Spectral Dynamics Inc.

United States

Spectral Dynamics Inc.

United States
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Underwood M.,Spectral Dynamics Inc. | Ayres R.,Spectral Dynamics Inc. | Keller T.,Spectral Dynamics Inc.
Conference Proceedings of the Society for Experimental Mechanics Series | Year: 2011

With the unrestricted release of MIL-STD-810G, which includes Method 527 - Multi-Exciter Testing, there is more interest than ever in performing vibration tests, which involve using more than one shaker. Also, in the tradition of earlier releases of MIL-STD-810, the use of actual measured (field) data is encouraged wherever possible. While it is acknowledged that Tailoring of the measured data will most probably be required and a Modal survey of the proposed test setup is desirable, many of the steps required to use field data have not been fully reported. This paper will examine some of the detailed requirements for using measured data to perform a multi-exciter random vibration test in the laboratory. Using MIL-STD-810G and IEST committee DTE-022 as background, measurements that can be transformed into a 4-shaker test will be used as an example. While both Time Waveform Replication and Random multi-shaker tests can be established from measured field data, this paper will concentrate on the methodology associated with such Random tests. Using power and cross-spectral densities, from measured field data, the entire system Spectral Density Matrix is filled, to completely define the field vibration environment. Test results will be compared with field measurements and suggestions will be made as to the potential recommended steps needed to assure a successful field simulation. ©2010 Society for Experimental Mechanics Inc.


Underwood M.,Spectral Dynamics Inc. | Ayres R.,Spectral Dynamics Inc. | Keller T.,Spectral Dynamics Inc.
Sound and Vibration | Year: 2011

With the unrestricted release of MIL-STD-810G, which includes Method 527 - Multi-Exciter Testing, there is more interest than ever in performing vibration tests that involve using more than one shaker. Also, in the tradition of earlier releases of MIL-STD-810, use of actual measured field data is encouraged wherever possible. While it is acknowledged that tailoring of measured data will probably be required and a modal survey of the proposed test setup is desirable, many of the steps required to use field data have not been fully reported. This article examines some of the detailed requirements for using measured data to perform a multi-exciter random vibration test in the laboratory. Using MIL-STD-810G and IEST Committee DTE-022 as background, measurements that can be transformed into a four-shaker test will be used as an example. While both time waveform replication and random multishaker tests can be established from measured field data, we concentrate on the methodology associated with such random tests. Using power and cross-spectral densities from measured field data, the entire system spectral density matrix is filled to completely define the field vibration environment. Test results are compared with field measurements and suggestions made as to potential recommended steps needed to assure a successful field simulation.


Underwood M.,Spectral Dynamics Inc. | Ayres R.,Spectral Dynamics Inc. | Keller T.,Spectral Dynamics Inc.
Sound and Vibration | Year: 2011

There is currently quite a bit of interest in using field data as much as possible for performing multi-shaker laboratory simulations. With the introduction of MIL-STD-810G in 2008, and especially Method 525, Time Waveform Replication, multi-shaker replication tests are being attempted and performed more than ever. As with any multi-exciter test, it is important to characterize the entire test configuration, including shakers, amplifiers, fixtures, transducers and cables before starting the test. To minimize test errors, especially if long time records are being used, system characterization should be updated during the test, perhaps every control loop. Also, even though the purpose of the test is carefully reproducing time waveforms from field measurements, the control process may take place in the time domain, the frequency domain or both. We show here the development of a unique approach to creating and controlling time records with a "seamless" transition from block to block.


Ayres R.,Spectral Dynamics Inc. | Underwood M.A.,Spectral Dynamics Inc. | Keller T.,Spectral Dynamics Inc.
Sound and Vibration | Year: 2013

Many different multi-exciter configurations have been created to produce motion in six degrees-of-freedom (6-DOF) simultaneously. This article examines some of these configurations and gives examples of controlling one popular setup, using advanced MIMO (multiple-input and multiple-output) control. Several types of problems were encountered with each configuration, and possible causes and suggested remedies are presented.

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