Hello everyone! I am new to fenics and trying to improve my skills by trying to solve some basic problems. Currently I am trying to solve scattering problem on a cylinder. But I got stuck on a step with Robin boundary conditions. I dont understand how to implement it on outer boundary. from fenic…

See for instance: https://fenicsproject.org/pub/tutorial/html/._ftut1014.html for Legacy DOLFIN and https://jsdokken.com/dolfinx-tutorial/chapter3/robin_neumann_diriclet.html?highlight=robin for DOLFINx

Thanks for useful links. Read everything for legacy, but applying new code involving weak formulation for my case I got error. I attach code and bug report below: from fenics import * import sympy as sym import matplotlib.pyplot as plt from mshr import * import math import numpy as np def mu(u): …

[image] Apoh: def Dirichlet(x, on_boundary): This function should be called inside, and similarly for [image] Apoh: def ABC(self,x, on_boundary):

Sorry, English is foreign language for me. What do you mean by inside?

[image] Apoh: class Boundary_in(SubDomain): def Dirichlet(x, on_boundary): Should be class Boundary_in(SubDomain): def inside(x, on_boundary): And the same for the Boundary_out class

Thanks. I have one more question, hope this one is the last. I looke through legacy documentation, and found out, that it doescnt work with complex functions. I understand that the only way to solve is to split up my equation in weak form into imaginary and real parts and then check absolute value …

I would strongly suggest using DOLFINx if you are new to FEniCS, especially as it has complex number support. For a normal projection, simply define a facetnormal, and call u = Function(V) n = FacetNormal(mesh) un = dot(u, n) * n For tangential projections see Tangential gradient operator error: …

Thanks, but still, how could I deal with x-dependence in Robin BC. Putting it inside weak formulation symbolically causes error, cause LU solve doesnt know how to deal with it

with x-dependence i guess you mean that the Robin condition is dependent of the physical location in space? If so, you can use x=SpatialCoordinate(mesh) in your variational forms, where x[0] is the x coordinate, x[1] is y etc

Hello, I have followed your advice and now solving with dofinx version in docker. But now I have another problem. Since here we use not mshr, but pygmsh to create mesh, I come into some troubles. I followed one of your tutorials on mesh plotting ( Mesh generation and conversion with GMSH and PYGMSH |…

Robin conditions

General

dokken January 4, 2023, 3:35pm 12

You have not marked the physical surface (volume of the mesh, and thus it cannot load it), see for instance: Problem converting gmsh to xdmf for fenics - #2 by dokken

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Robin conditions

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