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Home > Forums > Structural Engineers > Activities > Finite Element Analysis engineering Forum

Ground check MSC Nastran

Read More Threads Like This One

compositecurves (Structural)

6 Aug 12 3:46

Hi everybody,

I have a question about the groundcheck. What's the aim of this check??
I launched a static analysis to do this check but i found 4 fail and 2 pass (Kgg). I don't know what should I do to correct this and to obtain 6 pass.
I checked all C-BUSH nodes and they are coincident...
The limit of the strain energy is fixed to 1E-03
look at the attached picture to better understand what i mean.

Thanx

rb1957 (Aerospace)

10 Aug 12 8:44

is your model restraining the 6 rigid body motions ?

are your CELAS elements creating an uncontrolled section in your model ? i've modelled a door on a fuselage, the door attached with springs restraining in the Y-direction only, which left three rigid body motions unrestrained (X, Z, and RZ i believe) and i had suppress (and checked that there was essential zero load on these constraints).

compositecurves (Structural)

10 Aug 12 9:56

Hi rb1957

What do you mean by restraining the 6 rigid body motion??

im modelling a big sttructure which is composed of two part. these parts are connected using C-BUSH (1E+12, 1E+12, 1E+12, 2.14E+9, 2.14E+9 , 1E+12) element connecting two RBE2 123 elements

rb1957 (Aerospace)

10 Aug 12 11:52

"What do you mean by restraining the 6 rigid body motion??" ... oh dear, oh dear, oh dear.

a model needs to be restrained otherwise it'll go flying off into space. Even if you're applying equal load and reactions (ie you know the nett load on the strcuture is zero, but the computer doesn't).

what happens if you remove the CBUSHs ? (the CBUSH has N1 and N2 that are co-incident, so for elements using N1 replace N1 with N2)

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