Modal tuning for reduced-order hybrid stick model development

This paper presents a novel Model Order Reduction technique proposed for highly iterative aeroelasticity analyses within an aircraft design development process. Recognizing the limitations of conventional stick models and existing reduction techniques in capturing behaviours of complex structures, the focus of this paper is on the development and validation of a Hybrid Stick Model to enhance computational efficiency while preserving the dynamic fidelity of the Global Finite Element Model. Through strategically incorporated dominant modes within a frequency range of interest, a low-fidelity Stick Model is significantly enhanced. This research explains the methodology and theoretical efficacy behind the proposed Hybrid Stick Model. We present two case studies to assess the fidelity of the proposed Model Order Reduction methodology. The first case considers two Stick Models: a reference and a desired model. We develop the desired model to represent a predetermined deviation to examine the effects of modal truncation on static and dynamic fidelity, emphasizing the importance of the Nyquist criterion and cumulative modal effective mass fraction. A model variation sensitivity study is conducted to investigate the impact of reference to desired model deviations, focusing on changes in cross-sectional area. The findings highlight a greater challenge with reducing mass and stiffness distributions compared to increasing them, suggesting the favourability of underpredicted initial reference models with respect to natural frequency. The second case study analyzes a simplified asymmetric tapered wing, showcasing the complete Model Order Reduction technique. Beginning with a Global Finite Element Model, the high-level computational representation is reduced to a Stick Model, revealing its dynamic limitations. Denoting the Global Finite Element Model as the baseline, the modal characteristics are employed on the simplified Stick Model, resulting in a Hybrid Stick Model. The investigation delves into the influence of modal participation and retained modes for two discrete gust incidences. An aeroelastic response assessment showcases the performance of a Hybrid Stick Model employing five dominant modes from the Global Finite Element Model; both gust incidences resulted in an error reduction of approximately 60 % compared to the traditional Stick Model. Further static and dynamic error mitigation was observed as the number of retained modes increased, resulting in a near-zero error at full modal contribution. The Hybrid Stick Model’s handling capabilities are evaluated through varying mass distributions. Results conclude that Hybrid Stick Models remain well-aligned in the presence of mass configuration changes contrary to the Stick Model. The presented case studies highlight the successful implementation of the novel Model Order Reduction methodology, demonstrating improved accuracy and efficiency for aerospace applications. The introduced approach establishes a promising framework for future applications in the field of Aerospace, with a focus on incorporating experimental mode shapes from physical Ground Vibration Testing results. This methodology strives to minimize experimental and computational discrepancies, fostering enhanced Finite Element Model alignment and credibility in aircraft modelling and simulation.

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