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How to make bilge keel based on CFD results.

Updated: Mar 10, 2020

Bilge keel

Despite the fact that the results of model tests in the towing tank may differ from CFD calculations, the qualitative picture of the flow around the hull coincides very precisely. CFD provides an even more complete picture of the flow process. For example, the current stream lines around the hull cannot be obtained as a result of model tests. The hull with smeared ink dots gives an idea of ​​only the flow in close proximity to the hull surface. It is generally impossible to obtain a picture of the pressure distribution around the body by traditional methods of model tests.

The results of CFD calculations can be used not only for theoretical optimization of the hull shape, but also for quite practical tasks. One such task is to locate the bilge keel. Ideally, the bilge keel should not greatly increase the resistance of the ship's hull, so it is advisable to position it in accordance with the location of the stream lines around the bilge of the ship. It is quite simple to do if there are results of CFD calculation with stream lines around the bilge. Due to the fact that Shape Maker allows you to visualize CFD calculation data, this can be easily done directly in the model of the hull surface.

1. To begin with, we will determine the location of the bilge keel on the mid-ship frame and its height.

Bilge keel positionoing at mid-ship frame.
Bilge keel positionoing at mid-ship frame.

2. After that, we will choose the points of start and end of the line of connection of the bilge keel to the shell.

Bulge keel line on surface (yellow color).
Bulge keel line on surface (yellow color). View compressed 10 times in longitudional dimension for better overview.

3. We build a line of connection of the keel to the hull according to the location of the stream lines.

Bilge keel surface.
Bilge keel surface.

4. In order to build the surface of the keel, we use the construction of a profile perpendicular to the skin. The profile is built on the bilge line and at any point it is perpendicular to the shell. We modify the bilge line so that the surface of the profile looks smoother and more convenient to manufacture. To minimize the resistance of the bilge keel, it is important that the profile surface does not intersect with streamlines. Subsequently, when the position of the bilge line is determined, it is possible to make a real surface of the bilge keel, intended for production.

Bilge keel fit with stream lines.

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