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On Wave-Defect Interaction in Pressurized Conduits

Author(s): Moez Louati

Linked Author(s): Moez LOUATI

Keywords: Pressurized conduits; Wave Defect Interaction; 2D compressible model; Bragg-type resonance; Wave scattering

Abstract: Pressurized water systems are continually in flux, with routine operational changes inducing numerous high-speed hydraulic disturbances or signals that propagate at speeds of the order of 1 km/s. Such acoustic signals have great potential for being used as means of defect (e. g., leaks, bursts, blockages, wall thinning) detection and in-pipe communication. The use of pressure signals for defect detection and in-pipe communication are essential for developing the next generation of UWS engineering—Smart UWS—where UWS are better instrumented, operated and managed, and where emergencies, failures, threats and inefficiencies are rapidly and reliably diagnosed, assessed and remedied. A fundamental challenge that confronts the use of pressure signals for defect detection and/or in -pipe communication is how pressure (water-hammer) waves, whether induced by a hydraulic element such as a valve or pump or by a sensor or transmitter, are scattered and dispersed in pipes. The current study uses analytical and numerical means to investigate wave scattering and dispersion in conduit with multiple non-uniformities. The non-uniformity is in the pipe diameter and represent blockages, wall-thinning, pipes in series, etc. A two-dimensional (2D) numerical model that solves axi -symmetric and compressible transient flow in a pipe at low Mach number is developed, where an explicit Finite Volume Scheme (FVS) based on Riemann solvers is used to solve the hyperbolic part (i. e., longitudinal and radial waves) and a central differential scheme is used to solve the parabo lic part (i. e., longitudinal and radial momentum diffusion). The analytical solution is based on the method of separation of variables. The initial results show that waves whose source scale is of the order of the pipe diameter, which is akin to hydraulic devices such as valves and pumps, propagate as a plane wave and experience enormous reflections (Bragg-type resonance) due to the non-uniformities for a particular frequency range and maximum transmission otherwise. The ranges of large reflection and maximum transmission convey much information about the non-uniformities and are key to defect detection in pipes. Waves whose source scale is significantly smaller than the pipe diameter, which is akin to in -water sensors and signal transmitters of in-water pipe communication systems, experience similar behavior to the larger scale sources but are further affected by (i) dispersion due to multi-wave paths and (ii) fading (i. e., reduction in amplitude) due to refraction. Such results are instrumental in the development of acoustic communication using the water in the pipe as the medium.


Year: 2013

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