Spectral characteristics of asynchronous data in operational modal analysis
Abstract
Operational modal analysis (OMA) has gained popularity for identifying the modal properties of a structure for its high economy and feasibility. Conventionally, time synchronisation among data channels is required to determine mode shape. OMA can be conducted more flexibly if synchronisation is not required. The power spectral density (PSD) matrix of data and its spectral properties are often used for analysing potential modes. Conventionally known properties assume synchronous data and do not carry over to asynchronous data. This paper investigates the spectral properties of asynchronous OMA data. A stationary process with imperfect coherence is proposed that is conducive to OMA while capturing the key asynchronous characteristics. The theoretical properties of PSD matrix are derived and validated using synthetic and experimental data. Although conventional methods do not allow mode shape to be determined from asynchronous data, the present work reveals the possibility by noting that the data are measured under the same excitation and hence share a common PSD in the modal force. On this basis, a simple method is proposed for determining the mode shape. For perfectly incoherent data channels, it is not possible to determine the relative sense of their mode shape values, which is a fundamental limitation of such data. In implementation, the sense can be determined from intuition or estimated from the residual coherence between channels. Experimental application reveals practical issues in OMA with asynchronous data. This work aspires to provide the pathway for more flexible implementation of OMA, for example, using asynchronous data from multiple smart phones.
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Prior findings indicate that natural frequencies remain reasonably unaffected, while damping values tend to be significantly overestimated.
“Their findings indicate that natural frequencies remain reasonably unaffected, while damping values tend to be significantly overestimated.”
Mode shapes are the modal quantities most affected by lack of synchronization and require corrections for reliable use in SHM applications.
“Mode shapes are the modal quantities most affected by lack of synchronization and require corrections for reliable use in SHM applications.”
Previous studies [12,18] pointed out that even a tiny time misalignment is sufficient to lose the physical phase relationship between sensorized DOFs.
“As already mentioned, previous studies [12,18] pointed out that even a tiny time misalignment is sufficient to lose the physical phase relationship between sensorized DOFs.”
The use of digital sensor networks in OMA-based SHM applications is known to be affected by non-deterministic sampling, which occurs at both intra-node and inter-node levels.
“The use of digital sensor networks in OMA-based SHM applications is known to be affected by non-deterministic sampling, which occurs at both the intra-node and the inter-node levels.”
There is still a lack of a comprehensive methodology capable of systematically accounting for the sources of clock misalignment on the final modal parameters.
“Although the behavior of operational modal parameters in the presence of timing-uncertain conditions has been documented in a few seminal studies (e.g., [12,18]), there is still a lack of a comprehensive methodology capable of systematically accounting for the sources of clock misalignment on the final modal parameters.”
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- Authors
- Zhu, Y.-C., & Au, S.-K.
- Affiliations
- Institute for Risk and Uncertainty and Centre for Engineering Dynamics; University of Liverpool; Liverpool UK
- University of Liverpool (GB)
- ORCID
- Au, Siu-Kui
- Venue
- Structural Control and Health Monitoring
- Publisher
- Wiley
- Published
- 2017-02-06
- Volume
- 24
- Issue
- 11
- Pages
- e1981
- ISSN
- 1545-2255 (ISSN-L)
- OpenAlex
- W2587745781
- Cited by
- 18
- References
- 35
- Citations by year
- 2025: 2 · 2024: 2 · 2023: 1 · 2022: 1 · 2021: 2 · 2020: 5 · 2019: 1 · 2018: 2 · 2017: 2
- FWCI
- 2.86
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- Locations
- Structural Control and Health Monitoring (publishedVersion)
- Funders
- Engineering and Physical Sciences Research Council (EP/M507301/1, EP/N017897/1)
- Topics
- Physical Sciences › Engineering › Civil and Structural Engineering › Structural Health Monitoring Techniques
- Physical Sciences › Engineering › Civil and Structural Engineering › Bladed Disk Vibration Dynamics
- Physical Sciences › Engineering › Control and Systems Engineering › Control Systems and Identification
- Keywords
- operational modal analysis, asynchronous data, mode shape identification, coherence, stationary processes, modal force
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