Modelling Tool for Elastic Wave Guide Properties of Flexible Pipes

Abstract eng:
Wave guide modelling of flexible pipes has a wide range of applications. Risers used in the oil and gas industry, suffering under internal and external flow induced vibrations, hydraulic hoses acting as structural wave guides in power transmission systems, and also diagnosis of cardiovascular diseases in the larger blood vessels are just some of the areas. Depending upon the stiffness properties of the pipe and the frequency range under considerations different modelling techniques can be applied. At sufficiently low frequency relative to the stiffness of the pipe a one-dimensional beam model may be sufficient. At higher frequencies the plane cross-section assumptions of e.g. a Timoshenko beam become too restrictive whereas a two-dimensional shell model of the pipe wall still may be valid. Then, at even higher frequencies, deformations modes across the thickness of the pipe wall need to be taken into considerations and a full-blown three-dimensional elasticity model is then needed. In this work an analytical shell model of the wave guide properties of a flexible pipe is carried out. The flexible pipe is modelled as a thin walled constantly curved cylinder and the dispersion relation between the frequency and wave number associated with the waves along the length of the pipe is determined. The dispersion relation of this model is compared to a corresponding Timoshenko beam model and a wave finite element model modelled with solid elements. This provides a tool for choosing between the modelling techniques described above when modelling flexible pipes.

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