This paper presents a Fluid-Structure Interaction (FSI) method for sails. In this FSI method the pressure field around the sail is determined using the Computational Fluid Dynamics (CFD) package FINE/Marine using the ISIS solver. This computational method is based on the Reynolds-Averaged Navier-Stokes Equations (RANSE). The computed pressure field serves as input for a basic structural model implemented in the Nastran-based Finite Element Analyses (FEA) package Femap which determines the deformation of the sail subject to the aerodynamic load. In an iterative procedure the distribution of the surface pressure and the deformation of the sail attain a stable equilibrium. The aim of the FSI method is to determine the steady flying shape of the sail and to obtain the aerodynamic forces generated by the sail taking into account the deformation of the sail.
A method is presented for 2D sail sections as well as a method for 3D upwind sails. These methods are capable of determining the steady deformation of the sail. The results of the method for 2D sail sections are compared with a set of experimental data. This comparison shows that the deformed shape of a 2D mast and sail section compares satisfactorily with measured data for various combinations of slackness and angles of attack.
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 har-monic 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.
Wind-Tunnel Pressure Measurements on Rigid Model-Scale Downwind Sails
This paper describes an experiment that was carried out in the Twisted Flow Wind Tunnel at The University of Auckland to measure a detailed set of pressure distributions on a rigid 1/15th scale model of a modern asymmetric spinnaker. It was observed that the pressures varied considerably up the height of the spinnaker. The fine resolution of pressure taps allowed the extent of leading edge separation bubbles, pressure recovery region, and effect of sail curvature to be observed quite clearly. It was found that the shape of the pressure distributions could be understood in terms of conventional aerodynamic theory. The sail performed best at an apparent wind angle of about 55°, which is its design angle, and the effect of heel was more pronounced near the head than the foot.
FSI Investigation on Stability of Downwind Sails with an Automatic Dynamic Trimming
Gennakers are lightweight and flexible sails, used for downwind sailing configurations. Qualities sought for this kind of sail are propulsive force and dynamic stability. To simulate accurately the flow around such a sail, several problems need to be solved. Firstly, the structural code has to take into account cloth behavior, orientation and reinforcements. Flexibility is obtained by modeling wrinkles. Secondly, the fluid code needs to reproduce the atmospheric boundary layer as an input boundary condition, and be able to simulate separation. Thirdly, fluid-structure interaction (FSI) is strong due to the lightness and the flexibility of the structure. The added mass is three orders of magnitude greater than the mass of the sail, and large structural displacement occurs, which makes the coupling between the two solvers difficult to achieve. Finally, the problem is unsteady, and dynamic trimming is important to the simulation of spinnakers .
The main objective is to use numerical simulations to model spinnakers, in order to predict both propulsive force and sail dynamic stability. Recent developments  are used to solve these problems, using a finite element program dedicated to sails and rig simulations coupled with a RANSE solver. The FSI coupling is done through a quasi-monolithic method. An ALE formulation is used, hence the fluid mesh follows the structural deformation while keeping the same topology. The fluid mesh deformation is carried out with a fast, robust and parallelized method based on the propagation of the deformation state of the sail boundary fluid faces .
Tests are realized on a complete production chain: a sail designer from Incidences has designed two different shapes of an IMOCA60 spinnaker with the SailPack software. An automatic procedure was developed to transfer data from Sailpack to a structure input file taking into account the orientation of sailcloth and reinforcements. The same automatic procedure is used for both spinnakers, in order to compare dynamic stability and propulsion forces. Then a new method is developed to quantify the stability of a downwind sail.
Advancements in Free Surface RANSE simulations for Sailing Yacht Applications
The analysis of yacht hulls performance using RANSE based free surface simulations has become an accepted approach over the last decade. Access to this technology has been eased by the development of user-friendly software and by the increase of computational power. Results are widely accepted as superior to previous non-viscous approaches and have to compete with towing tank results in terms of accuracy. However, many practical applications suffer from a numerical smearing of the free surface interface between air and water which can be described as numerical ventilation. This problem occurs when the intersection between bow and calm water surface form an acute angle and is further pronounced if the stem is rounded or blunt. It is therefore especially linked to sailing yacht applications. The problem manifests itself as a non-physical suction of the air-water mixture under the yacht hull, causing a significant underprediction of viscous resistance. While this is the easily observable appearance of the problem, a second issue is its effect on wave resistance. It can be shown that wave damping is significantly increased, causing a prediction of wave resistance which is also too low. The paper provides a review of the Volume-of-Fluid method. It discusses the resultant implications for practical applications. A remedy to circumvent the problem is described and its impact on the accuracy of the result is shown. Simulations on an identical appended hull with and without interface smearing are compared. Effects on free surface visualization and numerical accuracy are shown. The paper finishes with a thorough verification and validation of a fully appended yacht in accordance with ITTC standards.
Database building and statistical methods to predict sailing yachts hydrodynamics
The model characterizing the hydrodynamic forces acting on a sailing yacht hull can be built using extensive tank testing or CFD computations carried out on the studied hull shape. Unfortunately, in most cases involving sailing yachts, time and money are limited and testing each hull at the required speeds and attitudes is impossible. The idea is then to rely on a hydrodynamic model gathering results on various hulls; able to describe the evolution of the hydrodynamic forces depending on the hull shape through geometrical variables. The building and calibration of this type of model requires numerous computations but once the model is built, this approach is very fast. Furthermore, these models can provide a better understanding of the trends than tests on isolated hull shapes since they contain the results on a whole database of hulls. This type of approach using meta-models can be used in various fields to produce lots of results in a very short time and a better understanding of the phenomena involved. This paper presents a methodology to produce the database, select the relevant explanatory variables and build the formulations in the context of sailing yachts hydrodynamics. The regressions allowing the prediction of the running attitude and forces are presented.
A simplified Method to Assess Acceleration loads on Sailing Yacht Masts
The behaviour of sailing boats in open sea is strictly related to their hydro and aerodynamic performances and to the wide range of loads acting on the hull and rigging system. Their evaluation could be done only by a careful seakeeping analysis with particular attention to the acceleration loads caused by hull motions which can create severe problems to mast and rigging up to extreme consequences such as dismasting. The main reasons of dismasting are related both to human errors and to the lack of load knowledge; as a matter of fact Classification Societies' Rules are quite poor about this subject and the structural design if often committed to the designer experience. The aim of this work is to investigate on the hull dynamic responses which mainly influence the mast and rigging loads with particular attention focused on the pitching behaviour of the vessel. With this goal in mind the seakeeping behaviour of a number of sailing yachts, different each other in sizes and typology, has been investigated. Despite the small size of the database, the achieved results allowed to formulate a preliminary simplified method to estimate the pitch Ratio Amplitude Operator (RAO), based only on the boat length. From the pitch RAO knowledge a very rough and quick formulation to evaluate the longitudinal acceleration in the mast centre of gravity has been obtained.
Numerical Study of Asymmetric Keel Hydrodynamic Performance through advanced CFD
The hydrodynamics of an asymmetric IACC yacht keel at angle of yaw are presented using simulations performed by advanced computational fluid dynamics using state-of-the-art software. The aim of the paper is to continue working on the improvement of numerical viscous flow predictions for high-performance yachts using Large Eddy Simulation and Detached Eddy Simulation on unstructured grids. Quantitative comparisons of global forces acting on the keel and wake survey are carried out. Qualitative comparisons include flow visualisation, unsteady and separated flow and other features. Star-CCM+ and the trimmed cell method give better forces and wake prediction compared to the unstructured mesh of ANSYS Fluent. Both solvers give good flow visualisation near and far field of the keel.
The angle formed by ship wakes is usually found close to the value predicted by Kelvin, α=19.47°. However we recently showed that the angle of maximum wave amplitude can be significantly smaller at large Froude number. We show how the finite range of wavenumbers excited by the ship explains the observed decrease of the wake angle as 1/Fr for Fr>0.5, where Fr=U/(gL)^0.5 is the Froude number based on the hull length L. At such large Froude numbers, sailing boats are in the planing regime, and a decrease of the wave drag is observed. We discuss in this paper the possible connection between the decrease of the wake angle and the decrease of the wave drag at large Froude number.
Conceptual ideas on a double surface sail inflated by dynamic pressure
This paper presents conceptual ideas on an unconventional sailing system. It is designed in principle and compared in terms of performance with two established sailing systems. The concept is a double surface sail, which is to be inflated by the dynamic pressure at the leading edge of the profile. The fundamental principle is the same as used by paragliders and kites, where openings at the leading edge of the wing allow the air to “fill” the profile to give it a beneficial aerodynamic shape. For the analysis of the
structural mechanics of the sail system qualitative model tests in a wind tunnel are conducted. A profile segment is exposed to different angles of attack and the trim mechanism of mast rotation is varied. The resulting profile shapes and the profiles of the comparative sail types are then analysed to determine their characteristics by conducting 2D flow simulations. Also the effects of mast rotation to change the profile characteristics of camber and thickness are reviewed. The double surface sail showed a good-natured behaviour at a wide range of angles of attack and a competitive performance potential compared to conventional sail sections and a wing sail section.
Comparison of full 3D-RANSE simulations with 2D-RANSE / Lifting Line Method calculations for the flow analysis of rigid wings for high performance multihulls
This paper reports about a comparison of a 3D RANS investigation to calculate the flow around wing sails with a method based on 2D RANS calculations of flow around wing profiles in conjunction with a lifting line method to account for 3-dimensional flow phenomena. Both methods shown here are of general use for wing investigations, however in the context of this paper they are used for rigid wings with two elements: a main element with a hinged flap, as they are currently used on some performance multihulls. Wing sails can well be analyzed using conventional three dimensional RANS based flow investigation methods; however the computational costs for these investigations are quite high. In this paper, an alternative approach to 3D RANS investigations is introduced. It is based on planar flow 2D RANS profile investigations in conjunction with a lifting line method to account for 3-dimensional flow phenomena and induced drag. The lifting line method uses an iterative approach in order to make use of non-linear profile lift coefficients. This approach is so computational efficient that it can be combined with constrained optimization methods in order to optimize performance of the wing. The paper describes the motivation for the development, the lifting line theory and validation efforts. Some applications of the new method are shown, demonstrating the ability of the method to be used for wing sail design and operation optimization.
A comparison of downwind sail coefficients from tests in different wind tunnels
This paper contains results from five different tests on model sailing yacht rigs and sails. The tests were conducted by the author in four different wind tunnels over a fifteen year period between 1991 and 2007. The tests were conducted as part of development programmes for Whitbread 60 and America’s Cup Class yachts and for particular racing teams. They were originally subject commercial confidentiality so have not been published previously. Although the aim of the original tests was to compare sail designs and develop the performance of the individual yachts this aim of this study is somewhat different and uses the data to compare wind tunnels. The paper describes features of the wind tunnels that affect the results together with the test requirements for investigation of downwind sailing performance. A large number of individual results are presented from tests over a range of apparent wind angles and curves of maximum lift and drag coefficients from each tunnel are then compared. Although the original tests were not designed for benchmarking wind tunnels the sail coefficients from the different tests showed broad similarity within a tolerance band, which helps validate the technique of wind tunnel testing of sailing yacht rigs. Conclusions have been drawn from the results about the effect of lift on the drag of downwind sails and the overall accuracy of wind tunnel tests on rigs.
Delayed Detached Eddy Simulation of Sailing Yacht Sails
Wind tunnel experiments on a 1:15th model-scale AC33-class yacht were modeled with Reynolds-average Navier-Stokes simulations (RANS) and Delayed Detached Eddy Simulations (DDES). Numerical simulations were performed with two different grids, where the node distance was halved from the coarser to the finer grid, and with three different time steps, where the smallest one was 1/4th of the largest one. High-grid-resolution DDES allowed drawing the topology of the turbulent structures in the sail wake and discovering new flow features, which were hardly detectable with low-grid-resolution DDES and, particularly, with RANS. It was found that the span-wise twist of the spinnaker leads to a mid-span helicoidal vortex, which has a horizontal axis almost parallel to the apparent wind and rotates in the same direction of the tip vortex generated from the head of the sail. Vortical span-wise tubes are released from the trailing edges of the mainsail and the spinnaker and, while convecting downstream, these structures roll around the tip and mid-span vortices of the spinnaker. Vortical tubes are also detached intermittently from the sails’ feet and these break down into smaller and smaller structures while convecting downstream.
An experimental Investigation of Asymmetric Spinnaker Aerodynamics Using Pressure and Sail Shape Measurements
A method for determining the aerodynamic forces and moments produced by sails at full-scale is investigated in this work. It combines simultaneous on-water pressure and sail shape measurements. The system has been given the acronym FEPV (Force
Evaluation via Pressures and VSPARS). The experimental pressure and sail shape data
were obtained from on-water tests conducted on a Stewart 34 Class yacht equipped with an asymmetric spinnaker. Data were recorded for a range of apparent wind angles in light winds, in order to check the reliability, accuracy and repeatability of the system. The flow around the sails is studied qualitatively by analysing the pressure distributions and sail shape. It was found that the results showed similar trends to the published literature, in spite of the low wind speeds during the tests. The accuracy of the system was investigated by wind tunnel tests, with particular reference to the determination of the entire sail shape from the stripe images and the VSPARS outputs, and was found to be relatively good, even for the foot shape which is outside the camera viewing region.
In the field of aeroelasticity, flutter is a well-known instability phenomenon. Flutter is a synchronized vibration which takes place in a flexible structure moving through a fluid medium. It occurs when two regular, rhythmic motions coincide in such a way that one feeds the other, drawing additional energy from surrounding flow. A classic case of wing flutter might combine wing bending with either wing twisting. Flutter appeared for the first time on racing yacht keels with composite fins, so in water, in 2004, on both the IMOCA 60 POUJOULAT-ARMORLUX, which lost her keel, and SILL. Following these problems - particularly following the loss of the keel of Bernard STAMM sailboat, accident that could have dramatic consequences for the skipper - HDS company focused on the phenomenon. This paper will introduce the strategy of HDS faced to the problem and the analytical and numerical methods implemented to estimate the flutter critical speed. Our model is based on a truncated modal basis for the most energetic modes which are generally, for a bulb keel, the lateral bending predominant mode and the torsion predominant mode. One of our requirements was to make a simple model in order to integrate the calculation of the flutter critical speed in the first design loops of a composite or steel keel. Besides, an other requirement was to be able to calculate flutter critical speed on other type of appendages: hydrofoils, dagerfoils, daggerboards, rudders...This model has worked well for the two cases of flutter appeared on IMOCA sailboat keels. Besides, to verify the quality of the model and to complete our analysis of flutter phenomenon on racing yacht keels, a 3 dimensional multiphysic simulation has been developed using the software ADINA.
In this paper, a dynamic computation of the Groupama 3 foil is performed. Foils are thin profiles, placed under the hull of a ship, allowing it to provide a lifting force. This study is placed in the context of the 2013 America’s Cup, which will see the appearance of a new kind of high performance multihull. At high speeds, the foils are subject to intense hydrodynamic forces and to movement due to the sea state. The deformations are then sizable and there is a risk of ventilation, cavitation or vibration which could lead to a large modification of the hydrodynamic forces or to the destruction of the foil. The foil being light compared to the added mass effect, the interaction is a strongly coupled problem. In this paper, the problem is solved using a segregated approach. The main problems resulting of such a method are the numerical stability and remeshing. These problems are detailed and some results presented. As a first test case, the simulation of a vortex excited elastic plate proposed by Hubner is presented. This case is very demanding in terms of coupling stability and mesh deformation. Then, the foil of Groupama 3 is modeled in a simplified form without hull and free surface, and then in a more realistic conditions with free surface and waves.
An unsteady FSI Investigation into the Cause of the Demasting of the Volvo 70 Groupama 4
This paper describes the use of an unsteady fluid-structure interaction (FSI) tool as an investigative tool into the cause of the dismasting of the VOR 70 Groupama 4. As more than one rig component failed during the dismasting, the cause of failure was not immediately apparent. The investigation therefore required isolating the cause of failure between two closely related rig components. The FSI coupling process and the determination of the initial rig loading based on a steady FSI computation and measured data will be described. The setup for two unsteady failure cases will be discussed and the results of those investigations will be examined.
The Work Achieved with the Sail Dynamometer Boat “Fujin”, and the Role of Full Scale Tests as the Bridge Between Model Tests and CFD
The work achieved with the sail dynamometer boat Fujin was reported. At first, the sail shapes and performance for upwind conditions were measured in steady sailing conditions. The results were compared with the numerical calculations. The database of three-dimensional coordinates of the sail shapes was also tabulated with the aerodynamic coefficients. The sail shape database provides a good benchmark for the validation of sail CFD in full scale level. Then, the aerodynamic force variation during tacking maneuvers was measured by Fujin, and a new simulation model of tacking maneuver was proposed. The simulated results showed good agreement with the measured data. Finally, the scale effect problem of wind tunnel tests was discussed. Wind Tunnel tests using model sails are performed at the region of critical Reynolds number. Therefore, the wind tunnel test had to be performed very carefully. On the other hand, the full scale tests using a sail dynamometer boat are free from scale effect problems and appear more promising.
Estimating a yacht’s Hull-sailplan balance and sailing performance using experimental results and VPP methods
This paper describes an approach to calculate the longitudinal position of the hydrodynamic and aerodynamic force centres on a sailing yacht, and the resulting rudder angle required to hold a steady course across a complete range of sailing conditions. The paper discusses the effect on performance, in terms of boat speed, by means of experimental tank testing to derive the hydrodynamic data; wind tunnel testing to derive the aerodynamic data; and the use of a 4 plus degree of freedom (DOF) velocity prediction program (VPP). It highlights the data required to carry out such analysis and is summarised in a worked example. The main objective of this paper is to outline a process which is achievable within a design office environment and skill set, whereby a designer can use generic data derived from experimental or CFD and amalgamate it with theoretical and regression models for individual components to ensure that the “balance” question is satisfactorily addressed at a stage in the design and development process where meaningful changes can be made to geometry.
The IMOCA 60 Class has a complicated set of appendages: with canted and tilted keels, cambered daggerboards that can be designed to be fitted to the hull in different orientations along with toed-in and twin rudders that can also be configured in different orientations. Curved dagger-boards and straight boards with positive lift inducing dihedral angles have been used in number of recent IMOCA 60 designs and in other classes, principally multi-hulls. These were considered an option by the client for their new Open 60 design and so a research and development programme was instigated by Owen Clarke Design to compare new curved designs with conventional straight daggerboards optimised for upwind conditions. It was felt that the modelling of the trim of the yacht was very important to the calculation and sharing of loads between all of the appendages, and so our group chose to use a combination of one third scale high speed towing tanks tests and computational fluid dynamics (CFD), rather than CFD alone to investigate the relative performance between these dagger-board types.
Smart Materials Application on High Performance Sailing Yachts for Energy Harvesting
Piezoelectric patches are bounded on a keel bulb in order to harvest vibration energy by converting electrical output. Unsteady computational fluid dynamics method is also used to find the structural boundary condition such as the hydrodynamic pressure fluctuation. Finite element analysis (FEM) is used to find structural and electrical responses.
Long Term Immersion in Natural Seawater of Flax / Biocomposite
The present article gives information on 2 years seawater aging effect on injected flax/PLA biocomposite. Biocomposite suffer from relatively high moisture absorption which is controlled by vegetal fibre. Simple rule of mixture allows for
flax fibre the determination of a weight gain at saturation around 12% which is close to already published values. Bundles of fibres and especially middle lamellae influence water uptake. Water alters biocomposites, and flax fibres since their mechanical properties are reduced (Young modulus and tensile strength) with aging. Linear relationship is observed between water uptake and loss of mechanical properties. Load-unload cycles highlight damage occuring earlier as biocomposite undergo aging. These damages can be induced by fibre degradation and washing out of soluble components especially the fibre bundles cement, by debonding of fibre bundles linked to their swelling.
When the future wind direction is uncertain, the tactical decisions of a yacht skipper involve a stochastic routing problem. The objective of this problem is to maximise the probability of reaching the next mark ahead of all the other competitors. This paper describes a system that models this problem. The tidal current at any location is assumed to be predictable, while the wind forecast is based on current observations. Boat performance in different wind conditions is defined by the output of a velocity prediction program, and we assume a known speed loss for tacking and gybing. The resulting computer program can be used during a yacht race to choose the optimum course, or it can be used for design purposes to simulate yacht races between different design candidates. As an example of application, we compare strategies that minimise the average time to sail the leg, as opposed to those that maximise the probability of winning, and show how optimal routing strategies are different for leading and trailing boats.
Development of an America's Cup 45 Tacking Simulator
This paper describes the development of an AC45 simulator conducted as a student Master’s project at the University of Southampton. The main aim was to be able to asses and improve the tacking skills of the helm and the crew through systematic training. The physical interface of the simulator replicates the seating position of the helmsman and the main trimmer and the graphical representation provides the users with visual cues of the simulated boat, boundaries and marks for a sample race course. The theoretical model uses hydrodynamic manoeuvring coefficients based on empirical formulae and experimental data. The aerodynamic forces are pre-calculated using a full-scale RANS CFD simulation. The accuracy of the model is verified against the AC45 racing tracking data to ensure that the speed loss during a tack, experienced by the users of the simulator, is as close to reality as possible. The ultimate aim of the project was to study the potential of the simulator to assess and train the crews, improving their skill in tacking the boat effectively. This has been done by examining the performance of two groups of users over a series of practice sessions. The simulator could be potentially used for training the helmsmen of the Youth America’s Cup Red-Bull teams, which have limited budgets, training days and sailing experience compared to the professional AC sailors.
Coupled Open Navigation and Augmented Reality Systems for Skippers
This paper describes a new measurement and vision system for sailboat race. This system is composed of an open navigation processor and a see-through Augmented Reality (AR) glasses. This open navigation
processor allows to plug most sensors in order to measure wind conditions, boat speed, dynamic motions and other parameters. Moreover, it is able to implement several wind correction algorithms in order to improve the true wind computation. On the other hand, the open navigation processor communicates with a see-through AR glasses through wireless network. The interest of this system is that it is flexible and can overlay any text, 2D or 3D objects on the true real world view, so the skipper is free to display the useful data.
Study of the Influence of Singularities Created by Automated Fiber Placement on the Performance of Composite Materials for Naval Structures
The Automated Fiber Placement (AFP) process shows great potential for efficient production of large composite materials structures, in the construction of racing yachts. However, during the manufacturing of complex shapes, unavoidable singularities are induced on the entire structure manufactured. The lack of knowledge concerning the influence of these defects on the performance of composite materials led us to study the effects of two main singularities, the overlap and the gap. Ultrasound inspection and Scanning Electronic Microscopy have been performed to compare the microstructures of a plate without defects with plates containing these singularities. This study also compared the mechanical properties of a plate made by manual layup with those of a plate made by automated layup, by tensile tests on carbon / epoxy specimens.
Tag Shepherd: A Low-Cost and Non-Intrusive Man Overboard Detection System
This paper presents a man overboard detection system based on the monitoring of a group of sailors. It introduces a set of existing solutions proposed to track and rescue a person falling into the water. Based on the state of the art, it describes our original solution which is low-cost and low footprint compared to the other ones. It was developed to be a plug-n-play system that can be generalized for every sailor to detect a man overboard.
Advanced Structural Analysis Method for Aeroelastic Simulations of Sails
This paper presents an advanced method to predict the structural behaviour of modern fiber-membrane sails and its validation by on-board sail photographic survey. The presented structural analysis method is an improvement of a direct stiffness method that shows good numerical stability and is able to treat nonlinearities with the same level of performance of a dynamic method, but less time consuming. In order to achieve this performance, a damping-like force has been added to the structural system. By tuning a damping factor, the behaviour of the structural analysis code can be switched from a classical static method to a dynamic-like one. Thus, this method allows running accurate analyses of fiber-membrane sails with battens by taking into account both the geometric nonlinearity and wrinkling behaviour of membrane structures in a timely manner. Furthermore, it is also very effective when sails are coupled with rigging elements, e.g. when the luff sag calculation is required. This advanced structural analysis method is coupled with a nonlinear vortex lattice method to enable a proper aeroelastic simulation of sails in upwind conditions, within the SMAR-Azure technology. The SMAR-Azure fully integrated aeroelastic analysis method has been extensively validated using on-board photographic survey. In this paper, the comparison between the calculated and the real flying sail shapes of the fiber-membrane sail plan of the 55ft race boat “Living Doll” is presented.
Sail-wind interaction belongs to the category of fluid-structure interactions of
multiphysics, where structural deformation and fluid flow influence each other. The
objective of this paper is to demonstrate the capability of Fluidyn-MP, a multiphysics
simulation code, in analyzing the behavior of sail under wind loads. Finite Volume based
scheme is used to simulate fluid flow (CFD solver ) and a Finite Element based scheme
employed to analyse the structural behaviour (CSD solver). Coupling between the two
codes involves data transfer across the interface, as also updating the fluid mesh in case
of significant structural deformation. Fluidyn-MP, an integrated code that handles the two
solvers and coupling automatically, is employed to study the behavior of sail under wind
load. The example shown highlights the features and capabilities of the code.
Sailing Site Investigation Through CFD Modelling of Micrometeorology
To have a prior accurate knowledge of the local wind currents on a water body is of crucial importance for the performance of the sailing team. In the recent years, Computational Fluid Dynamics (CFD) has proven itself a powerful tool in atmospheric modelling. By solving the Navier-Stokes equations and with correct description of the atmospheric boundary layer and turbulence at the domain boundaries, the local influences of the shore topography and the obstacles on the wind flows can be investigated in detail. Two examples of the use of CFD (Fluidyn PANWIND software) are presented here. The first one shows the coastal wind analysis of 2012 Olympic sailing site of Weymouth, UK. The local wind effects due to the harbour and hill have been determined and compared to observations of wind velocity and direction for several wind conditions. The second example required to model the wind over the training base of the French Sailing Teamin Brest, France. This landlocked bay, surrounded by two steep hills and linked to the Atlantic Ocean by a strait, emphasizes the need for a CFD simulation of the wind which provided the patterns of wind around the racing areacompared with empirical observations.
The present paper presents an overview of the Lecco Innovation Hub project and in particular of the Sailing Yacht Lab project which aims to be a full scale measurement device in the sailing yacht research field. A description of scientific frame, measurement capabilities as well as of the principal design, building process, project management and committing are provided.
Kite and Classical Rig Sailing Performance Comparison on a One Design Keel Boat
An implementation of a kite modelling approach into 6 degrees of freedom sailboat dynamic simulator is introduced. This enables an evaluation of kite performance in comparison with classical rig sailing. A “zero-mass” model was used to model kite forces. Influence of the wind gradient was properly taken into account which led to significant modifications in the calculation of the relative wind, both in magnitude and in orientation. The modelling is performed with real aerodynamic characteristics given by experimental data. An optimization is done to determine the best kite flight configuration in terms of performance. Validation steps of the sail yacht simulator are performed for a classical rig on the example of an 8 meter one design yacht. The experimental setup is described and validation results are discussed. An interpolation technique in space and time of the wind mesh was used, based on measurements made at four different locations of the navigation spot. Boat motions were recorded by high resolution GPS and inertial unit systems. Speed polar diagram results, reached by kite propulsion, were predicted versus true wind angle. At last a comparison is made for upwind and downwind legs in sea trials conditions, between simulations with the classical rig and the kite. It is shown that the boat towed by kite would achieve much better sailing performance.