modeling on simulink u oxygen flow control problem

[Errico24]

Good morning.
My problem is as follows: I have an oxygen cylinder at a certain pressure, and it is connected to a plant by means of a valve that can regulate its flow.
since I have not much experience with simulink I wanted to ask you how you can shape this situation.
In practice I have calculated what oxygen flow is needed to my plant and I have to adjust the flow according to this.
as you can realize the model of the reservoir that is emptied and therefore in time decreases the pressure.
I also found the "ball valve" block on the simscape library but in input it allows me to adjust only the opening of the valve between 0 (closed) and 1 (open). how I can relate the required flow rate (in l/s) with the valve opening.
I also tried to use the "controlled volumetric flow rate source" but in the output it still gives me the wrong results (for example, imposed a flow rate of 10l/s and went out to check with a flow sensor it gave me 13 l/s).
I tried to search on the internet for similar problems modeled on simulink but I didn't find anything like that.
I hope I have clearly exposed the problem, otherwise I will add more information.

thanks in advance to those who will direct me

 

[Stan9411]

I press that I don't take absolutely gas. However, simulink and simscape use them, although exclusively with regard to the “mechanical” part.

this to say that an answer I don’t have, but maybe if you generalize the issue you also push some other more experienced user to give suggestions.

I go for points:

as you can realize the model of the reservoir that is emptied and therefore in time decreases the pressure.

Mah. I would say that when the valve is closed, the tank is an isolated system, so I suppose they value the typical relationships that bind volume and pressure of an ideal gas. when the valve opens it, I think it is worth the equations of energy balance (bernoulli? boh I go to memory of what I remember from the university) that bind the fluid speed with the difference of upstream pressure and valley.

with this I want to say that probably the dynamics of this phenomenon is described by hand writing equations in the generic blocks of simulink instead of using pre-programmed ones of simscape “gas”. Of course you must know these equations.... but you are a student so who better than you...

I also found the "ball valve" block on the simscape library but in input it allows me to adjust only the opening of the valve between 0 (closed) and 1 (open). how I can relate the required flow rate (in l/s) with the valve opening.

This is a control problem. simulink is made for these things, I'm surprised that a user (you), however inexperienced, can't imagine the solution. I suppose you will have to “read” the flow in your system with a sensor and create a small control loop that instantly manages the opening of the valve between 0 and 1 (see “back control” to understand the theory behind it).

I also tried to use the "controlled volumetric flow rate source" but in the output it still gives me the wrong results (for example, imposed a flow rate of 10l/s and went out to check with a flow sensor it gave me 13 l/s).

I think I'm inexplicable. . I think there's some bad news. example: how come you talk about liters? all mathworks products reason with the units of the international system, so I suppose that even gas simscape has all the blocks in m, kg, s .. for a volumetric flow rate you should have m^3/s . you sure you did not make some strange conversion somewhere? or you put a mass flow sensor waiting for a volumetric flow reading



Let us know, hoping that the discussion will take place with some gas-dynamic expert. I am always happy when you spread a little knowledge of matlab and simulink on the forum

 

[Errico24]

first of all thanks for the answers.

with this I want to say that probably the dynamics of this phenomenon is described by hand writing equations in the generic blocks of simulink instead of using pre-programmed ones of simscape “gas”. Of course you must know these equations.... but you are a student so who better than you...

Yeah, you're right. Surely the problem can be described through equations but I thought there were already pre-set blocks. I will therefore have to review these topics better. in all honesty I am not really a student model; we say that sometimes the desire to try us and the effort employed do not always find feedback in the results ..

How come you talk about liters? all mathworks products reason with international system units

I converted the results from m^3/s in l/s as I had values from a real plant and therefore I needed in this unit of measurement for comparison. But I checked and conversions are correct. I probably wrong to set some valve parameters.

However from your answers I realized that more than having a problem with simulink, I have a problem in the mathematical formulation. so as always the answer is to study theory better.
thanks to your availability.

I still listen to anyone who wants to give me some other advice on simulink; Also because now that you mentioned the back controls I was thinking of introducing some control, as it can be a pid.