Hi,
I am trying to simulate a geometrically nonlinear shell bending problem using iso-geometric analysis in LS Dyna. NURBS elements were introduced only a few years ago and no tutorials are available online regarding these elements. Can someone provide some references or let me know if you have ever worked on NURBS elements?
To be specific, I want to simulate the bending of a tape spring (cut out from a cylindrical shell) by applying rotations at both the ends (made of circular arcs). In the output, I need to plot Moment vs angle at the ends.
Thanks very much! Happy New Year 2020!
Hi @harsha,
Unfortunately I am not familiar with these NURBs elements, but I am curious as to why you are trying this method? I just checked in the LS-Dyna manual and found the page for *Element_shell_nurbs_patch. Is that what you are asking about? Here are a few links that may be useful. I may not be able to help much but I can try to answer any specific questions that you may have.
https://www.dynalook.com/conferences/international-conf-2010/DavidBenson-LSTC_Conf_2010.pdf
Hi @negativevolume,
Thanks for your reply. I have started working on my simulations using the keyword that you mentioned. I was looking for some tutorials to make my learning faster.
1. Iso-geometric elements use the same shape functions for analysis that were used to generate the geometry, hence the name. These shape functions (B-splines, NURBS etc.) provide higher orders of continuity compared to the Lagrange polynomials that are used in traditional FEA.
2. Irrespective of the mesh, the geometry remains exact (no discretization).
3. These shape functions have inter-element continuity by design and hence are preferred for formulating rotation-free finite elements. Rotation-free shell elements are numerically more stable.
I am using these elements as part of my research. I want to compare these elements with other "traditional" triangular shell elements.
Thank you!
Cheers,
Harsha.
Ah I see, very cool. I'd be interested to read about this study if you choose to publish! But yes, the world of LS-Dyna video tutorials is very slim as it is for traditional forms of analysis so I'm not sure much is out there. Those links may be useful for you along the way though. The link below is where I would normally point people to examples to work through but I do not see any on this modeling technique.
Are you experienced in "traditional" forms of LS-Dyna simulation? Knowing your experience level will help me help you.
Are you a graduate student? It looks like LSTC offers a class for this $175 for students. Maybe your PI could cover that if it is vital toward your research. Then you could come here and educate all of us!
I am a PhD student. I am not experienced in LS-Dyna at all. We use ABAQUS in our group. The only reason I am using LS-Dyna now is that it is the only commercial software with NURBS elements.
And, yes, I am going to the LS-Dyna conference in May, 2020 🙂 However, it is almost 5 months away. I have to get my project done before that!
Thanks for all the information you have provided. I will let you know when I publish my research.
Cheers,
Harsha.
Hi,
I am interested in this topic as I am also doing a related research. I am also a graduate student and I am currently working on Isogeometric Analysis which I would like to apply on different pipe fittings to be modelled as solid NURBS.
I tried first modelling a simple solid cylinder object in Rhino CAD and export it as IGES. When I import it to LS Prepost, however, the model is converted and used shell elements on the faces instead. I need to work with solid elements, not shell elements.
I am thinking of just creating solid models directly on LS Prepost, but I find it not very user friendly and may get difficult when I do my actual pipe fitting models. So I want to ask for advice on finding a way to import solid models without converting to shell faces from any other CAD software.
Or is there a way to create solid NURBS elements out of the imported shell faces?
Looking forward to your advice. I am just a few days new to LS Prepost and LS Dyna which caught my interest since these are the only software I found available with actual trivariate solid NURBS elements for preprocessing and isogeometric analysis.
Thank you very much!