Modelling vibrations of a pipeFood and cosmetics
One can model vibrations in a pipe with mechanical simulation tools that help understand dynamics of the system. When the modelled pipe is filled by a fluid, acoustics phenomena is coupled with mechanics and a multiphysics fluid-structure interaction type of problem has to be solved.
Objectives from modelling the vibrations of the pipe
In some industries (e.g. food or cosmetics) there is a need to check viscoelasticity properties in fluids flowing through pipes while they are processed.
There are contactless devices that can measure viscoelasticity using a wave coupling technique: a low frequency compression wave propagates through the sample to be characterised, acting as a volume palpation, while “reading” ultrasound pulses probe the sample in these various stages of compression.
Results from simulation and information extracted
Simulation of acoustic and elastic waves can predict the vibration modes of the fluid and the pipe for different configurations that can be found in industrial applications: variation of designs (thickness, length, diameter, bended pipe, etc.) and use of different materials.
It also helps to visualise and understand the behaviour of the pressure field during volume palpation in order to calibrate the ultrasound measurement and to optimise the viscoelasticity measurement.
Vibrations of the pipe at lower frequency
In this figure one can see the pipe filled with fluid at a low frequency excitation :
- its mechanical deformation on the left (scaled for visualisation purpose);
- the acoustic wave (palpation) in the fluid on the right.
Both on the left and on the right the pipe is cut in half for visualisation purpose. The source tranducer which excites the pipe is localised where the orange arrows point at (mid-height).
Vibrations of the pipe at higher frequency
This figures shows the same pipe with the same variable quantities (mechanical deformation on the left and acoustics wave on the right). This time the excitation frequency is higher.
For a given set of materials and pipe dimensions, vibrations modes of the pipe and fluid can be very different for different frequencies, leading to different viscoelasticity measurements.
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