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System state dependent boundary condition
Posted 15 apr 2014, 05:04 GMT-4 Fluid & Heat, Modeling Tools & Definitions, Parameters, Variables, & Functions Version 4.4 0 Replies
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Consider a porous media is of arbritrary length (1D) and the water movement within is mathematically expressed by the Richards equation.
The lower boundary is defined to be a zero flux boundary condition.
The upper boundary is an atmospheric boundary condition, i.e. a vector over time, with discrete boundary fluxes. If at an arbritrary timeintervall "delta_t_i", the boundary flux provided is larger than the porous media can physically sustain* water flow, convergence problems in COMSOL simulations arise.
The model has been implemented in coefficient form.
The question is: How can flux boundary conditions be defined in a way that a system dependent swith for the boundary type is deone, i.e from Neumann to Dirichlet? (NeumannDirichlet conditions)
The solution in general
* In evaporation 2 stages of evaporation may be differentiated: Stage 1 and Stage 2. Rule: Stage 1, athmospheric conditions limits the evaporation, Stage 2 hydraulic properties of the porous media limit evaporation. The above mentioned problem arises when entering stage 2 evaporation in simulation of this kind
Hello Tobias Weber
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