Aligned with the International Maritime Organization's (IMO) aim to lower greenhouse gas emissions, the use of Wind-Assisted Ship Propulsion (WASP) in maritime transport is gaining increased attention. The study and optimization of WASP remain challenging due to complex physics and the high number of parameters involved. This includes interactions between aerodynamics, hydrodynamics, and structural dynamics, which require advanced multi-physics modeling. Additionally, numerous factors must be optimized, from design and control parameters to route selection, all within the variable maritime environment. Addressing these challenges demands multi-model approaches and multi-criteria optimization methods to maximize energy efficiency effectively. In this context, the laboratories of Ecole Navale, IFREMER, ENSM, and ENSTA Bretagne are collaborating on several research projects, with a selection of two thematic studies presented here.The first study is carried out as part of the SHIVA and SAWASP projects, jointly led by Ecole Navale, IFREMER and ENSTA Bretagne. The goal of these projects is to optimize the hydrodynamic performance of innovative, fully electric, Vertical-Axis Propellers (VAPs) and their optimal use in conjunction with a wind-assisted ships. To achieve this, the SHIVA project implements a multi-criteria optimization of the propeller blade-pitching laws, utilizing multi-fidelity numerical and experimental surrogate models. These optimizations enable the determination of a set of optimal pitch laws for different operating points of the propeller. In the SAWASP project, a 6-meter wind-assisted ship equipped with VAPs is developed to study the optimal aerodynamic-hydrodynamic coupling. In particular, the energy gains from using VAPs as the main propulsion system, generating a lateral anti-drift force, are studied. The use of Reinforcement Learning (RL) methods to maintain optimal ship operation performance at sea, as an uncertain environment, is also part of this project.The second study is conducted within the framework of the SOMOS project, jointly managed by ENSM and ENSTA Bretagne. The project's goal is to create and validate a set of numerical tools, that allow for rapid and precise assessment of the energy efficiency of wind-assisted ships. For the purposes of this study, a modular and comprehensive ship motion solver is formulated as an optimal control optimization problem, to evaluate, compare, and optimize energy performance. Such an approach is very complex to implement and, depending on the fidelity-level used, may require very high modeling costs. This is why most research efforts focus on specific aspects of the broader problem, often overlooking the coupling of maritime routing, ship motion analysis, and the optimization of control parameters along the planned sea route. The present work provides an innovative approach for the calculation of optimized trajectories for wind-assisted ship, by both considering the ship's maneuvering capabilities and the optimization of ship control and/or design parameters. In contrast to conventional routing methods, the proposed approach achieves high computational efficiency and relies on direct multiple shooting methods to determine optimal ship control parameters (RPM, rudder angle, etc.) and design variables (rotor Flettner or sail positioning, rudder area, etc.) along the sea route, satisfying the constraints of complying with the ship's equations of motion.

The paper presents the results obtained through the development of an innovative and disruptive floating VAWT concept. It focusses on both experimental and numerical approaches launched within the purpose to characterize the wake of the VAWT concept and calibrate analytical model to be further considered for Offshore Wind Farm Yield Assessment. Model tests performed in the basin facilities operated by Ifremer (Boulogne-sur-mer) allowed to accurately characterize the wake of the VAWT thanks to LDV measurements. They have highlighted the resorption mechanisms which take place in VAWT wake and that considerably reduced turbine wake compared to HAWT concepts. Based on this exhaustive experimental database, the adaptation and calibration of the analytical Ouro-Lazennec model offer strong capabilities for front end developments and yield assessment allowing optimizing farm configuration depending on annual wind conditions and production maximization.

_ In this paper, the hydroelastic response of a NACA0015 composite hydrofoil is studied experimentally and numerically. The foil is made of composite materials with fibers not aligned with the span of the foil, which results in the occurence of a bend-twist coupling in the material. Computations are performed using a partitioned approach. The flow problem is solved using a boundary element method. The structural response of the foil is modelled with two different finite element models. In the first one, the foil is modelled with 2D shell and 3D solid finite elements and in the second model, the foil is modelled with 1D beam finite elements. The experiments are conducted in an open circulation water channel. Hydrodynamic forces and structural displacements are measured for several angles of attack, free stream velocities and submergence depth. This paper shows that the mechanical behaviour of a composite hydrofoil submitted to hydrodynamic loads can be modelled with 1D beam finite elements. This model gives results very similar to a finite element analysis realized with 2D shell and 3D solid finite elements, which are commonly used to model composite structures. The present work also shows that the experimental results can be well predicted by numerical simulations, but it requires a precise modeling of the bend-twist coupling in the materials constituting the foil. Keywords Hydrofoil; Equivalent Beam; Fluid-Structure Interactions; Composite; Bend-Twist Coupling

As a first step toward a multi-fidelity optimization tool for hydrofoils, the present work assesses the ability of the in-house code PUFFIn to be used as a “low-fidelity” solver within the multi-fidelity framework. The code, based on the Boundary Element Method (BEM) and the potential flow theory, is used to study the performance of a typical windsurf hydrofoil operating near the free surface. The hydrofoil is composed of a front wing and a rear stabilizer in a plane-like configuration. Computations are performed for single body configurations (only one wing) and two-body configurations (front wing and stabilizer). First, three linearized models of the free surface are compared for the single front wing configuration with several values of the Froude number: the symmetry, anti-symmetry and Neumann-Kelvin conditions. The results show that for relatively high Froude number, the anti-symmetry and the Neumann-Kelvin conditions provide very similar forces. Then, the predictions of the BEM solver are compared with “high-fidelity” RANS computations, in terms of pressure drag and lift, pressure distribution on the hydrofoil and free surface elevation. Several Froude numbers and submergence depths are studied. The global lift and drag variations predicted by the BEM with the anti-symmetry and Neumann-Kelvin conditions on the single-body configurations are similar to the RANS predictions. For the two-body configurations, the Neumann-Kelvin condition outperforms the anti-symmetry condition. Based on the BEM/RANS comparison, the potential flow solver reveals to be a relevant tool for multi-fidelity optimization.

Lifting hydrofoils are gaining importance, since they drastically reduce the wetted surface area of a ship, thus decreasing resistance. To attain efficient hydrofoils, the geometries can be obtained from an automated optimisation process. However, hydrofoil simulations are computationally demanding, since fine meshes are needed to accurately capture the pressure field and the boundary layer on the hydrofoil. Simulation-based optimisation can therefore be very expensive. To speed up the fully automated hydrofoil optimisation procedure, we propose a multi-fidelity framework which takes advantage of both an efficient low-fidelity potential flow solver dedicated to hydrofoils and a high-fidelity RANS solver enhanced with adaptive grid refinement and dedicated foil-aligned overset meshes, to attain high accuracy with a limited computational budget. Both solvers are shown to be reliable for automatic simulation, and remarkable correlation between potential-flow and RANS results is obtained. Two different multi-fidelity frameworks are compared for a realistic hydrofoil: only RANS based and potential-RANS based. According to the optimisation results, the drag is able to be reduced by 17% and 8% in these frameworks, within a realistic time frame. Thus, industrial optimisation of hydrofoils appears possible. Finally, critical areas of future improvement regarding the robustness and efficiency of the optimisation procedure are discussed in this study.

The low center of gravity and low center of thrust of Vertical Axis Wind Turbines (VAWT) are interesting characteristics when considering Floating-Offshore Wind Turbine (FOWT) application. The motion due to the floating platform adds extra complexity to the unsteady aerodynamics of VAWT. Hence, both numerical and experimental studies become very challenging. This paper focuses on the assessment of TubinesFoam, a fast tool consisting of the actuator line method (ALM) embedded in OpenFoam. Then, instead the typical bladed-solved Navier–Stokes equations, the ALM inserts the blade forces into the field as body forces into the momentum equation. A modified version of the turbinesFoam library that includes surge motion for multiple rotors has been evaluated by comparison with an experimental set of data from a twin-rotor performing surge in a wind tunnel. This paper includes the main equations describing the kinematics implemented in the numerical code, as well as a convergence analysis of mesh size, time step and surge cycles. The numerically predicted thrust forces agreed with the experimental results for both investigated tip speed ratios for the case with no surge motion. The numerical and experiment results including surge motion indicated a minimal influence of the surge motion for the cases evaluated here. The last verification using CFD computations from the literature showed that the turbinesFoam tool properly captures the main features of the surge motion. This verified numerical method is a promising tool to understand the effects of geometrical parameters on the performance and the wake development of VAWTs farms in floating-offshore environments.

A Floating-Offshore Vertical Axis Wind Turbine (FOVAWT) might experience a six-degree-of-freedom (DOF) motion due to the ocean waves. This 6-DOF motion can affect the unsteady aerodynamic forces and the performance of FOVAWTs. However, investigations considering floating conditions are very limited. This paper focuses on the evaluation of a numerical tool in predicting the instantaneous thrust forces of a double-rotor VAWT undergoing surge motions. The numerical method consists of an actuator line model embedded with a fluid dynamic technique: the TurbineFOAM library. The experimental tests for the numerical verification were carried out in a wind tunnel using a contra-rotating O-shape rotor. The data used for comparison consisted of (a) a non-surge case and, (b) surge motions allowing 20, 10 and 5 rotor revolutions per surge period (Ns). The results depicted a very good agreement between the numerical and experimental forces for the non-surge case. For the surge cases tested here, the average thrust force per surge period was very similar between the numerical and experimental results for all Ns . This suggests a minimal influence of the surge motion on the thrust forces. It was observed that the larger Ns the minor the impact on both, the instantaneous angle of attack and relative velocity of the blades. The present assessed method has the potential to explore the effects of a 6-DOF motion on the aerodynamic forces and performance of multiple VAWTs.

Lifting hydrofoils are gaining importance, since they drastically reduce the wetted surface area of a ship hull, thus decreasing resistance.To attain efficient hydrofoils, the geometries can be obtained from an automated optimization process, based on simulations.However, hydrofoil high-fidelity simulations are computationally demanding, since fine meshes are needed to accurately capture the pressure field and the boundary layer on the hydrofoil.Moreover, the immersed depth varies dynamically, which makes the simulation of hydrodynamic forces challenging.Simulation-based optimization can therefore be very expensive.Automated surrogate models, trained by a limited number of simulations, can reduce the required computational demand for the optimization process.Furthermore, if an efficient low-fidelity hydrofoil performance prediction tool is available, using surrogate models in a multi-fidelity framework [2] can provide a further reduction in the total required simulation cost, by combining the accuracy of a few high-fidelity simulations with the adequate exploration capability of a greater number of low-fidelity computations.In this study, we propose a hydrofoil optimization procedure based on two simulation methods, a dedicated hydrofoil potential flow solver [1] for low-fidelity and RANS for both medium-and highfidelity.The RANS solver uses adaptive grid refinement [2] to attain maximum accuracy with the lowest computational budget.Moreover, two distinctive improvements are provided within the surrogate modeling process.The first one aims to increase the accuracy of the uncertainty estimation when very few sample points are available and the second one provides better noise-canceling for the data in the sample points, with an estimation of the uncertainty due to the noise filtering.In this study, the proposed automated multi-fidelity surrogate model procedure will be tested for a parameterized geometric model of a realistic hydrofoil.The influence of the surrogate modeling technique and the effect of different combinations of fidelity levels on the efficiency of the optimization and the performance of the hydrofoil will be investigated.

In this paper, the 10 kW WindQuest Vertical Axis Wind Turbine (VAWT) has been instrumented by strain gauges during its trials in the Ifremer in situ test site of Brest to study the effects of the structural dynamic response of the blades under operating conditions. Static and dynamic effects have been investigated as a function of the rotational speed when the rotor operates under stable wind conditions. The analysis segregates the influence of the gravitational, inertial, and aerodynamic loading components on the flapwise bending stress of the blades. The study of the cyclic variations on the blade strain at different Tip-Speed Ratios leads to the identification of the dynamic stall effect on the unsteady loads, while the spectral analysis describes the system eigenfrequencies excited by the interaction of the wind and the structure's motion. The results provide useful data to validate numerical models for VAWT blades with similar design and evaluate the structural fatigue.

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. URANS equations are solved with a mixture model to capture the free surface, 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.

For high-performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. The present work investigates solutions to control the onset of cavitation thanks to a combination of leading edge and trailing edge flaps. Numerical and experiments in a hydrodynamic tunnel are conducted in order to assess the effect of specific geometric parameters on the hydrodynamic performance and cavitation inception. The hydrofoils are manufactured using an additive 3D printing technique and tested in the cavitation tunnel of IRENav at an inflow velocity of 6.67m/s (Re=106). The effect on the hydrodynamic performances and cavitation buckets of a 70% chord trailing edge flap and a 20% chord leading edge flap of NACA 0012 is investigated. The results show that the lift coefficient increases and the cavitation bucket shifts up and decreases with the flaps deflection. The experimental results are in good agreement with the numerical ones by highlighting the capacity of the flaps to modify both the operating domain and the cavitation bucket of the hydrofoil. Eventually, the PLA 3D printed foils prove to be a fast, unexpensive and reliable technologies for cavitation studies.

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.

The present study investigates experimentally and numerically the impact of composite materials on hydro-elastic performances of a hydrofoil experiencing Fluid–Structure Interactions, and focus on the bend–twist coupling phenomenon. Four flexible hydrofoils piercing the free surface, with identical geometry of extruded plan-form, a constant NACA0015 section, are tested in a cantilevered configuration in a hydrodynamic flume. The hydrofoils are built from the same mold with different materials (carbon or glass fiber) and different layups. The layups are designed to allow or not bend–twist coupling by the use of ± 45°plies in the structure. Two different coupled FSI numerical approaches are developed to model the hydrofoils behavior: a low fidelity code based on the coupling of a Vortex Lattice Method and a beam theory and a high fidelity code made of the coupling of the structural model code–ASTER and an OpenFOAM VoF hydrodynamic model with free surface. Mechanical characterization of the hydrofoils highlights the differences on the structures which are exacerbated in the hydrodynamic tests. The bend–twist coupling induces a modification of the angle of attack at the tip, leading to a significant difference of the generated lift and thus the deformation. The bend–twist coupling and the hydrodynamic performances are simulated by the numerical approaches.

Authors : Fatiha Mohammed Arab, Benoit Augier, Francois Deniset, Pascal Casari, Jacques Andre Astolfi Abstract : For the top high performance foiling yachts, cavitation is often a limiting factor for take-off and top speed. This work investigates solutions to delay the onset of cavitation thanks to structural morphing. The structural morphing is based on compliant leading and trailing edge, with effect similar to flaps. It is shown here that the commonly accepted effect of flaps regarding the control of lift and drag forces can also be used to postpone the inception of cavitation. A numerical and experimental study is conducted in order to assess the effect of the geometric parameters of hydrofoil on their hydrodynamic performances and in cavitation inception. The effect of a 70% trailing edge and a 30% leading edge of NACA 0012 is investigated using Xfoil software at a constant Reynolds number 106. The simulations carried out for a range flaps deflections and various angles of attack. So, the result showed that the lift coefficient increase with the increase of flap deflection, but also with the increase of angle of attack and enlarged the bucket cavitation. To evaluate the efficiency of the Xfoil software, a 2D analysis flow over a NACA 0012 with leading and trailing edge flap was studied using Fluent software. The results of the two methods are in a good agreement. To validate the numerical approach, a passive adaptive composite model is built and tested in the hydrodynamic tunnel at the Research Institute of French Naval Academy. The model shows the ability to simulate the effect of flap by a LE and TE structural morphing due to hydrodynamic loading.

This article describes the experimental comparison of the DTU 10MW HAWT with the WindQuest 10MW VAWT scaled models when both fitted on the Nautilus-10 semi-submersible. For the campaign in Ifremer Wind&Wave tank, different rotor representations are tested from inertia only to hybrid testing with propellers and a Software in the Loop. The hybrid testing uses a tabulated approach for thrust computation and is discussed in this article. The different thrust reproduction methods are compared to OpenFAST simulations calibrated during the Lifes50+ project and used as reference points. When quantifying the scale model's fidelity to Open Fast, cross-correlation was increased up to 14% with the use of the SiL Thanks to the validation of hydrodynamic simulations based on experimental responses of the floater, it is shown that the VAWT rotor can be upscaled to 13MW for the same platform.

In this work, a collaborative experimental study has been conducted to assess the effect an imposed internal pressure has on the controlling the hydrodynamic performance of a compliant composite hydrofoil. It was expected that the internal pressure together with composite structures be suitable to control the hydrodynamic forces as well as cavitation inception and development. A new concept of morphing hydrofoil was developed and tested in the cavitation tunnel at the French Naval Academy Research Institute. The experiments were based on the measurements of hydrodynamic forces and hydrofoil deformations under various conditions of internal pressure. The effect on cavitation inception was studied too. In parallel to this experiment, a 2D numerical tool was developed in order to assist the design of the compliant hydrofoil shape. Numerically, the fluid-structure coupling is based on an iterative method under a small perturbation hypothesis. The flow model is based on a panel method and a boundary layer formulation and was coupled with a finite-element method for the structure. It is shown that pressure driven compliant composite structure is suitable to some extent to control the hydrodynamic forces, allowing the operational domain of the compliant hydrofoil to be extended according to the angle of attack and the internal pressure. In addition, the effect on the cavitation inception is pointed out.