space-dependent boundary conditions

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space-dependent boundary conditions

James
Hi,

For boundaries or interior boundaries, would it be possible to use the space-dependent boundary conditions in FEAtool? For example, for a X-Z 2D model, can we use the concentration or convective flux profile along X or Z direction instead of using a constant value? Are there any examples for such space-dependent boundary conditions?

Thank you for consideration.
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Re: space-dependent boundary conditions

Precise Simulation
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Yes, see for example step 22 in the cylinder benchmark tutorial:

https://www.featool.com/doc/fluid_dynamics_04_flow_around_cylinder1#tut_cfd04

and in the corresponding instationary m-script file model

https://github.com/precise-simulation/featool-multiphysics/blob/master/examples/ex_navierstokes6.m#L74
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Re: space-dependent boundary conditions

James
Thanks. Now I know how to set up the space-dependent boundary conditions.
Could you tell me what the unit is for the flux boundary conditions? e.g. for a 1D diffusion-advection model, the  third type flux boundary condition can be -n*(-D(dC/dx)+uC)=No, which can be found in the boundary condition options. What is the unit for n here and what is the unit for No? I cannot find the description for n in the online materials. Thanks.
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Re: space-dependent boundary conditions

Precise Simulation
Administrator
James wrote
Could you tell me what the unit is for the flux boundary conditions? e.g. for a 1D diffusion-advection model, the  third type flux boundary condition can be -n*(-D(dC/dx)+uC)=No, which can be found in the boundary condition options. What is the unit for n here and what is the unit for No? I cannot find the description for n in the online materials. Thanks.
For boundary conditions "n := {nx, ny, nz}" are the components of the outward pointing normal vector, so unitless. The other units depend on your chosen unit system. FEATool in itself is designed without adherence to any specific unit system, so the unit of "No" and all other coefficients (geometry length scale, D, C, etc) all depend on what you decide them to represent. In SI units for example:

unit length scale ~ [m], C ~ [mol/m^3],   D ~ [m^2/s], u ~ [m/s], d/dx ~ [1/m] => No ~ [mol/m^2/s]