{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,8]],"date-time":"2026-04-08T16:14:12Z","timestamp":1775664852579,"version":"3.50.1"},"reference-count":25,"publisher":"Acoustical Society of America (ASA)","issue":"6","license":[{"start":{"date-parts":[[2023,6,23]],"date-time":"2023-06-23T00:00:00Z","timestamp":1687478400000},"content-version":"vor","delay-in-days":22,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"},{"start":{"date-parts":[[2023,6,23]],"date-time":"2023-06-23T00:00:00Z","timestamp":1687478400000},"content-version":"tdm","delay-in-days":22,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2023,6,1]]},"abstract":"<jats:p>The Kirchhoff\u2013Helmholtz representation of linear acoustics is generalized to thermoviscous fluids, by deriving separate bounded-region equations for the acoustic, entropy, and vorticity modes in a uniform fluid at rest. For the acoustic and entropy modes we introduce modal variables in terms of pressure and entropy perturbations, and develop asymptotic approximations to the mode equations that are valid to specified orders in two thermoviscous parameters. The introduction of spatial windowing for the mode variables leads to surface source and dipole distributions as a way of representing boundary conditions for each mode. For the acoustic mode the boundary source distribution is expressible in terms of the fluid normal velocity, the normal heat flux, and the vector \u03c9\u00d7n\u0302, where \u03c9 is the vorticity on the boundary and n\u0302 is the unit normal; only the first of these is present in the usual lossless-fluid version of the Kirchhoff\u2013Helmholtz representation. Use of the generalized thermoviscous representation to project exterior sound fields from surface data, where the data may contain contributions from all three linear modes, is shown to be robust to cross-modal contamination. The asymptotic limitations of the thermoviscous modal equations are discussed in an appendix.<\/jats:p>","DOI":"10.1121\/10.0019801","type":"journal-article","created":{"date-parts":[[2023,6,25]],"date-time":"2023-06-25T02:10:18Z","timestamp":1687659018000},"page":"3447","update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":4,"title":["Acoustics of thermoviscous fluids: The Kirchhoff\u2013Helmholtz representation in generalized form"],"prefix":"10.1121","volume":"153","author":[{"given":"C. L.","family":"Morfey","sequence":"first","affiliation":[{"name":"School of Engineering, University of Leicester 1 , Leicester LE1 7RH, United Kingdom"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9393-4918","authenticated-orcid":false,"given":"M. C. 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