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Modelling the wind, sail and rig interactions on a sailing yacht is a complex subject, because the quality of simulation depends on the accuracy of both structural and fluid simulations which strongly interact. Moreover, the sails are submitted to highly unsteady oscillations due to waves, wind variations, course changes or trimming for example, bu...
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... the algorithms and the philosophy of the coupling of ARAVANTI were applied to the URANSE code ISIS CFD and ARA. An implicit/iterative algorithm (see Fig.4) is used to coordinate the data exchanges between the fluid and structure solvers and obtain a stable coupling. This algorithm is structured into three hierarchical loops. ...
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... second one, denoted here the FSI loop, aims at solving the non-linearity's of the fluid problem (it correspond to the non-linear loop when dealing with non-FSI computations). In the case of FSI computation, the dashed box in Fig.4 is added. In particular, it includes the resolution of the structure problem (structure loop). ...
Citations
... As a first approach, a finite element method has been coupled to a flow solver (Renzsch et al., 2013(Renzsch et al., , 2016Trimarchi et al., 2013) to predict the sail flying shape in static simulations. Lombardi et al. (2012), Durand (2012) and Durand et al. (2010Durand et al. ( , 2014 successfully achieved unsteady fluid-structure interaction simulations. Still, so far, such simulations have not been compared to full-scale or wind tunnel experimental unsteady data, such as the dynamic curling behaviour at a fixed trim. ...
When sailing downwind with a spinnaker, the “verge of curling” is one of the common recommendations that sailors follow for efficient sailing. Wind tunnel experiments on spinnaker models conducted by Aubin et al. (2017) in the Twisted Flow Wind Tunnel of the Yacht Research Unit of the University of Auckland have shown that curling can be related to better performance at Apparent Wind Angle ≥ 100°. In the present article, we will focus on the aerodynamic performance jump observed at Apparent Wind Angle AWA = 100°, where the drive force increases up to 15% when the sail starts to flap. Thanks to four triggered HD cameras and coded targets stuck on the sail, three flying shapes of the spinnaker are reconstructed by photogrammetry for different sheet lengths from over trimmed to flapping occurrence. The pimpleFOAM solver from OpenFOAM is used to simulate the aerodynamics of the three rigid extracted flying shapes. Results highlight the ability of the model to simulate the experimental jump observed closed to curling and the significant confinement effect of the roof of the wind tunnel.
... Results could be compared to wind tunnel validation cases like Renzsch and Graf (2013). Lombardi et al. (2012) and Durand et al. (2010);Durand (2012); Durand et al. (2014) successfully achieved unsteady fluidstructure interaction simulations, but so far such simulations have not been compared to full-scale or wind tunnel experimental unsteady data, with time-resolved measurements as presented in Deparday et al. (2016a). ...
... 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 [3]. ...
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 [4]. The main objective is to use numerical simulations to model spinnakers, in order to predict both propulsive force and sail dynamic stability. Recent developments [2] 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 [3]. 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.
... An arbitrary Lagrangian Eulerian (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 (Durand et al., 2010). ...
Modelling the wind, sail and rig interactions on a sailing yacht is a complex subject, because the quality of simulation depends on the accuracy of both structural and fluid simulations which strongly interact. Moreover, the sails are submitted to highly unsteady sollicitations due to waves, wind variations, course changes or trimming for example, but sometimes also due to the unsteadiness of the flow itself (vortex shedding,…). The problem for downwind sails is even more complex because the flow is often detached from the sails, and the sails are subject to large shape changes. IRENav, K-Epsilon and the DSPM team of LHEEA have jointly developed a coupled computational tool able to compute the fluid-structure interaction characterizing the dynamic behaviour of sails in wind. This coupled simulation tool is composed of an original finite element code ARA [2] developed by K-Epsilon dedicated to simulate sails but also the rig of sailing boats (mast, shrouds, sheets,...). A wrinkle formulation is included to model the local deformations of sails without being obliged to use too many elements. This code is coupled to the URANSE solver ISIS-CFD [1] (internationally distributed by NUMECA Int. as FINETM/Marine) developed by the DSPM team of LHEEA. The fluid-structure interaction between sails and wind is a difficult problem because of the strong coupling which characterizes the deformation of a sail which is a lightweight and very flexible structure. For instance, the typical ratio between the mass of a spinnaker and its added mass is of the order of one over one thousand. The approach followed by the authors is based on the use of an improved strongly coupled methodology. The stability of the multi-step procedure is ensured by the use of the Jacobian matrix characterising the coupling between the structure and the fluid, this Jacobian being approximated with the help of a perfect fluid solver AVANTI, developed by K-Epsilon. Although not monolithic, this algorithm is very stable, fast and parallelized. An original mesh deformation tool has also been developed to transmit the deformation of the sail to the fluid domain without being obliged to rebuild from scratch a new grid. This method, based on the combination of an explicit advance front methods and smoothing is also parallelized, fast, robust and used to compute the large deformation of unstructured mesh around multiple bodies like a spinnaker and main sail interacting altogether.
Several applications will be presented. A first experimental comparison will be performed on a well controlled test case with an original experiment developed by IRENav, consisting in a square of spinnaker fabric mounted on two carbon battens which are moved in a forced oscillation. Finally, more realistic calculations on an unsteady sailing spinnaker with an automatic trimming algorithm, interacting with a main sail will be presented to illustrate the potential of the present fluid-structure coupling.
... Sail-like thin laminates, and more generally inflatable structures, have been analysed with finite element (FE) methods, see e.g. [8,9]. In such studies the fabric has generally been modelled using the membrane model, which assumes that the bending components are negligible. ...
We propose a method of modelling sail type structures which captures the wrinkling behaviour of such structures. The method is validated through experimental and analytical test cases, particularly in terms of wrinkling prediction. An enhanced wrinkling index is proposed as a valuable measure characterizing the global wrinkling development on the deformed structure. The method is based on a pseudo-dynamic finite element procedure involving non-linear MITC shell elements. The major advantage compared to membrane models generally used for this type of analysis is that no ad hoc wrinkling model is required to control the stability of the structure. We demonstrate our approach to analyse the behaviour of various structures with spherical and cylindrical shapes, characteristic of downwind sails over a rather wide range of shape and constitutive parameters. In all cases convergence is reached and the overall flying shape is most adequately represented, which shows that our approach is a most valuable alternative to standard techniques to provide deeper insight into the physical behaviour. Limitations appear only in some very special instances in which local wrinkling-related instabilities are extremely high and would require specific additional treatments, out of the scope of the present study.
... Ainsi le calcul doit impérativement prendre en compte l'ensemble du gréement et des points d'accroche pour espérer correctement calculer la forme des voiles en navigation. Dans cette optique, des recherches ontété poursuivies donnant lieu au développement de logiciels spécifiques : Flow-Membrane propriété de la voilerie internationale North-Sails (non publié), Heppel [54] en 2002 avec le logiciel Relax et Razenbach [108] pour la voilerie Quantum, Flexail [111], et enfin ARAVANTI (voir figure 1.4 et [36]) par k-Epsilon, présenté dans cette thèse. Ces logiciels sont basés sur des approcheséquivalentes : un code structureélément finis pour les voiles (modèle de membrane) et pour le gréement avec deséléments poutres et câbles. ...
This thesis, devoted to simulations of sailboat sail, was initiated by K-Epsilon, acompany specialized in numerical computations for naval hydrodynamics, IRENav, the Frenchnaval academy laboratory and LHEEA from Ecole Centrale Nantes. In this context a finiteelement program was developed dedicated to computing sail membranes and sailboat structures.The program was coupled with an inviscid fluid solver. A more detailed modeling of the flow andinteraction was realized by implementing a coupling with a fluid solver code which solves theReynolds Averaged Navier-Stokes Equations, developed by the DSPM team from LHEEA. Forthe coupling it was necessary to look at the interface over which a transfer of variables betweenthe fluid and structure occurs. Another key consideration was the deformation of the fluid solversmesh. The part has been revisited and extended to reach the development of a fast, robust, andparallelized method to treat the considered deformations. For good solution convergence andstability properties an iterative, partitioned algorithm that relies on an approximation of theinterface’s Jacobian evaluated by the inviscid code and integrated in the structure’s equationswas used. Finally, applications employing these methodologies are presented. Comparisons weremade with an instrumented sailboat. A second experiment of an oscillating cloth was developedto validate the case of interaction of a fluid with a light and flexible structure. Results were usedto validate the RANSE solver coupling. A more realistic calculation was also conducted on anunsteady sailing spinnaker with an automatic trimming algorithm, showing the potential of thepresent coupling.
... Downwind sail fluid structure interactions have been presented, where a weak steady coupling is performed between RANS and FE solvers [9]. From a structural perspective, the sailcloth is usually analyzed with CST membranes [4]. Such elements derive from a rather simplified formulation, based on the geometrical observation that a triangle is uniquely defined by the sides length, therefore that the element's strain can be entirely evaluated using such measure. ...
Sail analysis is a rapidly evolving field, since it has a big impact in the performances of yachts. In the present approach, a weak coupling in Arbitrary Lagrangian Eulerian (ALE) configuration has been chosen. The flow is analyzed with a Reynolds Averaged Navier Stokes (RANS) Finite Volume (FV) solver with turbulence models, whereas the structural analysis is performed with non-linear MITC Shell Finite Elements (FE). The approach and examples are presented and discussed with regards to a two dimensional downwind sail section in turbulent flow.
... Downwind sail fluid structure interactions have been presented, where a weak steady coupling is performed between RANS and FE solvers [9]. From a structural perspective, the sailcloth is usually analyzed with CST membranes [4]. Such elements derive from a rather simplified formulation, based on the geometrical observation that a triangle is uniquely defined by the sides length, therefore that the element's strain can be entirely evaluated using such measure. ...
... The first support is the instrumented sail boat, subject of this paper, which is adapted to full scale and real condition study. The second support is a laboratory experiment consisting in a swiveling sail which has been described in a previous paper [6]. It represents a good test case for the FSI issue on soft surface, without the inboard instrumentation problems and a well controlled environment. ...
This work presents an experimental study on the aero-elastic wind/sails/rig interaction at full scale in real navigation conditions with the aim to give an experimental validation of unsteady Fluid Structure Interaction (FSI) models applied to yacht sails. An onboard instrumentation system has been developed on a J80 yacht to measure simultaneously and dynamically the navigation parameters, yacht motion, and sails flying shape and loads in the standing and running rigging. The first results recorded while sailing upwind in head waves are shown. Variations of the measured parameters are characterized and related to the yacht motion (trim mainly). Coherence between the different parameters is examined. In the system's response to the dynamic forcing (pitching motion) we try to distinguish between the aerodynamic effect of varying apparent wind induced by the motion and the structural effect of varying stresses and strains due to the motion and inertia. The simulation results from the FSI model compare very well with the experimental data for steady sailing conditions. For the unsteady conditions obtained in head waves, the first results show a good agreement between measurements and simulation.
Tests were realized on a complete production chain: a sail designer from Incidences-Sails has designed two different shapes of an IMOCA60 gennaker 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 gennakers, in order to compare dynamic stability and propulsion forces. A new method is then developed to quantify the practical stability of a downwind sail.
