چكيده به لاتين
Fluid-Structure Interaction (FSI) mechanisms such as Poisson and Junction coupling in a pipeline system generate additional pressure head fluctuations and jumps during waterhammer. Accordingly, this phenomenon can be an effective event in transient-based defects detection (TBDD) methods. The present thesis aims to analyze the transient reflections for deteriorations detection considering fluid-structure interaction in a pipeline.
In this study, a transient (waterhammer) model is extended in order to instantaneously implementation of fluid-structure interaction and extended deteriorations in a reservoir-pipe-valve system. The hydraulic equations are solved by the method of characteristics (MOC) and the structural equation along with the suggested boundary conditions of pipe supports are solved by the finite element method (FEM) in the time domain. Furthermore, Analytical expressions for the magnitudes of pressure head jumps caused by Poisson coupling are derived. To this end, the four first-order differential equations model and the full MOC method are used. These relations are utilized for investigating the importance of FSI modeling in the transient-based defect detection process. Moreover, the effects of pipeline supports on the transient responses considering FSI are studied in the time and frequency domain in order to detecting the pipeline supports deterioration. In the inverse transient analysis (ITA) for defects detection using the extended transient model, an optimization method based on the genetic algorithm is implemented. The Cramér–Rao lower bound (CRLB) theorem is utilized to compute the lower bound variance of noise-induced estimation errors and the uncertainty quantification of the TBDD method.
The results reveal that both pipe wall vibration (FSI) and pipe wall deteriorations may affect transient pressure head during waterhammer in a similar, and possibly indistinguishable way. Furthermore, Poisson and junction coupling result in changes in the magnitude, shape, and timing of pressure head jumps caused by extended deteriorations. Neglecting FSI in TBRA would skew the estimated locations, lengths, and numbers of the deteriorations in systems with considerable pipe wall axial vibration, thus making TBRA a more complicated method in flexible pipe systems. The current study demonstrates that the pipeline supports deterioration can be detected using the analysis of transient responses when FSI is considered. Quantification of the maximum feasible accuracy (location and size) for the transient-based extended defects detection in a pipeline reveals the influence of relevant physical parameters including valve closure time, measurement time length, and noise level on the best possible localization of deteriorations. The results demonstrate a trade-off between the size and the location/length of extended defect estimates subject to different maneuver times, roughly offering half the wave speed times maneuver duration as the resolution limit.
