Mailman 3 June 2023 - SfePy

Non linear material
by J. Sanz 12 Jul '23

12 Jul '23

Hello, I have a problem with a simulation including non lineal material.The problem involves a cantilever beam. The free end is moved 20 mm in X direction. I have compared the results with Ansys. The stresses are different, in particular at the pastification zone. Yield point of the material Relastic = 130 MPa, Epsilon elastic =0.00173 The material is bilinear, it has two slopes, young 1 and young2. The slope changes in the yield point. The no linear material function is based on calculating the strains in every cell. It is assigned the second young modulus for those strains higher than epsilon elastic. If lower, first young modulus is set. You can find attached the files and comparison. The picture with the comparison has the same scale, so the colours represent the same stress range. My doubts are the next: 1-I am not sure if the material definition is right. Can you confirm this for me? 2-Order of the stress strain evaluation, I set it to 3 because it provides the closest results. 3-The output file .vtk contains only nodal solution. How to get the elemental solution as well? Thanks, Jesus Sanz

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ANN: SfePy 2023.2
by Robert Cimrman 29 Jun '23

29 Jun '23

I am pleased to announce the release of SfePy 2023.2. Description ----------- SfePy (simple finite elements in Python) is a software for solving systems of coupled partial differential equations by finite element methods. It is distributed under the new BSD license. Home page: https://sfepy.org Mailing list: https://mail.python.org/mm3/mailman3/lists/sfepy.python.org/ Git (source) repository, issue tracker: https://github.com/sfepy/sfepy Highlights of this release -------------------------- - replace numpy.distutils by scikit-build (cmake) - interface for the PRIMME eigenvalue problem solver - new declarative modal analysis example - new terms: nonlinear diffusion and nonlinear volume forces For full release notes see [1]. Cheers, Robert Cimrman [1] http://docs.sfepy.org/doc/release_notes.html#id1 --- Contributors to this release in alphabetical order: Robert Cimrman Giuseppe Colletta Vladimir Lukes Yosef Meller

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Calculating strains from given nodal displacements
by Sebastian Bachmann 26 Jun '23

26 Jun '23

Hi! I have a tetrahedral mesh and know the nodal displacements of the mesh from an external software. I now want to calculate the element' strains and thought I give sfepy a go. However, the learning curve is very steep and I struggle a bit with this - I thought - easy task. I thought I basically need this function here: https://sfepy.org/doc-devel/primer.html#post-processing but how do I initially setup the problem and set the already solved displacement vector? This is what I got so far: ``` import numpy as np from sfepy.discrete.fem import Mesh, FEDomain from sfepy.discrete import Problem # Given: mesh and nodal displacements mesh = Mesh.from_file('the_mesh.vtk') u_vec = np.random.random((mesh.n_nod, 3)) # here I would insert the actual displacements. Use random numbers for testing domain = FEDomain('domain', mesh) omega = domain.create_region('Omega', 'all') # ??? pb = Problem('elasticity', domain=domain, ...) # ??? # ??? strain = pb.evaluate('ev_cauchy_strain.2.Omega(u)', mode='el_avg') ``` Am I on the right track here? Thanks in advance! Best, Sebastian

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How are matrix updates controlled?
by Yosef Meller 19 Jun '23

19 Jun '23

Since the stiffness matrix (in an elastic problem, say) depends on the shape and actual locations of mesh points, conceptually it should change on each time step. Yet, solving an elastodynamic problem and printing the intermediate M, C, K matrices, they don't seem to change - though there is code called to recompute them from the nls solver (td_solvers.py get_matrices() function). What needs to happen for the matrices to update really? Is it assumed that the mesh doesn't change much, so that no updates are needed?

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