A numerical method to optimize the design of a space inflatable membrane reflector

International audienceA numerical method is proposed to optimize the design of a space inflatable membrane reflector. The initial geometry is expressed by polynomial series weighted by a set of shape parameters. The problem is formulated as a minimization of a cost function representing the difference between the effective shape of the reflector and a perfect parabolic surface. The minimization is performed using the Nelder-Mead method or downhill simplex method. The cost function is computed at each vertex of a simplex defined in the space of optimization parameters by solving direct problem thanks to a finite element method. The finite element model handles geometrical non-linearities and takes into account phenomena like membrane wrinkling and torus buckling which may affect the reflector shape when inflated

A numerical method to optimize the design of a space inflatable membrane reflector

International audienceA numerical method is proposed to optimize the design of a space inflatable membrane reflector. The initial geometry is expressed by polynomial series weighted by a set of shape parameters. The problem is formulated as a minimization of a cost function representing the difference between the effective shape of the reflector and a perfect parabolic surface. The minimization is performed using the Nelder-Mead method or downhill simplex method. The cost function is computed at each vertex of a simplex defined in the space of optimization parameters by solving direct problem thanks to a finite element method. The finite element model handles geometrical non-linearities and takes into account phenomena like membrane wrinkling and torus buckling which may affect the reflector shape when inflated

A New Embedded Full Strain Components Sensor

International audienceA new concept of strain (or stress) tensor sensor is presented. Fully embedded in the structure, it measures the full 3D strain tensor while suppressing its own influence, i.e allowing to find the strain (or stress) that would exist without the sensor, thanks to the Eshelby theorem. Furthermore, this theorem proves that the strain field is homogenous in the spherical (or ellipsoidal) body of the sensor, leading to perfect conditions of use for the six Bragg grating glass fibers which measure the strain of the body. After a brief overview of the theory, both mechanical and optical, we will present the results of the test performed using a prototype. This device is a simplified version of the sensor (3 channels) submitted to a hydrostatic pressure in order to assess the precision and the repeatability of the measure

Superposition of fiber Bragg and LPG gratings for embedded strain measurement

AbstractWhen a fiber Bragg grating strain sensor is embedded inside a structure, the interaction of the sensor with the host material can lead to spurious results if the radial strain is neglected. In this article, we use numerical simulations to show that the axial and radial strains can be simultaneously measured with a single fiber in which a Bragg grating and a long-period grating are superimposed. Moreover, we present an optimal architecture of the sensor

EFEKTIFITAS PEMBERIAN METHYLPREDNISOLONE POST-OPERATIF TERHADAP OEDEMA PASCA ODONTEKTOMI GIGI MOLAR TIGA BAWAH

ABSTRAKNama : Nandani Wulansari Fakultas : Kedokteran GigiProgram Studi : Pendidikan Kedokteran GigiJudul : Efektifitas Pemberian Methylprednisolone Post-Operatif terhadap Oedema Pasca Odontektomi Gigi Molar Tiga BawahGigi molar tiga adalah salah satu gigi yang sering mengalami kelainan saat erupsi yang disebut dengan impaksi. Tindakan ektraksi gigi impaksi dengan pembedahan disebut sebagai odontektomi. Odontektomi sering menyebabkan komplikasi, salahsatunya adalah oedema. Terapi anti-inflamasi seringkali diberikan untuk mengontrol gejala inflamasi yang muncul setelah odontektomi. Golongan obat lainnya yang juga sering digunakan dalam mengatasi proses inflamasi adalah kortikosteroid. Kortikosteroid dianggap sebagai anti-inflamasi yang lebih kuat dibandingkan dengan golongan obat anti-inflamasi non-steroid (NSAIDs). Penelitian ini bertujuan untuk mengetahui efektifitas pemberian methylprednisolone post-operatif terhadap oedema pasca odontektomi gigi molar tiga bawah. Jenis penelitian ini adalah eksperimental klinis. Subjek penelitian (n=16) dibagi dalam dua kelompok yaitu kelompok perlakuan yang disertai terapi pemberian methylprednisolone 4mg dan kelompok kontrol tanpa disertai pemberian methylprednisolone 4mg. Penilaian oedema dilakukan melalui pengukuran wajah dengan metode Neupert pada rentang waktu 24 jam, 48 jam, dan 72 jam setelah odontektomi, kemudian hasil pengukuran dianalisis statistik. Berdasarkan hasil uji statistik t tidak berpasangan didapatkan bahwa tidak ada perbedaan efektifitas terhadap oedema yang signifikan (

Minimum Localizable Damage for Stochastic Subspace-based Damage Diagnosis

International audienceThis article describes an approach to evaluate the minimum localizable damage for stochastic subspace-based damage diagnosis. Localizability is defined as the sensitivity to small and local damages (detectability), the ability to narrow down the exact damage location (localization resolution) and the test response of undamaged parameters (false localization alarms). For the analysis, damage is defined as a change in model-based design parameters, for example, material constants or cross-sectional values in a finite element model. Subsequently, the parameter changes are linked to changes in the global damage-sensitive features using sensitivity vectors, and inherent uncertainties (due to stochastic loads and measurement noise) are quantified. This way, local structural parameters can be tested for changes using statistical hypothesis tests, such as the general likelihood ratio and the statistical minmax localization test. Due to the numerical conditioning of the damage localization problem, the sensitivity vectors have to be clustered before damage can be localized. Sensitivity clustering corresponds to a substructuring of the finite element model, where the number of clusters (the localization resolution) is a user-defined input parameter. The main results of this paper are mathematical criteria to calculate the damage detectability and the false alarm susceptibility for different localization resolutions. Moreover, an automated substructuring routine is described that finds the optimal substructure arrangement as a compromise between high damage detectability, high localization resolution, and low false alarm susceptibility. For proof of concept, a numerical case study is presented, where the damage localizability is determined and validated for a cable-stayed bridge

Statistical subspace based damage localization on Saint-Nazaire Bridge mock-up

International audienceThe subject of damage localization is an important issue for Structural Health Monitoring (SHM) particularly in mechanical or civil structures under ambient excitation. In this paper, the statistical subspace-based damage localization method has been applied on a benchmark application, namely a 1/200 scale model of the Saint-Nazaire Bridge, which is a cable-stayed bridge located on the Loire River near the river's mouth. The employed damage localization method combines data-driven features with physical parameter information from a finite element model in statistical tests, avoiding typical ill-conditioning problems of FE model updating. Damage is introduced in the mockup for cable failures on some of the 72 cables. The purpose of the experiment is to assess the capability of damage assessment methods to find a cable failure

Dimensionnement optimal des structures membranaires préssurisées - Application à une antenne gonflable parabolique.

National audienceSee http://hal.archives-ouvertes.fr/docs/00/59/27/86/ANNEX/r_3K3833XY.pd

Modélisation numérique et expérimentale des instabilités hors plan sur une membrane tendue

L'étude porte sur la caractérisation expérimentale et numérique des instabilités hors plan d'une membrane tendue. Un dispositif expérimental de traction sur deux axes découplés a été mis au point. La mesure des ondulations liées à l'instabilité de la membrane est réalisée à l'aide de la méthode de projection de franges. Nous présentons ici une partie des résultats expérimentaux destinés à valider les algorithmes numériques de traitement de l'instabilité dans le cas de films très minces. Nos résultats sont comparés à ceux obtenus à l'aide d'un code de calcul commercial

Architecture de capteurs à fibre optique pour la mesure simultanée des déformations axiales et radiales

International audienceL’objectif de cet article est de montrer qu’il est possible de mesurer simultanément les déformations axiale et radiale d’une structure en utilisant un seul capteur à fibre optique. Dansun premier temps nous étudions analytiquement deux types de sollicitations exercées sur un cylindre : une traction pure et un chargement thermique. Nous montrons qu’il est indispensable de mesurer les déformations axiales et radiales, si l’on veut déterminer avec précision la déformation axiale d’un capteur enfoui. Dans un second temps, nous proposons plusieurs architectures de capteurs permettant de réaliser ces mesures simultanées et examinons leurs performances respectives. Nous en concluons que la structure la plus performante est constituée de la juxtaposition d’un réseau de Bragg classique et d’un réseau longue période