng, Yongbin; Jeng, Geng-Yuan; Kahn, Abraham; Lai, Yihui; McDonnell, T.; Mohammed, Ameer; Palmer, C.; Perez-Gokhale, Ruhi; Ricci-Tam, F.; Yang, Zishuo; Yao, Yao (Elsevier, 2022-11)
    Results on the effects of ionizing radiation on the signal produced by plastic scintillating rods manufactured by Eljen Technology company are presented for various matrix materials, dopant concentrations, fluors (EJ-200 and EJ-260), anti-oxidant concentrations, scintillator thickness, doses, and dose rates. The light output before and after irradiation is measured using an alpha source and a photomultiplier tube, and the light transmission by a spectrophotometer. Assuming an exponential decrease in the light output with dose, the change in light output is quantified using the exponential dose constant D. The D values are similar for primary and secondary doping concentrations of 1 and 2 times, and for antioxidant concentrations of 0, 1, and 2 times, the default manufacturer's concentration. The D value depends approximately linearly on the logarithm of the dose rate for dose rates between 2.2 Gy/h and 100 Gy/h for all materials. For EJ-200 polyvinyltoluene-based (PVT) scintillator, the dose constant is approximately linear in the logarithm of the dose rate up to 3900 Gy/h, while for polystyrene-based (PS) scintillator or for both materials with EJ-260 fluors, it remains constant or decreases (depending on doping concentration) above about 100 Gy/h. The results from rods of varying thickness and from the different fluors suggest damage to the initial light output is a larger effect than color center formation for scintillator thickness <= 1 cm. For the blue scintillator (EJ-200), the transmission measurements indicate damage to the fluors. We also find that while PVT is more resistant to radiation damage than PS at dose rates higher than about 100 Gy/h for EJ-200 fluors, they show similar damage at lower dose rates and for EJ-260 fluors.
  • Energetic particle loss mechanisms in reactor-scale equilibria close to quasisymmetry
    Paul, E. J.; Bhattacharjee, A.; Landreman, M.; Alex, D.; Velasco, J. L.; Nies, R. (IOP Publishing, 2022-12)
    Collisionless physics primarily determines the transport of fusion-born alpha particles in 3D equilibria. Several transport mechanisms have been implicated in stellarator configurations, including stochastic diffusion due to class transitions, ripple trapping, and banana drift-convective orbits. Given the guiding center dynamics in a set of six quasihelical and quasiaxisymmetric equilibria, we perform a classification of trapping states and transport mechanisms. In addition to banana drift convection and ripple transport, we observe substantial non-conservation of the parallel adiabatic invariant which can cause losses through diffusive banana tip motion. Furthermore, many lost trajectories undergo transitions between trapping classes on longer time scales, either with periodic or irregular behavior. We discuss possible optimization strategies for each of the relevant transport mechanisms. We perform a comparison between fast ion losses and metrics for the prevalence of mechanisms such as banana-drift convection (Velasco et al 2021 Nucl. Fusion 61 116059), transitioning orbits, and wide orbit widths. Quasihelical configurations are found to have natural protection against ripple-trapping and diffusive banana tip motion leading to a reduction in prompt losses.