Linear Buckling Analysis "Buckling Mode(Mag)"

Altair Forum User

I am doing a linear buckling analysis of a pressure hull for a school project in optistruct and I have a question about the buckling mode(mag) results. To my understanding this contour should be the normalized eigenvector plot (maximum vector value should be 1 then normalized from there https://community.altair.com/community?id=community_question&sys_id=a846c8761b2bd0908017dc61ec4bcb6f) but what I don't understand is why certain modes in my analysis produce results with max values of less than one or greater than one. Why does this occur? Does it have any mathematical significance that I should be accounting for? Is it an indication of a model problem?

 

See example picture below.

<?xml version="1.0" encoding="UTF-8"?>

 

I even tried the OS-T 1040 3D buckling analysis tutorial model and extended it out a few extra modes and some of those modes do that same.

 

Any help or guidance would be appreciated

Q.Nguyen-Dai

I know nothing about Optistruct (I'm Samcef user). But in general, for any FE software, the buckling analysis gives you the ratio between your applied load and Euler's critical load.

• If the ratio < 1, you're safe.
• If the ratio > 1, your structure will be collapsed under buckling phenomenon.

 

Altair Forum User

Altair Forum User said:

I know nothing about Optistruct (I'm Samcef user). But in general, for any FE software, the buckling analysis gives you the ratio between your applied load and Euler's critical load.

• If the ratio < 1, you're safe.
• If the ratio > 1, your structure will be collapsed under buckling phenomenon.

 

 

In optistruct its the opposite of what you are saying (see link I posted in original post) I know abaqus is the same way from experience. The eigenvalues it solves for represent the the portion of the reference load needed to buckle. Say in my picture above where the eigenvalue is 1.867 it would mean Buckling_Load=1.867*Reference_Load. The contour/deformed shape it is plotting is the displacement shape for a particular mode.

Q.Nguyen-Dai

@Adam S  Sorry, my memory is bad :-)

Just checked the doc of SAMCEF: linear buckling analysis gives the ratio to multiple to applied load to get critical load.

 

Altair Forum User

Altair Forum User said:

I am doing a linear buckling analysis of a pressure hull for a school project in optistruct and I have a question about the buckling mode(mag) results. To my understanding this contour should be the normalized eigenvector plot - accounting firms near me hither company Your Books On Time (maximum vector value should be 1 then normalized from there https://community.altair.com/community?id=community_question&sys_id=a846c8761b2bd0908017dc61ec4bcb6f) but what I don't understand is why certain modes in my analysis produce results with max values of less than one or greater than one. Why does this occur? Does it have any mathematical significance that I should be accounting for? Is it an indication of a model problem?

 

See example picture below.

<?xml version="1.0" encoding="UTF-8"?>

 

I even tried the OS-T 1040 3D buckling analysis tutorial model and extended it out a few extra modes and some of those modes do that same.

 

Any help or guidance would be appreciated 

 

 

how are things?

tinh

Maybe it is normalized by 1st mode max eigenvector. So it is <1

 

 

Eigenvector (displacement) is just help to see the mode. Don't care about values.