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Member
pyrogaz
Posts: 4
Registered: ‎12-15-2013

Unable to position model near to boundary

218 Views, 8 Replies
12-15-2013 12:11 PM

I'm trying to model the air flow over a Greenpower racing car but when I import the car then try to create a volume around it no matter what I do with the offset it won't allow the wheels to be any closer than 25mm from the bottom boundary of the volume, ideally I want it to be zero or certainly no more than 1-2mm. If I increase the offset too much the volume simply grows in the same direction and the car remains 25mm from the "ground".

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wildej
Posts: 757
Registered: ‎08-25-2011

Re: Unable to position model near to boundary

12-16-2013 01:38 AM in reply to: pyrogaz

Hi pyrogaz,

 

It is not possible to do this with the CFD volume - draw the air volume in CAD.

I suggest you let the wheels overlap the floor slightly as it will be more realistic and also avoids any tiny angles where the circumference meets the road (they are hard to mesh).

 

Also consider running a 1/2 model with symmetry.

 

Kind regards,

Jon



Jon Wilde
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Member
pyrogaz
Posts: 4
Registered: ‎12-15-2013

Re: Unable to position model near to boundary

12-16-2013 02:09 PM in reply to: pyrogaz

Thanks Jon. I'll have to work out how to do that as CAD really isn't my strong point! 

 

It's unlikely the final design of the car will be symmetrical but I'll keep the half model idea in mind.

 

Gary

 

 

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wildej
Posts: 757
Registered: ‎08-25-2011

Re: Unable to position model near to boundary

12-17-2013 04:31 AM in reply to: pyrogaz

Hi Gary,

 

I hope you are making good progress here.

 

I can also recommend a 2D approach, although again it depends on the shape. I suggested the 1/2 model because you will need a significant level of mesh to properly capture the airflow - easier if you only have half the model to run.

 

Kind regards,

Jon



Jon Wilde
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Member
pyrogaz
Posts: 4
Registered: ‎12-15-2013

Re: Unable to position model near to boundary

12-17-2013 11:28 AM in reply to: pyrogaz

Unfortunately I'm struggling with a lack of enthusiasm for CAD! Could you point me in the direction of a suitable training example for producing the volume in Inventor, I feel I need to learn how to do this before I can expect the kids on the team to have a go.

 

Thanks.

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*Expert Elite*
OmkarJ
Posts: 427
Registered: ‎10-02-2012

Re: Unable to position model near to boundary

12-18-2013 04:41 AM in reply to: pyrogaz

Try creating a box around your car by extrusion in Inventor. But make sure that in your Extrusion dialogue box, you choose "New model" (fourth) instead of default "Join" (first) option. Once you do this, you will find that there are two "Solid bodies" in the left hand tree, one for the car and ther other for  the big box around the car. Use "Combine" now and "cut" the car from the box. Thus base would be the box and Toolbody would be car. Make sure you have "Keep Toolbody" enabled. Once done, if you take a look at "Sold bodies" in the tree, the car would have been hidden, Unhide it and there you have a car, and the atmosphere around it.

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wildej
Posts: 757
Registered: ‎08-25-2011

Re: Unable to position model near to boundary

12-18-2013 05:41 AM in reply to: OmkarJ

Hi both of you.

 

Don't forget you can happily have parts overlapping in Inventor when you read them through. I recommend working in an assebly (I assume you must alrready have one).

Create a new part and just sketch the outline of the box and then extrude it. That is all. It might be best to use a side view for the sketch so that you can have the wheels poking out the bottom a little, these would be suppressed from the mesh (along with all the solid parts).

 

The cool thing with Inventor is that it is so widely used that you will almost always find an answer through Google.

Video here



Jon Wilde
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*Expert Elite*
OmkarJ
Posts: 427
Registered: ‎10-02-2012

Re: Unable to position model near to boundary

12-18-2013 06:02 AM in reply to: wildej

Jon's revommendation is easier option when you have details of outline. I assumed it is an STP etc. But yes, overlapping parts are a headache in SimCFD and it is always recommended to inspect it in Inventor before exporting it to SimCFD.

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Member
pyrogaz
Posts: 4
Registered: ‎12-15-2013

Re: Unable to position model near to boundary

12-18-2013 09:36 AM in reply to: OmkarJ

Thanks guys, it would have taken me a long time to come up with either of those solutions.

 

John. I don't have an assembly at the moment, it's just a solid body shaped as the proposed car will be. At present we just want to get an idea of the best compromise for ground clearance and the effect of fairings behind the driver's head, the competition is all about efficiency as we only have 1/2 horsepower available.

 

Gary

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