scholarly journals Optical and acoustical measurement of ballistic noise signatures

2021 ◽  
Author(s):  
Matthew Blevins ◽  
Gregory Lyons ◽  
Carl Hart ◽  
Michael White
Keyword(s):  
Acoustic Waves ◽  
Preliminary Analysis ◽  
Imaging System ◽  
Pressure Sensors ◽  
Physical Mechanisms ◽  
Ballistic Projectiles ◽  
Localization And Tracking ◽  
Ongoing Project ◽  
Experimental Effort ◽  
The U.S

Supersonic projectiles in air generate acoustical signatures that are fundamentally related to the projectile’s shape, size, and velocity. These characteristics influence various mechanisms involved in the generation, propagation, decay, and coalescence of acoustic waves. To understand the relationships between projectile shape, size, velocity, and the physical mechanisms involved, an experimental effort captured the acoustic field produced by a range of supersonic projectiles using both conventional pressure sensors and a schlieren imaging system. The results of this ongoing project will elucidate those fundamental mechanisms, enabling more sophisticated tools for detection, classification, localization, and tracking. This paper details the experimental setup, data collection, and preliminary analysis of a series of ballistic projectiles, both idealized and currently in use by the U.S. Military.

Meddling in the Ballot Box

2020 ◽  
Author(s):  
Dov H. Levin
Keyword(s):  
Statistical Analysis ◽  
Theoretical Model ◽  
Preliminary Analysis ◽  
Great Powers ◽  
Archival Research ◽  
Micro Level ◽  
Election Results ◽  
Level Analysis ◽  
The U.S ◽  
Scholarly Attention

This book examines why partisan electoral interventions occur as well as their effects on the election results in countries in which the great powers intervened. A new dataset shows that the U.S. and the USSR/Russia have intervened in one out of every nine elections between 1946 and 2000 in other countries in order to help or hinder one of the candidates or parties; the Russian intervention in the 2016 U.S. elections is just the latest example. Nevertheless, electoral interventions receive scant scholarly attention. This book develops a new theoretical model to answer both questions. It argues that electoral interventions are usually “inside jobs,” occurring only if a significant domestic actor within the target wants it. Likewise, electoral interventions won’t happen unless the intervening country fears its interests are endangered by another significant party or candidate with very different and inflexible preferences. As for the effects it argues that such meddling usually gives a significant boost to the preferred side, with overt interventions being more effective than covert ones in this regard. However, unlike in later elections, electoral interventions in founding elections usually harm the aided side. A multi-method framework is used in order to study these questions, including in-depth archival research into six cases in which the U.S. seriously considered intervening, the statistical analysis of the aforementioned dataset (PEIG), and a micro-level analysis of election surveys from three intervention cases. It also includes a preliminary analysis of the Russian intervention in the 2016 U.S. elections and the cyber-future of such meddling in general.

scholarly journals Spectral broadening of acoustic waves by convected vortices

2018 ◽  
Vol 841 ◽  
pp. 50-80 ◽  
Author(s):  
Vincent Clair ◽  
Gwénaël Gabard
Keyword(s):  
Scattered Field ◽  
Acoustic Waves ◽  
Acoustic Scattering ◽  
Two Dimensions ◽  
Wind Tunnels ◽  
Spectral Broadening ◽  
Sound Fields ◽  
Physical Mechanisms ◽  
Doppler Shifts ◽  
Acoustic Spectra

The scattering of acoustic waves by a moving vortex is studied in two dimensions to bring further insight into the physical mechanisms responsible for the spectral broadening caused by a region of turbulence. When propagating through turbulence, a monochromatic sound wave will be scattered over a range of frequencies, resulting in typical spectra with broadband sidelobes on either side of the tone. This spectral broadening, also called ‘haystacking’, is of importance for noise radiation from jet exhausts and for acoustic measurements in open-jet wind tunnels. A semianalytical model is formulated for a plane wave scattered by a vortex, including the influence of the convection of the vortex. This allows us to perform a detailed parametric study of the properties and evolution of the scattered field. A time-domain numerical model for the linearised Euler equations is also used to consider more general sound fields, such as that radiated by a point source in a uniform flow. The spectral broadening stems from the combination of the spatial scattering of sound due to the refraction of waves propagating through the vortex, and two Doppler shifts induced by the motion of the vortex relative to the source and of the observer relative to the vortex. The fact that the spectrum exhibits sidebands is directly explained by the directivity of the scattered field which is composed of several beams radiating from the vortex. The evolution of the acoustic spectra with the parameters considered in this paper is compared with the trends observed in previous experimental work on acoustic scattering by a jet shear layer.

Direct Visualization of Acoustic Waves Propagating Within a Single Anisotropic Crystalline Plate with Hybrid Acoustic Imaging System

2012 ◽  
Vol 23 (4) ◽  
pp. 197-206 ◽  
Author(s):  
Chiaki Miyasaka ◽  
Kenneth L. Telschow ◽  
Bernhard R. Tittmann ◽  
Jeffry T. Sadler ◽  
Ik Keun Park
Keyword(s):  
Acoustic Waves ◽  
Imaging System ◽  
Acoustic Imaging ◽  
Direct Visualization

Empirical Eigenfunctions and Medial Surface Dynamics of a Human Vocal Fold

2005 ◽  
Vol 44 (03) ◽  
pp. 384-391 ◽  
Author(s):  
N. Tayama ◽  
D. A. Berry ◽  
M. Döllinger
Keyword(s):  
Vocal Fold ◽  
High Speed ◽  
Computational Models ◽  
Imaging System ◽  
Vocal Folds ◽  
Sustained Oscillation ◽  
Medial Surface ◽  
Physical Mechanisms ◽  
Vocal Fold Vibration ◽  
Modes Of Vibration

Summary Objectives: The purpose of this investigation was to use an excised human larynx to substantiate physical mechanisms of sustained vocal fold oscillation over a variety of phonatory conditions. During sustained, flow-induced oscillation, dynamical data was collected from the medial surface of the vocal fold. The method of Empirical Eigenfunctions was used to analyze the data and to probe physical mechanisms of sustained oscillation. Methods: Thirty microsutures were mounted on the medial margin of a human vocal fold. Across five distinct phonatory conditions, the vocal fold was set into oscillation and imaged with a high-speed digital imaging system. The position coordinates of the sutures were extracted from the images and converted into physical coordinates. Empirical Eigenfunctions were computed from the time-varying physical coordinates, and mechanisms of sustained oscillation were explored. Results: Using the method of Empirical Eigenfunctions, physical mechanisms of sustained vocal fold oscillation were substantiated. In particular, the essential dynamics of vocal fold vibration were captured by two dominant Empirical Eigenfunctions. The largest Eigenfunction primarily captured the alternating convergent/ divergent shape of the medial surface of the vocal fold, while the second largest Eigenfunction primarily captured the lateral vibrations of the vocal fold. Conclusions: The hemi-larynx setup yielded a view of the medial surface of the vocal folds, revealing the tissue vibrations which produced sound. Through the use of Empirical Eigenfunctions, the underlying modes of vibration were computed, disclosing physical mechanisms of sustained vocal fold oscillation. The investigation substantiated previous theoretical analyses and yielded significant data to help evaluate and refine computational models of vocal fold vibration.

Numerical and Experimental Research on a Podded Propulsor

2014 ◽  
Author(s):  
Mohammed Islam ◽  
Ron Ryan ◽  
David Molynuex
Keyword(s):  
Preliminary Analysis ◽  
Numerical Study ◽  
Open Water ◽  
Navier Stokes ◽  
Experimental Program ◽  
Propulsive Performance ◽  
Podded Propulsor ◽  
Thrust And Torque ◽  
Straight Ahead ◽  
Experimental Effort

This paper presents methodologies and some results of a numerical and experimental program to evaluate the effects of static azimuthing conditions on the propulsive characteristics of a puller podded propulsor in open water. In the experimental effort, the model propulsor was instrumented to measure thrust, torque and rotational speed of the propeller, and three orthogonal forces and moments, and azimuthing angle of the pod. The experimental results included the bare propeller (ahead only) and the combined propeller and pod over a range of advance coefficients at various static azimuthing angles in the range of −180° to 180°. A complementary numerical study is being carried out to predict the hydrodynamic forces of podded propulsor in static azimuthing conditions. A Reynolds-Averaged Navier Stokes solver is used to predict the propulsive performance of the bare propeller as well as the podded propulsor system. The thrust and torque for the bare propeller were compared to the corresponding measurements. The propeller thrust and torque as well as the loads on the pod in straight-ahead condition and at static azimuthing angles were then compared with the measurements. Preliminary analysis demonstrates that the RANS solver could predict the performance coefficients of the bare propeller as well as the podded propulsor in straight-ahead and static azimuthing angles in puller configurations.

scholarly journals Multi-objective source scaling experiment

2021 ◽  
Author(s):  
D. Costley ◽  
Luis De Jesús Díaz, ◽  
Sarah McComas ◽  
Christopher Simpson ◽  
James Johnson ◽  
...  
Keyword(s):  
Shock Wave ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Engineer Research ◽  
Different Types ◽  
Source Scaling ◽  
Explosive Charges ◽  
A Site ◽  
Development Center ◽  
The U.S

The U.S. Army Engineer Research and Development Center (ERDC) performed an experiment at a site near Vicksburg, MS, during May 2014. Explosive charges were detonated, and the shock and acoustic waves were detected with pressure and infrasound sensors stationed at various distances from the source, i.e., from 3 m to 14.5 km. One objective of the experiment was to investigate the evolution of the shock wave produced by the explosion to the acoustic wavefront detected several kilometers from the detonation site. Another objective was to compare the effectiveness of different wind filter strategies. Toward this end, several sensors were deployed near each other, approximately 8 km from the site of the explosion. These sensors used different types of wind filters, including the different lengths of porous hoses, a bag of rocks, a foam pillow, and no filter. In addition, seismic and acoustic waves produced by the explosions were recorded with seismometers located at various distances from the source. The suitability of these sensors for measuring low-frequency acoustic waves was investigated.

Determination and Comparison of the Dynamic Characteristics of a Perfectly Premixed Flame in Both Single and Annular Combustion Chambers

2008 ◽  
Author(s):  
Dan Fanaca ◽  
Panduranga Reddy Alemela ◽  
Florian Ettner ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer ◽  
...  
Keyword(s):  
Pressure Sensors ◽  
Operating Conditions ◽  
Model Parameters ◽  
Test Rig ◽  
Combustion Chambers ◽  
Physical Constraints ◽  
Dynamical Characteristics ◽  
Annular Combustor ◽  
Novel Model ◽  
Experimental Effort

In this paper we apply a new method to obtain the dynamical characteristics of premixed flames in acoustically complex systems like an annular combustor. For this a novel model based reduction method was applied which describes the acoustic field as a superposition of a discrete number of eigenmodes. The measured dynamic signals are decomposed into modal components which are then used to fit the model parameters. With this approach the complete characterisation of the annular test rig requires significantly less experimental effort, i.e. simultaneous pressure measurements, than before. After describing the new procedure, we show the validation of the acoustical model. Using this model, we were able to obtain the characteristics of the flame in the annular combustor with a much smaller number of pressure sensors as the model provides physical constraints that would otherwise have to be measured. The comparison of the characteristic flame parameters between the single burner and the annular combustor configurations for the same operating conditions shows that in the annular combustor slightly longer convective time delays are found which are consistent with the static flame characterisation showing longer flames in the annular combustor than in the single burner test rig.

scholarly journals Generalized laws of refraction and reflection at interfaces between different photonic artificial gauge fields

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Moshe-Ishay Cohen ◽  
Christina Jörg ◽  
Yaakov Lumer ◽  
Yonatan Plotnik ◽  
Erik H. Waller ◽  
...  
Keyword(s):  
Acoustic Waves ◽  
Total Internal Reflection ◽  
Cold Atoms ◽  
Imaging System ◽  
Gauge Fields ◽  
Reflection And Transmission ◽  
System A ◽  
Snell Law ◽  
Potential Landscape ◽  
Artificial Gauge Fields

AbstractArtificial gauge fields the control over the dynamics of uncharged particles by engineering the potential landscape such that the particles behave as if effective external fields are acting on them. Recent years have witnessed a growing interest in artificial gauge fields generated either by the geometry or by time-dependent modulation, as they have been enablers of topological phenomena and synthetic dimensions in many physical settings, e.g., photonics, cold atoms, and acoustic waves. Here, we formulate and experimentally demonstrate the generalized laws of refraction and reflection at an interface between two regions with different artificial gauge fields. We use the symmetries in the system to obtain the generalized Snell law for such a gauge interface and solve for reflection and transmission. We identify total internal reflection (TIR) and complete transmission and demonstrate the concept in experiments. In addition, we calculate the artificial magnetic flux at the interface of two regions with different artificial gauge fields and present a method to concatenate several gauge interfaces. As an example, we propose a scheme to make a gauge imaging system—a device that can reconstruct (image) the shape of an arbitrary wavepacket launched from a certain position to a predesigned location.

The Physical Mechanisms by Which the Leading Patterns of SST Variability Impact U.S. Precipitation

2010 ◽  
Vol 23 (7) ◽  
pp. 1815-1836 ◽  
Author(s):  
Hailan Wang ◽  
Siegfried Schubert ◽  
Max Suarez ◽  
Randal Koster
Keyword(s):  
United States ◽  
Gulf Of Mexico ◽  
Great Plains ◽  
Moisture Transport ◽  
Diabatic Heating ◽  
Moisture Flux ◽  
Physical Mechanisms ◽  
Sst Variability ◽  
Precipitation Response ◽  
The U.S

Abstract This study uses the NASA Seasonal-to-Interannual Prediction Project (NSIPP-1) AGCM to investigate the physical mechanisms by which the leading patterns of annual mean SST variability impact U.S. precipitation. The focus is on a cold Pacific pattern and a warm Atlantic pattern that exert significant drought conditions over the U.S. continent. The precipitation response to the cold Pacific is characterized by persistent deficits over the Great Plains that peak in summer with a secondary peak in spring, and weakly pluvial conditions in summer over the Southeast (SE). The precipitation response to the warm Atlantic is dominated by persistent deficits over the Great Plains with the maximum deficit occurring in late summer. The precipitation response to the warm Atlantic is overall similar to the response to the cold Pacific with, however, considerably weaker amplitude. An analysis of the atmospheric moisture budget combined with a stationary wave model diagnosis of the associated atmospheric circulation anomalies is conducted to investigate mechanisms of the precipitation responses. A key result is that, while the cold Pacific and warm Atlantic are two spatially distinct SST patterns, they nevertheless produce similar diabatic heating anomalies over the Gulf of Mexico during the warm season. In the case of the Atlantic forcing, the heating anomalies are a direct response to the SST anomalies, whereas in the case of Pacific forcing they are a secondary response to circulation anomalies forced from the tropical Pacific. The diabatic heating anomalies in both cases force an anomalous low-level cyclonic flow over the Gulf of Mexico that leads to reduced moisture transport into the central United States and increased moisture transport into the eastern United States. The precipitation deficits over the Great Plains in both cases are greatly amplified by the strong soil moisture feedback in the NSIPP-1 AGCM. In contrast, the response over the SE to the cold Pacific during spring is primarily associated with an upper-tropospheric high anomaly over the southern United States that is remotely forced by tropical Pacific diabatic heating anomalies, leading to greatly reduced stationary moisture flux convergences and anomalous subsidence in that region. Moderately reduced evaporation and weakened transient moisture flux convergences play secondary roles. It is only during spring that these three terms are all negative and constructively contribute to produce the maximum dry response in spring. The above findings based on the NSIPP-1 AGCM are generally consistent with observations, as well as with four other AGCMs included in the U.S. Climate Variability and Predictability (CLIVAR) project.

Digitization as Adaptation

2002 ◽  
pp. 227-237
Author(s):  
Steven K. Wyman ◽  
Verne McFarland
Keyword(s):  
World Wide ◽  
Imaging System ◽  
Systems Development ◽  
Life Cycles ◽  
Document Management ◽  
Regional Office ◽  
Document Management System ◽  
External Pressures ◽  
Key Aspects ◽  
The U.S

In 1994, the U.S. Environmental Protection Agency’s Superfund Program began to develop a paper imaging system known as the Superfund Document Management System (SDMS). SDMS came into being as an attempt to improve management of and access to Agency records. An Agency workgroup composed primarily of Superfund records managers developed functional criteria for the application, and elected an Agency regional office for implementation pilot. At the time of this writing all EPA Superfund regional offices have implemented SDMS. For reasons described in this chapter, even as SDMS achieved institutional acceptance it faced pressures to adapt to internal and external pressures. The emergence of the World Wide Web, the inevitability of electronic records, the rising costs of maintaining large paper collections all combined to produce a niche different in key aspects from that which the system was originally designed to occupy. This chapter discusses how the interactions of two life cycles — records and systems development — affected the fitness of the system to its environment.

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