META META-thread: Marine - Ship Hulls & Appendages

[Mr. Mattia Brenner 6]

--------------- Ship Hulls & Appendages ----------------

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Thanks,

Mattia

 

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• Modeling of a wake equalizing duct
   
• Modeling of a SWATH
   
• Simple modeling of a generic ship bow
   
• Modeling of a motorboat
   
• Modeling of a Wigley hull
   
• Modeling of a rudder bulb
   
• Creating a basic shell expansion drawing

[Mr. surya ananth 0]

Hi,

 

While modeling a high speed hull in CAESES I am having difficulty arriving to faired buttocks and waterlines.

 

This is especially the case at junction of two adjacent patches.

 

The defining functions have been kept continuous and in some cases the slope taken care of for the adjacent patches.

 

For the attached case, I have defined an area input for fspline ( control function -> area input -> mid -> midbilge_area_z) which doesn't give me smooth buttock curves ( especially between midbdy_alt surface and midbdy_f surface). 

 

Kindly suggest what is to be done.

 

Regards

Surya

query.fdbc

[Mr. Paulo Macedo 0]

Hi Surya,

I believe that your problem is that the nurbs bilge curve that comes from the aftbody is a 3 point based curve, while the the fspline that comes from the forebody is a 6 point curve. Even though you set the area of the fspline to be the same of the nurbs, they will be slightly different. This will cause the control points of the surfaces to be missaligned at the joint position.

What I recommend is to try to be as consistent as possible (using the same types of curves) along the model. The easiest way is in your model to change the aftbody bilge to a fspline.

 

Fsplines are very powerful, but they are quite unstable. They can snap out if you set too much control over them or have a small disturbance in the inputs might create undesirable ondulations. I recommend the use of them only when you stricly need to know the area of the region (like when modelling by a defined sac under dwl).
Bsplines are harder to set-up, but they are way more robust. Nurbs curves are also easier to handle. Once you start using them, it is hard to go back to fsplines.

 

Between midbody_alt and midboy_f, there are two things that make them not match perfectly. One is that the fob end angle is not 0, causing your control point at midbody_alt to be misalligned. The second problem is that you are forcing the section curve to be "unit speed", changing the parametrisation of the surface (it is also a quite expensive feature and should be avoided). If you ought to use unit speed, you might have to extend it to neighboring surfaces.

Your midbilge_area_z curve has a tangent discontinuity at x=44.2m that causes a visual change in curvature in between the surfaces. You could use a offset curve to smoothly unite image curves with shorter domain ([0-0.95] , [0.05,1]) of c2_2 and c3.

Finally, I recommend again the remodelling of the fspline curves to nurbs or bsplines.

Hope that helps.
Cheers,
Paulo

[Mr. surya ananth 0]

Hi Paulo,

 

Thanks for going through the file.

 

I am trying out what you suggested. Will soon update you on that.

 

Th problem with using a nurbs though is that apart from the angle controls(top and bottom) I can only change the weight (for the three point definition) which I am finding inadequate to get the proper shape.

 

Anyhow will try that again. :)

 

Regards

Surya

[Mr. favour ogbenna 0]

Hi Mattia,

I have been working to understand the concept behind modelling of a vessel with boubous bow.I downloaded the model and I'm confused at the feature definition defining the 3rd aft surface (from the center). please I need a break down.