Autodesk Inventor

[#1]

hi all!

I`m new to FEA, and would be happy to get some feedback and help to analyse my results.

I`m simulating 200metres of seawater pressure on a Personal submarine hull. The hull is 6mm thick and have five internal frames.

Had some issues on where to put the constraint. Figured I could use a fixed constraint on the conning tower hatch seat.

When i run the simulation I get a warning telling me that there are one or more thin bodies being treated as solids.

I tried to convert the hull to a shell, but the results where not good.

My concern is the yield strenght. The steel i`m using has a yield strenght of 275MPa.

I get a max stress of 213,7MPa. Does that tell me that i am 61,3MPa under the material yield strenght?

and what does excatly the safety factor tell me?

results attached

-Andrè

[#2]

Without a closer look at your model I couldn't say if that was the best place to set up your constraints or not.

As far as the yield strength vs Von Mises stress, yes, that's exactly what it's telling you.  You've got some extra strength beyond what Inventor believes you'll need.  The safety factor is just another way of looking at this same information: if your material yield strength is assigned a value of 1.0, and an area of your part has a safety factor of 3.0, then you have a 300% safety factor.

Take Inventor's FEA results with a grain of salt when you're looking at this sort of thing, though - it's a good guideline, and it will help you analyze your designs and see where you need to improve them, but if you're doing simulations that lives are going to really depend on, you need some of the heavy duty simulation software from Autodesk.  Simulation Mechanical or CFD, or Simulation 360.  Buckling is going to be a concern in your situation here, and Inventor will NOT predict buckling.

[#3]

What LT.Rusty said about the limitations of Inventor Simulation are true, but I think there is more that should be said here.

It sounds like you are not only new to FEA, but maybe also to mechanical / structural design?  (I base this assumption on your question about what the safety factor is, so if I am wrong, please know I mean no offense.)

It sounds like you need to hire an engineer.  Stress analysis isn't something you can learn from a discussion forum, or even a program tutorial.  You must have a solid mechanical / structural engineering foundation to be able to decide if the results you get from the analysis are even worth anything.

Stress analysis is all about making acceptable assumptions to simplify the model, and choosing the correct input to examine a specific problem.  If you don't understand the principles of mechanical design, you won't know which assumptions are acceptable, or which inputs are correct, or even if the results are close to reality.

Take special care when human safety is involved, as it appears is the case with your submarine.

-cwhetten

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