Showing papers by "Dassault Aviation published in 2010"

Reynolds-Stress Model Flow Prediction in Aircraft-Engine Intake Double-S-Shaped Duct

Abstract: The purpose of the present paper is to assess the predictive capability of Reynolds-averaged Navier-Stokes computations using seven-equation Reynolds-stress model wall-normal-free closures for flows in aircraft-engine intake double-S-duct configurations. The intake studied operates at high subsonic Mach numbers and is characterized by high turning angle of the second S-leg, inducing a particularly complex flow structure up to the engine face. Computations were run using two wall-topology-free second-moment closures and a baseline two-equation model, carefully checked for grid convergence, and compared with available experimental measurements. Computational data were then used to analyze the flowfield structure.

Higher-Order Stabilized Finite Elements in an Industrial Navier-Stokes Code

Abstract: This chapter covers Dassault Aviation’s contribution to Workpackage 3 of the ADIGMA Project, which focuses on the extension of its stabilized finite element industrial Navier-Stokes code to higher-order elements. Mesh generation aspects are treated and especially the issue of highly-stretched curved elements close to the wall boundary of Navier-Stokes meshes. The high-order approach is carefully assessed using inviscid subsonic and transonic, laminar, and high Reynolds number turbulent flows.

Noise radiated by a rod-airfoil configuration using DES and the Ffowcs-Williams & Hawkings' analogy

Abstract: To comply with noise reduction objectives in relation with more stringent international acoustic certification rules has become an important challenge for aircraft manufacturers. Dassault Aviation has been developing an innovative numerical sequence aiming at predicting the noise generated by new airfoil designs. This paper presents the numerical approach and an application to the noise radiated by a rod-airfoil configuration. Numerical results are compared to experimental data from Jacob et al[1]. DES (Detached Eddy Simulation) computations are performed to simulate the unsteady flow field. Sound in the far field is extracted from wall pressure fluctuations using the Ffowcs-Williams and Hawkings’ analogy[2][3]. The results are in good agreement with experimental data.

Learning Ontologies with Deep Class Hierarchies by Mining the Content of Relational Databases

Abstract: Relational databases are valuable sources for ontology learning. Previous work showed how precise ontologies can be learned and be fruitfully exploited to solve practical problems, such as ensuring integration and interoperation of heterogeneous databases. However, a major persisting limitation of the existing approaches is the derivation of ontologies with flat structure that simply mirror the schema of the source databases. In this paper, we present the RTAXON learning method that shows how the content of the databases can be exploited to identify categorization patterns from which class hierarchies can be generated. This fully formalized method combines a classical database schema analysis with hierarchy mining in the stored data. RTAXON is one of the methods implemented in RDBToOnto, a comprehensive tool that support the transitioning process from access to the data to generation of populated ontologies.

Using Transfer Function Calculation and Extrapolation to Improve the Efficiency of the Finite-Difference Time-Domain Method at Low Frequencies

Abstract: The finite-difference time-domain method (FDTD) needs a long computation time to solve low-frequency (LF) problems. In this paper, we suggest a new way to improve the efficiency of the FDTD method, especially for LF problems such as lightning indirect effects studies. The procedure consists in first calculating the system's response to a quasi-impulse excitation. The quasi-impulse response is extrapolated using the matrix pencil method in order to obtain a totally damped waveform. Next, the system's transfer function is calculated and the response to any excitation is deduced. Thus, this method allows for solving problems with a slow response. For instance, the tool is used to calculate currents induced on wires inside a composite aircraft struck by lightning. Very good agreements with FDTD complete simulations are found. Furthermore, the method allows an important computation time saving.

Magnetic excitation in weak stripe domains: Ferromagnetic resonance and Brillouin light sattering studies

Abstract: Ferromagnetic films with perpendicular anisotropy and above a critical thickness exhibit weak stripe magnetic domains. The dynamic response of such systems with inhomogeneous state under moderate applied field can then be a probe of the local as of the macroscopic magnetization evolution. The static properties of Permalloy (Py) films of different thicknesses are obtained by VSM and MFM. Then the dynamic response is both investigated with a micro-stripe line device (FMR) and by Brillouin light scattering (BLS). For thick Py films three modes are observed below saturation which merge into a single one in the staturated state. Micromagnetic simulations have been performed to get the various resonance frequencies and the spatial distribution of the modulus of the dynamic magnetization for each mode. BLS spectra also show frequency multi-modes (at low q) in the non saturated state.

A numerical tool to estimate lightning indirect effects on a composite aircraft

Abstract: Nowadays, with the increasing use of composite materials, lightning indirect effects on aircraft are an important problem of interest. Currents and voltages induced by the lightning strike can perturb the equipment working. The purpose of this study is to develop a numerical tool allowing the estimation of current coupling on wires involved by the lightning strike. The model permits to consider several thousands of wires and is a powerful and useful tool, assisting the aircraft manufacturer in the certification process.

The effect of human shadowing on RF signal strengths of IEEE802.11a systems on board business jets

Abstract: Wireless networks provide the technology that allows the service provisioning of a number of applications to mobile stations. In recent years, aircraft manufacturers have been evaluating the possibility of offering this technology on-board their aircrafts. This will help manufacturers to reduce cable complexity while offering new services to the passengers.12

Induced anisotropies in a ferromagnet coupled to a polycrystalline antiferromagnet

Abstract: The effect of thermal activation of a polycrystalline antiferromagnet (AF) coupled to a ferromagnet (FM) on the unidirectional anisotropy responsible for positive shift of the resonant frequency (fR) of the FM is presented. Hysteresis loops and ferromagnetic resonance plots of Co35Fe65/Ni50Mn50 are evaluated and matched with those obtained from experiments. The contribution of the AF magnetic structure to fR is highlighted. An inverse relation between fR and AF grain size is predicted.

Goal-Oriented Mesh Adaptation in an Industrial Stabilized Finite Element Navier-Stokes Code

Abstract: This chapter describes Dassault Aviation’s contribution to Workpackage 5 of the ADIGMA Project. The adjoint operator developed in the framework of optimum design is used to estimate the error in the solution with respect to a given target quantity. Local values of this error estimation are used as a criterion to refine the mesh. This yields significant improvement over traditional criteria based on the residual or on gradients of physical quantities. The method is carefully tested using inviscid, transonic, laminar, and high Reynolds number turbulent flows.

Multi-domain industrial benchmarks for eddy-current modelling: the COFREND working group

Abstract: Description of the COFREND working group dedicated to the multi-domain industrial benchmarks for eddy-current modelling and some of their configurations.

'HOWARD' : un modèle pour la propagation d'ondes de choc acoustiques en milieu hétérogène, au-delà de l'approximation parabolique

Abstract: La simulation numerique de la propagation d'ondes de choc acoustiques necessite de prendre en compte des echelles temporelles et spatiales tres differentes (plusieurs ordres de grandeur). Les temps de calcul eleves rendent les approches directes dans des configurations realistes (equations d'Euler ou de Navier-Stokes) prohibitives pour le moment. Ceci justifie le recours a des equations modeles. Le modele le plus courant est base sur l'approximation parabolique standard, dont le domaine de validite reste neanmoins limite aux faisceaux collimates. Pour aller au-dela et s'affranchir de ces limitations, une nouvelle approche nommee HOWARD ("Heterogenous One Way Approximation for the Resolution of Diffraction") a ete mise au point. Elle permet de simuler la propagation d'ondes de choc acoustiques en milieux heterogenes sans limite de validite angulaire, contrairement aux approximations paraboliques utilisees habituellement. Seul le champ retro-diffuse est neglige (approximation de milieu faiblement heterogene). Dans un premier temps, cette methode sera exposee en detail et comparee aux methodes existantes. Puis, differentes configurations seront etudiees pour en illustrer les potentialites.

Maximin design on non hypercube domain and kernel interpolation

Abstract: In the paradigm of computer experiments, the choice of an experimental design is an important issue. When no information is available about the black-box function to be approximated, an exploratory design have to be used. In this context, two dispersion criteria are usually considered: the minimax and the maximin ones. In the case of a hypercube domain, a standard strategy consists of taking the maximin design within the class of Latin hypercube designs. However, in a non hypercube context, it does not make sense to use the Latin hypercube strategy. Moreover, whatever the design is, the black-box function is typically approximated thanks to kernel interpolation. Here, we first provide a theoretical justification to the maximin criterion with respect to kernel interpolations. Then, we propose simulated annealing algorithms to determine maximin designs in any bounded connected domain. We prove the convergence of the different schemes.

Analyse de l'exploitation des broches en UGV aéronautique

Abstract: Le fraisage grande vitesse des pieces aeronautiques de grandes dimensions necessite a la fois un taux d'enlevement de copeaux important ainsi qu'une qualite de finition garantissant les tolerances de ces pieces a haute valeur ajoutee. Implantees sur des machines outils UGV, les electrobroches doivent supporter, sur des phases d'usinage de plusieurs heures, des sollicitations physiques importantes. Malgre les avancees technologiques, les broches apparaissent aujourd'hui comme le maillon faible des machines d'usinage a grande vitesse aeronautique. Ce papier propose un concept innovant de surveillance des broches d'UGV qui permet de suivre l'usure de celles-ci, particulierement au niveau de leurs roulements a billes, cause principale de leurs defaillances. Pour cela des broches FISCHER ont ete instrumentees de plusieurs accelerometres, puis integrees sur machines FOREST-LINE. Grâce aux signaux vibratoires enregistres par un systeme de surveillance concu specifiquement et a partir d'un etat de l'art sur la surveillance des roulements que nous avons realises, un critere vibratoire adapte au suivi de l'etat des paliers des broches a ete developpe. De plus, les signaux et informations enregistres lors de l'usinage par le meme systeme de surveillance permettent de relier l'endommagement des roulements aux sollicitations subies par la broche lors de son utilisation afin d'assurer aussi une reelle surveillance du procede en lui-meme.