Piecewise system with discrete elements

ZacLee

Please find attached my message file with the mesh printed following your recommendation. I'm probably getting the wrong physics because I am measuring the wrong physical quantities. Normally, the reaction at the node should follow a piecewise function, as it only starts moving after contact. If you can help me solve this or suggest another way of modeling it, I would be grateful.

message.txt

257kB

Best regards

jeanpierreaubry

ZacLee
i will hve a look
what the units and dimensions?

ZacLee

Dear,jeanpierreaubry

All units are in SI: MKS. The two springs have 4m lenghts and the the damper on wich the mass is attached is 4.5m lenght. Please, npte also that the gap betwen the two springs is 1m.

Thank you.

Best regards

jeanpierreaubry

ZacLee
then the values of stiffness and mass are way out of the physics in my opinion
neverheless
here is how to modify the mesh

i have added 2 line elements named 'choc' between MASS and the ends of the springs
the attached file is the gmsh .geo file
but it is easy to find

ex1.txt

585B

out what is what

jeanpierreaubry

jeanpierreaubry
and here is the command file that goes with it
i think i have results that look realistic with the strange stiffness and mass
i modified some of them

ex1-comm.txt

4kB

ZacLee

Dear jeanpierreaubry,

Thank you verymuch for your help. The system is a piecewise Non linear energy Sink (NES). Normally, the stifness is low compared to a normal absorver as we want to transfer the energy from a primary system to the NES. I'll try to execute the files you sent to me.

Best regards

ZacLee

Dear, @jeanpierreaubry
I apologize for bothering you again. After recreating the model as you suggested (I followed your instructions exactly), I received an error message regarding a node that I did not create. The error indicates that there is a displacement in the DX direction for a node that does not exist in the node set.

Could you help clarify this issue for me?

Best regards,

message.txt

48kB

jeanpierreaubry

ZacLee
look at the message file under LIRE_MAILLAGE

the mesh has been badly build
you have many nodes that should not exist
there are intermediate nodes between the ends of the springs, for example N9 to N22
something is wrong within the hypothesis at mesh time
as far as i am concerned i never use salome so i cannot help
but your previous mesh did not had that fault

in France where i live it is now bed time

ZacLee

Dear, jeanpierreaubry
I've got the model to work. i'm having this results

The mass displacement is purely linear as if we hadn’t the gap before the contact. This is the problem I was having in the beginning. If you still have the results you’ve got from this model, I would appreciate if you can share.
Maybe it’s just a lack of understanding of the physical behavior from my side. Nevertheless, thank you for your help. Your advices were very helpful.
Best regards

jeanpierreaubry

with this in BC do not you have too many nodes fixed?

_F(DZ=0.0,GROUP_NO=('FIXE_N', 'MASS', 'U_SPRING_CN', 'U_SPRING_FN', 'B_SPRING_CN', 'B_SPRING_FN'))),

ZacLee

Dear,jeanpierreaubry

If the contact nodes CN are free to move move in Z direction, I’m getting a rigid body mode. So the calculations is being ended with an error message. That’s why I modelled only the mass as a free to move in Z direction.

jeanpierreaubry

ZacLee
it does not happen to me
i have a behavior as expected

ZacLee

jeanpierreaubry Can you please share your result file?

Best regards

jeanpierreaubry

ZacLee
here it is

ex1.txt

5kB

ZacLee

jeanpierreaubry Thank you verymuch. I just plotted your results and it's the correct one. I think my problem ccomes from my definition of the "choc" line. I meshed also this element and it creates two more nodes. Can you tell me how did you meshed the "choc" element if it was the case? I'll keep trying to work on the model. I apologize for my insistance. It's part of my PhD work, that's why I'm trying to get it working properly.

Best regards and thank you for your help

ZacLee

jeanpierreaubry
I’ve succeeded to have a model that’s look more like yours. But, I don’t understand why I have the error on DZ displacement of the mass node N5. Normally, it’s made in purpose that the mass should move.
Here the message file, if you could have a look

message1.txt

43kB

jeanpierreaubry

ZacLee
for what i can see
there should be a SEG2 element from N1 to N5 with AMOR group

M3 should not be in AMOR group

please review your mesh and group assignment before going any further in the analysis

if i was your PhD master you would have had some warning!!

when all this is finished you will have to explain me the physical how you can build
B_SPRING and U_SPRING elements 4 meter long with a mass of 1e-08 kg
and an active MASS of 0.1369 kg
how is that possible?

ZacLee

jeanpierreaubry
Thank you very much for your advices and your help. Actually, I'm discovering the software, and the physics I'm trying to model is a a nonlinear absorber. For these king of absober, the masses are really very smalls and ideally not to high stifnesses. The dimensions of the elements are just a first approach to have a model that works. After that, I'm going to build analytical calculation to have a real parameters.

i'll restart again the meshing procedure.

Best regards

ZacLee

Dear @jeanpierreaubry

I have finally obtained a working model. Thank you alot!
My issue was with the mesh generation using the MESH module of Salomé Méca, where there was a small problem with the interpretation of the elements. I therefore created the model in GMSH and then imported it into Salomé with the generated elements. I thank you for your patience and support.

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