Solution in NGSolve

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6 years 3 months ago #694 by Username

Solution in NGSolve was created by Username

Hi,

I solve the following problem:
The cantilever beam is fixed with one end firmly fixed at the other end and loaded with a concentrated force F = 1e5 N. The beam section is a square, and a = b = 1. The beam length is l = 10. The elastic modulus is E = 2.1e11, the Poisson's ratio is nu = 0.2.

The solution in Ansys is very different from the solution of the solution in NGSolve .

Think it is because I incorrectly set load in NGSolve. Can you explain how to set the load on a certain face? What could be the reason for this difference in the result?

Files: geometry , mesh , PDE and python file .

christopher
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6 years 3 months ago #696 by christopher

Replied by christopher on topic Solution in NGSolve

Hi,
You have to give the surface a seperate boundary number

Code:

solid p2 =  plane (10,1,1;1,0,0) -bc=3;

and then set the coefficientfunction only for bc 3 and 0 elsewhere:

Code:

# A surface force in z-direction for each piece of the boundary
define coefficient coef_surface_force_z
0, 0, 1e5, 

The BVP from Python doesn't work for vector valued vector entries and matrix valued matrix entries yet, so I replaced the following line in your Python file to get it running:

Code:

# BVP(bf=a, gf=u, lf=f, pre=c, maxsteps=1000).Do()
u.vec.data = a.mat.Inverse(fes.FreeDofs()) * f.vec

Best
Christopher

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cwinters
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6 years 3 months ago #697 by cwinters

Replied by cwinters on topic Solution in NGSolve

Hi,

you could also write everything in python.
Using linear strain and stress tensors, you get the bilinear form

Code:

a = BilinearForm(fes)
a += SymbolicBFI( 2*mu*InnerProduct(epsilon(u),epsilon(v)) + lam*Trace(u.Deriv())*Trace(v.Deriv()))

and for the force you can use

Code:

force = CoefficientFunction( (0,1e5,0) )

f = LinearForm(fes)
f += SymbolicLFI( force*v, definedon=mesh.Boundaries("force"))
f.Assemble()

The "definedon" restricts to the surface you wanted.

Best,
Christoph

Attachments:

..._2018-08-16.py

The following user(s) said Thank You: Username

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