WARNING: Maximum density, 2.663 kg/m3, clipped in mesh x

[AntonioM1991]

Dear developers,

I’m encountering an issue after I updated FDS from version 6.7.5 to 6.7.6.

Different fire scenarios, very different from one another, return the following warning followed by a simulation crash due to numerical instability (the maximum velocity and pressure errors in the .out file are ~10E8):

WARNING: Maximum density, 2.663 kg/m3, clipped in mesh 3.

I remark that the fire scenarios successfully run weeks ago with the 6.7.5 version of FDS.

I guess that this error is related with the new version of FDS. I haven’t found yet someone with the same issue on web or any topic explaining how to solve it correctly. I can’t figure out why the fire scenarios returns such a high value of gas density.

I read the FDS user guide both for version 6.7.5 and 6.7.6 and I noticed two additional chapters in the new release, 7.11.1 and 7.11.2, which I think refer to the error I get. Is it possible that the FDS code was modified in this part as well, and possibly causes that issue?

I’m using the latest (2021.3.0901) version of Pyrosim to generate the input files.

Thanks to everyone who will reply to this message.

[rmcdermo]

Please attach your input file and we'll take a look. Thanks

[AntonioM1991]

Scenario ERROR.docx

That is the FDS input file. Thank you so much. Best Regards.

[mcgratta]

I cannot find where the problem occurs. My guess is that you have 9 enclosed spaces within the domain, and gas is filling one of them. I would look at the geometry and try to eliminate closed spaces. FDS can find them, and declare them to be pressure zones, but if the gases build up within them, the upper limit on density will be hit.

[Panachaia]

Dear all, ii have same problem " WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1" Please help me how to fix this problem. Time Step: 3600, Simulation Time: 203.14 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 Time Step: 3630, Simulation Time: 203.38 s

ERROR: Numerical Instability - FDS stopped (CHID: SCENARIO_S18) [runfds.exe] subprocess exit: 0

[Panachaia]

SCENARIO_S18.zip

[rmcdermo]

It appears you have just sent us a Pyrosim file. Send us the FDS input file (append .txt) and we will take a look.

[rick-fds]

I also encountered the same problem

Time Step: 1, Simulation Time: 0.08 s Time Step: 2, Simulation Time: 0.17 s Time Step: 3, Simulation Time: 0.25 s Time Step: 4, Simulation Time: 0.33 s Time Step: 5, Simulation Time: 0.37 s Time Step: 6, Simulation Time: 0.41 s Time Step: 7, Simulation Time: 0.46 s Time Step: 8, Simulation Time: 0.50 s Time Step: 9, Simulation Time: 0.56 s Time Step: 10, Simulation Time: 0.60 s Time Step: 20, Simulation Time: 0.84 s Time Step: 30, Simulation Time: 1.01 s Time Step: 40, Simulation Time: 1.13 s Time Step: 50, Simulation Time: 1.22 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 警告：最大密度， 0.117 kg/m3，夾在網格12 中。 Time Step: 60, Simulation Time: 1.28 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 Time Step: 70, Simulation Time: 1.29 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 12 Time Step: 74, Simulation Time: 1.29 s

ERROR: Numerical Instability - FDS stopped (CHID: MESH-TESTv3) [runfds.exe] subprocess ex 20221030.txt it: 0

[drjfloyd]

@rick-fds As noted earlier in this thread, we can't diagnose the problem without an input file.

[rick-fds]

file.docx

[mcgratta]

You have sent me an image of the input file in a Word document. What shall I do with this -- copy it by hand?

[rick-fds]

MESH-TEST V5.zip MESH-TEST V5.zip sorry i provide my fds file for your reference

[mcgratta]

I want the text file with the suffix .fds. Do not send my the PyroSim file.

[rick-fds]

sorry i have no idea how to write down or in put the text file

[drjfloyd]

Open the folder containing the psm file. There should be a subfolder where Pyrosim ran fds. In that folder is a .fds file. We need that. Change the extension to .txt, go to the issue tracker web page for this issue, and drag that txt file into the reply box.

[rick-fds]

sorry: i have no idea whats wrong ??

Job TITLE : fire Job ID string : mesh0_8_v2

Time Step: 1, Simulation Time: 0.07 s Time Step: 2, Simulation Time: 0.13 s Time Step: 3, Simulation Time: 0.20 s Time Step: 4, Simulation Time: 0.27 s Time Step: 5, Simulation Time: 0.29 s Time Step: 6, Simulation Time: 0.32 s Time Step: 7, Simulation Time: 0.35 s Time Step: 8, Simulation Time: 0.38 s Time Step: 9, Simulation Time: 0.41 s Time Step: 10, Simulation Time: 0.45 s Time Step: 20, Simulation Time: 0.75 s Time Step: 30, Simulation Time: 0.90 s Time Step: 40, Simulation Time: 0.96 s Time Step: 50, Simulation Time: 1.01 s Time Step: 60, Simulation Time: 1.05 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 Time Step: 70, Simulation Time: 1.06 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 10 Time Step: 76, Simulation Time: 1.06 s

ERROR: Numerical Instability - FDS stopped (CHID: mesh0_8_v2) [runfds.exe] subprocess exit: 0

[rick-fds]

sorry is this one?

[rick-fds]

mesh0.8.txt

[drjfloyd]

No you have attached the .psm file. We need the .fds file.

[drjfloyd]

Here is a windows explorer view showing a folder where a .psm file is saved. When I run that file using FDS, pyrosim makes another folder which is seen in this view:

If I go to that folder note there is a .fds file there. This is the file you need to find, change the extension to .txt, and post in this issue:

[rmcdermo]

@rick-fds Please be careful about what you post, so that it can remain readable for the rest of us. Don't just reply to the email if it is going to generate pages of garbage. Thanks

[rick-fds]

I am very sorry: But when I convert the file to txt, the tex mesh0_8_v2.txt t will become garbled, so I provide the smvv file

[drjfloyd]

If the text is garbled then you did not use the .fds file. The .fds file is an ASCII text file. You can open it with notepad and read it. The smvv file is a proprietary format for Pyrosim, it is not the .fds file. The .fds file should be in the same folder as the .smvv file.

[rick-fds]

sorry is this mesh0.8 v2.psm ?

mesh0.8 v2 (2).txt

[drjfloyd]

Look at the image you attached. One of the files in that image has the extension .fds.

[rick-fds]

Minimum density, 0.117 kg/m3, clipped in Mesh 10 this is my.txt mesh(all0.8test).txt

[drjfloyd]

Did you verify that this was the correct file by opening it in notepad as I suggested? I don't think you did as if you did this is clearly not an ASCII text. You have once again attached the .psm file. We need the .fds file. We need the file in red:

[rick-fds]

Thank you very much I'm from Taiwan I'm currently in a hurry for my master thesis about fire simulation very and need help

mesh(all0_8test).txt

[drjfloyd]

That is the correct file. We can now take a look at it.

[mcgratta]

I am running your case. First question: why have you chosen to divide one of your meshes into 3 smaller meshes? By doing this, you have increased the run time by approximately a factor of 3.

More importantly, there are 135 regions within your domain that are sealed. These are what we call "pressure ZONEs" and they can lead to numerical instability. It is a known bug. Until we fix it, I suggest that you fill these sealed regions using solid obstructions.

You can also try the latest version to see if that helps.

[rick-fds]

First question: I'm trying to fix into a grid. Second question: I don't understand there are 135 regions within your domain that are sealed. How do I know where

[drjfloyd]

You also have a high molecular weight fuel without defining the specific heat on SPEC. This can also result in issues. Suggest you use the predefined SPEC of DODECANE (you also haven't defined a SOOT_YIELD or CO_YIELD so your fire won't produce either).

[drjfloyd]

Add slice files at different elevations for PRESSURE ZONE

[rick-fds]

thanks you much

[mcgratta]

OK, never mind my previous questions. I ran your input file and the calculation fails after 2.4 s, at which time the heat release rate is 4.5 GW. That is nearly 4 times the amount of energy required by the flux capacitor (1.21 GW). I suggest you use this energy to transport yourself back in time and rethink what you are doing here. My guess is that you intend to model a spreading fire, but instead you have just assigned everything that is made of CERAMIC FIBER to burn instantly at a rate of 1400 kW/m². You might want to investigate IGNITION_TEMPERATURE.

[rick-fds]

Job TITLE : fire Job ID string : mesh(all0_8test)

Time Step: 1, Simulation Time: 0.27 s Time Step: 2, Simulation Time: 0.53 s Time Step: 3, Simulation Time: 0.80 s Time Step: 4, Simulation Time: 0.87 s Time Step: 5, Simulation Time: 0.94 s Time Step: 6, Simulation Time: 0.99 s Time Step: 7, Simulation Time: 1.05 s Time Step: 8, Simulation Time: 1.09 s Time Step: 9, Simulation Time: 1.13 s Time Step: 10, Simulation Time: 1.16 s Time Step: 20, Simulation Time: 1.39 s Time Step: 30, Simulation Time: 1.56 s Time Step: 40, Simulation mesh(all0_8test).TXT Time: 1.69 s Time Step: 50, Simulation Time: 1.79 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 4 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 4 ALWAYS

[mcgratta]

The simulation is poorly constructed. You have introduced too much energy into the domain and caused a numerical instability.

[rick-fds]

How can this model that took me months to build be bad? There is a way to do it.

[drjfloyd]

Length of time put into building a model really does not eliminate the possibility that you have made errors. Kevin has pointed out one issue, that your inputs result in an insanely large fire at t=0.

You have a very complicated geometry. FDS is not a simple model, it takes time to learn how to use it properly. You should not expect to just install Pyrosim and then be off to races and be able model any complex thing you want.

A good strategy when trying to model something very complex, especially if you are not an expert in the modelling tool, is to start with a simpler version of the problem. In this case, maybe just model a small portion of this large structure. Something that doesn't take long to run but will let you see how your inputs behave. Then look carefully at the model predictions and ask yourself if the results seem reasonable.

[mcgratta]

Do you think that a fire that grows from 0 to 4.5 GW in 2.5 seconds is appropriate? If so, you should look for alternative fire modeling software.

[rick-fds]

I'm very sorry to both professors but can you help me to find the wrong settings such as formula materials, fire original settings, I'm very anxious and can only ask you two for help How do I know where is the setting error in Minimum density, 0.117 kg/m3, clipped in Mesh 4 0.117 kg/m3

[mcgratta]

No, we are not professors and we cannot teach you basic fire dynamics.

[rick-fds]

I need it very, very much, you guide me to solve this problem please please please

[drjfloyd]

It is not our role to teach you how to use this software. There are over 2000 example input files between the FDS User's, Verification, and Validation Guides that you can use to learn how to use FDS on your own. SFPE offers classes in the usage of FDS. There are multiple textbooks that teach fire dynamics. There is a user forum (https://groups.google.com/g/fds-smv) where someone might offer to help, but I wouldn't count on a significant amount of help as most people replying there have full time jobs that are not teaching FDS to students.

[rick-fds]

I have the same problem and would like to know where the problem is and can be fixed, thank you. ENV: {PATH=C:\Program Files\PyroSim 2021\fds;C:\Program Files\PyroSim 2021\fds\mpi;C:\WINDOWS;C:\WINDOWS\system32, OMP_STACKSIZE=16M, OMP_NUM_THREADS=4, I_MPI_WAIT_MODE=1} CMD: "C:\Program Files\PyroSim 2021\fds\runfds.exe" mpiexec.exe -localonly -n 1 fds.exe mesh(all0_8test).fds WDIR: C:\Users\USER\Desktop\mesh(all0_8test)

Starting FDS ...

MPI Process 0 started on LAPTOP-R3CL7QBU

Reading FDS input file ...

WARNING: DEVC SD1-4 is not within any mesh. WARNING: DEVC SD2-7 is not within any mesh.

Fire Dynamics Simulator

Current Date : November 5, 2022 22:50:21 Revision : FDS6.7.6-0-g5064c500c-release Revision Date : Thu May 27 12:19:10 2021 -0400 Compiler : Intel ifort 2021.1 Compilation Date : Tue 06/01/2021 11:25 AM

MPI Enabled; Number of MPI Processes: 1 OpenMP Enabled; Number of OpenMP Threads: 4

MPI version: 3.1 MPI library version: Intel(R) MPI Library 2021.1 for Windows* OS

Job TITLE : fire Job ID string : mesh(all0_8test)

Time Step: 1, Simulation Time: 0.27 s Time Step: 2, Simulation Time: 0.53 s Time Step: 3, Simulation Time: 0.64 s Time Step: 4, Simulation Time: 0.69 s Time Step: 5, Simulation Time: 0.73 s Time Step: 6, Simulation Time: 0.76 s Time Step: 7, Simulation Time: 0.78 s Time Step: 8, Simulation Time: 0.79 s Time Step: 9, Simulation Time: 0.80 s Time Step: 10, Simulation Time: 0.81 s Time Step: 20, Simulation Time: 0.87 s Time Step: 30, Simulation Time: 0.91 s Time Step: 40, Simulation Time: 0.93 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 Time Step: 50, Simulation Time: 0.95 s Time Step: 60, Simulation Time: 0.95 s Time Step: 70, Simulation Time: 0.96 s Time Step: 80, Simulation Time: 0.98 s Time Step: 90, Simulation Time: 0.99 s Time Step: 100, Simulation Time: 1.00 s WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 WARNING: Minimum density, 0.117 kg/m3, clipped in Mesh 1 Time Step: 162, Simulation Time: 1.03 s

ERROR: Numerical Instability - FDS stopped (CHID: mesh(all0_8test)) [runfds.exe] subprocess exit: 0 mesh(all0_8test).txt

[drjfloyd]

We have already told you what your problem is.