fem analysis

[mekeuro]

Hello, guys, I have a question to ask you:
I was commissioned to build a steel structure, a small half ton quarry crane.
all in tubular that I still owe dimension, of course.
I have in mind to design it like the reticolar cranes that you see on the building sites.
during the project, the client wants you to release a pre-analysis of calculation, a structural "relation" where stress, deformations and maximum moment are highlighted, binding reactions and other.
I use catia v5 and v6 I would like to know if it is reliable in performing this structural calculation.
I don't need a millimeter precision on deformations and at least on tensions, on the moment or on the cut.
reliable means that if the fem solver will give me a max deformation of 0.5 cm in the design phase, I also agree to find it from 1cm or 3 cm in the execution phase but not 10cm or 20cm this would mean a catastrophe! !
thank you very much to those who will answer me
you can also answer my private mail f.massaro80@libero.it It would be better.

 

[meccanicamg]

Hello mekeuro,
as in all post simulation final reports it says: do not use the values of the fem as values to be used as real. always rely on standardized calculation formulas and regulations.

In fact, it is never certain that the fem values are accurate if not adequately compared to multiple experimental cases sized with practical formulas and after having undergone mechanical stress on an adequate number of testes and prototypes.

the cat's solutor has the same reliability as the other solutors and applies the same rule. I normally for static applied to mechanics with cosmos get a maximum of 10 / 15% of deviation of localized deformations (which in fact are not there) and generally I find myself on average to a 2 / 5% on average values in areas where there are no concentrations of froze.

fem analysis must always be interpreted, it is not reality, but a possible realistic mode according to the constraints and laws we impose on the model.

 

[mekeuro]

Thank you for your kind answer, even if I don't know your name, I'm French. Then tell me yours
I know that the values of fem analysis always differ from reality, I was interested in knowing whether for example there is a "classification" so we say the fem resolvers approaching and moving far away from reality
and if he catches in this "classification" he goes far from reality, so he is not reliable.
but as you told me: the cat's solutor has the same trustworthiness as the other solutors and is the same rule.......... .

I deduce that: either I solve with the caty or I solve with the "pinko pallino" I always have the same problem.
Thanks again and good work
to the next

 

[meccanicamg]

Thank you for your kind answer, even if I don't know your name, I'm French. Then tell me yours
I know that the values of fem analysis always differ from reality, I was interested in knowing whether for example there is a "classification" so we say the fem resolvers approaching and moving far away from reality
and if he catches in this "classification" he goes far from reality, so he is not reliable.
but as you told me: the cat's solutor has the same trustworthiness as the other solutors and is the same rule.......... .

I deduce that: either I solve with the caty or I solve with the "pinko pallino" I always have the same problem.
Thanks again and good work
to the next

My name is manuel:

the solutors have more or less all the same potential, similar if not same algorithms of convergence.

one of the mistakes that you can have by comparing two fem analysis is: put huge mesh against mesh very thick. in the second there will be a lot of high voltage concentrated points but this does not correspond to reality.

catia is a high-end modeler, superior to inventor and solidworks although it is not only a dedicated fem. then you will have better tools for convergence and to manipulate the model. but the concept of reliability depends on how you set the analysis.

for rhetorical structures there are appropriate programs for calculation as a rule.

I forgot... I think catia does it too: you have two systems to treat the structure: 1) single-dimensional beam elements 2) complete geometry. the second is much more expensive and makes little sense when making structures with standard profiles of which geometries are known, so I recommend analysis as a beam element.

 

[mekeuro]

Thanks manuel