MULTIPLE SPAR HULLS - interconnected

[bill_boggia]

Hi,

I am new to FREESHIP and am thinking of using it to model the stability of an unusual floating structure to check its stability.

The structure consists of a central vertical cylinder (spar) surrounded by 6 equally spaced smaller spars. These peripheral spars are connected by tubular steelwork to the central spar. The geometry is symmetric.

I intend to model the structure in 3D CAD, import surfaces into Polycad, and use Polycad to export into FREESHIP.

Having explored the software I am wondering if FREESHIP will be able to handle this unusual geometry. I intend to have a go and see what happens - but I would be grateful if there is anyone on the forum who might know if FREESHIP can do this kind of a task. I figure that the structure can be modelled as a series of joined surfaces which effectively create a single skin (single hull ?) - albeit of an unusual configuration.

If I am 'barking up the wrong tree' altogether then I would be grateful if someone would let me know before I invest too much time in trying to make this work in FREESHIP.

Sincerely

Bill Boggia :-)

[globaldude]

Not fair Bill , naturally we all now want to know what you're up to ! ??.
How stable do you want it and why ? what does it do ?.
I realise you'd probably rather throw a hagiss at me than disclose your secret weapon but don't blame me for asking you , you should have been more subtle with your request .:)

[bill_boggia]

Hi Globaldude,

It's a fair question - but I didne want to get into specifics too much as it's a bit commercially sensative at the moment. I'm happy to divulge more once I'm oot the 'firing line'.

It's a floating structure that has already been built and all stability assessments have been made - I am just looking for the cheapest way to check the work already done - independantly.

OK I'll tell you: It's a marine hagis harvester :D

Bill :-)

[globaldude]

I knew it !. LOL , ha, thats exelent . Bloody scottys, youre even funny when we can't hear your accent --- yeah yeah, whart akusent.

[globaldude]

Anyway, if its built and you haven't protected your design/IP by now you'll be stuffed unless you haven't disclosed it yet , IE kept it under wraps.
But sooner or later you'll need to trial it - incedently thats your cheapest method -- make that, the ultimate stability test .

[bill_boggia]

Well I've built my multi-spar model in COSMOS, imported the iges into Rhino evaluation version and upgraded the surface definition to Bspline.

Exported into PolyCAD and used the .geo file for import into Freeship.

Model check in Freeship says 'Model OK'

Input project information in the project dialogue box and proceeded to CALCULATION and got the following error message whilst calculating cross curves:

'Calculation SSD is impossible - internal volume do not close, or increase estimated Z of CofG'.

I checked all the surface normals and they show arrows on the outside of the surface pointing into the surface - presumably this represents the direction of the water pressure and is therefore OK ?

I have tried increasing the Z elevation for the CofG but get the same error message.

Incidently - cross curves do get plotted - but because of the error message I do not know if I can trust them.

Can anyone shed some light on this for me please.

Thanks

Bill :-)

[Spiv]

Bill,
do you know of Victor?
He writes Freeship.

You can find his thread here: http://www.boatdesign.net/forums/showthread.php?t=15963&referrerid=21040 .

Not sure if he will answer, but you might ask him the question.