低气压放电等离子体军事应用分析

首先利用平面电磁波在非磁化均匀等离子体中的色散方程,对不同参数等离子体的电磁特性进行了研究。然后根据等离子体的产生方式及其参数特点,分析了低气压放电等离子体军事应用的可行性。最后重点分析了低气压放电等离子体在等离子体天线和等离子体雷达隐身中应用的原理及其特性。     

平面电磁波在非均匀等离子体柱上的散射研究

基于微分形式的麦克斯韦方程组,采用严格两点边值方法求解等离子体柱对入射平面波的散射问题.结合柱约束空间径向非均匀等离子体分布特征推导电磁波散射系数的数学模型,计算了不同入射波频率、等离子体频率、等离子体碰撞频率条件下散射场的分布.结果表明:电磁波的散射场由等离子体特征参数、入射波频率及极化方式共同决定;等离子体碰撞频率对平行极化波的散射场分布影响较大.     

分舱段圆柱壳声散射数值和试验研究

基于有限元方法建立了填充不同介质的有限长分舱段圆柱壳声散射数值计算模型,仿真了填充空气-空气、空气-水、水-水三类两舱段圆柱壳声散射特性,并完成了三类两舱段圆柱壳体声散射试验,获取和分析了两舱段圆柱壳体声散射的时间角度谱和频率角度谱特性。利用物理声学方法分析了壳体表面、端面以及内部填充水介质对散射声场的影响,揭示了两舱段圆柱壳声散射频率角度谱中呈现的干涉条纹特征形成机理,为水下分舱段目标,如水下无人航行器的主动声呐探测和识别提供理论支撑。     

半空间内二维圆柱声散射理论解析解

采用理论解析方法研究半空间内二维非紧致圆柱的声散射。齐次Helmholtz方程的解在柱坐标系内用自由空间格林函数的级数展开式表示。基于镜像源方法,利用刚性半空间边界反射圆柱散射声波来解决半空间边界和圆柱之间的多重散射。结合等效源原理,处理半空间边界质量型阻抗特性和刚度型阻抗特性对声传播的影响,推导单位强度简谐单极子点声源产生声场的理论表达式。总声场可以表示为四个分量的总和:入射声场、反射波以及圆柱和镜像圆柱的散射声场。采用边界积分方法对声散射进行计算,以验证理论公式的正确性。点声源模型的理论解析值与边界积分方法数值解在研究的波数和观察点角度范围内一致。     

等离子体中太赫兹波传输及成像探测特性研究

本文根据散射矩阵方法模拟等离子体并建立了非均匀等离子体理论模型,并在此基础上计算了0.1 THz^10 THz频段的全波段太赫兹波在其中的传输特性。根据介质阻挡放电原理在实验室环境下搭建等离子体射流产生装置并产生非均匀等离子体,进行了太赫兹时域光谱(THz-TDS)以及宽带太赫兹源在等离子体中的透射光谱测量以及太赫兹波对等离子体遮挡下目标物的反射成像的试验。理论和实验结果均表明,较高频太赫兹波在等离子体中有良好的穿透性,这为太赫兹波在黑障区的通信以及雷达探测应用打下研究基础。     

具有非均匀热压强磁流体速度的定量研究北大核心CSCD

应用数值模拟方法,研究了非均匀等离子体压强梯度对圆柱位型磁流体速度的影响,并与均匀等离子体压强时的结论进行了比较,得到的主要结论包括:压力梯度对径向速度几乎无影响。无论等离子体压强是否均匀,角向速度和轴向速度的演化规律相似,但轴向速度对压力梯度更敏感。当等离子体压强均匀时,角向速度和轴向速度均为负值;当等离子体压强非均匀时,角向速度和轴向速度均正负参半,这体现了等离子体压强梯度对磁流体不稳定性的驱动效应。由于等离子壁对流体的阻碍作用,所有速度在等离子体壁处均衰减为零。     

均匀热压强时径向本征函数的研究北大核心CSCD

应用半解析方法,数值计算了不同均匀热压强时,径向本征函数随圆柱等离子体半径和粘度的演化规律。数值模拟结果表明:当等离子体热压强均匀时,压强对长波模式磁流体系统的径向本征函数基本无影响;短波模式时,均匀等离子体热压强对径向本征函数的极值大小和极值所处的位置均有明显影响,说明径向本征函数对波长的变化比较敏感。     

均匀热压强时径向本征函数的研究

应用半解析方法,数值计算了不同均匀热压强时,径向本征函数随圆柱等离子体半径和粘度的演化规律。数值模拟结果表明:当等离子体热压强均匀时,压强对长波模式磁流体系统的径向本征函数基本无影响;短波模式时,均匀等离子体热压强对径向本征函数的极值大小和极值所处的位置均有明显影响,说明径向本征函数对波长的变化比较敏感。     

具有非均匀热压强磁流体速度的定量研究

应用数值模拟方法,研究了非均匀等离子体压强梯度对圆柱位型磁流体速度的影响,并与均匀等离子体压强时的结论进行了比较,得到的主要结论包括:压力梯度对径向速度几乎无影响。无论等离子体压强是否均匀,角向速度和轴向速度的演化规律相似,但轴向速度对压力梯度更敏感。当等离子体压强均匀时,角向速度和轴向速度均为负值;当等离子体压强非均匀时,角向速度和轴向速度均正负参半,这体现了等离子体压强梯度对磁流体不稳定性的驱动效应。由于等离子壁对流体的阻碍作用,所有速度在等离子体壁处均衰减为零。     

矩量法在分形介质粗糙面电磁散射中的应用探究

目的:研究矩量法(MoM)在分形介质粗糙面电磁散射中的应用。方法:应用矩量法计算介质粗糙面的双站和单站散射。结果:给出一维带限Weierstrass分形粗糙面的表达式及介质表面的积分方程。结论:计算一维分形介质粗糙面的双站和单站散射,并分别给出有耗介质和无耗介质粗糙面的数值结果。     

Physical Simulation of Mold-Filling Processing of Thin-Walled Castings under Traveling Magnetic Field

Mold-filling process of thin-walled castings under the condition of traveling magnetic field has been studied by physical simulation method using gallium melt and fast speed photography. Flow morphology and its formation mechanism were obtained and discussed for thin-walled casting. The influences of magnetic field density on the filling ability, filling velocity and mold filling time have been studied. The differences in filling capability between gravity casting and casting under the traveling magnetic field have been compared. The results indicate that the mold filling ability of the gallium melt increases greatly under the condition of traveling magnetic field; the filling time is shortened from 18 s under gravity field to 3 s under the traveling magnetic field and average flow rate of the melt increases from 1.6 to 8.68 cm3/s; the change law of the cross-section morphology of the gallium melt during the mold filling is that at first, the cross-section area does not change, then it decreases gradual     

等离子体离子注入PIC仿真的MATLAB实现

MATLAB是当今先进计算软件之一,它提供的各类工具箱和内置函数给应用者带来了极大的方便。本文通过调用MATLAB中偏微分方程工具箱和插值函数实现了方管内表面等离子体离子注入的Particle-In-Cell模拟,并与传统其他语言程序的计算结果对比,结果基本一致。文章还讨论了不同尺寸的内电极对离子平均注入能量的影响,结果表明:即使有内部电极"钳位",平均注入能量也不高;在管壁偏压相同的情况下,尺寸较大的内电极因为"钳位"效果较好而具有较高的平均离子注入能量。最后提供了MATLAB对不规则形状靶件的计算结果,证明了MATLAB软件对不规则形状靶件的PIC模型有较好的适应性。MATLAB的应用为等离子体的模拟提供了简便易学的新途径。     

Critical current test results of 13 T-46 kA Nb3Al cable-in-conduit conductor

In the framework of ITER-EDA, a 13 T-46 kA Nb₃Al conductor with stainless steel jacket has been developed in order to demonstrate applicability of an Nb₃Al conductor with react-and-wind technique to ITER-TF coils. Using a 3.5 m sample consisting of a pair of conductors with 0% and 0.4% bending strain, the critical current performances of the Nb₃Al conductors were studied to verify that the conductor achieves the expected performance and the bending strain of 0.4% does not originate degradation. The critical currents were measured at background magnetic fields of 7, 9, 10 and 11 T at temperatures from 6 to 9 K. The expected critical currents were evaluated taking into account the variation of the strain in the cross-section due to the bending strain as well as self-field and non-uniform current distribution as results of an imbalance in the joint resistance and inductances. The calculation results indicate that the current distribution is almost uniform and the experimental results showed good agreement with the expected critical currents. Accordingly, we can conclude that the fabrication process of this conductor is appropriate and the react-and-wind technique using the Nb₃Al conductor is applicable to ITER-TF coils. In addition, the critical current of the Nb₃Al conductor is expected to be 108 kA at 13 T and 4.5 K, resulting in a sufficient margin against the nominal current of 46 kA. Furthermore, it was found that the decrease in the critical current by thermal strain can be made small by applying the bending strain to the conductor so as to reduce the compressive strain at higher fields, i.e. inner side of the coil, in the conductor cross-section.     

基于模型实时辨识自适应控制算法的时变机械系统振动主动控制

参数时变的现象广泛存在于机械系统。如果系统参数随着时间而发生较大变化,振动主动控制方案就需要考虑时变参数对控制算法的影响。针对动力学特性变化较大的时变机械系统振动,提出一种模型实时辨识自适应控制算法,该算法将传统的滤波自适应算法与递归预测误差方法相结合,利用改变梯度的递归预测误差方法实时估计控制通道模型。建立弹簧质量支承的非均匀截面杆纵向振动时域模型,模型中随时间而变化的弹簧刚度导致模型动力学特性发生较大变化。用模型实时辨识自适应控制算法对建立的杆模型进行振动控制数值仿真,仿真结果表明,所提出的控制算法能有效抑制时变系统的窄带和宽带振动。相对于现有的方法,该控制算法能实现更好的控制性能。最后,将所提出的控制算法应用到时变的摇摆系统振动控制,实验结果验证了所提出控制算法的可行性和有效性。     

Power losses of liquid nitrogen cooled high-current cables

This paper surveys the experimental and theoretical investigations on current induced losses of high power cables. Measurements on compact and tube conductor cable models have been carried out at room temperature and liquid nitrogen temperature (77 K). Further measurements on a 2000 mm² fully transposed litz conductor have been performed. Using the experimental results published, the methods of calculation have been tested with regard to the applicability at very large conductor cross-section or high conductivity. If necessary, improvements of the methods of calculation are suggested.     

随机风场中覆冰四分裂导线防舞研究

针对提出的一种适用于四分裂导线的防舞装置,采用数值模拟方法研究其防舞效果。给出新月型覆冰四分裂导线空气动力系数随攻角变化的风洞试验结果,为数值模拟研究提供基本参数。采用数值方法模拟沿线路变化的多点互相关风速时程样本,进而确定作用于覆冰导线上的空气动力载荷。数值模拟研究特征段线路安装防舞装置前后的运动过程,结果表明,该防舞装置可大大降低导线的运动幅值,对舞动具有有效的防止作用。     

Numerical investigation of buoyancy effects in vertical ITER-TF-CICC at normal operating conditions

Increasing the size of an experimental fusion device is an important factor towards achieving plasma ignition conditions; this could however generate new problems such as the build up of buoyancy flow in long, vertical parts of cable-in-conduit conductors (CICC). In this article, the impact of buoyancy effects to the conductor cooling behaviour is simulated for a conductor part at an inner leg of an ITER TF coil. The MAGS code system had to be extended by a two-channel thermohydraulic model based on the model of the MITHRANDIR code. Additionally, gravity was included. Using realistic nuclear heating assumptions, buoyancy flow shows no significant impact to the coil operation temperature margins, even if the thermal coupling is restricted to convective heat transfer between hole and bundle. The time constant of the buoyancy flow build up is of the same order of magnitude of a typical ITER cycle. An example with artificially enhanced nuclear heating by a factor of four is also included for the illustration of consequences of buoyancy effects to CICC vertical flow.     

频谱带宽和功率可变多普勒信号的计算机模拟

计算机模拟的多普勒信号，可以为各种多普勒信号处理方法的研究提供信号源，从而了解各种不同处理方法的性能。本文提出的方法，运用白噪声通过一时变滤波器的原理，模拟产生平均频率，带宽和功能均随时间变化的多普勒信号。     

A thin film phantom for blood flow simulation and Doppler test

The thin film phantom is a new type of ultrasound resolution test object. It consists of a thin planar substrate that is acoustically matched to the surrounding media. Precisely located scatterers on the surface of the substrate generate echo signals. The patterning of scatterers on the substrate allows echogenicity to be controlled as a function of position, which enables the production of a test object with highly reproducible and controllable scattering characteristics. We show that by vibrating the substrate in a suitable manner, an echo signal may be generated that simulates bidirectional flow. We demonstrate that a vibration of low amplitude at frequency f₀ produces a Doppler spectral signal at f₀ and -f₀, within the limits of aliasing. Furthermore, by driving the film with a bandlimited noise signal, we illustrate how a velocity distribution may be simulated. A time-varying flow velocity may be simulated by varying the noise bandwidth with time. Finally, using this technique, we demonstrate a system that simulates an arterial flow pattern, including its characteristic velocity distribution in forward and reverse directions simultaneously     

Subnanosecond Single Electron Source in the Time-Domain

We describe here the realization of a single electron source similar to single photon sources in optics. On-demand single electron injection is obtained using a quantum dot connected to the conductor via a tunnel barrier of variable transmission (quantum point contact). Electron emission is triggered by a sudden change of the dot potential which brings a single energy level above the Fermi energy in the conductor. A single charge is emitted on an average time ranging from 100 ps to 10 ns ultimately determined by the barrier transparency and the dot charging energy. The average single electron emission process is recorded with a 0.5 ns time resolution using a real-time fast acquisition card. Single electron signals are compared to simulation based on scattering theory approach adapted for finite excitation energies.