×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Shell buckling

Shell buckling

Shell buckling

(OP)
Hey!!!

I designed a simple long thin open ended cylinder in ANSYS and the type of loading is hydrostatic pressure.
I calculated the buckling pressures for different modes shapes (n=1,2,3...) using Von-mises and Donnel's equation.Both have used classical simply supported boundary conditions.I constrained all translations(x,y,z) on one end and two translation(x,y) on other end as classical simply supported conditions.There is a huge difference in theoretical and ansys results.

I am sure that that is happening because of boundary conditions.Can anyone explain or tell me what are classical simply supported boundary conditions for cylindrical shell?

Regards

RE: Shell buckling

if you're constraining the perimeter in X- and Y- i suspect there'd be a problem.

i'd play with your model with different constraint scenarios untill you get correct hoop behaviour (under tension).

i've also seen odd behaviour depending on how i created the geometry.

RE: Shell buckling

(OP)
u r right about constraining the perimeter! what would u suggest as boundary conditions?

RE: Shell buckling

i'd contrain the perimeter axially (googly eyes at each node, laterally (Y-) at two nodes (say a diameter), and up/down (Z-) at one node (pick one of the Y- nodes).

then see if you get good "hoop" behaviour.

RE: Shell buckling

If you want good "hoop" behavior, how about starting with a cylindrical coordinate system and inputting your BCs in that csys?

RE: Shell buckling

(OP)
I actually haven't used cylindrical coordinates?

RE: Shell buckling

surprise

You're modelling a cylinder under internal pressure and you haven't ever used cylindrical coordinate systems before and you're wondering why you have problems?curse

RE: Shell buckling

(OP)
I am not designing a cylinder under internal pressure.I am designing a cylinder under hydrostatic pressure.Going through literature,I came to know that we can model it using Cartesian Coordinates.It shouldn't effect the solution.

Regards

RE: Shell buckling

Um - OK. If you want to believe that, sure.

It's a cylinder. That's the reason that cylindrical coordinate systems were invented... Next you'll be asking about spheres, and then admitting that you've never used spherical coordinate systems either.

RE: Shell buckling

@TGS4 : I am confused, how will choice of coordinate systems affect solution if the BC's can be accurately described with a Cartesian co-ordinate system.

Isn't there a way to use a local co-ordinate system instead of the global co-ordinate system ?

RE: Shell buckling

Please tell me how you can define u-theta=0 or u-r=0 from a cylindrical coordinate in a Cartesian coordinate system? Or even better - how would you define rot-theta=0?

Sure, you could use a local cylindrical coordinate system. That's the point.

RE: Shell buckling

You can define those with a local Cartesian coordinate system

RE: Shell buckling

Quote (missil3)

You can define those with a local Cartesian coordinate system
Sure - with a lot of trig functions: sine, cosine, etc. My point is that if you are:
a) modelling something that is a cylinder, and
b) applying boundary conditions that would be best described in a cylindrical coordinate system, and
c) yet haven't ever used cylindrical coordinate systems before, and finally
d) have unexplained problems

then you may have a problem with your boundary conditions (and the coordinate system that you have defined them in).

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources