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The “hydrodynamic” module of the Mohid system is able to simulate the flow in water masses where the flow velocity is lower than the celerity of the pressure wave. This module has been used to simulate hydrodynamic processes in oceans (Atlantic NE and Atlantic SW), in coastal areas (several areas along the Portuguese and Brazil coasts), in more than 30 estuaries and lagoons (European, African and Brazilian estuaries and lagoons) and in water dams (south of Portugal). All these study areas have complex flows and intense ecological activity with a strong relation with hydrodynamic processes. The “hydrodynamic” module aims to be a numerical tool oriented to help understanding biogeochemical processes and resolve ecological problems associated with human activity.


bullet Hydrostatic flow (a non-hydrostatic version is currently under development, click bellow to see a recent result)

Kelvin-Helmholtz instability in a water basin - animation 2.2 MB -

(Full version - 9.1MB available here)

bulletBoussinesq approximation

Numerical characteristics

Main characteristics

Spatial discretization Finite volumes
Horizontal Grid Orthogonal
Vertical Grid Generic coordinates
Computation points distribution Arakawa C
Time discretization ADI

Forces discretization

Forces computed explicitly Coriolis, tide potential, baroclinic pressure gradient, atmosphere forcing (wind stress and pressure), horizontal advection and diffusion of momentum
Forces computed implicitly Barotropic pressure gradient, bottom friction, vertical advection and diffusion of momentum
Baroclinic pressure spatial discretization Cartesian referential (or z level referential)
Horizontal advection of momentum
bulletHybrid (upwind + central differences)
bullet2º order upwind
Vertical advection of momentum
bulletHybrid (upwind + central differences)
Diffusion of momentum Central differences

Boundary conditions

Barotropic pressure gradient:
bulletWater level
bulletBarotropic velocity


bulletNull gradient
bulletRadiation - Flather, 1976
bulletRadiation – Blumberg & Kantha, 1985
bulletFlow relaxation

The last three boundary conditions use a reference solution that can be imposed using two methodologies:

bulletInput data – the solution is imposed as model input data
bulletOne way nesting -  the solution is compute by a courser grid model
bulletBaroclinic pressure gradient:
bulletBaroclinic velocity
bulletTemperature and salinity
bulletNull gradient
bulletRadiation – Marchesiello et al., 2001
bulletCelerity constant
bulletCelerity – Orlansky, 1976
bulletFlow relaxation:
bulletInput data
bulletOne way nesting
Coriolis, horizontal advection and diffusion of momentum:

imposed null value


Null gradient












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This site was last updated in 05-03-2006

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