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PEOPLE@HES-SO – Annuaire et Répertoire des compétences
PEOPLE@HES-SO – Annuaire et Répertoire des compétences

PEOPLE@HES-SO
Annuaire et Répertoire des compétences

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Blecha Luc

Blecha Luc

Professeur Hes associé

Compétences principales

System Engineering

Dynamique des structures

Mécanique des fluides

Mechanisms for Space

Mécanismes compliants

ingénierie navale

Mobilité électrique

  • Contact

  • Enseignement

  • Publications

  • Conférences

Contrat principal

Professeur Hes associé

Téléphone: +41 24 557 62 71

Haute école d'Ingénierie et de Gestion du Canton de Vaud
Route de Cheseaux 1, 1400 Yverdon-les-Bains, CH
HEIG-VD
BSc HES-SO en Systèmes industriels - Haute école d'Ingénierie et de Gestion du Canton de Vaud
  • Résistance des matériaux 2
  • Conception
BSc HES-SO en Microtechniques - Haute école d'Ingénierie et de Gestion du Canton de Vaud
  • Résistance des matériaux
BSc HES-SO en Ingénierie et gestion industrielles - Haute école d'Ingénierie et de Gestion du Canton de Vaud
  • Elements de machines

2023

The geometric albedo of the hot Jupiter HD 189733b measured with CHEOPS
Article scientifique ArODES

A. F. Krenn, M. Lendl, J. A. Patel, L. Carone, M. Deleuil, Luc Blecha

Astronomy & Astrophysics,  672, A24

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Résumé:

Context. Measurements of the occultation of an exoplanet at visible wavelengths allow us to determine the reflective properties of a planetary atmosphere. The observed occultation depth can be translated into a geometric albedo. This in turn aids in characterising the structure and composition of an atmosphere by providing additional information on the wavelength-dependent reflective qualities of the aerosols in the atmosphere. Aims. Our aim is to provide a precise measurement of the geometric albedo of the gas giant HD 189733b by measuring the occultation depth in the broad optical bandpass of CHEOPS (350–1100 nm). Methods. We analysed 13 observations of the occultation of HD 189733b performed by CHEOPS utilising the Python package PyCHEOPS. The resulting occultation depth is then used to infer the geometric albedo accounting for the contribution of thermal emission from the planet. We also aid the analysis by refining the transit parameters combining observations made by the TESS and CHEOPS space telescopes. Results. We report the detection of an 24.7 ± 4.5 ppm occultation in the CHEOPS observations. This occultation depth corresponds to a geometric albedo of 0.076 ± 0.016. Our measurement is consistent with models assuming the atmosphere of the planet to be cloud-free at the scattering level and absorption in the CHEOPS band to be dominated by the resonant Na doublet. Taking into account previous optical-light occultation observations obtained with the Hubble Space Telescope, both measurements combined are consistent with a super-stellar Na elemental abundance in the dayside atmosphere of HD 189733b. We further constrain the planetary Bond albedo to between 0.013 and 0.42 at 3σ confidence. Conclusions. We find that the reflective properties of the HD 189733b dayside atmosphere are consistent with a cloud-free atmosphere having a super-stellar metal content. When compared to an analogous CHEOPS measurement for HD 209458b, our data hint at a slightly lower geometric albedo for HD 189733b (0.076 ± 0.016) than for HD 209458b (0.096 ± 0.016), or a higher atmospheric Na content in the same modelling framework. While our constraint on the Bond albedo is consistent with previously published values, we note that the higher-end values of ~0.4, as derived previously from infrared phase curves, would also require peculiarly high reflectance in the infrared, which again would make it more difficult to disentangle reflected and emitted light in the total observed flux, and therefore to correctly account for reflected light in the interpretation of those phase curves. Lower reported values for the Bond albedos are less affected by this ambiguity.

2010

Mechanical interaction between cells and fluid for bone tissue engineering scaffold :
Article scientifique ArODES
modulation of the interfacial shear stress

Luc Blecha, L. Rakotomanana, F. Razafimahery, A. Terrier, D. P. Pioletti

Journal of Biomechanics,  43, 5, 933-937

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Résumé:

An analytical model of the fluid/cell mechanical interaction was developed. The interfacial shear stress, due to the coupling between the fluid and the cell deformation, was characterized by a new dimensionless number Nfs. For Nfs above a critical value, the fluid/cell interaction had a damping effect on the interfacial shear stress. Conversely, for Nfs below this critical value, interfacial shear stress was amplified. As illustration, the role of the dynamic fluid/cell mechanical coupling was studied in a specific biological situation involving cells seeded in a bone scaffold. For the particular bone scaffold chosen, the dimensionless number Nfs was higher than the critical value. In this case, the dynamic shear stress at the fluid/cell interface is damped for increasing excitation frequency. Interestingly, this damping effect is correlated to the pore diameter of the scaffold, furnishing thus target values in the design of the scaffold. Correspondingly, an efficient cell stimulation might be achieved with a scaffold of pore size larger than 300 μm as no dynamic damping effect is likely to take place. The analytical model proposed in this study, while being a simplification of a fluid/cell mechanical interaction, brings complementary insights to numerical studies by analyzing the effect of different physical parameters.

2009

Targeted mechanical properties for optimal fluid motion inside artificial bone substitutes
Article scientifique ArODES

Luc Blecha, L. Rakotomanana, F. Razafimahery, A. Terrier, D.P. Pioletti

Journal of Orthopaedic Research,  27, 8, 1082-1087

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Résumé:

Our goal was to develop a method to identify the optimal elastic modulus, Poisson's ratio, porosity, and permeability values for a mechanically stressed bone substitute. We hypothesized that a porous bone substitute that favors the transport of nutriments, wastes, biochemical signals, and cells, while keeping the fluid-induced shear stress within a range that stimulates osteoblasts, would likely promote osteointegration. Two optimization criteria were used: (i) the fluid volume exchange between the artificial bone substitute and its environment must be maximal and (ii) the fluid-induced shear stress must be between 0.03 and 3 Pa. Biot's poroelastic theory was used to compute the fluid motion due to mechanical stresses. The impact of the elastic modulus, Poisson's ratio, porosity, and permeability on the fluid motion were determined in general and for three different bone substitute sizes used in high tibial osteotomy. We found that fluid motion was optimized in two independent steps. First, fluid transport was maximized by minimizing the elastic modulus, Poisson's ratio, and porosity. Second, the fluid-induced shear stress could be adjusted by tuning the bone substitute permeability so that it stayed within the favorable range of 0.03 to 3 Pa. Such method provides clear guidelines to bone substitute developers and to orthopedic surgeons for using bone substitute materials according to their mechanical environment.

2005

How plate positioning impacts the biomechanics of the open wedge tibial osteotomy :
Article scientifique ArODES
A finite element analysis

Luc Blecha, P. Y. Zambelli, N. A. Ramaniraka, P. - E. Bourban, J. - A. Manson, D. P. Pioletti

Computer Methods in Biomechanics and Biomedical Engineering,  8, 5, 307-313

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Résumé:

A numerical model of the medial open wedge tibial osteotomy based on the finite element method was developed. Two plate positions were tested numerically. In a configuration, (a), the plate was fixed in a medial position and (b) in an anteromedial position. The simulation took into account soft tissues preload, muscular tonus and maximal gait load. The maximal stresses observed in the four structural elements (bone, plate, wedge, screws) of an osteotomy with plate in medial position were substantially higher (1.13–2.8 times more) than those observed in osteotomy with an anteromedial plate configuration. An important increase (1.71 times more) of the relative micromotions between the wedge and the bone was also observed. In order to avoid formation of fibrous tissue at the bone wedge interface, the osteotomy should be loaded under 18.8% (∼50 kg) of the normal gait load until the osteotomy interfaces union is achieved.

2021

Miniaturised stepper motor for space applications
Conférence ArODES

Simon Hayoz, Luc Blecha, Sandro Liberatoscioli, Fabrice Rottmeier, Thomas Würgler, Majid Charif, Asier Martinez

Proceedings of the 19th European Space Mechanisms and Tribology Symposium (ESMATS 2021)

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Résumé:

The development of the smallSats industry and the novel variety of on-boards instruments lead more and more to a miniaturisation of the space mechanisms. In addition to the smaller size, the reduction of the cost and the time to the market became primary objectives for recurring components used in space systems. With this variety of new applications, stepper motors are also more widely used as they bring key features such as powered and unpowered holding torque as well as accurate positioning using step count and open-loop control drastically reducing system complexity and costs. After a thorough review of stepper motors compatible for space applications, an important lack of product availability was found in the small size range, especially on the European market. Therefore, throughout its harmonisation dossier, European Space Agency (ESA) would like to increase the family of available stepper motors compatible with space environment.

2020

Micro-vibration attenuation using novel flexible pivot design
Conférence ArODES

Luc Blecha, Yoël Puyol, Simon Hayoz, Martin Humphries, Fabrice Rottmeier

Proceedings of the 45th Aerospace Mechanisms Symposium

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Résumé:

Flexible pivots present numerous advantages such as no wear, no particle generation and predictable torque. In addition, the patented design presented in this paper adds high stiffness tunability, large angle, nearly constant radial stiffness over the entire range of motion, and infinite life capability. A design optimization software has been developed to generate within a few hours custom flexible pivot designs matching specific application requirements such as pivot angle, torsional, radial, axial, bending stiffness, maximal stress, and buckling factors. The flexible pivot design is an enabling technology for many applications and in particular for ultra-stable pointing mechanisms. A novel concept of an ultra-stable pointing mechanism using a flexible pivot is presented. It is shown with a simple Nastran model that the micro-vibration impact on pointing mirror stability can be theoretically decreased by 3 to 8 orders of magnitude in the 50-200 Hz frequency range, and by more than 9 orders of magnitude above 200 Hz in comparison with a design using ball bearings. The achieved pointing accuracy makes the need of a fine pointing mechanism unnecessary. The total mass, volume and costs can thus be drastically reduced in comparison to the existing solution today on the market that uses coarse and fine pointing mechanisms. A fully functional and motorized breadboard has been built and showed full hemispherical pointing range.

2019

Innovation in large angle flexible pivot design and material accelerated fatigue screening test results
Conférence ArODES

Yoël Puyol, Luc Blecha, Martin Humphries, Simon Hayoz, Fabrice Rottmeier

Proceedings of the 18th European Space Mechanisms and Tribology Symposium (ESMATS 2019)

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Résumé:

In the last decades, more and more space applications required actively controlling the orientation of certain devices like scanning mirrors, antennas, calibration units mounted on satellites and spacecraft. The benefit of using compliant mechanisms for such applications is multiple. First, frictionless flexible joints present no generation of wear particles and do not require lubrication which allows to use flexures near optical surfaces. Second, lifetime including long time storage can be extended to infinite as material is used below its infinite fatigue limit. Third, micro-vibration can be damped by tuning the stiffness of the flexure to obtain first eigenfrequency of the system far below micro-vibration excitation frequencies. Finally, compliant joints accommodate easily thermo-elastic constraints between the surrounding structure and the supported payload. Flexible pivots are therefore most often the retained choice in the context of long life, clean and precise applications for space applications. The AlmaFlex is a novel flexure design family that has been invented and patented by Almatech SA. The pivot design has been further developed in the frame of the associated Core Technology Program (CTP) which led to the Large Angle Flexible Pivot (LAFP): a flexible pivot capable of ±70° rotations for infinite life in cryogenic conditions while maintaining the centre shift below 10μm and keeping actuation torque in the Newton meter range. To achieve targeted performances, efforts have been set on design optimization, material selection, manufacturing processes and post-treatments. This paper presents the design of the LAFP, its optimization process as well as the accelerated fatigue test results performed on an extensive selection of test samples. The Almaflex design is based on pure bending deformations of blades. The flexure consists in two symmetric identical rings, a rotor and stator mounted on a synchronizing ring. Each stage comprises a set of four blades plus T-bars connecting the ring to its center which is then connected to the synchronizing ring via connecting members also using T-bars. Larger angular ranges can also be obtained by using additional stages. This design allows very good decoupling between each DoF which is particularly useful for stiffness optimization considering in-orbit operations, launch locking, gravity sag adjustments, thermo-elastic aspects...

2016

Analytical optimization and test validation of the submicron dimensional stability of the CHEOPS space telescope's CFRP structure
Conférence ArODES

Luc Blecha, D. Zindel, H. Cottard, T. Beck, V. Cessa, C. Broeg, F. Ratti, N. Rando

Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II

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Résumé:

The CHEOPS (CHaracterising ExOPlanet Satellite), which is an ESA mission developed in cooperation with Switzerland and a number of other member-states, is the first one dedicated to search for transits by means of ultrahigh precision photometry on bright stars already known to host planets. The optical design is based on a Ritchey-Chretien style telescope to provide a de-focussed image of the target stars. The telescope’s mirrors M1, M2 as well as the focal plane detector are supported by a thermally controlled CFRP structure suspended on isostatic mounts. The dimensional stability of the structural system supporting the optics is a key requirement as it directly impacts the instrument’s accuracy. The M1 and M2 mirrors are supported by a tubular CFRP telescope design which has been optimized by analyses down to carbon fibre layer level with the support of extensive sample test results for model correlation and accurate dimensional stability predictions. This sample characterization test campaign has been conducted on samples with different carbon fibre layups (orientation and stack sequence) to measure accurately the Coefficient of Thermal Expansion (CTE) over a wide temperature range extending from -80°C to +80°C. Using the correlated Finite Element Model, the fibre orientation layup that minimized the relative displacement between the M1 and M2 mirrors, including the consideration of the thermo-elastic contributions of the isostatic mounts on the overall stability of this optical system, has been identified and selected for the baseline design of the CHEOPS Structure. A dedicated Structural and Thermal Model (STM2), which was then refurbished to a PFM, was manufactured and tested with an ad hoc setup to verify the overall structural stability of the optical train assembly [2]. The relative distance between M1 and M2 was measured under thermal vacuum conditions using laser interferometer techniques. Thermal cycling tests were initially conducted to eliminate and characterize settling effects. Then, the structure’s stability was measured at three stabilised operational temperatures: -5, -10 and -15°C. The thermally induced M1-M2 misalignment on the optical axis was measured to be between -0.156 and -0.168 micron/°C. Relative mirror tilt and lateral centre shifts were also measured. The obtained focal distance, tilt and centre shift stability between mirrors M1 and M2 were all compliant with the system level requirements such that both an STM and PFM model of the CHEOPS CFRP Structure were successfully qualified and delivered in due time for integration on the spacecraft.

Development and testing of a high-precision position and attitude measuring system for a space mechanism
Conférence ArODES

Gabriel Paciotti, Jacques-Eric Bidaux, Hervé Girard, Fabrice Rottmeier, Luc Blecha

Proceedings of the 43rd Aerospace Mechanisms Symposium, 4-6 May 2016, Santa Clara, CA, USA

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Résumé:

Pyrovalves, i.e., valves actuated by a pyrotechnical device, are very often used in space propulsion systems for their fast response, high reliability, low mass and low cost. However, they are hazardous and single use items. Their operation induces shocks and can generate contaminants. If a slower actuation is required or possible, shape memory-based actuators avoid the generation of shocks and contaminants while being fully resettable and non-hazardous devices. The goal of this project was to develop a bi-stable Shape Memory Alloy (SMA) actuator for a specific Slow Acting Latch Valve with long life capability. The benefits of this actuator makes it interesting not only for valve actuation but also for any device that has to be actuated in a smooth and reliable way. This paper presents the development of a bi-stable actuator based on high temperature shape memory alloys.

Development and testing of a bi-stable actuator based on a high transition temperature shape memory alloy
Conférence ArODES

Gabriel Paciotti, Jacques-Eric Bidaux, Hervé Girard, Fabrice Rottmeier, Luc Blecha

Proceedings of the 43rd Aerospace Mechanisms Symposium

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Résumé:

Pyrovalves, i.e., valves actuated by a pyrotechnical device, are very often used in space propulsion systems for their fast response, high reliability, low mass and low cost. However, they are hazardous and single use items. Their operation induces shocks and can generate contaminants. If a slower actuation is required or possible, shape memory-based actuators avoid the generation of shocks and contaminants while being fully resettable and non-hazardous devices. The goal of this project was to develop a bi-stable Shape Memory Alloy (SMA) actuator for a specific Slow Acting Latch Valve with long life capability. The benefits of this actuator makes it interesting not only for valve actuation but also for any device that has to be actuated in a smooth and reliable way. This paper presents the development of a bi-stable actuator based on high temperature shape memory alloys.

2015

Design and dynamic optimization of a tristable x-ray attenuator mechanism for the STIX instrument
Conférence ArODES

M. Lai, Fabrice Rottmeier, Martin Humphries, Luc Blecha

Proceedings of the 16th European Space Mechanisms and Tribology Symposium (ESMATS 2015)

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Résumé:

The STIX (Spectrometer/Telescope for Imaging X-rays) instrument on the ESA Solar Orbiter satellite is designed to study the Sunrays emissions. The wide energy range of incident X-ray fluxes, expected during the solar flares, requires the incorporation of a moveable X-ray attenuator covering and uncovering the instrument detectors depending on X-ray fluxes intensity. In the frame of the STIX Detector Module Prime Contract with ESA, Almatech has designed an attenuator mechanism provided with 2 end-strokes and 1 neutralmid- stroke stable positions. In particular, the two stable end-stroke positions avoid the use of a dedicated launchlock device to reduce complexity, lower the total mass while increasing the system reliability, all in the same time. Flexures as well as end-position switches are used as accelerator/decelerator devices in the mechanism. A cam-shaped switch trigger design allows the optimization of their dynamic contributions in the system. This article first presents the design of the STIX Attenuator Mechanism and then focuses on presenting the optimization of its dynamic response that plays a major role in the limitation of exported force, micro vibrations and torque to the spacecraft on one hand, as well as on the required actuation power on the other hand.

2014

Development and preliminary testing of a high precision long stroke slit change mechanism for the SPICE instrument
Conférence ArODES

Gabriel Paciotti, Martin Humphries, Fabrice Rottmeier, Luc Blecha

Proceedings of the 42nd Aerospace Mechanisms Symposium

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Résumé:

In the frame of ESA’s Solar Orbiter scientific mission, Almatech has been selected to design, develop and test the Slit Change Mechanism of the SPICE (SPectral Imaging of the Coronal Environment) instrument. In order to guaranty optical cleanliness level while fulfilling stringent positioning accuracies and repeatability requirements for slit positioning in the optical path of the instrument, a linear guiding system based on a double flexible blade arrangement has been selected. The four different slits to be used for the SPICE instrument resulted in a total stroke of 16.5 mm in this linear slit changer arrangement. The combination of long stroke and high precision positioning requirements has been identified as the main design challenge to be validated through breadboard models testing. This paper presents the development of SPICE’s Slit Change Mechanism (SCM) and the two-step validation tests successfully performed on breadboard models of its flexible blade support system.

2012

The STEAMR instrument :
Conférence ArODES
optical design, development & testing

Mark Whale, Matthias Renker, Axel Murk, Urban Frisk, Olle Janson, Luc Blecha, Gabriel Paciotti, Graham Bell, Richard Wylde, Anthony Murphy

Proceedings of the 23rd International Symposium on Space Terahertz Technology 2012 (ISSTT 2012)

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Résumé:

The STEAMR instrument is a Swedish national contribution to the ESA PREMIER mission, which is a candidate for the upcoming Earth Core Explorer mission. The STEAMR instrument is envisaged as a multi-beam limb sounding satellite, which will utilise 14 simultaneously observing beams in two 12 GHz wide bands from 323 to 357 GHz. To maximize spatial sampling in the elevation direction the observing beams have an elliptical geometry, which defines the incoming beams as being astigmatic. In this paper we present an antenna optics scheme which corrects for this inherent astigmatism, thereby ensuring optimum imaging of the incoming to the circularly symmetric receiver feed horns. Furthermore, the design, synthesis and electromagnetic verification of a prototype focal plane array for the STEAMR instrument is also reported.

2010

A novel tool to compute the non-linear dynamic behavior of an hydrofoil sailing yacht
Conférence ArODES

Joël Cugnoni, Davy Moyon, Stéphane Dyen, Luc Blecha

Proceedings of the second international conference on innovation in high performance sailing yachts

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Résumé:

This article presents a novel method to compute in an efficient way, the coupled fluid-structure non-linear behaviour of hydrofoil sailing yacht. A parametric model of the pressure exerted by the fluid on the hydrofoil is determined from steady state 3D fluid simulation taking into account free surface and cavitation. The fluid pressure is applied to a calibrated structural model taking into account the local and global structure deformation impacting the local angle of attack and fluid velocity. This tool was used to compute the maximal stress in the linking arm of the Hydroptere when sailing on flat water and in wave conditions. Non-linear and transient behaviour of the structure is found to significantly impact the maximal stress in the structure.

2006

Dynamic shear stress at cell's membrane is governed by mechanical interaction between fluid and cell
Conférence ArODES

Luc Blecha, L. Rakotomanana, F. Razafimahery, P. - Y. Zambelli, D. P. Pioletti

Journal of Biomechanics

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