Current Issue : April - June Volume : 2020 Issue Number : 2 Articles : 5 Articles
In this paper, an observer-based adaptive backstepping attitude maneuver controller (briefly, OBABC) for flexible spacecraft is\npresented. First, an observer is constructed to estimate the flexible modal variables. Based on the proposed observer, a\nbackstepping control law is presented for the case where the inertia matrix is known. Further, an adaptive law is developed to\nestimate the unknown parameters of the inertia matrix of the flexible spacecraft. By utilizing Lyapunov theory, the proposed\nOBABC law can guarantee the asymptotical convergence of the closed-loop system in the presence of the external disturbance,\nincorporating with the L2-gain performance criterion constraint. Simulation results show that the attitude maneuver can be\nachieved by the proposed observer-based adaptive backstepping attitude control law....
Single event effects (SEEs) in ground level and avionic applications are mainly induced\nby neutrons and protons, of which the relative contribution of the latter is larger with increasing\naltitude. Currently, there are two main applicable standards--JEDEC JESD89A for ground level and\nIEC 62396 for avionics--that address the procedure for testing and qualifying electronics for these\nenvironments. In this work, we extracted terrestrial spectra at different altitudes from simulations\nand compared them with data available from the standards. Second, we computed the SEE rate\nusing different approaches for three static random access memory (SRAM) types, which present a\nstrong SEE response dependence with energy. Due to the presence of tungsten, a fissile material when\ninteracting with high energy hadrons, the neutron and proton SEE cross sections do not saturate after\n200 MeV, but still increase up to several GeV. For these memories, we found standard procedures\ncould underestimate the SEE rate by a factor of up to 4-even in ground level applications--and up to\n12 times at 12 km. Moreover, for such memories, the contribution from high energy protons is able to\nplay a significant role, comparable to that of neutrons, even at commercial flight altitudes, and greater\nat higher altitudes....
The combustion of kerosene with the polymer additive polyisobutylene (PIB) was\nexperimentally investigated. The aim of the study was to measure the effect of PIB kerosene\non the efficiency of combustion chamber cooling and the combustion efficiency of the liquid propellant\nfor a rocket engine operating on kerosene and gaseous oxygen (GOX). The study was conducted\non an experimental rocket engine using kerosene wall film cooling in the combustion chamber.\nFire tests showed that the addition of polyisobutylene to kerosene had no significant effect on the\ncombustion efficiency. However, analysis of the wall temperature measurement results showed that\nthe use of PIB kerosene is more effective for film cooling than pure kerosene, which can increase the\nefficiency of combustion chamber cooling and subsequently increase its reliability and reusability.\nThus, the findings of this study are expected to be of use in further investigations of wall film\ncooling efficiency....
Electric propulsion (EP) systems offer considerably more degrees of freedom (DOFs)\nwithin the design process of aircraft compared to conventional aircraft engines. This requires large,\ncomputationally expensive design space explorations (DSE) with coupled models of the single\ncomponents to incorporate interdependencies during optimization. The purpose of this paper\nis to exemplarily study these interdependencies of system key performance parameters (KPIs),\ne.g., system mass and efficiency, for a varying DC link voltage level of the power transmission system\nconsidering the example of the propulsion system of the CENTRELINE project, including an electric\nmotor, a DC/AC inverter, and the DC power transmission cables. Each component is described by\na physically derived, analytical model linking specific subdomains, e.g., electromagnetics, structural\nmechanics and thermal analysis, which are used for a coupled system model. This approach\nstrongly enhances model accuracy and simultaneously keeps the computational effort at a low\nlevel. The results of the DSE reveal that the system KPIs improve for higher DC link voltage despite\nslightly inferior performance of motor and inverter as the mass of the DC power transmission cable\nhas a major share for a an aircraft of the size as in the CENTRELINE project. Modeling of further\ncomponents and implementation of optimization strategies will be part of future work....
Morphing structures suitable for unmanned aerial vehicles (UAVs) have been investigated\nfor several years. This paper presents a novel lightweight, morphing concept based on the exploitation\nof the â??lever effectâ? of a bistable composite plate that can be integrated in an UAV horizontal tail.\nFlight dynamics equations are solved in Simulink environment, thus being able to simulate and\ncompare different flight conditions with conventional and bistable command surfaces. Subsequently,\nbistable plates are built by using composite materials, paying particular attention to dimensions,\nasymmetric stacking sequence and total thickness needed to achieve bistability. NACA0011 airfoil is\nchosen for proving this concept. Wind tunnel tests demonstrate that the discrete surface is capable of\nwithstanding the aerodynamic pressure. A remotely piloted vehicle is employed to test the discrete\nhorizontal tail command during the take-off. The results show that, choosing a proper configuration\nof constraints, stacking sequence and aspect ratio for the bistable laminate, it is possible to tailor\nthe snap-through mechanism. The proposed concept appears lighter and increases aerodynamic\nefficiency when compared to conventional UAV command surfaces....
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