Hydrodynamics

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.

Approximations

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)

Boussinesq 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

	Hybrid (upwind + central differences)
	2º order upwind

Vertical advection of momentum

Hybrid (upwind + central differences)

Diffusion of momentum

Central differences

Boundary conditions

Barotropic pressure gradient:

	Water level
	Barotropic velocity

	Imposed
	Null gradient
	Cycle
	Radiation - Flather, 1976
	Radiation – Blumberg & Kantha, 1985
	Flow relaxation

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

	Input data – the solution is imposed as model input data
	One way nesting - the solution is compute by a courser grid model

	Baroclinic pressure gradient:
	Baroclinic velocity
	Temperature and salinity

Imposed

Null gradient

Radiation – Marchesiello et al., 2001

	Celerity constant
	Celerity – Orlansky, 1976

Flow relaxation:

	Input data
	One way nesting

Coriolis, horizontal advection and diffusion of momentum:

velocity

	imposed null value
	Null gradient

This site was last updated in 05-03-2006