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  • 2021 Volume 38 Issue 5
    Published: 26 March 2021
      
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  • Numerical Simulation of a Forward-facing Step Flow Controlled byDBD Plasma
    2021, 38(5): 1-7.
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    In order to explore the control effect of dielectric barrier discharge (DBD) on a forward facing step’s flow separation, the source item of body force was introduced into the N-S equations by Fluent User Defined Function (UDF) by numerically simulation. The results show that the flow separation on the step wall can be effectively controlled by DBD on the upper wall at the flow velocity of 20m/s, and the separation area can be reduced by about 80%.
  • Research on Rubber Forming of Aircraft Conduits Shelter Groove
    2021, 38(5): 8-14.
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    The space can be saved and the weight of the aircraft can be reduced through the pipe avoidance groove when there are crossed-pipes on the aircraft. In order to effectively solve the forming problem of the pipe avoidance groove, the forming method of polyurethane rubber stamping is selected. The finite element analysis software ABAQUS is used to analyze the rubber forming process of the pipe avoidance groove. The effects of feed rate and rubber hardness on the die fitting and the wall thickness distributions of copper and aluminum pipes are studied. The optimized parameters of the finite element analysis are used to compard with the experimental results. The results show that under the same feed rate and the same hardness of the polyurethane rubber, the die fitting of aluminum tube is better than that of copper tube; the tube wall thickening and thinning trend at the pipe avoidance groove are basically the same after forming; the increase and decrease rate of wall thickness are less than 5%, which meets the requirements of practical application.
  • Evaluation of UAV storage solution based on G1 method
    2021, 38(5): 15-22.
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    In order to deal with the fast-response mission scenarios in the future ,reduce the preparation time of UAV response task and ensure the mission performance of UAV, aiming at the problem of efficient storage of UAV, the evaluation of UAV storage scheme is studied. From the two dimensions of efficiency and cost, 24 indicators are divided to establish the evaluation index system of uav batch storage scheme, and the G1 method is used to calculate the index weight. Finally, the UAV storage scheme is evaluated by experts by introducing actual storage cases. The evaluation index system of UAV storage scheme proposed in this paper provides a scientific basis for efficient storage of UAV, and also provides a reference for research in related fields.
  • Studies into the hail ingestion airworthiness conformance test method of turbofan engines
    2021, 38(5): 23-29.
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    The validation methods on turbofan engine hail ingestion complying with CCAR 33《Airworthiness Standards：Aircraft En-gines》 was studied. Analyzing the airworthiness terms of CCAR 33 and the tests for foreign engines, the methods of test pa-rameters selection was researched, the requirement of test equipment and measurement system was proposed, the ways and the keystone of test data processing was determined. It has reference meaning for the test on outdoor testbed for Airworthiness Con-formance of hail ingestion based on CCAR 33.78.
  • Simplification and verification of n-dodecane mechanism
    2021, 38(5): 30-37.
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    The composition of aviation kerosene is complicated. In order to construct its chemical reaction dynamic model, this paper constructs and simplifies the combustion mechanism of the main alternative fuel of aviation kerosene, n-dodecane. N-Dodecane is widely used as a single-component surrogate fuel for aviation kerosene, and it is also an important component of multi-component alternative fuel. Through the combination of path flux analysis method and decoupling methodology, the reduced mechanism of n-dodecane with 63 components and 189 reactions was obtained. Under the conditions of temperature 650K-1300K, equivalent ratio 0.5-2.0, and pressure 8-15atm, the ignition delay time, component concentration (CO2, H2O, etc.), laminar flame speed are simulated and compared with experimental data. The results show that the reduced mechanism accurately simulates the flame retardation period of n-dodecane under high pressure, the trend of CO2, H2O and other component concentrations under low equivalence ratio, and the laminar flame speed. This work provides data support for constructing the combustion reaction kinetics model of aviation kerosene multi-component surrogate fuel.
  • Dynamics Optimization Design of Geared Turbofan Engine Low Pressure Rotor System
    2021, 38(5): 38-43.
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    The low pressure rotor of geared turbofan (GTF) engine has the characteristic of long span and high rotational speed, which leads to difficulty to the rotor dynamic design. This paper introduced the structural characteristic of GTF engine low pressure rotor briefly, at the same time, calculated the critical rotating speed and strain energy distribution. Furthermore, this paper focused on some pri-mary structural parameters such as supporting stiffness , the size of section and supporting span which influences the critical rotating speed and strain energy distribu-tion a lot, finding their effect regulation. The result can provide reference and guidance for the structural design and vabration study of GTF engine. According to the analysis result, proper structural parameters are chosen so that the dynamic structure of low pressure rotor is optimized.
  • An anti-occlusion and automatic correction KCF algorithm
    2021, 38(5): 44-50.
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    Abstract: In the process of KCF tracking the target due to various interferences in the background, the tracking of the object will be biased,The continuous accumulation of deviation will eventually lead to the problem of target tracking failure.Based on this problem, this article proposes a way to combine the KCF algorithm with the Mean-shift algorithm,When the tracking accuracy of the KCF algorithm decreases, the Mean-Shift algorithm is introduced to further determine the target position and obtain the correct position of the tracking target.In order to solve the problem that the KCF algorithm cannot accurately relocate after the target is occluded, the following solutions are proposed,First, judge whether the target is occluded by the ratio of the center point of the image block to the average value of the neighborhood response,and retain the information of the previously unoccluded frames,Then determine the position of the target on the image by ORB feature matching,Test through partial sequences on the TB data set,The test results show that the improved algorithm can effectively solve the problem that the target will fail to track when the target is occluded and the background is severely disturbed. Keywords:Kernel Correlation Filtering (KCF); Mean-shift algorithm; target tracking; ORB feature matching
  • Dynamic gesture recognition based on multi-domain convolutional neural network
    2021, 38(5): 51-57.
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    The tracking and recognition of dynamic gestures has always been the focus and difficulty in the visual field. In view of the traditional gesture tracking method, the poor tracking effect limits the accuracy of dynamic gesture recognition, a dynamic gesture recognition algorithm under the multi-domain convolutional neural network tracking framework is proposed. Multi-domain convolutional neural network is used to implement gesture tracking in the algorithm, and according to the characteristics of gesture tracking, the network structure is streamlined, and the universal fc6 layer is constructed. The applicability of dynamic gesture tracking is enhanced, and the tracking effect is improved in this algorithm. Secondly, the VGG-19 network is used to identify the dynamic gesture trajectory feature map constructed by the tracking network. The tracking problem is reduced to a binary classification of target and background, and multi-domain convolutional neural networks are used to learn commonality of tracking targets. The shallow convolutional neural network is used to enhance the spatial information, so the dynamic gesture tracking and recognition result is improved. The recognition rate of the four types of self-built dynamic gestures is as high as 97.5%, and 93.33% recognition rate is obtained in Chalearn Gesture Data International Standard gesture database, which verifies the effectiveness of the algorithm.
  • Improvement of Canny edge detection based on Otsu algorithm of gradient
    2021, 38(5): 58-65.
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    Aiming at the problems such as the sensitivity of salt and pepper noise in Canny algorithm, blurred image edges after filtering, inaccurate gradient calculation, and difficult threshold setting, we established a method that can retain edge information while filtering and select high and low thresholds reasonably according to the image gradient extreme value to improve positioning accuracy Improved Canny algorithm. In this paper, K-nearest neighbor mean filtering is first used to replace gauss filtering, which enhances the denoising ability while retaining image edge information. Secondly, the Scharr operator is used to replace the original gradient template to calculate the image gradient, and the operator kernel is improved to make the calculation result more accurate while reducing the operation time; finally, after non-maximum suppression, the gradient map is used with a suppression factor Otsu algorithm, adaptively select high and low thresholds in Canny algorithm. Simulation experiment results show that the algorithm has good signal-to-noise ratio, edge detection effect and adaptability.
  • An improved WiFi fingerprint location algorithm
    2021, 38(5): 66-72.
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    Due to the wide use of WiFi devices and the increasing demand for indoor positioning system, the location algorithm based on WiFi system has attracted extensive interest of researchers. This paper mainly studies the fingerprint location algorithm of WiFi. Through the research and analysis of the advantages and disadvantages of the WiFi fingerprint location algorithm based on WKNN and the WiFi fingerprint location algorithm based on kernel Kmeans + RVM, an improved algorithm is proposed for the reasons of low positioning accuracy and unstable collected signal. In the offline phase, kernel Kmeans + RVM algorithm is used to optimize the fingerprint database; in the online phase, the distance between the fingerprint node and the node to be tested, and the distance between the selected k neighboring nodes and its center node are weighted to obtain the weight and obtain the positioning and positioning. The simulation results show that the algorithm can effectively solve the defects of the original algorithm, and has better improvement in positioning error and stability.
  • An Empirical Study of Internal Control Based on the Mediating Effect of Social Responsibility on Corporate Performance
    2021, 38(5): 83-92.
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  • Cyclicity of Hopf bifurcation in some piecewise Liénard systems
    2021, 38(5): 93-96.
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    Hilbert’s 16th problem is an important mathematical problem proposed by the famous mathematician Hilbert concerning the existence and distribution of limit cycles of plane polynomial systems. This problem has not been completely solved yet. Based on this, we study the bifurcation of limit cycles near the origin of some piecewise Liénard systems. By perturbing, we obtain the cyclicity N(m,n,1,2), m,n belongs to {1，2，3}.