Combining Nontraditional 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 basis for FRF estimation and subsequent modal parameter estimation and validation. As discussed in the paper by Dr. Coppolino (Experimental modal analysis using non-traditional response variables. In: IMAC Proceedings, 2021), there are situations where test analysis cross orthogonality is difficult to determine on inaccessible key regions of a test article. In that chapter, 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. This is important as strain and pressure have been shown to be useful measurements for modal analysis (Zienkiewicz et al., The finite element method: its basis and fundamentals, 6th edn. Butterworth-Heinemann, Oxford, p 563–584, 2005; Kranjc et al., J Sound Vib 332:6968, 2013; Kranjc et al., J Vib Control 22(2):371–381, 2016; Dos Santos et al., Strain-based experimental modal analysis: new concepts and practical aspects. In: Proceedings of ISMA. IEEE, Piscataway, p 2263–2277, 2016; Dos Santos et al., An overview of experimental strain-based modal analysis methods. In: Proceedings of the international conference on noise and vibration engineering (ISMA), Leuven, p 2453–2468, 2014). But they have not been used in augmentation with acceleration. Two specific examples discussed are fluid pressure and strain. Experimentally, this presents several problems. For example, in the most simple structures it is expected 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. Use of strain, pressure, and acceleration data all together for modal analysis purposes would reduce the need to place accelerometers in locations that are difficult to access. This chapter aims to present experimental results of strain and pressure FRF-based modal analysis on a rectangular steel plate and attempts to propose ways to combine these variables in the modal parameter estimation process.