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Jaime Saelices

Wetted surface optimization

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Hi,

 

I want to optimize the wetted surface of a hull (heeled or not). My main concern is what curves of the hull must be transform into parameters. I've followed some of the tutorials that comes with CAESES but all of them modified the displacement or Cp (in my case both are constraints in the problem). I guess some people thought in this issues as well. Any advice would be great.

 

Thanks a lot.

 

Regards.

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Hi Jamie,

 

I prepared a partially-parametric model to tackle your problem. I applied a combination of transformations and shifts to a simple yacht hull. First, I used a scale transformation in order to scale the hull in Y and X dimensions. Then, I used a Lackenby shift to change cb and cp if necessary (I know, you want to keep these values constant.) Finally, I used a Surface Delta shift in order to shift volume in the underwater hull.

post-45-0-57338500-1416343257_thumb.png Pink area shows reduced volume

post-45-0-09862100-1416343358_thumb.png Pink area shows added volume

The Delta Surface is modeled in a way, that it reduces the volume below a certain boundary and adds the same amount of volume above this boundary. So the volume and the mainframe area are kept constant.

post-45-0-89933400-1416343683_thumb.png

In order to control the Surface Delta shift, you have control over the actual value of shift and the x-position where the maximum shift is applied.

post-45-0-52227300-1416343830_thumb.png post-45-0-96050700-1416343854_thumb.png Position and elevation of Surface Delta Shift

By using a Hydrostatics Computation, which comes with CAESES/ FRIENDSHIP Framework, the volume and the prismatic coefficient were compared to the initial value of the imported yacht hull.

post-45-0-77478700-1416344069_thumb.png Sections of final hull and imported hull compared to each other

So far, the Delta Surface shift is kind of limited, due to the feature definition I wrote to define the functions and boundary curves controlling the shift. If you want to have it more variable, you can simply define your own functions and boundary curves. Currently I use the keel curve, the draft line and a curve which is exactly in the middle between these curves (zero curve) with respect to the z-axis, to control the volume shift.

post-45-0-76018500-1416344982_thumb.png

What do you think? If you have questions, please do not hesitate to ask!

 

Cheers

 

P.S.: Most likely a fully parametric approach would be more variable and more effective. The advantage of the current approach is, that you can simply exchange the imported hull (as long as it is as simple as the one in the project). The only thing you have to do is to adapt the parameters, such as Lpp, draft, ... and so on.

 

Matthias

partially_parametric_yacht_hull.fdb

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Hi Matthias,

 

Great job! Once parameterized the geometry which variables would you use as DV for optimization algorithm? Obviously main constraints would be displacement and Cp. Please allow me a couple of days in order to check your solution `cause am currently involved in another task.

 

Thanks a lot!

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Hi Jamie,

 

it is hard to answer this question as long as you don't know the parametric model in detail.

 

1. When you use the same approach for your parametric model as I used for the partially parametric approach, constraints for cb and cp would not be necessary, as the section definition would automatically hold these values.

 

2. I would probably define sectionwise angles for keel, waterline and deck.

 

3. Moreover I would introduce parameter, controling the values of the section area underwater and overwater.

 

4. Finally it is necessary to introduce parameters to follow the longitudinal curves such as keel line, water line and deck line.

 

This is just a first guess. As a first step you could try to adapt one of our sample hulls, namely "yacht hull".

 

Kind regards

 

Matthias

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Hi Matthias,

 

Back again with this issue. I`ve been analyzing your partial parametric approach. When you perform the surface deltashift you use a curve engine in order to obtain the deltasurface. This kind of approach may be useful but am unable to see the capabilities of using it. Because the parametric model is created for a later optimization algorithm implementation my main concern derive in the definitions of the constraints and design variables. As a first approach I will use the hull itself as delta surface. Several points (its coordinates obviously) of this surface will be the design variables of the problem. Using the displacement and center of buoyancy as main constraints (inequality constraints). Geometry constraints will not be needed as several points of the surface will be modified in the optimization.

 

I realize that new internal volume optimization procedures are available in new versions of FFW but I hope that with this method It could be possible to get an enhanced hull form.

 

As soon as I define the project will send you for your check.

 

Thanks a lot for your help!

 

Regards.

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Hi again, while working in the project I realize that the optimization should be done in the upright position and also when heeled. The problem is when using Hydrostatics connection it requires an angle for heel but it does not ask for a displacement so am wondering if the underwater volumes are actually isovolumes but i dont think so. However the most important heeled angle is 25 degrees due to sailing conditions.

 

Another question is the possibility of inclusion of wetted surface calculation into the Hydrostatic connection. I assume the following values are:

 

sections_V --> Volume displacement

sections_IT --> Flotation inertia

sections_B --> Coordinates of center of buoyancy

sections_F --> Coordinates of center of flotation

sections_IT --> Traversal moment of inertia of waterplane

sections_IL --> Longitudinal moment of inertia of waterplane

 

Is this correct?

 

Regards.

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Thanks Claus.

 

I do not know it you are in sync with the case Matthias gave me a few weeks ago. He used several features that for me are some "tricky". I would like to know the logic under them and how to create the surface used for delta shift transformation. Particularly am interested in defining that surface and some points on it in order to apply a subsequent optimization algorithm.

 

Thanks again.

 

Regards.

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