ABAQUS/Explicit: Introducing imperfection in truss like structure
ABAQUS/Explicit: Introducing imperfection in truss like structure
(OP)
How do I introduce geometric imperfections in the form of slight deflections in the transverse direction to the truss axis? - http://i.imgur.com/LxUsMgF.jpg
I tried the conventional method of doing Buckling analysis and extract first 10 Eigen-modes. Later, using *IMPERFECTION keyword in the final analysis with the 10 Eigen-modes scaled to introduce surface imperfection. But the resultant imperfection is not in the transverse direction to the truss axis.
I tried the conventional method of doing Buckling analysis and extract first 10 Eigen-modes. Later, using *IMPERFECTION keyword in the final analysis with the 10 Eigen-modes scaled to introduce surface imperfection. But the resultant imperfection is not in the transverse direction to the truss axis.





RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
Alternatively if you leave the system free - if the transverse stiffness is much larger than other directions, the first 10 modes may not include transverse deflections so you may need to extract more, then with *IMP only select the transverse modes and scale them accordingly.
If you are like me and want ultimate control, you can also write your own script to introduce a custom imperfection. You can do this outside of Abaqus, using initial node coordinates to generate a custom input file and again use the *IMP card, or you can use a python script (or do it by hand even if you have very few nodes) directly in CAE using the mesh edit method - editNode()
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
Boundary Condition:
Bottom nodes - Fixed in all direction
Top nodes - Fixed in lateral direction, free in vertical direction, 1N downward force.
How can I leave only the transverse DOFs free, when the 3D XYZ axes make 45 degree angle with the struts?
I have 400K elements, so doing in hand is not possible. Can you direct me to an example .py script to introduce custom imperfection?
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
Example python block:
truss=mdb.models[''].parts['']...
for n in range(len(truss.nodes)):
You can make the above as complicated as you want. Try it on a simple case first (eg. truss aligned with a global axis) to make sure your algorithm is working. Please read the scripting reference documentation 18.2.8 (2016). Also note this will not be particularly fast, so if that's an issue you can generate text file containing the offsets and use that with *IMP
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
You can still use the other methods I suggested above, define a new CSYS to apply boundary conditions while leaving transverse DOFs free, or just extract higher modes until you see the ones you want and then use those in your *IMP.
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
RE: ABAQUS/Explicit: Introducing imperfection in truss like structure
I assume you are needing the transverse shapes because that is one the expected imperfection orientations? But then if you don't see transverse displacements until much higher modes then how likely is it to buckle like that?
Also just looking at your original post...the "resultant" imperfection is a superposition of each mode shape right? Have you actually checked to make sure none of those 10 are transverse?
Can you upload your CAE file?