SimScale CAE Forum

Error : "Gauge pressure field started diverging."

This the link of my previous post regarding the project that i am working.
i am trying validate an in-pipe hydro turbine.
while doing the simulation run i got this error : “Gauge pressure field started diverging. Please check the mesh quality near the reported location and try refining the mesh. If the problem occured near a boundary, please check the boundary conditions”

i read the above links, and tried to change different parameters of mesh…

tried to reduce fineness of mesh… = it was 5, i made it to 6 [SAME ERROR CAME]

in case of local refinement, i gave the value for Maximum edge length= 8.7e-5( this was one of the smaller edge of the cad model of turbine ) [ERROR: THIS TIME IT SHOWED TO USE LARGER MACHINE]

then i increased the fineness of mesh from 6 to 7 [ still running…its been around 20 minutes]

in the above link ,i didnt try 1,2,3 as it says that " If you are aiming for the correct y+ range, ignore this measure." i dont know much about it.so i didnt…

how to solve this??? please help

thank you

Hi there :slight_smile:

The first step is to locate where the issue happens. The error message specifies which parameter diverged and also the exact location in the model. This information is valuable, and can be a starting point for the troubleshooting process.

To gain more insight into the causes of divergence, the following basic steps are useful:

  1. Create a ‘probe point‘ result control and input the coordinates displayed in the error message. In doing so, you will see exactly where the divergence occurred;
  2. If the point is close to one of the boundaries, double-check all boundary conditions, making sure they are correct;
  3. If the point is located inside the domain, inspect the mesh around the area. The ‘mesh quality‘ visualization feature is very useful in this step. Even just a few bad quality cells can create instabilities in the simulation, ultimately leading to divergence.

One more method to locate the problematic area is by using isovolumes as you can read in this page: How to Check and Improve Mesh Quality | SimScale

What you can do in this case is to further refine these faces, or even increase the ‘Small feature suppression’ under the Advanced concepts (this could potentially help).

Best regards,
Fillia

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even though that error is there, i continued the post prosessing…
pressure, velocity are steady and blue…

u mean to say ‘to refine the mesh?’

ok…i will try…


mesh operation failed

https://www.simscale.com/workbench/?pid=4647100771582061026&mi=run%3A291%2Csimulation%3A288&mt=SIMULATION_RUN

Hello @thansiya ,

One quick comment on the mesh error: did you try to select the problematic edge by hovering your mouse over the edge’s name?

There’s a very detailed topology which is likely causing the mesh to fail:

Basically, the model used for this meshing operation is not clean and contains a number of very small faces/gaps.

I also noticed that you tried to run a simulation (which failed) some minutes ago. The mesh quality from the mesh that was used is very bad:

I’d recommend that you revisit the mesh quality article that you linked in your first post to gain more insights. On a side note: the two main ways to improve mesh quality are tweaking the mesh settings and also cleaning up the CAD model.

There’s not only a single approach that works, however, as a personal preference, I always recommend cleaning up the CAD model, as I find it to be a more reliable solution that works for all cases.

The most common problems are small faces and small gaps. With the mesh quality feature (described in the docs that you linked), you should be able to pinpoint the issues :slight_smile:

Just as a couple of examples:

Cheers

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thanku soo much…i will try this

hey… i got it…
this time not even a single error came…
thanks aaaaaa LLot ! :relieved: @tsite @RicardoParis
i did read the documentation that u all send me…but it took some time to catch-up those things…i was not able understand many things :sweat_smile: but due to these errors, i think i got some idea about this simulation set-up…

i got the results but, i am not sure whether i am right or wrong…
its part of my university project …
can u tell me ,how can i validate my results with this…

how is it judged? iss the results right?? https://www.simscale.com/workbench/?pid=5718719288333594843&rru=d8b47e06-c440-48d0-9927-516ddd4239a5&ci=2faec5a8-7fc3-426a-9917-cd27e2ed3856&ct=PLOT&mt=SIMULATION_RESULT

the input values are briefed here:
flow rate = 323 m3/h =66.3342 kg/s
pressure outlet = 0 Pa
rotational velocity 35.0097 rad/s
shown in table 3 of the journal. i guess we need to compare this simulation result with fig.4 (graph)…

pls help me to figure this out…its been only a small part of my work :slightly_smiling_face:

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Hi,

If you have experimental/analytical data from the paper, then you can simply compare your result to theirs. If you don’t have any data, then the usual approach is to perform a mesh sensitivity study.

In case you are interested in this topic, a good place to start would be in this article.

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but here …i dont know how to compare the results…the prameter of x and y axis is little different…
for the given discharge , there is only one graph and in the table its corresponding power output


[fig 4 volumetric flow rate velocity variations.]

can u look into the figure 4 of the journal and say what is the option/parameter under the simscale that i must look into to validate the results generated. ( is it the area average,forceplot,convergence…? and i if so which parameter under that option)…
are the results generated comparable…( right/wrong) with the result of the graph.

in the y-axis of the results generated it is showing ,time in seconds. Can we change the parameter of this y axis to some thing else in simscale ???
i needed the torque ,lift and drag forces too

sry i am not able to figure out,as there are more than one Uy values…and many more in simscale result.

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From a quick skim over the paper, it looks like a velocity along the length of the pipe?

In such case, I’d recommend downloading the results from SimScale and bringing them to ParaView (see the steps here).

In ParaView, you could use a “Plot over line” filter to obtain velocities along the length of the pipe. In case you run into issues with the filters, the Paraview forums would be a good place to ask around - they also have a pretty active community.

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yes i will try. :slightly_smiling_face: thank you
apart from that, is my work done correct…?

i could also see that ,torque is given in the journal.As such,simscale also provides torque value ( by summing up moment values).by doing so …i could reach no where to the given torque value of journal.
ie : in journal , torque = 30.8358 Nm
one of the result that i got is approximately =1.824 Nm

so… much of difference in the value…
i am not able to judge where have it gone wrong

i have inputed values acc to journal…
ie: flow rate =323m3/h = 0.08972 m3/s
rotational speed = 35.0097 rad /s
gauge pressure =0

Hello!

I’d say that the validation is on you to conduct - please refer to post number 10 in this thread.

Besides a mesh sensitivity study, I’d also recommend thoroughly reviewing the setup. From a quick inspection, this value looks very different from the one you mentioned.

Cheers

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sorry this is the right link…i got confused as i got so many run…

https://www.simscale.com/workbench/?pid=5718719288333594843&mi=run%3A239%2Csimulation%3A208&mt=SIMULATION_RUN

yes i am trying paraview ( installation is going on )…this is going too long…

i know this is my thing to do and all…but…as far as know i have put all the input values right.
while the results dont match.
i thought may be its something about simscale…
and i am stuck now…
means even if i do things in paraview,the results will be the same isnt?
unless i change something in this simulation setup…and i am clueless , about wat went wrong in between…

anyway thanks a lot for ur concern…
:slightly_smiling_face:

Hi,

The post number 10 is actually a different one. It’s the one that I mentioned mesh sensitivity studies (and linked this article, which is pretty useful).

In any case, as I mentioned, the validation is on you :slight_smile: If someone wants to chime in - feel free!

Cheers

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yes… i read that but i didnt get the point…