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arXiv 2018年

作者： Zhang, Yudong Xu, Aiguo Zhang, Guangcai Chen, Zhihua National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing China Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China Center for Applied Physics and Technology MOE Key Center for High Energy Density Physics Simulations College of Engineering Peking University Beijing100871 China

Several different kinds of criteria for non-equilibrium phase separation to discriminate the two stages, the spinnodal decompostion (SD) and domain growth (DG), are compared and further investigated. The characteristic domain size and morphological function present two geometric criteria. Both of them can only provide rough estimations for the crossover from SD to DG. The reason for domain size is that the crossover in this description covers a process, instead of a specific time. The reason for the morphological function is that the result may rely on chosen threshold value. However, both the non-equilibrium strength and the entropy production rate are physical criteria and are more convenient to provide critical times. In fact, not only the non-equilibrium strength defined in the moment space opened by all the independent components of the used non-equilibrium quantities but also those defined in its subspaces can be used as criteria. Each of those criteria characterizes the phase separation process from its own perspective. Consequently, the obtained critical times may show slight differences. It should be pointed out that these slight differences are not contradictive, but consistent with each other and complementary in describing the complex phenomena. Copyright © 2018, The Authors. All rights reserved.

关键词： Phase separation

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Nonlinear dynamic analysis of supercavitating vehicles based on two-dimensional bifurcation 30

Nonlinear dynamic analysis of supercavitating vehicles based...

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30th International Symposium on Ballistics, BALLISTICS 2017

作者： Wu, Jintao National Key Laboratory of Transient Physics Nanjing University of Science and Technology 200 Xiao Ling Wei Street Xuan Wu District Nanjing Jiangsu China

ISBN: (纸本)9781605954196

To ensure the steady motion of underwater supercavitating vehicles, based on a four-dimensional dynamic model, the complex dynamical behaviors of vehicles are analyzed by using dynamic analysis tools, the conditions and ranges of variable parameters for the stable motion of vehicles are determined by two-dimensional bifurcation method. And the motion of supercavitating vehicles changing with feedback control gain of fin deflection angle and cavitation number is explored. The results indicate that the dynamical behaviors of supercavitating vehicles not only depend on system parameters, but also closely depend on initial conditions of the system. It can be found some novel nonlinear phenomenon in the system, such as transient period, transient chaos and state transitions and so on. Vibrations and shocks can be suppressed effectively by adjusting fin deflection angle reasonably. The researches have an important guiding significance to the stability control of supercavitating vehicles.

关键词： Vehicles

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Coexisting attractors in a underwater supercavitating vehicle system 30

Coexisting attractors in a underwater supercavitating vehicl...

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30th International Symposium on Ballistics, BALLISTICS 2017

作者： Lv, Yipin Xiong, Tianhong Yi, Wenjun National Key Laboratory of Transient Physics Nanjing University of Science and Technology 200 Xiao Ling Wei Street Xuan Wu District Nanjing Jiangsu China

ISBN: (纸本)9781605954196

Although supercavity can improve the speed of underwater vehicles greatly, the state of into water and parameters of system often lead vehicles move instability. This paper focuses on this problem. The existence of various coexisting attractors in this system is verified by distribution diagram of dynamic behaviors, and the motion of the vehicle varying with parameters and initial conditions is explored by basins of attraction. The results show that there are a few kinds of coexisting attractors at some parameter combinations of this system, such as two types of stable equilibrium points coexist with each other, a stable equilibrium point coexists with a limit cycle, a limit cycle coexists with a chaotic attractor and a 1-periodic cycle coexists with a 2-periodic cycle and so on, which explain the influence of parameters and initial values on the stability of vehicles qualitatively. In practical application, the stability of vehicles can be improved by setting parameters of system or adjusting initial launching conditions.

关键词： Vehicles

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Modeling and Stability Analysis for Dual-Spinning Projectiles with Canards

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Journal of Donghua University(English Edition) 2017年第5期34卷 670-676页

作者：管军李新华易文俊常思江 National Key Laboratory of Transient Physics Nanjing University of Science and TechnologyNanjing 210094China The Northwest Industrial Group Company Ltd.Xi'an 710043China School of Power and Engineering Nanjing University of Science and TechnologyNanjing 210094China

To develop the guided spin-stabilized projectiles with high hit precision,a class of dual-spinning stabilized projectile equipped with canards in atmospheric is *** 7 degrees of freedom(DOF) nonlinear equations are written in a non-rolling body *** work reported here focuses on the ballistic property analysis including the spin rates,incidence angle,ballistic drift and lateral *** dual-spinning projectiles are fundamentally less stable than conventional spin-stabilized ***,the gyroscopic stability is also studied in this *** models are given in this work,and the results of numerical analysis are discussed.

关键词： dual-spinning projectiles 7 degrees of freedom(DOF) nonlinear modeling stability analysis

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Modeling and control of supercavitating vehicle 30

Modeling and control of supercavitating vehicle

引用

30th International Symposium on Ballistics, BALLISTICS 2017

作者： Xiong, Tianhong Lv, Yipin Yi, Wenjun National Key Laboratory of Transient Physics Nanjing University of Science and Technology 200 Xiao Ling Wei Street Xuan Wu District Nanjing Jiangsu China

ISBN: (纸本)9781605954196

A supercavitating vehicle dynamic model is introduced based on the piecewise linear planing force function through the nonlinear planing force of a supercavitating vehicle, which is a four dimensional piecewise linear system and its dynamic characteristics (such as the equilibrium point and stability) are analyzed. The controller of the piecewise linear system is designed from the Lyapunov stability theory. It has been found that the controller shows good performance in the process for stabilizing the system and is also applicable for the non-piecewise linear dynamic model of the supercavitating vehicle. By controlling the deflection of the cavitator at the vehicle nose, the stable navigation of the supercavitating vehicle in the longitudinal plane can be achieved.

关键词： Controllers

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

arXiv

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arXiv 2018年

作者： Xu, Aiguo Zhang, Guangcai Zhang, Yudong Wang, Pei Ying, Yangjun National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China Center for Applied Physics and Technology MOE Key Center for High Energy Density Physics Simulations College of Engineering Peking University Beijing100871 China Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China

To kinetically model implosion and explosion related phenomena, we present a theoretical framework for constructing Discrete Boltzmann Model(DBM) with spherical symmetry in spherical coordinates. To this aim, a key technique is to use local Cartesian coordinates to describe the particle velocity in the kinetic model. Thus, the geometric effects, like the divergence and convergence, are described as a "force term". To better access the nonequilibrium behavior, even though the corresponding hydrodynamic model is one-dimensional, the DBM uses a Discrete Velocity Model(DVM) with 3 dimensions. A new scheme is introduced so that the DBM can use the same DVM no matter considering the extra degree of freedom or not. As an example, a DVM with 26 velocities is formulated to construct the DBM in the Navier-Stokes level. Via the DBM, one can study simultaneously the hydrodynamic and thermodynamic nonequilibrium behaviors in the implosion and explosion process which are not very close to the spherical center. The extension of current model to the multiple-relaxation-time version is straightforward. Copyright © 2018, The Authors. All rights reserved.

关键词： Spheres

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Discrete boltzmann method for non-equilibrium flows: Based on Shakhov model

arXiv

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arXiv 2018年

作者： Zhang, Yudong Xu, Aiguo Zhang, Guangcai Chen, Zhihua Wang, Pei National Key Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics P. O. Box 8009-26 Beijing100088 China Key Laboratory of Transient Physics Nanjing University of Science and Technology Nanjing210094 China Center for Applied Physics and Technology MOE Key Center for High Energy Density Physics Simulations College of Engineering Peking University Beijing100871 China

A general framework for constructing discrete Boltzmann model for non-equilibrium flows based on the Shakhov model is presented. The Hermite polynomial expansion and a set of discrete velocity with isotropy are adopted to solve the kinetic moments of discrete equilibrium distribution function. Such a model possesses both an adjustable specific heat ratio and Prandtl number, and can be applied to a wide range of flow regimes including continuous, slip, and transition flows. To recover results for actual situations, the nondimensionalization process is demonstrated. To verify and validate the new model, several typical non-equilibrium flows including the Couette flow, Fourier flow, unsteady boundary heating problem, cavity flow, and Kelvin-Helmholtz instability are simulated. Comparisons are made between the results of discrete Boltzmann model and those of previous models including analytic solution in slip flow, Lattice ES-BGK, and DSMC based on both BGK and hard-sphere models. The results show that the new model can accurately capture the velocity slip and temperature jump near the wall, and show excellent performance in predicting the non-equilibrium flow even in transition flow regime. In addition, the measurement of non-equilibrium effects is further developed and the non-equilibrium strength D∗ n in the n-th order moment space is defined. The nonequilibrium characteristics and the advantage of using D∗ n in Kelvin-Helmholtz instability are discussed. It concludes that the non-equilibrium strength D∗ n is more appropriate to describe the interfaces than the individual components of Δ∗n. Besides, the D∗3and D∗3,1can provide higher resolution interfaces in the simulation of Kelvin-Helmholtz instability. Copyright © 2018, The Authors. All rights reserved.

关键词： Prandtl number

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Numerical simulation of interior ballistic process of railgun based on the multi-field coupled model

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Defence technology（防务技术） 2016年第2期12卷 101-105页

作者： Qing-hua LIN Bao-ming LI National Key Laboratory of Transient Physics Nanjing University of Science & Technology

Railgun launcher design relies on appropriate models. A multi-field coupled model of railgun launcher was presented in this paper. The 3D transient multi-field was composed of electromagnetic field, thermal field and structural field. The magnetic diffusion equations were solved by a finite-element boundary-element coupling method. The thermal diffusion equations and structural equations were solved by a finite element method. A coupled calculation was achieved by the transfer data from the electromagnetic field to the thermal and structural fields. Some characteristics of railgun shot, such as velocity skin effect, melt-wave erosion and magnetic sawing, which are generated under the condition of large-current and high-speed sliding electrical contact, were demonstrated by numerical simulation.

关键词：电磁轨道炮耦合模型数值模拟内弹道热扩散方程有限元法多场耦合三维瞬态

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Ignition simulation of a capillary plasma generator in a 30mm electrothermal-chemical gun

Ignition simulation of a capillary plasma generator in a 30m...

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2018国际防务技术大会（ICDT）

作者： Yan-jie NI Yong JIN Xu-ming ZHAO Ying LI Bao-ming LI National Key Laboratory of Transient Physics Nanjing University of Science and Technology Product Research Institute Inner Mongolia North Heavy Industries Group Copr.LTD China Ordnance Society China Academy of Ordnance

An axisymmetric two-dimensional interior ballistics model of the solid propellant ETC gun(2 D-IBSPETCG) is presented to describe the process of the 30 mm ETC *** on the initial parameters,detailed distribution of the ballistics parameters with the *** the distribution of the ballistics parameters,the influence of the CPG during the ignition process can be *** of the axial flowing plasma,the propellant in the chamber is ignited within 0.13 *** plasma makes the temperature of the gas increase from several thousand K(conventional ignition) to several ten thousand K(plasma ignition).Low density and high temperature gas appears near the exit of the *** distribution of the gas velocity is influenced by the structure of the CPG.

关键词： Electrothermal-chemical launch Two-dimensional interior ballistics model Ignition simulation Capillary plasma generator

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Research on proximity effect of electromagnetic railgun

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Defence technology（防务技术） 2016年第3期12卷 223-226页

作者： Yu-tao LOU Hai-yuan LI Bao-ming LI National Key Laboratory of Transient Physics Nanjing University of Science and Technology

The rails of electromagnetic railgun can be ablated by the temperature rise due to current *** current distributions on the rails and armature are not only affected by the skin effect,but also influenced by the proximity effect which is rarely *** paper illustrated the difference between skin effect and proximity effect,and the influencing factors of proximity effect were *** show that the current is concentrated on the surface around rails due to the skin effect,and the proximity effect exacerbates the current density on the inner surfaces of *** in distance from rails enhances the proximity effect,but has nothing to do with the skin effect,which also augments the rail resistance,resulting in temperature *** can explain the reason why the ablation is often detected in the small caliber *** results in this paper can provide support for design and optimization of electromagnetic railgun.

关键词： Electromagnetic railgun Proximity effect Skin effect Ablation

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