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Rapid distortion analysis of high speed homogeneous turbulence subject to periodic shear
The effect of unsteady shear forcing on small perturbation growth in compressible flow is investigated. In particular, flow-thermodynamic field interaction and the resulting effect on the phase-lag between applied shear and Reynolds stress are examined. Simplified linear analysis of the perturbation pressure equation reveals crucial differences between steady and unsteady shear effects. The analytical findings are validated with numerical simulations of inviscid rapid distortion theory (RDT) equations. In contrast to steadily sheared compressible flows, perturbations in the unsteady (periodic) forcing case do not experience an asymptotic growth phase. Further, the resonance growth phenomenon found in incompressible unsteady shear turbulence is absent in the compressible case. Overall, the stabilizing influence of both unsteadiness and compressibility is compounded leading to suppression of all small perturbations. As a result, the underlying mechanisms are explained.
Highly efficient, high speed vertical photodiodes based on few-layer MoS 2
Not provided.
Online Learning of Effective Turbine Wind Speed in Wind Farms
To develop better wind farm controllers that can meet more complex objectives, methods of modeling the wind turbine wakes at low computational expense are needed. Gaussian process (GP) regression offers a computationally inexpensive framework for learning complex functions from noisy measurements with very few datapoints. In this work, an online learning approach is presented to learn the rotor-averaged wind velocity at downstream wind turbines with GPs, using the available datastream of wind field measurements and wind turbine control set-points. This framework can readily be integrated into model-based controls methods because the model a) is updated online at low computational expense, b) assumes a mathematically favorable Gaussian form, and c) explicitly quantifies the stochastic nature of the wake field so that the trade-off between exploration and exploitation, and the uncertainty in the prediction, can be utilized. We show that a GP-learned model can match true values with errors within 0.5% on average, with as few as 5 training data points.
At-Speed Defect Localization by Combining Laser Scanning Microscopy and Power Spectrum Analysis.
Abstract not provided.
Will Advanced Public Charging Infrastructure Speed Up Electrification of Future Transportation?
This study focuses on evaluating impacts of advanced, urban public charging infrastructure on the battery electric vehicle (BEV) adoption in the U.S market. Under various infrastructure scenarios (e.g., current and developed conditions), we investigate the infrastructure impacts on the near-term BEV adoption using a consumer-choice based market simulation approach. Our results suggest that current public charging infrastructure has continuous and significant impacts on the near-term BEV adoption. Additional infrastructure investment could further stimulate the public acceptance of BEVs. We also find that the actual infrastructure impact may vary depending on the assumption of how charging deployment could affect consumers' access of chargers and consumers' daily available charging time. However, this impact variability could be reduced when infrastructure is getting mature.
Use Of Convolutional Neural Network Image Classification And High-Speed Ion Probe Data Towards Real-Time Detonation Characterization In A Water-Cooled Rotating Detonation Engine
Conference paper for the ASME 2022 Turbomachinery Technical Conference & ExpositionJune 13-17, 2022, Rotterdam, The Netherlands<br>
COS: A Parallel Performance Model for Dynamic Variations in Processor Speed, Memory Speed, and Thread Concurrency
Abstract not provided
Characterizing Speed and Scale of Cryptocurrency Discussion Spread on Reddit
Cryptocurrencies are a novel and disruptive technology that has prompted a new approach to how currencies work in the modern economy. As such, online discussions related to cryptocurrencies often go beyond posts about the technology and underlying architecture of the various coins, to subjective speculations of price fluctuations and predictions. Furthermore, online discussions, potentially driven by foreign adversaries, criminals or hackers, can have a significant impact on our economy and national security if spread at scale. This paper is the first to qualitatively measure and contrast discussion growth about three popular cryptocurrencies with key distinctions in motivation, usage, and implementation – Bitcoin, Ethereum, and Monero on Reddit. More specifically, we measure how discussions relevant to these coins spread in online social environments – how deep and how wide they go, how long they last, how many people they reach, etc. More importantly, we compare user behavior patterns between the focused community of the official coin subreddits and the general community across Reddit as a whole. Our Reddit sample covers three years of data between 2015 and 2018 and includes a time period of a record high Bitcoin price rise. Our results demonstrate that while the largest discussions on Reddit are focused on Bitcoin, posts about Monero (a cryptocurrency often used by criminals for illegal transactions on the Dark Web) start discussions that are typically longer and wider. Bitcoin posts trigger subsequent discussion more immediately but Monero posts are more likely to trigger a longer lasting discussion. We find that moderately subjective posts across all three coins trigger larger, longer, and more viral discussion cascades within both focused and general communities on Reddit. Our analysis aims to bring the awareness to online discussion spread relevant to cryptocurrencies in addition to informing models for forecasting cryptocurrency price that rely on discussions in social media.
High-Speed (20 kHz) Digital In-line Holography (DIH) to Quantify the Impact of a Viscous Drop on a Thin Film.
Abstract not provided.
A fluidic low-speed air-speed indicator
Fluidic parallel flow low airspeed indicator for V/STOL instrumentation tested in wind tunnel
Low-speed longitudinal aerodynamic characteristics of a model of a blunt-nose hypersonic lifting spacecraft having variable- speed wings
Longitudinal aerodynamic characteristics of hypersonic lifting body spacecraft with variable sweep wings
Space shuttle: MSFC booster (B-005) low speed static stability and landing investigation, high speed grit study
An experimental wind tunnel investigation on the Marshall Space Flight Center's (MSFC) booster configuration of the space shuttle system is discussed. Tests were conducted in the MSFC 14" x 14" trisonic wind tunnel. Parameters investigated include; (1) a landing study at Mach number of .3 with the booster at three discrete heights above a ground plane (maximum height above ground plane was six inches) and: (2) a static stability study at subsonic Mach numbers, which included eleven deflections of 0, 10, 20 and 30 degrees with canard deflections of 0, 5, 10 and 15 degrees. Both a trapezoidial and a delta shaped canard were investigated at the above conditions; a grit size study was made over the entire Mach range from .3 to 5.0.
Aerodynamic investigations into various low speed L/D improvement devices on the 140A/B space shuttle orbiter configuration in the Rockwell International low speed wind tunnel (OA86)
Tests were conducted to investigate various base drag reduction techniques in an attempt to improve Orbiter lift-to-drag ratios and to calculate sting interference effects on the Orbiter aerodynamic characteristics. Test conditions and facilites, and model dimensional data are presented along with the data reduction guidelines and data set/run number collation used for the studies. Aerodynamic force and moment data and the results of stability and control tests are also given.
Balancing of high speed interconnect shafting for operation above multiple bending critical speeds
The present work first reviews the key elements of rotating system dynamics which are crucial to the control of lateral vibration levels for supercritical shafting of the type which is considered for use in advanced aircraft applications. Then the results of an analytical investigation of procedures for balancing flexible shafts designed for critical operation are discussed. Some of the conclusions made were: (1) even in undamped configuration, reasonably low vibration levels can be achieved through a sequential multiplane-multispeed balancing process; and (2) combination of analytical response and balancing prediction procedures yields a powerful tool for the dynamic analysis and design of advanced shaft-bearing systems.