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Tank TK000 with more than one outlet

Creator
Creator

Dear people,

 

My university has installed amesim in the labs this year and I am a student working on a summer research project on spacecraft control. It is my first exposure to amesim. The emphasis is on control sequence simulation rather than completely accurate mechanial simulation. I am trying to control a simplified model of spacecraft propulsion subsystem. It has two tanks (fuel and oxidizer) and two engines connected through valves. One engine is meant as a backup engine. The two engines can't be fired at once.

 

In the control sequence, whether an engine is fired or not depends of pressures at different points of the system. In my model the tanks are basically pressure sources. I have found out about TK000 "tank modelled as constant pressure source" which sounds like what I need for tank modeling.

 

However these tanks need to be connected to two parallel fuel lines. One engine at each end (with valves in-between).

 

I need to extend TK000 to have a second outlet. I also need valves with dual output. I do not know how to go about doing this and I would appreciate some guidance.

 

Thank you so much.

7 REPLIES

Re: Tank TK000 with more than one outlet

Siemens Phenom Siemens Phenom
Siemens Phenom

Hi @WhyNotMe,

 

welcome to the forum!

 

From what you describe the best library to address your needs would be the aircraft fuel system library ($AME/libacf). If your university has installed an academic license you will have access to this library.

 

If that's not the case, it's still possible to fiddle with the hydraulic library but... it's going to be fiddling around when the aircraft fuel system library should answer your needs perfectly. Multiple inlets at different heights, pressurized tanks...

Re: Tank TK000 with more than one outlet

Creator
Creator

Dear Emmanuel,

Thank you so much for your reply.

 

Yes I have been exploring the aircraft fuel system library including the satellite propulsion demo provided by amesim, however as an electrical engineering student I felt overwhelmed by the mechanical specifics.

 

Here is the system that I need to implement however it seems like a rather high-level view and probably quite alot of components have been ommitted from the schematic, but would be needed to simulate it. As an electrical engineering student I feel quite overwhelmed by the needed overhead and I do not understand much when looking at the satellite propulsion demo.

 

Only one engine can fire at once and engines can only fire when their corresponding pressures are high enough, which depends on the state of the valve (open or closed). The project is meant to study control sequences (open valve, close valve.., etc.) rather than very accurate mechanical simulation.

 

I am considering writing my own components in Modelica if I cannot figure it out.

 

By the way, is it possible to "send" commands (by means of control signals) to a system while it is simulating? Or does the system to simulate need to be fully defined (deterministic) at the onset of the simulation?

 

Thank you.

Re: Tank TK000 with more than one outlet

Siemens Phenom Siemens Phenom
Siemens Phenom

I see, thanks for the details and the layout.

 

In that case you can start simple:

- assume that both outlets are at the same level, hence you just fork the outlet into 2 pipes with a 3-ports node:

Amesim_propulsion.png

 

- As for varying inputs during the simulation, in the Simulation library you can use the externinput block.

Amesim_extern_input.png

 

This can be manually controlled with a dashboard using sliders/buttons...

 

See the demo platform/platform facilities/statechart/Interactive which will introduce both this capability and state machine building in Amesim.

 

I hope this helps.

 

[edit] I probably forgot some pumps in there....

 

Re: Tank TK000 with more than one outlet

Creator
Creator

Dear Emmanuel,

 

Thank you so much. This works as intended! (except for the engine part).

 

A few questions:

  1. Why is the hydraulic chamber needed?
  2. I've put two pumps powered by prime movers, one at the outlet of each tank. Is this how it's done?
  3. What is the difference between an orifice and a valve? It seems like in your example the orifice is being used as a valve. However in the libraries I've seen both valves and orifices.

Also, what would be the best way to simulate the engines?  I kind of feel bad having access to a software so powerful and not making use of it. If I use the aicraft fuel library is there a way to make an engine fire only if both oxidizer and fuel are in the input fluid? I haven't seen anything about oxidizer in the library. In the satellite propulsion demo there is only a MMH tank with no oxidizer tank. Sorry if i sound clueless, I'm not really a mechanical guy. However i would like to learn.

 

About the Aircraft Fuel System library:

  1. The dynamic demux ACFDMX001 component  is used to connect multiple lines to the tank penetration port, is this right? Is the fluid flow determined by the pressure differential? Or is there a set fluid flow from the left inlet to the multiple outlets on the right?

Thank you so much for your help.

Re: Tank TK000 with more than one outlet

Creator
Creator

The user's guide for the Liquid Propulsion library has an example that looks exactly like what I need, with oxidizer, fuel, combustion chamber, valves, engine. However I don't remember seeing this library in the right pane. Is it a standard library?

 

One more question about your example: is there a way to add some "slugginess" to the system so that the sensors do not react instantly to valve opening or closing? Some time delay would be good.

 

About the pumps: is one pump+prime mover at the outlet of each tank enough, or is it something I'll have to experiment with? What if the valve is closed, can the pump be "damaged" since it is pumping an (i assume incompressible) liquid against a closed volume?

 

Thank you so much.

Re: Tank TK000 with more than one outlet

Siemens Phenom Siemens Phenom
Siemens Phenom

Hi,

 

looks like you've been doing some good investigation over the weekend Smiley Happy

 

I'll quickly answer your questions in this post and switch to your other post later on.

 


WhyNotMe wrote:...

A few questions:

  1. Why is the hydraulic chamber needed?
  2. I've put two pumps powered by prime movers, one at the outlet of each tank. Is this how it's done?
  3. What is the difference between an orifice and a valve? It seems like in your example the orifice is being used as a valve. However in the libraries I've seen both valves and orifices.

[...]

 

About the Aircraft Fuel System library:

  1. The dynamic demux ACFDMX001 component  is used to connect multiple lines to the tank penetration port, is this right? Is the fluid flow determined by the pressure differential? Or is there a set fluid flow from the left inlet to the multiple outlets on the right?

Thank you so much for your help.


1. Hydraulic chamber.

In Amesim, orifices and valves compute the flow rates from the pressure difference at ports. This is a constraint which ususally helps numerically.

Hence in-between such components you always need a component computing the intermediate pressure. That's what the hydraulic volumes does.

I advise you leave the default value of the volume to start with and then for completion you can run some different cases with different volume values. The bigger the volume, the smallest the pressure change with the flow rate.

 

2. I'll pass this one, looks like you've answered it with the liquid propulsion demo.

 

3. Numerically, orifice and valves are identical, they restrict the flow. In the template model I drew, the orifice has a fixed restriction diameter whereas the valve (controlled orifice here) can vary its diameter with the control input. Exploring the libraries you will see there are a lot of models for valves.

 

 

For the aircraft fuel, you are correct, the demux port allows connecting as many outlet as necessary to the tank (different heights, fluid or gas...). See demos for use cases. As stated above, orifices always compute flow rate from pressure difference. To impose a flow I think you have to use a pump set to a specific regime.

Re: Tank TK000 with more than one outlet

Siemens Phenom Siemens Phenom
Siemens Phenom

For slugginess as you call it, a realistic approach is to plug first order laf to the output of the sensors (which always give you instantaneous values). Play with the time constant and comapre input and output of the delay block.

 

This looks like this:

sensor_delay.jpg

 

 

For the pump pumping against a closed volume, it depends on the pump technology. A fixed displacement pump will quickly make the simulation fail as the pressure will rise very quickly. A centrifugal pump should stall the flow depending on its characteristic curve.

 

 

 

A general advice, each library has a dedicated pdf manual with tutorials and examples. Check the Help (F1), in the contents, browse to Libraries, and browse.