Fluid loading effects for acoustical sensors in the atmospheres of Mars, Venus, Titan, and Jupiter

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.

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.

The inertial terms in equations of motion for bubbles in tubular vessels or between plates

Equations resembling the Rayleigh-Plesset and Keller-Miksis equations are frequently used to model bubble dynamics in confined spaces, using the standard inertial term RR+3R([middle dot]) (2)/2, where R is the bubble radius. This practice has been widely assumed to be defensible if the bubble is much smaller than the radius of the confining vessel. This paper questions this assumption, and provides a simple rigid wall model for worst-case quantification of the effect on the inertial term of the specific confinement geometry. The relevance to a range of scenarios (including bubbles confined in microfluidic devices; or contained in test chambers for insonification or imaging; or in blood vessels) is discussed.

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

This paper uses a finite element method (FEM) to compare predictions of the attenuation and sound speeds of acoustic modes in a fluid-filled pipe with those of the analytical model presented in the first paper in this series. It explains why, when the predictions of the earlier paper were compared with experimental data from a water-filled PMMA pipe, the uncertainties and agreement for attenuation data were worse than those for sound speed data. Having validated the FEM approach in this way, the versatility of FEM is thereafter demonstrated by modeling two practical applications which are beyond the analysis of the earlier paper. These applications model propagation in the mercury-filled steel pipework of the Spallation Neutron Source at the Oak Ridge National Laboratory (Tennessee), and in a long-standing design for acoustic sensors for use on planetary probes. The results show that strong coupling between the fluid and the solid walls means that erroneous interpretations are made of the data if they assume that the sound speed and attenuation in the fluid in the pipe are the same as those that would be measured in an infinite volume of identical fluid, assumptions which are common when such data have previously been interpreted.

Real-time on-line ultrasonic monitoring for bubbles in ceramic 'slip' in pottery pipelines

When casting ceramic items in potteries, liquid 'slip' is passed from a settling tank, through overhead pipelines, before being pumped manually into the moulds. It is not uncommon for bubbles to be introduced into the slip as it passes through the complex piping network, and indeed the presence of bubbles is a major source of financial loss to the ceramics industry worldwide. This is because the bubbles almost always remain undetected until after the ceramic items have been fired in a kiln, during which process bubbles expand and create unwanted holes in the pottery. Since there it is usually an interval of several hours between the injection of the slip into the moulds, and the inspection of the items after firing, such bubble generation goes undetected on the production line during the manufacture of hundreds or even thousands of ceramic units. Not only does this mean hours of wasted staff time, power consumption and production line time: the raw material which makes up these faulty items cannot even be recycled, as fired ceramic cannot be converted back into slip. Currently, the state-of-the-art method for detecting bubbles in the opaque ceramic slip is slow and invasive, can only be used off-line, and requires expertise which is rarely available. This paper describes the invention, engineering and in-factory testing across Europe of an ultrasonic system for real-time monitoring for the presence of bubbles in casting slip. It interprets changes in the scattering statistics accompanying the presence of the bubbles, the latter being detected through perturbations in the received signal when a narrow-band ultrasonic probing wave is transmitted through the slip. The device can be bolted onto the outside of the pipeline, or used in-line. It is automated, and requires no special expertise. The acoustic problems which had to be solved were severe, and included making the system capable of monitoring the slip regardless of the material of pipe (plastic, steel, etc.) and nature of the slip (which can be very variable). It must also be capable of detecting bubbles amongst the myriad solid particles and other species present in the flowing slip. The completed prototype was tested around several factories in Europe, and proved not only to be more versatile, but also more sensitive, than the state-of-the-art method.