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Operational Modal Analysis of Aeronautical Structures via Tangential Interpolation

Gabriele Dessena, Marco Civera, Oscar E. Bonilla-Manrique

Abstract

Over the last decades, progress in modal analysis has enabled increasingly routine use of modal parameters, including those extracted from in-situ measurements, for applications such as structural health monitoring and finite element model updating. For output-only identification, or Operational Modal Analysis (OMA), widely adopted approaches include Stochastic Subspace Identification (SSI) methods and the Natural Excitation Technique combined with the Eigensystem Realization Algorithm (NExT-ERA). Nevertheless, SSI-based techniques may become cumbersome on large systems, while NExT-ERA fitting can struggle when measurements are contaminated by noise. To alleviate these, this work investigates an OMA frequency-domain formulation for aeronautical structures by coupling the Loewner Framework (LF) with NExT, yielding the proposed NExT-LF method. The method exploits the computational efficiency of LF together with the impulse response function retrieval enabled by NExT. NExT-LF is assessed on two experimental benchmarks: the eXperimental BeaRDS 2 high-aspect-ratio wing main spar and an Airbus Helicopters H135 bearingless main rotor blade. The identified modal parameters are compared against available experimental references and results obtained via SSI with Canonical Variate Analysis and NExT-ERA. The results show that the modes identified by NExT-LF correlate well with benchmark data, particularly for high-amplitude tests and in the low-frequency range.

Operational Modal Analysis of Aeronautical Structures via Tangential Interpolation

Abstract

Over the last decades, progress in modal analysis has enabled increasingly routine use of modal parameters, including those extracted from in-situ measurements, for applications such as structural health monitoring and finite element model updating. For output-only identification, or Operational Modal Analysis (OMA), widely adopted approaches include Stochastic Subspace Identification (SSI) methods and the Natural Excitation Technique combined with the Eigensystem Realization Algorithm (NExT-ERA). Nevertheless, SSI-based techniques may become cumbersome on large systems, while NExT-ERA fitting can struggle when measurements are contaminated by noise. To alleviate these, this work investigates an OMA frequency-domain formulation for aeronautical structures by coupling the Loewner Framework (LF) with NExT, yielding the proposed NExT-LF method. The method exploits the computational efficiency of LF together with the impulse response function retrieval enabled by NExT. NExT-LF is assessed on two experimental benchmarks: the eXperimental BeaRDS 2 high-aspect-ratio wing main spar and an Airbus Helicopters H135 bearingless main rotor blade. The identified modal parameters are compared against available experimental references and results obtained via SSI with Canonical Variate Analysis and NExT-ERA. The results show that the modes identified by NExT-LF correlate well with benchmark data, particularly for high-amplitude tests and in the low-frequency range.
Paper Structure (9 sections, 24 equations, 11 figures, 4 tables)

This paper contains 9 sections, 24 equations, 11 figures, 4 tables.

Table of Contents

  1. Introduction
  2. Methodology
  3. Loewner Framework
  4. Natural Excitation Technique
  5. NExT-LF
  6. The eXperimental BeaRDS 2 Flexible Wing Spar Model
  7. Airbus Helicopters H135 Bearingless Main Rotor Blade
  8. Discussion
  9. Conclusions

Figures (11)

  • Figure S1: NExT-LF workflow.
  • Figure S2: XB-2 wing main spar geometrical characteristics and corresponding accelerometer locations (). The odd-numbered accelerometers are positioned on the positive $z$ side, whereas the even-numbered sensors are mounted on the negative $z$ side (retrieved from Dessena2025c).
  • Figure S3: PSDs of the eight acceleration response channels measured on the XB-2 wing main spar (retrieved from Dessena2025c).
  • Figure S4: Equivalent FRFs obtained from the NExT-derived IRF of the XB-2 wing spar. (a) to (h) show the FRFs obtained, respectively, by setting output channel signals 1 to 8 the reference signal for NExT.
  • Figure S5: Stabilisation diagrams obtained using NExT-LF (a), NExT-ERA (b), and SSI (c) for the modal identification of the XB-2 wing spar (retrieved from Dessena2025c).
  • ...and 6 more figures