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Liquid scintillation counting method with sonic oscillations, noting decreased preparation time and increased counting efficiency
Rocket nozzle effect on acoustic losses from model motor chambers oscillating in first longitudinal mode
Velocity measuring system using optical Doppler methods under severe air turbulence, vibration and acoustic noise conditions
Test plan for vibration and acoustic tests on experimental shroud and payload
Mechanism simulating vibrational and acoustic properties of sonic booms
A device to simulate the vibrational and acoustical properties of a sonic boom was developed and evaluated. The design employed a moving circular diaphragm which produced pressure variations by altering the volume of an air-tight enclosure that was located adjacent to an acoustical test chamber. A review of construction oriented problems, along with their solutions, is presented. The simulator is shown to produce the effects of sonic booms having pressure signatures with rise times as low as 5 milliseconds, durations as short as 80 milliseconds, and overpressures as high as 2.5 pounds per square foot. Variations in the signatures are possible by independent adjustments of the simulator. The energy spectral density is also shown to be in agreement with theory and with actual measurements for aircraft.
The approach of an aircraft manufacturer to ride quality in air transportation is presented. The subjects discussed are: (1) the external and internal environment in terms of vibration and acoustic sources and general response, (2) guidelines and criteria reflecting current practice, (3) present and future efforts to develop rideability criteria, and (4) requirements for data, criteria, and research in various rideability areas.
Sound absorption data from tests of four candidate low-temperature reusable surface insulation materials are presented. Limitations on the use of the data are discussed, conclusions concerning the effective absorption of the materials are drawn, and the relative significance to Vibration and Acoustic Test Facility test planning of the absorption of each material is assessed.
The results of an experimental study to determine the noise attenuation characteristics of aircraft type fuselage structural panels were presented. Of particular interest was noise attenuation at low frequencies, below the fundamental resonances of the panels. All panels were flightweight structures for transport type aircraft in the 34,050 to 45,400 kg (75,000 to 100,000 pounds) gross weight range. Test data include the results of vibration and acoustic transmission loss tests on seven types of isotropic and orthotropically stiffened, flat and curved panels. The results show that stiffness controlled acoustically integrated structures can provide very high noise reductions at low frequencies without significantly affecting their high frequency noise reduction capabilities.
Thin, unbacked, aluminum film filters were used on two extreme ultraviolet (XUV) instruments flown on the Apollo Telescope Mount of Skylab by the Naval Research Laboratory to transmit the XUV radiation while blocking the longer wavelength radiation that would saturate the detector. The requirements placed on these filters - large size, resistance to degradation by high acoustic and vibration fields, and low pinhole transmittances - were far more severe than those placed on any filters previously flown. Special techniques were developed for vacuum evaporation of the aluminum, removal of the films from the substrates, supporting the films and mounting them to obtain finished filters, and storing them so that no degradation took place. A description of these techniques will be given.
In the present paper, the advantages and drawbacks of a multichannel amplifier operating in a vibration or acoustic facility are discussed. The configuration of the facility and the multichannel amplifier proposed is a compromise based on the particular requirements and anticipated work load in a specific case under consideration.
Several arrays were designed and tested. Tests included vibrational and acoustical tests, radiant heating tests, and thermal conductivity tests. A feasible manufacturing technique was established for producing the protection system panels.
Advanced rotorcraft technology and tilt rotor aircraft were discussed. Rotorcraft performance, acoustics, and vibrations were discussed, as was the use of composite materials in rotorcraft structures. Rotorcraft aerodynamics, specifically the aerodynamic phenomena of a rotating and the aerodynamics of fuselages, was discussed.
A data base management and prediction system called vibroacoustic payload environment prediction system (VAPEPS) was developed to serve as a repository for shuttle or extendable booster payload component flight and ground test data. This system is to be made available to the aerospace community for multiple uses including that of establishing the vibroacoustic environment for new payload components. The VAPEPS data includes that spectral information normally processed from vibration and acoustic measurements (e.g., power spectra, sound pressure level spectra, etc.). Results of development to provide this capability by NASA Goddard Space Flight Center and Lockheed Missiles and Space Company are described.
An image processing system is the combination of an image processor with other control and display devices plus the necessary software needed to produce an interactive capability to analyze and enhance image data. Such an image processing system installed at NASA Langley Research Center, Instrument Research Division, Acoustics and Vibration Instrumentation Section (AVIS) is described. Although much of the information contained herein can be found in the other references, it is hoped that this single handbook will give the user better access, in concise form, to pertinent information and usage of the image processing system.
An experiment to investigate more versatile, lower cost surface tension propellant acquisition approaches for future satellite and spacecraft propellant tanks is designed to demonstrate a propellant off-load capability for a full-tank gallery surface tension device, such as that employed in the shuttle reaction control subsystem, and demonstrate a low-cost refillable trap concept that could be used in future orbit maneuver propulsion systems for multiple engine restarts. A Plexiglas test tank, movie camera and lights, auxiliary liquid accumulator, control electronics, battery pack, and associated valving and plumbing are used. The test liquid is Freon 113, dyed blue for color movie coverage. The fully loaded experiments weighs 106 pounds and is to be installed in a NASA five-cubic-foot flight canister. Vibration tests, acoustic tests, and high and low temperature tests were performed to quality the experiment for flight.
Experimental modal analysis is extremely important with regard to verification of analytical models, identification of vibration and acoustic problems, and structural modification and sensitivity analysis. With the expanding access of the testing environment to computational power, the complexity of existing approaches, as well as the development of new approaches, to the estimation of modal parameters has grown tremendously. Currently, the state of the art in experimental modal analysis involves methods that can be grouped in four categories: forced normal mode excitation method, frequency response function method, damped complex exponential function method, and mathematical input-output model methods. The theoretical basis of each of these general approaches, with appropriate references, is reviewed briefly.
Modal analysis has emerged as a valuable tool in many phases of the engineering design process. Complex vibration and acoustic problems in new designs can often be remedied through use of the method. Moreover, the technique has been used to enhance the conceptual understanding of structures by serving to verify analytical models. A new modal parameter estimation procedure is presented. The technique is applicable to linear, time-invariant systems and accommodates multiple input excitations. In order to provide a background for the derivation of the method, some modal parameter extraction procedures currently in use are described. Key features implemented in the new technique are elaborated upon.