Flutter derivatives from free decay tests of a rectangular B/D = 10 section estimated by optimized system identification methods. (1st February 2018)

• Record Type: Journal Article
• Authors: Andersen, Michael Styrk; Øiseth, Ole; Johansson, Jens; Brandt, Anders
• Is Part Of: Engineering structures. Volume 156(2018)
• Page Start: 284
• Page End: 293
• Publication Date: 2018-02-01
• Subjects: Torsional flutter -- Coupled flutter -- Flutter derivatives -- Free vibration -- System identification -- Aeroelasticity; Structural engineering -- Periodicals; Structural analysis (Engineering) -- Periodicals; Construction, Technique de la -- Périodiques; Génie parasismique -- Périodiques; Pression du vent -- Périodiques; Earthquake engineering; Structural engineering; Wind-pressure; Periodicals; 624.105
• DOI: 10.1016/j.engstruct.2017.11.059
• Languages: English
• ISSNs: 0141-0296

Abstract

Highlights: The accuracy of free vibration flutter derivatives are optimized. State of the art are critically reviewed and a novel method is proposed. The derivatives are estimated from still air to post critical flutter wind speeds. Positive A 2 ∗ are identified for the B / D = 10 section at low reduced wind speeds. Negative A 2 ∗ are identified for the B / D = 10 section at high reduced wind speeds. Abstract: The present paper suggests a hybrid system identification method to estimate the flutter derivatives from coupled free vibration tests. An optimized covariance-based method is used as the initial guess in the modified unifying least squares method. This combination optimizes the accuracy described by the coefficients of determinations between measured and synthesized signals. Flutter derivatives are identified at high wind speeds, close to and even above the critical flutter wind speed. Results for a sharp-edged rectangular section with a width-to-depth ratio B / D = 10 are presented for two different torsional-to-vertical frequency ratios. In one case the torsional frequency are lower than the vertical, due to a high mass moment of inertia, which makes it possible to estimate the flutter derivatives at very high reduced wind speeds. This reveals that the torsional aerodynamic damping derivative A 2 ∗ reaches a positive maximum followed by a continuous decreasing tendency and eventually negative A 2 ∗ values are identified. This implies that torsional flutter for the B / D = 10 section can be avoided if the structural damping is designed to balance the negative torsional aerodynamic damping expressed by the positive peak value for A 2 ∗ .