Why am I getting 2000000000% overstress?

Why am I getting 2000000000% overstress?

Example: BC.ifu

A common user error in FE/Pipe will give an unrealistic solution such as 2000000000% overstress for any part of the model. The main reason why this could be is due to missing boundary conditions. The other problem that can cause such high magnitudes of stress is due to mismatching midsurface radii in Cylindrical Shells template (STRINGS).

When the user forgets, or does not at a restriction as a boundary condition, then the solution will be very high due to the fact that the model, for FE/Pipe is floating in mid air.

The attached BC.ifu has the problem of boundary conditions. Open this file and run it and you will see in ASME Overstressed Areas under Reports that the stress is 2000000000% overstressed as shown below.

 

The easy way of fixing this problem is to add a new boundary condition in the Loads/Displacement window as shown below.

 

This boundary condition will tell FE/Pipe that the model is not floating in the air, so results now will be reasonable.

FIXITY is not the only way to add restraints to a model for accurate results. DISPLACEMENT can be added too, the user may fix only certain degrees of freedom, for example, prevent only axial displacement, and leave the rest free to rotate and translate.

FIXITY will fix all 6 degrees of freedom, while DISPLACEMENT will have to specified by the user which degrees of freedom to keep fixed.

There are some other cases that can have this same problem, but it is not due to boundary conditions. In the Cylindrical Strings Template (STRINGS), this problem might occur if there is an input error in the midsurface radius specified by the user. This usually happens when a skirt is being added, and the midsurface radius of the skirt does not match the midsurface radius of the vessel shell. The user should careful check all the midsurface radii when getting these unrealistic results.

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