[WuMing00]

Hello everyone,
I have a question regarding the application of a boundary condition dependent on the distribution of a variable on a surface. I understand how to apply this type of boundary condition using expressions based on, for example, the average of a quantity over a surface. However, I am wondering if it is possible to apply a variable boundary condition based on the pointwise distribution of a variable on a surface.

Thank you

[ghorrocks]

Yes, you can do pointwise calculation of boundary variables. Not all boundary types support it but many do.

[WuMing00]

Hi Glenn, thank you for your answer.
I'm not able to find the syntax to define the correct expression.
To make a simple example, let's say I have to set a heat source on a surface named 'Surface_1' proportional to the pointwise distribution of temperature on the surface itself. If I want to define the heat source as a function of the average value of the temperature, the expression would be like 'Coefficient * areaAve(Temperature)@Surface_1.' What is the correct syntax to implement a similar expression but using the pointwise temperature distribution on the surface?

Thank you

[ghorrocks]

To apply a pointwise boundary condition on a wall, let's say you want to apply the convection heat transfer equation of q(dot) = h(T-T(far)), you simply set a source term on the surface to a CEL expression like
5[W m^-2 K^-1]*(T - 20[C])

You should then apply a source term linearisation coefficient of 5 [W m^-2 K^-1] (this is described in the manual). This will assist convergence.

You could also do this using a heat flux boundary condition on the wall rather than a source term - I am not sure how the linearisation is handled in this case, and if it is poorly handled you will get poor convergence or divergence.

[WuMing00]

Thank you very much for your help!

Best Regards