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  • 1
    Publication Date: 2022-05-25
    Description: Author Posting. © IEEE, 2015. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Ocean Engineering 40 (2015): 237-249, doi:10.1109/JOE.2013.2294291.
    Description: A study of sound propagation over a submarine canyon northeast of Taiwan was made using mobile acoustic sources during a joint ocean acoustic and physical oceanographic experiment in 2009. The acoustic signal levels (equivalently, transmission losses) are reported here, and numerical models of 3-D sound propagation are employed to explain the underlying physics. The data show a significant decrease in sound intensity as the source crossed over the canyon, and the numerical model provides a physical insight into this effect. In addition, the model also suggests that reflection from the canyon seabed causes 3-D sound focusing when the direction of propagation is along the canyon axis, which remains to be validated in a future experiment. Environmental uncertainties of water sound speed, bottom geoacoustic properties, and bathymetry are addressed, and the implications for sound propagation prediction in a complex submarine canyon environment are also discussed.
    Description: The Quantifying, Predicting and Exploiting (QPE) Uncertainty Initiative Experiment was supported jointly by the National Science Council, Taiwan, under Project NSC98-2623-E002-018-D and the U.S. Office of Naval Research (ONR) under Grant N00014-08-1-0763. The work of Y.-T. Lin was supported by the U.S. ONR under Grants N00014-10-1-0040 and N00014-13-1-0026. The work of T. F. Duda was supported by the U.S. ONR under Grant N00014-11-1-0194.
    Keywords: Acoustics ; Noise ; Numerical models ; Solid modeling ; Sonar equipment ; Underwater vehicles ; Vehicles
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Nature Publishing Group (NPG)
    Publication Date: 2015-01-09
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉England -- Nature. 2015 Jan 8;517(7533):121. doi: 10.1038/517121b.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/25567245" target="_blank"〉PubMed〈/a〉
    Keywords: Acoustics ; Animals ; Chiroptera/physiology ; Echolocation/*physiology ; Female ; Humans ; Music ; Noise ; *Periodicals as Topic ; Public Health ; *Sound ; *Webcasts as Topic
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2015-08-15
    Description: Human vocal development occurs through two parallel interactive processes that transform infant cries into more mature vocalizations, such as cooing sounds and babbling. First, natural categories of sounds change as the vocal apparatus matures. Second, parental vocal feedback sensitizes infants to certain features of those sounds, and the sounds are modified accordingly. Paradoxically, our closest living ancestors, nonhuman primates, are thought to undergo few or no production-related acoustic changes during development, and any such changes are thought to be impervious to social feedback. Using early and dense sampling, quantitative tracking of acoustic changes, and biomechanical modeling, we showed that vocalizations in infant marmoset monkeys undergo dramatic changes that cannot be solely attributed to simple consequences of growth. Using parental interaction experiments, we found that contingent parental feedback influences the rate of vocal development. These findings overturn decades-old ideas about primate vocalizations and show that marmoset monkeys are a compelling model system for early vocal development in humans.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Takahashi, D Y -- Fenley, A R -- Teramoto, Y -- Narayanan, D Z -- Borjon, J I -- Holmes, P -- Ghazanfar, A A -- New York, N.Y. -- Science. 2015 Aug 14;349(6249):734-8. doi: 10.1126/science.aab1058.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA. Department of Psychology, Princeton University, Princeton, NJ 08544, USA. ; Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA. ; Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA. Department of Mechanical and Aerospace Engineering and Program in Applied and Computational Mathematics, Princeton University, Princeton, NJ 08544, USA. ; Princeton Neuroscience Institute, Princeton University, Princeton, NJ 08544, USA. Department of Psychology, Princeton University, Princeton, NJ 08544, USA. Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26273055" target="_blank"〉PubMed〈/a〉
    Keywords: Acoustics ; Animals ; Biomechanical Phenomena ; Callithrix/*growth & development/physiology/psychology ; Female ; Male ; Models, Biological ; Muscle Tonus ; Vocal Cords/growth & development/physiology ; *Vocalization, Animal
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 4
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    Nature Publishing Group (NPG)
    Publication Date: 2015-12-18
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Tian, Peng -- England -- Nature. 2015 Dec 17;528(7582):S176-8. doi: 10.1038/528S176a.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26673024" target="_blank"〉PubMed〈/a〉
    Keywords: Acoustics ; Beijing ; Chemistry/statistics & numerical data ; China ; Cities/economics/*statistics & numerical data ; Research/economics/*statistics & numerical data
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 5
    Publication Date: 2019-07-19
    Description: The overpressure phenomenon is a transient fluid dynamic event occurring during rocket propulsion system ignition. This phenomenon results from fluid compression of the accelerating plume gas, subsequent rarefaction, and subsequent propagation from the exhaust trench and duct holes. The high-amplitude unsteady fluid-dynamic perturbations can adversely affect the vehicle and surrounding structure. Commonly known as ignition overpressure (IOP), this is an important design-to environment for the Space Launch System (SLS) that NASA is currently developing. Subscale testing is useful in validating and verifying the IOP environment. This was one of the objectives of the Scale Model Acoustic Test, conducted at Marshall Space Flight Center. The test data quantifies the effectiveness of the SLS IOP suppression system and improves the analytical models used to predict the SLS IOP environments. The reduction and analysis of the data gathered during the SMAT IOP test series requires identification and characterization of multiple dynamic events and scaling of the event waveforms to provide the most accurate comparisons to determine the effectiveness of the IOP suppression systems. The identification and characterization of the overpressure events, the waveform scaling, the computation of the IOP suppression system knockdown factors, and preliminary comparisons to the analytical models are discussed.
    Keywords: Acoustics
    Type: M15-4565 , Aerospace Testing Seminar; Oct 27, 2015 - Oct 29, 2015; Los Angeles, CA; United States
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  • 6
    Publication Date: 2019-07-19
    Description: Characterization of launch vehicle unsteady aerodynamics is a field best studied through experimentation, which is often carried out in the form of large scale wind tunnel testing. Measurement of the fluctuating pressures induced by the boundary layer noise is customarily made with miniature pressure transducers installed into a model of the vehicle of interest. Literature shows that noise level increases between two to five decibels (dB referenced to 20 micropascal) can be induced when the transducer surface is not mounted perfectly flush with the model outer surface. To reduce this artificially induced noise, special transducer holders have been used for aeroacoustic wind tunnel testing by NASA. This holder is a sleeve into which the transducer fits, with a cap that allows it to be mounted in a recessed hole in the model. A single hole in the holder allows the transport of the tunnel medium so the transducer can discriminate the fluctuating pressure due to the turbulent boundary layer noise. The holder is first dry fitted into the model and any difference in height between the holder and the model surface can be sanded flush. The holder is then removed from the model, the transducer glued inside the holder, and the holder replaced in the model, secured also with glue, thus eliminating the problem of noise level increases due to lack of flushness. In order to work with this holder design, special transducers have been ordered with their standard screen removed and the diaphragm moved as close to the top of the casing as possible to minimize any cavity volume. Although this greatly reduces induced noise due to the transducers being out of flush, the holders can also induce a cavity resonance that is usually at a very high frequency. This noise is termed transducer mount induced noise (XMIN). The peak of the mode can vary with the cavity depth, boundary layer noise that can excite the mode, tunnel flow medium, and the build of the transducers. Because the boundary layer flow interaction with the microphone holder seems to have some effect on the cavity resonance response, the NASA/Marshall Space Flight Center (MSFC) aeroacoustic team postulated that changing the design of the holder might reduce the cavity resonance response. An experiment was performed at the MSFC Trisonic Wind Tunnel comparing a new holder design with the traditional MSFC holder. The new holder design is intended to mimic the Kulite Semiconductors, Inc. B-screen, where the single hole of the traditional MSFC holder is replaced by a series of ten 0.007 inch diameter holes. This particular design serves to protect the transducer diaphragm as in the manufacturer's B-screen, but also increases the frequency of the XMIN such that it is not apparent in the data collected from aeroacoustic wind tunnel tests. MSFC compared the two holder designs by installing two transducers in standard holders on one side of a ten inch long ten degree cone, and two transducers in B-screen holders on the opposite side for a series of runs at different conditions. Over 11-13 February, 2013, the model was run at Mach numbers between 0.80 and 1.96 at angles of attack at 0 deg, plus or minus 1 deg, plus or minus 2 deg, plus or minus 4 deg, and plus or minus 8 deg. Model roll attitudes at 0 deg, 90 deg, and 180 deg were tested to isolate potential tunnel bias. This paper presents results from the test showing that the proposed holder design significantly reduces the influence of XMIN on measured fluctuating pressure levels.
    Keywords: Acoustics
    Type: M15-4270 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 7
    Publication Date: 2019-07-13
    Description: An empirical model for jet-surface interaction (JSI) noise produced by a round jet near a flat plate is described and the resulting model evaluated. The model covers unheated and hot jet conditions (1 less than or equal to jet total temperature ratio less than or equal to 2.7) in the subsonic range (0.5 less than or equal to M(sub a) less than or equal to 0.9), surface lengths 0.6 less than or equal to (axial distance from jet exit to surface trailing edge (inches)/nozzle exit diameter) less than or equal to 10, and surface standoff distances (0 less than or equal to (radial distance from jet lipline to surface (inches)/axial distance from jet exit to surface trailing edge (inches)) less than or equal to 1) using only second-order polynomials to provide predictable behavior. The JSI noise model is combined with an existing jet mixing noise model to produce exhaust noise predictions. Fit quality metrics and comparisons to between the predicted and experimental data indicate that the model is suitable for many system level studies. A first-order correction to the JSI source model that accounts for the effect of nozzle aspect ratio is also explored. This correction is based on changes to the potential core length and frequency scaling associated with rectangular nozzles up to 8:1 aspect ratio. However, more work is needed to refine these findings into a formal model.
    Keywords: Acoustics
    Type: GRC-E-DAA-TN19479 , SciTech 2015; Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 8
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21341 , 2015 Spring Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 9
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21243 , Acoustics Technical Working Group Meeting (ATWG 2015); Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 10
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21236 , Acoustics Technical Working Group Meeting (Acoustics TWG 2015); Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 11
    Publication Date: 2019-07-13
    Description: Analytical models have been developed to predict the sound absorption and sound transmission loss of tuned chamber core panels. The panels are constructed of two facesheets sandwiching a corrugated core. When ports are introduced through one facesheet, the long chambers within the core can be used as an array of low-frequency acoustic resonators. To evaluate the accuracy of the analytical models, absorption and sound transmission loss tests were performed on flat panels. Measurements show that the acoustic resonators embedded in the panels improve both the absorption and transmission loss of the sandwich structure at frequencies near the natural frequency of the resonators. Analytical predictions for absorption closely match measured data. However, transmission loss predictions miss important features observed in the measurements. This suggests that higher-fidelity analytical or numerical models will be needed to supplement transmission loss predictions in the future.
    Keywords: Acoustics
    Type: NF1676L-22468 , Aerospace Testing Seminar; Oct 27, 2015 - Oct 29, 2015; Los Angeles, CA; United States
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  • 12
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-22104 , APS Annual Division of Fluid Dynamics Meeting; Nov 22, 2015 - Nov 24, 2015; Boston, MA; United States
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  • 13
    Publication Date: 2019-07-13
    Description: An aircraft system noise study is presented for the Blended-Wing-Body (BWB) aircraft concept with three open rotor engines mounted on the upper surface of the airframe. It is shown that for such an aircraft, the cumulative Effective Perceived Noise Level (EPNL) is about 24 dB below the current aircraft noise regulations of Stage 4. While this makes the design acoustically viable in meeting the regulatory requirements, even with the consideration of more stringent noise regulations of a possible Stage 5 in the next decade or so, the design will likely meet stiff competitions from aircraft with turbofan engines. It is shown that the noise levels of the BWB design are held up by the inherently high noise levels of the open rotor engines and the limitation on the shielding benefit due to the practical design constraint on the engine location. Furthermore, it is shown that the BWB design has high levels of noise from the main landing gear, due to their exposure to high speed flow at the junction between the center body and outer wing. These are also the reasons why this baseline BWB design does not meet the NASA N+2 noise goal of 42 dB below Stage 4. To identify approaches that may further reduce noise, parametric studies are also presented, including variations in engine location, vertical tail and elevon variations, and airframe surface acoustic liner treatment effect. These have the potential to further reduce noise but they are only at the conceptual stage.
    Keywords: Acoustics
    Type: NF1676L-20542 , AIAA SciTech 2015; Jan 05, 2015 - Jan 08, 2015; Orlando, FL; United States
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  • 14
    Publication Date: 2019-07-13
    Description: Farassat's formulations provide an acoustic prediction at an observer location provided a source surface, including motion and flow conditions. This paper presents compact forms for the monopole term of several of Farassat's formulations. When the physical surface is elongated, such as the case of a high aspect ratio rotorcraft blade, compact forms can be derived which are shown to be a function of the blade cross sectional area by reducing the computation from a surface integral to a line integral. The compact forms of all formulations are applied to two example cases: a short span wing with constant airfoil cross section moving at three forward flight Mach numbers and a rotor at two advance ratios. Acoustic pressure time histories and power spectral densities of monopole noise predicted from the compact forms of all the formulations at several observer positions are shown to compare very closely to the predictions from their non-compact counterparts. A study on the influence of rotorcraft blade shape on the high frequency portion of the power spectral density shows that there is a direct correlation between the aspect ratio of the airfoil and the error incurred by using the compact form. Finally, a prediction of pressure gradient from the non-compact and compact forms of the thickness term of Formulation G1A shows that using the compact forms results in a 99.6% improvement in computation time, which will be critical when noise is incorporated into a design environment.
    Keywords: Acoustics
    Type: NF1676L-20080 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 15
    Publication Date: 2019-07-13
    Description: This paper explores the effects of variable-depth geometry on the amount of noise reduction that can be achieved with acoustic liners. Results for two variable-depth liners tested in the NASA Langley Grazing Flow Impedance Tube demonstrate significant broadband noise reduction. An impedance prediction model is combined with two propagation codes to predict corresponding sound pressure level profiles over the length of the Grazing Flow Impedance Tube. The comparison of measured and predicted sound pressure level profiles is sufficiently favorable to support use of these tools for investigation of a number of proposed variable-depth liner configurations. Predicted sound pressure level profiles for these proposed configurations reveal a number of interesting features. Liner orientation clearly affects the sound pressure level profile over the length of the liner, but the effect on the total attenuation is less pronounced. The axial extent of attenuation at an individual frequency continues well beyond the location where the liner depth is optimally tuned to the quarter-wavelength of that frequency. The sound pressure level profile is significantly affected by the way in which variable-depth segments are distributed over the length of the liner. Given the broadband noise reduction capability for these liner configurations, further development of impedance prediction models and propagation codes specifically tuned for this application is warranted.
    Keywords: Acoustics
    Type: NF1676L-20142 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 16
    Publication Date: 2019-07-13
    Description: This paper presents a summary of the computational predictions and measurement data contributed to Category 7 of the 3rd AIAA Workshop on Benchmark Problems for Airframe Noise Computations (BANC-III), which was held in Atlanta, GA, on June 14-15, 2014. Category 7 represents the first slat-noise configuration to be investigated under the BANC series of workshops, namely, the 30P30N two-dimensional high-lift model (with a slat contour that was slightly modified to enable unsteady pressure measurements) at an angle of attack that is relevant to approach conditions. Originally developed for a CFD challenge workshop to assess computational fluid dynamics techniques for steady high-lift predictions, the 30P30N configurations has provided a valuable opportunity for the airframe noise community to collectively assess and advance the computational and experimental techniques for slat noise. The contributed solutions are compared with each other as well as with the initial measurements that became available just prior to the BANC-III Workshop. Specific features of a number of computational solutions on the finer grids compare reasonably well with the initial measurements from FSU and JAXA facilities and/or with each other. However, no single solution (or a subset of solutions) could be identified as clearly superior to the remaining solutions. Grid sensitivity studies presented by multiple BANC-III participants demonstrated a relatively consistent trend of reduced surface pressure fluctuations, higher levels of turbulent kinetic energy in the flow, and lower levels of both narrow band peaks and the broadband component of unsteady pressure spectra in the nearfield and farfield. The lessons learned from the BANC-III contributions have been used to identify improvements to the problem statement for future Category-7 investigations.
    Keywords: Acoustics
    Type: NF1676L-20163 , AIAA Aviation Technology, Integration, and Operations Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 17
    Publication Date: 2019-07-13
    Description: The results of an experimental study of the noise generated by a baseline high-fidelity airframe model are presented. The test campaign was conducted in the open-jet test section of the NASA Langley 14- by 22-foot Subsonic Tunnel on an 18%-scale, semi-span Gulfstream airframe model incorporating a trailing edge flap and main landing gear. Unsteady surface pressure measurements were obtained from a series of sensors positioned along the two flap edges, and far field acoustic measurements were obtained using a 97-microphone phased array that viewed the pressure side of the airframe. The DAMAS array deconvolution method was employed to determine the locations and strengths of relevant noise sources in the vicinity of the flap edges and the landing gear. A Coherent Output Power (COP) spectral method was used to couple the unsteady surface pressures measured along the flap edges with the phased array output. The results indicate that outboard flap edge noise is dominated by the flap bulb seal cavity with very strong COP coherence over an approximate model-scale frequency range of 1 to 5 kHz observed between the array output and those unsteady pressure sensors nearest the aft end of the cavity. An examination of experimental COP spectra for the inboard flap proved inconclusive, most likely due to a combination of coherence loss caused by decorrelation of acoustic waves propagating through the thick wind tunnel shear layer and contamination of the spectra by tunnel background noise at lower frequencies. Directivity measurements obtained from integration of DAMAS pressure-squared values over defined geometric zones around the model show that the baseline flap and landing gear are only moderately directional as a function of polar emission angle.
    Keywords: Acoustics
    Type: NF1676L-20180 , AIAA Aviation 2015; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 18
    Publication Date: 2019-07-13
    Description: A two-dimensional impedance eduction theory is extended to three-dimensional sound fields and peripherally varying duct liners. The approach is to first measure the acoustic pressure field at a series of flush-mounted wall microphones located around the periphery of the flow duct. The numerical solution for the acoustic pressure field at these microphones is also obtained by solving the three-dimensional convected Helmholtz equation using the finite element method. A quadratic objective function based on the difference between the measured and finite element solution is constructed and the unknown impedance function is obtained by minimizing this objective function. Impedance spectra educed for two uniform-structure liners (a wire-mesh and a conventional liner) and a hard-soft-hard peripherally varying liner (for which the soft segment is that of the conventional liner) are presented. Results are presented at three mean flow Mach numbers and fourteen sound source frequencies. The impedance spectra of the uniform-structure liners are also computed using a two-dimensional impedance eduction theory. The primary conclusions of the study are: 1) when measured data is used with the uniform-structure liners, the three-dimensional theory reproduces the same impedance spectra as the two-dimensional theory except for frequencies corresponding to very low or very high liner attenuation; and 2) good agreement between the educed impedance spectra of the uniform structure conventional liner and the soft segment of the peripherally varying liner is obtained.
    Keywords: Acoustics
    Type: NF1676L-19964 , AIAA Aviation 2015; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 19
    Publication Date: 2019-07-13
    Description: Two impedance eduction methods are explored for use with data acquired in the NASA Langley Grazing Flow Impedance Tube. The first is an indirect method based on the convected Helmholtz equation, and the second is a direct method based on the Kumaresan and Tufts algorithm. Synthesized no-flow data, with random jitter to represent measurement error, are used to evaluate a number of possible microphone locations. Statistical approaches are used to evaluate the suitability of each set of microphone locations. Given the computational resources required, small sample statistics are employed for the indirect method. Since the direct method is much less computationally intensive, a Monte Carlo approach is employed to gather its statistics. A comparison of results achieved with full and reduced sets of microphone locations is used to determine which sets of microphone locations are acceptable. For the indirect method, each array that includes microphones in all three regions (upstream and downstream hard wall sections, and liner test section) provides acceptable results, even when as few as eight microphones are employed. The best arrays employ microphones well away from the leading and trailing edges of the liner. The direct method is constrained to use microphones opposite the liner. Although a number of arrays are acceptable, the optimum set employs 14 microphones positioned well away from the leading and trailing edges of the liner. The selected sets of microphone locations are also evaluated with data measured for ceramic tubular and perforate-over-honeycomb liners at three flow conditions (Mach 0.0, 0.3, and 0.5). They compare favorably with results attained using all 53 microphone locations. Although different optimum microphone locations are selected for the two impedance eduction methods, there is significant overlap. Thus, the union of these two microphone arrays is preferred, as it supports usage of both methods. This array contains 3 microphones in the upstream hard wall section, 14 microphones opposite the liner, and 3 microphones in the downstream hard wall section.
    Keywords: Acoustics
    Type: NF1676L-20029 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 20
    Publication Date: 2019-07-13
    Description: A new model for estimating the noise radiation during maneuvering flight is developed in this paper. The model applies the Quasi-Static Acoustic Mapping (Q-SAM) method to a database of acoustic spheres generated using the Fundamental Rotorcraft Acoustics Modeling from Experiments (FRAME) technique. A method is developed to generate a realistic flight trajectory from a limited set of waypoints and is used to calculate the quasi-static operating condition and corresponding acoustic sphere for the vehicle throughout the maneuver. By using a previously computed database of acoustic spheres, the acoustic impact of proposed helicopter operations can be rapidly predicted for use in mission-planning. The resulting FRAME-QS model is applied to near-horizon noise measurements collected for the Bell 430 helicopter undergoing transient pitch up and roll maneuvers, with good agreement between the measured data and the FRAME-QS model.
    Keywords: Acoustics
    Type: NF1676L-19704 , American Helicopter Society Annual Forum; May 05, 2015 - May 07, 2015; Virginia Beach, VA; United States
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  • 21
    Publication Date: 2019-07-13
    Description: An advanced form of background subtraction is presented and applied to aeroacoustic wind tunnel data. A variant of this method has seen use in other fields such as climatology and medical imaging. The technique, based on an eigenvalue decomposition of the background noise cross-spectral matrix, is robust against situations where isolated background auto-spectral levels are measured to be higher than levels of combined source and background signals. It also provides an alternate estimate of the cross-spectrum, which previously might have poor definition for low signal-to-noise ratio measurements. Simulated results indicate similar performance to conventional background subtraction when the subtracted spectra are weaker than the true contaminating background levels. Superior performance is observed when the subtracted spectra are stronger than the true contaminating background levels. Experimental results show limited success in recovering signal behavior for data where conventional background subtraction fails. They also demonstrate the new subtraction technique's ability to maintain a proper coherence relationship in the modified cross-spectral matrix. Beam-forming and de-convolution results indicate the method can successfully separate sources. Results also show a reduced need for the use of diagonal removal in phased array processing, at least for the limited data sets considered.
    Keywords: Acoustics
    Type: NF1676L-19807 , AIAA Aviation 2015; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 22
    Publication Date: 2019-07-13
    Description: The cross-spectral acoustic analogy is used to predict auto-spectra and cross-spectra of broadband shock-associated noise in the near-field and far-field from a range of heated and unheated supersonic off-design jets. A single equivalent source model is proposed for the near-field, mid-field, and far-field terms, that contains flow-field statistics of the shock wave shear layer interactions. Flow-field statistics are modeled based upon experimental observation and computational fluid dynamics solutions. An axisymmetric assumption is used to reduce the model to a closed-form equation involving a double summation over the equivalent source at each shock wave shear layer interaction. Predictions are compared with a wide variety of measurements at numerous jet Mach numbers and temperature ratios from multiple facilities. Auto-spectral predictions of broadband shock-associated noise in the near-field and far-field capture trends observed in measurement and other prediction theories. Predictions of spatial coherence of broadband shock-associated noise accurately capture the peak coherent intensity, frequency, and spectral width.
    Keywords: Acoustics
    Type: NF1676L-19824 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 23
    Publication Date: 2019-07-13
    Description: A resonant interaction between an 8:1 aspect ratio rectangular jet and flat-plates, placed parallel to the jet, is addressed in this study. For certain relative locations of the plates, the resonance takes place with accompanying audible tones. Even when the tone is not audible the sound pressure level spectra is often marked by conspicuous peaks. The frequencies of the spectral peaks, as functions of the streamwise length of the plate and its relative location to the jet as well as the jet Mach number, are explored in an effort of understand the flow mechanism. It is demonstrated that the tones are not due to a simple feedback between the plates trailing edge and the nozzle exit; the leading edge also comes into play in determining the frequency. An acoustic feedback path, involving diffraction from the leading edge, appears to explain the frequencies of some of the spectral peaks.
    Keywords: Acoustics
    Type: AIAA Paper 2015-2999 , GRC-E-DAA-TN27597 , Ohio State University Graduate Seminar; Nov 20, 2015; Columbus, OH; United States|AIAA Aeroacoustics Meeting; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 24
    Publication Date: 2019-07-13
    Description: Preliminary results are presented from a test conducted to determine how well microphone phased array processing software could pull an acoustic signal out of background noise. The array consisted of 24 microphones in an aerodynamic fairing designed to be mounted in-flow. The processing was conducted using Functional Beam forming software developed by Optinav combined with cross spectral matrix subtraction. The test was conducted in the free-jet of the Nozzle Acoustic Test Rig at NASA GRC. The background noise was produced by the interaction of the free-jet flow with the solid surfaces in the flow. The acoustic signals were produced by acoustic drivers. The results show that the phased array processing was able to pull the acoustic signal out of the background noise provided the signal was no more than 20 dB below the background noise level measured using a conventional single microphone equipped with an aerodynamic forebody.
    Keywords: Acoustics
    Type: GRC-E-DAA-TN27489 , Acoustics Technical Working Group Meeting; Oct 20, 2015 - Oct 21, 2015; Cleveland, OH; United States
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  • 25
    Publication Date: 2019-07-13
    Description: The absorption coefficient for material specimens are needed to quantify the expected acoustic performance of that material in its actual usage and environment. The ASTM C423-09a standard, "Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberant Room Method" is often used to measure the absorption coefficient of material test specimens. This method has its basics in the Sabine formula. Although widely used, the interpretation of these measurements are a topic of interest. For example, in certain cases the measured Sabine absorption coefficients are greater than 1.0 for highly absorptive materials. This is often attributed to the diffraction edge effect phenomenon. An investigative test program to measure the absorption properties of highly absorbent melamine foam has been performed at the Riverbank Acoustical Laboratories. This paper will present and discuss the test results relating to the effect of the test materials' surface area, thickness and edge sealing conditions. A follow-on paper is envisioned that will present and discuss the results relating to the spacing between multiple piece specimens, and the mounting condition of the test specimen.
    Keywords: Acoustics
    Type: GRC-E-DAA-TN26791 , Aerospace Testing Seminar; Oct 27, 2015 - Oct 29, 2015; Los Angeles, CA; United States
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  • 26
    Publication Date: 2019-07-13
    Description: The study of noise from a two-shaft contra-rotating open rotor (CROR) is challenging since the shafts are not phase locked in most cases. Consequently, phase averaging of the acoustic data keyed to a single shaft rotation speed is not meaningful. An unaligned spectrum procedure that was developed to estimate a signal coherence threshold and reveal concealed spectral lines in turbofan engine combustion noise is applied to fan and CROR acoustic data in this paper.
    Keywords: Acoustics
    Type: ISABE-2015-20243 , GRC-E-DAA-TN25297 , International Society of Airbreathing Engines (ISABE); Oct 25, 2015 - Oct 30, 2015; Phoenix, AZ; United States
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  • 27
    Publication Date: 2019-07-13
    Description: Classic tonal screech noise created by under-expanded supersonic jets; Long Penetration Mode (LPM) supersonic phenomenon -Under-expanded counter-flowing jet in supersonic free stream -Demonstrated in several wind tunnel tests -Modeled in several computational fluid dynamics (CFD) simulations; Discussion of LPM acoustics feedback and fluid interactions -Analogous to the aero-acoustics interactions seen in screech jets; Lessons Learned: Applying certain methodologies to LPM -Developed and successfully demonstrated in the study of screech jets -Discussion of mechanically induced excitation in fluid oscillators in general; Conclusions -Large body of work done on jet screech, other aero-acoustic phenomenacan have direct application to the study and applications of LPM cold flow jets
    Keywords: Acoustics
    Type: M15-4693 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 28
    Publication Date: 2019-07-13
    Description: The authors provide a brief overview of the classic tonal screech noise problem created by underexpanded supersonic jets, briefly describing the fluid dynamic-acoustics feedback mechanism that has been long established as the basis for this well-known aeroacoustics problem. This is followed by a description of the Long Penetration Mode (LPM) supersonic underexpanded counterflowing jet phenomenon which has been demonstrated in several wind tunnel tests and modeled in several computational fluid dynamics (CFD) simulations. The authors provide evidence from test and CFD analysis of LPM that indicates that acoustics feedback and fluid interaction seen in LPM are analogous to the aeroacoustics interactions seen in screech jets. Finally, the authors propose applying certain methodologies to LPM which have been developed and successfully demonstrated in the study of screech jets and mechanically induced excitation in fluid oscillators for decades. The authors conclude that the large body of work done on jet screech, other aeroacoustic phenomena, and fluid oscillators can have direct application to the study and applications of LPM counterflowing supersonic cold flow jets.
    Keywords: Acoustics
    Type: M15-4529 , AIAA/CEAS Aeroacoustics Conference/AIAA Aviation and Aeronautics Forum and Exposition 2015; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 29
    Publication Date: 2019-07-13
    Description: The 9- by 15-Foot Low Speed Wind Tunnel is an acoustic testing facility with a long history of aircraft propulsion noise research. Due to interest in renovating the facility to support future testing of advanced quiet engine designs, a study was conducted to document the background noise level in the facility and investigate the sources of contaminating noise. The anechoic quality of the facility was also investigated using an interrupted noise method. The present report discusses these aspects of the noise environment in this facility.
    Keywords: Acoustics
    Type: GRC-E-DAA-TN23684 , AIAA Aviation; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 30
    Publication Date: 2019-07-12
    Description: Combustion instability in solid rocket motors and liquid engines is a complication that continues to plague designers and engineers. Many rocket systems experience violent fluctuations in pressure, velocity, and temperature originating from the complex interactions between the combustion process and gas dynamics. During sever cases of combustion instability fluctuation amplitudes can reach values equal to or greater than the average chamber pressure. Large amplitude oscillations lead to damaged injectors, loss of rocket performance, damaged payloads, and in some cases breach of case/loss of mission. Historic difficulties in modeling and predicting combustion instability has reduced most rocket systems experiencing instability into a costly fix through testing paradigm or to scrap the system entirely.
    Keywords: Acoustics
    Type: M16-4947
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  • 31
    Publication Date: 2019-07-12
    Description: A rotorcraft roof sandwich panel has been redesigned to optimize sound power transmission loss (TL) and minimize structure-borne sound for frequencies between 1 and 4 kHz where gear meshing noise from the transmission has the most impact on speech intelligibility. The roof section, framed by a grid of ribs, was originally constructed of a single honeycomb core/composite face sheet panel. The original panel has coincidence frequencies near 700 Hz, leading to poor TL across the frequency range of 1 to 4 kHz. To quiet the panel, the cross section was split into two thinner sandwich subpanels separated by an air gap. The air gap was sized to target the fundamental mass-spring-mass resonance of the double panel system to less than 500 Hz. The panels were designed to withstand structural loading from normal rotorcraft operation, as well as 'man-on-the-roof' static loads experienced during maintenance operations. Thin layers of VHB 9469 viscoelastomer from 3M were also included in the face sheet ply layups, increasing panel damping loss factors from about 0.01 to 0.05. Measurements in the NASA SALT facility show the optimized panel provides 6-11 dB of acoustic transmission loss improvement, and 6-15 dB of structure-borne sound reduction at critical rotorcraft transmission tonal frequencies. Analytic panel TL theory simulates the measured performance quite well. Detailed finite element/boundary element modeling of the baseline panel simulates TL slightly more accurately, and also simulates structure-borne sound well.
    Keywords: Acoustics
    Type: NASA/CR-2015-218769 , NF1676L-21025
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  • 32
    Publication Date: 2019-07-19
    Description: Aircraft community noise is a significant concern due to continued growth in air traffic, increasingly stringent environmental goals, and operational limitations imposed by airport authorities. The ability to quantify aircraft noise at the source and ultimately at observers is required to develop low noise aircraft designs and flight procedures. Predicting noise at the source, accounting for scattering and propagation through the atmosphere to the observer, and assessing the perception and impact on a community requires physics-based aeroacoustics tools. Along with the analyses for aero-performance, weights and fuel burn, these tools can provide the acoustic component for aircraft MDAO (Multidisciplinary Design Analysis and Optimization). Over the last decade significant progress has been made in advancing the aeroacoustic tools such that acoustic analyses can now be performed during the design process. One major and enabling advance has been the development of the system noise framework known as Aircraft NOise Prediction Program2 (ANOPP2). ANOPP2 is NASA's aeroacoustic toolset and is designed to facilitate the combination of acoustic approaches of varying fidelity for the analysis of noise from conventional and unconventional aircraft. The toolset includes a framework that integrates noise prediction and propagation methods into a unified system for use within general aircraft analysis software. This includes acoustic analyses, signal processing and interfaces that allow for the assessment of perception of noise on a community. ANOPP2's capability to incorporate medium fidelity shielding predictions and wind tunnel experiments into a design environment is presented. An assessment of noise from a conventional and Hybrid Wing Body (HWB) aircraft using medium fidelity scattering methods combined with noise measurements from a model-scale HWB recently placed in NASA's 14x22 wind tunnel are presented. The results are in the form of community noise metrics and auralizations.
    Keywords: Acoustics
    Type: NF1676L-19374 , SciTech 2015; Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 33
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    In:  CASI
    Publication Date: 2019-07-27
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21273 , 2015 Acoustics Technical Working Group Meeting; 21ý22 Apr. 2015; Hampton, VA; United States
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  • 34
    Publication Date: 2019-07-12
    Description: An acoustic analogy is proposed that directly includes nonlinear propagation effects. We examine the Lighthill acoustic analogy and replace the Green's function of the wave equation with numerical solutions of the generalized Burgers' equation. This is justified mathematically by using similar arguments that are the basis of the solution of the Lighthill acoustic analogy. This approach is superior to alternatives because propagation is accounted for directly from the source to the far-field observer instead of from an arbitrary intermediate point. Validation of a numerical solver for the generalized Burgers' equation is performed by comparing solutions with the Blackstock bridging function and measurement data. Most importantly, the mathematical relationship between the Navier- Stokes equations, the acoustic analogy that describes the source, and canonical nonlinear propagation equations is shown. Example predictions are presented for nonlinear propagation of jet mixing noise at the sideline angle
    Keywords: Acoustics
    Type: NASA/TM-2015-218706 , L-20532 , NF1676L-20761
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  • 35
    Publication Date: 2019-08-13
    Description: The Scale Model Acoustic Test (SMAT) is a 5% scale test of the Space Launch System (SLS), which is currently being designed at Marshall Space Flight Center (MSFC). SMAT consists of a 5% scale representation of the ignition overpressure sound-suppression system (IOP-SS) that is being tested to quantify the water flow and induced air entrainment in and around the mobile launcher exhaust hole. This data will be compared with computational fluid dynamics (CFD) simulations using the newly developed Loci-STREAM Volume of Fluid (VoF) methods. Compressible and incompressible VoF methods have been formulated, and are currently being used to simulate the water flow of SMAT IOP-SS. The test data will be used to qualitatively and quantitatively assess and validate the VoF methods.
    Keywords: Acoustics
    Type: M15-4341 , JANNAF Propulsion Meeting; Jun 01, 2015 - Jun 05, 2015; Nashville, TN; United States
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  • 36
    Publication Date: 2019-08-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21277 , 2015 Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 37
    Publication Date: 2019-08-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21225 , Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 38
    Publication Date: 2019-07-13
    Description: An acoustic analogy is proposed that directly includes nonlinear propagation effects. We examine the Lighthill acoustic analogy and replace the Green's function of the wave equation with numerical solutions of the generalized Burgers' equation. This is justified mathematically by using similar arguments that are the basis of the solution of the Lighthill acoustic analogy. This approach is superior to alternatives because propagation is accounted for directly from the source to the far-field observer instead of from an arbitrary intermediate point. Validation of a numerical solver for the generalized Burgers' equation is performed by comparing solutions with the Blackstock bridging function and measurement data. Most importantly, the mathematical relationship between the Navier-Stokes equations, the acoustic analogy that describes the source, and canonical nonlinear propagation equations is shown. Example predictions are presented for nonlinear propagation of jet mixing noise at the sideline angle.
    Keywords: Acoustics
    Type: NF1676L-21172 , Spring Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 39
    Publication Date: 2019-07-13
    Description: NASA has a long history of investigating human response to aircraft flyover noise and in recent years has developed a capability to fully auralize the noise of aircraft during their design. This capability is particularly useful for unconventional designs with noise signatures significantly different from the current fleet. To that end, a flexible software architecture has been developed to facilitate rapid integration of new simulation techniques for noise source synthesis and propagation, and to foster collaboration amongst researchers through a common releasable code base. The NASA Auralization Framework (NAF) is a skeletal framework written in C++ with basic functionalities and a plugin architecture that allows users to mix and match NAF capabilities with their own methods through the development and use of dynamically linked libraries. This paper presents the NAF software architecture and discusses several advanced auralization techniques that have been implemented as plugins to the framework.
    Keywords: Acoustics
    Type: Paper Number 298 , NF1676L-21046 , INTER-NOISE 2015; Aug 09, 2015 - Aug 12, 2015; San Francisco, CA; United States
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  • 40
    Publication Date: 2019-07-13
    Description: The capabilities offered by small unmanned vertical lift aerial vehicles, for example, quadcopters, continue to captivate entrepreneurs across the private, public, and civil sectors. As this industry rapidly expands, the public will be exposed to these devices (and to the noise these devices generate) with increasing frequency and proximity. Accordingly, an assessment of the human response to these machines will be needed shortly by decision makers in many facets of this burgeoning industry, from hardware manufacturers all the way to government regulators. One factor of this response is that of the annoyance to the noise that is generated by these devices. This paper presents work currently being pursued by NASA toward this goal. First, physics-based (CFD) predictions are performed on a single isolated rotor typical of these devices. The result of these predictions are time records of the discrete tonal components of the rotor noise. These time records are calculated for a number of points that appear on a lattice of locations spread over the lower hemisphere of the rotor. The source noise is then generated by interpolating between these time records. The sound from four rotors are combined and simulated-propagation techniques are used to produce complete flyover auralizations.
    Keywords: Acoustics
    Type: NF1676L-21051 , InterNoise 2015; Aug 09, 2015 - Aug 12, 2015; San Francisco, CA; United States
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  • 41
    Publication Date: 2019-07-13
    Description: One goal of NASAs Commercial Supersonic Technology Project is to identify candidate noise metrics suitable for regulating quiet sonic boom aircraft. A suitable metric must consider the short duration and pronounced low frequency content of sonic booms. For indoor listeners, rattle and creaking sounds and floor and chair vibrations may also be important. The current study examined the effect of such vibrations on the annoyance of test subjects seated indoors. The study involved two chairs exposed to nearly identical acoustic levels: one placed directly on the floor, and the other isolated from floor vibrations by pneumatic elastomeric mounts. All subjects experienced both chairs, sitting in one chair for the first half of the experiment and the other chair for the remaining half. Each half of the experiment consisted of 80 impulsive noises played at the exterior of the sonic boom simulator. When all annoyance ratings were analyzed together there appeared to be no difference in mean annoyance with isolation condition. When the apparent effect of transfer bias was removed, a subtle but measurable effect of vibration on annoyance was identified.
    Keywords: Acoustics
    Type: NF1676L-20617 , International Symposium on Nonlinear Acoustics; Jun 29, 2015 - Jul 03, 2015; Lyon; France
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  • 42
    Publication Date: 2019-07-13
    Description: Characterization of flight vehicle unsteady aerodynamics is often studied via large scale wind tunnel testing. Boundary layer noise is measured by miniature pressure transducers installed in a model. Noise levels (2-5 dB ref. 20 Pa) can be induced when transducer is mounted out of flush with model outer surface. This effect must be minimized to accurately determine aerodynamically induced acoustic environments.
    Keywords: Acoustics
    Type: M15-4602 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 43
    Publication Date: 2019-07-13
    Description: An efficient multi-objective design tailoring procedure seeking to improve the vibroacoustic performance of a fuselage panel while maintaining or reducing weight is presented. The structure considered is the pultruded rod stitched efficient unitized structure, a highly integrated composite structure concept designed for a noncylindrical, next-generation flight vehicle fuselage. Modifications to a baseline design are evaluated within a six-parameter design space including spacing, flange width, and web height for both frame and stringer substructure components. The change in sound power radiation attributed to a design change is predicted using finite-element models sized and meshed for analyses in the 500 Hz, 1 kHz, and 2 kHz octave bands. Three design studies are carried out in parallel while considering a diffuse acoustic field excitation and two types of turbulent boundary-layer excitation. Kriging surrogate models are used to reduce the computational costs of resolving the vibroacoustic and weight objective Pareto fronts. The resulting Pareto optimal designs are then evaluated under a static pressurization ultimate load to assess structural strength and stability. Results suggest that choosing alternative configurations within the considered design space can reduce weight and improve vibroacoustic performance without compromising strength and stability of the structure under the static load condition considered, but the tradeoffs are significantly influenced by the spatial characteristics of the assumed excitation field.
    Keywords: Acoustics
    Type: NF1676L-16239 , Journal of Aircraft; 52; 2; 692-702
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  • 44
    Publication Date: 2019-08-27
    Description: Systems and methods for the suppression of unwanted noise from a jet discharging into a duct are disclosed herein. The unwanted noise may be in the form of excited duct modes or howl due to super resonance. A damper member is used to reduce acoustic velocity perturbations at the velocity anti-node, associated with the half-wave resonance of the duct, weakening the resonance condition and reducing the amplitudes of the spectral peaks.
    Keywords: Acoustics
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  • 45
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: M16-4924 , Aerospace Testing Seminar; Oct 27, 2015 - Oct 29, 2015; Los Angeles, CA; United States
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  • 46
    Publication Date: 2019-07-13
    Description: A resonant interaction between an 8:1 aspect ratio rectangular jet and flat-plates, placed parallel to the jet, is studied experimentally. For certain locations of the plate relative to the jet, the resonance takes place with a loud accompanying tone. The sound pressure level spectra are often marked by multiple peaks. The frequencies of the spectral peaks are studied as a function of the streamwise length of the plate, its relative location to the jet as well as the jet Mach number. It is demonstrated that the tones are not due to a simple feedback between the plate's trailing edge and the nozzle's exit; the leading edge of the plate also comes into play in the frequency selection. With parametric variation, it is found that there is an order in the most energetic spectral peaks; their frequencies cluster in distinct bands. The 'fundamental', i.e., the lowest frequency band is explained by an acoustic feedback involving diffraction at the plate's leading edge.
    Keywords: Acoustics
    Type: GRC-E-DAA-TN23098 , AIAA/CEAS Aeroacoustics Conference; Jun 22, 2015 - Jun 26, 2015; Dallas, TX; United States
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  • 47
    Publication Date: 2019-07-13
    Description: The objective of this study was to outline an approach for the quantification of uncertainty in sonic boom measurements and to investigate the effect of various near-field uncertainty representation approaches on ground noise predictions. These approaches included a symmetric versus asymmetric uncertainty band representation and a dispersion technique based on a partial sum Fourier series that allows for the inclusion of random error sources in the uncertainty. The near-field uncertainty was propagated to the ground level, along with additional uncertainty in the propagation modeling. Estimates of perceived loudness were obtained for the various types of uncertainty representation in the near-field. Analyses were performed on three configurations of interest to the sonic boom community: the SEEB-ALR, the 69o DeltaWing, and the LM 1021-01. Results showed that representation of the near-field uncertainty plays a key role in ground noise predictions. Using a Fourier series based dispersion approach can double the amount of uncertainty in the ground noise compared to a pure bias representation. Compared to previous computational fluid dynamics results, uncertainty in ground noise predictions were greater when considering the near-field experimental uncertainty.
    Keywords: Acoustics
    Type: NF1676L-19063 , AIAA SciTech 2015 Meeting; Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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  • 48
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21339 , 2015 Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 49
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21264 , Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 50
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Acoustics
    Type: NF1676L-21246 , 2015 Acoustics Technical Working Group Meeting; Apr 21, 2015 - Apr 22, 2015; Hampton, VA; United States
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  • 51
    Publication Date: 2019-07-13
    Description: When equipment designs must perform in a broad band vibration environment it can be difficult to avoid resonances that affect life and performance. This is especially true when an organization seeks to employ an asset from a heritage design in a new, more demanding vibration environment. Particle dampers may be used to provide significant attenuation of lightly damped resonances to assist with such a deployment of assets by including only a very minor set of modifications. This solution may be easier to implement than more traditional attenuation schemes. Furthermore, the cost in additional weight to the equipment can be very small. Complexity may also be kept to a minimum, because the particle dampers do not require tuning. Attenuating the vibratory response with particle dampers may therefore be simpler (in a set it and forget it kind of way) than tuned mass dampers. The paper will illustrate the use of an "equivalent resonance test jig" that can assist designers in verifying the potential resonance attenuation that may be available to them during the early trade stages of the design. An approach is suggested for transforming observed attenuation in the jig to estimated performance in the actual service design. KEY WORDS: Particle Damper, Performance in Vibration Environment, Damping, Resonance, Attenuation, Mitigation of Vibration Response, Response Estimate, Response Verification.
    Keywords: Acoustics
    Type: M15-4884 , Aerospace Testing Seminar 2015; Oct 27, 2015 - Oct 29, 2015; Los Angeles, CA; United States
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  • 52
    Publication Date: 2019-07-12
    Description: This book discusses the acoustics and noise control in spacecraft crew compartments, using experience and lessons learned from the Apollo, Orbiter, and ISS Programs.
    Keywords: Acoustics
    Type: NASA/SP-2015-624 , JSC-CN-34152
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  • 53
    Publication Date: 2019-08-26
    Description: A surface acoustic wave (SAW) based thin film deposition monitor device and system for monitoring the deposition of ultra-thin films and nanomaterials and the analysis thereof is characterized by acoustic wave device embodiments that include differential delay line device designs, and which can optionally have integral reference devices fabricated on the same substrate as the sensing device, or on a separate device in thermal contact with the film monitoring/analysis device, in order to provide inherently temperature compensated measurements. These deposition monitor and analysis devices can include inherent temperature compensation, higher sensitivity to surface interactions than quartz crystal microbalance (QCM) devices, and the ability to operate at extreme temperatures.
    Keywords: Acoustics
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  • 54
    Publication Date: 2019-07-13
    Description: Application of previously formulated semi-analytical models for the prediction of broadband noise due to turbulent rotor wake interactions and rotor blade trailing edges is performed on the historical baseline F31/A31 contra-rotating open rotor configuration. Simplified two-dimensional blade element analysis is performed on cambered NACA 4-digit airfoil profiles, which are meant to serve as substitutes for the actual rotor blade sectional geometries. Rotor in-flow effects such as induced axial and tangential velocities are incorporated into the noise prediction models based on supporting computational fluid dynamics (CFD) results and simplified in-flow velocity models. Emphasis is placed on the development of simplified rotor in-flow models for the purpose of performing accurate noise predictions independent of CFD information. The broadband predictions are found to compare favorably with experimental acoustic results.
    Keywords: Acoustics
    Type: NF1676L-18963 , AIAA SciTech 2015 (Science and Technology Forum); Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
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