On the modeling of light aircraft landing gears

International audienceLight aircrafts are designed to be used in both developed and undeveloped areas of a country. Hard landingconditions such as shocks and rebounds may occur. In this context, a good, efficient, robust and easy to maintainlanding gear is vital. Its main role is to dissipate the energy of the impact. The aim of this work is to study aninnovative light aircraft landing gear equipped with a damper. The study includes comparing its dissipationperformance with two traditional light aircraft landing gears: a classical flat spring landing gear and a landing gearwith Sandow cords. These systems’ modeling is carried out through three steps. Firstly, Bush tire is modeled withfinite elements considering tire geometry and material specificities. Secondly, combined finite elements withstructural elements are used to model the different landing gear systems. Thus, stress, deformation and energywithin landing gears components could be obtained. Finally, aircraft rolling simulations are conducted. Systems’transient responses while rolling over ramp are evaluated, as well as the efforts and rebound displacementstransmitted to the aircraft. A dissipation efficiency comparative study between the landing gears is conducted. Inaddition, the influence of simulation’ conditions such as inflation pressure, rolling velocity or runway flatness isinvestigated

Thermomechanical analysis of an aircraft tire in cornering using coupled ale and lagrangian formulations

International audienceThe thermomechanical behavior of an aircraft tire is predicted, using experimental devices, a model based on finite element software and an appropriate method of expressing the heat generated by skid in terms of the local friction coefficient, depending on the temperature. In the thermomechanical model, a steady state mechanical analysis is combined with a transient thermal problem. This combined approach is based on three main computing steps: the deformation step, the dissipation step and the thermal step. The deformation step calculates the stress and the velocity fields, which are used as inputs in the dissipation step to calculate the heat generated due to friction. The internal dissipation is assumed to be negligible. Finally, the thermal step yields new thermal maps based on the heat flux computed in the dissipation step. The coupling is established by updating the friction coefficient in the first two steps

On the modeling of aircraft tire

International audienceA method is presented here for modeling and predicting the rolling and yaw behavior of an aircraft tire which is subjected to a strong inflation pressure and a concentrated load on the axle, in contact with a flat, rigid surface. Finite element methods were used to model and simulate the aircraft tire/ground interactions. The incompressibility of the material, the large transformations and the unilateral contact with Coulomb friction law were all taken into account. Imaging methods were used to examine the complex structure of the tire cross-section. Comparisons are made between the data obtained with the model, the experimental data and those provided by the manufacturer. The tire response predictions were found to depend considerably on the material and the geometrical characteristics of the tire

On the direct bonding of two silicon surfaces: experiments and modeling

International audienceSilicon direct bonding is a well known process in optic. In this communication we will present principles of molecular adhesion, chemical and mechanical characterization of the interface and a numerical study to predict the mechanical resistance of assemblies

Turbulence Removal in Atmospheric Dynamics through Laminar Channels

El método adoptado en este paper para describir la dinámica atmosférica ha implicado el desarrollo de estructuras geométricas invariantes al tiempo con lo que implican que puede modelizarse de forma fractal/multifractal. Los escenarios evaluados tipo Schrödinger y Madelung conducen a un comportamiento atmosférico de las turbulencias que se puede describir en términos de modulación y discretización. A traves de estos modelos se establece que los canales laminares en toda la atmósfera actúan como un medio superconductor de masas. Para ello se han usado datos experimentales de un ceilómetro y una plataforma de radar que confirma mediante la dinámica vertical de enjambres de insectos que el modelo funciona.Dynamics in atmospheric structures are analyzed using the Scale Relativity Theory in Schrödinger-type and Madelung-type scenarios. In the Schrödinger-type scenario, the group invariances of the special linear group SL(2R)-type under Riccati-type gauges implies morphological atmospheric manifestations through frequency modulation, particularly through period doubling. In the Madelung-type scenario, the same group invariances type, manifested through harmonic mappings, implies the functionality of atmospheric mass conductions through mass superconducting-type by scale transition from nondifferentiable atmospheric dynamics to differentiable atmospheric dynamics. The compatibility of these two scenarios under the correlations of atmospheric morphologiesfunctionalities implies Stoler-type coherences of the atmospheric dynamics through the removal of atmospheric turbulence by means of laminar channels. Finally, these theories are successfully employed to analyze the vertical atmospheric dynamics of cases of insect swarms.19 páginas 26 notas bibliográfica

Finite Element Modeling of an Aircraft Tire Rolling on a Steel Drum: Experimental Investigations and Numerical Simulations

The aim of this study is to investigate the thermal evolution of an aircraft tire rolling at high velocities up to take off values. As this kind of experiment is difficult to realize on a real runway, experimental tests were realized on aircraft tires rolling on a steel drum. The rotating drum facility allows to apply variable velocities beyond the take off limits, at fixed skidding angles and loadings. The rolling conditions, vertical loading, velocity and cornering conditions were adopted to correspond to the real conditions of an aircraft tire running or skidding on a flat runway. In the experimental part, the influence of skidding angle, velocity and loading on the thermal evolution of the tire tread were investigated. The thermo-mechanical finite element analysis of a pneumatic radial tire structure was performed taking into account the hyper-viscoelastic rubber behavior, with heating mechanisms developed by the inelastic deformation and by friction. Three-dimensional finite element simulations of an aircraft tire rolling on a steel drum were carried out using Abaqus/Standard finite element solver. The comparison of the temperature distribution on the tire tread between numerical results and the experimental data shows the same overall tendencies. The good correlation between numerical and experimental data shows that numerical simulation could predict the thermal evolution of the tire in critical situations. The authors would like to mention that for confidentiality reason, certain numerical data could not be revealed

Multigrid methods for unilateral contact problems with friction

In this paper, multigrid methods are tested on unilateral problems with friction. An optimal strategy is presented and efficiency of the solver is discussed on several examples

Thermomechanical modelling of aircraft tyre cornering

International audienceSome numerical models are proposed for simulate the aircraft tyre behaviour in critical situations. Fully coupled thermomechanical analysis procedures taking into account finite deformation, dynamics and frictional contact are studied. The proposed models are compared with experimental data such as contact area, lateral and longitudinal stiffness, vertical deflection, surface temperature evolution due to friction, self-alignment torque, and lateral friction coefficients. A good agreement is observed at low speed (less than 70 km/h). The model is able to be extrapolated and to predict results at high speeds, in which case it is not possible to obtain realistic experimental data