Hi,
I have a round tank model with bottom reinforced structural underfloor support welded onto the outside surface. The model is at the assembly level with two parts (tank and support). The tank is fixed at the bottom edge of the strake. The tank is constructed with the surface for FEA purpose (real model is not surface), bottom support is with real weldment. It is global bonded and all the relevant constraints have been applied. After evaluating the model stability, the program told me that one rotation constraint about the center axis is missing on the group of support and bottom floor. I have applied a rotation constraint on it, but it brings more missing constraints instead of fixing it. I am currently confused that why introducing one more constraint can make the model more unstable?
Can anyone please instruct? Or how to fix this issue. The model is attached for reference.
Short answer - Trial and error
Long answer
It looks like the problem is with the part "Tank -FEA.sldprt". It is having a hard time attaching the sloped bottom to the tank walls. I had to knit all the contiguous vertical surfaces of the tank wall together. I was able to solve it by explicitly adding a bonded contact set between the edges of the sloped bottom and the faces of the touching cylinder. And for some reason you need to remove global contacts.
The feature "Boundary-Surface1" may not be necessary for the analysis butting the sloped edges directly onto the cylinder would be cleaner.
You need to do the same for the assembly although the global bonded seems to be ok there. You can remove the mesh controls. They don't seem to be helping.
Hope that helps.