During servicing of subsurface transportation pipelines, axial pressure generated by high-temperature and high-pressure working conditions is released through upheaval buckling deformation. When the overall deformation of the pipeline exceeds limits, the weakest part of the pipeline will suddenly break and fail, causing serious economic losses and social problems. To ensure safe pipeline operations, it is necessary to monitor the upheaval buckling mechanism of pipelines with a new type of monitoring technology to realize structural reliability assessment under complex loads. Based on Brillouin optical time-domain analysis (BOTDA) distributed optical fiber sensing technology, this study proposes a method to identify buried pipelines’ structural state to solve the problem of detecting upheaval buckling with initial defects under unknown loads. Based on the BOTDA principle, the proposed method comprises a distributed structural response monitoring approach for pipelines. The Euler-Bernoulli beam deflection curve calculation method is used to establish a pipeline buckling displacement reconstruction algorithm to quantitatively identify the occurrence and development of pipeline upheaval buckling. The initial-defect buried pipeline model test is used to verify the feasibility of the proposed method. The results show that the proposed method for identifying the upheaval buckling of buried pipelines can realize quantitative identification of front and back buckling behavior of submarine pipelines under unknown loads, which has important practical significance and application value.
Due to the factors such as environment, material aging, and fatigue loads, structural members are prone to crack damage during the service, which could lead to the risk of collapse as the crack-induced strain accumulates. This paper proposes a method for structural crack identification and location based on a distributed optical fiber dynamic strain monitoring method. The Savitzky-Golay smooth filtering method was used to extract the crack information from the obtained dynamic strain signal. Based on the local strain anomaly of the structure and the nonlinear vibration characteristics of the "breathing" crack model, the cracks distributed along the structure can be located. According to the change of harmonic component, the crack development process can be identified, and early identification and localization of structural cracks during operation can be realized, which provides a practical approach of the damage monitoring for the cracked structures.
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