Simscape block pip (G)

I’m noticing that when I use the Pipe (G) block in Simscape for checking pressure loss, it’s always giving me a bigger number than what my calculations say. Can you tell me how the Pipe (G) block figures out the pressure loss?

Answer 1

[Ayush Modi]

Hi,

The pressure drop calculation done by the block Pipe (G) in Simscape contains two parts:

• The pressure losses due to momentum flux
• The pressure losses due to viscous friction

Refer the following MathWorks documentation for more information on how these terms are calculated:

https://www.mathworks.com/help/simscape/ref/pipeg.html

Why the pressure loss is different ?

Pressure drops which are too low can cause numerical stability issues. This is not an issue restricted to pipes, other components can also suffer from numerical instability due to low pressure drop. Indeed, a low pressure drop across a pipe means that there is a low resistance (i.e. the fluid easily flows through the pipe). Thus, a small pressure fluctuation on one side of the pipe can lead to a significant flow through the pipe. This is similar to what happens in a circuit with a resistor of low resistance: a low change in voltage can result in a large current through the resistor. In the case of a numerical simulation, this means that numerical noise can be amplified when the pressure drop is low. To ensure robust simulation, the Simscape block "Pipe (G)" adds an artificial amount of velocity change across the pipe. When the flow velocity is low, this artificial amount can create discrepancies in the pressure drop between analytical and simulated results.

Hope this helps!