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Temperature Compensation using Constraint based Dynamic Time Warping in Guided Waves
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0009-0009-3220-2399
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0003-0726-065X
Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Signals and Systems.ORCID iD: 0000-0002-6216-6132
2024 (English)In: Proceedings of the 10th European Workshop on Structural Health Monitoring (EWSHM 2024), June 10-13, 2024 in Potsdam, Germany, NDT.net , 2024Conference paper, Published paper (Other academic)
Abstract [en]

Introduction: Guided waves being highly sensitive to temperature variations, temperature compensation algorithms, such as Optimal Baseline Selection, Baseline Signal Stretch and Scale Transform demonstrate effective performance under limited conditions. Dynamic Time Warping (DTW) has shown excellent compensation performance, however it comes with a substantial computational burden of O(N*N), where N represents the number of samples in each signal. Methodology: DTW works by construction of cost matrix that maps every point in one time series to all the points in the other time series, that results in complexity O(N*N).This problem can be solved by narrowing the search window using global constraints. The two most common constraints in the literature are the Sakoe-Chiba band and the Itakura Parallelogram. This paper uses Sakoe-Chiba band as a global constraint, the Sakoe-Chiba band is defined through a window size parameter which determines the largest temporal shift allowed from the diagonal. Temperature compensation performance of DTW Sakoe-Chiba is tested using the available OGW dataset #2 provided by Jochen Moll et al. The OGW dataset has been generated using 12 number of piezoelectric transducers bounded to CFRP (Carbon Fiber Reinforced Plastic) plate and varying the temperature from 20-60 degree with an increment of 0.5 degree. The signal is recorded for 1300 microseconds, that results in 13000 samples/time stamps(N). Initial results show that the Sakoe-Chiba constraint based DTW performs well and at a significantly lower cost, as indicated below. Result: The largest temporal shift (r) is estimated using Local Peak Coherence (LPC),for signal at 20 and 60 degree r is 135 samples. This results in complexity O(N*2r) which is very less than conventional DTW compensation technique O(N*N). In the final paper, the analysis will be replicated across a range of temperatures, and the performance of damage detection will be thoroughly discussed.

Place, publisher, year, edition, pages
NDT.net , 2024.
Series
e-Journal of Nondestructive Testing, ISSN 1435-4934
Keywords [en]
Guided waves, Structural health monitoring, Temperature compensation, Sakoe-chiba constraint, Dynamic time warping
National Category
Reliability and Maintenance
Research subject
Signal Processing
Identifiers
URN: urn:nbn:se:ltu:diva-109792DOI: 10.58286/29794Scopus ID: 2-s2.0-85202552998OAI: oai:DiVA.org:ltu-109792DiVA, id: diva2:1896378
Conference
11th European Workshop on Structural Health Monitoring (EWSHM 2024), Potsdam, Germany, June 10-13, 2024
Note

Full text license: CC-BY-4.0;

Funder: Centre of Hydrogen Energy Systems Sweden (CH2ESS);

Available from: 2024-09-10 Created: 2024-09-10 Last updated: 2025-02-03Bibliographically approved
In thesis
1. Baseline Signal Strategies for Structural Health Monitoring using Ultrasound Guided Waves
Open this publication in new window or tab >>Baseline Signal Strategies for Structural Health Monitoring using Ultrasound Guided Waves
2025 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Structural Health Monitoring (SHM) using ultrasonic guided waves is an advanced and efficient technique for evaluating the integrity of critical infrastructure such as pipelines, pressure vessels, and aerospace structures. Despite its numerous advantages, the reliability and effectiveness of guided wave-based SHM systems are often compromised by environmental and operational variations, particularly temperature fluctuations. Temperature changes significantly influence wave propagation by altering material properties, wave velocity, and signal behaviour. These variations lead to signal misalignment and reduced defect detection accuracy, posing a major challenge for real-time monitoring systems. This research addresses the impact of temperature-induced signal variations by developing robust baseline signal strategies to improve temperature compensation in guided wave-based SHM systems.

The study introduces Dynamic Time Warping (DTW) and its advanced adaptations as key methods for aligning signals under fluctuating thermal conditions. DTW is a widely used signal processing technique that optimizes the alignment between two signals by stretching or compressing their time domains, ensuring accurate comparison and analysis. The quadratic computational complexity of DTW poses a significant challenge for its application in Structural Health Monitoring (SHM) using guided waves, particularly for real-time operations under changing Environmental and Operational Conditions (EOCs). 

To address this, the first approach employs a DTW approximation to accelerate the warping process, called Fast-DTW achieving significant computational efficiency without compromising much on performance. In contrast, the second approach uses the Full DTW algorithm but improves its efficiency by incorporating the Sakoe-Chiba constraint to restrict the warping path to a narrow region around the diagonal, effectively reducing computational cost. Additionally, the method leverages the fact that temperature-induced shifts in guided wave signals are typically limited to a few time stamps. Third, we propose a global constraint for temperature compensation of guided waves, referred to as the Triangular Global Constraint (Tri-DTW). The performance of the proposed method is compared with the Sakoe-Chiba Global Constraint (SC-DTW). Tri-DTW performs well, demonstrating better warping performance with four times reduced computational complexity. Finally, we present Hilbert-DTW, a novel approach that extracts the envelope and phase of signals and leverages phase differences to achieve accurate alignment. This method reformulates the cost matrix to prioritize signal alignment while preserving amplitude variations, eliminating the need for constraints or modified DTW variants.

Collectively, these strategies provide a robust framework for baseline signal management and temperature compensation in guided wave-based SHM systems. By improving signal alignment accuracy and reducing distortion caused by temperature effects, the proposed methods significantly enhance the reliability, adaptability, and performance of SHM technologies.

In conclusion, this research advances the field of SHM by addressing temperature-induced challenges through innovative signal processing techniques. The integration of fast DTW algorithms, optimized constraints, and the Hilbert-DTW provides a comprehensive solution for maintaining SHM system performance under varying thermal conditions, enabling more reliable and accurate monitoring of critical infrastructure.

Place, publisher, year, edition, pages
Luleå: Luleå tekniska universitet, 2025
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords
Baseline Signal Strategies, Dynamic Time Warping (DTW), Environmental Variations, Guided Waves, Hilbert Transform, Real-Time Monitoring, Sakoe-Chiba Constraint, Signal Alignment, Signal Processing, Structural Health Monitoring (SHM), Temperature Compensation, Triangular Constraint (Tri-DTW), Ultrasonic Guided Waves
National Category
Signal Processing
Research subject
Signal Processing
Identifiers
urn:nbn:se:ltu:diva-111180 (URN)978-91-8048-726-9 (ISBN)978-91-8048-727-6 (ISBN)
Presentation
2025-03-05, E632, Luleå University of Technology, Luleå, 10:00 (English)
Opponent
Supervisors
Available from: 2025-01-02 Created: 2025-01-02 Last updated: 2025-02-10Bibliographically approved

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Kumar, NarendraGupta, PayalCarlson, Johan E.

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