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Transient velocity BC not registering in a free surface analysis.

23 REPLIES 23
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Message 1 of 24
PaulNielsen
497 Views, 23 Replies

Transient velocity BC not registering in a free surface analysis.

I am running a free surface analysis with a transient velocity inlet BC that is tamped up from 0 m/s to a set value which is then kept constant throughout the simulation. I started the calculations on a Friday and left it running over the weekend as its a big simulation and when I came back after the weekend it had finished "successfully". However, the inlet velocity remained 0 m/s throughout the entire simulation! This has happened to me before with a similar setup.

 

Is this a known bug that is going to be fixed or is there a way to make sure that the defined boundary conditions will in fact be acting correctly?

23 REPLIES 23
Message 2 of 24
Jon.Wilde
in reply to: PaulNielsen

Hi Paul,

 

Does the BC stay zero for a while or being to ramp up immediately? I ask incase CFD lowered the time step enough to miss any change.

 

Otherwise, we might need to escalate this one...

 

Thanks!

Jon

 

Message 3 of 24
PaulNielsen
in reply to: Jon.Wilde

I set it up like this:

 

value [m/s]   |   time [s]

0                 |      0

0.2              |      10

0.2              |      1000

Message 4 of 24
PaulNielsen
in reply to: Jon.Wilde

I can add that this has only happened in cloned scenarios. Never when i've started setting up a model from scratch. I would however prefer to rely on being able to clone scenarios.

Message 5 of 24
Jon.Wilde
in reply to: PaulNielsen

Could you share the model with us and the steps you took? I would like to see if it can be replicated 🙂

Message 6 of 24
Amal.C
in reply to: PaulNielsen

Hi Paul,

 

May I ask which operating system you are working on? Win 7 or Win 10?

 

Thanks,

Amal



Amal Cheikh rouhou
Message 7 of 24
PaulNielsen
in reply to: Amal.C

It has happened on both actually. The most recent one was on win 7.

Message 8 of 24
PaulNielsen
in reply to: Jon.Wilde

Unfortunately I cannot share the specific model. It is a 2D free surface simulation on a weir (a continuation from this model) with a transient velocity inlet and a pressure outlet. 

 

This usually occurs when having cloned a design scenario and updated with a new geometry. Usually the BC have to be reapplied as the numbering of the edges may differ but this still produced 0 velocity throughout the simulation. 

 

I have now instead a constant velocity from the start to bypass this and it seems to be ok atm. However I would like to be able to use transient BC aswell. Especially if we want to add motion to the mix.

Message 9 of 24
matt.bemis
in reply to: PaulNielsen

Hi @PaulNielsen,

 

I will start to troubleshoot this on my end because I already have a similar CFD project from a previous support case. What jumps out to me is that you are updating the design after the clone. Updating designs is a tedious process and I suspect that's where the issue is arising. Can you please confirm the BC issue only occurs after a design is cloned and then geometry is updated? If so, I will follow this workflow exactly. 

 

Also, where is the CAD coming from? What is the native file format?

 

Thanks,



Matt Bemis

Technical Support Specialist

Message 10 of 24
PaulNielsen
in reply to: matt.bemis

From my recollection it has occured only after cloning and updating geometry. However i haven't exactly documented each time it works and when it doesn't. As I mentioned I have sometimes redefined each BC after updating design as the edges numeration changed in the newer design. But even then i had the issue with the transient BC.

 

All my models are created in inventor. 

Message 11 of 24
PaulNielsen
in reply to: PaulNielsen

Last Friday I started a completely fresh simulation set up from scratch, within the same weir project, but this time a combination of 2D, free surface and motion. I tried with transient velocity inlet but it didn't register. It remained at 0 m/s when it should have been higher. I had to use a constant velocity BC to get something done over the weekend. 

 

At least I now know my model works, would just really need for the transient BC to work with it! Smiley Wink 

Message 12 of 24
matt.bemis
in reply to: PaulNielsen

HI @PaulNielsen,

 

Thanks a lot for the update! This definitely helps me narrow down the issue and increases chance of me reproducing it. I am testing a free surface model right now and will like you know if I can reproduce the issue.

 

Thanks,



Matt Bemis

Technical Support Specialist

Message 13 of 24
matt.bemis
in reply to: matt.bemis

Hi @PaulNielsen,

 

Okay, update here. I ran the free surface model from this webinar (See 4:53. Thanks @Jon.Wilde 😄 ) using a transient piecewise linear BC. The flow did not go to 0 at any point. Which method of variation are you using to vary the flow BC?

 

Next I will clone and rerun it. I can try 2D if I have to but it may be a little harder to quantify a wrong BC. 

 

Thanks,

 



Matt Bemis

Technical Support Specialist

Message 14 of 24
PaulNielsen
in reply to: matt.bemis

Hi Matt, just read this reply. For some reason I've stopped getting email-notification when someone replies to this post. 

 

I used a piecewise linear variation method and all my simulations have been in 2D.

Message 15 of 24
PaulNielsen
in reply to: PaulNielsen

I can also add that the BC is component based (instead of the default Normal) in the positive X-direction.

Message 16 of 24
matt.bemis
in reply to: PaulNielsen

Hi @PaulNielsen,

 

Thanks for the information. So I've been doing some testing on my end and am still having a hard time reproducing this issue. I built a test model similar to what you've been describing. Basically I have a 2D free surface model. The inlet BC is transient piecewise linear velocity in Vx. You will notice the scenario recorded below is "transient BC2"; "transient BC" is the exact same. I was trying to trigger this issue by cloning and rerunning. 

 

Please let me know your thoughts! We can always escalate this to a formal case and chase it a bit harder. As usual, the challenge will be to identify the steps to reproduce. Until then there is not much we can do to get the problem fixed. 

 

Thanks,

 



Matt Bemis

Technical Support Specialist

Message 17 of 24
matt.bemis
in reply to: matt.bemis

I think embedding the video didn't work. Video here



Matt Bemis

Technical Support Specialist

Message 18 of 24
PaulNielsen
in reply to: matt.bemis

Hi Matt.

 

Looking at your video to me it seems like you have the same issue as me where the simulation is stuck on your starting value of your velocity BC. For comparison maybe setup you table the same way as I did, i.e. start 0cm/s a time 0s and ramp it up to 30cm/s.

Message 19 of 24
matt.bemis
in reply to: PaulNielsen

Hi @PaulNielsen,

 

I am not getting email notifications anymore either 😕 pretty inconvenient. This has happened in the past and the issue goes away randomly. 

 

 

Thanks for the heads up on how to set the BC. I will fix this and rerun.



Matt Bemis

Technical Support Specialist

Message 20 of 24
matt.bemis
in reply to: matt.bemis

Hi @PaulNielsen,

 

Check out my screencast of using a piecewise linear BC like you specified above. I also cloned it and reran to confirm it is not a cloning issue. So far, nothing seems wrong. 



Matt Bemis

Technical Support Specialist

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