Comparison of Operational Modal Analysis Methods for Aerospace Applications

Resumo

Structures engineered by professionals must endure various loads contingent upon operational requirements. Among these, dynamic loads like vibrations pose a significant challenge due to their potential to induce undesired behavior, leading to damage, operational impracticality, and even structural failure. Therefore, comprehending how structures respond to vibrations is paramount for ensuring integrity and safety. Operational Modal Analysis (OMA) emerges as a crucial tool in this pursuit. OMA serves as a potent technique for assessing modal parameters dictating structural dynamical behavior, encompassing natural frequencies, damping ratios, and mode shapes. The OMA process involves measuring structure responses to assumed white-noise input, generating correlation functions in the time-domain, and subsequently deriving auto-power and cross-power spectra families. What sets OMA apart from other methods like experimental modal analysis (EMA) is its utilization of real boundary conditions and operational inputs, enabling analysis without interrupting structure operations. This paper focuses on applying OMA to various structures, comparing established modal extraction methods from literature, specifically the Numerical Algorithm for Subspace Identification (N4SID), and the Stochastic Subspace Identification methods SSI-COV and SSI-DATA. Initially, the OMA method is validated on a steel cantilever beam, where modal parameters estimated by these methods are compared with theoretical data derived from modal simulations using the Finite Element Method, ensuring the accuracy of OMA results. Subsequently, a wing from an aircraft and a drone structure are subjected to testing to estimate their modal parameters for operational safety assurance. Results indicate a good correlation between theoretical and experimental modal parameters across all tests, affirming the efficacy of the OMA approach. Overall, this paper explores the application of three Operational Modal Analysis (OMA) methods across diverse structures pertinent to the aerospace industry, aiming to unveil their dynamic characteristics.