Performance Improvement of Small UAVs Through Energy-Harvesting Within Atmospheric Gusts

Fixed-wing mini aerial vehicles usually at low altitudes often exposed to turbulent environments. Gust soaring is a flight technique of energy harvesting in such a complex and stochastic domain. Presented work shows the feasibility and benefits of exploiting non-stationary environment for a small UAV. Longitudinal dynamics trajectory is derived showing significant benefits in extended flight with sinusoidal wind profile. Optimization strategy for active control has been performed with the aim of obtaining most effective set of gains for energy retrieval. Moreover, three-dimensional multi-point model confirmed feasibility of energy harvesting in a more complex spatial wind field. Influence of unsteady aerodynamics is determined on overall energy gain along the flight path with active proportional control. Most contributing aerodynamic parameters are identified and suggested as basic objective function of an UAV design for energy harvesting in gusty environment. In addition, passive approach of control related to structural dynamics is investigated, pointing out its potential and possible improvements with aeroelastic tailoring

Performance improvement of small Unmanned Aerial Vehicles through gust energy harvesting

Fixed-wing miniature aerial vehicles usually fly at low altitudes that are often exposed to turbulent environments. Gust soaring is a flight technique of energy harvesting in such a complex and stochastic domain. The presented work shows the feasibility and benefits of exploiting a nonstationary environment for a small unmanned aerial vehicle. A longitudinal dynamics trajectory is derived, showing significant benefits in extended flight with a sinusoidal wind profile. An optimization strategy for active control is performed, with the aim of obtaining the most effective set of gains for energy retrieval. Moreover, a three-dimensional multipoint model confirms the feasibility of energy harvesting in a more complex spatial wind field. The influence of unsteady aerodynamics is determined on the overall energy gain along the flight path with active proportional control. The aerodynamic derivatives describing the contribution to lift by a change in angle of attack and elevator deflection are identified as the most contributing aerodynamic parameters for energy harvesting in a gusty environment, and are therefore suggested as a basic objective function of an unmanned aerial vehicle design for such a flight strategy

Damage of woven composite under translaminar cracking tests using infrared thermography

The aim of this work is to increase the study of the notch translaminar propagation of the woven structures, using the InfraRed Thermography (IRT). A test of notch propagation under quasi-static traction was developed and used to study the failure phenomena on two different draping sequences. For each study, a local estimation of dissipated energies, associated with different damages, is carried out using the measurement of the surface temperature field. The study of heat source fields combined with micrographic observations allowed to define the matrix micro-cracking as the predominant damage phenomenon in crack tip. The critical energy release rate, obtained using IRT, corresponds to critical energy release rate reported in the literature for translaminar rupture of laminates. Furthermore, when brittle cracking develops in a thermosetting matrix laminate, the majority of irreversible mechanical energy (>90%) is dissipated as heat. In the case of brittle cracking, the developed method proves to be an efficient alternative technique for the local measure of energy release rate, even in cases where the variations in stiffness due to cracking phenomena remain low

Modèle de Gurson à matrice de Coulomb et Drucker-Prager : solutions exactes sous chargement isotrope

Alors que la solution du problème d'analyse limite du modèle sphérique de Gurson - à matrice de von Mises et en symétrie sphérique - est bien connue, elle n'est pas, à notre connaissance, disponible dans les deux cas de chargement isotrope (traction, compression) pour les matrices de Coulomb et Drucker-Prager. Dans la présente note, nous établissons les solutions exactes en traction-compression isotropes pour une sphère creuse soumise à une traction ou compression isotrope externe. On fournit une comparaison avec des approches 3D par éléments finis du problème d'analyse limite. Il convient de mentionner que les solutions analytiques établies sont utiles non seulement en tant que solutions de référence mais qu'elles peuvent aussi servir comme partie de la solution générale en vitesses du modèle de la sphère creuse soumise à des sollicitations arbitraires

Asymmetric friction: Modelling and experiments

International audienceThe effect of asymmetry with respect to sliding direction has been recently proved to be important in the analysis of static contact interactions of some automotive mechanical structures. In the present paper, we consider a nonclassical friction law, based on a dissymmetry of friction in a given sliding direction. A simple analytical micro-model has been adopted to derive the macroscopic model via averaging. Not only does it allow the law macroscopic characteristics to be determined but it also theoretically proves the existence of such dissymmetry of friction. The thermodynamic admissibility of the law is then shown from the derivation of a generalized standard model including friction. To complete the analysis, the existence of asymmetric friction conditions is confirmed from an experimental point of view. We then compare theoretical computations resulting from the analytical model with experimental results

Co-design of aircraft vertical tail and control laws using distributed electric propulsion

International audienceDistributed Electric Propulsion is investigated as a way to increase directional control of aircraft and reduce the vertical tail surface area. A co-design approach is presented where a H ∞ control method is used to both synthesize longitudinal/lateral control law gains and allocation module while sizing the vertical tail surface area and the propeller actuator bandwidth. The variation of the vertical tail surface area is captured throughout a collection of linearized aircraft systems representing different sizes of the vertical tail reassembled in a Linear Fractional Representation. This approach allows a reduction of 60% of the vertical tail surface area while maintaining desired dynamic behaviors with low actuator bandwidth

Towards an Aircraft with Reduced Lateral Static Stability Using Differential Thrust

International audienceIn the context of aircraft drag reduction, we study the possibility of reducing the area ofthe vertical tail using Distributed Electric Propulsion (DEP) while maintaining lateral stabilitywith active Differential Thrust (DT). Distributed Electric Propulsion is usually thought of asa mean to increase aerodynamic efficiency by exploiting the benefic effects of accelerating airaround key parts of the aircraft. However, it can also be seen as a collection of actuationdevices generating additional moments through Differential Thrust. When the engines aredistributed along the lateral axis, the aircraft designer may take advantage of the increase ofcontrol authority on yaw to reduce the static stability or the control authority provided bythe Vertical Tail (VT). This in turn would allow a reduction of vertical tail surface area. Inorder to explore and assess this idea, we suggest a framework to compare flight qualities ofa traditional configuration versus a configuration using Distributed Electric Propulsion andDifferential Thrust. The framework provides information on the flight envelop and stability ofthe aircraft by computing a map of the equilibriums. Thanks to a global approach, it allows tostudy any aircraft or DEP configurations in any flight phase. In addition, a key feature of theframework is the inclusion of the VeDSC[1] method to compute analytically the contribution ofthe vertical tail to lateral stability. It allows to study effects of a 30% reduction of VT surfacearea. Here are presented the first results and potential of using differential thrust to reducethe area of the vertical tail and the reasons for us to continue developing this framework

The Caterpillar Gallery: Quadric Surface Theorems, Parametric Design and Digital Fabrication

The use of certain quadratic surface theorems has mainly been associated in architecture with the design of classical vaults, domes and piping. The work presented by the authors is intended to explore the potential of these theorems to be used in the generation law for more complex shapes in contemporary architecture. The paper shows the case study of a built full-scale prototype, The Caterpillar gallery, a project stemming from the combination of geometric research and teaching innovation. Formal and structural experimentation take place in this project where, by starting from geometrical considerations, an efficient way of generating longitudinal spaces is proposed. One of the mentioned theorems applied to rotational cones provides the starting point for the generation of a set of concatenated surfaces that, once assembled, constitute a very stable self-supporting structure with a variety of possible applications

Measure of fracture toughness of compressive fiber failure in composite structures using infrared thermography

Fracture toughness is one of the most important properties of any material for a lot of design applications involving damage and crack growth. Unfortunately, its value can be difficult to evaluate with standard methods such as the ‘‘compliance’’ method. In this work, two special cases have been studied and infrared thermography has been used to overcome the limitations of conventional methods. Compressive fiber failure in unidirectional composite laminate has been chosen due to its difficulty to evaluate toughness. Infrared thermography has been employed to follow compressive failure mode developing during an indentation test and a compression after impact test, and to evaluate the fracture toughness of compressive fiber failure. The obtained results show a good correspondence with the value found in a previous work on FE analysis of impact damage and are consistent with the literature