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Ship hull lofting

9 REPLIES 9
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Message 1 of 10
DrCheesy
3717 Views, 9 Replies

Ship hull lofting

I am attempting to develop a 3D model of a ships hull for use in CFD simulations. I have a lines plan of the vessel I am modelling which has allowed me to define a number of sections and rails for a loft operation.

 

The issue that I have is that the resulting loft surface is not smooth in some areas. There is no point in doing a flow analysis around a ship unless I get the hull shape spot on.

 

For each of the sections I defined a number of points and then fitted a spline through the points. I found that the resulting curves really did not match the lines plan curves very well so had to do a lot of playing around with spline handles.

 

Has anyone got any experience of trying to develop models like this or could offer some advice on how to progress please?

 

I cant attach the .ipt file because it exceeds the file size limit even when compressed so have put it on my webpage - http://staffweb.cms.gre.ac.uk/~T.Tilford/inventor.htm

 

 

9 REPLIES 9
Message 2 of 10

Hi DrCheesy,

 

As I recall there are a couple of users on here that have a lot of experience with Inventor and ship hulls. stevec781 is one of them, and I think he has some insights into what works and doesn't work well.

 

If you search this forum for "Ship Hull", "Hull", "Boat Hull", ect. I think you'll find some information and examples.

 

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

Message 3 of 10
graemev
in reply to: DrCheesy

As an aside, if you move the End of Part marker up to the top before saving, it will reduce the file size for posting.  (It may not be enough in this particular case, but worth noting.)

Message 4 of 10
JDMather
in reply to: DrCheesy


@DrCheesy wrote:
 

I cant attach the .ipt file because it exceeds the file size limit even when compressed..

 


As noted - did you roll up the EOP before zipping?

Find the red End of Part marker in the browser.
(End of Folded on sheet metal parts EOF)
Drag the red EOP to the top of the browser hiding all features.

Save the file with the EOP in a rolled up state.

Right click on the file name and select Send to Compressed (zipped) Folder.

Attach the resulting *.zip file here.


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Message 5 of 10
stephengibson76
in reply to: DrCheesy

Inventor really is not good at modelling organic shapes like ships hulls, you are better off designing the hull in other software.  Generally we will bring a hull skin into inventor from another program and model all of the structure projecting cut geometry from this imported skin.  There are lots of programs specifically for hull design but if you are just playing and want something free http://www.delftship.net/ is perfect.

 

If you really want to pursue this in inventor, think about losing the radius to point transition on the transom, remember that less lofting sections is often better and you get a much better transition between the sections, play with the conditions and transitions tabs on the loft command, think about splitting your loft into a number of lofts.

 

A lot of the ships Ive done have a standard section for 90% of the length, (barges and jack-ups) but we still use other software to produce these relativly simple shapes, it is almost imposible to fair a hull in inventor and very tricky to see where its actually going a bit pear shaped...

 

good luck

Stephen Gibson



View stephen gibson's profile on LinkedIn


Message 6 of 10
stevec781
in reply to: stephengibson76

There is a couple of problems.

 

Your points arent fair, and you have used a normal spline constrained to the points, so this is why you have lumps, the spline is forced to points that arent fair.  You would be better using a CV spline and just using your points to eyeball the line for fairness, but a lot of work to delete all those constraints.  When I convert your splines to CV type you can see areas where they are too close and crossing the spline.

 

curve not fair.JPG

 

 

 

 

control vertex.JPG

 

You will have some challenges fairing the lines in Inventor.  Programs like maxsurf and rhino have the ability to nudge a control point using the keyboard arrows 1mm at a time.  It is impossible to fair a hull by dragging control points with a mouse, and the more control points the harder it is.

 

If you want to do it in inventor, delete your constraints, change your splines to CV and turn your mouse sensitivity down.  Create your surfaces then stitch into a solid and export to cfd.

 

If you want to do it fast do it in rhino, you have 25 free saves for educational purposes and read up on the nudge ability.  You will be amazed at how much difference a 1mm nudge can make when fairing in body plan view. Then you can export to inventor or just keep working in rhino.

 

If you google rhino marine tutorial you will find a pdf.  Its first tutorial is exactly what you are doing.

 

Others may have better ideas, my extent of working with hull shapes in inventor goes no further than importing it as an iges.

 

Nice effort though.

Message 7 of 10
BarryZA
in reply to: stevec781

I have been looking into this for myself and also came across Polycad -http://www.polycad.co.uk/ which from a quick look looks more versatile. I think it also allows you to export as .iges, whereas with Delftship you have to upgrade to the paid version for this feature.

If you run Delftships "father" FreeSHIP which you can still find for download, you can still export to .iges I think.

 

I have had a look at openFOAM (on linux!) for CFD which looks pretty solid.

Message 8 of 10
stevec781
in reply to: DrCheesy

Delftship is only 150 euros and does so much more.

Message 9 of 10
DrCheesy
in reply to: DrCheesy

Just wanted to say thanks for all the advice!

 

I am having a shot at refining my model to improve the fairing using CV splines. I had to upgrade to the 2014 version as they are not an option in the 2012 version I was using (which stumped me for a bit...)

 

If this doesn't go well I will give Deftship a go - I have downloaded the free version at the moment but would happily upgrade if needed.

 

All the best1

 

Message 10 of 10
stevec781
in reply to: DrCheesy

In the delftship help there is a section on flow lines, available in the full version.  It might be interesting for you to compare these against your cfd model.

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