Shallow water equations | Wikipedia audio article
Channel: wikipedia tts
Date: 02/10/2019

This is an audio version of the Wikipedia Article:
https://en.wikipedia.org/wiki/Shallow_water_equations


00:02:28 1 Equations
00:02:37 1.1 Conservative form
00:05:55 1.2 Non-conservative form
00:11:05 2 One-dimensional Saint-Venant equations
00:12:24 2.1 Equations
00:13:32 2.2 Conservation of momentum
00:16:12 2.3 Characteristics
00:19:14 2.4 Derived modelling
00:19:53 2.4.1 Dynamic wave
00:22:29 2.4.2 Diffusive wave
00:22:38 2.4.3 Kinematic wave
00:23:29 2.5 Derivation from Navier–Stokes equations
00:24:46 3 Wave modelling by shallow water equations
00:25:39 4 Turbulence modelling using non-linear shallow water equations
00:28:46 5 Notes
00:29:50 6 Further reading
00:31:05 7 External links
00:31:14 Further reading
00:31:23 External links



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SUMMARY
=======
The shallow water equations are a set of hyperbolic partial differential equations (or parabolic if viscous shear is considered) that describe the flow below a pressure surface in a fluid (sometimes, but not necessarily, a free surface).  The shallow water equations in unidirectional form are also called Saint-Venant equations, after Adhémar Jean Claude Barré de Saint-Venant (see the related section below).
The equations are derived from depth-integrating the Navier–Stokes equations, in the case where the horizontal length scale is much greater than the vertical length scale.  Under this condition, conservation of mass implies that the  vertical velocity scale of the fluid is small compared to the horizontal velocity scale.  It can be shown from the momentum equation that vertical pressure gradients are nearly hydrostatic, and that horizontal pressure gradients are due to the displacement of the pressure surface, implying that the horizontal velocity field is constant throughout the depth of the fluid.  Vertically integrating allows the vertical velocity to be removed from the equations.  The shallow water equations are thus derived.
While a vertical velocity term is not present in the shallow water equations, note that this velocity is not necessarily zero.  This is an important distinction because, for example, the vertical velocity cannot be zero when the floor changes depth, and thus if it were zero only flat floors would be usable with the shallow water equations.  Once a solution (i.e. the horizontal velocities and free surface displacement) has been found, the vertical velocity can be recovered via the continuity equation.
Situations in fluid dynamics where the horizontal length scale is much greater than the vertical length scale are common, so the shallow water equations are widely applicable.  They are used with Coriolis forces in atmospheric and oceanic modeling, as a simplification of the primitive equations of atmospheric flow.
Shallow water equation models have only one vertical level, so they cannot directly encompass any factor that varies with height. However, in cases where the mean state is sufficiently simple, the vertical variations can be separated from the horizontal and several sets of shallow water equations can describe the state.