Modeling a vessel nozzle
Modeling a vessel nozzle
(OP)
Hi all,
I need to model a vessel nozzle with specific length, thickness, material specs and flange to mate a standard pipe specs. My main goal is to obtain a stiffness value (lb/inch and lb/inch/degree of roration). I need to figure this out when modeling and finally analyzing a piping system. And my question is where specifically should I apply the load and anlyze so ANSYS could give me a rotational stifness.
Regards.
PhilEduard
I need to model a vessel nozzle with specific length, thickness, material specs and flange to mate a standard pipe specs. My main goal is to obtain a stiffness value (lb/inch and lb/inch/degree of roration). I need to figure this out when modeling and finally analyzing a piping system. And my question is where specifically should I apply the load and anlyze so ANSYS could give me a rotational stifness.
Regards.
PhilEduard





RE: Modeling a vessel nozzle
RE: Modeling a vessel nozzle
That said, my appraoch is to model the end of the pipe with a spyder arrangement and then apply the loads (forces and/or moments) to the single spyder node. Let me know if this is what you are after, and I will try to give you more details.
RE: Modeling a vessel nozzle
Phil
RE: Modeling a vessel nozzle
Phil
RE: Modeling a vessel nozzle
Phil.
RE: Modeling a vessel nozzle
As a word of caution, I would feel very confident in saying that an FE model of a vessel-nozzle intersection that uses less than 1000 elements is NOT going to give you good results. For calculating nozzle stiffness, such an undersized model may tend to over-estimate the stiffness. On the other hand, it may under-estimate it too. The only way to know for sure is to make sure that your mesh is "grid-converged", that is that your answer is independant of the mesh size. Trust me, you'll need a heck of a lot more elements than 1000.
Good luck.
RE: Modeling a vessel nozzle
RE: Modeling a vessel nozzle
RE: Modeling a vessel nozzle
RE: Modeling a vessel nozzle
Can some help me to understand the boundary conditions that I need to place on the nozzle edge?. I have tried to do a simple model with “ALL”: d/D , T/t etc parameters according with those methods.
My “model” is a shell model (with pro/mechanical as software) and I have placed the two shell body ends far enough from the nozzle interception so no distortion are done by this two boundary conditions (both have all translation and rotations fixed).
I have tried to simulate the effect of the flange stiffness adding to the model a flange in this nozzle extreme, so the bore is preserved round when internal pressure is applied.
The circumferential membrane stress just due to internal pressure (cylindrical coord system aligned with the shell body) on the shell-nozzle interception are quite similar with those from WRC368 but the bending components are high with those by WRC 368.
In others words, how WRC368 and WRC107-297 considerer the nozzle “FREE” edge?.
Regards.
RE: Modeling a vessel nozzle
Second - I would not be overly surprised by differences in beding stresses between FEA and the WRC method(s). All of these WRC methods are based on some rather simplying assumptions and/or calculation methodologies. They simply cannot take into account every little detail that a well-designed FE model can. So, how big is the difference.
Lastly - Although I think that _some_ work like this (comparing FE result to WRC 107/297/368) has been done, I think that they have only looked at a few select cases. If in fact you are trying "ALL" - or even a big chunk of - the relevant parameters, this would be very interesting indeed. I would seriously suggest that you consider publishing such an interesting bit of research. Perhaps you would consider presenting it at the ASME Pressure Vessels Piping Conference http://www.asmeconferences.org/PVP06
To answer your last question - I don't know if there is enough information in the WRC bulletins to say for certain how they handle the nozzle "free" end. Like I said before, if the authors made some simplifying assumptions, then they have neglected such a detail.
Good luck!
RE: Modeling a vessel nozzle
Your question is another interesting one to me too. Could you post this thread on Caesar forum? Maybe Ray and rick could handle the question. Or let me know, I couldn copy and paste exactly your question, refer your name and post it in Caesar forum. Thanks.
Phil
RE: Modeling a vessel nozzle
Can you give me the adress of this forum
Thanks.
RE: Modeling a vessel nozzle
http://www.coade.com/support_discussion.asp
Phil
RE: Modeling a vessel nozzle
I am still very interested in your work. With the deadline for the ASME PVP Conference rapidly approaching, have you thought about submitting your evaluations as a paper? Contact me off-line at tgs4mail@gmail.com to discuss further.