Transient Coupled Fluid Flow and Heat Transfer Error

[david.ponce]

Hello,

I've been working on a project using Autodesk Simulation Multiphysics 2013 focused on studying the Heat Transfer of an electrical furnace used for thermal desoprtion (environmental remediation technique). Running thermal analysis was quite easy, while including a Multiphsyics Analysis has been more complicated.

I've decided to run a Transient Coupled Fluid Flow and Heat Transfer analysis, considering the air natural convection inside the furnace. I've reached the point in which the analysis runs, performs a series of iterations, but after a while pops up an error message which I don't fully understand:

"The analysis of (...) did not finish! Please see the Summary for possible problems. Would you like to see the log file now?"

The log file (ds.lgt text file attached) neither describes the analysis process nor points out possible errors in the model.

Here are a few things I've considered to be the source of the problem, though I'm not 100% sure of any of them:

a) I previously installed MPICH2 in my computer following the instructions from this webpage: 

http://usa.autodesk.com/adsk/servlet/ps/dl/item?siteID=123112&id=17176796&linkID=13806469

b) There is only one fluid part in my model, but it is in contact with most solid parts. Fluid parts are commonly meshed as tetrahedras, but doing so requires that the solid parts are also meshed as tetrahedras. Does it affect the FEM analysis?

c) On a guide entitled "Autodesk Simulation Multiphysics 2013 - Seminar Notes" I read that this software has a CFD limitation which allows me to analyze incompressible viscous flow. Clearly air does not fit in the category. Does this mean I can't run a multiphysics simulation with air? (I've performed unsteady fluid flow analysis with air, but including a Heat Transfer analysis could add certain limitations...)

If anyone has any idea how to solve this problem, I'm open to any suggestion.

Here's a brief description of the furnace:

The furnace uses 5 cylindrical heaters and is thermically insulated with ceramic fiber (with a constant thermal conductivity). Also, it has a chimney exposed to the atmosphere, allowing air inside the furnace to escape through the chimney, causing considerable heat loss in my system. My goal is to predict the temperature of the soil after a certain amount of time (2 hours, 5 hours, etc.). To keep things simple, I consider a constant temperature of 500°C in the heaters, a constant convection load on the external surfaces, and an Inlet/Outlet on the top surface of the chimney. I don't consider radiation loss nor temperature dependent properties of the materials. The 3D mesh settings are set as default (100% of size). 

Attached you will find the error message, the log file and the analysis information, which shows 16 iterations before the error appears.

Thanks for your time.

[AstroJohnPE]

I suggest that you remove the non-english character from the folder name "horno el�ctrico 2013" and give it another try.

a) MPICH is not the problem since the analysis got this far.

b) Tet mesh should be fine.

c) A more accurate way of stating the limitation is "CFD is limited to applications when the fluid density can be considered to be constant". So any fluid/gas can be used but with some limitations. Buoyancy is the obvious exception, but I believe the software solves it using forces instead of density variations.

In a multiphysics analysis, the thermal processor is also running for part of the analysis. I do not think this is the case in your situation, but sometimes the error may be with the thermal analysis, but the software shows the fluid log file. So look in the report to see if you can access the thermal log files. Otherwise, browse to the folder "assemblyl - horno electrico sin entradas.ds_data\1" and look at the files ds.LGT and ds.L11. Those are the two log files for the thermal analysis.

[david.ponce]

Hi,

First of all, thanks for clarifying certain concepts about the Multiphysics parameters such as meshing and limitations. As for the error message, changing the folder name "horno el�ctrico 2013", did not solve the issue (I will, however, use English characters from now on).

I've decided to try perfoming a Transient Coupled Fluid Flow and Heat Transfer analysis on a much simpler model: a steel pot used to heat water.

The model consists on 2 parts, the steel cylindrical pot and the water volume inside it, both with material propoerties provided by Autodesk Simulation Material Library. Here are a few analysis parameters:

- All tetrahedra 3-D solid meshing

- Constant 100°C at the bottom of the pot

- Prescribed Inlet/Outlet on the Top surface of the water part

- Use buoyancy Effect, Reference Temperature: 25°C, Acceleration due to body force: 9.81 m/s2

- Time: 300s, 5 Steps

- Max Iter: 100

- Temp Tol = 0.05, Vel Tol = 0.05

The "Check Model" tool detects no error, so I run the simulation. The software performs iterations for the fluid analysis for a few seconds, and then the error message pops up: 'The analysis of "C:\Users\David\Documents\Inventor\Electric Furnace\MPT - Pot filled with water.ds_data\1\ds" did not finish! Please see the Summary for possible problems. Would you like to see the log file now?'.

The ds.LGT file suggests the thermal analysis didn't begin, while the ds.L11 is blank. Anyhow, I'm out of ideas as to what should I do next.

Once again, thanks for your time.

D. Ponce

P.S.: I attach the master report of the new, much simpler model, as well as the ds.lgt and ds.l11 files.