Papers by Christian Jochum
HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2020
This paper describes an onboard measurement campaign held in Grande-Riviere, Gaspesie, province o... more This paper describes an onboard measurement campaign held in Grande-Riviere, Gaspesie, province of Quebec, Canada, in October 2015, involving a 13-meter trawler equipped with a 50-square-meter kite. The aim of the campaign was the assessment of the boat performances when kite is used. To achieve this purpose, in addition to the kite control system, a set of sensors has been installed. Thus data were recorded, as boat velocity, force generated by kite, fuel consumption, boat attitude, torque and rotational speed of propeller shaft, rudder angle and wind velocity. During the trials, runs with kite in static flight were done, with around 12 knots of true wind speed. The data post processing is presented in this paper, and allows to estimate a lift to drag ratio around 6 of the kite and the tethers. This is consistent with other experimental data published.
HAL (Le Centre pour la Communication Scientifique Directe), 2017
HAL (Le Centre pour la Communication Scientifique Directe), Jul 3, 2017
International audienceThis paper describes an on board measurement campaign held in Grande-Rivièr... more International audienceThis paper describes an on board measurement campaign held in Grande-Rivière, Gaspésie, Province of Québec, Canada, in October 2015, involving a 13-meter trawler equipped with a 50-square-meter kite. The aim of the campaign was to access the boat performance when the kite is used for auxiliary propulsion. To achieve this purpose, in addition to the kite control system, a set of sensors was installed. During the trials, runs with kite in static flight were done, with around 12 knots of true wind speed. The data post processing is presented in this paper, and allows an estimate of the lift coefficient and the lift to drag ratio of the kite and the tethers. The collected data are consistent with other experimental data published.Cet article décrit une campagne de mesure en mer réalisée sur un chalutier de 13 mètres équipé d'un kite de 50 mètres carrés. Cette campagne s'est déroulée à Grande Rivière, Gaspésie, Province de Québec, Canada, en octobre 2015. Le...
A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulen... more A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulence measurements over a 36-h period at a highly energetic tidal energy site in Alderney Race. This system enables the evaluation of the six components of the Reynolds stress tensor throughout a large proportion of the water column. The present study provides mean vertical profiles of the velocity, the turbulence intensity and the integral lengthscale along the streamwise, spanwise and vertical direction of the tidal current. Based on our results and considering a tidal-stream energy convertor (TEC) aligned with the current main direction, the main elements of turbulence prone to affect the structure (material fatigue) and to alter power generation would likely be: (i) the streamwise turbulence intensity (I<sub>x</sub>), (ii) the shear stress, <i>v</i>′<i>w</i>′, (iii) the normal stress, <i>u</i>′<sup>2</sup> and (iv) the vertical...
Ocean Engineering, 2021
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
Journal of Sailing Technology, 2018
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.
Green Energy and Technology, 2018
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.
Materialwissenschaft und Werkstofftechnik, 2016
The use of thick carbon fibre reinforced thermosets appears recently for naval and offshore effic... more The use of thick carbon fibre reinforced thermosets appears recently for naval and offshore efficient design. However internal residual stresses are developed during the curing of thermosets, as shown by defects like fibre wavinesses, cracks and bubbles, especially with increasing thickness. The understanding of phenomena involved during the curing of thick epoxy was described in a previous work by a by a finite element modeling of the thermal, chemical and mechanical couplings . To enable a better quality control, pulsed lasers have recently been used in non‐destructive inspection and characterization of composites and enable quality comparison from a reference stress free sample [2]. The experimental set‐up of the laser shock technique was assessed by simulation approach. Description of material parameters required is presented in the first part of the paper, based on previous experiments and models to identify material parameters for any degree of cure, assuming a dependency to the degree of cure only at room temperature. In this framework, this study presents the effects of epoxy heterogeneity, induced by the curing process of a thick matrix, for internal stress level and damage prediction. The plasticity of the matrix was described by a Ramberg‐Osgood model and an hydrodynamic constitutive law. As a first approach, a simple cut‐off fracture model based on the maximal tensile stress is used to identify the weakest parts of the solid matrix. Simulation comparison with a homogeneous fully cured stress free sample enables a first average residual stress level estimation.
Composite Structures, 2012
Long fibre laminate compressive failure is due to a microbuckling instability which leads to a ki... more Long fibre laminate compressive failure is due to a microbuckling instability which leads to a kink band and a brittle failure of the fibres. This failure mechanism is well known, but more or less pertinently explained in the literature. Some references also showed that local microbuckling instability depends on parameters that belong to the scale of the elementary ply, like thickness and corresponding lay-up. The compressive strength of the unidirectional ply is therefore no more an intrinsic material property, but results from a structural effect of the design. In this paper, the so-called ''structure effect'' is included in a simple way as an analytical formula in the phenomenological compressive failure criterion which was initially presented by Budiansky and Fleck works. The criterion presented is expressed analytically for unidirectional composite and stands for the local compressive failure strength at ply scale in fibres direction.
Improved Performance of Materials, 2017
Although the mechanical behavior of various types of laminated wood has been already explored in ... more Although the mechanical behavior of various types of laminated wood has been already explored in the literature [1, 2], there is still a lack about static and dynamic testing and modeling approaches of the plywood. This study aims to describe a plywood composed of 10 layers of beech glued together with a melamine-urea-formaldehyde resin. Tests were performed on samples from two wood boards with different stacking sequences. The experimental data presented are provided from tensile tests performed in both fiber and transverse directions, out of plane compression tests, as well as dynamic tests in particular the Taylor gun test and the Hopkinson bar. This paper proposes three models based on composite theories to simulate the static behavior of plywood. An application to the finite element method to simulate the static tensile and compression tests is presented. The comparisons between experimental data and the models' results reveal that a plywood can be modeled as single block of a homogeneous anisotropic equivalent material whose properties are estimated following the rule of mixtures and classical laminate theory.
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulen... more A system of two coupled four-beam acoustic Doppler current profilers was used to collect turbulence measurements over a 36-h period at a highly energetic tidal energy site in Alderney Race. This system enables the evaluation of the six components of the Reynolds stress tensor throughout a large proportion of the water column. The present study provides mean vertical profiles of the velocity, the turbulence intensity and the integral lengthscale along the streamwise, spanwise and vertical direction of the tidal current. Based on our results and considering a tidal-stream energy convertor (TEC) aligned with the current main direction, the main elements of turbulence prone to affect the structure (material fatigue) and to alter power generation would likely be: (i) the streamwise turbulence intensity ( I x ), (ii) the shear stress, v ′ w ′ ¯ , (iii) the normal stress, u ′ 2 ¯ and (iv) the vertical integral lengthscale ( L z ). The streamwise turbulence intensity, ( I x ), was found to ...
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Papers by Christian Jochum