There are various ways of fixing geometry in the part module by merging edges, stitching, removing redundant entities etc. Try this first. If you use virtual geometry then you'll be restricted to using tet elements which shouldn't be necessary.
Shell elements will have a linear stress distribution through the thickness so would be no good for calculating the peak stress. Solid elements will capture the stress distribution through the thickness better. In your case the peak stress is at a sharp corner so any results will be meaningless...
When you have circular regions it's best to split them up into 90 degree segments. In this case use the small square hole to create a segment from the hole centre and then partition the remainder of the circular region into 90 degree segments. You should be able to get structured regions.
You've applied rotational restraints to a solid model when there are no rotational degrees of freedom. The example you chose would have been more apt if it had been a shell model.
Use stress linearization to remove the peak stress. If you created the peak stress by application of a point load or restraint (which wouldn't exist in reality) then either ignore the stress there or model it better if that's a region of concern. There should be crane design codes available, but...
Use existing flat faces to partition the whole thing, then partition the arcs into 90 degree segments using planes created from 3 points. It looks like you did that with some of the arcs but didn't do it for all of them. It seems strange that the whole thing isn't already structured throughout...
It depends on what you want from the results and how you're going to assess them. There won't be a stress concentration effect from a fillet radius but then that stress contribution would be classed as a peak stress component used in fatigue assessment. If it's a non fatigue assessment then the...
If it's a very big fillet, ie. not just a fillet weld for example, and you've removed it then you'll have altered the structural stiffness and so all your results wouldn't be correct. If it is a weld fillet radius then you wouldn't normally include it as I've yet to find a welder who can make a...
Your large mesh is too coarse to give any meaningful results. You appear to begin with a mesh size that has the same size as the objest you're studying. Any comparisons with a refined mesh will be a waste of time.
Results will depend on the value you use for natural convection and on the conductivity of the material. To be correct both of these values should be temperature dependent. In addition you should also have radiation from the surface.
The image you included shows a flat disc. To create a uniform roll then you'd just extrude that disc along the axis. To create a non uniform roll then sketch the outline and sweep it around the axis for 360 degrees or whatever.
