time dependent dirichlet boundary condition

[sezerh24]

Hi,

How can i implement time dependent dirichlet boundary condition. Lets say I am solving for the temperature in 1D, at the left boundary T left b = T0 + A*t, where T0 is is the temperature at boundary at t = 0; A is a constant and t is the time in this case.

Thank you

[sezerh24]

Indeed, I had find out how to implement time dependent bc. I knew about ramp function, however, I did not know that the system can update the boundary condition at each time: here is the implementation of time dependent BC:

Tf is the surface temperature and it change with the time according to the following function:

Tf(t) = Tₐ + (1100-(Tₐ-273.18))(1-exp(-exp(0.71log(t/124.8)))) - 100*(1-exp(-exp(0.71*log(t/124.8))))

function bconditionsT!(f,u,bnode,data)
v=ramp(bnode.time,dt=(0,final_t),du=(Tf(bnode.time), Tf(bnode.time)))
boundary_dirichlet!(f,u,bnode,species=Tₙ,region=1,value=v)
boundary_dirichlet!(f,u,bnode,species=mₙ,region=2,value=0)
end

[j-fu]

I think you don't need the ramp function here - you can just write
v=Tf(bnode.time)

The ramp function is meant to help with the situation where e.g. at t=0 we have a zero initial value, and want to set a nonzero Dirichlet bc u=u_d for t>0. In this case, the timestep adapation would struggle. Using ramp(t, dt=(0,delta), du=(0,u_d)) allows to ramp up the bc from zero during the small time interval (0,delta), and the time step control can adapt.

[j-fu]

Note to self - there should be an example clarifying this...