Damping of Torsional Beam Vibrations

David Hoffmeyer*

*Corresponding author for this work

Research output: Book/ReportPh.D. thesisResearch

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Abstract

This thesis contains an extended summary describing damping of torsional and cou-pled bending-torsion vibrations in flexible beam structures by supplemental damping devices. Torsion occurs in various large structures and it is shown how to apply both passive and active dissipation mechanisms to control the dynamic response.
The first part of the thesis considers different modelling aspects of torsional beam vibrations. A novel concept is presented where damping is introduced by restraining the out-of-plane axial warping displacements associated with torsion. Modelling such local forces typically requires a three-dimensional description. Solving the corresponding equations in state-space may be computationally very inefficient and emphasis is thus on equivalent yet simpler and computationally efficient models. An analytical procedure is presented together with finite element models consisting of beam elements and 3D isoparametric elements for dynamic analysis.
Damping of pure torsional vibrations by restraining warping with viscous dampers is presented in the second part of the thesis. A 3D FE model is set up with discrete viscous dampers and the results are used to calibrate an analytical model with the discrete dampers modelled by an equivalent viscous bimoment. The partial restraining of warping caused by the local dampers gives rise to a residual flexibility incorporated into the equivalent analytical model. Significant damping ratios are obtained for cross-sections with open contours and the residual flexibility is easily determined based on the 3D model.
The third part considers damping of coupled bending-torsion vibrations by active feedback control. A 3D model with discrete actuators is again used to calibrate a beam element model with positive position feedback control. The apparent negative stiffness component of the applied linear filter increases the damping potential, and when only restraining the warping component of the coupled response, noticeable damping ratios are obtained for the effective beam element model.
The final and fourth part considers multiple tuned mass absorbers targeting the same fully coupled mode. The non-resonant background modes contribute to the support motion of the absorbers, and this effect is represented by two additional terms and calibrated based on information from the complete structure. An approximate balancing procedure furthermore indicates the necessity of inhomogeneous sizing of the absorbers.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages172
ISBN (Electronic)978-87-7475-569-2
Publication statusPublished - 2019
SeriesDCAMM Special Report
NumberS263
ISSN0903-1685

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