DESIGN OF BEAM-WAVE INTERACTION BASED ON HIGH EFFICIENCY OF A HIGH-POWER BROADBAND KLYSTRON

The paper mainly presents the design of beam-wave interaction of a C-band high-peakpower high-efficiency broadband klystron.The beam-wave interaction section is designed based on considerations of efficiency and bandwidth synthetically.As a part of beam-wave interaction section,buncher section is simulated by Particle-In-Cell(PIC) code to observe the bunching process of electron beam to achieve high conversion efficiency of electron beam and RF field.When it comes to the other part,output circuit is designed as a three-section filter by an output cavity loaded with Chebyshev filter,and the cold test results are given.The beam-wave interaction is simulated by EGUN code and Arsenal-MSU code respectively.The simulated results indicated that,the existence of power dips in the operating bandwidth is verified by Arsenal-MSU code,comparing proper results by EGUN code.Then,the method that design parameters are not adjusted except parameters of buncher cavities to remove potential power dips is described.What is more,the simulated results of electron optics system are given by EGUN code and Arsenal-MSU code respectively.The further hot test results of klystron prove that the whole design of beam-wave interaction is effective.

Experimental and numerical studies on interactions of a spherical flame with incident and reflected shocks

Observations are presented from experiments and calculations where a laminar spherical CH4/air flame is perturbed successively by incident and reflected shock waves. The experiments are performed in a standard shock tube arrangement, in which a high-speed shadowgraph imaging system is used to record evolutions of the flame. Numerical simulations are conducted by using second-order wave propagation algorithms, based on two-dimensional axisymmetric Navier-Stokes equations with detailed chemical reactions. Qualitative agreements are obtained between the experimental and numerical results. Under actions of incident shock waves, Richtmyer-Meshkov instability responsible for the flame deformation is induced in the flame, and the distoned flame takes a barrel shape. Then, under subsequent actions of the shock wave reflected from a planar wall, the flame takes an inclined non-symmetrical kidney shape in a symmetric cross section, which means a mushroom-like shape of the flame comes finally into being. The vorticity direction in the ring cap has been altered by the reflected shock＇s action, which makes the head of the mushroom-like flame extend quickly to the side wall.

Modulational instability of the coupled waves between fast magnetosonic wave and slow Alfvén wave in the laser–plasma interaction

By performing modulational instability analysis of the the nonlinear coupled dimensionless equations between a fast magnetosonic wave(FMSW)propagating obliquely with the magneticfield and a low-frequency slow Alfvén wave(SAW),we obtain the dispersion relation of the perturbation wave.The growth rate of the perturbation wave is obtained.It is found that the growth rate increases as background magnetic field increases,which is in agreement with that reported by Tiwary et al(2016 Phys.Plasmas 23122307).A critical perturbation wave number is found.When the perturbation wave number is greater than or equal to the critical value,the growth rate is positive and it increases as the perturbation wave number increases,while the wave is stable.The maximum growth rate is reached when the frequency of the FMSW is half of the ion cyclotron frequency.The minimum growth rate is reached when the propagation direction of the perturbation wave is the same as that of the FMSW.

Linear theory of beam–wave interaction in double-slot coupled cavity travelling wave tube

A three-dimensional model of the double-slot coupled cavity slow-wave structure （CCSWS） with a solid round elec- tron beam for the beam-wave interaction is presented. Based on the ＂cold＂ dispersion, the ＂hot＂ dispersion equation is derived with the Maxwell equations by using the variable separation method and the field-matching method. Through numerical calculations, the effects of the electron beam parameters and the staggered angle between adjacent walls on the linear gain are analyzed.

Two-Dimensional Soliton Interaction for Multi-component Bose-Einstein Condensates

For two-component disk-shaped Bose-Einstein condensates with repulsive atom-atom interaction, the small amplitude, finite and long wavelength nonlinear waves can be described by a Kadomtsev-Petviashvili-Ⅰ equation at the lowest order from the originai coupled Gross-Pitaevskii equations. One- and two-soliton solutions of the Kadomtsev- Petviashvili-1 equation are given, therefore, the wave functions of both atomic gases are obtained as well. The instability of a soliton under higher-order long wavelength disturbance has been investigated. It is found that the instability depends on the angle between two directions of both soliton and disturbance.

STRONG INSTABILITY OF STANDING WAVES FOR A SYSTEM NLS WITH QUADRATIC INTERACTION

We study the strong instability of standing waves for a system of nonlinear Schr¨odinger equations with quadratic interaction under the mass resonance condition in dimension d=5.

THE ROLE OF MERIDIONAL WIND STRESS IN THE TROPICAL UNSTABLE AIR-SEA INTERACTION

With a simple tropical coupled ocean-atmosphere model, this paper presents an analysis aiming to understand the relative role of the meridional and zonal wind stresses in the tropical unstable air-sea interaction. The roles of the zonal wind stress, the meridional wind stress and the both are considered respectively into the coupled system. It is demonstrated that the meridional component of the wind stress does not lead to any instability under the local thermal balance assumption, but it does lead to a weak instability under the sea surface temperature advection assumption. Unstable air-sea interaction is dominated by the zonal component of the wind stress, suggesting that ignoring the meridional wind stress is approximately feasible in studying the tropical unstable air-sea interaction.

The instability conditions of a gas trapped in weak weakly interacting Fermi magnetic field

In this paper the analytical expression of free energy expressed by small parameter r of a weakly interacting Fermi gas trapped in weak magnetic field is derived by using ＇the maximum approximation＇ method and the ensemble theory. Based on the derived expression, the exact instability conditions of a weakly interacting Fermi gas trapped in weak magnetic field at both high and low temperatures are given. From the instability conditions we get the following two results. （1） At the whole low-temperature extent, whether the interactions are repulsive or attractive with （αn-k 4εF/3） （n and εF denote the particle-number density and the Fermi energy respectively, α = 4πah^2/m, and a is s-wave scattering length） positive, there is a lower-limit magnetic field of instability; in addition, there is an upper-limit magnetic field for the system of attractive interactions with （αn ＋ 4εF/3） negative. （2） At the whole high-temperature extent, the system with repulsive interactions is always stable, but for the system with attractive interactions, the greater the scattering length of attractive interactions ｜α｜ is, the stronger the magnetic field is and the larger the particle-number density is, the bigger the possibility of instability in the system will be.

Instability Mechanism of a Rotating Disc Subjected to Various Transverse Interactive Forces

In the past three decades, numerous papers have bee n publishedon the dynamics of rotating discs. most of them have focused on the ma thematical modeling and solution for a specific interactive force, such as a n elastic force produced by a stationary spring or a damping force from a statio nary viscous damper. Few of them have looked into the instability mechanisms. This study has established a generalized approach to investigate the instability mechanisms that are involved in the interaction between a rotating and an arbit rary interactive force. An energy flux equation has been developed, which leads to the following conclusions: (1) The possibility of the occurrence of instability due to any interactive forc es may be identified based on the energy flux analysis, even without solving equ ations. (2) Instabilities will occur if the interactive forces are in phase with the vel ocity measured at the interactive point from the coordinates rotating with the d isc. (3) Instability cannot occur when a rotating disc is subjected to a stationary c onstant lateral force, but a stationary harmonic lateral force, a moving constan t lateral force or a moving harmonic lateral force may cause instability. (4) Conservative forces may only cause coupling instability associated with two modes, and non-conservative forces usually cause terminal instability where onl y one mode is involved.

Contrasts of bimodal tropical instability waves(TIWs)-induced wind stress perturbations in the Pacific Ocean among observations,ocean models,and coupled climate models

The coupling between wind stress perturbations and sea surface temperature(SST)perturbations induced by tropical instability waves(TIWs)in the Pacific Ocean has been revealed previously and proven crucial to both the atmosphere and ocean.However,an overlooked fact by previous studies is that the loosely defined“TIWs”actually consist of two modes,including the Yanai wave-based TIW on the equator(hereafter eTIW)and the Rossby wave-based TIW off the equator(hereafter vTIW).Hence,the individual feedbacks of the wind stress to the bimodal TIWs remain unexplored.In this study,individual coupling relationships are established for both eTIW and v TIW,including the relationship between the TIW-induced SST perturbations and two components of wind stress perturbations,and the relationship between the TIW-induced wind stress perturbation divergence(curl)and the downwind(crosswind)TIW-induced SST gradients.Results show that,due to different distributions of eTIW and vTIW,the coupling strength induced by the eTIW is stronger on the equator,and that by the vTIW is stronger off the equator.The results of any of eTIW and vTIW are higher than those of the loosely defined TIWs.We further investigated how well the coupling relationships remained in several widely recognized oceanic general circulation models and fully coupled climate models.However,the coupling relationships cannot be well represented in most numerical models.Finally,we confirmed that higher resolution usually corresponds to more accurate simulation.Therefore,the coupling models established in this study are complementary to previous research and can be used to refine the oceanic and coupled climate models.

公路边坡稳定性评价指标体系构建及应用

山区公路边坡数量多、穿越地质单元多,影响边坡稳定性的因素多而复杂,构建评价指标体系有利于对边坡稳定性做出快速判断。然而,现有评价指标体系构建中很少考虑多个影响因素相互作用对边坡稳定性的影响,影响稳定性评价结果的合理性。本文选择安徽汤屯高速公路30个代表性边坡为样本,利用相互作用关系矩阵方法构建了评价指标体系。得到主要认识包括:利用相互作用关系矩阵确定了指标重要性排序和权重取值,从8个评价指标筛选出边坡尺寸、边坡坡度、边坡高度、岩体强度、结构面方位、结构面特性、结构面组合、岩体结构单元类型七个指标构建稳定性评价指标体系;按半定量专家取值法对指标赋分,结合指标权重计算不稳定指数(SII),划分边坡不稳定指数等级。基于相互作用关系矩阵的指标重要性排序方法为权重确定提供了一种定量计算方法,所构建的边坡不稳定指数法所得结果较好地反映了边坡稳定性实际情况,具有较好的推广应用价值。

隧道穿越富水断层破碎带掌子面失稳演化特性研究

以某隧道穿越富水断层破碎带施工为工程背景,基于流–固耦合理论,建立了隧道穿越富水断层破碎带施工三维流–固耦合数值模型,研究隧道施工过程中掌子面失稳演化特性,分析了掌子面挤出位移、塑性区体积和掌子面涌水量的变化规律。结果表明:随着掌子面逐渐迫近断层破碎带,掌子面挤出位移、塑性区体积和涌水量呈现由“略微增加”到“明显增加”再到“急剧增大”的变化规律。防突体厚度越大,发生突水突泥灾害的概率越小,该隧道穿越F4断层施工的极限防突体厚度为5.2 m。

强迫流与不稳定流的相互作用

通过数值试验的方法，研究非保守系统中的基流平衡被破坏和重建过程中，产生非平衡中尺度环流与不稳定能量造成的对流关系，着重探索在形成持续时间较长、尺度较大的深厚湿对流的物理过程中，强迫与不稳定的相互作用。研究结果表明：强迫流比不稳定流小一个量级。强迫流虽然本身的量值较小，但是强迫流是不稳定流的触发机制。如果环境场具有深厚的不稳定层（垂直或倾斜方向），并且环境场强迫出一定振幅的呈上升运动的强迫流，则在0～3小时以后，将在强迫流上升运动中心激发出不稳定流上升运动中心，或使已经存在的不稳定流上升运动中心向强迫流上升运动中心移动。

非圆Tokamak载流线圈的磁弹性分析

基于曲梁理论和Ｂｉｏｔ－Ｓａｖａｒｔ定律描述超导载流线圈全部形变的理论模型，采用边值问题的齐次微分方程封闭形式解析通解和非齐次微分方程数值特解相叠加的半解析半数值方法，对非圆Ｄ型Ｔｏｋａｍａｋ载流线圈弯曲，失稳的磁弹性相互作用进行了研究；并且就线圈初始扰动位移对失稳临界电流的影响也进行了定量分析．数值模拟结果表明：线圈失稳的临界电流随线圈曲率半径的增大而增大，随线圈非完全对称排列这一初始缺陷的增大而减小．

换流变压器铁心饱和型不稳定性预测

换流器交流侧二次谐波分量和直流侧基频分量通过交直流系统间的相互作用,会导致高压直流输电系统出现谐波不稳定现象,换流变压器的铁心饱和会进一步加剧这种不稳定。本文研究了换流变压器铁心饱和不稳定产生的机理,分析了系统交直流侧的频率阻抗特性,建立了铁心饱和型谐波不稳定等效电路,通过谐波传递矩阵推导出饱和稳定判定因子,提出预测铁心饱和不稳定现象的方法。最后在电力系统电磁暂态计算软件PSCAD/EMTDC中建立仿真回路验证了该方法的正确性。

金属矿山多矿柱承载与失稳破坏研究

金属矿空场法开采遗留了大量采空区,尤其是近地表的采空区群具有重大的安全隐患,是矿山安全的危险源之一。采空区的稳定性与矿柱的承载及失稳破坏密切相关,在采空区垮塌过程中,多个矿柱间的载荷传递效应可能诱发相邻矿柱的连锁性失稳破坏,从而造成采空区群大规模失稳坍塌。因此对单矿柱稳定性研究方法、多矿柱载荷传递行为及失稳破坏机制等进行了归纳总结,相关研究成果表明:当前针对多矿柱载荷传递行为的相关研究较少,载荷传递机制尚不清楚,难以实现对多矿柱连锁性失稳破坏行为的预测;应该着眼于矿柱之间以及多矿柱与围岩体之间的相互作用,以便于深刻揭示多矿柱系统的承载与失稳破坏机制。介绍了多矿柱承载与失稳破坏机制方面的相关研究成果,可以为防控大规模空区群失稳灾害提供参考。

正方形排布管束流体弹性不稳定性数值计算模型研究

研究了正方形排布管束的流体弹性不稳定的数值计算模型。在刚体运动方程与Newmark积分方法的基础上建立了三维流固耦合振动模型。对湍流模型与模型的轴向尺寸影响进行了计算分析研究,结果表明采用LES模型比RANS模型更为准确,轴向尺寸d的模型可以反映完整的流场信息,在此基础上,提出了适用的计算模型。采用计算模型对临界流速进行了计算,并同文献实验数据进行了对比,结果显示计算的临界流速同实验数据吻合较好,振幅计算在低速时精度较高,在高速时误差较大。研究结果为数值计算模型的应用提供了参考和依据。

车网耦合下的牵引供电系统谐振不稳定机理分析

在国内电气化铁路的现场测试中发现了1种有别于谐波谐振现象的新型谐振不稳定问题,该文围绕高速列车与牵引供电网(以下简称车网)耦合系统中谐振不稳定问题的产生机理及影响规律进行了分析。采用阻抗分析法,建立了dq参考坐标系下小信号车、网阻抗传递函数模型;基于广义奈奎期特(Nyquist)判据,探寻了谐振不稳定现象的发生机理;分析了列车四象限整流器控制参数与牵引供电网参数对谐振不稳定的影响规律。仿真与实验结果表明,列车控制系统中电流环和锁相环的比例增益,以及牵引供电网等效电感等参数对谐振不稳定最为灵敏,因此在机车控制参数优化以及新建轨道线路设计时需重点考虑,这可为抑制谐振不稳定问题提供参考。

悬臂铁磁板磁弹性耦合作用的力学分析

对有限板宽的悬臂铁磁板在外磁场中的磁弹性相互耦合作用的力学行为，建立了描述板弯曲和稳定性的理论模型及有限元定量分析程序。

波与基流相互作用下的对称不稳定中尺度环流的发展

通过建立包含扰动和基流方程组的数值模式,全面讨论了扰动与对称不稳定纬向基流的相互作用。研究表明:扰动与基流的相互作用表现为以下两个方面:(1) 扰动改变了基流,而改变了的基流又对扰动有反馈作用;(2) 扰动的平均输送同时也改变扰动自身的结构,从而影响扰动的发展。由对称不稳定基流激发的扰动倾斜环流使基流环境场发生的改变不利于对称不稳定的进一步发展;而由扰动的平均输送所产生的影响则有利于对称不稳定的进一步发展,并且后者的作用强于前者。