I have a time depended Neumann boundary, exp(t) for 1d wave equation, I code it into the weak form, but when I put it into the while loop, it got an error from dolfin import * import numpy as np c=1000 Length=100.0 mesh = IntervalMesh(1000,0,Length) V=FunctionSpace(mesh, "Lagrange", 1) class Rig…

Sorry, I didn’t see the rest part of the error. The post has been modified.

[image] Miraboreasu: u=Function(V) You are redefining the trial function u before you are defining your variational form, and Therefore you obtain an error message. As a general rule, you should try to define the variational formulation outside for loops.

If I put variational formulation out the while loop, how to update the time for the boundary?

Define either an Expression or a Constant which can you can update the value of inside the for-loop. See for instance: Time-integration of elastodynamics equation — DOLFIN documentation or Bitbucket

I am follow the How to apply time varying boundary conditions coming from a function? I test this with two def, one is exp(t), another one is a long equation, but except t, all other letters are defined, which are numbers. blast=Constant((Po*(1-t/t1)*exp(-b*((t-t2)/t1)))/E) def blast_func(t): …

[image] Miraboreasu: def blast_func(t): return (Po*(1-t/t1)*exp(-b*((t-t2)/t1)))/E You need to make sure that the return type of blast_func is a float. Currently you are using ufl.exp (as it is import with dolfin). You need to use numpy.exp to make the return type a float. For further qu…

I replace the exp with np.exp from dolfin import * import numpy as np E=3300000000.0 rho=1300.0 c = sqrt(E/rho) Po=30000000.0 t1=0.00015 t2=0.001 b=1.0 Length=100.0 mesh = IntervalMesh(1000,0,Length) V=FunctionSpace(mesh, "Lagrange", 1) class Right(SubDomain): def inside(self,x,on_boundary)…

Again, you keep on redeclaring variables. In this case it is b [image] Miraboreasu: b=1.0 that is redeclared as [image] Miraboreasu: A, b = assemble_system(a, L, bc) Call the first b something different, for instance b_.

Thank you dokken, another boundaries question, I learn another way to set the mixed boundary conditions( 22. Poisson equation with multiple subdomains — FEniCS Project ), namely for x in [0,Length] u=(Length, t)=0 u_x(0, t)=func(t) The first (previous) version is from dolfin import * import numpy…

Time depended Neumann boundary

dokken February 17, 2021, 4:03pm 2

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Time depended Neumann boundary

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