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slewing ring, 45 degree rolles, how to simulate?

Question asked by Markku Sutinen on Mar 11, 2015
Latest reply on Mar 17, 2015 by Jared Conway

Dear higly respected and goodwill experts all aroung the SWX-universe,

 

Could someone please assist me with this case: I have a crane pedestal column, let's say ø 1000 mm diameter and wall thickness of 8mm or so. On top of that pipe there is a flange, 40mm thick. Unfortunately flange is much larger in diameter than pipe because slewing ring is ø1400mm. So in practice bolt pattern has 200mm greater radius than pipe. This produces bending moment and all kind of twistings to flange. Beneath the flange there is a pattern of gussets for support. On flange there is a deformable solid ring with bolt holes representing slewing ring (its outermost part), which is constrained to flange with preloaded bolt elements and no-penetration contact set (friction µ=0). There is no goorve etc, only bolts holding that system in its place.

 

I've placed force(s) (tipping moment+weight) as remote load, direct transfer. If I just put that load on top face of the slewing ring, everything is somewhat ok and stress levels are tolerable, even plane deviations are in allowed limits. Second method was to split that top face to 4 (90 degree) segments and recalculate remote moments etc to normal forces pushing an pulling two opposite surfaces up and down. No significant difference so far, but next thing is where I run out of my skills:

 

If I placed that same load on 45 degree surfaces, stress levels escalates to 2000, even 10 000+ MPa and displacements 60 to 100+mm (I suspect that solver crashes at some point and results are not reliable?).

 

According my understanding 45 degree roller surface produces as non-desired side effect a equal lateral force and this makes my slewing ring deform to ellipse, which in turn further bends my flange, which in adverse makes slewing ring to deform like a Möbius curvature..  My next task would be to define required corrections, but in order to do that, I'd need a working FE study at first.

 

I don't have a non-linear lisence available, but assuming that linear steady state study is/ shall be enough, could someone pelase give hints, how to proceed:

Q1: is my assumption of "45 degree side effect" correct?

Q2: Is there anything too careful in my load case (I assume that no, because 360 degree direct transfer force gives about same results as 2 forces on two 90 degree sections)

Q3: if inner ring somehow supports or prevents outer ring's deformations, is there any commonly approved methods to apply that effect in my study? I've heard about "equivalent modulus of elasticity?)

 

Thanks in advance for your prompt replies..

Markku

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