Acoustic waveguide characteristics of gas transmission pipelines
Date
1999
Authors
Rossi, John Michael
Major Professor
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Han, Hsiu C.
Committee Member
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Abstract
A new type of acoustic online monitoring system for use on gas transmission pipelines is proposed. The capability of acoustic signals to travel long distances along the axis of the pipeline is critical to the feasibility of the proposed system. To understand the mechanics of acoustic wave motion within the pipeline system, a cylindrical acoustic waveguide is studied. The model represents a gas transmission pipeline and consists of four layers: a gas core, a steel tube, a polyethylene coating, and the surrounding medium. Expressions for the particle displacements and stress components in each of the four layers are derived. The frequency equation is derived from continuous displacement and stress boundary conditions. From these equations, the longitudinal mode wave motions in four different waveguides are calculated.
The four waveguides represent typical gas transmission pipelines with air, water, clay, and soil claddings. The results indicate that the material properties of the surrounding medium determine the existence of guided wave motions within the gas core. Water and clay clad systems support guided wave motions while air and soil clad systems do not. It is found that for small values of phase constant, the ratio between the compressional wave velocity in the gas core and the shear or compressional wave velocity in the cladding determines the ability of the pipeline system to guide acoustic waves along its axis. Results also indicate that the steel pipe wall is not capable of guiding acoustic waves along the axis of the pipeline system.
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