Help with bosfluids

[laura80]

Hello

I am studying the surge because of close of valve. I need to calculate the unbalance force in the pipe, when a valve closes in 30 sec. I get a steady state. Then I select the option "transient", but I do not anything, I let the valve still openned, and the flowrate and the pressures change, in a time of 1sec aproximately, and this results in unbalance forces. ¿why is this produced by? I think that the pressures and the flow trough the pipe should be constant, if I start from a steady state....

thanks in advance

 

[BigInch]

When you close the valve, fluid velocities change. Change in fluid velocities result in changes in pressure; see the Bernoulli theorm.

Let your acquaintances be many, but your advisers one in a thousand’ ... Book of Ecclesiasticus

 

[laura80]

Off course the velocity changes if i close the valve, but i am saying that i select the option transient but i do not make the valve closes. I kipt the position of the valve 100 per 100 open all the time, and the flow changes, and produces unbalance forces...i do not understand...

 

[MortenA]

He says that he dosnt change anything.

I dont know Bosfluid from personal experience - but i use other program e.g. Flowmaster and HYSYS. How big is teh change (and the forces)? Sometimes these program change the axis in the graphs that prsents the results and very small changes may seem big until you actually start to change parameters in the transient simulations.

The change may come from "numerical noise". Remember that the SS solution does have some residual error - just not a lot.

Pipeline studio e.g. actually uses different "fluids" in the SS and the transiet simulation (or at least its an option) - since some of the things that you may wanna check in transient (e.g. batches of fluids going through a pipe) dosnt make sense in a SS simulation. You may not have the same fluid defined for your transient and your SS simulation.

Last: Contact product support - that why you pay your maintenance fee!

Best regards

Morten

 

[LSThill]

laura80 (Mechanical)

Reference to BOS Fluid Transients Analysis

Did you Read:

Chapter 2
Section 1 – Steady State and Transient Program General Input
Section 2 – Program Utilities
Section 3 – Valve Closure and Transient Pressure Waves
Section 4 – Waterhammer Example Problem
Section 5 – Acoustic Frequencies Example Problem
Section 6 – Solution Theory
Section 7 – Safety Relief Valve Notes and Examples
Section 8 – SRG and SHW File Formats

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T. +31 79 361 5150
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http://www.dynaflow.com

 

[laura80]

I found out the mistake!!!

I had an element "orifice" next to other one, and this resulted in a non linear working of the model, this was the reason of a bad operation of my model. Thanks every one for your help.