Bayesian oma of offshore rock lighthouses

Surprises with close modes, symmetry and alignment

Conference paper (2019)

Authors

James Mark William Brownjohn University of Exeter
Alison Raby Plymouth University
Siu Kui Au University of Liverpool
Zuo Zhu University of Liverpool
Xinrui Wang University of Liverpool
A. Antonini Coastal Engineering - CEG
Research Group
Coastal Engineering (CEG) (TU Delft)
Copyright: © 2019 James Brownjohn, Alison Raby, Siu Kui Au, Zuo Zhu, Xinrui Wang, A. Antonini
Bayesian Assessment Identification OMA System Condition Lighthouse
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Published Date

2019

Language

English

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Faculty

Civil Engineering & Geosciences

Department

Hydraulic Engineering

Research Group

Coastal Engineering

Abstract

A set of seven rock lighthouses around the British Isles was studied by a combination of forced and ambient vibration tests executed with some extreme logistical constraints. Forced vibration testing of the circular section masonry towers combined with experimental modal analysis identified modes with alignment assumed the same as the shaker as well as some interesting effects of helideck retrofit, whereas operational modal analysis revealed the considerable degree of uncertainty in mode shape alignment. Hence Bayesian operational modal analysis was used to characterise the uncertainty and find the best representation of mode shape direction. While perfectly axisymmetric towers would show a single frequency omnidirectional mode, OMA reveals the split modes and allows un unbiased view of directionality. The variability and uncertainty of these mode shape directions are further revealed using Bayesian OMA.