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751.
N.I. Ismail A.H. Zulkifli M.Z. Abdullah M. Hisyam Basri Norazharuddin Shah Abdullah 《中国航空学报》2013,26(5):1093-1105
Abstract Implementing the morphing technique on a micro air vehicle (MAV) wing is a very chal- lenging task, due to the MAWs wing size limitation and the complex morphing mechanism. As a result, understanding aerodynamic characteristics and flow configurations, subject to wing structure deformation of a morphing wing MAV has remained obstructed. Thus, this paper presents the investigation of structural deformation, aerodynamics performance and flow formation on a pro- posed twist morphing MAV wing design named perimeter reinforced (PR)-compliant wing. The numerical simulation of two-way fluid structure interaction (FSI) investigation consist of a quasi- static aeroelastic structural analysis coupled with 3D incompressible Reynolds-averaged Navier- Stokes and shear-stress-transport (RANS-SST) solver utilized throughout this study. Verification of numerical method on a rigid rectangular wing achieves a good correlation with available exper- imental results. A comparative aeroelastic study between PR-compliant to PR and rigid wing per- formance is organized to elucidate the morphing wing performances. Structural deformation results show that PR-compliant wing is able to alter the wing's geometric twist characteristic, which has directly influenced both the overall aerodynamic performance and flow structure behavior. Despite the superior lift performance result, PR-compliant wing also suffers from massive drag penalty, which has consequently affected the wing efficiency in general. Based on vortices investigation, the results reveal the connection between these aerodynamic performances with vortices formation on PR-comoliant wing. 相似文献
752.
F. Durret J. S. Kaastra J. Nevalainen T. Ohashi N. Werner 《Space Science Reviews》2008,134(1-4):51-70
An excess over the extrapolation to the extreme ultraviolet and soft X-ray ranges of the thermal emission from the hot intracluster
medium has been detected in a number of clusters of galaxies. We briefly present each of the satellites (EUVE, ROSAT PSPC
and BeppoSAX, and presently XMM-Newton, Chandra and Suzaku) and their corresponding instrumental issues, which are responsible
for the fact that this soft excess remains controversial in a number of cases. We then review the evidence for this soft X-ray
excess and discuss the possible mechanisms (thermal and non-thermal) which could be responsible for this emission. 相似文献
753.
In this paper we review the possible mechanisms for production of non-thermal electrons which are responsible for the observed
non-thermal radiation in clusters of galaxies. Our primary focus is on non-thermal Bremsstrahlung and inverse Compton scattering,
that produce hard X-ray emission. We first give a brief review of acceleration mechanisms and point out that in most astrophysical
situations, and in particular for the intracluster medium, shocks, turbulence and plasma waves play a crucial role. We also
outline how the effects of the turbulence can be accounted for. Using a generic model for turbulence and acceleration, we
then consider two scenarios for production of non-thermal radiation. The first is motivated by the possibility that hard X-ray
emission is due to non-thermal Bremsstrahlung by nonrelativistic particles and attempts to produce non-thermal tails by accelerating
the electrons from the background plasma with an initial Maxwellian distribution. For acceleration rates smaller than the
Coulomb energy loss rate, the effect of energising the plasma is to primarily heat the plasma with little sign of a distinct
non-thermal tail. Such tails are discernible only for acceleration rates comparable or larger than the Coulomb loss rate.
However, these tails are accompanied by significant heating and they are present for a short time of <106 years, which is also the time that the tail will be thermalised. A longer period of acceleration at such rates will result
in a runaway situation with most particles being accelerated to very high energies. These more exact treatments confirm the
difficulty with this model, first pointed out by Petrosian (Astrophys. J. 557:560, 2001). Such non-thermal tails, even if possible, can only explain the hard X-ray but not the radio emission which needs GeV or
higher energy electrons. For these and for production of hard X-rays by the inverse Compton model, we need the second scenario
where there is injection and subsequent acceleration of relativistic electrons. It is shown that a steady state situation,
for example arising from secondary electrons produced from cosmic ray proton scattering by background protons, will most likely
lead to flatter than required electron spectra or it requires a short escape time of the electrons from the cluster. An episodic
injection of relativistic electrons, presumably from galaxies or AGN, and/or episodic generation of turbulence and shocks
by mergers can result in an electron spectrum consistent with observations but for only a short period of less than one billion
years. 相似文献
754.
Non-thermal components are key ingredients for understanding clusters of galaxies. In the hierarchical model of structure
formation, shocks and large-scale turbulence are unavoidable in the cluster formation processes. Understanding the amplification
and evolution of the magnetic field in galaxy clusters is necessary for modelling both the heat transport and the dissipative
processes in the hot intra-cluster plasma. The acceleration, transport and interactions of non-thermal energetic particles
are essential for modelling the observed emissions. Therefore, the inclusion of the non-thermal components will be mandatory
for simulating accurately the global dynamical processes in clusters. In this review, we summarise the results obtained with
the simulations of the formation of galaxy clusters which address the issues of shocks, magnetic field, cosmic ray particles
and turbulence. 相似文献
755.
Yiwei WANG Christian GOGU Nicolas BINAUD Christian BES Raphael T.HAFTKA Nam H.KIM 《中国航空学报》2017,30(3)
Airframe maintenance is traditionally performed at scheduled maintenance stops.The decision to repair a fuselage panel is based on a fixed crack size threshold,which allows to ensure the aircraft safety until the next scheduled maintenance stop.With progress in sensor technology and data processing techniques,structural health monitoring (SHM) systems are increasingly being considered in the aviation industry.SHM systems track the aircraft health state continuously,lead ing to the possibility of planning maintenance based on an actual state of aircraft rather than on a fixed schedule.This paper builds upon a model-based prognostics framework that the authors developed in their previous work,which couples the Extended Kalman filter (EKF) with a first order perturbation (FOP) method.By using the information given by this prognostics method,a novel cost driven predictive maintenance (CDPM) policy is proposed,which ensures the aircraft safety while minimizing the maintenance cost.The proposed policy is formally derived based on the trade-off between probabilities of occurrence of scheduled and unscheduled maintenance.A numerical case study simulating the maintenance process of an entire fleet of aircrafts is imple mented.Under the condition of assuring the same safety level,the CDPM is compared in terms of cost with two other maintenance policies:scheduled maintenance and threshold based SHM maintenance.The comparison results show CDPM could lead to significant cost savings. 相似文献
756.
This paper presents an analytical solution for static analysis of thick rectangular beams with different boundary conditions.Carrera's Unified Formulation (CUF) is used in order to consider shear deformation theories of arbitrary order.The novelty of the present work is that a boundary discontinuous Fourier approach is used to consider clamped boundary conditions in the analytical solution,unlike Navier-type solutions which are restricted to simply supported beams.Governing equations are obtained by employing the principle of virtual work.The numerical accuracy of results is ascertained by studying the convergence of the solution and comparing the results to those of a 3D finite element solution.Beams subjected to bending due to a uniform pressure load and subjected to torsion due to opposite linear forces are considered.Overall,accurate results close to those of 3D finite element solutions are obtained,which can be used to validate finite element results or other approximate methods. 相似文献
757.
This paper deals with the technical features of designing an information-controlling system to prevent critical operating conditions of the helicopter flight, a technique for evaluating its effectiveness, analysis and synthesis of the measurement channels, forming of warning signals, and information support of the crew in abnormal situations. 相似文献
758.
In the paper, processes of high-energy electron beam interaction with plasma particles in a discharge channel of a stationary plasma thruster are analyzed and the results are presented. 相似文献
759.
C. J. Hansen M. A. Caplinger A. Ingersoll M. A. Ravine E. Jensen S. Bolton G. Orton 《Space Science Reviews》2017,213(1-4):475-506
Junocam is a wide-angle camera designed to capture the unique polar perspective of Jupiter offered by Juno’s polar orbit. Junocam’s four-color images include the best spatial resolution ever acquired of Jupiter’s cloudtops. Junocam will look for convective clouds and lightning in thunderstorms and derive the heights of the clouds. Junocam will support Juno’s radiometer experiment by identifying any unusual atmospheric conditions such as hotspots. Junocam is on the spacecraft explicitly to reach out to the public and share the excitement of space exploration. The public is an essential part of our virtual team: amateur astronomers will supply ground-based images for use in planning, the public will weigh in on which images to acquire, and the amateur image processing community will help process the data. 相似文献
760.
H. M. Cuppen C. Walsh T. Lamberts D. Semenov R. T. Garrod E. M. Penteado S. Ioppolo 《Space Science Reviews》2017,212(1-2):1-58
The cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of \({\sim}25\) experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions. 相似文献