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- 2017 (3) (entfernen)
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- Accelerometer (1)
- Acoustic emission (1)
- Composite materials (1)
- Fibre optic sensing (1)
- Monitoring (1)
- Non-destructive testing (1)
- Pipelines (1)
- Scaled boundary finite element method (SBFEM) (1)
- Simulations (1)
- Ultrasonic guided waves (1)
Pipelines and industrial piping systems are particularly relevant regarding technical safety, availability and maintenance. Large flow rates of hazardous substances imply that even smallest leakages can lead to high environmental impacts. Therefore, and to ensure the availability of infrastructure, an early detection and localization of potentially hazardous degradations to the walls (e.g. cracks, pittings, sedimentation, etc.) of the containments is necessary. However, in many cases it is not feasible to equip pipelines with a large number of point sensors at reasonable expense.
The principle of distributed fibre optic sensing relies on one single optical fibre, which simultaneously acts as a spatially continuous sensor as well as the signal transducer. Therefore, extensive structures can be provided with this type of sensor with comparatively low efforts.
As a consequence, monitoring oil and gas pipelines using distributed fibre optic sensors is on the upswing. Besides the established methods to measure temperature and strain, distributed acoustic sensing (DAS) has lately received considerable attention as a means to detect and localize third party threats to pipelines (approach of vehicles, digging, mechanical manipulation).
The so far not utilized potential of DAS as a means for continuous condition monitoring of pipes by detecting and localizing acoustic signals that point to certain damage scenarios, is currently under investigation in an interdisciplinary research project at BAM (AGIFAMOR, Ageing Infrastructures – Fibre Optic Monitoring of Pipes).
In order to qualify distributed acoustic fibre optic sensors for this application area, we especially focus on detecting and identifying the relevant acoustic emissions of interesting degradations as well as on the optimal way of application of the optical fibres to the specimen to achieve an optimal signal transmission of acoustic signals.
Composite pressure vessels are important components for storing gases under high pressure. Beside others, a common type of pressure vessel is made of a metal liner overwrapped with a fibre reinforced plastic material. Conventional hydrostatic tests, used to assess the integrity of pressure vessels, may overstress the material, and thus, may reduce the remaining life-time of the tested component. Therefore, a truly nondestructive structural health monitoring (SHM) system would not only allow to ensure a safer usage and extended life-time, but also to exclude the necessity of the periodic inspection and testing of pressure vessels.
We propose to use guided ultrasonic waves which have a potential to detect the main damage types such as cracking in the metal liner, fibre breaks and composite Matrix delamination. For designing such a SHM system, the multimodal ultrasonic wave propagation and the defect-mode interaction must be fully understood.
In this contribution, we present simulation results obtained by means of finite element modelling. Based on the findings, suggestions about appropriate wave modes, their interaction with different flaw types as well as the necessary excitation and suitable sensor configuration are made. Finally, we suggest a first approach of a reliable SHM system for composite pressure vessels.
This paper addresses the computation of dispersion curves, mode shapes and propagation of elastic guided waves. It summarizes the approaches based on the Scaled Boundary Finite Element Method.
Descriptions for plates, rods, pipelines and waveguides with an arbitrary cross section are included. The important steps for the approximation of the displacement in bounded and unbounded domains are stated. The grid generation process is explained. It is highlighted that the Scaled Boundary Finite Element Method is very efficient, if large portions of the domain are either straight or with a constant curvature. The computation of dispersion curves for layered structures is presented.