|Number of pages||196|
|Publication status||Published - 2019|
|Series||Ph.d.-serien for Det Ingeniør- og Naturvidenskabelige Fakultet, Aalborg Universitet|
Bibliographical notePhD supervisor:
Prof. Lars Damkilde, Aalborg University
M.Sc. Søren Andreas Nielsen, Universal Foundation A/S
Note re. dissertationVibration-based structural monitoring is an interdisciplinary field within the Structural Health Monitoring (SHM) domain. It refers to the implementation of a strategy that allows to monitor structural integrity based on vibration measurements collected from a structure during its operation. Its real-life deployment consists of several interconnected tasks such as the design of the monitoring system, which comprises different sensors arranged in a specific layout, and the choice or design of appropriate signal processing methods to analyze the measurements. Such monitoring systems are applied on various engineering structures, e.g. wind turbines, offshore structures, bridges, high rise buildings, gearboxes, rotors and engines.
Methods that analyze vibration measurements and give the actual information about the structural condition are at the heart of the SHM problem. In practice the integrity of structures is monitored during their operation, hence under unknown, unmeasured, ambient excitation conditions. These particular conditions pose some challenges for the underlying methods, which may lead to false alarms appearing during damage detection or inaccurate estimates of modal parameters, if not treated correctly.
In this thesis three problems revolving around these conditions were considered. First, a time domain method to remove periodic frequencies originating from rotating components on the structure was presented. Second, a statistical framework to quantify the uncertainty in the estimates of Modal Assurance Criterion and Modal Phase Collinearity was developed. Lastly, a data driven damage detection method robust to changes in the excitation properties under the healthy state of the structure was designed.
The proposed methods were validated for their theoretical properties in numerical simulations as a proof of concept. Their pertinence to real-life vibration problems was illustrated based on full-scale structures like an offshore meteorological mast at the North Sea, an operating ferry, Dogna and Z24 bridges and a small-scale plate. The industrial readiness of some of the methods was inferred by their transfer to the commercial software for modal analysis and SHM.