The fortran program called "voile.f"(E.S.E.M and Ivan Fédioun)
The "voile.f" program is a CFD (Computational Fluid Dynamics) code (based on singularity)
developed by Ivan
Fédioun. This software was developed at the beginning in order to have
a numerical tool to valid the double tilted wingsails concept. After several upgrades, this software
now includes the two beams and takes into account the interaction between all the aerodynamics
components of the boat (the two sails and the two beams). The choice of a singularity code
in comparison with a full 3D Navier-stokes code was easy to understand. The geometry
of the boat is fully 3D and to integrate this code into the futur S.D.T, it was necessary
to have an unsteady, simple and quick code... that's why we choose a singularity code. We made also
several simplifications:
- The fluid is supposed to be perfect (non viscous and non compressible).
- We used the potential flow theory on each element of the boat.
- A mirror image of the boat is build to evaluate the interaction between all the boat's elements. So, the code is working with 8 elements instead of 4.
- The speed profil (in front of the boat) is twisted with a classic 1/7eme profil
(often used in Fluid Mechanics) due to the wind boudary layer which is 22 meters height.
Evolution of the speed inside the boudary layer: 1/7eme (blue) and logarithmic (red) profil (ratios).
- To estimate the aerodynamic forces with the code, experimental caracterics of the solid
wing sail profils are used (for exemple a NACA N23012 profil).
Evolution of the Cx as a function of the attack angle (in degrees).
Evolution of the Cz as a function of the attack angle (in degrees).
Evolution of the Cm as a function of the attack angle (in degrees).
At the present moment, the sails caracteristics of the futur boat are unknown but this kind of numerical tool will be of great interest to evaluate the boat performance in function of the profil's choice. Also, we include into the code a fluid viscous notion (we use of experimental datas) which is not present in the code equations used for modelling the aerodynamic part.
From the boat specifications, the program can calculated the following forces and
momentum:
- Forces: Propulsion, Drift, Lift
- Momemtum: Roll, Pitch, Yaw
We made several calculations to evaluate the sail tilt on the
boat forces, especially on the rolling momentum:
Evolution of the rolling momentum as a function of the sail's tilt (in degrees).
Of cource, this tilt modifies the others boat's forces:
Evolution of the propulsion as a function of the sail's tilt (in degrees).
Evolution of the pitching momentum as a function of the sail's tilt (in degrees).
Evolution of the drift force as a function of the sail's tilt (in degrees).
Evolution of the yaw momentum as a function of the sail's tilt (in degrees).
Evolution of the lift force as a function of the sail's tilt (in degrees).
The "Dim the Duck" Tool
"Dim the Duck" is a tool developed under Excel (Mircosoft) in order to quickly evaluate the boat dimensions. This tool takes into account the lifting parts of the boat (aerodynamics, hydrodynamics) and the passives parts (hulls...) as well. From given caracteristics (wind direction, boat width, weight, lift coefficients...), this tool can evaluate the boat specifications by changing different variables (such as sail tilt, sail surface...) until a global criterion (acceleration value, minimization of the rolling momentum) is reached.
Boat specifications as calculated by "Dim The Duck" (sorry in french..)
"Dim the Duck" integrates severals simplifications:
- The aerodynamic coefficients are proportionnal to the attack angle.
- The sails skid is not taking into account.
- The interaction between the different parts of the boat is not taken into account.
- The wind twist due to the boudary layer is not modelled.
Genetics Algoritms
"Dim the Dick" and "voile.f" are both useful tools to evaluate the boat specifications. But the number of parameters are too important. So the use of optimization methods could be very useful. We're trying to developed such tools and Genetics Algoritms could be the solution we are looking for.
The S.D.T (3D Dynamic Simulator)
The boat stability is really an open problem. To avoid this lack of informations,
the development of a simulator becomes a real necessity. The S.D.T must be able to
simulate the dynamic comportement of the boat during a run (from zero to the highest speed).
The program (programming language used: C), is composed by different pieces for each part of
the boat (foils, hull, sails,...). "voile.f" will also be used
to simulate the aerodynamics part of the boat. For the moment, this simulator is still in
development but it's realisation is a major priority for INNOVOILE.