Structure Analysis with both Beam and Shell elments

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Structure Analysis with both Beam and Shell elments
I noted there are two seperate shell and beam solvers in Elmer. i assume it should be possible to solve a structure with both shell and beam elements included, is that correct?
I can just add two solvers in the .sif file, is that correct? Is there any example projects that with both shell and beam elements?
I can just add two solvers in the .sif file, is that correct? Is there any example projects that with both shell and beam elements?
Re: Structure Analysis with both Beam and Shell elments
An ideal implementation of the coupled shell and beam analysis would be to assemble both models to a single system which would then be solved simultaneously. Nevertheless this type of approach has not yet been implemented. Since the models have compatible DOFs, it might be possible to implement this relatively easily. When time permits, I could look at this.
A hierarchic model could already be possible (solve a shell model first, then a beam model and iterate), but such a model is expected to have a limited applicability.
 Mika
A hierarchic model could already be possible (solve a shell model first, then a beam model and iterate), but such a model is expected to have a limited applicability.
 Mika

 Posts: 25
 Joined: 10 Jul 2019, 17:12
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Re: Structure Analysis with both Beam and Shell elments
Thanks Mika! It is very nice of you to help to look into this. When do you think you maybe able to find some time for this?
mika wrote: ↑23 Mar 2020, 18:00An ideal implementation of the coupled shell and beam analysis would be to assemble both models to a single system which would then be solved simultaneously. Nevertheless this type of approach has not yet been implemented. Since the models have compatible DOFs, it might be possible to implement this relatively easily. When time permits, I could look at this.
A hierarchic model could already be possible (solve a shell model first, then a beam model and iterate), but such a model is expected to have a limited applicability.
 Mika
Re: Structure Analysis with both Beam and Shell elments
I will try to make a first look at the necessary amount of coding within a couple of weeks, say. If the implementation turns out to be more complicated than expected, this may change to be a longerterm goal.
 Mika
 Mika

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Re: Structure Analysis with both Beam and Shell elments
Thanks Mika, it would be appreciated if you could kinldy me informed with the status.
Re: Structure Analysis with both Beam and Shell elments
I used some hours for this and wrote changes to the shell solver so that the shell solver can also assemble and solve a pure beam model, obsoleting the separate solver for the beam equations basically. However, in my earlier comments I ignored an issue which makes the DOFs of the shell model and the beam model only partially compatible. The generalized nodal forces of the beam model are three forces and three moments, while one of the generalized nodal forces in the shell model is a reaction related to the elongation of the shell normal, which is not taken into account in the current beam model. This makes the started line of development not so straightforward as I thought, since at the moment a beam stiffness matrix cannot be assembled into the shell stiffness matrix simply without enforcing additional constraints somehow. It seems I need to reconsider the problem to find the easiest way to proceed.
 Mika
 Mika

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Re: Structure Analysis with both Beam and Shell elments
Thanks, Mika. Is there any latest update on this? I am working on marine FEM models, as you may understand, the structures that invovled both shell and beam is quite common. It would be appreciated if Elmer can be fitted with this kind of function.
mika wrote: ↑14 Apr 2020, 14:59I used some hours for this and wrote changes to the shell solver so that the shell solver can also assemble and solve a pure beam model, obsoleting the separate solver for the beam equations basically. However, in my earlier comments I ignored an issue which makes the DOFs of the shell model and the beam model only partially compatible. The generalized nodal forces of the beam model are three forces and three moments, while one of the generalized nodal forces in the shell model is a reaction related to the elongation of the shell normal, which is not taken into account in the current beam model. This makes the started line of development not so straightforward as I thought, since at the moment a beam stiffness matrix cannot be assembled into the shell stiffness matrix simply without enforcing additional constraints somehow. It seems I need to reconsider the problem to find the easiest way to proceed.
 Mika
Re: Structure Analysis with both Beam and Shell elments
Hi,
The devel version now contains the first version of an enhancement which allows a shell model to have onedimensional beam sections. At the moment the combined model can be assembled in the case of linear analysis only (Large Deflection = False in the solver section of the shell model).
Parameters of the beam model are currently read from material sections, so elementwise organized data cannot yet be given. In particular one of the principal directions of the beam cross section (the y3axis) can be given by specifying the value of the keyword "Director".
The shell model doesn't inherently know about a moment around the shell director (normal) of the midsurface, while the beam formulation (see the chapter "Onedimensional Equations for Elastic Beams" in Elmer Models Manual) which has been used as a starting point employs the full resultant couple (moment) vector with three components. To cope with this discrepancy, the beam stiffness matrix is manipulated internally in such a way that the resultant couple vector cannot have a component with respect to the director vector of the beam. The beam and shell directors are now defined independently, but it is natural to construct the combined model so that the shell and beam directors agree in places where the domains of the two models intersect.
Testing has been minimal so far and solving some verification cases would be needed. At the moment there is just one example
https://github.com/ElmerCSC/elmerfem/tr ... m_Sections
to instruct writing a sif fie.
 Mika
The devel version now contains the first version of an enhancement which allows a shell model to have onedimensional beam sections. At the moment the combined model can be assembled in the case of linear analysis only (Large Deflection = False in the solver section of the shell model).
Parameters of the beam model are currently read from material sections, so elementwise organized data cannot yet be given. In particular one of the principal directions of the beam cross section (the y3axis) can be given by specifying the value of the keyword "Director".
The shell model doesn't inherently know about a moment around the shell director (normal) of the midsurface, while the beam formulation (see the chapter "Onedimensional Equations for Elastic Beams" in Elmer Models Manual) which has been used as a starting point employs the full resultant couple (moment) vector with three components. To cope with this discrepancy, the beam stiffness matrix is manipulated internally in such a way that the resultant couple vector cannot have a component with respect to the director vector of the beam. The beam and shell directors are now defined independently, but it is natural to construct the combined model so that the shell and beam directors agree in places where the domains of the two models intersect.
Testing has been minimal so far and solving some verification cases would be needed. At the moment there is just one example
https://github.com/ElmerCSC/elmerfem/tr ... m_Sections
to instruct writing a sif fie.
 Mika

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 Joined: 25 Jan 2019, 01:28
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Re: Structure Analysis with both Beam and Shell elments
https://github.com/mrkearden/beam_solver
Files in link above. 12 Meter long, 3 Meter wide plate with a stiffener on the center line along. Elmer beamsolver was 6.97% of the theory solution
The shell solver was 5000 times the theory solution.
There may be errors in all 3 solutions, I am still checking.
Files in link above. 12 Meter long, 3 Meter wide plate with a stiffener on the center line along. Elmer beamsolver was 6.97% of the theory solution
The shell solver was 5000 times the theory solution.
There may be errors in all 3 solutions, I am still checking.
 Attachments

 shellandbeam.png
 (130.98 KiB) Not downloaded yet

 Posts: 641
 Joined: 25 Jan 2019, 01:28
 Antispam: Yes
Re: Structure Analysis with both Beam and Shell elments
Resolved the beamsolver case. There was an error in calculation of section properties.
beamsolver provides reasonable answer
beamsolver provides reasonable answer
 Attachments

 mycase.sif
 (2.36 KiB) Downloaded 34 times

 beamsolver.png (13.4 KiB) Viewed 804 times