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  • 1
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    Deep water towed array measurements at close range (2014)
    Acoustical Society of America
    Details
    Publication Date: 2022-05-25
    Description: Author Posting. © Acoustical Society of America, 2013. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 134 (2013): 3230, doi:10.1121/1.4818869.
    Description: During the North Pacific Acoustic Laboratory Philippine Sea 2009 experiment, towed array receptions were made from a towed source as the two ships transited from a separation of several Convergence Zones through a Closest Point of Approach at 3 km. A combination of narrowband tones and broadband pulses were transmitted covering the frequency band 79–535 Hz. The received energy arrives from two general paths—direct path and bottom bounce. Bearing-time records of the narrowband arrivals at times show a 35° spread in the angle of arrival of the bottom bounce energy. Doppler processing of the tones shows significant frequency spread of the bottom bounce energy. Two-dimensional modeling using measured bathymetry, a geoacoustic parameterization based upon the geological record, and measured sound-speed field was performed. Inclusion of the effects of seafloor roughness and surface waves shows that in-plane scattering from rough interfaces can explain much of the observed spread in the arrivals. Evidence of out-of-plane scattering does exist, however, at short ranges. The amount of out-of-plane scattering is best observed in the broadband impulse-beam response analysis, which in-plane surface roughness modeling cannot explain.
    Description: This work was supported by the Office of Naval Research, Ocean Acoustics, under contract N00014-11-M-0170.
    Repository Name: Woods Hole Open Access Server
    Type: Article
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  • 2
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    Ocean Bottom Seismometer Augmentation of the Philippine Sea Experiment (OBSAPS) cruise report (2012)
    Woods Hole Oceanographic Institution
    Details
    Publication Date: 2022-05-25
    Description: The Ocean Bottom Seismometer Augmentation to the Philippine Sea Experiment (OBSAPS, April-May, 2011, R/V Revelle) addresses the coherence and depth dependence of deep-water ambient noise and signals. During the 2004 NPAL Experiment in the North Pacific Ocean, in addition to predicted ocean acoustic arrivals and deep shadow zone arrivals, we observed "deep seafloor arrivals" that were dominant on the seafloor Ocean Bottom Seismometer (OBS) (at about 5000m depth) but were absent or very weak on the Distributed Vertical Line Array (DVLA) (above 4250m depth). These "deep seafloor arrivals" (DSFA) are a new class of arrivals in ocean acoustics possibly associated with seafloor interface waves. The OBSAPS cruise had three major research goals: a) identification and analysis of DSFAs occurring at short (1/2CZ) ranges in the 50 to 400Hz band, b) analysis of deep sea ambient noise in the band 0.03 to 80Hz, and c) analysis of the frequency dependence of BR and SRBR paths as a function of frequency. On OBSAPS we deployed a fifteen element VLA from 12 to 852m above the seafloor, four short-period OBSs and two long-period OBSs and carried out an 11.5day transmission program using a J15-3 acoustic source.
    Description: Funding was provided by the Office of Naval Research under Contract Nos. N00014-10-1-0994 and N00014-10-1-0987.
    Keywords: Underwater acoustics ; Ambient sounds ; Roger Revelle (Ship) Cruise RR1106
    Repository Name: Woods Hole Open Access Server
    Type: Technical Report
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  • 3
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    TLNS3D/CDISC Multipoint Design of the TCA Concept (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: This paper presents the work done to date by the authors on developing an efficient approach to multipoint design and applying it to the design of the HSR TCA (High Speed Research Technology Concept Aircraft) configuration. While the title indicates that this exploratory study has been performed using the TLNS3DMB flow solver and the CDISC (Constrained Direct Iterative Surface Curvature) design method, the CDISC method could have been used with any flow solver, and the multipoint design approach does not require the use of CDISC. The goal of the study was to develop a multipoint design method that could achieve a design in about the same time as 10 analysis runs.
    Keywords: Aircraft Design, Testing and Performance
    Type: 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop; Volume 1; Part 1; 561-586; NASA/CP-1999-209691/VOL1/PT1
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  • 4
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    TLNS3D/CDISC Multipoint Design of the TCA Concept (1999)
    In:  CASI
    Details
    Publication Date: 2004-12-03
    Description: This paper presents the work done to date by the authors on developing an efficient approach to multipoint design and applying it to the design of the HSR TCA configuration. While the title indicates that this exploratory study has been performed using the TLNS3DMB flow solver and the CDISC design method, the CDISC method could have been used with any flow solver, and the multipoint design approach does not require the use of CDISC. The goal of the study was to develop a multipoint design method that could achieve a design in about the same time as 10 analysis runs.
    Keywords: Aircraft Design, Testing and Performance
    Type: 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop; Volume 1; Part 1; 561-587; NASA/CP-1999-209691/VOL1/PT1
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  • 5
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    Attenuated direct and scattered wave propagation on simulated land mobile satellite service paths in the presence of trees (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Measurements were made of direct path with no trees, attenuated direct, and tree scattered signal levels at 1.3 GHz. Signals were received in two small groves of mixed hardwood trees. In the groves studied, average total signal levels were about 13 dB below adjacent no-trees locations, with attenuated direct signal levels about 14.6 dB below the no-trees case and scattered signals about 17.3 dB below the no-trees case. A simple model for land mobile satellite service (LMSS) propagation in groves of trees is proposed. The model assumes a constant scattered signal contribution at 17 dB below no-trees levels added to an attenuated direct signal which varies, depending on the number and density of trees in the direct path. When total signal levels are strong, the attenuated direct signal dominates. When total signal levels are more than 15 dB below no-trees levels, the scattered signals dominate.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Jet Propulsion Lab., Proceedings of the Mobile Satellite Conference; p 101-106
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  • 6
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    Applications of a transonic wing design method (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A method for designing wings and airfoils at transonic speeds using a predictor/corrector approach was developed. The procedure iterates between an aerodynamic code, which predicts the flow about a given geometry, and the design module, which compares the calculated and target pressure distributions and modifies the geometry using an algorithm that relates differences in pressure to a change in surface curvature. The modular nature of the design method makes it relatively simple to couple it to any analysis method. The iterative approach allows the design process and aerodynamic analysis to converge in parallel, significantly reducing the time required to reach a final design. Viscous and static aeroelastic effects can also be accounted for during the design or as a post-design correction. Results from several pilot design codes indicated that the method accurately reproduced pressure distributions as well as the coordinates of a given airfoil or wing by modifying an initial contour. The codes were applied to supercritical as well as conventional airfoils, forward- and aft-swept transport wings, and moderate-to-highly swept fighter wings. The design method was found to be robust and efficient, even for cases having fairly strong shocks.
    Keywords: AERODYNAMICS
    Type: NASA, Ames Research Center, NASA Computational Fluid Dynamics Conference. Volume 2: Sessions 7-12; p 343-358
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  • 7
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    Design and test of an NLF wing glove for the variable-sweep transition flight experiment (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Gloves for M = 0.7 and 0.8 design points were computationally designed and analyzed at conditions over the proposed flight test envelope. The resulting computational pressure distributions were analyzed in a boundary layer stability code. These results indicate that the available pressure distributions offer a wide range of combinations of cross flow and Tollmien-Schlichting N-factors. The glove designs along with the baseline configuration were tested in an entry into the National Transonic Facility. Analysis of the force and moment data showed no significant differences in the performance and stability and control characteristics between the baseline and gloved configurations. The rolling moment constraint was met over the entire flight test envelope for the gloved configuration. Pressure distributions for the NTF test confirmed the design pressure distributions were achieved. However, it was decided that with minor modifications to the inboard region of the glove, useful available data could be significantly increased by adding another row of pressure orifices at span station 167.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 753-776
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  • 8
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    Design of the low-speed NLF(1)-0414F and the high-speed HSNLF(1)-0213 airfoils with high-lift systems (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The design and testing of Natural Laminar Flow (NLF) airfoils is examined. The NLF airfoil was designed for low speed, having a low profile drag at high chord Reynolds numbers. The success of the low speed NLF airfoil sparked interest in a high speed NLF airfoil applied to a single engine business jet with an unswept wing. Work was also conducted on the two dimensional flap design. The airfoil was decambered by removing the aft loading, however, high design Mach numbers are possible by increasing the aft loading and reducing the camber overall on the airfoil. This approach would also allow for flatter acceleration regions which are more stabilizing for cross flow disturbances. Sweep could then be used to increase the design Mach number to a higher value also. There would be some degradation of high lift by decambering the airfoil overall, and this aspect would have to be considered in a final design.
    Keywords: AERODYNAMICS
    Type: Research in Natural Laminar Flow and Laminar-Flow Control, Part 3; p 637-671
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  • 9
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    Computational design of natural laminar flow wings for transonic transport application (1986)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Two research programs are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wind planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first program supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. Boundary-layer and static-pressure data will be measured on this design during the supporting wind-tunnel and flight tests. These data will then be analyzed and used to infer the relationship between crossflow and Tollmein-Schlichting disturbances on laminar boundary-layer transition. A wing was designed computationally for a corporate transport aircraft in the second program. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs. Wing surface pressure distributions, which support the design objective and were derived from transonic three-dimensional analyses codes, are also presented. Current status of each of the research programs is included in the summary.
    Keywords: AERODYNAMICS
    Type: Langley Symposium on Aerodynamics, Volume 1; p 415-443
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  • 10
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    A study of land mobile satellite service multipath effects using SATLAB software (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A software package is proposed that uses the known properties of signals received in multipath environments along with the mathematical relationships between signal characteristics to explore the effects of antenna pattern, vehicle velocity, shadowing of the direct wave, distributions of scatters around the moving vehicle and levels of scattered signals on the received complex envelope, fade rates and fade duration, Doppler spectrum, signal arrival angle spectrum, and spatial correlation. The data base may be either actual measured received signals entered as ASCII flat files or data synthesized using a built in model. An example illustrates the effect of using different antennas to receive signals in the same environment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL, Proceedings of the Fifteenth NASA Propagation Experimenters Meeting (NAPEX 15) and the Advanced Communications Technology Satellite (ACTS) Propagation Studies Miniworkshop p 176-185 (SEE N94-1603; JPL, Proceedings of
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