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TCV in WaterCAD

Ref :- http://communities.bentley.com/products/hydraulics___hydrology/f/5925/t/62107

Hi
Regarding Victor's question,
Assume a pipeline with a TCV. Coefficient Type is 'Discharge Coefficient' (Cv).

initial Cv= 0.25

Fully Open Cv: 0.5

Valve Type is Globe

Pattern (Valve Settings) is Fixed.

Question): Run the model. How Q and Relative Closure of the TCV are calculated? What is the role of Cv in calculation of Q and Relative Closure? I know how a TCV operates and how Headloss, Cv and relation between relative closure and opening area in various kinds of valves are considered. Then my question is about how of calculating Q and Relative Closure in TCV? I mean when the software knows Cv initially, Cv fully open,diameter, valve type and other hydraulic characteristics of the model, How does it do to calculate a) Flow and B) relative Closure and C) relation between relative Closure and Cv?

Answer): My interpret is, the software uses energy equations for each pipe (start and stop point of each pipe) to show what the amount of Q is. Relative Closure is equal to 1-[Cv (initial)/Cv (fully open)]. With this parameters (Q, V, D, Cv, Relative Closure) all equations can be solved. Is my interpret correct?

Parents

Offline Jesse Dringoli Tue, Sep 13 2016 11:40 AM
Regarding how it calculates the relative closure: this is based on the valve type, initial Cv and fully open Cv. Behind the scenes, the Valve Type represents a curve of relative closure vs. relative discharge coefficient. You can read more about this in the second article that Mark mentioned.

Regarding how it calculates the flow - this is indeed where energy balance comes into play. In a case where you have a downstream boundary condition, the program iterates to balance energy across the network based on the physical characteristics, demands, that assumed boundary HGL, and the relationship between flow and headlos that the TCV's Cv represents. The more flow the more headloss, but the boundary condition needs to be satisfied. The program will settle on a balanced solution and you'll see the corresponding flow and headloss across the TCV.

In case where you only have demands downstream of the TCV, it's easier to solve - the flow through the TCV is simply the sum of the downstream demand, and the headloss across the TCV will correspond to that flow, given the Cv.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows
Bentley Communities Site Administrator
Bentley Systems, Inc.
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Offline Jesse Dringoli Tue, Sep 13 2016 11:40 AM
Regarding how it calculates the relative closure: this is based on the valve type, initial Cv and fully open Cv. Behind the scenes, the Valve Type represents a curve of relative closure vs. relative discharge coefficient. You can read more about this in the second article that Mark mentioned.

Regarding how it calculates the flow - this is indeed where energy balance comes into play. In a case where you have a downstream boundary condition, the program iterates to balance energy across the network based on the physical characteristics, demands, that assumed boundary HGL, and the relationship between flow and headlos that the TCV's Cv represents. The more flow the more headloss, but the boundary condition needs to be satisfied. The program will settle on a balanced solution and you'll see the corresponding flow and headloss across the TCV.

In case where you only have demands downstream of the TCV, it's easier to solve - the flow through the TCV is simply the sum of the downstream demand, and the headloss across the TCV will correspond to that flow, given the Cv.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows
Bentley Communities Site Administrator
Bentley Systems, Inc.
Cancel
Vote Up 0 Vote Down

Cancel

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