How a nabla bulbous bow can be modeled?

[Mr. Iorga Stefan 1]

Hello,

 

I've started to learn Caeses for a while - hull modeling techniques are quite understandable, feature definition, etc - though, all the models provided includes delta bulbs connected to the hull with a coons-patch.

 

The trends in shipbuilding, as you all know, involve a nabla bulbous bow, due to seakeeping, mostly slamming (hammer blow - in romanian), etc.

 

I've taken a break working in Caeses, since I've been quite occupied with various projects, school, some work, etc., and I don't yet have the time to dig into Caeses more than I did last summer/autumn.

 

Anyway, I wanted to ask you some guidelines, maybe a forebody hull model you want to share, with a nabla bulb, faired nicely, without a coons-patch - let's say similar to KCS.

 

Thank you very much,

Stefan

 

 

 

 

[Matthias Maasch 21]

Dear Stefan,

 

In general, all our parametric bulbous bow designs should be able to be shaped like delta, nabla or oval type bulbs. It is just a matter of finding the right values for all functions. For a nabla bulb one should reduce lower fullness of the bulb profile, increase the upper fullness a bit and also increase the keel start angle (deadrise). Also one should raise the maximum beam function (increase the start z value). I think when applying this changes to the bulbous bow setup it should look like a nabla type bulb.

 

The modeling of the connection of bulbous bow and hull is sometimes a bottle neck and is different from hull to hull. In one of my cases I found it to be

sufficient to use the surface-to-surface-fillet feature (you can find this feature e.g. in the RoPax-sample > derivativeJointCurve feature) between the bulbous bow and the lower hull.  With the similar feature which creates a fillet between surface and curve (you can find this feature in the Features tab > Hull Design > Smooth joint to stem) I created the small triangle-like surface above the bulbous bow (so to say the start of the stem). From the position where the stem has its minimum x-value I used the second mentioned feature again. So I got rid of the coons patch completely. As both features create the same 4-Points-BSpline-Curve it is possible to model this part watertight, as long as these fillets are short in x-length. 

 

 

1) The hull surface goes almost to the end of the waterline (e.g. waterline:end:x - 1)

2) Surface to surface fillet, based on the 4-Points-BSpline

3) Smooth joint to stem feature

4)Again the Smooth joint to stem feature (as usual)

 

Why did I create the surfaces 3) and 4) and not only one surface for the stem part? -- Because this makes the small triangle-like part above the bulbous bow a bit more flexibel with regard to the surface resolution.

 

I hope this helps. I will create a small sample for that in the next days.

 

Best regards

 

Matthias 

[Mr. Iorga Stefan 1]

Dear Stefan,

 

In general, all our parametric bulbous bow designs should be able to be shaped like delta, nabla or oval type bulbs. It is just a matter of finding the right values for all functions. For a nabla bulb one should reduce lower fullness of the bulb profile, increase the upper fullness a bit and also increase the keel start angle (deadrise). Also one should raise the maximum beam function (increase the start z value). I think when applying this changes to the bulbous bow setup it should look like a nabla type bulb.

 

The modeling of the connection of bulbous bow and hull is sometimes a bottle neck and is different from hull to hull. In one of my cases I found it to be

sufficient to use the surface-to-surface-fillet feature (you can find this feature e.g. in the RoPax-sample > derivativeJointCurve feature) between the bulbous bow and the lower hull.  With the similar feature which creates a fillet between surface and curve (you can find this feature in the Features tab > Hull Design > Smooth joint to stem) I created the small triangle-like surface above the bulbous bow (so to say the start of the stem). From the position where the stem has its minimum x-value I used the second mentioned feature again. So I got rid of the coons patch completely. As both features create the same 4-Points-BSpline-Curve it is possible to model this part watertight, as long as these fillets are short in x-length. 

 

foreShip.PNG

 

1) The hull surface goes almost to the end of the waterline (e.g. waterline:end:x - 1)

2) Surface to surface fillet, based on the 4-Points-BSpline

3) Smooth joint to stem feature

4)Again the Smooth joint to stem feature (as usual)

 

Why did I create the surfaces 3) and 4) and not only one surface for the stem part? -- Because this makes the small triangle-like part above the bulbous bow a bit more flexibel with regard to the surface resolution.

 

I hope this helps. I will create a small sample for that in the next days.

 

Best regards

 

Matthias 

 

Thanks for sharing this out - and a small sample will be excellent, not only to me, but to all newbies in Caeses, wondering about this matter.

Sorry for writing so little, though, when I'll be ready with a such a model, I'll gladly share it here.

 

Thank you very much Matthias !

 

Kind regards,

Stefan