Dear all,

I am using PHOENICS 3.5.1 to simulate wind flows around and inside buildings. The simulation is one phase, using KEMODL turbulence without temperature. I am importing a STL file from AutoCAD and when I run the VR Viewer I have a strange simulation result. The fluid only recognizes parts of the geometry. I have noticed that when I simplify the geometry the problem does not occur anymore. What I have to do to use detailed geometries without having this problem?

Thanks in advance.

Sileno

it has to do with your objects. Probably they are not compatible for stl import. To export a stl file from autocad must satisfy some basic criteria. First of all to be a solid, secondly to lie in positive coordinates. Possibly you have created non solid objects or some of them have negative coordinates. Check it when you type stlout, then you will see in autocad coomand prompt, which of your objects have been exported succesfully. Dxf is a better and more flexible format (objects could be non solid..).

One question and for me . Could you tell me which version exactly of visual fortran do you use for 3.5.1 for windows (i suppose)? thanks

good luck.

Sileno,

Normally when the fluid does not recognise the building the CFD mesh is not quite right. H

ow have you set up the mesh ?Is the mesh fine enough to capture the data you are looking at?

I would suggest looking at using PARSOL. This feature is very good at this sort of problem.

Hope this helps,

Leon.

It doesn't have to do with solution data!! the problem is that they are missing objects (part of the geometry!!!so it is not associated to cfd mesh fineness. good luck!

Leon and "user",

Thanks for replying my mensage.

1. I had already done all the recommendations about the stl generation. I think that´s not the problem. Anyway I´d like to know how to do it using dxf files, 'cause it didn´t work last time I tried.

2. I'm really using a very simple grid mesh, since I´m still testing the first results. I´ll try to refine it to see what happens.

Thanks

Sileno

Sileno

I have undertaken many conversions as you trying to do. This is what I did to start off.

Create a simple cube in your 3d drawing package and export as a stl file. Import the shape. Create an identical shape in Phoenics. Put them next to each other, but not touching - you wnat suffcient space for the air to flow around both objects.

Then set up a sample run to see the differnces- there should be no differnce. Play with the mesh and agin see the differences.

Next try a cube with a pyramid on top (a simple representation of a house) and repeat the above.

This should give you a feel for the grid requirements and the stl conversion.

I have found dxf format to be particularly difficult in the past. As to me the export to dxf format from the few drawing packages I have used, appears to be less stable / requires the 3d geometry to be drawn in a particular way to work properly.

Most 3d designs typically are drawn to look right with shapes added as needed, and this can some times cause major problems.

Hope this helps.

Leon

Hello everybody,

Some suggestions:

(1)Make sure that your problematic objects define mesh (you may have to go to q1 and changes the status manually with the help of notepad or wordpad skills). When you do that, it is possible that your mesh becomes completely "crazy". Go to geometry and free all cells so that the mesh will be remade.

(2)Also at geometry, you will have a parameter called "(something) tolerance". This number defines what is the smallest object that can be recognized by mesh (for instance, depending upon this number, the object will not be able to define mesh...). This will help PARSOL to work.

Good luck!

Carlos

Sileno,

Have you used Design Workshop? There is a lite version available on their website. I am modelling the same type of problem as you and have found this programme to be quite benifical in creating roof structures. The geometry can be converted to dat files by shapemaker.

I am not sure if this will help or not, but I'll throw this out anyway. I was importing stl files from acad into phoenics but from cartesian (acad) to cylindrical polar (phoenics). I ran into problems if the 'facetratio' in autocad was not set to 1. I also used a 'facetres' of 1.0

This may have nothing to do with your problem, but hopefully it may help someone.

Also, are your importing all your objects in as one stl file or are do you have seperate files for different objects?

Hello everybody

For wile my problem is solved. It was only the mesh refinement at all. Anyway I'd like to thank everyone who has helped me.

See you in the next discussion.

Sileno