Current Issue : April - June Volume : 2017 Issue Number : 2 Articles : 6 Articles
Soft error caused by single event upset has been a severe challenge to aerospace-based computing. Silent data corruption (SDC) is\none of the results incurred by soft error. SDC occurs when a program generates erroneous output with no indications. SDC is the\nmost insidious type of results and very difficult to detect. To address this problem, we design and implement an invariant-based\nsystem called Radish. Invariants describe certain properties of a program; for example, the value of a variable equals a constant.\nRadish first extracts invariants at key program points and converts invariants into assertions. It then hardens the program by\ninserting the assertions into the source code.When a soft error occurs, assertions will be found to be false at run time and warn the\nusers of soft error. To increase the coverage of SDC, we further propose an extension of Radish, named Radish D, which applies\nsoftware-based instruction duplication mechanism to protect the uncovered code sections. Experiments using architectural fault\ninjections show that Radish achieves high SDC coverage with very low overhead. Furthermore, Radish D provides higher SDC\ncoverage than that of either Radish or pure instruction duplication....
A framework based on multibody dynamics has been developed for the static and dynamic aeroelastic analyses of flexible high\naspect ratio wing aircraft subject to structural geometric nonlinearities. Multibody dynamics allows kinematic nonlinearities\nand nonlinear relationships in the forces definition and is an efficient and promising methodology to model high aspect ratio\nwings, which are known to be prone to structural nonlinear effects because of the high deflections in flight. The multibody\ndynamics framework developed employs quasi-steady aerodynamics strip theory and discretizes the wing as a series of rigid bodies\ninterconnected by beam elements, representative of the stiffness distribution, which can undergo arbitrarily large displacements\nand rotations. The method is applied to a flexible high aspect ratio wing commercial aircraft and both trim and gust response\nanalyses are performed in order to calculate flight loads. These results are then compared to those obtained with the standard linear\naeroelastic approach provided by the Finite Element Solver Nastran. Nonlinear effects come into play mainly because of the need\nof taking into account the large deflections of the wing for flight loads computation and of considering the aerodynamic forces as\nfollower forces....
This paper attempts to investigate the flutter characteristic of sandwich panel composed of laminated facesheets and a functionally\ngraded foam core.The macroscopic properties of the foam core change continuously along this direction parallel to the facesheet\nlamina. The model used in the study is a simple sandwich panel-wing clamped at the root, with three simple types of grading\nstrategies forFGMcore: (1) linear grading strategy in the chord-wise direction, (2) linear grading strategy in the span-wise direction,\nand (3) bilinear grading of properties of foam core across the panel. The results show that use of FGM core has the potential to\nincrease the flutter speed of the sandwich panel. Finally, a minimum weight design of composite sandwich panel with lamination\nparameters of facesheet and density distribution of foam core as design variables is conducted using particle swarm optimization\n(PSO)....
Online onboard aeroengine models (OBEMs) have been widely used in health management, fault diagnostics, and fault-tolerant\ncontrol. A mismatch between the OBEM and the actual engine may be caused by a variety of factors such as health degradation\nor sensor fault and may influence the effectiveness of the systems mentioned above. However, mismatch caused by unpredictable\nsensor fault is hardly distinguished from that caused by health degradation through the tuning process. A fault-tolerant OBEM\ntuning structure is provided to perform the online tuning function when health degradation and sensor fault coexist. This system\nincludes three parts that include improved fault diagnostics and isolation (IFDI), a fault-tolerant OBEM tuning system (FTOTS),\nand a channel switching module. IFDI is used to distinguish the cause of mismatch and provide fault information, a FTOTS is used\nto complete an online tuning process based on information obtained from the IFDI, and the channel switching module is used to\nswitch the working process from the IFDI to the FTOTS. Several simulation results show that this system is able to distinguish the\ncauses of mismatch and complete online tuning in the case of sensor faults....
The objective of this study is to experimentally verify a new aerodynamic control concept of a high-angle-of-attack slender body.\nIn the concept, penetrating flow channels are installed to the apex of the slender body. The blowing or suction is generated at\nthe channel exits in response to the surface pressure distribution. First, the effects of the flow channels on the aerodynamic\ncharacteristics are experimentally investigated in a low-speed wind tunnel. The result shows the Suction-Blowing type channel\nis the most effective because its control effect does not reduce even in higher mainstream flow velocity.The peak value of the side\nforce and yawing moment can be reduced by up to 64% and 49%, respectively. In addition, visualization of the surface flow pattern\nby the oil flow method shows that the Suction-Blowing type channel makes not only the primary separation line on the body side\nbut also the secondary separation line on the body back become symmetric....
This study presents a novel integrated guidance and control method for near space interceptor, considering the coupling among\ndifferent channels of the missile dynamics, which makes the most of the overall performance of guidance and control system.\nInitially, three-dimensional integrated guidance and control model is employed by combining the interceptor-target relative motion\nmodel with the nonlinear dynamics of the interceptor, which establishes a direct relationship between the interceptor-target relative\nmotion and the deflections of aerodynamic fins. Subsequently, regarding the acceleration of the target as bounded uncertainty of the\nsystem, an integrated guidance and control algorithm is designed based on robust adaptive backstepping method, with the upper\nbound of the uncertainties unknown.Moreover, a nonlinear tracking differentiator is introduced to reduce the ââ?¬Å?compute explosionââ?¬Â\ncaused by backstepping method. It is proved that tracking errors of the state and the upper bound of the uncertainties converge to\nthe neighborhoods of the origin exponentially. Finally, simulations results show that, compared to the conventional guidance and\ncontrol design, the algorithm proposed in this paper has greater advantages in miss distance, required normal overload, and flight\nstability, especially when attacking high-maneuvering targets....
Loading....