HAL (Le Centre pour la Communication Scientifique Directe), 2013
Le titre de l'ouvrage associe à dessein deux termes contradictoires pour caractériser l'o... more Le titre de l'ouvrage associe à dessein deux termes contradictoires pour caractériser l'objet étudié : les matériaux, certes déformables, qui relèvent de l'état solide. Ce premier volume traite des seuls comportements linéaires de ces matériaux. Le livre étudie ainsi les matériaux constitutifs des structures du secteur industriel, supposés homogènes et isotropes, lorsque les champs de déplacement sont proportionnels aux chargements appliqués. L'étude débute par une méthode de caractérisation globale fondée sur une décomposition des structures en pièces élémentaires (théorie des mécanismes). Très souvent, industriellement, ces structures peuvent être schématisées géométriquement et mécaniquement par des poutres ou des plaques. Le livre présente donc, de manière assez exhaustive, la modélisation des assemblages de poutres droites soumises à tous les types de sollicitations (effort normal, effort tranchant, torsion et flexion) et à leurs combinaisons. La schématisation des plaques est également exposée. Quelques exercices corrigés illustrent les notions abordées. Dans sa présentation l'ouvrage adopte une approche suffisamment formelle pour ne pas constituer une simple collection de cas particuliers, tout en permettant au lecteur une applicabilité assez directe des méthodes exposées à des cas industriels concrets. Un second volume traite des approches non linéaires
HAL (Le Centre pour la Communication Scientifique Directe), 2017
GSEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage... more GSEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage with complex shapes dedicated to the America's Cup flying catamarans. The aerodynamic loading and the boat weight are counteracted by the appendages and mainly the dagger-board. Consequently, the appendage structural design is very critical. Based on a 3D lifting line and a modified beam element method, the GSEA Design FSI method takes less than one minute to compute. An illustrating example on a L-shape appendage shows that the FSI results compared to a non-FSI results can be particularly different at the elbow. Thanks to the short computational time of the method, multi-objective optimizations can be performed. For instance, a second illustrating example shows the optimization of the appendage weight and stiffness.
High explosive hydro forming (HEHF) is a suitable technique for large metal plate forming. Manufa... more High explosive hydro forming (HEHF) is a suitable technique for large metal plate forming. Manufacturing stages of such a part requires an adapted design of explosive charge configurations to define the mechanical loading exerted on the part. This mechanical loading remains challenging to be experimentally determined but necessary for predictive numerical simulation in the design of parts to form. Providing that the actual mechanical impulse would allow the neglecting of the modelling of the detonation stage, this considerably increases the computational time. The present work proposes an experimental method for obtaining the exerted mechanical loading by HEHF on the part to form. It relies on the development of low-cost sensor based on a polyvinyliden fluorid (PVDF) gauge. In addition to it, an analytical approach based on shock physics is proposed for the sensor signal interpretation. The method considers the multi-layer aspect of the sensor and its intrusiveness with respect to w...
The use of traction kites as auxiliary propulsion systems for ships appears to be a high-potentia... more The use of traction kites as auxiliary propulsion systems for ships appears to be a high-potential alternative for fuel saving. To study such a system a tether model based on the catenary curve has been developed. This model allows calculating static flight positions of the kite on the edge of the wind window. The effect of the wind velocity gradient is taken into account for the evaluation of the aerodynamic forces acting on kite and tether. A closed-form expression is derived for the minimum wind velocity required for static flight of the kite. Results are presented for a kite with a surface area of 320 m 2 and a mass of 300 kg attached to a tether with a diameter of 55 mm and a mass per unit length of 1.20 kg m −1. The minimum wind speed measured at 10 m altitude to launch the kite is found to be around 4.5 m/s. After the launching phase, we show that the optimal tether length for static flight is 128.4 m with a minimum wind speed of 4.06 m/s. The presented approach shows an error up to 9% for a zero-mass kite model with a straight massless tether regarding the maximal propulsion force estimation.
References : [1] Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Comparison of 3D non-... more References : [1] Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Comparison of 3D non-linear lifting line method calculations with 3D RANSE simulations and application to the prediction of the global loading on a cornering kite. In: Proceedings of the 15th Journées de l’Hydrodynamique, Brest, France, 22-24 Nov 2016. [2] Solminihac A., Nême A., Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Kite as a Beam: A Fast Method to get the Flying Shape. In: Schmehl, R (eds) Airborne Wind Energy, Green Energy and Technology, Chap. 4, pp. 77-95. Springer (2018). [3] Duport C., Deberque M., Leroux J.-B., Roncin K., Jochum C.: Local results verification of a 3D non-linear lifting line method for Fluid-Structure interaction simulation on a towing kite for vessels. In: Proceedings of the 11th Symposium on High-Performance Marine Vehicles, Zevenwacht, South Africa, 11-13 Sep 2017. [4] Maison A., Nême A., Leroux J.-B.: De la problématique du dimensionnement de grands kites. In:...
The present work takes place in the framework of the "Jib Sea" project. The main purpose of the p... more The present work takes place in the framework of the "Jib Sea" project. The main purpose of the project is to develop a new sail design made of articulated composite panels, for large merchant ships. The French laboratory "ENSTA Bretagne, IRDL" is involved in this industrial project to provide its expertise on fluid-structure interactions modelling. A fast and robust approach to model fluidstructure interactions for yacht sails is presented. Specifically, interaction effects between the jib and the mainsail are taken into account in the flow model presented. This is achieved using the lifting-line theory combined with a discrete vortex method, involving distributions of lumped-vortex elements along sail sections. The flow model is coupled with a structural finite element software, using shell elements for the modelling of sail membranes, beam stringers for battens modelling and a quasi-static resolution based on a dynamic backward Euler scheme. Numerical comparisons with experiments are conducted on a 50 m² composite mainsail prototype and a conventional jib , built and hoisted on an onshore balestron rig. Measurements, such as strain gauges or cable tensions, are synchronized with a wind sensor. These data collected together enable both global and local numerical-experimental comparisons for forces and moments, providing a validation of the proposed fluid-structure interactions modelling of yacht sails. A good matching between experimental and numerical modelling is observed on local comparisons. Indeed, relative differences are all less than 25% for ∈ [−20; 20] and < 10 kn. Global comparison results exhibit validations with experiments for | | < 10 deg and < 10 kn, where numerical-experimental relative differences are less than 10%. 1. NOMENCLATURE Variation coefficient [−] Chord length [ ] Integration element [ ] Euler number [−] Force [ ] ℎ Batten height [ ] Imaginary number [−] , Index [−] Length [ ] Moment [. ] Number of element [−] Element for DVM [−] U Wind velocities [. −1 ] V Flow velocities [. −1 ] Complex velocity [. −1 ] Complex number [−] Angle for LLT [ ] Γ Global circulation [ 2. −1 ] Local vortex circulation [ 2. −1 ] Δ Pressure variation [. ] Δ Elongation [ ] Relative error [−] Local angle per element [ ] Mean [ ] or [. ] Standard deviation [ ] or [. ] 0 Density [. −3 ] Induced velocity [. −1 ] 〈 〉 Out-of-plane bending stiffness [. 2 ] Leading edge
This paper describes an experimental setup aiming to control and measure performances of small le... more This paper describes an experimental setup aiming to control and measure performances of small leading edge inflatable tube kites, with surface area of less than 35 m². This setup can be deployed either onshore or on a dedicated boat. This article focuses on the onshore results. A 3D load cell is used to obtain the position of the kite under a straightline assumption. A wind profiler (SODAR) is deployed to determine the wind speed and direction at the kite position. A specific post-processing of the data is presented, including phase averaging. The guideline of this work is to estimate the variation of the aerodynamic lift coefficient and lift to drag ratio along figure-of-eight trajectories. Results, for a chosen particular case, show a decrease of lift coefficient of about 20% of the maximum value during turning maneuvers of the kite. The lift to drag ratio evolution along a trajectory is also observed to go through a local minimum during turning maneuvers of the kite in this case. Influence of weight and inertia is highlighted introducing a point mass model of the kite and tethers. Buckling phenomena of the kite inflatable leading edge tube are highlighted and it is shown that they cause control problems.
International Journal of Structural Stability and Dynamics, 2020
This paper deals with the lateral buckling behavior of an axially compressed beam interacting wit... more This paper deals with the lateral buckling behavior of an axially compressed beam interacting with the ground on which it is resting. Such a simple model is supposed to reproduce the same trends as observed during the lateral buckling of offshore pipelines on the seabed. In such practical analyses, the pipe-soil interaction relies the ground to the neutral axis of the pipeline. It is shown that, although such a constraint significantly affects the buckling behavior of the pipeline, it can not reflect the torsional component of the buckling modes. However, this component is encountered in practice and may further modify the critical loads. Therefore, in the present preliminary study, the interaction between the beam in hand and the surrouding ground is modeled by a connection (a continuous distribution of lateral springs) related to the bottom line of the beam. In this way, the real contact between the soil and the bottom line of a pipe is mimicked, allowing for both flexural and torsional deformations in the buckling response. The problem is investigated analytically, using an Euler-Bernoulli beam model with an isotropic linear elastic constitutive law and also an elastic interaction law. Original analytical solutions are derived and compared to numerical results obtained through finite element computations. In comparison with classical solutions (with the connection related to the neutral axis), new types of buckling modes may appear when considering torsional effects, depending on the boundary conditions, with generally much lower critical loads. These first results are certainly representative of some features of the global/localized lateral buckling of offshore pipelines, indicating that torsional effects should also be taken into account in such more comprehensive analyses.
Designing new large kite wings requires engineering tools that can account for flow-structure int... more Designing new large kite wings requires engineering tools that can account for flow-structure interaction. Although a fully coupled simulation of deformable membrane structures under aerodynamic load is already possible using Finite Element and Computational Fluid Dynamics methods this approach is computationally demanding. The core idea of the present study is to approximate a leading edge inflatable tube kite by an assembly of equivalent beam elements. In spanwise direction the wing is partitioned into several elementary cells, each consisting of a leading edge segment, two lateral inflatable battens, and the corresponding portion of canopy. The mechanical properties of an elementary cell-axial, transverse shear, bending, and torsion stiffness-and the chordwise centroid position are determined from the response to several imposed elementary displacements at its boundary, in the case of a cell under an uniform pressure loading. For this purpose the cells are supported at their four corners and different non-linear finite element analyses and linear perturbation computations are carried out. The complete kite is represented as an assembly of equivalent beams connected with rigid bodies. Coupled with a 3D non-linear lifting line method to determine the aerodynamics this structural model should allow predicting the flying shape and performance of new wing designs.
A dynamic kite flight can affect ship motions. Ship equations of motion associated with the analy... more A dynamic kite flight can affect ship motions. Ship equations of motion associated with the analytical zero-mass kite model are developed. Aiming a realistic amplitude modeling of the kite excitation, a linear modification of the aerodynamic kite specs with the turning rate of the kite velocity heading is proposed. A good agreement with experimental data is obtained. Equations of motion are solved on a reaching path alternatively with a weak and a strong coupling between the ship and the kite. Differences between the two coupling methods become significant when a harmonic of the kite excitation approaches the natural roll frequency of the ship. For the presented case of study, these critical conditions can be avoided with longer tethers or larger kite trajectories.
Modélisation de l'impact balistique sur cloisons métalliques de bâtiments de surface
L'une des missions de l'entite DGA/DCE/GERBAM est l'etude de la vulnerabilite des bât... more L'une des missions de l'entite DGA/DCE/GERBAM est l'etude de la vulnerabilite des bâtiments de surface aux missiles. Nos travaux contribuent a la substitution de campagnes d'essais couteuses par des simulations numeriques permettant l'identification de lois de vulnerabilite empiriques plus globales. En particulier, nous souhaitons predire lors de l'impact d'eclats metalliques sur plaques metalliques, la perforation ou la non perforation de la cible ainsi que la fragmentation du projectile et de la cible. Nous choisissons de representer ces phenomenes de rupture par des conditions de perte d'unicite de la solution en vitesse (bifurcation) dans l'equilibre thermomecanique (Neme et Dahan, 1995). Ce critere de rupture a l'avantage de ne pas faire intervenir de parametre specifique (e.g. un endommagement critique) devant etre identifie sur des experimentations appropriees. Dans notre etude concernant les problemes d'impact, les effets de la vitesse de deformation sont preponderants. Ceux-ci sont classiquement pris en compte en utilisant une loi elastoviscoplastique de type unifie (e.g. Johnson-Cook). Dans ces conditions, le critere de bifurcation associe ne fait intervenir que les caracteristiques elastiques du materiau. Par contre l'utilisation d'un comportement (Thermo) Elastique Plastique Viscoplastique (TEPV) permet d'obtenir un critere de bifurcation faisant intervenir les caracteristiques plastiques et viscoplastiques du materiau. Cette nouvelle loi TEPV est proposee a l'instar de travaux anterieurs (Cailletaud et Sai, 1995) portant sur l'interaction plasticite-viscoplasticite en fluage. Deux variables thermodynamiques sont introduites, traduisant l'influence respective des dislocations bloquees et mobiles sur la deformation inelastique macroscopique. La somme de ces deux variables represente la deformation plastique totale. Notre formulation en grande transformation utilise le taux de deformation tourne dans le repere corotationnel D=q -1 D q. Nous faisons l'hypothese de decomposition du taux de deformation en part elastique, plastique, viscoplastique et thermique. L'introduction d'un parametre c dependant de la temperature et compris entre 0 et 1, permet de transcrire l'influence relative des dislocations bloquees et libres sur la deformation plastique macroscopique induite. D = D e + (1 - c)D p + cD vp + αT1 La plasticite (Dp) ainsi que la viscoplasticite (D vp ) sont associees au sens de Von Mises. D'autre part, une approche thermodynamique specifique basee sur le postulat d'une dissipation massique positive est developpee (Quirion et Neme, 2002). Elle conduit a une expression du coefficient de conversion de la puissance plastique en chaleur assez complexe et en general non constante. Un modulateur plastique est introduit dans l'expression du taux de dissipation intrinseque permettant de mieux calibrer le couplage thermomecanique.
Nowadays, noise and vibration problems tend to become an important part of the design process in ... more Nowadays, noise and vibration problems tend to become an important part of the design process in the naval industry. Vibrations often affect the passengers comfort, but more dangerously may damage the structure, embarked merchandise and equipments. A simple way to avoid vibrations is to prevent the resonance conditions. The paper presents a study about the vibration of local structures (beam structures and stiffened panels) with application in the marine industry. The model has been implemented in FORTRAN into a numerical module and will be integrated in the near future with the LBR-5 generic stiffened structure optimization code.
Nowadays, noise and vibration problems tend to become an important part of the design process in ... more Nowadays, noise and vibration problems tend to become an important part of the design process in the automotive and naval industries. Vibrations often affect the passengers comfort, but more dangerously may damage the structure, embarked merchandise and equipments. A simple way to avoid vibrations is to prevent the resonance conditions. The paper presents a study about the vibration of beam structures and stiffened panels. The main application is to determine the eigenfrequencies of structures like platforms, trailer chassis and as well as stiffened shell -beam assemblies. The research work covers analytical vibration modeling of 3D beam structures and 3D stiffened shells, as well as the finite element analyses necessary for the validation. The analysis combines the assumption of undamped free vibrations with the simple harmonic motion for the displacement. The 3D numerical model (6 degrees of freedom per node) uses Euler-Bernoulli beam equations in the axial, torsional and flexural...
This paper deals with the accuracy of several analytical models for the prediction of the hydrody... more This paper deals with the accuracy of several analytical models for the prediction of the hydrodynamic force and pressure distribution acting on a body entering initially calm water. The problem of water entry is important for the analysis of slamming loads undergone by boats operating in waves, as well as of the steady behaviour of high-speed planing vessels. The considered models are briefly described and the obtained results are compared to those of numerical computations and experimental observations for a number of two-dimensional and axisymmetric cases of water impact.
This paper presents a numerical and experimental study of fluid structure interaction during the ... more This paper presents a numerical and experimental study of fluid structure interaction during the impact of a solid body on a water surface. The main request is the modeling of the slamming forces acting on the ship structure in severe sea conditions. The numerical work uses the finite element modeling of a structure impact with free water surface. The first analysis use the commercial finite element code ABAQUS/Standard and combines the assumption of small displacements for the ideal fluid and the solid with an asymptotic formulation for accurate pressure evaluation on the boundary of the wet surface. For deformable strickers, two methods are developed. The first method employs a weak fluid-structure coupling. The second method, more accurate, uses an implicit fluid-structure coupling using a convergence criterion. The second analysis is represented by the simulations of slamming with ABAQUS/Explicit. The simulation uses a viscous, compressible fluid and a soft-exponential law to ma...
This paper presents a study of fluid structure interaction during the impact of a ship on a water... more This paper presents a study of fluid structure interaction during the impact of a ship on a water surface. The analysis combines the assumption of small displacements for the ideal fluid and the solid with an asymptotic formulation for accurate pressure evaluation on the wet surface boundary. A fluid-heat analogy is used to obtain the regular displacement, velocity and pressure fields in the fluid domain with ABAQUS/Standard finite element code. PYTHON and FORTRAN languages are also employed to connect fluid and structure data. Two methods are developed. The first method employs a weak fluid-structure coupling. The average discrepancy between our numerical results and experiments was 22% for the peak pressures for conical shell structures. The wet surface velocity was well predicted. The second method (implicit fluid-structure coupling using a convergence criterion) is more accurate. Recent results with an improved, numerical hydrodynamic model based on CFD are also presented.
HAL (Le Centre pour la Communication Scientifique Directe), 2013
Le titre de l'ouvrage associe à dessein deux termes contradictoires pour caractériser l'o... more Le titre de l'ouvrage associe à dessein deux termes contradictoires pour caractériser l'objet étudié : les matériaux, certes déformables, qui relèvent de l'état solide. Ce premier volume traite des seuls comportements linéaires de ces matériaux. Le livre étudie ainsi les matériaux constitutifs des structures du secteur industriel, supposés homogènes et isotropes, lorsque les champs de déplacement sont proportionnels aux chargements appliqués. L'étude débute par une méthode de caractérisation globale fondée sur une décomposition des structures en pièces élémentaires (théorie des mécanismes). Très souvent, industriellement, ces structures peuvent être schématisées géométriquement et mécaniquement par des poutres ou des plaques. Le livre présente donc, de manière assez exhaustive, la modélisation des assemblages de poutres droites soumises à tous les types de sollicitations (effort normal, effort tranchant, torsion et flexion) et à leurs combinaisons. La schématisation des plaques est également exposée. Quelques exercices corrigés illustrent les notions abordées. Dans sa présentation l'ouvrage adopte une approche suffisamment formelle pour ne pas constituer une simple collection de cas particuliers, tout en permettant au lecteur une applicabilité assez directe des méthodes exposées à des cas industriels concrets. Un second volume traite des approches non linéaires
HAL (Le Centre pour la Communication Scientifique Directe), 2017
GSEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage... more GSEA Design developed a fluid structure method (FSI) suitable for early design stage of appendage with complex shapes dedicated to the America's Cup flying catamarans. The aerodynamic loading and the boat weight are counteracted by the appendages and mainly the dagger-board. Consequently, the appendage structural design is very critical. Based on a 3D lifting line and a modified beam element method, the GSEA Design FSI method takes less than one minute to compute. An illustrating example on a L-shape appendage shows that the FSI results compared to a non-FSI results can be particularly different at the elbow. Thanks to the short computational time of the method, multi-objective optimizations can be performed. For instance, a second illustrating example shows the optimization of the appendage weight and stiffness.
High explosive hydro forming (HEHF) is a suitable technique for large metal plate forming. Manufa... more High explosive hydro forming (HEHF) is a suitable technique for large metal plate forming. Manufacturing stages of such a part requires an adapted design of explosive charge configurations to define the mechanical loading exerted on the part. This mechanical loading remains challenging to be experimentally determined but necessary for predictive numerical simulation in the design of parts to form. Providing that the actual mechanical impulse would allow the neglecting of the modelling of the detonation stage, this considerably increases the computational time. The present work proposes an experimental method for obtaining the exerted mechanical loading by HEHF on the part to form. It relies on the development of low-cost sensor based on a polyvinyliden fluorid (PVDF) gauge. In addition to it, an analytical approach based on shock physics is proposed for the sensor signal interpretation. The method considers the multi-layer aspect of the sensor and its intrusiveness with respect to w...
The use of traction kites as auxiliary propulsion systems for ships appears to be a high-potentia... more The use of traction kites as auxiliary propulsion systems for ships appears to be a high-potential alternative for fuel saving. To study such a system a tether model based on the catenary curve has been developed. This model allows calculating static flight positions of the kite on the edge of the wind window. The effect of the wind velocity gradient is taken into account for the evaluation of the aerodynamic forces acting on kite and tether. A closed-form expression is derived for the minimum wind velocity required for static flight of the kite. Results are presented for a kite with a surface area of 320 m 2 and a mass of 300 kg attached to a tether with a diameter of 55 mm and a mass per unit length of 1.20 kg m −1. The minimum wind speed measured at 10 m altitude to launch the kite is found to be around 4.5 m/s. After the launching phase, we show that the optimal tether length for static flight is 128.4 m with a minimum wind speed of 4.06 m/s. The presented approach shows an error up to 9% for a zero-mass kite model with a straight massless tether regarding the maximal propulsion force estimation.
References : [1] Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Comparison of 3D non-... more References : [1] Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Comparison of 3D non-linear lifting line method calculations with 3D RANSE simulations and application to the prediction of the global loading on a cornering kite. In: Proceedings of the 15th Journées de l’Hydrodynamique, Brest, France, 22-24 Nov 2016. [2] Solminihac A., Nême A., Duport C., Leroux J.-B., Roncin K., Jochum C., Parlier Y.: Kite as a Beam: A Fast Method to get the Flying Shape. In: Schmehl, R (eds) Airborne Wind Energy, Green Energy and Technology, Chap. 4, pp. 77-95. Springer (2018). [3] Duport C., Deberque M., Leroux J.-B., Roncin K., Jochum C.: Local results verification of a 3D non-linear lifting line method for Fluid-Structure interaction simulation on a towing kite for vessels. In: Proceedings of the 11th Symposium on High-Performance Marine Vehicles, Zevenwacht, South Africa, 11-13 Sep 2017. [4] Maison A., Nême A., Leroux J.-B.: De la problématique du dimensionnement de grands kites. In:...
The present work takes place in the framework of the "Jib Sea" project. The main purpose of the p... more The present work takes place in the framework of the "Jib Sea" project. The main purpose of the project is to develop a new sail design made of articulated composite panels, for large merchant ships. The French laboratory "ENSTA Bretagne, IRDL" is involved in this industrial project to provide its expertise on fluid-structure interactions modelling. A fast and robust approach to model fluidstructure interactions for yacht sails is presented. Specifically, interaction effects between the jib and the mainsail are taken into account in the flow model presented. This is achieved using the lifting-line theory combined with a discrete vortex method, involving distributions of lumped-vortex elements along sail sections. The flow model is coupled with a structural finite element software, using shell elements for the modelling of sail membranes, beam stringers for battens modelling and a quasi-static resolution based on a dynamic backward Euler scheme. Numerical comparisons with experiments are conducted on a 50 m² composite mainsail prototype and a conventional jib , built and hoisted on an onshore balestron rig. Measurements, such as strain gauges or cable tensions, are synchronized with a wind sensor. These data collected together enable both global and local numerical-experimental comparisons for forces and moments, providing a validation of the proposed fluid-structure interactions modelling of yacht sails. A good matching between experimental and numerical modelling is observed on local comparisons. Indeed, relative differences are all less than 25% for ∈ [−20; 20] and < 10 kn. Global comparison results exhibit validations with experiments for | | < 10 deg and < 10 kn, where numerical-experimental relative differences are less than 10%. 1. NOMENCLATURE Variation coefficient [−] Chord length [ ] Integration element [ ] Euler number [−] Force [ ] ℎ Batten height [ ] Imaginary number [−] , Index [−] Length [ ] Moment [. ] Number of element [−] Element for DVM [−] U Wind velocities [. −1 ] V Flow velocities [. −1 ] Complex velocity [. −1 ] Complex number [−] Angle for LLT [ ] Γ Global circulation [ 2. −1 ] Local vortex circulation [ 2. −1 ] Δ Pressure variation [. ] Δ Elongation [ ] Relative error [−] Local angle per element [ ] Mean [ ] or [. ] Standard deviation [ ] or [. ] 0 Density [. −3 ] Induced velocity [. −1 ] 〈 〉 Out-of-plane bending stiffness [. 2 ] Leading edge
This paper describes an experimental setup aiming to control and measure performances of small le... more This paper describes an experimental setup aiming to control and measure performances of small leading edge inflatable tube kites, with surface area of less than 35 m². This setup can be deployed either onshore or on a dedicated boat. This article focuses on the onshore results. A 3D load cell is used to obtain the position of the kite under a straightline assumption. A wind profiler (SODAR) is deployed to determine the wind speed and direction at the kite position. A specific post-processing of the data is presented, including phase averaging. The guideline of this work is to estimate the variation of the aerodynamic lift coefficient and lift to drag ratio along figure-of-eight trajectories. Results, for a chosen particular case, show a decrease of lift coefficient of about 20% of the maximum value during turning maneuvers of the kite. The lift to drag ratio evolution along a trajectory is also observed to go through a local minimum during turning maneuvers of the kite in this case. Influence of weight and inertia is highlighted introducing a point mass model of the kite and tethers. Buckling phenomena of the kite inflatable leading edge tube are highlighted and it is shown that they cause control problems.
International Journal of Structural Stability and Dynamics, 2020
This paper deals with the lateral buckling behavior of an axially compressed beam interacting wit... more This paper deals with the lateral buckling behavior of an axially compressed beam interacting with the ground on which it is resting. Such a simple model is supposed to reproduce the same trends as observed during the lateral buckling of offshore pipelines on the seabed. In such practical analyses, the pipe-soil interaction relies the ground to the neutral axis of the pipeline. It is shown that, although such a constraint significantly affects the buckling behavior of the pipeline, it can not reflect the torsional component of the buckling modes. However, this component is encountered in practice and may further modify the critical loads. Therefore, in the present preliminary study, the interaction between the beam in hand and the surrouding ground is modeled by a connection (a continuous distribution of lateral springs) related to the bottom line of the beam. In this way, the real contact between the soil and the bottom line of a pipe is mimicked, allowing for both flexural and torsional deformations in the buckling response. The problem is investigated analytically, using an Euler-Bernoulli beam model with an isotropic linear elastic constitutive law and also an elastic interaction law. Original analytical solutions are derived and compared to numerical results obtained through finite element computations. In comparison with classical solutions (with the connection related to the neutral axis), new types of buckling modes may appear when considering torsional effects, depending on the boundary conditions, with generally much lower critical loads. These first results are certainly representative of some features of the global/localized lateral buckling of offshore pipelines, indicating that torsional effects should also be taken into account in such more comprehensive analyses.
Designing new large kite wings requires engineering tools that can account for flow-structure int... more Designing new large kite wings requires engineering tools that can account for flow-structure interaction. Although a fully coupled simulation of deformable membrane structures under aerodynamic load is already possible using Finite Element and Computational Fluid Dynamics methods this approach is computationally demanding. The core idea of the present study is to approximate a leading edge inflatable tube kite by an assembly of equivalent beam elements. In spanwise direction the wing is partitioned into several elementary cells, each consisting of a leading edge segment, two lateral inflatable battens, and the corresponding portion of canopy. The mechanical properties of an elementary cell-axial, transverse shear, bending, and torsion stiffness-and the chordwise centroid position are determined from the response to several imposed elementary displacements at its boundary, in the case of a cell under an uniform pressure loading. For this purpose the cells are supported at their four corners and different non-linear finite element analyses and linear perturbation computations are carried out. The complete kite is represented as an assembly of equivalent beams connected with rigid bodies. Coupled with a 3D non-linear lifting line method to determine the aerodynamics this structural model should allow predicting the flying shape and performance of new wing designs.
A dynamic kite flight can affect ship motions. Ship equations of motion associated with the analy... more A dynamic kite flight can affect ship motions. Ship equations of motion associated with the analytical zero-mass kite model are developed. Aiming a realistic amplitude modeling of the kite excitation, a linear modification of the aerodynamic kite specs with the turning rate of the kite velocity heading is proposed. A good agreement with experimental data is obtained. Equations of motion are solved on a reaching path alternatively with a weak and a strong coupling between the ship and the kite. Differences between the two coupling methods become significant when a harmonic of the kite excitation approaches the natural roll frequency of the ship. For the presented case of study, these critical conditions can be avoided with longer tethers or larger kite trajectories.
Modélisation de l'impact balistique sur cloisons métalliques de bâtiments de surface
L'une des missions de l'entite DGA/DCE/GERBAM est l'etude de la vulnerabilite des bât... more L'une des missions de l'entite DGA/DCE/GERBAM est l'etude de la vulnerabilite des bâtiments de surface aux missiles. Nos travaux contribuent a la substitution de campagnes d'essais couteuses par des simulations numeriques permettant l'identification de lois de vulnerabilite empiriques plus globales. En particulier, nous souhaitons predire lors de l'impact d'eclats metalliques sur plaques metalliques, la perforation ou la non perforation de la cible ainsi que la fragmentation du projectile et de la cible. Nous choisissons de representer ces phenomenes de rupture par des conditions de perte d'unicite de la solution en vitesse (bifurcation) dans l'equilibre thermomecanique (Neme et Dahan, 1995). Ce critere de rupture a l'avantage de ne pas faire intervenir de parametre specifique (e.g. un endommagement critique) devant etre identifie sur des experimentations appropriees. Dans notre etude concernant les problemes d'impact, les effets de la vitesse de deformation sont preponderants. Ceux-ci sont classiquement pris en compte en utilisant une loi elastoviscoplastique de type unifie (e.g. Johnson-Cook). Dans ces conditions, le critere de bifurcation associe ne fait intervenir que les caracteristiques elastiques du materiau. Par contre l'utilisation d'un comportement (Thermo) Elastique Plastique Viscoplastique (TEPV) permet d'obtenir un critere de bifurcation faisant intervenir les caracteristiques plastiques et viscoplastiques du materiau. Cette nouvelle loi TEPV est proposee a l'instar de travaux anterieurs (Cailletaud et Sai, 1995) portant sur l'interaction plasticite-viscoplasticite en fluage. Deux variables thermodynamiques sont introduites, traduisant l'influence respective des dislocations bloquees et mobiles sur la deformation inelastique macroscopique. La somme de ces deux variables represente la deformation plastique totale. Notre formulation en grande transformation utilise le taux de deformation tourne dans le repere corotationnel D=q -1 D q. Nous faisons l'hypothese de decomposition du taux de deformation en part elastique, plastique, viscoplastique et thermique. L'introduction d'un parametre c dependant de la temperature et compris entre 0 et 1, permet de transcrire l'influence relative des dislocations bloquees et libres sur la deformation plastique macroscopique induite. D = D e + (1 - c)D p + cD vp + αT1 La plasticite (Dp) ainsi que la viscoplasticite (D vp ) sont associees au sens de Von Mises. D'autre part, une approche thermodynamique specifique basee sur le postulat d'une dissipation massique positive est developpee (Quirion et Neme, 2002). Elle conduit a une expression du coefficient de conversion de la puissance plastique en chaleur assez complexe et en general non constante. Un modulateur plastique est introduit dans l'expression du taux de dissipation intrinseque permettant de mieux calibrer le couplage thermomecanique.
Nowadays, noise and vibration problems tend to become an important part of the design process in ... more Nowadays, noise and vibration problems tend to become an important part of the design process in the naval industry. Vibrations often affect the passengers comfort, but more dangerously may damage the structure, embarked merchandise and equipments. A simple way to avoid vibrations is to prevent the resonance conditions. The paper presents a study about the vibration of local structures (beam structures and stiffened panels) with application in the marine industry. The model has been implemented in FORTRAN into a numerical module and will be integrated in the near future with the LBR-5 generic stiffened structure optimization code.
Nowadays, noise and vibration problems tend to become an important part of the design process in ... more Nowadays, noise and vibration problems tend to become an important part of the design process in the automotive and naval industries. Vibrations often affect the passengers comfort, but more dangerously may damage the structure, embarked merchandise and equipments. A simple way to avoid vibrations is to prevent the resonance conditions. The paper presents a study about the vibration of beam structures and stiffened panels. The main application is to determine the eigenfrequencies of structures like platforms, trailer chassis and as well as stiffened shell -beam assemblies. The research work covers analytical vibration modeling of 3D beam structures and 3D stiffened shells, as well as the finite element analyses necessary for the validation. The analysis combines the assumption of undamped free vibrations with the simple harmonic motion for the displacement. The 3D numerical model (6 degrees of freedom per node) uses Euler-Bernoulli beam equations in the axial, torsional and flexural...
This paper deals with the accuracy of several analytical models for the prediction of the hydrody... more This paper deals with the accuracy of several analytical models for the prediction of the hydrodynamic force and pressure distribution acting on a body entering initially calm water. The problem of water entry is important for the analysis of slamming loads undergone by boats operating in waves, as well as of the steady behaviour of high-speed planing vessels. The considered models are briefly described and the obtained results are compared to those of numerical computations and experimental observations for a number of two-dimensional and axisymmetric cases of water impact.
This paper presents a numerical and experimental study of fluid structure interaction during the ... more This paper presents a numerical and experimental study of fluid structure interaction during the impact of a solid body on a water surface. The main request is the modeling of the slamming forces acting on the ship structure in severe sea conditions. The numerical work uses the finite element modeling of a structure impact with free water surface. The first analysis use the commercial finite element code ABAQUS/Standard and combines the assumption of small displacements for the ideal fluid and the solid with an asymptotic formulation for accurate pressure evaluation on the boundary of the wet surface. For deformable strickers, two methods are developed. The first method employs a weak fluid-structure coupling. The second method, more accurate, uses an implicit fluid-structure coupling using a convergence criterion. The second analysis is represented by the simulations of slamming with ABAQUS/Explicit. The simulation uses a viscous, compressible fluid and a soft-exponential law to ma...
This paper presents a study of fluid structure interaction during the impact of a ship on a water... more This paper presents a study of fluid structure interaction during the impact of a ship on a water surface. The analysis combines the assumption of small displacements for the ideal fluid and the solid with an asymptotic formulation for accurate pressure evaluation on the wet surface boundary. A fluid-heat analogy is used to obtain the regular displacement, velocity and pressure fields in the fluid domain with ABAQUS/Standard finite element code. PYTHON and FORTRAN languages are also employed to connect fluid and structure data. Two methods are developed. The first method employs a weak fluid-structure coupling. The average discrepancy between our numerical results and experiments was 22% for the peak pressures for conical shell structures. The wet surface velocity was well predicted. The second method (implicit fluid-structure coupling using a convergence criterion) is more accurate. Recent results with an improved, numerical hydrodynamic model based on CFD are also presented.
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