[Eoas-seminar] Fw: EOAS Colloquium Announcement, September 5, 2025

[eoas-seminar at lists.fsu.edu]

Hi all,

This is a friendly reminder that EOAS will hold its first colloquium of the 2025–2026 academic year this afternoon. Due to a newly scheduled urgent P&T meeting, the colloquium will begin 30 minutes later than originally planned, at 3:30 PM instead of 3:00 PM.

Cheers,

Ming and Zhaohua
________________________________
From: 'Zhaohua Wu' via info at coaps <info at coaps.fsu.edu>
Sent: Friday, August 29, 2025 8:40 AM
To: EOAS seminar <eoas-seminar at lists.fsu.edu>; 'Shawn Smith' via info at coaps <info at coaps.fsu.edu>
Subject: [INFO] EOAS Colloquium Announcement, September 5, 2025

Hi all,
You are cordially invited to attend the weekly EOAS Colloquium Series for the 2025–2026 academic year. The first colloquium will be held one week from today. Details are provided below:
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Time:
3:00 - 4:00 PM, Friday, September 5.

Location:
EOA 1044

Speaker:
Dr. Zhaohua Wu, EOAS, Florida State University

Title:
Reconciliation of Conservation Laws for Waves in a Spatially Varying and Inhomogeneously Moving Medium

Abstract:
Waves are propagating disturbances that redistribute energy across space. Their propagation involves the exchange of energy between the waves and the surrounding medium. This energy exchange can serve two primary roles: (1) facilitating the propagation of the wave, and (2) acting as an energy source or sink for the wave, potentially leading to instabilities. The tendency of the medium to return to its original state after the wave passes suggests that its principal function is to enable wave propagation—implying that wave energy conservation should hold, even in the presence of local energy exchange with the medium. However, previous studies have shown that in inhomogeneously moving mean flows—a specific class of varying media—the conserved quantity is wave action rather than wave energy. This apparent contradiction has remained unresolved. In this study, we address and resolve this sixty-year dilemma. By approximating a continuously varying medium as a series of infinitesimally small, piecewise constant segments and accounting for energy reflection at their interfaces, we demonstrate that wave action conservation is, in fact, an emergent form of wave energy conservation in spatially varying and inhomogeneously moving media, where waves deform as they propagate. Furthermore, we show that wave action conservation can be derived directly from the fundamental law of energy conservation. This result applies universally to all isolated wave systems in varying media, encompassing both hydrodynamic and non-hydrodynamic waves.

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Cheers,

Ming Ye and Zhaohua Wu

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