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# pressure and flow rate in a closed fluid circuit

Hi,

I am trying to model a closed fluid circuit. I have valves in place to ensure unidirectional flow. Is it possible to prescribe both a flow rate and the pressure at the starting point? Or is it that I can prescribe only of them as a boundary condition and achieve the other through changing the parameter values in the components of my circuit?

Thanks.

2 REPLIES
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Solution
Accepted by topic author ameswimmer
‎12-14-2016 11:04 AM

## Re: pressure and flow rate in a closed fluid circuit

Hi,

LMS Amesim components are based on the bond graph theory, which is particularly suited to represent physical dynamic systems and the exchange of energy among different physical domains ensuring its conservation.

Following this approach, each Amesim component port exchanges two kind of variables, called “effort” and “flow”, whose product returns the power passing through the port. For instance, in the hydraulic domain these variables are pressure and flow rate respectively.

The equations coded in each submodel allow to compute the “effort” variable starting from the “flow” variable or viceversa, resulting in its causality (to check the submodel causality, right click on icon --> external variables…). Here below an example:

Therefore, it is not possible to provide both flow rate and pressure to a hydraulic component. However, this is not a blocking point at all given that this philosophy does represent the way hydraulic equipment work. Take a swashplate pump for instance: the flow rate supplied is a function of the pressure difference across the pump.

For what concerns your application, I suggest you to use either a pressure source followed by a resistive element (e.g. an orifice) that will return the flow rate or, vice versa, a flow rate source followed by a capacitive element (e.g. a volume) that will compute the pressure.

I hope it helps,

FedericoC

## Re: pressure and flow rate in a closed fluid circuit

Thanks FedericoC!

Will read read up on the bond graph theory for more details.