Shams Q.A.,NASA |
Zuckerwar A.J.,ASM Corporation |
Burkett C.G.,ASM Corporation |
Weistroffer G.R.,ASM Corporation |
Hugo D.R.,Rochester Institute of Technology
Journal of the Acoustical Society of America | Year: 2013
Clear air turbulence (CAT) is the leading cause of in-flight injuries and in severe cases can result in fatalities. The purpose of this work is to design and develop an infrasonic array network for early warning of clear air turbulence. The infrasonic system consists of an infrasonic three-microphone array, compact windscreens, and data management system. Past experimental efforts to detect acoustic emissions from CAT have been limited. An array of three infrasonic microphones, operating in the field at NASA Langley Research Center, on several occasions received signals interpreted as infrasonic emissions from CAT. Following comparison with current lidar and other past methods, the principle of operation, the experimental methods, and experimental data are presented for case studies and confirmed by pilot reports. The power spectral density of the received signals was found to fit a power law having an exponent of -6 to -7, which is found to be characteristics of infrasonic emissions from CAT, in contrast to findings of the past. © 2013 U.S. Government.
Allen A.,NASA |
Przekop A.,ASM Corporation
41st International Congress and Exposition on Noise Control Engineering 2012, INTER-NOISE 2012 | Year: 2012
A lighter, more robust airframe design is required to withstand the loading inherent to next generation non-cylindrical commercial airliners. The Pultruded Rod Stitched Efficient Unitized Structure concept, a highly integrated composite design involving a stitched and co-cured substructure, has been developed to meet such requirements. While this structure has been shown to meet the demanding out-of-plane loading requirements of the flat-sided pressurized cabin design, there are concerns that the stiff co-cured details will result in relatively high acoustic radiation efficiencies at frequencies well below the thin skin acoustic coincidence frequency. To address this concern and establish a set of baseline vibroacoustic characteristics, a representative test panel was fabricated and a suite of tests were conducted that involved measurements of panel vibration and radiated sound power during point force and diffuse acoustic field excitations. Experimental results are shown and compared with Finite Element and Statistical Energy Analysis model predictions through the use of modal and energy correlation techniques among others. The behavior of the structure subject to turbulent boundary layer excitation is also numerically examined.
Nayani S.N.,ASM Corporation |
51st AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition 2013 | Year: 2013
Grid modification methods have been under development at NASA to enable better predictions of low boom pressure signatures from supersonic aircraft. As part of this effort, two new codes, Stretched and Sheared Grid - Modified (SSG) and Boom Grid (BG), have been developed in the past year. The CFD results from these codes have been compared with ones from the earlier grid modification codes Stretched and Sheared Grid (SSGRID) and Mach Cone Aligned Prism (MCAP) and also with the available experimental results. NASA's unstructured grid suite of software TetrUSS and the automatic sourcing code AUTOSRC were used for base grid generation and flow solutions. The BG method has been evaluated on three wind tunnel models. Pressure signatures have been obtained up to two body lengths below a Gulfstream aircraft wind tunnel model. Good agreement with the wind tunnel results have been obtained for both on-track and off-track (up to 53 degrees) cases. On-track pressure signatures up to ten body lengths below a Straight Line Segmented Leading Edge (SLSLE) wind tunnel model have been extracted. Good agreement with the wind tunnel results have been obtained. Pressure signatures have been obtained at 1.5 body lengths below a Lockheed Martin aircraft wind tunnel model. Good agreement with the wind tunnel results have been obtained for both on-track and off-track (up to 40 degrees) cases. Grid sensitivity studies have been carried out to investigate any grid size related issues. Methods have been evaluated for fully turbulent, mixed laminar/turbulent and fully laminar flow conditions. © 2013 by the American Institute of Aeronautics and Astronautics, Inc.
Min J.B.,NASA |
Xue D.,ASM Corporation |
Shi Y.,ASM Corporation
Composite Structures | Year: 2014
A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens. © 2014.
Sivakumar R.,ASM Corporation
OCEANS 2012 MTS/IEEE: Harnessing the Power of the Ocean | Year: 2012
This paper describes the unique and versatile properties of AeroKret coating developed, manufactured, and marketed by AS&M Inc, and its diverse applications with emphasis on marine industry. © 2012 IEEE.
Campbell R.L.,NASA |
Nayani S.N.,ASM Corporation
53rd AIAA Aerospace Sciences Meeting | Year: 2015
An evaluation of two methods for improving the process for generating unstructured CFD grids for sonic boom analysis and design has been conducted. The process involves two steps: the generation of an inner core grid using a conventional unstructured grid generator such as VGRID, followed by the extrusion of a sheared and stretched collar grid through the outer boundary of the core grid. The first method evaluated, known as COB, automatically creates a cylindrical outer boundary definition for use in VGRID that makes the extrusion process more robust. The second method, BG, generates the collar grid by extrusion in a very efficient manner. Parametric studies have been carried out and new options evaluated for each of these codes with the goal of establishing guidelines for best practices for maintaining boom signature accuracy with as small a grid as possible. In addition, a preliminary investigation examining the use of the CDISC design method for reducing sonic boom utilizing these grids was conducted, with initial results confirming the feasibility of a new remote design approach. © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Hutcheson F.V.,NASA |
Brooks T.F.,NASA |
Burley C.L.,NASA |
Bahr C.J.,NASA |
And 2 more authors.
20th AIAA/CEAS Aeroacoustics Conference | Year: 2014
The results of an experimental study on the effects of engine placement and vertical tail configuration on shielding of exhaust broadband noise radiation are presented. This study is part of the high fidelity aeroacoustic test of a 5.8% scale Hybrid Wing Body (HWB) aircraft configuration performed in the 14- by 22-Foot Subsonic Tunnel at NASA Langley Research Center. Broadband Engine Noise Simulators (BENS) were used to determine insertion loss due to shielding by the HWB airframe of the broadband component of turbomachinery noise for different airframe configurations and flight conditions. Acoustics data were obtained from flyover and sideline microphones traversed to predefined streamwise stations. Noise measurements performed for different engine locations clearly show the noise benefit associated with positioning the engine nacelles further upstream on the HWB centerbody. Positioning the engine exhaust 2.5 nozzle diameters upstream (compared to 0.5 nozzle diameters downstream) of the HWB trailing edge was found of particular benefit in this study. Analysis of the shielding performance obtained with and without tunnel flow show that the effectiveness of the fuselage shielding of the exhaust noise, although still significant, is greatly reduced by the presence of the free stream flow compared to static conditions. This loss of shielding is due to the turbulence in the model near-wake/boundary layer flow. A comparison of shielding obtained with alternate vertical tail configurations shows limited differences in level; nevertheless, overall trends regarding the effect of cant angle and vertical location are revealed. Finally, it is shown that the vertical tails provide a clear shielding benefit towards the sideline while causing a slight increase in noise below the aircraft.
Zuckerwar A.J.,ASM Corporation
Journal of the Acoustical Society of America | Year: 2010
The principle of the compact nonporous windscreen is based on the great penetrability of infrasound through matter. The windscreen performance is characterized by the ratio of the sound pressure at an interior microphone, located in the center of a windscreen, to the incident sound pressure in the free field. The frequency dependence of this pressure ratio is derived as a function of the windscreen material and geometric properties. Four different windscreen geometries are considered: a subsurface, box-shaped windscreen, a cylindrical windscreen of infinite length, a cylindrical windscreen of finite length, and a spherical windscreen. Results are presented for windscreens made of closed-cell polyurethane foam and for typical dimensions of each of the above geometries. The cylindrical windscreen of finite length, featuring evanescent radial modes, behaves as a unity-gain, low-pass filter, cutting off sharply at the end of the infrasonic range. The remaining geometries reveal a pass band that extends well into the audio range, terminated by a pronounced peak beyond which the response plummets rapidly. © 2010 Acoustical Society of America.
Przekop A.,ASM Corporation |
Guo X.,Daniel Webster College |
Journal of Sound and Vibration | Year: 2012
Three procedures to guide selection of an efficient modal basis in a nonlinear random response analysis are examined. One method is based only on proper orthogonal decomposition, while the other two additionally involve smooth orthogonal decomposition. Acoustic random response problems are employed to assess the performance of the three modal basis selection approaches. A thermally post-buckled beam exhibiting snap-through behavior, a shallowly curved arch in the auto-parametric response regime and a plate structure are used as numerical test articles. The results of a computationally taxing full-order analysis in physical degrees of freedom are taken as the benchmark for comparison with the results from the three reduced-order analyses. For the cases considered, all three methods are shown to produce modal bases resulting in accurate and computationally efficient reduced-order nonlinear simulations. © 2012 Elsevier Ltd.
PubMed | Yale University, ASM Corporation and Eastern Virginia Medical School
Type: Journal Article | Journal: Military medicine | Year: 2017
A cohort of 207 veterans admitted to a residential substance use treatment program was followed for 5 years following discharge to determine factors associated with reduced relapse or mortality following discharge. Subsequent utilization of medical and psychiatric hospitalization and emergency room utilization was also examined. Retrospective chart review was conducted using demographic, diagnostic, and prior treatment as independent variables. Dependent variables included aftercare compliance and subsequent morbidity as measured by relapse, emergency room visits, subsequent hospitalizations, and mortality. Cox proportional hazards models were used to examine factors associated with relapse and mortality. Aftercare attendance was higher in those who completed treatment (p < 0.01). Factors associated with higher risk of relapse included comorbid disorders, failure to complete the index residential substance use treatment program, and psychiatric rehospitalization. Factors associated with higher mortality included failure to complete residential substance use treatment, longer medical rehospitalization, and nicotine dependence. Longer psychiatric rehospitalization was associated with a lower risk of mortality. Comorbid psychiatric conditions and failure to complete residential substance use treatment were associated with higher relapse. Limitations include that this population has severe substance use disorder, that subjective report of symptom severity was not assessed and that attendance at Alcoholics Anonymous aftercare was not surveyed.