Visualise Eigensolution using Netgen/NGSolve

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1

Hey community,

i’m quite new to NGSolve. I try to make some studies on acoustics in various geometries (2d and 3d).
After assembling the matrices (for Helmholtz PDE) i can solve the eigenproblem.

Next i want to visualise the different modes on the geometry. Can you give me a hint to the right approach or some examples? Perhaps it’s very easy and i just didn’t get the concept right.

Thanks for your support!

2

Hi,
if you use the Arnoldi solver of NGSolve then you store the modes in the multidim gridfunction:

from netgen.geom2d import unit_square
from ngsolve import *

mesh = Mesh(unit_square.GenerateMesh(maxh=0.3))

fes = H1(mesh,order=5,dirichlet="bottom|left|right|top",complex=True)

u,v = fes.TrialFunction(), fes.TestFunction()

a = BilinearForm(fes)
a += SymbolicBFI(grad(u)*grad(v))
b = BilinearForm(fes)
b += SymbolicBFI(u*v)

a.Assemble()
b.Assemble()

u = GridFunction(fes,multidim=50)
vlam = ArnoldiSolver(a.mat,b.mat,fes.FreeDofs(),u.vecs,1)
Draw(u)

Then you can visualize the different eigenfunctions with Visual → and change multidim component

Best
Christopher

3

Thank you very much! This really helped me out.