Problem with obstruction in FDS6

[omaki...@gmail.com]

Hello,

I have been used FDS 5 for cone calorimeter simulation. Now I am trying to move to FDS6. I made the cone heater geometry in FDS 5 and did not have problem. But when I used same geometry in FDS6, the obstruction could not be formed properly. Interesting thing is that the obstruction can be formed when I reduced element size half. I converted .stl file to .fds file. I have attached the figures and put some parts of the OBST code for the cone heater. Can you please explain why it happened?

&OBST XB=  0.091358,  0.096790,  0.178272,  0.183704,  0.079000,  0.080605, SURF_ID6='INERT','Burner','INERT','Burner','INERT','INERT'/
&OBST XB=  0.091358,  0.096790,  0.178272,  0.183704,  0.080605,  0.082210, SURF_ID6='INERT','Burner','INERT','Burner','INERT','INERT'/
&OBST XB=  0.091358,  0.096790,  0.178272,  0.183704,  0.082210,  0.083815, SURF_ID6='INERT','Burner','INERT','Burner','INERT','INERT'/
&OBST XB=  0.091358,  0.096790,  0.178272,  0.183704,  0.083815,  0.085420, SURF_ID6='INERT','Burner','INERT','Burner','INERT','INERT'/
&OBST XB=  0.091358,  0.096790,  0.178272,  0.183704,  0.085420,  0.087025, SURF_ID6='INERT','Burner','INERT','Burner','INERT','INERT'/

Thank you.

Kind regards,
Nam

[Kevin]

When the user-specified obstructions are not exactly aligned with the grid, FDS must make assumptions about how to "snap" the obstructions to the grid. Some of these assumptions have changed. I suggest when doing a case like this that you make the obstructions exactly conform to the grid. Even if you change resolution, create a new geometry. I would think that you have some simple script to make the cone.

[Nam Kim]

Thank you very much Kevin,

I was trying to build the cone geometry as close as a real one. I created the 3D model using CAD and then converted to FDS format. That is why the obstruction did not conform the grid, particularly Z axis. I will try to simplify the script. Thank you.

Kind regards,

Nam

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