IES-VE User Forum

Hi
i have imported a model from sketchup and i have done all the apache settings to get the simulation for the airflows and now i want to see the graphic representation of the temp, pressure and velocity but when i want to run it, the page opens where i should have 3 green checks i get only two. the last one is a red cross because my aspect pixel ratio is much more than the 50:1

how do i alter the ASPECT PIXEL RATIO ???

Try increasing the size of your grid and using LESS CAPS.

Cell aspect ratio is the length of one cell dimension to another. A long thin cell, 1m:0.01m will have a high aspect ratio 100:1. A nice cube cell will have an aspect ratio of 1:1.

High aspect ratio cells can make a solution unstable. The 50:1 number used in Microflo as the point where you get a red cross is an arbitrary number. Sometimes you will get a solution at 100:1 but fail at 15:1.

The easiest way to reduce the aspect ratio of the cells is to use a finer mesh:

1) go to Microflo>>Settings>>CFD_settings>>CFD_Grid_Settings
2) reduce the "default grid spacing"
3) hit the "generate grid" icon in the left hand side of the MIcroflo window (the one with the yellow star icon)

You should really do something a bit more sophisticated though, and use a finer mesh close to the building(s) and a coarser ones further away.

If you import a model from Sketchup it is likely to have lots of unimportant geometry that constrains the mesh (cell lines have to align along grid constraints) but will have little effect on the flow. In reality it is probably best to redo the geometry in ModelIT and simplify it greatly.