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Nov 1980

Volume 68, Issue S1, pp. S1-S116

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back to top Session P. Shock and Vibration II and Noise III: Applications of Novel Analysis Techniques to Machinery Vibration and Noise
Invited Papers
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Vibration and noise relationships: Some simple rules for the machinery design engineer (A)

David Feit, Spruce M. Cox, and E. J. Richards

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S23-S24 (1980); (2 pages)

Online Publication Date: 11 Aug 2005

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In a world in which the expert is king, countries become very small and communication between them becomes very difficult. This is so in the world of acoustics; symposia are divided into specialist sections, and experts only want to hear from greater experts than themselves. Unfortunately new technologies develop across such separations, and from time to time it is necessary to try to bridge the gaps in a manner which is simple enough to persuade each group to interest itself more widely. Such a technology is that of trying to design industrial machinery which, while increasing productivity, reduces its noise and minimizes deafness. Machinery noise emanates from heavy impacts between parts. The vibration which results from this is the flow of vibration into parts that can radiate efficiently; the noise radiated depends upon the magnitude and the wave form of this vibration, upon its frequency and upon the balance between the rate of radiation and the rate of absorption in the machine. The seriousness of the noise, and the methods of reduction must depend upon the form of the units by which it is measured. This paper goes back to first principles in trying to provide the basic physical insights which will permit an approach to machinery noise which can both be used by the design engineer looking for simple design rules, while also tempting the expert acoustician, vibration engineer and psychoacoustician to extend his interests into what must surely become a new branch of acoustic technology.
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Modern analysis procedures for multiple input/output problems (A)

J. S. Bendat

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S24-S24 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Modern analysis procedures for solving multiple input/output problems are not only more efficient than older techniques but also provide greater engineering insight into the physical meaning of various relationships. Applications include identification of system properties and response effects, estimation of time delays and propagation velocities, determination of energy sources, and utilization of practical statistical error formulas to evaluate results. This lecture will review some of these matters to explain basic concepts on how to obtain conditioned spectral density functions, partial and multiple coherence functions to analyze random vibration and noise data representing multiple random records, where arbitrary correlations can exist among the records.
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An application of coherence functions for evaluating dynamic excitation sources (A)

S. Barrett

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S24-S24 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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The feasibility of using coherence functions to evaluate the relative contributions of multiple dynamic inputs to the vibration environment of a spacecraft component was examined. Data for the study were generated by applying simultaneous vibratory and acoustic random inputs to a realistic test model consisting of an instrumentation truss from a Titan launch vehicle, with a lightly loaded panel added to provide response data. Both independent and correlated inputs were used. A digital computer program was written to analyze the test data, using a mathematical approach based on iterative computational algorithms developed by Bendat. This approach is simpler than earlier matrix methods and is thought to be more economical in terms of computer time. It was found that the coherence function technique was effective in evaluating sources of excitation, for both correlated and noncorrelated cases. To calculate coherence functions with high accuracy, it is necessary to use smoothed estimates of the associated auto and cross spectra. The effect of varying the number of data samples used in the smoothing process was briefly investigated. [Work performed under NASA Contract NASI‐14370.]
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Application of multiple input/output analysis techniques to industrial acoustic &vibrational problems (A)

P. T. Wu

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S24-S24 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Multiple input/output analysis techniques are reviewed. Applications of these techniques to two acoustic and vibrational problems were suggested. The first application is for elimination of extraneous noise for in situ sound power measurement. The second application is for locating a structural vibration source within a complex mechanical system in a noisy environment. Field data for both cases are presented to illustrate the result.
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Novel technique being explored to warn of impending failures of operational systems (A)

J. C. S. Yang and N. Dagalakis

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S24-S25 (1980); (2 pages)

Online Publication Date: 11 Aug 2005

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When you hear a mysterious new sound when driving your car you know that it usually means trouble. Now such signals can be translated into a “signature” which identifies the problem by a technique called “Random Decrement”. First the vibrations have to be picked up by a sensor, like the pickup in a record player. Then these signals which appear meaningless in their original form are sorted, and a characteristic signature is established which engineers can relate to the mechanical properties of the system. If a flaw such as a fatigue crack develops, the signature changes, thus warning the operator of impending failure. The “Random Decrement” technique is particularly well suited to the class of problems in which characteristics are desired of an in‐service structure subjected to unknown random excitation such as wind, earthquakes, waves, sound, traffic loads, etc. Analysis requires only the measurement of the dynamic response of a structure, and not the excitation. Continuous automatic monitoring is possible. The method has been applied in flight flutter testing of the F‐16 aircraft, in monitoring the seals during operation of a wind tunnel, in detecting cracks, and measuring damping in structures such as ships, bridges, pipes, and machinery. More recently it is being used in a joint ONR‐USGS research program for remote detection of underwater structural failures in ocean platforms.
Contributed Papers
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The use of partial and multiple coherence spectral analysis of accelerometer recordings in source and path identification of structure‐borne noise on surface ships (A)

J. S. Kalme and D. L. Winegrad

J. Acoust. Soc. Am. Volume 68, Issue S1, pp. S25-S25 (1980); (1 page)

Online Publication Date: 11 Aug 2005

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Partial and multiple coherence spectral analysis was performed on accelerometer data, recorded on a U.S. Navy surface ship. A total of 48 accelerometers were mounted at predetermined locations on the ship, and vibration data were recorded on a 14‐channel instrumentation tape recorder. The data were recorded in four groups, each consisting of twelve pickups. Taking groups of four pickups at a time with high pairwise coherences, a four‐channel analog‐to‐digital converter and minicomputer were used to digitize and process the data. Partial and multiple coherence spectral analysis was performed on the digitized data. The analysis was found to be very useful in identifying major sources of structure‐borne noise at various frequencies. Also the analysis was helpful in identifying major noise paths. The analysis was performed at the David W. Taylor Naval Ship Research and Development Center at Annapolis, MD, under the Surface Ship Silencing Program.
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