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Can SW simulate volume filling of a cylinder?

Question asked by Suraj Khosla on May 31, 2015
Latest reply on Jun 2, 2015 by Bill McEachern

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Is there a way of using the flow simulation tools within SolidWorks to fill an empty cylinder with a specified flow rate and as an output, get the time for the cylinder to be filled fully? This would all be done on a static cylinder in its in-stroke, all the is required is the time to find how long it takes for the cylinder in that position to fill.

I understand that I can use hand calculations to solve this (simply calculating the volume and comparing against flow rate) but I am trying to show this as a simulation also.

Andrei Popov May 31, 2015 11:41 PM

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No, because CFD is using the mass conservation principle, which means the mass that enters the domain should exit and be the same mass. Actually should be the same mass flow rate. In your case you fill up a cavity with mass but nothing exits. I calculated the flow through a valve that lets the fluid entering/exiting a piston chamber but the calculation domain was just the top of the cylinder, the mass flow calculation was done previously on a spreadsheet. The time was set by the RPM of the crankshaft. For your problem you need multi-physiscs which Solidworks is not capable to simulate, maybe Simulia-Abaqus can.

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Andrei Popov May 31, 2015 11:41 PM
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No, because CFD is using the mass conservation principle, which means the mass that enters the domain should exit and be the same mass. Actually should be the same mass flow rate. In your case you fill up a cavity with mass but nothing exits. I calculated the flow through a valve that lets the fluid entering/exiting a piston chamber but the calculation domain was just the top of the cylinder, the mass flow calculation was done previously on a spreadsheet. The time was set by the RPM of the crankshaft. For your problem you need multi-physiscs which Solidworks is not capable to simulate, maybe Simulia-Abaqus can.
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- Andrei Popov @ Andrei Popov on Jun 1, 2015 5:37 PM
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  I have to correct myself: It's not multi-physics the requirement but the possibility to do morphing mesh (which SW cannot do) as in this video:
  
  Star-CCM+ LES Simulation of Helical Valve Using Morphing Mesh - YouTube
  
  Simulia-Abaqus cannot do morphing mesh but ANSYS and Star-CCM+ can.
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  - Bill McEachern @ Andrei Popov on Jun 2, 2015 1:44 PM
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    You just need an Euler code to do this and the right sort of physics implemented. Easy peazy in say Abaqus explicit or LS-Dyna. You could not do it in a lagrangian a code- like your typical FEA code. Flow Sim is an Euler code but you would need to be a bit creative as I mentioned earlier and understand the approximation you are formulating.
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Yosef Yoeli Jun 1, 2015 4:51 PM
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Hi Suraj,

Please check the link:
https://youtu.be/jVo9_arlqd0?list=PLPit5zMJpdHK2L9k6i2HlNyn6Y5unzH74
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Christopher Schaefer Jun 2, 2015 9:16 AM
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It's technically a free-surface problem which is not solvable at this time using SWx Flow Sim. However, there is a tank evacuation calculator in Flow Sim that may be wrangled in to service for this type of problem. Search this forum for tank evacuation.
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Andrei Popov Jun 2, 2015 12:52 PM
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Just found there is a solution in the Knowledge Base S-056539 that deals with this problem:

2. Tank filling or evacuation with time dependent simulation.
This is a very involved simulation.
You can simulate this phenomenon using a Time Dependent simulation, with the High Mach number option ON.

This option is required to calculate propagation of compression waves (see note below). But this option forces the calculation time step to be very small. Typical values are of the order of 1E-7s. Consequently, consequently this calculation will require a very large number of iterations to be run, and consequently a lot of time. Perhaps 5 ms is the real time which can be calculated, unless you are willing to accept days of calculation time.. Suppose for instance that the model is quite simple and that an iteration takes 2s to solve. If the time step is 2E-7s, solving 5ms of physical time will take 14 hours (25000 iterations). It is worth noting that you cannot manually modify the time step when you use the High Mach number option. If you are trying to simulate a phenomenon which takes sensibly more than a few ms, the calculation time is likely to be days. Also, in the case of tank evacuation, it may be required to simulate an external flow to correctly simulate the jet of fluid just outside the opening (as opposed to simply defining a lid with an environment pressure boundary condition on it).

Example This is the simulation of a spherical tank being filled from 1 to 2 bars (absolute) from an opening at the end of a small pipe. Here are some numbers to understand how computationally intensive this is:
● Iterations: 184093
● Physical Time: 50 ms
● CPU time: 13238 s = 3h40min
● Fluid Cells: 881
● Partial Cells: 656

But still I don't understand how the mass conservation principle is followed
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- Bill McEachern @ Andrei Popov on Jun 2, 2015 1:46 PM
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  the mass conservation is a on a cell by cell basis not the whole problem. And further mass accumulation is a part of mass conservation. Just model a simple control volume (finite volume). mass in = mass gain/loss in volume + mass leaving volume.
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Bill McEachern Jun 2, 2015 1:40 PM
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You could approximate this by having 2 species - fill the cylinder with one and make it light with very low conductivity so the mixing is low and the other heavy and again with low conductivity and then add a goal for say some high volume or mass fraction for the cylinder volume. That should get it close.
In regards to the comments on mass conservation and this not being suitable for this code I disagree. All flow codes will solve for the mass conservation if at all possible. This is a function of the fact that two phase and free surfaces are not supported. You could also approximate this with an empty cylinder (very low pressure) and see how long it take to normalize to whatever ambient is......you just need to pose a question the code can answer.
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Chris Michalski Jun 2, 2015 1:51 PM
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Most of you guys are discussing the wrong kind of cylinder.
As Andrei noted in his answer to Suraj, Flow can't simulate filling a hydraulic/pneumatic cylinder (actuator) and moving the piston/rod from compressed to full-stroke.
You are commenting on filling something more like a high pressure gas cylinder (tank) which can be done in Flow because it does not require phase change in the mesh.
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- Bill McEachern @ Chris Michalski on Jun 2, 2015 2:39 PM
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  Hi Chris,
  
  The OP did start with this....."Is there a way of using the flow simulation tools within SolidWorks to fill an empty cylinder with a specified flow rate and as an output, get the time for the cylinder to be filled fully? This would all be done on a static cylinder in its in-stroke, all the is required is the time to find how long it takes for the cylinder in that position to fill." Can you blame us for being a bit confused? anyway the CEL (Coupled Eulerian Lagrangian) in Abaqus explicit could do the problem with good fidelity but ........the point is probably moot.
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Can SW simulate volume filling of a cylinder?

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