Acoustic attenuation, phase and group velocities in liquid-filled pipes II: simulation for Spallation Neutron Sources and planetary exploration

The influence of pipeline thickness and radius on guided wave attenuation in water-filled steel pipelines: Theoretical analysis and experimental measurement

The influence of pipeline thickness and radius on the attenuation of guided waves in water-filled steel pipelines is investigated using theoretical analysis and experimental measurement. Attenuations of individual axisymmetric modes in unburied water-filled steel pipelines are predicted by an analytical model under different pipeline radius-thickness ratios. Model predictions indicate that attenuation of the fundamental mode increases as the ratio rises. This effect is investigated by finding the displacement variations under different ratios. Laboratory experiments were also carried out in four unburied steel pipelines with three distinctly different radius-thickness ratios using acoustic transducers to acquire signals uniformly spaced along the axis of the pipe. By applying the iterative quadratic maximum likelihood algorithm, the attenuations could be accurately estimated from the measurement data for individual modes. Experimental results show that attenuation of the fundamental axisymmetric mode is sensitive to radius-thickness ratio, but high-order modes are barely affected, agreeing with the model predictions mentioned in this paper. The characteristics of water-filled buried pipelines are also investigated using an analytical model to understand the relation between wave attenuation and the radius-thickness ratio.

Propagation of monopole source excited acoustic waves in a cylindrical high-density polyethylene pipeline

Acoustic wave propagation (up to 50 kHz) within a water-filled high-density polyethylene (HDPE) pipeline is studied using laboratory experiments and theoretical analysis. Experiments were carried out in a 15 m length of cylindrical HDPE pipeline using acoustic transducers to acquire signals uniformly spaced along the axis of the pipe. By proposing the use of the iterative quadratic maximum likelihood algorithm to this experimental configuration, wavenumbers, attenuations, and mode amplitudes could be accurately extracted from the measurement data. To allow comparisons with theoretical analysis, dispersion curves of the wavenumbers, attenuations, and acoustic power characteristics of the axisymmetric and nonaxisymmetric modes are predicted by extending an existing waveguide model. The model extensions included the introduction of a monopole acoustic source into the water medium so that amplitude variations with respect to individual modes and frequencies could be investigated in detail. In addition, stiffness coefficients of HDPE material are carefully used to account for viscoelastic effects. The comparisons between the theoretical predictions and experimental results demonstrate a very good match and are a validation of the theoretical model.

Arterial pulse attenuation prediction using the decaying rate of a pressure wave in a viscoelastic material model

The present study examines the possibility of attenuating blood pulses by means of introducing prosthetic viscoelastic materials able to absorb energy and damp such pulses. Vascular prostheses made of polymeric materials modify the mechanical properties of blood vessels. The effect of these materials on the blood pulse propagation remains to be fully understood. Several materials for medical applications, such as medical polydimethylsiloxane or polytetrafluoroethylene, show viscoelastic behavior, modifying the original vessel stiffness and affecting the propagation of blood pulses. This study focuses on the propagation of pressure waves along a pipe with viscoelastic materials using the Maxwell and the Zener models. An expression of exponential decay has been obtained for the Maxwell material model and also for low viscous coefficient values in the Zener model. For relatively high values of the viscous term in the Zener model, the steepest part of the pulse can be damped quickly, leaving a smooth, slowly decaying wave. These mathematical models are critical to tailor those materials used in cardiovascular implants to the mechanical environment they are confronted with to repair or improve blood vessel function.

Numerical studies of cavitation erosion on an elastic–plastic material caused by shock-induced bubble collapse

We present a study of shock-induced collapse of single bubbles near/attached to an elastic–plastic solid using the free-Lagrange method, which forms the latest part of our shock-induced collapse studies. We simulated the collapse of 40 μm radius single bubbles near/attached to rigid and aluminium walls by a 60 MPa lithotripter shock for various scenarios based on bubble–wall separations, and the collapse of a 255 μm radius bubble attached to aluminium foil with a 65 MPa lithotripter shock. The coupling of the multi-phases, compressibility, axisymmetric geometry and elastic–plastic material model within a single solver has enabled us to examine the impingement of high-speed liquid jets from the shock-induced collapsing bubbles, which imposes an extreme compression in the aluminium that leads to pitting and plastic deformation. For certain scenarios, instead of the high-speed jet, a radially inwards flow along the aluminium surface contracts the bubble to produce a ‘mushroom shape’. This work provides methods for quantifying which parameters (e.g. bubble sizes and separations from the solid) might promote or inhibit erosion on solid surfaces.

Sonar equations for planetary exploration

The set of formulations commonly known as "the sonar equations" have for many decades been used to quantify the performance of sonar systems in terms of their ability to detect and localize objects submerged in seawater. The efficacy of the sonar equations, with individual terms evaluated in decibels, is well established in Earth's oceans. The sonar equations have been used in the past for missions to other planets and moons in the solar system, for which they are shown to be less suitable. While it would be preferable to undertake high-fidelity acoustical calculations to support planning, execution, and interpretation of acoustic data from planetary probes, to avoid possible errors for planned missions to such extraterrestrial bodies in future, doing so requires awareness of the pitfalls pointed out in this paper. There is a need to reexamine the assumptions, practices, and calibrations that work well for Earth to ensure that the sonar equations can be accurately applied in combination with the decibel to extraterrestrial scenarios. Examples are given for icy oceans such as exist on Europa and Ganymede, Titan's hydrocarbon lakes, and for the gaseous atmospheres of (for example) Jupiter and Venus.

Extraterrestrial sound for planetaria: A pedagogical study

The purpose of this project was to supply an acoustical simulation device to a local planetarium for use in live shows aimed at engaging and inspiring children in science and engineering. The device plays audio simulations of estimates of the sounds produced by natural phenomena to accompany audio-visual presentations and live shows about Venus, Mars, and Titan. Amongst the simulated noise are the sounds of thunder, wind, and cryo-volcanoes. The device can also modify the speech of the presenter (or audience member) in accordance with the underlying physics to reproduce those vocalizations as if they had been produced on the world under discussion. Given that no time series recordings exist of sounds from other worlds, these sounds had to be simulated. The goal was to ensure that the audio simulations were delivered in time for a planetarium's launch show to enable the requested outreach to children. The exercise has also allowed an explanation of the science and engineering behind the creation of the sounds. This has been achieved for young children, and also for older students and undergraduates, who could then debate the limitations of that method.

Isentropic wave propagation in a viscous fluid with uniform flow confined by a lined pipeline

The axisymmetric wave propagation in a viscous fluid with the presence of a uniform flow confined by a circular pipeline is investigated. Particular considerations are imposed on the features of the acoustic wave propagating in the liquid where the thermal conduction is neglected. The boundary constraints at the wall are reasonably discussed for both lined-walled and rigid-walled pipelines. Numerical comparisons of the phase velocity and wave attenuation among three different boundary configurations (rigid wall, steel-composed wall, and aluminum-composed wall) are presented. Meanwhile, the effects of the fluid viscosity and acoustic impedance are coherently analyzed. In the end, parametric analysis of the influence of the acoustic impedance is given in the case of a steel-composed pipeline.

Investigation of a method for real time quantification of gas bubbles in pipelines

The need to measure the dynamic void fraction (the proportion of flowing bubbly liquid that is gas) is common across many power, processing and manufacturing industries. Many such pipelines and liquids are optically opaque, and work on margins that require a low cost solution that is not commensurate with the size of the challenge. Such a solution will therefore be a compromise, and in this paper costs are reduced by using a narrowband acoustic solution that cannot, on its own, contain enough information to characterize the void fraction in real time unambiguously. The ambiguity is reduced using likely estimates of the general shape of the bubble size distribution so that, with a single source-receiver pair attached to the outside of the pipe, the absolute gas content can be estimated. While the data that are required a priori (the general shape of the bubble size distribution) are not identical to the output of the inversion (the absolute void fraction of gas entrained as bubbles in the flow), the requirement for such a priori information could limit the usefulness of the technique in industry.

Acoustic attenuation, phase and group velocities in liquid-filled pipes III: nonaxisymmetric propagation and circumferential modes in lossless conditions

Equations for the nonaxisymmetric modes that are axially and circumferentially propagating in a liquid-filled tube with elastic walls surrounded by air/vacuum are presented using exact elasticity theory. Dispersion curves for the axially propagating modes are obtained and verified through comparison with measurements. The resulting theory is applied to the circumferential modes, and the pressures and the stresses in the liquid-filled pipe are calculated under external forced oscillation by an acoustic source. This provides the theoretical foundation for the narrow band acoustic bubble detector that was subsequently deployed at the Target Test Facility (TTF) of the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), TN.

The use of acoustic inversion to estimate the bubble size distribution in pipelines

The most popular technique for estimating the gas bubble size distribution (BSD) in liquids is through the inversion of measured attenuation and/or sound speed of a travelling wave. The model inherent in such inversions never exactly matches the conditions of the measurement, and the size of the resulting error (which could well be small in quasi-free field conditions) cannot be quantified if only a free field code exists. Users may be unaware of errors because, with sufficient regularization, such inversions can always be made to produce an answer, the accuracy of which is unknown unless independent (e.g. optical) measurements are made. This study was commissioned to assess the size of this error for the mercury-filled steel pipelines of the target test facility (TTF) of the spallation neutron source at Oak Ridge National Laboratory, TN, USA. Large errors in estimating the BSD (greater than 1000% overcounts/undercounts) are predicted. A new inversion technique appropriate for pipelines such as TTF gives good BSD estimations if the frequency range is sufficiently broad. However, it also shows that implementation of the planned reduction in frequency bandwidth for the TTF bubble sensor would make even this inversion insufficient to obtain an accurate BSD in TTF.

The use of extra-terrestrial oceans to test ocean acoustics students

The existence of extra-terrestrial oceans offers the opportunities to set examination questions for which students in underwater acoustics do not already know the answers. The limited set of scenarios in Earth's oceans that can be presented to students as tractable examination questions means that, rather than properly assessing the individual scenario, students can rely on knowledge from previous examples in assessing, for example, which terms in equations are large and small, and what numerical values the answers are likely to take. The habit of adapting previous solutions with which the student is comfortable, to new scenarios, is not a safe approach to learn, as it ill equips the future scientist or engineer to identify and tackle problems which contain serious departures from their experience.

Demonstration comparing sound wave attenuation inside pipes containing bubbly water and water droplet fog

This paper describes a demonstration and explanation of sound absorption in water due to bubbles, and in air due to a fog of water droplets. It is suitable for 10-12 year olds, but the paper indicates where further exploration of the simplifications in the explanations provided for that age range would allow the demonstration to be used for undergraduate and Masters-level teaching. Applications to submarines, the space shuttle, and neutron generators are described. The demonstration is designed for transportation in a family-sized car.