Exemple Ship Resistance and hydrodynamic drag with the software Mecaflux Standard.
To evaluate the resistance of a ship hull shape , In naval hydrodynamics, the method of "Double model" are used. This method of calculating resistance, use to towing in deep immersion, a form, composed of the ship's hull model , and its symmetry, to the waterline.The measured drag is then halved. This experiment at sea is expensive and complex, it is carried in the wind tunnel.
profiles, tested in the wind tunnel or geometrically simple, whose drag (Cd) is already set in Mecaflux Standard , can therefore help us to evaluate the viscous hydrodynamic resistance. We can evaluate a "order of magnitude" for the force with MECAFLUX , this method does not take into account the wave resistance (see hydrodynamic resistance naval froude) .
Example of calculation of hull resistance with Mecaflux Standard:
The simple method presented here is to choose a geometric object as close as possible to the "Double model" of the boat hull: Mecaflux standard offers in the tab "drag and lift" , a series of database objects for which the drag parameters are included. You can quickly evaluate the resistance to the advancement of the object in a fluid of your choice, by entering the dimensions in the diagram.
Imagine that we need an order of magnitude of the resistance to the advancement of a boat hull 10m long by 2m wide by 1m deep.
- We can use an ellipsoid of 10m by 2m and halve the drag found: half ellipsoid like our hull. (This method does not take into account surface effects)
- -select an ellipse in "body drag"
- -Enter a length of 10 meters
- -Enter a diameter of 2 m
The resistance results are:
4175 Newtons ( 425 Kg.f ) divided by 2 = 2087 Newtons (213 Kg.f) = 213 kilogram-force resistance to the advance or drag for a boat of 10 meters by 2 meters wide, 1 meter deep moving at 10 knots.
We estimate our ship resistance to the advance from the ellipsoid and estimate it about 2100 Newtons (excluding wave resistance).
For a more precise evaluation of the drag resistance of the form of a carene ship, submarine or airship will use the software HELICIEL, which will also provide us the 3D model of the submerged part of the hull shape depending on a variety of hydrodynamic profiles.
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