Hello
I'm trying to define a needle valve curve and I'm a bit confused with the definition for "relative closure". Does anyone know if this is in reference to the the valve area (A/Ao) or valve stroke (Z/Zf)
Thanks
Hello,
The relative closure is in reference to whatever you'd like it to be. To explain this a bit: basically when you define a custom valve characteristics curve, it is a table of relative closure versus relative discharge coefficient. The relative discharge coefficients are relative to the "fully open" discharge coefficient which you must enter in the properties of the valve.
If your valve manufacturer provides a rating curve of area versus discharge coefficient, then use that. If they provide it as the stroke versus discharge coefficient, use that. The important part is when you define a closure pattern for your valve: the "relative closure" in the time versus relative closure pattern is in reference to your relative closure versus relative discharge coefficient curve. So, if that was based on area, your closure pattern will refer to area and if it was based on stroke then it will be based on stroke.
For example say you have a valve whose discharge coefficient is 10cfs/ftH2O0.5 when fully open and 2cfs/ftH2O0.5 when at 'half stroke'. Your valve characteristics curve would have an entry of 50% relative closure with a corresponding relative discharge coefficient of 20% and you'd enter 10cfs/ftH2O0.5 for the fully open discharge coefficient. Let's say you then had a closure pattern that had the valve close to half stroke at time = X. The program will then understand that it needs to use a discharge coefficient of 2cfs/ftH2O0.5 at time = X.
I hope this helps. If you're using HAMMER, there's a bit more (including an example model) in this Technote:
http://communities.bentley.com/Products/Hydraulics___Hydrology/w/Hydraulics_and_Hydrology__Wiki/modeling-reference-_2D00_-valves-of-various-types.aspx
If you need help understanding any other feature in our products in the future, please submit a service ticket to Technical Support.
Regards,
Jesse Dringoli
Bentley Technical Support
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.