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Pump system won't simulate

Pump system won't simulate

I've been tearing my hair out trying to learn how to use OpenModelica for the last week as I need to use it for a university project. I'm trying to model a fuel system testbed and have had some success with FuelSystem1.mo (attached), however there's some disparity between the simulated measurements and those from the physical system. This is likely down to a number of things and there of course are a lot of things I don't fully understand in OM yet, but I thought a good starting point to improving it would be to use a better pump.

FuelSystem1 uses a controlled pump with a nominal mass flow rate of 0.0316 kg/s, a measurement which was taken from the physical testbed during normal operating conditions. I think this parameter should be an output of the model rather than an input, and may be partly why the results are off. I tried to replace the pump by adding in a prescribed pump and defining the flow characteristics according to the manufacturer's data for the physical pump (see FuelSystem3, attached). The equations/variables for the system are balanced but I can't get it to successfully run a simulation - what can I do to fix this?

Any other tips that might help me develop my model and better understand Modelica would be greatly appreciated!

Might be worth adding - there's supposed to be two flow sensors, one between pipes 13 & 20 and the other between 18 & 19. These were again preventing the system from running a successful simulation, I've no idea how.

Cheers,

Calum
FuelSystem3.mo

FuelSystem1.mo

Edited by: Sulzer685 - Oct-23-20 11:12:54
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Re: Pump system won't simulate

Hi Calum,

First of all, I would advise you to use another pump model than the MSL pump. It is not very user friendly and has at least two drawbacks:
- When you specify a pump curve the curve must have its maximum pressure exactly at V_flow=0 to avoid double solutions
- It does not work well at zero flow, zero speed or with reversed flow

These issues have been successfully fixed in the Modelica Buildings Library (MBL). There is even a paper describing in detail how these deficiencies have been circumvented in MBL (https://simulationresearch.lbl.gov/wett … tter.pdf).

Similary, the valve models in MBL are very easy to use.

So my advice is to use MBL for your system. However, I am unsure how well it is supported by OpenModelica.

Best regards
Rene Just Nielsen

Edited by: justnielsen - Oct-23-20 11:29:23
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Re: Pump system won't simulate

Thanks. I downloaded MBL and have had a go at using the pump models from that. Can't seem to get that to work either but I'll persevere.

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