References of "Golinval, Jean-Claude"
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See detailExperimental techniques for ballistic pressure measurements and recent development in means of calibration
Elkarous, Lamine ULg; Coghe, Frederik; Pirlot, Marc et al

in Journal of Physics: Conference Series (2013), 459

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See detailA Methodology for The Appropriation And The Isolation of Nodal Diameter Modes in Cyclic Symmetric Structures
Nyssen, Florence ULg; Viguié, Régis; Simon, Daniel et al

in Proceedings of ASME 2013 International Design Engineering Technical Conference & Computers and Information in Engineering Conference IDETC/CIE 2013 (2013, August)

This paper presents a methodology enabling the appropriation and the isolation of a chosen nodal diameter modes in cyclic symmetric structures. In particular, a study about the minimum number and the ... [more ▼]

This paper presents a methodology enabling the appropriation and the isolation of a chosen nodal diameter modes in cyclic symmetric structures. In particular, a study about the minimum number and the optimized location of the excitation sources required in laboratory conditions to isolate a specific nodal diameter mode is conducted. This work includes a theoretical approach based on energy concepts. It is followed by the numerical and experimental validations on a stator stage of an axial compressor. The concept of modal appropriation is investigated here as the first step of the calibration procedure before engine tests. [less ▲]

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See detailDamage detection in composites by vibrothermography and local resonances
Demy, Philippe ULg; Golinval, Jean-Claude ULg; Simon, Daniel

in Mechanics & Industry (2013), 14(2), 137-143

Vibrothermography is an active thermographic technique able to detect singularities like delamination in composite materials. Carbon fibre laminates are increasingly used, especially in aviation industry ... [more ▼]

Vibrothermography is an active thermographic technique able to detect singularities like delamination in composite materials. Carbon fibre laminates are increasingly used, especially in aviation industry where defect detection is directly related to safety. Physical causes of the internal heating mechanism linked to defect interaction with the elastic waves may be friction, viscoelastic hysteresis or plasticity. The method can efficiently detect flaws on complex geometries and only requires that both internal faces or edges are free to vibrate. The purpose of this work is to determine the relation between the observed heating right above a delamination by an IR camera and the frequency of a sinusoidal excitation between 8 and 27 kHz. The results clearly show specific heating peaks at certain frequencies. The comparison with local resonance frequencies of the delamination computed by simplified FEM shows similarities with the appearance of heating peaks. An experimental study having as goal to exploit the presence of those peaks and thus to increase the sensitivity of the method shows the interest for a high sweep sinusoidal excitation of the chirp type. The final objective of this research is to set up a serviceable short and reliable vibrothermographic test for non-destructive testing of composite materials. [less ▲]

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See detailExcitation of nodal diameter mode-shapes of a stator ring of a turbojet engine using a limited number of excitation sources
Nyssen, Florence ULg; Golinval, Jean-Claude ULg; Viguié, Régis et al

in Proceedings of ASME Turbo Expo 2013 (2013, June 05)

When considering engine tests, the sensors used to monitor the rotor parts mainly consist in strain gauges whose information is very sensitive to the gauge positioning, especially in high stress gradient ... [more ▼]

When considering engine tests, the sensors used to monitor the rotor parts mainly consist in strain gauges whose information is very sensitive to the gauge positioning, especially in high stress gradient regions. Therefore, to reduce the risk of misinterpreting the response given by the gauges, their calibration is required. Because strain gauges are positioned so that specific modes will be monitored, their calibration must be carried out for these modes. For cyclic symmetric structures, their high spectral density imposes the use of dedicated calibration techniques. In the present paper, the concept of modal appropriation is investigated as the first step of the calibration procedure. This paper aims at presenting the development of an experimental approach enabling the isolation/appropriation of specific nodal diameter modes of a stator stage of an axial compressor using a limited number of excitation sources. A special emphasis has been brought to the minimum number and the optimized location of the excitation sources (shakers) required in laboratory conditions to appropriate specific nodal diameter modes and thereby retrieve the related modal features needed for the gauges calibration and mechanical design. [less ▲]

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See detailDetection and Localisation of Damage on Industrially Produced Concrete Slabs Through Time- and Frequency-Domain Approaches
Nguyen, Viet Ha; Mahowald, Jean; Golinval, Jean-Claude ULg et al

in Carrera, E; Miglioretti, F; Petrolo, M (Eds.) 6th ECCOMAS Thematic Conference on Smart Structures and Materials (SMART2013) (2013, June)

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency ... [more ▼]

The objective of this work is to address the problem of damage detection in civil engineering structures using non-destructive techniques and dynamic measurements. To this purpose, time- or frequency-domain methods are used for the diagnostics. It consists in practical output-only techniques as Stochastic Subspace Identification (SSI) for modal identification or Enhanced Principal Component Analysis (EPCA) for detecting the presence of damage. The use of the Hankel matrix instead of the observation matrix improves effectively the robustness of these methods. Damage localization is based on Frequency Response Functions (FRFs) and sensitivity analysis of PCA results. The efficiency of the above-mentioned methods has been demonstrated in earlier studies mainly on numerical models and small-scale laboratory experiments [3, 4]. It was also tested successfully on industrial examples to perform machine condition monitoring using a reduced set of sensors [2]. In this work, the investigation is performed on precast prestressed and non-prestressed concrete slabs. Successive damages were artificially introduced in the slabs by loading heavy weights and by cutting steel wires, which induced cracks in the structure. The examples show the consequences of the considered techniques for damage identification. The results that are very different between prestressed and non-prestressed slabs may be used as input for the condition control of this kind of structures. [less ▲]

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See detailUse of Time- and Frequency-Domain Approaches for Damage Detection in Civil Engineering Structures
Nguyen, Viet Ha; Mahowald, Jean; Maas, Stefan et al

in Maia, NMM; Neves, NM; Sampaio, RPC (Eds.) International Conference on Structural Engineering Dynamics : ICEDyn 2013, Sesimbra 17-19 June 2013 (2013, June)

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the ... [more ▼]

The aim of this paper is to apply both time- and frequency-domain-based approaches on real-life civil engineering structures and to assess their capability for damage detection. The first structure is the Champangshiehl Bridge located in Luxembourg. Several damage levels were intentionally created by cutting a growing number of prestressed tendons and vibration data were acquired by the University of Luxembourg for each damaged state. The second example consists in reinforced and prestressed concrete panels. Successive damages were introduced in the panels by loading heavy weights and by cutting steel wires. The illustrations show different consequences in damage identification by the considered techniques. [less ▲]

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See detailON THE MODELING OF ADHESIVE CONTACT AND STICTION FAILURE IN MICRO-SWITCHES
Wu, Ling ULg; Noels, Ludovic ULg; Golinval, Jean-Claude ULg

in Ouisse (FEMTO-ST – ENSMM, France); Deü (CNAM, FR), J.F. (Eds.) MEDYNA 2013 Proceedings (2013, April)

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently ... [more ▼]

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently glued, limiting the life-time of the MEMS. This is especially true when contact happens between surfaces where elasto-plastic asperities deform permanently until the surfaces reach plastic accommodation, increasing the surface forces. To predict this behavior, a micro adhesive-contact model is developed, which accounts for the surfaces topography evolutions during elasto-plastic contacts. This model can be used at a higher scale to study the MEMS behavior, and thus its life-time. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. [less ▲]

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See detailA Micro Model for Elasto-Plastic Adhesive-Contact in Micro-Switches: Application to cyclic loading
Wu, Ling ULg; Golinval, Jean-Claude ULg; Noels, Ludovic ULg

in Tribology International (2013), 57

Stiction is a major failure mode in micro-electromechanical systems. In previous works, a statistical rough surfaces interaction model, for which only elastic adhesive contact has been considered, was ... [more ▼]

Stiction is a major failure mode in micro-electromechanical systems. In previous works, a statistical rough surfaces interaction model, for which only elastic adhesive contact has been considered, was developed for multiscale analyzes. However, during the impact between rough surfaces, plastic deformations of asperities cannot always be neglected. In the present work, the adhesion between rough surfaces is studied considering the elasto-plastic deformations of the asperities, and a model predicting the resulting micro adhesive-contact forces is derived. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. To determine the degree of plasticity involved, the impact energy of the movable electrode at pull-in is estimated. Thus the maximal adhesive force evolution during cyclic loading is predicted using the developed model. [less ▲]

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See detailNonlinear modal analysis of a full-scale aircraft
Kerschen, Gaëtan ULg; Peeters; Golinval, Jean-Claude ULg et al

in Journal of Aircraft (2013), 50

Nonlinear normal modes (NNMs), which are defined as a nonlinearextension of the concept of linear normal modes, are a rigorous tool for nonlinear modal analysis. The objective of this paper is to ... [more ▼]

Nonlinear normal modes (NNMs), which are defined as a nonlinearextension of the concept of linear normal modes, are a rigorous tool for nonlinear modal analysis. The objective of this paper is to demonstrate that the computation of NNMs and of their oscillation frequencies can now be achieved for complex, real-world aerospace structures. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft. Ground vibration tests of this aircraft exhibited softening nonlinearities in the connection between the external fuel tanks and the wing tips. The NNMs of this aircraft are computed from a reduced-order nonlinear finite element model using a numerical algorithm combining shooting and pseudo-arclength continuation. Several NNMs, involving, e.g., wing bending, wing torsion and tail bending, are presented, which highlights that the aircraft can exhibit very interesting nonlinear phenomena. Specifically, it is shown that modes with distinct linear frequencies can interact and generate additional nonlinear modes with no linear counterpart. [less ▲]

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See detailStiction Failure in Microswitches Due to Elasto-Plastic Adhesive Contacts
Wu, Ling ULg; Golinval, Jean-Claude ULg; Noels, Ludovic ULg

in Shaw, Gordon; Prorok, Bart; Starman, LaVern (Eds.) MEMS and Nanotechnology, Volume 6 (2013)

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See detailStiction failure in microswitches due to elasto-plastic adhesive contact and cyclic loading
Wu, Ling ULg; Golinval, Jean-Claude ULg; Noels, Ludovic ULg

Scientific conference (2012, November 24)

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. This is especially true when contact happens between surfaces where elastoplastic asperities ... [more ▼]

Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. This is especially true when contact happens between surfaces where elastoplastic asperities deform permanently until the surfaces reach plastic accommodation. Indeed before or at accommodation, the adhesive forces can become so important that the two surfaces remain permanently glued, limiting the life-time of the MEMS. To predict the behavior a micro adhesive-contact model is developed, which account for the surfaces topography evolutions during elasto-plastic contacts. This model can be used at a higher scale to study the MEMS behavior, and thus its life-time. The MEMS devices studied here are assumed to work in a dry environment. In these operating conditions only the Van der Waals forces have to be considered for adhesion. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. To determine the degree of plasticity involved, the impact energy of the movable electrode at pull-in is estimated. Thus the maximal adhesive force is predicted using the developed model.Within this formalism, the cyclic loading and accommodation effects can be taken into account, as represented on the picture, which shows the non-dimensional force vs. separation distance of two rough surfaces after different cycle numbers. [less ▲]

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See detailQualification d’un appareil d'éclairage décoratif soumis aux vibrations induites par un pont ferroviaire
Marin, Frédéric; Simon, Daniel; Golinval, Jean-Claude ULg

in Serra, Roger (Ed.) 3ième Colloque "Analyse Vibratoire Expérimentale" (2012, November)

Au même titre que la plupart des pièces mécaniques soumises aux vibrations, les appareils d'éclairage installés en extérieur sont amenés à satisfaire, en fonction de leurs conditions d’utilisation, aux ... [more ▼]

Au même titre que la plupart des pièces mécaniques soumises aux vibrations, les appareils d'éclairage installés en extérieur sont amenés à satisfaire, en fonction de leurs conditions d’utilisation, aux exigences de procédures d'essais appliquées sur table vibrante. Celles-ci ont pour but de garantir l'intégrité structurelle du luminaire lorsque, une fois sur site, il est soumis aux effets du vent. Dans le cas des appareils d'éclairage décoratifs installés sur un pont de chemin de fer de structure métallique, le vent n'étant plus la source principale de vibrations en comparaison du trafic ferroviaire, on est dès lors confronté à une absence de toute indication appropriée décrivant l'essai à mener. Par conséquent, l'objectif de cette étude est d'élaborer une spécification d'essai de durée réduite, appliquée en laboratoire sur table vibrante, et représentative de l'environnement vibratoire réel de l'appareil à certifier. Sur base des essais réalisés en laboratoire, des prescriptions de montage et d'installation sont également formulées afin de garantir des conditions d’utilisation et d’essai identiques. [less ▲]

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See detailDétection d'endommagement et résonances locales sur composite CFRP par vibrothermographie
Demy, Philippe ULg; Golinval, Jean-Claude ULg; Simon, Daniel

in Serra, Roger (Ed.) 3ième Colloque "Analyse Vibratoire Expérimentale" (2012, November)

La vibrothermographie est une technique de thermographie active capable de détecter des singularités de type délaminage ou décollement dans un matériau composite comme les laminés en fibres de carbone ... [more ▼]

La vibrothermographie est une technique de thermographie active capable de détecter des singularités de type délaminage ou décollement dans un matériau composite comme les laminés en fibres de carbone très utilisés actuellement en construction aéronautique (CFRP). Les causes physiques du mécanisme d'échauffement interne, suite à l'interaction avec les ondes élastiques, peuvent être la friction, l'hystérésis viscoélastique ou encore la déformation plastique. La méthode est efficace également sur des géométries complexes et requiert uniquement que les deux faces internes du délaminage soient libres de vibrer. Cette étude consiste à déterminer la relation entre l'échauffement observé et la fréquence d'une excitation sinusoïdale entre 8 et 27 kHz. Il apparaît clairement des pics d'échauffement pour certaines fréquences particulières. La comparaison avec les fréquences de résonance locale du défaut modélisé par éléments finis montre des similitudes avec l'apparition de certains de ces pics. Une étude expérimentale visant à exploiter la présence de ceux-ci montre l'intérêt d'un test vibrothermographique de type balayage rapide (chirp), dans l'optique de mettre sur pied un test court et fiable pour le contrôle non destructif de matériaux composites. [less ▲]

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See detailMéthodologie d’excitation de modes à diamètres nodaux d’un anneau statorique de turboréacteur
Nyssen, Florence ULg; Golinval, Jean-Claude ULg; Simon, Daniel et al

in Serra, Roger (Ed.) 3ième Colloque "Analyse Vibratoire Expérimentale" (2012, November)

Cette étude consiste à développer une approche expérimentale, permettant l’isolation de modes à diamètres nodaux spécifiques d’un étage statorique de compresseur basse pression, ayant pour objectif final ... [more ▼]

Cette étude consiste à développer une approche expérimentale, permettant l’isolation de modes à diamètres nodaux spécifiques d’un étage statorique de compresseur basse pression, ayant pour objectif final la calibration de jauges de déformation. Plus spécifiquement, une étude portant sur le nombre minimal de sources d’excitation (shakers) et sur leur répartition circonférentielle optimale a été menée, l’objectif suivi étant d’isoler des modes à diamètres cibles dans des conditions de laboratoire. La première partie de l’étude consiste en une approche théorique, basée sur les concepts d’appropriation modale en régime forcé. La combinaison optimale des positions des différents points d’excitation est choisie de façon à maximiser une fonction objectif, définie comme le rapport entre l’énergie injectée dans le mode cible et la valeur maximale des énergies injectées dans les modes présentant une fréquence naturelle proche du mode d’intérêt. Dans la deuxième partie de l’étude, des simulations numériques sur un modèle éléments finis de la structure ont été menées sur base des résultats théoriques obtenus. Enfin, la troisième partie a permis de valider expérimentalement les prédictions numériques via des analyses d’influence du nombre d’excitateurs et de leur position sur l’amplitude de la réponse fréquentielle. [less ▲]

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See detailIdentification modale de systèmes variant dans le temps à partir de réponses simulées sur un exemple d'éoliennes
Bertha, Mathieu ULg; Golinval, Jean-Claude ULg

Poster (2012, November)

Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems ... [more ▼]

Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems, classical identification methods have to be adapted to the non-stationary nature of the recorded signals. In this paper, it is proposed to study the dynamic behavior of an offshore five-megawatt wind turbine. First, a numerical model of the wind turbine is created to serve as reference. Then, the time-varying behavior of the system is evaluated by simulating a large number of possible configurations. To this purpose, time responses are generated from the numerical model submitted to different environmental conditions. The wind is considered as the main non-measured external excitation force on the structure and the responses are recorded at several locations to simulate a real measurement process. Special care is brought to the accessibility of the measurement locations and to the limited number of available sensors in practice. Using these simulated measurements, output-only identification methods are used to extract varying dynamic properties of the structure. The final objective of this work is to pave the way to online condition monitoring of wind turbines. [less ▲]

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See detailNonlinear Dynamic Analysis of Aerospace Structures
Kerschen, Gaëtan ULg; Noël, Jean-Philippe ULg; Renson, Ludovic ULg et al

Conference (2012, October)

Current practice in industry is to rely on linear finite element simulations. However, nonlinearity is a frequent occurrence in engineering structures. It is at the origin of rich and complex dynamical ... [more ▼]

Current practice in industry is to rely on linear finite element simulations. However, nonlinearity is a frequent occurrence in engineering structures. It is at the origin of rich and complex dynamical phenomena that cannot be observed in linear structures. Solving both the direct and inverse problems in nonlinear structural dynamics therefore warrants the development of appropriate methodologies. The focus of the presentation will first be on the inverse problem. We will describe the different steps of the nonlinear system identification process and discuss the current capabilities of existing methods. The presentation will then address the direct problem during which the identified model is used for accurately predicting the structure’s dynamic characteristics. A rigorous nonlinear extension of modal analysis will be presented, and we will show that it represents a very useful framework for understanding nonlinear dynamical phenomena and supporting design decisions. Two real-life aerospace structures will be considered for illustrating the proposed developments. [less ▲]

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See detailDamage detection and local resonances model in CFRP composite material by vibrothermography
Demy, Philippe ULg; Golinval, Jean-Claude ULg; Simon, Daniel

Scientific conference (2012, September)

Vibrothermography (VT) is an active non destructive technique able to detect singularities like delamination, even if the defect internal faces are in contact. Under sonic or ultrasonic mechanical ... [more ▼]

Vibrothermography (VT) is an active non destructive technique able to detect singularities like delamination, even if the defect internal faces are in contact. Under sonic or ultrasonic mechanical vibrations, a delamination may behave like a heat source principally due to friction between the rubbing faces and/or stress concentration in the area. The present article focuses on the understanding of the underlying phenomenon so-called "local resonances" and its correlation with the presence of temperature peaks observed at certain frequencies. For this purpose, a simplified finite element modal analysis of the delamination model is compared with the heating rate vs. frequency data's acquired by an infrared camera. Then, some conclusive results of sine sweep and chirp testing will be presented and discussed in regards to this theory. [less ▲]

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See detailModal identification of time-varying systems using simulated responses on wind turbines
Bertha, Mathieu ULg; Mayorga Rios, Jorge Patricio ULg; Golinval, Jean-Claude ULg

in Sas, P; Moens, D; Jonckheere, S (Eds.) Proceedings of ISMA2012-USD2012 (2012, September)

Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems ... [more ▼]

Wind turbines are good examples of time-varying systems as their modal properties depend on their instantaneous configuration. To catch the variations of modal parameters in time-varying systems, classical identification methods have to be adapted to the non-stationary nature of the recorded signals. In this paper, it is proposed to study the dynamic behavior of an offshore five-megawatt wind turbine. First, a numerical model of the wind turbine is created to serve as reference. Then, the time-varying behavior of the system is evaluated by simulating a large number of possible configurations. To this purpose, time responses are generated from the numerical model submitted to different environmental conditions. The wind is considered as the main non-measured external excitation force on the structure and the responses are recorded at several locations to simulate a real measurement process. Special care is brought to the accessibility of the measurement locations and to the limited number of available sensors in practice. Using these simulated measurements, output-only identification methods are used to extract varying dynamic properties of the structure. The final objective of this work is to pave the way to online condition monitoring of wind turbines. [less ▲]

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See detailÉtalonnage dynamique des capteurs piézoélectriques pour la mesure de haute pression balistique
Elkarous, Lamine ULg; Pirlot, Marc; Golinval, Jean-Claude ULg

in 4ème Conférence Internationale de métrologie - CAFMET2012 (2012, April 24)

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See detailDamage Detection on the Champangshiehl Bridge using Blind Source Separation
Nguyen, Viet Ha; Rutten, Christophe; Golinval, Jean-Claude ULg et al

in Strauss, Alfred; Frangopol, Dan M.; Bergmeister, Konrad (Eds.) Life-Cycle and Sustainability of Civil Infrastructure Systems (2012)

This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage ... [more ▼]

This paper addresses the problem of damage detection in civil engineering structures using characteristic subspaces obtained from principal component analysis (PCA) of output-only measurements. Damage detection is performed by comparing subspace features between a reference (healthy) state and a current (possibly damaged) state. The damage indicator used in this study is the angular coherence between sub-spaces. The considered damage detection procedure is illustrated on the Champangshiehl Bridge which is a two span concrete box girder bridge located in Luxembourg. Before its destruction, multiple damage levels were inten-tionally created by cutting a growing number of prestressed tendons. Vibration data were acquired by the University of Luxembourg for each damaged state at many locations on the bridge. As previous studies dem-onstrated the large importance of environmental factors on modal identification, special care was taken to evaluate this influence during the test campaign. [less ▲]

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