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Rubidium excited state line shapes from 4D-nF (n = 9, 12, 15, 20) broadened by helium
No full textPump-modulated laser absorption spectroscopy was used to experimentally measure the rubidium 42D5/2 → n2F line shapes broadened by 0-200 Torr of helium. The broadening rates are 175.4±6.6, 144±4, 104±23, and 118±88 MHz/Torr for n = 9,12,15,20 respectively, while the shift rates are +36 ± 8, +113 ± 5, +143 ± 19, and +155 ± 68 MHz/Torr. No asymmetry rates are reported. Broadening rates are seen to decrease slightly with n. The direction of the shift is to the blue, as with other Rb-He transitions, and the magnitude of the shift increases with n. Stark broadening is observed on the 4D5/2 → 152F and 4D5/2 → 202F transitions at pressures above 10 Torr, with fractional ionization of about 9%
Dynamics analysis of a Vacuum Lighter than Air Vehicle during descent
No full textThe Vacuum Lighter-than-Air Vehicle (VLTAV) was designed as an alternative to traditional Lighter-than-Air platforms, offering extended loiter time, increased payload capacity, and the potential to establish a floating network for a range of civil and military applications. To ensure reliable operation and mission effectiveness, it is essential to understand the dynamics characteristics of the VLTAV across various atmospheric environments. The VLTAV’s frame incorporates a celestial icosahedron geometry, providing structural efficiency and symmetry. Computational Fluid Dynamics (CFD) analysis is employed to assess the vehicle’s aerodynamic performance, focusing on drag coefficient estimation and its correlation with the Reynolds number. The aerodynamic characterization is then integrated into a comprehensive dynamics framework of VLTAV, encompassing the vehicle’s kinematics and dynamics, as well as atmospheric and gravitational models, to simulate its descent behavior in the atmospheres of Earth, Mars, and Venus, chosen for their contrasting atmospheric densities. Results indicate that Mars poses the most significant challenge due to its thin atmosphere, which reduces aerodynamic drag and results in higher descent velocities, especially when a payload is included. Conversely, Venus’s dense atmosphere provides highly favorable conditions, enabling the VLTAV to maintain altitude and operate effectively over a range of elevations. By adjusting payload mass, the VLTAV can be tuned to achieve specific float altitudes, making it a promising platform for scientific observation and extended aerial missions
Computational Investigation of Heat Generation and Dissipation in Lithium-Ion Batteries During Multi-Rate Charging
No full textThis study examines how heat affects lithium-ion batteries during their operation through detailed computer modeling. Our research uses computational fluid dynamics (CFD) to track heat flow and battery behavior in a rectangular pouch battery design. The model focuses on changes across the battery’s thickness, measuring key factors: how electrical current moves, how heat dissipates, and how lithium ions travel through the battery. We tested the battery under two main conditions. First, keeping it a steady room temperature of 298 K, and second, letting it generate heat naturally during use. For each scenario, we tried three different charging speeds: a standard rate (2C at 18 A/m2), a medium rate (4C at 53 A/m2), and a fast rate (6C at 88 A/m2). Our results show important patterns in battery behavior. When batteries charge and discharge faster, they lose capacity more quickly. This happens both when the temperature stays constant and when the battery heats up during use. Interestingly, when heat builds up, the battery takes longer to complete its chargedischarge cycles. This occurs because higher temperatures change how the battery works in two ways: they alter the electrical properties of the battery’s electrodes and make it easier for lithium ions to move around inside. To address these challenges, we investigated various cooling methods. Our findings suggest that controlling battery temperature is crucial for maintaining performance, especially during fast charging. These insights help explain why battery sometimes underperform and point to ways we can make them work better through improved cooling systems. This study advances our understanding of why batteries heat up during use and how this affects their performance, offering practical solutions for better battery management. Abstract © ASME
Assessing the Effects of Internal Blockage on Cavity Aeroacoustics
No full textCavity flow is well-studied for empty geometries, but the effects of adding internal blockage is largely unknown. This study uses computational fluid dynamics to simulate a rectangular cavity, increasing the volume blockage ratio from empty (0%) to four spherocylinders (20.7%) at Mach 0.95. Grid independence studies are performed for the spherocylinder and cavity grids. Results confirm Rossiter’s equation accurately predicts full-scale cavity modal frequencies. Increasing volume blockage ratio generally reduces sound pressure level and overall sound pressure level. However, there is one configuration that increases sound pressure level and overall sound pressure level, the two spherocylinders horizontal configuration. This configuration amplifies the dominant Rossiter mode, and has a significant increase in overall sound pressure level compared to the baseline empty cavity. This highlights that spatial configuration, not just volume-blockage-ratio, affects acoustic behavior
Application of Synthetically Trained Three-dimensional U-Net to the Detection of Moving Subpixel Objects
No full textHybrid Monte Carlo and molecular dynamics simulations were used to investigate the interaction of light interstitials in multi-element Ni-based alloys. We show that light interstitials such as boron and oxygen fundamentally alter interfacial chemistry by reshaping alloy-element distribution and segregation. Oxygen adsorption drove boron migration from the grain boundary to the free surface, where it co-enriched with Cr, Fe, and Mo and formed BO3 trigonal motifs embedded within mixed-metal oxide networks. Oxygen also promoted M-O-M chain formation, including Nb2O5 clusters at the free surface. In the absence of oxygen, boron segregated to the grain boundary, altering local metal chemistry and underscoring a dynamic, environment-sensitive behavior. Following chlorine exposure, the oxidized surfaces retained strong O-mediated connectivity while forming new Cl-M associations, particularly with Nb and Cr, and exhibited further surface enrichment in Cr, Fe, and Mo. High-temperature MD simulations revealed a dynamic tug-of-war: chlorine exerted upward pull and disrupted weakly anchored sites, while Nb- and BO3-rich oxide motifs resisted deformation. A new stabilization mechanism was identified in which subsurface boron atoms anchored overlying Cr centers, suppressing their mobility and mitigating chlorine-driven displacement. These results demonstrate boron\u27s dual role as a modifier of alloy-element segregation and a stabilizer of oxide networks, and identify Nb as a key element in reinforcing cohesion under halogen attack. More broadly, this study highlights the need to track light interstitial cross-talk and solute migration under reactive conditions, offering atomistic criteria for designing corrosion-resistant surface chemistries in Ni-based superalloys exposed to halogenated or oxidative environments
Seal for a Wave Rotor Disk Engine
No full textA unique seal for a wave rotor disk engine is disclosed herein. The seal is operable for sealing a region between a rotor and a rotor casing. The seal is spring loaded and will engage with the tip of the rotor to reduce pressure loss within the wave rotor disk engine
A Comparison of Bayesian Methods for Integrated Test and Evaluation
No full textTesting defense systems in operationally realistic scenarios is typically logistically difficult and expensive. For this reason, Bayesian methods have gained significant interest in recent years as a means of shifting testing “left” in the acquisition lifecycle—that is, integrating information from earlier phases of test to reach conclusions about system performance more quickly and to better infer operational performance when data from such scenarios is limited. Bayesian inference mathematically quantifies assumptions in the form of selecting prior distributions on the unknown parameters and strategies for integrating data collected under different conditions. In this article, we compare several Bayesian approaches for integrated test and evaluation, using the example of estimating the reliability of the Stryker family of vehicles from developmental and operational test data. We compute posterior reliability estimates for each method and conduct a sensitivity analysis to measure how each assumption influences the results. Altogether, the analysis not only shows the promise of Bayesian integration of information, but also the importance of careful and justifiable assumptions to ensure defensible results
Fuel Pump Power and Thermal Conceptual Design Investigation for a High Speed Vehicle
No full textThe design of a high-speed vehicle presents new challenges when compared to a lower speeds. At high speeds, there is no turbine or other rotating component within the propulsion system to generate electrical power, and or drive the fuel pump, necessitating an alternative means to turn the device to sustain thrust. As it is desirable to consider the power generation system earlier in the conceptual design process of high-speed vehicles, a means by which the power requirements of a generic geometry can be acquired quickly must be obtained, which for high speeds includes the power requirements of the fuel pump. In prior work, a conceptual design level 6DOF simulation was created to model the power and thermal requirements of high-speed vehicle subsystems. This work expands the previous work by implementing a fuel pump driven by an electric motor. The pump; modeled as a variable displacement pump, and motor are modeled and controlled in the developed SIMULINK model. A power and thermal analysis was performed for the entire subsystem and the profiles for each were extracted from the SIMULNK model. Upon simulation, both the power and thermal profiles for the fuel pump and motor subsystem were available for analysis at the conceptual design level
A multi-objective, bilevel programming methodology to identify spatiotemporal transportation distribution network vulnerabilities
No full textExcerpt: This research formulates and examines the bilevel material routing problem, wherein an upper-level problem identifies the respective times and locations for a limited number of fixed-duration attacks on arcs within a distribution network, and a lower-level problem subsequently routes shipments over the network between respective origins and destinations