SfePy September 2012

sfepy@python.org

5 participants
13 discussions

Re: Torque
by Robert Cimrman 09 Mar '18

09 Mar '18

In examples/large_deformation/hyperelastic.py a rotation by displacements is applied. By using a similar function the vectors defining the force couples could be defined for dw_surface_ltr (IMHO). Does it make sense? r. ----- Reply message ----- From: "Andre Smit" <freev...(a)gmail.com> To: <sfepy...(a)googlegroups.com> Subject: Torque Date: Sat, Dec 18, 2010 05:10 What is the best way to apply a torque load to a model? -- Andre -- You received this message because you are subscribed to the Google Groups "sfepy-devel" group. To post to this group, send email to sfepy...(a)googlegroups.com. To unsubscribe from this group, send email to sfepy-devel...(a)googlegroups.com. For more options, visit this group at http://groups.google.com/group/sfepy-devel?hl=en.

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1D line elements in SfePy
by Nimish 22 Jan '16

22 Jan '16

I am currrently looking for FEM packages to help me solve a system of beams and columns, basically a collection of 1D bernoulli/timoshenko line elements. I started reading SfePy docs and i am getting the idea that doing the above is not really possible here, am i right? Are only 2D area elements permitted in SfePy? Or is there any direct support for solving 1D line elements too.. Cheers Nimish

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Evaluate a solution in the arbitrary point in the domain
by Alec Kalinin 03 Apr '14

03 Apr '14

Dear SfePy users, Is it possible to evaluate a solution not only in the FEM mesh node, but in any arbitrary point in the domain with the given (x, y, z) coordinates? For example, consider Dirichlet problem for Poisson equation. We apply essential boundary conditions on the surface nodes and after the problem has been solved we have the solution vector, i.e. vector of values in the FEM mesh nodes. But I want to know the solution in point v(x, y, z) that is not FEM mesh node. What is the best way to obtain solution in this point v? Sincerely, Alec Kalinin

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Modeling an adjustable X-ray optic
by Tom Aldcroft 21 May '13

21 May '13

I'm working on modeling a next-generation X-ray mirror for which the shape can be actively controlled by use of many thin piezo-electric actuators mounted on the mirror surface. The mirror is basically a glass conical paraboloid with a 1 meter radius and 200 micron thickness (e.g. http://en.wikipedia.org/wiki/X-ray_optics). Our project is currently using a proprietary FEA package, but the model setup and turnaround time is slow, in part because there is only one part-time engineer who can run it. SfePy looks like a great package and we're hoping that it could be used to automate running a large number of different cases. I've spent some time reading the documentation but I have a few questions that I hope can be answered before going too much further. I want to apologize in advance if some of my wording is imprecise, I have a physics background but this topic is a bit outside my realm... - Is SfePy appropriate for this problem? - If a specify a grid with about 800 x 400 points (azimuthal, axial) and about 10 boundary conditions (corresponding to mount points), what is the rough order of magnitude of time to compute the solution? Is it seconds, minutes, hours, or days? - The linear elastic examples show a problem with a specified displacement. How do I specify an input force? The piezo essentially provides a tensile force along the surface. - Is there a way to specify the problem and solve in cylindrical coordinates? This is the natural coordinate system. - How do I specify 6-DOF constraints which correspond to the mirror mounts? Thanks in advance for any help! Tom Aldcroft

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updates after 2012.3
by Robert Cimrman 03 Oct '12

03 Oct '12

Hi, this is to inform you about the latest updates of the code. 1. The 'hierarchic' branch has been merged into the master. This branch introduces a hierarchical FE basis into the code and some other tools described below. Look at [1] for an example. It's not finished, but I have decided to merge it already, as the general ideas seem to be work, and I needed some of the developments in the master and vice-versa. The caveats are for now: - Only 2_4 (rectangles) and 3_8 (bricks) elements are supported. - Dirichlet boundary conditions are piece-wise linear - the higher order boundary dofs are set to zero. To allow them, projections to FE spaces on a region would have to be implemented. We are thinking about redesigning the C FE core to make tasks such as this easier. - Surface integral terms are not yet supported. - The post-processing is more difficult, as a linearization of the solution is required. - A test was written that checks the basis continuity between two elements. This test revealed that the standard nodal basis on 3_8 elements has wrong face orientations (the functions from the two face sides do not match) for approximation order >= 3. This will be fixed, hopefully before the next release. 2. New plotting modules / updated scripts: - script/save_basis.py can be used to visualize a FE basis or its gradient on a single element or on a (small) mesh. - New modules sfepy/postprocess/plot_facets.py and sfepy/postprocess/plot_dofs.py can be used to plot the reference elements and DOF numberings. Matplotlib with mplot3d is needed there. r. [1] http://docs.sfepy.org/doc-devel/examples/diffusion/sinbc.html

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Singular matrix warning
by Alec Kalinin 27 Sep '12

27 Sep '12

Hello SfePy, During the problem solution I got the error: sfepy: nls: iter: 0, residual: 5.088014e+00 (rel: 1.000000e+00) warning: singular matrix zeroing nan and inf entries... /usr/lib/python2.7/dist-packages/scipy/sparse/linalg/dsolve/umfpack/umfpack.py:556: RuntimeWarning: divide by zero encountered in double_scalars econd = 1.0 / self.info[UMFPACK_RCOND] warning: (almost) singular matrix! (estimated cond. number: inf) sfepy: rezidual: 0.01 [s] I attached the problem description and the mesh for this problem. What is the reason of the error? May be the mesh is not very detailed? Sincerely, Alexander Kalinin

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ANN: SfePy 2012.3
by Robert Cimrman 12 Sep '12

12 Sep '12

I am pleased to announce release 2012.3 of SfePy. Description ----------- SfePy (simple finite elements in Python) is a software for solving systems of coupled partial differential equations by the finite element method. The code is based on NumPy and SciPy packages. It is distributed under the new BSD license. Home page: http://sfepy.org Downloads, mailing list, wiki: http://code.google.com/p/sfepy/ Git (source) repository, issue tracker: http://github.com/sfepy Highlights of this release -------------------------- - several new terms - material parameters can be defined per region using region names - base function values can be defined per element - support for global options For full release notes see http://docs.sfepy.org/doc/release_notes.html#id1 (rather long and technical). Best regards, Robert Cimrman and Contributors (*) (*) Contributors to this release (alphabetical order): Alec Kalinin, Vladimír Lukeš

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Re: How does variables and integrals are evaluated?
by Robert Cimrman 11 Sep '12

11 Sep '12

Hi Alec, I meant volume integral as an Integral instance=quadrature points, not the volume term :). I will try your file when I get to my laptop. r. ----- Reply message ----- From: "Alec Kalinin" <alec.k...(a)gmail.com> To: <sfepy...(a)googlegroups.com> Subject: How does variables and integrals are evaluated? Date: Tue, Sep 11, 2012 10:11 Hello! It seems that the flux shape should be (5235, 4, 1, 1) (4 quadrature points). So you should use a volume integral in data_from_qp(), that you use in solving the problem, as extend_cell_data() returns the flux in the volume elements (averaged from the surface). Hmm... But the volume integral that is used in problem definition has the "dw_" prefix and cannot be used in evaluation mode. I think only "dq_" and "ev_" terms can be used in "qp" mode. I try to used "ev_grad" term but this term returns gradient (vector). It is also very nice, but I need scalar flux. :) To be more clear I attached my standalone problem definition python script and the mesh This is probably not optimal for surface terms (a better way would be to directly average the face data to face vertices), but it is how things are now. Yes, yes. This is not the problem to directly average the face elements data to the face vertices, it is about several lines of code. But I want to understand more about sfepy internals. :) Sincerely, Alexander -- You received this message because you are subscribed to the Google Groups "sfepy-devel" group. To view this discussion on the web visit https://groups.google.com/d/msg/sfepy-devel/-/hMvweknCgkkJ. To post to this group, send email to sfepy...(a)googlegroups.com. To unsubscribe from this group, send email to sfepy-devel...(a)googlegroups.com. For more options, visit this group at http://groups.google.com/group/sfepy-devel?hl=en.

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How does variables and integrals are evaluated?
by Alec Kalinin 11 Sep '12

11 Sep '12

Hello SfePy devels, Could you, please, explain me some SfePy internals? (1) Question 1. Surface processing. As I see in examples the 3D meshes contains only volume elements (tetrahedra) and no surface elements (triangles). But in problem solution pipeline we need to apply essential boundary conditions on surface nodes and need to evaluate some surface integrals, for example, for Neumann boundary conditions. How does SfePy working with surfaces? For essential boundary conditions, yes, we can take only the far nodes in tetrahedra. But for the surface integrals we need the surface elements -- triangles. Does SfePy extract boundary triangles from volume tetrahedra? (2) Question 2. Dimensions of the SfePy arrays. Consider the postprocesing hook: def post_process(out, pb, state, extend = False): electric_field = pb.evaluate('ev_grad.2.Omega(u)', mode='el_avg') print electric_field.shape flux = pb.evaluate('d_surface_flux.2.Gamma(m.K, u)', mode='el_avg') print flux.shape In my example shapes are: electric_field: (5235, 1, 3, 1) flux: (3898, 1, 1, 1) Could you explain me why the variables are 4-dimensional arrays. My understanding is following: 1. 1st dimension is the number of the tetrahedra element. 5235 is the total number of the volume element. By what is 3898? Is it a number of the tetrahedra which are contains in boundary or is it a number of triangles on the surface? 2. The 3d dimension is the dimension of variable. The grad is a 3 dimensional vector, the flux is a scalar. But what are the 2nd and 4th dimensions? Sincerely, Alexander.

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resistance between two points
by jmartinek 07 Sep '12

07 Sep '12

Hello, first of all, I would like to thank all the developers for sfepy and related tools, which is absolutely awsome, mainly because of the great flexibility. I am afraid I have a very basic problem which everyone knows how to solve except of me. I have two points (nodes) and I want to calculate heat resistance between them. By heat resistance I mean ratio of temperature difference and heat power, so the unit will be Kelvin per watt, K/W. I think there are two possible ways: 1) One node has defined temperature. The other node has defined power. Then I find temperature of the other node. But - how to assign power in watts? I wanted to get inspired by the example poisson_functions.py, but the "load" parameter is power density (in watts per cubic meter). Therefore, in one node there is infinite power density. 2) Both nodes have defined temperature. Now I need to calculate the total flux over surface surrounding any of the nodes. But how? Please, could you give me an advice, which of these two ways should I use and what examples from the documentation is the closest to my problem? Thank you very much, Jan Martinek

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SfePy September 2012