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Research on Guidance and Control Law Design of Decelerating Transition and Vertical Landing for a STOVL UAV

Journal of physics: Conference Series 2021年第1期1875卷

作者： Zixu Dong Yang Ren Kun Chen Yaohui Chen National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China China Research and development Academy of Machinery Equipment Beijing 100089 China

In this paper, an integrated design method for guidance and control laws for a short takeoff and vertical landing (STOVL) unmanned aerial vehicle (UAV) during decelerating transition and vertical landing phases under thrust vector control is studied. Based on the principle of time-scale separation, the outer-loop guidance law adopts an implicit dynamic inverse method to provide attainable overload vector control instructions for decelerating transition and vertical landing phases. Meanwhile, the inner-loop control law adopts an improved eigen-structure assignment method, which tracks guidance instructions and maintains a stable attitude. The attitude nozzles are joined to the attitude control with the dropping of dynamic pressure, thereby assisting aerodynamic surfaces to stabilize attitudes. Subsequently, the feasibility and effect of the control methods for a STOVL UAV during decelerating transition and vertical landing phases are verified by a 6-DOF flight simulation platform. The simulation results demonstrate that the integrated design method is beneficial for a quick evaluation of the overall scheme.

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A new kind of hairpin-like vortical structure induced by cross-interaction of sinuous streaks in turbulent channel

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Chinese physics B 2018年第8期27卷 331-340页

作者： Jian Li Gang Dong Hui Zhang Zhengshou Chen Zhaode Zhang l School of Naval Architecture and Mechanical-electrical Engineering Zhejiang Ocean UniversityZhoushan 316022China National Key Laboratory of Transient Physics Nanjing University of Science and TechnologyNanjing 210094China Key Laboratory of Offshore Engineering Technology of Zhejiang Province Zhoushan 316022China

This work is motivated by previous experimental and numerical studies which reveal that the hairpin vortex could be formed by the interaction between spanwise adjacent low-speed streaks. To prove that such an interaction mechanism is still applicable in the normal direction, two sinuous low-speed streaks with the same streamwise phase are set to be in the upper half and bottom half of a small size channel, respectively, and their evolution and interaction are investigated by direct numerical simulation. A new kind of hairpin-like vortical structure, distributed in the normal direction and straddled across both halves of the channel, is found during the cross-interaction process of the low-speed streaks. The influence of such a normal-distributed hairpin-like vortex （NHV） on the turbulent statistical regularity is also revealed. It is observed that the NHV can lead to a sudden surge of wall skin friction, but the value of the normal velocity as well as the streamwise and spanwise vorticity sharply decrease to zero in the center of the channel.

关键词： low-speed streaks hairpin vortex channel flow direct numerical simulation

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Carboxyl graphene oxide solution saturable absorber for femtosecond mode-locked erbium-doped fiber laser

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Chinese physics B 2018年第11期27卷 517-521页

作者： Rui-dong Lv Lu Li Yong-gang Wang Zhen-dong Chen Si-cong Liu Xi Wang Jiang wang Yong-fang Li School of Physics and Information Technology Shaanxi Normal University School of Science Xi'an Institute of Posts and Telecommunications State Key Laboratory of Transient Optics and Photonics Xi'an Institute of Optics and Precision MechanicsChinese Academy of Sciences

The carboxyl-functionalized graphene oxide(GO-COOH)is a kind of unique two-dimensional(2 D)material and possesses excellent nonlinear saturable absorption property and high *** this paper,we prepare saturable absorber(SA)device by depositing GO-COOH nanosheets aqueous solution on a D-shaped *** modulation depth(MD)and saturable intensity of the SA are measured to be 9.6%and 19 MW/cm^(2),*** inserting the SA into the erbium-doped fiber(EDF)laser,a passively mode-locked EDF laser has been achieved with the spectrum center wavelength of 1562.76 *** pulse duration,repetition rate,and the signal-to-noise ratio(SNR)are 500 fs,14.79 MHz,and 80 dB,*** maximum average output power is measured to be 3.85 *** results indicate that the GO-COOH nanosheets SA can be used as a promising mode locker for the generation of ultrashort pulses.

关键词： fiber lasers mode-locked pulse nonlinear optical materials carboxyl graphene oxide

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Recent update on the multi-physical model of electromagnetic railgun 31

Recent update on the multi-physical model of electromagnetic...

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31st International Symposium on Ballistics, BALLISTICS 2019

作者： Li, Baoming Lin, Qinghua Woodley, Clive National Key Laboratory of Transient Physics Nanjing University of Science and Technology P. O. Box Nanjing210094 China China Academy of Ordnance P. O. Box Beijing100089 China Department of Physics Imperial College 900 Blackett Laboratory Prince Consort Road LondonSW7 2AZ United Kingdom

ISBN: (纸本)9781605956107

This paper begins with a brief review of the development of computational codes on themulti-physical fields of electromagnetic railgun, followed by an introduction of recentupdates in the modeling of structural dynamics. The multi-physical fields model was partlyverified by experiments. The capacities of the computational code for the multi-physicalfields were demonstrated by several examples. Some details of the launching process wereillustrated, and the mechanisms of rail vibration, armature balloting motion, arc transition,rail gouging, and interface wear were discussed. The results show that the materialnonlinearity plays a key role in modeling the structural dynamic behaviors. © 2019 by International Ballistics Society All rights reserved.

关键词： Structural dynamics

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High-SNR snapshot multiplex spectrometer with sub-Hadamard-S matrix coding

arXiv

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arXiv 2019年

作者： Zhao, Zhuang Bai, Lianfa Han, Jing Yue, Jiang School of Electronic Engineering and Optoelectronic Technology Nanjing University of Science and Technology Nanjing210094 China National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China

We present a robust high signal-to-noise ratio (SNR) snapshot multiplex spectrometer with sub-Hadamard-S matrix coding. We demonstrated for the first time that the sub-Hadamard-S matrix coding could provide comparable SNR improvement with Hadamard-S matrix in Hadamard transform spectrometer (HTS). Normally, HTS should change the coding mask to obtain a reasonable spectrum result, causing unexpected time-consuming. An extra imaging path to collect the light intensity of the aperture is added in this paper. Both light intensity of the aperture and overlapped spectra are captured within one shot, turning Hadamard-S matrix coding into sub-Hadamard-S matrix coding. Simulations and experiments show that the proposed method could obtain comparable SNR improvement with the traditional HTS, maintaining snapshot. Copyright © 2019, The Authors. All rights reserved.

关键词： Spectrometers

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Discrete Boltzmann model for implosion- and explosion- related compressible flow with spherical symmetry

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Frontiers of physics 2018年第5期13卷 31-44页

作者： Ai-Guo Xu Guang-Cai Zhang Yu-Dong Zhang Pei Wang Yang-Jun Ying National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P.O. Box 8009-26 Beijing 100088 China Center for Applied Physics and Technology MOE Key Center for High Energy Density Physics Simulations College of Engineering Peking University Beijing 100871 China Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China

To kinetically model implosion- and explosion-related phenomena, we present a theoretical framework for constructing a discrete Boltzmann model （DBM） with spherical symmetry in spherical coordinates. To achieve this goal, a key technique is to use local Cartesian coordinates to describe the particle velocity in the kinetic model. Therefore, geometric effects, such as divergence and convergence, are described as a ＂force term＂. To better access the nonequilibrium behavior, even though the corre- sponding hydrodynamic model is one-dimensional, the DBM uses a discrete velocity model （DVM） with three dimensions. A new scheme is introduced so that the DBM can use the same DVM regard- less of whether or not there are extra degrees of freedom. As an example, a DVM with 26 velocities is formulated to construct the DBM at the Navier-Stokes level. Via the DBM, one can study simulta- neously the hydrodynamic and thermodynamic nonequilibrium behaviors in implosion and explosion processes that are not very close to the spherical center. The extension of the current model to a multiple-relaxation-time version is straightforward.

关键词： discrete Boltzmann model compressible flows spherical symmetry geometric effects thermodynamic nonequilibrium

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Modeling and numerical simulation on launch dynamics of integrated launch package in electromagnetic railgun

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Journal of physics: Conference Series 2020年第7期1507卷

作者： Qinghua Lin Baoming Li National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China

This paper presents a numerical approach to modeling launch dynamics of integrated launch package in railguns. This approach was based on the three-dimensional transient finite element solutions of the multi-physical field equations. Numerical simulations were conducted for a railgun system composed of the capacitor-based pulse forming network, advanced containment launcher, and integrated launch package. Some issues about induced eddy currents, stress distributions, and projectile lateral motions were discussed. The results show that the in-bore motion of the projectile is sensitive to the launch package configuration and launcher stiffness. Moreover, the armature under a heavy current is prone to serious deformation and then leads to launch failure. The launch dynamics model provides a method to predict the in-bore processes and evaluate the in-bore survivability of the integrated launch package in a railgun.

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Analysis on the Influence of Breech Voltage on the Pulsed Discharge Characteristics of Capacitive Pulsed Power Supply in EML

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Journal of physics: Conference Series 2020年第7期1507卷

作者： Zhenxiao Li Shuangpeng Hao Fuqiang Ma Baoming Li National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China

Corresponding to the different gradient of the ideal working current, the movement process of the armature in the railgun bore can be divided into rising phase, stable phase and decreasing phase. Based on the load characteristic and the lumped-element equivalent circuit of the railgun, the characteristics of the railgun's breech voltage in above three phases were analysed. Under the condition that the size of the launching system is close to the same, the change ranges of the breech voltage of the augmented railgun is much larger than that of the simple railgun, and the breech voltage of the augmented railgun is a very high forward voltage in the rising phase. The influence of the breech voltage on the discharge characteristics of the capacitive pulsed power supply was studied. In the rising phase, the high breech voltage of the augmented railgun has a significant adverse effect on the pulsed discharge characteristics of the capacitive pulsed power supply whose pulsed forming net consists of a large number of pulsed forming units with small energy storage and high resonance frequency. As a result, part of the stored energy of the capacitive pulsed power supply cannot be used effectively, which leads to the decrease of the working efficiency of the launching system. Using the launching system with a 13-MJ capacitive pulsed power supply and a medium calibre augmented railgun, the launching simulation and test were completed, and the analysis was verified. The research has important enlightenment for improving the match between the capacitive pulsed power supply and the railgun.

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Mechanism of controlling turbulent channel flow with the effect of spanwise Lorentz force distribution

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Chinese physics B 2017年第8期26卷 250-258页

作者：韩洋张辉范宝春李健江代文赵子杰 Science and Technology on Transient Physics Laboratory Nanjing University of Science and TechnologyNanjing 210094China

A direct numerical simulation（DNS） is performed to investigate the control effect and mechanism of turbulent channel flow with the distribution of spanwise Lorentz force. A sinusoidal distribution of constant spanwise Lorentz force is selected, of which the control effects, such as flow characters, mean Reynolds stress, and drag reductions, at different parameters of amplitude A and wave number k_x are discussed. The results indicate that the control effects vary with the parameter A and k_x. With the increase of A, the drag reduction rate D_r first increases and then decreases rapidly at low k_x,and slowly at high k_x. The low drag reduction（or even drag increase） is due to a weak suppression or even the enhancements of the random velocity fluctuation and mean Reynolds stress. The efficient drag reduction is due to the quasi-streamwise vortex structure induced by Lorentz force, which contributes to suppressing the random velocity fluctuation and mean Reynolds stress, and the negative vorticity improves the distribution of streamwise velocity. Therefore, the optimal control effect with a drag reduction of up to 58% can be obtained.

关键词： flow control turbulent channel flow Lorentz force direct numerical simulation

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Prediction of three-dimensional elastic behavior of filament-wound composites based on the bridging model

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Journal of physics: Conference Series 2020年第6期1507卷

作者： D M Yin B M Li H Ch Xiao National Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing 210094 China

With the high specific stiffness, specific strength and designable ability, filament-wound composites have been widely applied in many industries, such as aerospace, energy and transportation, and they are also the one of more ideal choices for the lightweight structural design of weapon system. However, their complex structures, which including the cross-overs, undulations, and overlaps between different winding passages of the fiber bundles, make it difficult to obtain their macro mechanical properties. And this work will provide a method to predict the three-dimensional equivalent elastic properties of the filament-wound composites based on the multi-scale homogenization principle. The representative volume element (RVE) in the meso-scale is defined on the basis of the filament winding pattern, which characterizes all the micro-architecture details of the filament wound composites, such as fiber undulation, winding angle and lamination arrangement. Referring to the principle of volume average in the analysis method of braided composites, a theoretical prediction model for the three-dimensional equivalent elastic constants of the filament wound composites is established by adopting the bridging model. Through this method, the results obtained for the previous experimental model are in good agreement with the experimental ones, which verifies the reliability of this model. In addition, the effects of some winding parameters, such as winding angle, on the equivalent elastic behavior of the filament-wound composites are analyzed. And the rules gained can provide a theoretical reference for the optimum design of filament-wound composites. The full version of this extended abstract will appear in Defence technology in 2020.

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