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  • 1
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    A feasibility study on the numerical modeling of interior noise fields (1986)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: New developments in electronics and computer control have made active methods of noise suppression feasible. To date, however, active methods of noise control have been applied principally in geometrically uniform spaces with localized sound sources. The purpose of this paper is to demonstrate how finite element techniques may be used to model sound fields and active control inside geometrically complex spaces with non-uniform acoustic boundaries and multiple spatially separated sources. A closed-form solution is derived for the case of a one-dimensional tube with a vibrating piston at each end. Results are compared with finite element solutions and the problem is then generalized to two-dimensions with non-uniform geometry and non-uniform acoustic boundaries.
    Keywords: ACOUSTICS
    Type: AIAA PAPER 86-1862
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    The LATDYN user's manual (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The LATDYN User's Manual presents the capabilities and instructions for the LATDYN (Large Angle Transient DYNamics) computer program. The LATDYN program is a tool for analyzing the controlled or uncontrolled dynamic transient behavior of interconnected deformable multi-body systems which can undergo large angular motions of each body relative other bodies. The program accommodates large structural deformation as well as large rigid body rotations and is applicable, but not limited to, the following areas: (1) development of large flexible space structures; (2) slewing of large space structure components; (3) mechanisms with rigid or elastic components; and (4) robotic manipulations of beam members. Presently the program is limited to two dimensional problems, but in many cases, three dimensional problems can be exactly or approximately reduced to two dimensions. The program uses convected finite elements to affect the large angular motions involved in the analysis. General geometry is permitted. Detailed user input and output specifications are provided and discussed with example runstreams. To date, LATDYN has been configured for CDC/NOS and DEC VAX/VMS machines. All coding is in ANSII-77 FORTRAN. Detailed instructions regarding interfaces with particular computer operating systems and file structures are provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TM-87635 , NAS 1.15:87635
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Acoustic treatment of the NASA Langley 4- by 7-meter tunnel: A feasibility study (1986)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A feasibility study for upgrading the NASA Langley 4- by 7-Meter Tunnel so that it may be used for aeroacoustic research related to helicopters is described. The requirements for noise research leading to the design of the next generation of helicopters impose a set of acoustic test criteria that no existing wind tunnel in the United States can presently meet. Included in this feasibility study are the following considerations: (1) an evaluation of general wind-tunnel requirements and desired tunnel background noise levels for helicopter aeroacoustic research; (2) an assessment of the present acoustic environment for testing model rotors; (3) a diagnostic investigation of tunnel background noise sources and paths; (4) acoustic treatment options for tunnel background noise reduction and a trade-off study between these options; (5) an engineering feasibility assessment of the selected option; and (6) an integrated analysis of study components and recommendations of treatment for an approach to meet the tunnel background noise reduction goal. It is concluded that the Langley 4- by 7-Meter Tunnel is a fundamentally suitable facility for helicopter aeroacoustic research. It is also concluded that acoustic treatment of this facility for meeting the required tunnel background noise goal can be accomplished technically at reasonable risk and cost.
    Keywords: ACOUSTICS
    Type: NASA-TP-2563 , L-16037 , NAS 1.60:2563
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    A preliminary design study on an acoustic muffler for the laminar flow transition research apparatus (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An acoustic muffler design of a research tool for studying laminar flow and the mechanisms of transition, the Laminar Flow and Transition Research Apparatus (LFTRA) is investigated. Since the presence of acoustic pressure fluctuations is known to affect transition, low background noise levels in the test section of the LFTRA are mandatory. The difficulties and tradeoffs of various muffler design concepts are discussed and the most promising candidates are emphasized.
    Keywords: AERODYNAMICS
    Type: NASA-CR-172374 , NAS 1.26:172374
    Format: application/pdf
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  • 5
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    ADAM: An Axisymmetric Duct Aeroacoustic Modeling system (1983)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An interconnected system of computer programs for analyzing the propagation and attenuation of sound in aeroengine ducts containing realistic compressible subsonic mean flows, ADAM was developed primarily for research directed towards the reduction of noise emitted from turbofan aircraft engines. The two basic components are a streamtube curvature program for determination of the mean flow, and a finite element code for solution of the acoustic propagation problem. The system, which has been specifically tailored for ease of use, is presently installed at NASA Langley Reseach Center on a Control Data Cyber 175 Computer under the NOS Operating system employing a Tektronix terminal for interactive graphics. The scope and organization of the ADAM system is described. A users guide, examples of input data, and results for selected cases are included.
    Keywords: ACOUSTICS
    Type: NASA-CR-3668 , NAS 1.26:3668
    Format: application/pdf
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  • 6
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    An evaluation of proposed acoustic treatments for the NASA LaRC 4 x 7 meter wind tunnel (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The NASA LaRC 4 x 7 Meter Wind Tunnel is an existing facility specially designed for powered low speed (V/STOL) testing of large scale fixed wing and rotorcraft models. The enhancement of the facility for scale model acoustic testing is examined. The results are critically reviewed and comparisons are drawn with a similar wind tunnel (the DNW Facility in the Netherlands). Discrepancies observed in the comparison stimulated a theoretical investigation using the acoustic finite element ADAM System, of the ways in which noise propagating around the tunnel circuit radiates into the open test section. The reasons for the discrepancies noted above are clarified and assists in the selection of acoustic treatment options for the facility.
    Keywords: ACOUSTICS
    Type: NASA-CR-172577 , NAS 1.26:172577 , COMTEK-8401
    Format: application/pdf
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  • 7
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    A finite element algorithm for sound propagation in axisymmetric ducts containing compressible mean flow (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: An accurate mathematical model for sound propagation in axisymmetric aircraft engine ducts with compressible mean flow is reported. The model is based on the usual perturbation of the basic fluid mechanics equations for small motions. Mean flow parameters are derived in the absence of fluctuating quantities and are then substituted into the equations for the acoustic quantities which were linearized by eliminating higher order terms. Mean swirl is assumed to be zero from the restriction of axisymmetry. A linear rectangular serendipity element is formulated from these equations using a Galerkin procedure and assembled in a special purpose computer program in which the matrix map for a rectangular mesh was specifically coded. Representations of the fluctuating quantities, mean quantities and coordinate transformations are isoparametric. The global matrix is solved by foreward and back substitution following an L-U decomposition with pivoting restricted internally to the blocks. Results from the model were compared with results from several alternative analyses and yielded satisfactory agreement.
    Keywords: ACOUSTICS
    Type: NASA-CR-145209 , RR-50624
    Format: application/pdf
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  • 8
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    Acoustical characteristics of the NASA Langley full scale wind tunnel test section (1975)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The full-scale wind tunnel at NASA-Langley Research Center was designed for low-speed aerodynamic testing of aircraft. Sound absorbing treatment has been added to the ceiling and walls of the tunnel test section to create a more anechoic condition for taking acoustical measurements during aerodynamic tests. The results of an experimental investigation of the present acoustical characteristics of the tunnel test section are presented. The experimental program included measurements of ambient nosie levels existing during various tunnel operating conditions, investigation of the sound field produced by an omnidirectional source, and determination of sound field decay rates for impulsive noise excitation. A comparison of the current results with previous measurements shows that the added sound treatment has improved the acoustical condition of the tunnel test section. An analysis of the data indicate that sound reflections from the tunnel ground-board platform could create difficulties in the interpretation of actual test results.
    Keywords: RESEARCH AND SUPPORT FACILITIES (AIR)
    Type: NASA-CR-132604 , WRH-74-2
    Format: application/pdf
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  • 9
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    Resonance testing of space shuttle thermoacoustic structural specimen (1977)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The resonance testing of a structural specimen related to the space shuttle vehicle is described. The specimen consisted of a thin aluminum skin reinforced by hat-section stringers and supported by two ribs or bulkheads of corrugated web. A representative section of the space shuttle thermal protection system was bonded to the outer surface of the skin. The tests were completed by using miniature accelerometers to collect vibration data from locations forming a predetermined mesh over the tiles and base structure. The signals were recorded on FM magnetic tape and subsequently analyzed on a modal analysis system.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-145154 , REPT-50621
    Format: application/pdf
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  • 10
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    A feasibility study of a 3-D finite element solution scheme for aeroengine duct acoustics (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The advantage from development of a 3-D model of aeroengine duct acoustics is the ability to analyze axial and circumferential liner segmentation simultaneously. The feasibility of a 3-D duct acoustics model was investigated using Galerkin or least squares element formulations combined with Gaussian elimination, successive over-relaxation, or conjugate gradient solution algorithms on conventional scalar computers and on a vector machine. A least squares element formulation combined with a conjugate gradient solver on a CDC Star vector computer initially appeared to have great promise, but severe difficulties were encountered with matrix ill-conditioning. These difficulties in conditioning rendered this technique impractical for realistic problems.
    Keywords: ACOUSTICS
    Type: NASA-CR-159359 , REPT-51200
    Format: application/pdf
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