Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

Shear band formation and strain localization on a regional scale: Evidence from anisotropic rocks below a major detachment (Betic Cordilleras, Spain)

International audienceRegional-scale deformation taking place in a strongly anisotropic, yet homogeneous metapelitic protolith during an apparently single tectonic event was systematically investigated as a function of the distance to the main tectonic contact (i.e., the Filabres shear zone, a major detachment in the Betic Cordilleras, Spain). The density of C3' shear bands (or extensional crenulation cleavage) reworking the earlier S2 schistosity increases exponentially towards the contact, in parallel with the decrease in the size of the shear domains. Systematic variations in angles and shape ratios are also reported. Deformation and age patterns, however, suggest that this spectacular trend at least partly results from a progressive localization of the deformation through time. This fossilized shear strain gradient was thus produced somewhat diachronously. Such shear strain patterns nevertheless provide a mean to constrain the rheological properties for such weak lithologies and a mean to better understand crustal deformation

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

The aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

International audienceThe aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model

Fluid Structure Interaction of Yacht Sails in the Unsteady Regime

The dynamic Fluid Structure Interaction (FSI) of yacht sails submitted to a harmonic pitching motion is numerically investigated to address both issues of aerodynamic unsteadiness and structural deformation. The model consists in an implicit dynamic coupling algorithm between a Vortex Lattice Method model for the aerodynamics and a Finite Element Method model for the structure dynamics. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces oscillate with phase shifts with respect to the motion. This results in hysteresis phenomena, which show aerodynamic equivalent damping and stiffening effects of the unsteady behaviour. The area of the hysteresis loop corresponds to the amount of energy exchanged by the system and increases with the motion reduced frequency and amplitude. In the case of a rigid structure, the aerodynamic forces oscillations and the exchanged energy are lower than for a flexible structure

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

The aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model

Inviscid approach for upwind sails aerodynamics. How far can we go?

This work presents a full-scale experimental study of a yacht rig and sails in real upwind sailing conditions and a comparison with Fluid Structure Interaction (FSI) simulations with the ARAVANTI model (Finite Element Method for the structure and Vortex Lattice Method for the fluid). An specific on-board instrumentation system simultaneously measures loads in the rig and sails, sailing data (wind, boat attitude and speed) and the shape of sails in real navigation conditions (flying shape). Flying shape parameters are extracted using the camera-based VSPARS system to characterize the effects of sail trims and to be compared with the results of the simulation. The potential flow solver gives fast and accurate predictions of both the flying shape and the loads in the rig in most conditions. The inviscid approach, commonly used in the early stage of design, must be checked, as in particular cases where the sails are heavily loaded, flow separation is significant and results from a potential flow solver are inaccurate. A new version of the model including the heel angle as an additional degree of freedom in the structural solver enables to detect when the inviscid flow approach overestimates the aerodynamic load. This upgrade improves the utility and reliability of the inviscid flow approach which remains relevant at the early stages of design as it is much more cost-effective than RANS models.Brest Métropole Océane, Région Bretagne and the European Union’s Seventh Framework Programme (FP7/2007-2013) under REA grant agreement PCOFUND-GA-2013-609102 (PRESTIGE-Campus France

Free-Surface Effects on Two-Dimensional Hydrofoils by RANS-VOF Simulations

Foiling yachts and crafts are both very sensitive to the flying height in terms of stability and performance, raising the scientific issue of the influence of the free-surface when the foil is at low submergence. This work presents numerical simulations of a 2D hydrofoil section NACA0012 at 5° angle of attack in the vicinity of the free-surface, for different values of the submergence depth, for a chord-based Froude number of 0.571 and a Reynolds number of 159,000. Unsteady-Reynolds Averaged Navier-Stokes (URANS) equations are solved with a mixture model to capture the free surface (Volume Of Fluid method), and using an automatic grid refinement. Verification of the numerical model and validation with data from the literature are presented. Deformation of the free surface and alteration of the hydrodynamic forces compared to the deep immersion case are observed for a submergence depth-to-chord ratio ℎ/c lower than 2. The foil drag increases up to more than three times the infinite-depth value at ℎ/c≈0.5. The lift force slightly increases until ℎ/c around 1, and then decreases sharply. For ℎ/c < 0.5, the pressure field around the foil is totally modified and the lift is swapped to downward. The study highlights the importance of considering the effect of finite submergence to compute foils’ hydrodynamic forces, for example to be used in Velocity Prediction Programs (VPP) of foiling crafts.ANR-19-STHP-0002 GENCI- [IDRIS] (Grant 2021-A10 [A0102A12500

How to be the best at sail pumping?

Pumping or flicking1 is often used by sailors to get extra propulsion while sailing (subject to restrictions by the racing rules2). Common unsteady sailing situations, due to crew action (e.g. manoeuver like gybing3) or environment conditions (e.g. pitching in waves4, 5) can be reproduced in tunnel testing with accurate flow and yacht attitude4 control. Repeated pumping generating unsteady effects on aerodynamic forces6 is investigated here with a dynamic trimming system. Results are presented for different apparent wind angles (AWA) to determine the best pumping conditions and better understand the physical mechanisms involved

Numerical study of a flexible sail plan : effect of pitching decomposition and adjustments

A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to analyse the effects of motion simplifications and rigging adjustments on aerodynamic forces. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops. These hysteresis phenomena do not result from a simple phase shift between forces and motion. Plotting the hysteresis loops in the appropriate coordinate system enables the associated energy to be determined. This amount of exchanged energy is shown to increase almost linearly with the pitching reduced frequency and to increase almost quadratically with the pitching amplitude in the investigated ranges. The effect of reducing the real pitching motion to a simpler surge motion is investigated. Results show significant discrepancies on the aerodynamic forces amplitude and the hysteresis phenomenon between pitching and surge motion. However, the superposition assumption consisting in a decomposition of the surge into two translations normal and collinear to the apparent wind is verified. Then, simulations with different dock tunes and backstay loads highlight the importance of rig adjustments on the aerodynamic forces and the dynamic behaviour of a sail plan