Autonomous take-off and landing of a tethered aircraft: a simulation study

The problem of autonomous launch and landing of a tethered rigid aircraft for airborne wind energy generation is addressed. The system operates with ground-based power conversion and pumping cycles, where the tether is repeatedly reeled in and out of a winch installed on the ground and linked to an electric motor/generator. In order to accelerate the aircraft to take-off speed, the ground station is augmented with a linear motion system composed by a slide translating on rails and controlled by a second motor. An onboard propeller is used to sustain the forward velocity during the ascend of the aircraft. During landing, a slight tension on the line is kept, while the onboard control surfaces are used to align the aircraft with the rails and to land again on them. A model-based, decentralized control approach is proposed, capable to carry out a full cycle of launch, low-tension flight, and landing again on the rails. The derived controller is tested via numerical simulations with a realistic dynamical model of the system, in presence of different wind speeds and turbulence, and its performance in terms of landing accuracy is assessed. This study is part of a project aimed to experimentally verify the launch and landing approach on a small-scale prototype.Comment: This is the longer version of a paper submitted to the 2016 American Control Conference 2016, with more details on the simulation parameter

Creep and fluidity of a real granular packing near jamming

We study the internal dynamical processes taking place in a granular packing below yield stress. At all packing fractions and down to vanishingly low applied shear, a logarithmic creep is evidenced. The experiments are analyzed under the scope of a visco-elastic model introducing an internal "fluidity" variable. For all experiments, the creep dynamics can be rescaled onto a unique curve which displays jamming at the random-close-packing limit. At each packing fraction, a stress value is evidenced, corresponding to the onset of internal granular reorganisation leading to a slowing down the creep dynamics before the final yield

Pro-poor intervention strategies in irrigated agriculture in Asia: poverty in irrigated agriculture: issues and options: Vietnam

Irrigated farming / Poverty / Farm income / Irrigation management / Institutions / Legal aspects / Water rates / User charges / Participatory management / Privatization / Participatory rural appraisal / Performance indexes / Irrigation programs / Irrigation systems / Pumping / Irrigation canals / Social aspects / Economic aspects / Rivers / Hydrology / Dams / Households / Income / Regression analysis / Drainage / Cooperatives / Water delivery / Water distribution / Rice / Financing / Drought / Vietnam / Red River Delta / Nam Duong Irrigation System / Nam Thach Han Irrigation System / Han River

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

Effects of propidium monoazide (PMA) treatment on mycobiome and bacteriome analysis of cystic fibrosis airways during exacerbation

Introduction and Purpose : Propidium monoazide (PMA)-pretreatment has increasingly been applied to remove the bias from dead or damaged cell artefacts, which could impact the microbiota analysis by high-throughput sequencing. Our study aimed to determine whether a PMA-pretreatment coupled with high-throughput sequencing analysis provides a different picture of the airway mycobiome and bacteriome. Results and Discussion : We compared deep-sequencing data of mycobiota and microbiota of 15 sputum samples from 5 cystic fibrosis (CF) patients with and without prior PMA-treatment of the DNA-extracts. PMA-pretreatment had no significant effect on the entire and abundant bacterial community (genera expressed as operational taxonomic units (OTUs) with a relative abundance greater than or equal to 1%), but caused a significant difference in the intermediate community (less than 1%) when analyzing the alpha biodiversity Simpson index (p = 0.03). Regarding PMA impact on the airway mycobiota evaluated for the first time here; no significant differences in alpha diversity indexes between PMA-treated and untreated samples were observed. Regarding beta diversity analysis, the intermediate communities also differed more dramatically than the total and abundant ones when studying both mycobiome and bacteriome. Our results showed that only the intermediate (or low abundance) population diversity is impacted by PMA-treatment, and therefore that abundant taxa are mostly viable during acute exacerbation in CF. Given such a cumbersome protocol (PMA-pretreatment coupled with high-throughput sequencing), we discuss its potential interest within the follow-up of CF patients. Further studies using PMA-pretreatment are warranted to improve our "omic" knowledge of the CF airways

Fluage et rupture dans un matériau granulaire

National audienceWe study experimentally the localization of deformation occuring at slow shear, in a 3D granular packing. We use an original method of measurement of deformation based on Diffusive Wave Spectroscopy. We evidence localized regions of strong deformations spanning a mesoscopic size of about 10 grains. We link the apparition rate of those spots to the concept of fluidity, recently used to describe the local and non-local rheology of soft glassy materials

Reduction of Vertical Tail Using Differential Thrust: Influence on Flight Control and Certification

International audienceThe flight control characteristics and certification compliance of a Distributed Electric Propulsion (DEP) aircraft using differential thrust is studied through exploration of flight envelops. Identification of critical flight phases specific to the use of propulsion systems as actuators for flight control is performed. In particular the influence of engine failures on the flight envelop and means of mitigation are given. It is concluded that an aircraft using differential thrust has a most advantageous flight envelop at the point of neutral directional static stability allowing a reduction of 45% of the vertical tail surface area. Additionally, the directional control could be entirely provided by differential thrust, eliminating the need for a rudder. Study of this type of aircraft showed specific failure modes that differ from the actual certification prescriptions. New more relevant definitions and parameters are proposed as basis to demonstrate compliance with high level certification objectives