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June 16, 2018, 15:12 |
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#1 |
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Okay, awesome. That doesn't really solve the problem, but at least we are getting closer.
Would you be comfortable posting your initial setup so that we can try to run it ourselves? It sounds like you know this simulaiton inside and out and are knowledgable about ANSYS, so I'd like to get up to speed with you. |
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June 17, 2018, 00:59 |
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#2 | |
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Quote:
where is the spring constant and the displacement from the equilibrium position. The cylinder oscillations shown in the original post indicate that on restart, as you have suggested. Can you check in the GUI or elsewhere? Ultimately, if this displacement cannot be retrieved or corrected on restart, then you may need to create a UDF for the cylinder motion (which seems straightforward, you have linked to posts on this forum elsewhere with the code). |
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June 17, 2018, 01:04 |
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#3 |
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Yes, like I said the center position is stored by Fluent's 6DOF solver and the co-ordinates before restarting are what they were when I stopped the simulation. That is also how I am plotting the figures attached in the original post. Also, the change of position in those figures is not sudden, so you can be assured that the on restarting the simulation does continue from the position where the cylinder was just before stopping.
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June 17, 2018, 01:15 |
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#4 | |
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As you have already determined, the position is consistent after restarting Fluent, but what about ? |
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June 17, 2018, 01:20 |
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#5 |
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June 17, 2018, 01:24 |
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#6 |
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I have not used the Six DOF solver before, and I do not have this version of ANSYS installed to have a quick check. Is there any mention in the Fluent guides? Otherwise have a look around the GUI?
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June 17, 2018, 01:30 |
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#7 |
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Yea, will do that. I have restarted a simulation for another case to see if this happens in that too. If it does, then next time I will use the UDF approach. But honestly, I would expect the same thing to happen there too cos the UDF will only have the mass, spring constant and 1dof as parameters, not initial equilibrium position.
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June 17, 2018, 01:47 |
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#8 | |
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Quote:
If you only want a single DOF such that the restoring force of the spring acts purely in the y-direction, then the force on the cylinder could be calculated with: Code:
force = -k*(DT_CG(dt)[1] - x_equilibrium[1]); Note: remember that indexing in C starts from zero instead of one, so DT_CG(dt)[1] corresponds to the second spatial coordinate (y for Cartesian). |
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June 17, 2018, 01:51 |
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#9 |
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June 19, 2018, 06:50 |
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#10 |
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March 4, 2021, 00:37 |
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#11 |
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June 17, 2018, 03:36 |
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#12 | |
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June 17, 2018, 03:53 |
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#13 |
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Well, this result is consistent with what we consider the problem to be: that the equilibrium position of the spring is being reset on restarting Fluent. I would expect (or at least hope) that using the UDF would solve this issue, and would also give you greater control and transparency on what you are actually solving.
Yes, a 3-D simulation would be much more computationally expensive. Remember to optimise your mesh and you could also start with an initial condition based on your 2-D result to help reduce the time it takes for the flow/oscillations to fully develop. |
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June 17, 2018, 04:02 |
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#14 | |
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Quote:
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June 17, 2018, 01:19 |
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#15 | |
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Please don't go out of your way to do this but. If you have some time to kill only then do it cos it will take a day easily. That was very kind of you to offer to simulate it yourself. |
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Tags |
dynamic mesh, restart problem, viv |
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