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Numerical investigation of a muzzle multiphase flow field using two underwater launch methods

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Defence Technology（防务技术） 2022年第8期18卷 1454-1469页

作者： Jing-hui zhang Yong-gang Yu Xin-wei zhang School of Energy and Power Engineering Nanjing University of Science&TechnologyNanjing210094China

A two-dimensional axisymmetric model, employing a dynamic mesh and user-defined functions, is used to numerically simulate the transient multiphase flow field produced by an underwater gun. Furthermore, a visualized shooting experiment platform with a high-speed camera is built to observe the evolution process of such a multiphase flow field. The simulated phase distribution diagram is agreed well with the shadow photo of the experiment, indicating that the numerical model is reasonable. Further examinations of the multiphase flow fields by using the submerged and sealed launch methods show that use of the sealed launch can significantly improve the interior ballistic performance of an underwater gun. In the cases by using these two types of underwater launch methods, the displacement of the projectile within the range of the muzzle flow field meets the exponential law over time. Moreover, a not fully developed bottle-shaped shock wave is formed when t = 0.4 ms, but this bottle-shaped shock wave expands more rapidly for the sealed launch. In addition, the amplitude of pressure oscillation for the sealed launch is larger than that of the submerged launch, but the pressure oscillation of the sealed launch lasts shorter.

关键词： Underwater launch Multiphase flow Muzzle flow field Numerical simulation Mach disk

Detection of electron-phonon coupling in two-dimensional materials by light scattering

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Nano Research 2021年第6期14卷 1711-1733页

作者： Jia-Min Lai Ya-ru Xie Jun zhang State Key Laboratory of Superlattices and Microstructures Institute of SemiconductorsChinese Academy of SciencesBeijing100083China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing100049China CAS Center of Excellence in Topological Quantum Computation University of Chinese Academy of SciencesBeijing101408China Beijing Academy of Quantum Information Science Beijing100193China

Electron-phonon coupling affects the properties of two-dimensional(2D)materials significantly,leading to a series of novel *** light scattering provides a powerful experimental tool to explore electron-phonon interaction in 2D *** review gives an overview of the basic theory and experimental advances of electron-phonon coupling in 2D materials detected by Raman and Brillouin scattering,*** the Raman scattering part,we review Raman spectroscopy studies of electron-phonon coupling in graphene,transition metal disulfide compounds,van der Waals heterostructures,strongly correlated systems,and 2D magnetic *** the Brillouin scattering part,we extensively introduce Brillouin spectroscopy in non-van der Waals 2D structures,including temperature sensors for phonons and magnons,interfacial Dzyaloshinsky-Moriya interaction and spin torque in multilayer magnetic structures,as well as exciton-polariton in semiconductor quantum well.

关键词： electron-phonon coupling Raman scattering Brillouin scattering two-dimensional(2D)materials

Effect of pile-cap connection on behavior of torsionally loaded pile groups

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2008年第3期9卷 303-312页

作者： Ling-gang KONG Li-min zhang Key Laboratory of Soft Soils and Geoenvironmental Engineering Ministry of Education Zhejiang University Hangzhou 310027 China Department of Civil Engineering The Hong Kong University of Science and Technology Hong Kong China

To evaluate the responses of fixed and pinned pile groups under torsion, a method is presented to analyze the nonlinear behavior of free-standing pile groups with rigid pile caps. The method is capable of simulating the nonlinear soil response in the near field usingp-y and r-θ curves, the far-field interactions through Mindlin＇s and Randolph＇s elastic solutions, and the coupling effect of lateral resistance on torsional resistance of the individual piles using an empirical factor. Based on comparisons of the solutions for fixed- and pinned-head, 1×2, 2×2, and 3×3 pile groups subjected to torsion, it was found that pile-cap connection significantly influences the torsional capacity of pile groups and the assignment of applied torques in the pile groups. In this study, the applied torques for the pinned-head pile groups are only 44%-64% of those for the corresponding fixed-head pile groups at a twist angle of 2^o. Such a difference is mainly due to the change of the lateral resistances of individual piles in the groups.

关键词： Pile group Pile foundations Torsional response Pile-cap connection Nonlinear analysis

Novel Model Using Kernel Function and Local Intensity Information for Noise Image Segmentation

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Tsinghua Science and Technology 2018年第3期23卷 303-314页

作者： gang Li Haifang Li Ling zhang College of Computer Science and Technology Taiyuan University of Technology

It remains a challenging task to segment images that are distorted by noise and intensity *** overcome these problems, in this paper, we present a novel region-based active contour model based on local intensity information and a kernel metric. By introducing intensity information about the local region, the proposed model can accurately segment images with intensity inhomogeneity. To enhance the model＇s robustness to noise and outliers, we introduce a kernel metric as its objective functional. To more accurately detect boundaries, we apply convex optimization to this new model, which uses a weighted total-variation norm given by an edge indicator function. Lastly, we use the split Bregman iteration method to obtain the numerical solution. We conducted an extensive series of experiments on both synthetic and real images to evaluate our proposed method, and the results demonstrate significant improvements in terms of efficiency and accuracy, compared with the performance of currently popular methods.

关键词： kernel metric image segmentation local intensity information convex optimization

Numerical study on evolution of subharmonic varicose low-speed streaks in turbulent channel flow

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Applied Mathematics and Mechanics(English Edition) 2016年第3期37卷 325-340页

作者： Jian LI gang DONG Jianlei zhang National Key Laboratory of Transient Physics Nanjing University of Science and Technology

The evolution of two spanwise-aligned low-speed streaks in a wall turbulent flow, triggered by the instability of the subharmonic varicose （SV） mode, is studied by a direct numerical simulation （DNS） method in a small spatial-periodic channel. The results show that the SV low-speed streaks are self-sustained at the early stage, and then transform into subharmonic sinuous （SS） low-speed streaks. Initially, the streamwise vortex sheets are formed by shearing, and then evolve into zigzag vortex sheets due to the mutual induction. As the intensification of the SV low-speed streaks becomes prominent, the tilted streamwise vortex tubes and the V-like streamwise vortex tubes can be formed simultaneously by increasing ＋~. When the SV low-speed streaks break down, new zigzag streamwise vortices will be generated, thus giving birth to the next sustaining cycle of the SV low-speed streaks. When the second breakdown happens, new secondary V-like streamwise vortices instead of zigzag streamwise vortices will be generated. Because of the sweep motion of the fluid induced by the secondary V-like streamwise vortices, each decayed low-speed streak can be divided into two parts, and each part combines with the part of another streak, finally leading to the formation of SS low-speed streaks.

关键词： low-speed streak subharmonic varicose mode turbulent boundary layer,direct numerical simulation

INCREASED SPHEruLITIC GROWTH RATES OF SEMICRYSTALLINE POLYMER DUE TO ENHANCED LIMITED LOCAL CHAIN SEGMENTAL MOBILITY AT THE INTERFACE OF DOUBLE-LAYER THIN FILMS

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Chinese Journal of Polymer Science 2013年第9期31卷 1276-1283页

作者： Ya-qiong zhang Zhi-gang Wang CAS Key Laboratory of Soft Matter Chemistry Department of Polymer Science and Engineering Hefei National Laboratory for Physical Sciences at the Microscale University of Science and Technology of China

In this work the nucleation and growth of spherulites for the below polylactide （PLA） layer in poly（ε- caprolactone）/polylactide （PCL/PLA） double-layer films during isothermal crystallization at various temperatures above the melting point of PCL have been investigated by using polarized optical microscopy （POM）. It is revealed that two types of spherulitic morphologies are observed in PCL/PLA double-layer films. One is the well defined highly birefringent spherulites, and the other one is the coarse spherulites. It is interesting to find that the spherulitic growth rate of the coarse spherulites is higher than that of the well defined spherulites. It is thought that the coarse spherulites nucleate and grow with the assistance of the interfaces between the PCL and PLA layers, and the well defined highly birefringent spherulites only nucleate and grow in the PLA layer.

关键词： Polylactide Poly(ε-caprolactone) Interface Crystallization Spherulite.

Measurements of momentum correlation and interaction parameters between antiprotons

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Nuclear Science and Techniques 2016年第6期27卷 67-73页

作者： Zheng-Qiao zhang Yu-gang Ma Shanghai Institute of Applied Physics Chinese Academy ofSciencesShanghai 201800China University of Chinese Academy of Sciences Beijing 100049China

The two-particle momentum correlation is influenced by the nuclear force between two particles,which has been intensively studied for nucleons and nuclei,but not much for antinucleons or *** this proceeding,we present our STAR measurements on momentum correlation function of antiproton-antiproton and proton-proton in Au+Au collisions at S_(NN)^(1/2)= 200 GeV at the Relativistic Heavy Ion *** nuclear force between two antiprotons is demonstrated,and the strong interaction parameters(the scattering length and the effective range) are *** measurement serves as an additional verification of CPT *** present information on the strong force in the antiproton-antiproton system provides a fundamental ingredient towards understanding the structure of more sophisticated antinuclei.

关键词：动量相关作用相互作用参数反质子测量重离子对撞机散射长度核力量金+金

Current Spreading Effects in Vertical GaN-Based Light-Emitting Diode on Si(111) Substrate

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Chinese Journal of Electronics 2016年第4期25卷 672-677页

作者： WEI Jingting zhang Baijun WANG gang Guangdong Polytechnic Institute The Open University of Guangdong School of Microelectronics State Key Laboratory of Optoelectronic Materials and TechnologiesSun Yat-sen University

The optimal design of Ga N-based Lightemitting diode(LED) is important for its *** this work,a new three-Dimensional(3D) circuit model with a resistor network is developed to study the current distribution in the active layer of vertical conducting Ga Nbased LED grown on Si(111) substrate with different structures and electrode *** consists of resistance of Transparent conductive layer(TCL),resistance of epitaxial layer,intrinsic diodes presenting the active layer,and Al N/Si junction as which the multilayer of Al N/Si is *** results of current distribution in active layers of two kinds of LED structures show that current distribution uniformity is greatly affected by the electrode pattern and the LED ***,the experimentally measured light emission uniformity agrees well with simulation *** electrical and optical characteristics of LED are obviously affected by the current distribution uniformity.

关键词： Light-emitting diodes Current distribution uniformity Circuit model

Algorithm for transient growth of perturbations in channel Poiseuille flow

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Applied Mathematics and Mechanics(English Edition) 2017年第11期38卷 1635-1650页

作者： Jianlei zhang gang DONG Yi LI National Key Laboratory of Transient Physics Nanjing University of Science and Technology School of Mathematics and Statistics University of Sheffield

This study develops a direct optimal growth algorithm for three-dimensional transient growth analysis of perturbations in channel flows which are globally stable but locally unstable. Different from traditional non-modal methods based on the Orr- Somrnerfeld and Squire （OSS） equations that assume simple base flows, this algorithm can be applied to arbitrarily complex base flows. In the proposed algorithm, a re- orthogonalization Arnoldi method is used to improve orthogonality of the orthogonal basis of the Krylov subspace generated by solving the linearized forward and adjoint Navier-Stokes （N-S） equations. The linearized adjoint N-S equations with the specific boundary conditions for the channel are derived, and a new convergence criterion is pro- posed. The algorithm is then applied to a one-dimensional base flow （the plane Poiseuille flow） and a two-dimensional base flow （the plane Poiseuille flow with a low-speed streak） in a channel. For one-dimensional cases, the effects of the spanwise width of the chan- nel and the Reynolds number on the transient growth of perturbations are studied. For two-dimensional cases, the effect of strength of initial low-speed streak is discussed. The presence of the streak in the plane Poiseuille flow leads to a larger and quicker growth of the perturbations than that in the one-dimensional case. For both cases, the results show that an optimal flow field leading to the largest growth of perturbations is character- ized by high- and low-speed streaks and the corresponding streamwise vortical structures. The lift-up mechanism that induces the transient growth of perturbations is discussed. The performance of the re-orthogonalization Arnoldi technique in the algorithm for both one- and two-dimensional base flows is demonstrated, and the algorithm is validated by comparing the results with those obtained from the OSS equations method and the cross- check method.

关键词： transient growth Poiseuille flow Arnoldi method Krylov subspace adjoint equation