Modeling Vessels
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gnogid
- Beiträge: 1
- Registriert: Do 15. Feb 2024, 15:29
Modeling Vessels
Hi, without fesu, is it generally better to model a vessel using the equivalent stiffness under the nozzle function, or by using a large pipe? I've found that with the vessel method, it does not take into account thermal expansion laterally or radially, meaning I would have to use hand calculations to properly model the system. On the other hand, using a pipe is also not ideal because it seems to not model radial thermal expansion or the stiffness properly, often throwing errors when I try to make a pipe using the true dimensions of the vessel. If anyone has any suggestions, I am happy to listen.
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rohr2support
- Beiträge: 466
- Registriert: Mi 14. Sep 2011, 08:23
Re: Modeling Vessels
Dear gnogid
If you have a pipe that is connected to a vessel nozzle there are different options how to treat the connection.
In most cases the nozzle is not exactly at the vessel anchor point. Therefore, if the vessel is hot, the vessel is expanding and the nozzle will move.
In the most simple case, the vessel can be modeled in ROHR2 with a simple anchor point (all 6 degrees of freedom blocked).
In this case the thermal expansion of the vessel can be modeled as an anchor point movement in the relevant load cases (when the vessel is hot).
If you use the "nozzle" function in ROHR2 at the end of the pipe this will be treated as an anchor point.
Another option would be to model the Vessel with a big pipe with the anchor point at the correct anchor point location of the vessel and the nozzle as a branch. In this case (if the material is correct) you can use ROHR2 to calculate the movement of the nozzle by defining the correct temperature in the relevant load cases.
In case you modeled the nozzle by using the "nozzle" function in ROHR2 the anchor point function will disappear as soon as you continue to draw the continuation of the line to model the branch and the vessel. ROHR2 assumes that you will correctly define the location of the anchor point, if you continue the line after the nozzle. This difference is clearly visible from the symbol of the vessel nozzle.
Using the nozzle feature, you can use the automatic methods from BS5500 or WRC to estimate the nozzle stiffness based on the vessel geometry.
This is independent on the fact that you use the nozzle as an anchor point to which you applied the anchor point movement or if you use it in the middle of the line and have modeled the vessel as pipe element.
Therefore it is not a contradiction to use the nozzle function and the still model the vessel as a pipe element to get an automatic calculation of the thermal expansion. If you still have an error message after reading this, the best solution is to send the model to the ROHR2 support so that we can figure out what is going wrong in your case.
Best regards
ROHR2 Support
If you have a pipe that is connected to a vessel nozzle there are different options how to treat the connection.
In most cases the nozzle is not exactly at the vessel anchor point. Therefore, if the vessel is hot, the vessel is expanding and the nozzle will move.
In the most simple case, the vessel can be modeled in ROHR2 with a simple anchor point (all 6 degrees of freedom blocked).
In this case the thermal expansion of the vessel can be modeled as an anchor point movement in the relevant load cases (when the vessel is hot).
If you use the "nozzle" function in ROHR2 at the end of the pipe this will be treated as an anchor point.
Another option would be to model the Vessel with a big pipe with the anchor point at the correct anchor point location of the vessel and the nozzle as a branch. In this case (if the material is correct) you can use ROHR2 to calculate the movement of the nozzle by defining the correct temperature in the relevant load cases.
In case you modeled the nozzle by using the "nozzle" function in ROHR2 the anchor point function will disappear as soon as you continue to draw the continuation of the line to model the branch and the vessel. ROHR2 assumes that you will correctly define the location of the anchor point, if you continue the line after the nozzle. This difference is clearly visible from the symbol of the vessel nozzle.
Using the nozzle feature, you can use the automatic methods from BS5500 or WRC to estimate the nozzle stiffness based on the vessel geometry.
This is independent on the fact that you use the nozzle as an anchor point to which you applied the anchor point movement or if you use it in the middle of the line and have modeled the vessel as pipe element.
Therefore it is not a contradiction to use the nozzle function and the still model the vessel as a pipe element to get an automatic calculation of the thermal expansion. If you still have an error message after reading this, the best solution is to send the model to the ROHR2 support so that we can figure out what is going wrong in your case.
Best regards
ROHR2 Support