Run-Time Information

Graphs showing temporal distributions of the time step, number of iterations necessary to solve the Richards equation at a particular time level, the cumulative number of iterations, and the dimensionless Peclet and Courant numbers. These variables can be drawn against either time or time level.

The Peclet number characterizes the spatial discretization. It defines the predominant type of solute transport process (notably the ratio of the advective and dispersive transport terms) in relation to coarseness of the finite element grid as follows.

The Peclet number increases when the advective transport dominates dispersive transport, i.e., such as when a relatively steep concentration front is present (other scenario’s are also possible). To achieve acceptable numerical results, the spatial discretization must be kept relatively dense to maintain a low Peclet number. Numerical oscillations can be virtually eliminated when the local Peclet numbers do not exceed about 5.

The Courant number is associated with the time discretization. The maximum permitted time step in HYDRUS is calculated so that the local Courant number is always less then 1.

See the X-Y Graph  topic for more information on this graph.

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