排序方式: 共有309条查询结果,搜索用时 62 毫秒
101.
The evolution of two-dimensional (2D) electron phase-space holes (electron holes) has been previously investigated with electrostatic Particle-in-Cell (PIC) simulations, which neglect ion dynamics. The electron holes are found to be unstable to the transverse instability, and their evolution is determined by the combined action between the transverse instability and the stabilization by the background magnetic field. In this paper, the effect of ion dynamics on the evolution of an electron hole is studied. In weakly magnetized plasma (Ωe < ωpe, where Ωe and ωpe are electron gyrofrequency and plasma frequency, respectively), the electron hole is still unstable to the transverse instability. However, it evolves a little faster and is destroyed in a shorter time when ion dynamics is considered. In strongly magnetized plasma (Ωe > ωpe), the electron hole is broken due to the lower hybrid waves, and its evolution is much faster. 相似文献
102.
Kelvin-Helmholtz (K-H) waves are formed from the triggeringof the K-H instability on the magnetopause, which is a candidatemechanism for solar wind entry into the magnetosphere, especially undernorthward interplanetary magnetic field conditions. In this study, aK-H wave event was identified from the observation of probe Bof the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission on 15 May 2008. A new method to determinethe wave parameters of the K-H waves in single-spacecraft observationsis proposed. The dominant wave period is determined by three kinds ofspectrograms for three key parameters, namely the ion density, the iontemperature, and the z component of magnetic field. The phasevelocity is estimated by calculating the center-of-mass velocity of thedetected K-H vortex region. This approximation is validated bycomparison with other alternative methods. The method to determine thewave parameters is a first step to further study K-H wave properties and their relationship with interplanetaryconditions. 相似文献
103.
Renjie JI Qian ZHENG Yonghong LIU Hui JIN Fan ZHANG Shenggui LIU Baokun WANG Shuaichen LU Baoping CAI Xiaopeng LI 《中国航空学报》2022,35(3):484-493
The nickel-based superalloy Inconel 718 is treated with Coupled Ultrasonic and Electric Pulse Treatment(CUEPT), and the surface grain is refined from the average size of 9550.0 nm to287.9, 216.3, 150.5, 126.3, 25.8 nm by different effective treatment currents, respectively. The ultraprecision turning experiments are carried out on the processed workpiece after CUEPT. The experimental results show that the average cutting force increases with the decrease of surface grain size.Moreover, a mathema... 相似文献
104.
Minghuan WANG Yongchao SHANG Changshun LIU Jiajie WANG Jinsong ZHENG Xufeng XU 《中国航空学报》2022,35(3):494-508
The radial ultrasonic rolling electrochemical micromachining(RUR-EMM) combined rolling electrochemical micromachining(R-EMM) and ultrasonic vibration was studied in this paper. The fundamental understanding of the machining process especially the interaction between multiphysics in the interelectrode gap(IEG) was investigated and discussed by the finite element method. The multiphysics coupling model including flow field model, Joule heating model, material dissolution model and vibration model ... 相似文献
105.
This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle(FWMAV), named NPU-Tinybird. Firstly, a complete modeling of NPU-Tinybird is determined, including the aerodynamic model based on the quasi-steady method, the kinematic and dynamic model about the mechanism of flapping and attitude control,combined with the single rigid body dynamic mod... 相似文献
106.
Accelerated Landweber iteration based control allocation for fault tolerant control of reusable launch vehicle 总被引:1,自引:0,他引:1
This paper presents a novel Fault Tolerant Control(FTC) scheme based on accelerated Landweber iteration and redistribution mechanism for a horizontal takeoff horizontal landing reusable launch vehicle(RLV). First, an adaptive law based on fixed-time non-singular fast terminal sliding mode control(NFTSMC), which focuses on the attitude tracking controller design for RLV in the presence of model couplings, parameter uncertainties and external disturbances, is proposed to produce virtual control co... 相似文献
107.
The LM-5B carrier rocket is a new-generation large-scale launch vehicle developed for space station launch missions. Its separation system includes fairing separation, space station module-rocket separation, and booster separation. The separation systems play an important role in the design of launch vehicles, and any failure during the separation process would affect the final completion of rocket flight mission. This paper presents the reliability design and analysis for the LM-5B carrier rock... 相似文献
108.
The cylinder block/valve plate interface is one of the most critical frictional interfaces of the swashplate-type axial piston pump. However, the poor lubrication interface caused rapid wear and high friction loss in an elastohydrodynamic lubrication system, decreasing the pump lifetime.Wear resistant bronze coatings were fabricated on 38CrMoAl substrate by Physical Vapor Deposition(PVD) and Chemical Vapor Deposition(CVD), respectively. Ball-on-disc wear tests were performed to comparatively inv... 相似文献
109.
In some military application scenarios, Unmanned Aerial Vehicles(UAVs) need to perform missions with the assistance of on-board cameras when radar is not available and communication is interrupted, which brings challenges for UAV autonomous navigation and collision avoidance. In this paper, an improved deep-reinforcement-learning algorithm, Deep Q-Network with a Faster R-CNN model and a Data Deposit Mechanism(FRDDM-DQN), is proposed. A Faster R-CNN model(FR) is introduced and optimized to obtain... 相似文献
110.
Aerodynamic surrogate modeling mostly relies only on integrated loads data obtained from simulation or experiment,while neglecting and wasting the valuable distributed physical information on the surface.To make full use of both integrated and distributed loads,a modeling paradigm,called the heterogeneous data-driven aerodynamic modeling,is presented.The essential concept is to incorporate the physical information of distributed loads as additional constraints within the end-to-end aerodynamic m... 相似文献