I´m trying to model the mechanical behavior (static, modal, and buckling analyses) of an underwater floating structure (an icosahedral capule or buoy) under hydrostatic pressure: Capsule.gh (49.0 KB).
- This structure should be modeled as freely suspended (not attached to anything), i.e. no-supports. However, this seems not possible with Karamba, am I right?
If I fix the 6 DoFs of one vertex, I´m able to obtain a feasible static analysis. Unfortunately, this unrealistic constraint severely affects both the buckling and the normal modes. The first three frequencies as well as the first three buckling factors are too low.
In the images you can check the first 10 buckling factors and the differences between the 1st (unfeasible) and the 4th (feasible) buckling modes:
Is there a way to force Karamba to perform modal and buckling analyses without any support? In principle, this should not be a problem for modern eigensolvers if the total resultant forces is zero (as it is in this case). If this were possible, I just would had to ignore the first 6 zero frequency and zero buckling factor modes.
If “2.” is not possible, would you tell me the best way to model a “freely suspended” structure in Karamba?
Thanks a lot!
PS: I´ve just found a web about Free-Floating FEA models where the author explains the 3-2-1 method. This method seems to work for the static analysis of floating (unsupported) structures.
PPS: In this forum thread, “jhardy1” user says two key things:
- a) If your structure is “free-floating” (e.g. aircraft in flight, free vibration modes, etc), then “Inertia Relief” can be a useful technique, if your software supports it; otherwise, the 3-2-1 approach can generally be applied, but it is important to note that the restraints should be carefully positioned such as to not attract any spurious net force that can’t actually go to the fictitious support nodes.
- b) In the 3-2-1 approach, you need to ensure also that the locations of the artificial restraint nodes don’t influence vibration modes shapes or buckling mode shapes of interest (e.g. if one of your restraints is halfway along a beam, you may not be able to recover the fundamental vibration mode of the beam).
Do you agree? Is inertia relief technique available in Karamba?