A New Method Using Pseudovelocity-Based Fatigue Analysis to Determine the Effectiveness of Acoustic Fields Used for Acoustic Testing
This paper summarizes results from the use of advanced adaptive multiple-input, multiple-output (i.e., MIMO) control for direct field acoustic testing to excite an aluminum-honeycombed 1.22 m × 2.44 m (4 ft × 8 ft) test panel with MSI-DFAT's near-diffuse acoustic field and four nondiffuse acoustic fields using three panel orientations, and two speaker configurations. The five fields have the same overall sound pressure level (OASPL) and 1/3-octave sound-pressure-level (SPL) spectrum. Test and analysis results demonstrate a dependence of the test panel's response characteristics to each acoustic-field excitation, showing that the near-diffuse field excites experimental-modal-analysis-identified test panel modes effectively, whereas nondiffuse fields excite these modes ineffectively. Differences are attributed to the relative diffuseness of fields. Partial fatigue damage values from 20 accelerometer locations are determined from pseudovelocity (PV) outputs from single-degree-of-freedom (SDOF) models at each modal frequency excited by their response time histories, for each acoustic field, to quantify the relative ability of acoustic fields to detect workmanship flaws of typical test articles. Fatigue-damage values are obtained from PV response time histories of SDOF models at identified modal frequencies, which are rainflow-cycle counted with the partial-damage coefficients calculated using the Palmgren-Miner rule. A new form of vibro-acoustic gain based on PV power spectral densities (PSDs) is also introduced and correlated with these experimental results, since the PV response PSDs of a test article undergoing random vibration are proportional to modal stress at their frequencies. This paper shows that the modal stress caused by acoustic-field types is an important consideration for acoustic testing of satellites and other spacecraft, since using a nondiffuse field may result in an acoustic test that doesn't detect workmanship flaws in a test article, even though the acoustic environment is achieving the same specified OASPL and average acoustic 1/3-octave SPL spectrum.Abstract
Contributor Notes
ABOUT THE AUTHORS
Marcos A. Underwood has a PhD in electrical engineering, with specialization in control and communication systems, and an MA in mathematics, both from the University of California in Los Angeles; an MS in structural engineering from San Jose State University; and a BS in mathematics and physics from California State University in Los Angeles. Dr. Underwood has worked with Philco-Ford Aeronutronic, Rockwell International Space Division on the Space Shuttle project, during which he worked with Harry Himmelblau, and Hughes Helicopters in structural dynamics and acoustics, early in his career, developing the use of digital vibration and acoustic control and analysis systems. Later, he also worked with Spectral Dynamics (SD), GenRad, STI, and again with SD as their systems architect and designer of their vibration and acoustic control and analysis systems over the years. After this phase, he held the positions of chief engineer, V.P. of engineering, and chief scientist at STI and SD. During these three phases, he developed some of the fundamental digital technology now used for vibration and acoustic control and analysis. He has been involved in the use, design, and development of digital control and analysis systems for vibration and acoustics for more than 50 years and holds many of the key patents in the field. He has authored numerous publications, is a fellow of the IEST, and is the chair of Working Group 022 of the IEST Design, Test, and Evaluation Division for recommended practice IEST-RP-DTE022, Multi-Shaker Test and Control. He currently works with MSI-DFAT as their chief scientist, helping them extend DFAT technology from his consultancy, Tu'tuli Enterprises.
Contact Author: Marcos A. Underwood, Ph.D. , m.a.u@att.net , Tu'tuli Enterprises, 33741 S. Highway 1, Gualala, CA 95445, USA.
Marc D. Lamparelli has a BSE in electrical engineering from the University of Michigan. Mr. Lamparelli has worked as a microwave engineer for Sanders Associates, Raytheon, and Omni Spectra. Later, he joined Bruel & Kjaer as a sales engineer and transitioned to regional manager. He worked briefly at DIFA Measuring Systems as general manager, followed by sales engineer positions at Measurement Instruments and Comtel Corporation, with both companies focused on test and measurement instrumentation. He joined Spectral Dynamics (SD) as a sales engineer, and, in addition to sales activities, he provided applications support and customer training before becoming Midwest sales manager at SD. He is now semiretired and providing consulting services to SD.
Contact Author: Marc D. Lamparelli , lamparellim@gmail.com , 1578 Redbud Drive, Troy, MI 48098, USA.