open TELEMAC-MASCARET The mathematically superior suite of solvers

Dear all,

I don't know whether it is suitable to ask in here or not.


I am confuss about the 3d Reynolds-averaged Navier stockes (RANS) equation and 3d shallow water equation. As far as I understand, TELEMAC3D is using 3d shallow water equation to simulate the velocity and water depth.

From Navier stockes equation to Reynolds-averaged Navier stockes equation is based on 2 assumptions Boussinesq approximation and Eddy viscosity concept or Boussinesq hypothesis.

and from Reynolds-averaged Navier stockes equation to the shallow water equation is based on the assumption that: the characteristic horizontal length scale is much larger than the characteristic vertical length scale. (ii) The characteristic vertical velocity is small in
comparison with the characteristic horizontal velocity.


Is anybody tell me what I am right or wrong. Thanks very much.

Best Regards

Harryyao

Hello,

The RANS equations are Navier-Stokes equations with the eddy viscosity concept. The Boussinesq hypothesis deals with the value of the eddy viscosity.

The Boussinesq approximation deals with floatability effects, it is a way to linearise the inverse of the density.

The Shallow Water Equations or Saint-Venant equations are basically an average on the vertical of the RANS equations. It assumes an hydrostatic pressure.

Telemac-3D IS NOT using shallow water equations. What could be called 3D Saint-Venant is the hydrostatic option of Telemac-3D.

The non-hydrostatic option of Telemac-3D solves the full 3D non hydrostatic RANS equations with a free surface.

I hope this clears up the matter a bit...

With best regards,

Jean-Michel Hervouet

Hi, Jean-Michel,


Thank you very much for your explain, According to your explain, the Telemac-3d can be solved both 3d shallow water eqution (3D Saint-Venant) and 3d RANS equation.

Do the telemac-2d also have 2 options? for the 2D Saint-Venant and 2D RANS equation. Form my use experience, I think for telemac2d, there is only one options for telemac 2d that is 2d Saint-Venant (2d shallow water equation).

Best Regards

Hello,

With Telemac-2D we solve Saint-Venant equations, but also Boussinesq equations.
The two options for Saint-Venant equations (TREATMENT OF THE LINEAR SYSTEM) refer to two different techniques for solving the equations : solving the equations in a couped way (called "primitive equations"), or eliminating the velocity from the continuity equation (called the "wave equation").

Regards,

JMH