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Nonlinear Acoustics

When the amplitude of sound pressure waves becomes very high, the assumptions underlying the linear wave equation are no longer valid. In this NAG Masterclass, Dr. Anne de Jong provides an overview of nonlinear phenomena, such as wave stiffening and streaming, as well as the modeling methods.

Modeling Methods for Nonlinear Acoustics

At very high sound pressures, wave crests propagate faster than troughs, causing a sine wave to distort into a sawtooth wave and form a shock wave. Dr. Anne de Jong derives the nonlinear wave equations from the conservation laws of fluid dynamics: from Kuznetsov (velocity potential) to Westervelt (acoustic pressure, as implemented in COMSOL). He also discusses time-averaged (DC) effects arising from the square of oscillating terms, with applications in thermoacoustic energy conversion, acoustic streaming, and acoustic levitation (radiation pressure).

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