Monday  |  Pecos  |  09:00 AM–09:20 AM

#14582–Combining Non Traditional Response Variables with Acceleration Data for Experimental Modal Analysis

Accelerometer data is the most commonly used data for experimental modal analysis of structures. Together with measuring applied force, it provides the foundation for FRF estimation and subsequent modal parameter estimation and validation. As discussed in the paper by Dr. Coppolino[1], there are situations where test analysis cross orthogonality is difficult to determine on inaccessible key regions of a test article. In that paper it is contended that it is in theory possible to augment data from accelerometers with data from other sensor sources at these key regions that have a proportionality to acceleration or displacement. Two specific examples discussed are fluid pressure and strain. Experimentally, this presents several problems. For example, in the most simple structures we expect to have maximum acceleration at locations of 0 strain and vice versa. This makes it difficult to relate the modal information contained in acceleration variable to the strain variable at the location of maximum acceleration. Given that the FRF information will have to be uniform in units, this is another cause of concern when combining pressure, strain and acceleration
In this research two experiments were conducted on a rectangular steel place. First experiment was an impact test with accelerometer and strain gages. Second experiment was with accelerometer, strain gages and microphones. Different ways of augmenting partial accelerometer data/ results from partial accelerometer data were tried and cross MAC[2] with full experimental data were checked. FRF synthesis from the modal vectors of the augmented data was also done and compared with measured acceleration FRF. The different ways of augmenting data also incorporated a way around the scaling and units issue discussed previously.
Use of stain, pressure and acceleration data all together for modal analysis purposes would reduce the need to place accelerometers in locations that are difficult to access. Very often structures are already instrumented with strain gages and this would obviate the need to add a accelerometer at all these locations. This paper aims to present experimental results of strain and pressure FRF based modal analysis and attempts to propose ways to combine these variables in the modal parameter estimation process.

Pranjal Vinze   University of Cincinnati
Randall Allemang   University of Cincinnati
Allyn Phillips   University of Cincinnati
Robert Coppolino   Measurement Analysis Corporation