Thermo-visco-acoustic metamaterials for underwater applications

Lead Research Organisation: University of Manchester
Department Name: Mathematics


The ability to control underwater noise has been of practical interest for decades. Such noise, radiating from e.g. offshore wind farms, turbines, and merchant vessels, frequently needs to be attenuated artificially given the close proximity of its generation to sensitive marine environments for example. The interest in defence applications is, of course to render a vessel as quiet as possible.
Over the last century a number of materials have been designed to assist with underwater noise attenuation. However, recently there has been an explosion of interest in the topic of acoustic metamaterials and metasurfaces. Such media have special microstructures, designed to provide overall (dynamic) material properties that natural materials can never hope to attain and lead to the seemingly rather strange notions of negative refraction, wave redirection, the holy grail of cloaking. Many of the mechanisms to create these artificial materials rely on the notion of resonance. This then provides the possibility of low frequency sound attenuation which is extremely difficult to achieve with normal materials. An example of a classical low frequency resonator is the Helmholtz resonator.
The mechanisms of sound attenuation, i.e. thermal and viscous, have not yet been properly understood for the many metamaterials under study, particularly in an underwater context. The aim of this project is to study this aspect via mathematical analysis and then to optimize designs in order to employ metamaterials for use in underwater noise reduction applications. Although there has been some initial interest over the last few years in the "in-air" context, the parameter regime underwater gives rise to new effects that need to be explored and understood thoroughly.


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Cotterill PA (2018) Thermo-viscous damping of acoustic waves in narrow channels: A comparison of effects in air and water. in The Journal of the Acoustical Society of America

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/R512035/1 30/09/2017 31/12/2022
1936217 Studentship EP/R512035/1 25/09/2017 30/05/2021 Erik Garcia Neefjes
Description We have been able to present some new results in fluid-filled narrow channels, focusing on the attenuation properties through boundary layers.
In particular, we have written the framework for a general newtonian fluid, but focused on air and water as the two main fluids.

We have then constructed a very general model for wave propagation in thermo-visco-elastic continua so that we may study gases, liquids and solids simultaneously. In particular, we have shown that the more restrictive theories can be obtained from this very general framework by taking the particular limits in the model. We are now working on canonical problems to apply this model.

We have now applied this model to some canonical problem including TVE half spaces and TVA channels embedded in TVE channels. Important dissipative effects such as stress relaxation have been included in the model. We are now in the process of writing up these results.
Exploitation Route It could be a useful tool for people to be able to simulate the behaviour of complicated materials via simulations. As a result this could be used for the design of novel materials focused on absorption properties.
Sectors Aerospace, Defence and Marine,Environment