• Doctorants - Post-doc,

Soutenance de thèse : Paul KERDRAON - ED SPI

Sujet : "Modélisation des phénomènes hydrodynamiques instationnaires sur un trimaran de course au large."

le 22 janvier 2021

 Paul KERDRAON soutiendra sa thèse le vendredi 22 janvier 2021 à 14 h depuis l'École Centrale de Nantes en visioconférence.

Directeur de Thèse : David LE TOUZE

Laboratoire : LHEEA

La présentation se fera en anglais, devant un jury composé de :
- Jean-Yves BILLARD, IRENav, Ecole Navale – Rapporteur
- Marc RABAUD, FAST, Univ. Paris-Saclay – Rapporteur
- Paola GUALENI, DITEN, Univ. de Gênes – Examinatrice
- David LE TOUZE, LHEEA, Centrale Nantes – Directeur de thèse
- Patrick BOT, IRENav, Ecole Navale – Co-encadrant
- Boris HOREL – Co-encadrant
- Pierre-Emmanuel GUILLERM, Naval Group – Invité

Keywords: Dynamic Velocity Prediction Program (DVPP); Sailing yacht; System-based modeling; Time-domain simulation; Hydrofoil; Performance prediction

Sailing yacht design has relied on steady state optimization for a long time. Velocity Prediction
Programs (VPP) are at the core of the design process of most of architect offices. Nonetheless they have proved inadequate to handle accurately the trade-offs demanded by the state-of-the-art appendages, especially in terms of stability. Besides, traditional tools, such as frequency-domain Boundary Element Methods, are generally unable to deal with the effects of sails on the seakeeping behavior of sailing yachts or wind-assisted ships. For those reasons, the use of time-domain simulation tools, called Dynamic Velocity Prediction Programs (DVPP) has known a substantial increase in the recent years.
The present thesis focuses on the study and development of a 6 degrees of freedom DVPP dedicated to offshore yachts. It implements a multibody algorithm allowing to simulate complex mechanical interactions between yacht elements. Different wind and wave models are available, complex conditions are represented by the superposition of several singular components. The calculation of the loads relies on a weakly non-linear system-based approach. The implemented models use either load calculations at runtime on the body mesh, polynomial regressions on pre-computed dataset or semi-empirical formulas.
Particular care has been drawn to the progressive validation of the numerical tool. Several validation cases are presented, from multibody textbook cases and simple hydrodynamic problems to reference experimental data on a Wigley hull form and on DTMB model 5512.
A towing tank campaign has been conducted to establish a validation database focused on specific severe conditions : high Froude numbers, relatively high steepness waves and highly non-linear motion.
The variations of the radiation coefficients with speed are studied, and a comparison with published low Froude models is presented. The experimental data is used for comparison and validation with the DVPP for two situations of interest: motions and loads in waves, and water entry-exit sequences. The results are encouraging and back up the choice of the models.
Finally, simulations of existing offshore yachts, an Ultim trimaran and an IMOCA monohull, are
presented. They consider different transient situations, from a maneuver to varying environmental conditions and point out the interest of dynamic studies, allowing to open a different field of optimization than VPPs.
This work resulted in an operational DVPP, which correctly simulates the behavior of offshore sailing yachts, especially when fitted with hydrofoils.
Publié le 15 janvier 2021 Mis à jour le 20 janvier 2021