Import and Export of Geometry

[Mark Beyer]

1. What is the best path to export plot3d or other format to be imported into GridTools for use with Fun3D?

2. Are there any plans to provide STEP geometry file import/export to support CAD?  Is Rhino the intended path forward for this?

3. Are there plans to add support for fairing design, or flap/ control surface details?

[Rob McDonald]

Mark,

Welcome to VSP, I hope you'll find it to be useful. I think you'll
find that making the most of VSP requires some substantial departures
from the traditional CAD way of doing things.

There has been a lot of work by diverse groups to connect VSP to CFD.
Every group/tool/application seems to require a slightly different
approach.

The most mature path is to Cart3D, but even with that target, there
are multiple ways to get there.

For an unstructured code like Fun3D/USM3D, I would suggest using the
CDFMesh capability to generate a quality triangle surface mesh and
then go from there. You'll then need to use a volume mesher that can
start from just a surface mesh. Many inviscid tools can do this --
TetGen is open source. If you want to start with viscous layers,
there are fewer to choose from I know AFLR3 from Mississippi State and
Steve Karman's tools from UT Chattanooga can fill this role. Maturing
this workflow has been on my list all year, but I haven't been able to
get to it.

We do have some users who have developed a VSP XSec-file based
approach to convert to Plot3D and then generate Overflow grids. I
don't know the details -- or even who the best contact would be.
However, someone who knows is probably on this list.

STEP output of a watertight surface is on the to-do list, but it'll be
more than a year before it is complete. We're in the process of a
major refactoring and rewrite of some core code. The STEP output will
come after that.

There are no plans for a direct CAD import. The imported geometry
would not be parametric, so there isn't that much utility in doing so.
We can already read in some discrete surface representations (such as
a STL file) and there are plans for assisted parameterization of that
kind of data. That work is more than a year out.

There are no plans to support any sort of fillet/chamfer type
operation. That kind of operation doesn't really fit in with the VSP
way of doing things. So, depending on the fairing, we may be able to
handle it -- but quite possibly not.

There is some very simple control surface support in the Airfoil tab.
It is probably sufficient to use a small deflection to estimate a
control surface derivative, but it isn't appropriate for a high lift
configuration.

If you're doing a high lift wing, you probably have the flap
coordinates as a file. VSP does not force input airfoil data to be
scaled [0,1], so if the slat extends into -x and the flap extends
beyond x=1, no problem. You can create a baseline wing -- usually the
cruise configuration. Then duplicate that wing for each element in
the high lift configuration. Change the airfoil files as appropriate
and you can build the high lift configuration.

You can then use parameter linking to connect the high-lift wings to
the cruise wing. That way, any parameter changes in the cruise wing
will be reflected in the high lift configuration.

The VSP Hangar has an example of this approach (I'm not sure if it is
linked), it should give you an idea of what I'm talking about.

http://hangar.openvsp.org/vspfiles/52

Rob

[Ricardo Díaz]

Hi everyone,

Although VSP is a great tool, the lack of a usable format of exporting geometry has make me search for other alternatives.

In fact, I've found a piece of software that fulfils my needs: SUMO (SUrface MOdeller)

You can find it on  http://larosterna.com/ , and is free to download.

Regards,

Ricardo Díaz.

2012/10/28 Rob McDonald <rob.a.m...@gmail.com>

[Rob McDonald]

Ricardo,

I am at least vaguely familiar with the project at Larosterna. They
have some interesting capabilities, but I am also sure that there are
some things that VSP can do that they can not.

I consider the 'alternative to CAD' domain for geometry tools to be
ripe for innovation. The more groups we have in this area -- each
pursuing different ideas -- the better. While any one tool may not
meet all of your needs, hopefully something out there will.

I'm disappointed to hear you say there is a "lack of a usable format
of exporting geometry" from VSP. VSP has dozens of export
capabilities which people use on a daily basis to get useful work
done. While we certainly can not do everything, our export capability
is one of our strengths.

I'm sure you had a specific need in mind when you made this statement.
Would you mind being specific about what kind of export capability
you need? I suspect it is STEP/IGES export to CAD....

If that is the case, have you tried the Rhino export capability? A
lot of people who want to feed traditional CAD or Grid Generation
tools have had success starting with the Rhino export from VSP. Rhino
has a free trial download. You can use it to convert the VSP files to
a variety of other formats.

As I mentioned, we have specific plans to support CAD-style export in
the future, hopefully you'll give us another shot after that is added.

Rob

[Ricardo Díaz]

Hi Rob,

I'm sorry if I sounded too much critical with VSP. English it's not my native language as you may suspect. I think OpenVSP is powerful software and I use it quite often. You guys are doing a great job.

It is just that I find myself using software like that in larosterna for it's capability of exporting in IGES.

I think IGES or STEP export capabilities would be a great improvement.

Regards,

Ricardo Díaz. 

2012/10/29 Rob McDonald <rob.a.m...@gmail.com>

[Mark Moore]

So why won't Rhino work for you until we get the direct STEP/IGES file export completed?

I've played with SUMO (but I'm not experienced with it).  From my perspective the key difference is that VSP enables more complex geometries, and is driven by parametric inputs that can then be accessible for optimization, and is more suited to do work all the areas of design, from internal packaging of components, to computing wetted areas, etc.

I couldn't see any way to get the wetted areas to do basic drag build-up.  Attempting to do internal packaging would be pretty painful (and I couldn't find an option for glass rendering of components to permit internal packaging visibility.

But for quickly creating a surface mesh of less complex vehicles, it looks great.  I didn't see many options for determining the grid resolution and distribution.

Thanks for sharing, it's great to see what others are doing in this area.

Mark

[Rob McDonald]

Ricardo,

No problem, I didn't think you were being too critical -- and I
welcome constructive criticism; it is one of the most powerful tools
for improvement.

I had a feeling that you were thinking of a specific weakness in VSP
(CAD export). I know that is something we need to implement. I
thought you might have had some difficulty expressing that need -- I'm
sorry if I came across as defensive.

My concern is that this forum is a permanent record which is
searchable on the internet. Someone may come along later, find your
post, and not try VSP because it is "bad at exporting". Since I
thought you had a specific use-case in mind, I wanted to get that as
part of the permanent record.

Have you tried exporting to Rhino and then converting to STEP/IGES?
You might find that it satisfies your needs. If it doesn't, let us
know and we'll try to help you figure things out.

Rob

[Salman David]

Hell Ricardo,

I am trying to export the job to stl. but the program freezes and goes for debugging. Could you please suggest?

Thanks Salman 

[Ricardo Díaz]

Hi Salman, 

I'm no expert in OpenVSP, but if you need help you should provide more information.

Does the error occur when exporting the non intersected geometry, exporting from compgeom, CFD mesh?

What kind of geometry are you trying to model?

Could you send your model?

Regards,

Ricardo.

2013/2/6 Salman David <salman....@gmail.com>

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[Salman David]

Ricardo,

Thanks very much for your reply. It looks like a general problem as I can not save the file at an formate. I can sketch, simulate and so on but cant save it at all. Thats why could not send you the file. Whenever I try to save it entire thing freezes and goes for debugging. I will really appreciate your concern. If you have anymore suggestion then please provide.

Cheers

[Mark Moore]

This is unique to your installation, no one has such problems.  Try installing the latest version on another machine, and if that doesn't work, please specify what type of machine you are using, where all the OpenVSP files are located, etc.

Do you have the OpenVSP.exe in the same folder as everything else?

Something is fundamentally wrong with your installation.

Mark

[Rob McDonald]

Salman,

Are you having problems with OpenVSP, or with larosterna or some other program?

Since this is a VSP list, most people here assume you are asking about
VSP. From your question, I have a feeling you might be asking about
something else.

If you can better explain exactly what is going on, we'll be able to
help you better.

Rob