Current Issue : July - September Volume : 2020 Issue Number : 3 Articles : 5 Articles
Boundary layer transition is a hot research topic in fluid mechanics and aerospace engineering. In low-speed flows, twodimensional\nTollmien-Schlichting (T-S) waves always dominate the flow instability, which has been modeled by Coder and\nMaughmer from 2013. However, in supersonic flows, three-dimensional oblique Tollmien-Schlichting waves become\ndominant in flow instability. Inspired by Coder and Maughmerâ??s NTS amplification factor transport equation for twodimensional\nTollmien-Schlichting waves in low-speed flows and Kroo and Sturdzaâ??s linear stability theory (LST) analysis\nresults for oblique Tollmien-Schlichting waves in supersonic flows, a new amplification factor transport equation for oblique\nTollmien-Schlichting waves has been developed based on LST. The compressible Falkner-Skan similarity equations are\nintroduced to build the relationships between nonlocal variables and local variables so that all the variables used in the\npresent model can be calculated using local variables. Applications of this new transport equation to the flows over\nsupersonic flat plate, 3% thick biconvex airfoil, and one modified supersonic laminar airfoil show promising results compared\nwith the standard LST analysis results....
Recent trend in the aeronautic industry is to introduce a novel prognostic solution for \ncritical systems in the attempt to increase vehicle availability, reduce costs, and optimize the \nmaintenance policy. Despite this, there is a general lack of literature about prognostics for hydraulic \nflight control systems, especially looking at helicopter applications. The present research was \nfocused on a preliminary study for an integrated framework of fault detection and failure prognosis \ntailored for one of the most common architectures for flight control actuation. Starting from a high\nfidelity dynamic model of the system, two different faults were studied and described within a \ndedicated simulation environment: the opening of a crack in the coils of the centering springs of the \nactuator and the wear of the inner seals. Both failure modes were analyzed through established \nmodels available in the literature and their evolution simulated within the model of the actuator. \nHence, an in depth feature selection process was pursued aimed at the definition of signals suitable \nfor both diagnosis and prognosis. Results were then reported through an accuracy sensitivity plane \nand used to define a prognostic routine based on particle filtering techniques. The more significant \ncontribution of the present research was that no additional sensors are needed so that the prognostic \nsystem can be potentially implemented for in service platforms....
To solve the problem of the effective cushioning of fast-moving mechanical components in small ring-shaped spaces, the factors\naffecting the compression and energy absorption properties of small-sized hollow metal tubes were studied. Simulation models\nwere constructed to analyse the influences of tube diameter, wall thickness, relative position, and number of stacked\ncomponents on the compression and energy absorption properties. The correctness of the simulation method and its output\nwere verified by experiments, which proved the effectiveness of compression and energy absorption properties of small-sized\nthin-walled metal tubes. The research provides support for the application of metal tube buffers in armament launch technology\nand engineering practice....
Aiming at the experimental test of the body freedom flutter for modern high aspect ratio \nflexible flying wing, this paper conducts a body freedom flutter wind tunnel test on a full span \nflying wing flutter model. The research content is summarized as follows: (1) The full span finite \nelement model and aeroelastic model of an unmanned aerial vehicle for body freedom flutter wind \ntunnel test are established, and the structural dynamics and flutter characteristics of this vehicle are \nobtained through theoretical analysis. (2) Based on the preliminary theoretical analysis results, the \ndesign and manufacturing of this vehicle are completed, and the structural dynamic characteristics \nof the vehicle are identified through ground vibration test. Finally, the theoretical analysis model is \nupdated and the corresponding flutter characteristics are obtained. (3) A novel quasi free flying \nsuspension system capable of releasing pitch, plunge and yaw degrees of freedom is designed and \nimplemented in the wind tunnel flutter test. The influence of the nose mass balance on the flutter \nresults is explored. The study shows that: (1) The test vehicle can exhibit body freedom flutter at \nlow airspeeds, and the obtained flutter speed and damping characteristics are favorable for \nconducting the body freedom flutter wind tunnel test. (2) The designed suspension system can \neffectively release the degrees of freedom of pitch, plunge and yaw. The flutter speed measured in \nthe wind tunnel test is 9.72 m/s, and the flutter frequency is 2.18 Hz, which agree well with the \ntheoretical results (with flutter speed of 9.49 m/s and flutter frequency of 2.03 Hz). (3) With the \nincreasing of the mass balance at the nose, critical speed of body freedom flutter rises up and the \nflutter frequency gradually decreases, which also agree well with corresponding theoretical results....
From the perspective of input and output, this paper constructs an evaluation index system for the status quo of technology\ninnovation resource allocation in Chinaâ??s aerospace industry. Taking the industrial panel data of 20 provincial regions from 2007\nto 2016 in China as samples, this paper uses the stochastic frontier method, which is improved by the projection pursuit model\nbased on accelerated genetic algorithm, to analyze the factors influencing the allocation efficiency of technology innovation\nresource in the aerospace industry and then make a static evaluation for the current situation. In addition, based on the perspective\nof velocity characteristics, this study uses the dynamic comprehensive evaluation model to evaluate the resource allocation of\ntechnology innovation in the aerospace industry. The empirical research shows that the resource allocation efficiency of\ntechnology innovation in the aerospace industry is generally at the lower middle level, indicating an unbalanced trend of â??reverseâ?\nallocation with the level of regional economic development. It is also found that the efficiency improvement effect in recent years is\nnot obvious. At last, based on the studyâ??s findings, some countermeasures and suggestions are put forward to improve the\ncurrent situation....
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