High-resolution modal analysis

TL;DR

This paper introduces a high-resolution modal analysis technique that overcomes Fourier transform limitations, enabling accurate modal parameter estimation in high-overlap scenarios up to 70% overlap.

Contribution

A novel high-resolution analysis algorithm combined with an order-detection method for improved modal analysis in high-overlap frequency domains.

Findings

Successfully separated twin modes of a square plate.

Achieved partial modal analysis of aluminium plates with up to 70% modal overlap.

Results closely match those from an improved Rayleigh method.

Abstract

Usual modal analysis techniques are based on the Fourier transform. Due to the Delta T . Delta f limitation, they perform poorly when the modal overlap mu exceeds 30%. A technique based on a high-resolution analysis algorithm and an order-detection method is presented here, with the aim of filling the gap between the low- and the high-frequency domains (30%<mu<100%). A pseudo-impulse force is applied at points of interests of a structure and the response is measured at a given point. For each pair of measurements, the impulse response of the structure is retrieved by deconvolving the pseudo-impulse force and filtering the response with the result. Following conditioning treatments, the reconstructed impulse response is analysed in different frequency-bands. In each frequency-band, the number of modes is evaluated, the frequencies and damping factors are estimated, and the complex amplitudes are finally extracted. As examples of application, the separation of the twin modes of a square plate and the partial modal analyses of aluminium plates up to a modal overlap of 70% are presented. Results measured with this new method and those calculated with an improved Rayleigh method match closely.