178 research outputs found
Development of composite calibration standard for quantitative NDE by ultrasound and thermography
No full textInspection of aircraft components for damage utilizing ultrasonic Non-Destructive Evaluation (NDE) is a time intensive endeavor. Additional time spent during aircraft inspections translates to added cost to the company performing them, and as such, reducing this expenditure is of great importance. There is also great variance in the calibration samples from one entity to another due to a lack of a common calibration set. By characterizing damage types, we can condense the required calibration sets and reduce the time required to perform calibration while also providing procedures for the fabrication of these standard sets. We present here our effort to fabricate composite samples with known defects and quantify the size and location of defects, such as delaminations, and impact damage. Ultrasonic and Thermographic images are digitally enhanced to accurately measure the damage size. Ultrasonic NDE is compared with thermography.This proceeding may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.
This proceeding appeared in Dayal, Vinay, Zach G. Benedict, Nishtha Bhatnagar, and Adam G. Harper. "Development of composite calibration standard for quantitative NDE by ultrasound and thermography." In AIP Conference Proceedings, vol. 1949, no. 1, p. 060006. AIP Publishing LLC, 2018, and may be found at
DOI: 10.1063/1.5031552.
Copyright 2018 The Author(s).
Posted with permission
Universal Statistical Properties of Inertial-particle Trajectories in Three-dimensional, Homogeneous, Isotropic, Fluid Turbulence
No full textWe obtain new universal statistical properties of heavy-particle trajectories in three-dimensional, statistically steady, homogeneous, and isotropic turbulent flows by direct numerical simulations. We show that the probability distribution functions (PDFs) P(Φ), of the angle Φ between the Eulerian velocity u and the particle velocity v, at a point and time, scales as P(Φ) ∼Φ−, with a new universal exponent ≃ 4
Performance and hardware complexity analysis of programmable radio platform for MIMO OFDM based WLAN systems
No full textEmerging wireless technologies and standards present a design space with multiple dimensions in terms of time, physical hardware space, and technology trends. Efficient evaluation of a desired combination of these dimensions to support multiple technologies and standards presents a significant challenge. We study the feasibility of a multiprotocol architecture without sacrificing the Quality of Service. An architecture facilitating such a mechanism can be implemented at different layers in the network stack with each layer offering a tradeoff between complexity and latency. Careful analysis of the physical layer reveals that most blocks of the transceiver can be reused for different protocols without significant architectural change. In addition to the feasibility analysis, we also identify common blocks in the network stack that could be possibly reused buying us significant hardware gains without sacrificing the aggregate system throughput. Our study presents the gate count complexity and the performance analysis of programmable radio architecture with the 802.11n (Draft 3.0) MIMO-OFDM based protocol stream and 802.11a OFDM based WLAN protocol stream. In this thesis, we demonstrate that multiple protocols can be supported using the same hardware under acceptable latency requirements. Complexity of the system in terms of gate count has been determined. It has been found that for shorter frame sizes, it is better to process less number of OFDM symbols at a time. However, for larger frame sizes, it is beneficial to process large number (four to eight) of OFDM symbols at a time. Also, the minimum clock rate required to run the hardware, would vary depending upon the number of OFDM Symbols processed. The switching and multiplexing overhead of the programmable radio platform has also been investigated. Finally, our simulator is capable of evaluating bottlenecks, if any.M.S.Includes bibliographical references (p. 75-76)
Flea outbreak at United Nations base in South Sudan: A public health challenge
No full textBackground: A large number Indian troops are deployed in International Peacekeeping Missions Worldwide and are exposed to emerging and re-emerging vectors and diseases in unfamiliar terrain. This article describes the experience of a flea outbreak among Indian UN Peacekeepers in a remote part of South Sudan. Methods: Health visits to the area confirmed presence of dog fleas. Flea bites disrupted daily routine of the unit and many troopers reported to medical facilities with severe dermatitis. Death of a field rat in the immediate vicinity along with detection of rat fleas was cause for worry as Plague and other flea-borne diseases are known to occur in the country in sylvatic form. Result: Conventional vector control measures had limited impact and unconventional measures had to be devised due to limited capacity in the inaccessible area. Severity of the problem, potential to cause flea-borne diseases and unavailability of conventional insecticides prompted the author to use Aviation Turbine Fuel (ATF) for area spray in the UN base. Conclusion: Healthcare providers in fast-evolving operational situations such as Peacekeeping Missions need to maintain high index of suspicion and often adopt innovative methods to ensure effective public health cover to troops
Collisions among elongated settling particles: The twofold role of turbulence
No full textWe study the collision rates of settling spheres and elongated spheroids in homogeneous, isotropic turbulence by means of direct numerical simulations aiming to understand microscale-particle encounters in oceans and lakes. We explore a range of aspect ratios and sizes relevant to the dynamics of plankton and microplastics in water environments. The results presented here confirm that collision rates between elongated particles in a quiescent fluid are more frequent than those among spherical particles in turbulence due to oblique settling. We also demonstrate that turbulence generally enhances collisions among elongated particles as compared to those expected for a random distribution of the same particles settling in a quiescent fluid, although we also find a decrease in collision rates in turbulence for particles of the highest density and moderate aspect ratios (A = 5). The increase in the collision rate due to turbulence is found to quickly decrease with aspect ratio, reach a minimum for aspect ratios approximately equal to 5, and then slowly increase again, with an increase up to 50% for the largest aspect ratios investigated. This non-monotonic trend is explained as the result of two competing effects: the increase in the surface area with aspect ratio (beneficial to increase encounter rates) and the alignment of nearby prolate particles in turbulence (reducing the probability of collision). Turbulence mixing is, therefore, partially balanced by rod alignment at high particle aspect ratios.(c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/)
A modified lattice Bhatnagar-Gross-Krook model for convection heat transfer in porous media
No full textThe lattice Bhatnagar-Gross-Krook (LBGK) model has become the most popular one in the lattice Boltzmann method for simulating the convection heat transfer in porous media. However, the LBGK model generally suffers from numerical instability at low fluid viscosity and effective thermal diffusivity. In this paper, a modified LBGK model, which incorporates the shear rate and temperature gradient in the equilibrium distribution functions, is developed for incompressible thermal flows in porous media at the representative elementary volume scale. With two additional parameters, the relaxation times in the collision process can be fixed at a proper value invariable to the viscosity and the effective thermal diffusivity. In addition, by constructing a modified equilibrium distribution function and a source term in the evolution equation of temperature field, the present model can recover the macroscopic equations correctly through the Chapman-Enskog analysis, which is another key point different from previous LBGK models. Several benchmark problems are simulated to validate the present model with the local computing scheme for the shear rate and temperature gradient, and the numerical results agree well with analytical solutions and/or those well-documented data in previous studies. It is also shown that the present model and the computational schemes for the gradient operators have a second-order accuracy in space, and better numerical stability of the present modified LBGK model than previous LBGK models is demonstrated. (C) 2015 Elsevier Ltd. All rights reserved.National Natural Science Foundation of China [51125024, 51390494]SCI(E)[email protected]
The exponential series: an addendum
No full textIn the accompanying article, the author
(Gaurav Bhatnagar) presents a heuristic derivation
of the well-known series for the exponential function
Physics-informed neural networks for rarefied-gas dynamics: Thermal creep flow in the Bhatnagar–Gross–Krook approximation
No full textThis work aims at accurately solve a thermal creep flow in a plane channel problem, as a class of rarefied-gas dynamics problems, using Physics-Informed Neural Networks (PINNs). We develop a particular PINN framework where the solution of the problem is represented by the Constrained Expressions (CE) prescribed by the recently introduced Theory of Functional Connections (TFC). CEs are represented by a sum of a free-function and a functional (e.g., function of functions) that analytically satisfies the problem constraints regardless to the choice of the free-function. The latter is represented by a shallow Neural Network (NN). Here, the resulting PINN-TFC approach is employed to solve the Boltzmann equation in the Bhatnagar-Gross-Krook approximation modeling the Thermal Creep Flow in a plane channel. We test three different types of shallow NNs, i.e., standard shallow NN, Chebyshev NN (ChNN), and Legendre NN (LeNN). For all the three cases the unknown solutions are computed via the extreme learning machine algorithm. We show that with all these networks we can achieve accurate solutions with a fast training time. In particular, with ChNN and LeNN we are able to match all the available benchmarks. © 2021 Author(s).12 month embargo; published online: 21 April 2021This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Providing Quality of Service Guarantees Using Only Edge Routers
No full textProviding strict bandwidth guarantees to packet flows in the Internet is an inherently challenging task. It requires signaling mechanisms, policing mechanisms, accurate and rapid accounting of network resources, and call admission control. We present a novel protocol that provides bandwidth guarantees to Internet packet flows. This protocol, called the Edge-assisted Quality of Service (EQOS) protocol, requires modifications to only a subset of an administrative domain’s routers, namely the edge routers on the domain’s periphery. Legacy routers within the core of the domain require no modifications. We present the results of several simulation experiments showing that EQOS is able to provide bandwidth guarantees to competing flows.Technical report DCS-TR-42
- …
