非圆截面等离子体MHD不稳定性的研究

本文采用阶跃电流模型研究了非圆截面环电流器等离子体的MHD不稳定性,使札哈洛夫(Zakharov)的工作推广到非圆截面,得到了新的稳定性判据。它指出了椭圆形变,三角形变,电流梯度以及q值(所谓的安全因子)对等离子体的β值的影响。为了得到最大的β值,本文给出了最佳q值公式。对等离子体的不同参数计算了临界β值,并与由局部模判据和气球模的数值计算所得到的结果进行了比较。文中指出,电流梯度的存在是对等离子体β值影响的重要因素;非圆截面等离子体比圆截面等离子体可能得到更高的β值。     

用正问题代码求逆问题的尝试

本文介绍了一种用正问题代码通过某种逆过程来求解逆问题的数值目的。我们使用这种目的在平衡代码SWEQU^[1]的基础上开发了一个名为SWSTAB的计算非圆截面托卡马克等离子体竖直不稳定性的程序。利用该程序我们计算了成型线圈条件下,上下不对称等离子体的竖直不稳定性,研究了等离子体形状因子(椭圆半轴比,三角形变)及等离子体与成型线圈之间距离对稳定性的影响,方便地得到了用其它目的不易得到的物理结果。     

起爆方式对非圆截面装药结构释能特性的影响

为了研究不同起爆方式下非圆截面装药结构的释能规律,采用AUTODYN软件开展了非圆截面装药结构在不同起爆方式下的释能特性数值模拟,分析了起爆方式对爆轰波形演变、破片质量、破片初速的影响。结果表明：由于装药结构的特殊性,采用端部单点起爆时装药能量分布不均匀,部分区域产生大量的无效小质量破片,且不同位置处的破片初速波动较大;采用端部两点和端部三点起爆时,能够对爆轰能量起到匀化效果,减少无效破片数量,提升破片初速的一致性。由此证明通过调整起爆方式可以对非圆截面装药结构的能量输出结构进行有效调控,对其周向能量场起到匀化效果。     

非圆小通道内水-空气垂直上升流动流型研究

微化工机械以及紧凑式换热器的发展,使非圆截面小通道在工程中获得大量应用,但现有文献针对非圆截面小通道内两相流动的研究报导屈指可数。本文采用可视化手段研究了水力直径分别为2．886 mm和1．443 mm的三角形截面并联小通道内水-空气垂直上升流动,表现气速0．1~100 m／s,表观水速0．1~6 m／s。根据观察和测量结果,总结得到了流型转变界限,并获得了典型流型图像。将本文的实验结果与前人的研究结果对比表明:通道的截面形状和水力直径均对非圆截面小通道内两相流型转变界限有显著的影响。     

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通过引入Cap-cyclide坐标和使用Wangerin函数,基于B Bernstein的能量原理,针对位于导体壁中的任意环径比和任意拉长比的非圆截面等离子体,不使用任何近似的方法,求得了等离子体的稳定解析解。进而利用计算机对解析结果进行数值计算,并通过β和稳定系数q的关系,分析和讨论了导体壁对非圆截面等离子体稳定性的影响。     

托卡马克中等离子体的平衡重建

本文描述了用外部磁测量信号,和等离子体总电流,以及角向β_p的测量值,重建托卡马克中等高子体半衡的方法。对圆截面、非圆截面和偏滤器位形;对不同的电流分布分别作了重建计算。数值研究了测量误差、探针布置对重建结果的影响。     

声管中的宽带脉冲法的水声材料吸声系数测量

现有的水声管吸声系数测量的脉冲法,由于水声管高度的限制,存在低频限制。提出了基于"后置""逆滤波的宽带脉冲声测试方法,在测量获得系统的传递函数后,换能器发射宽频短脉冲信号,然后对接收到的标准反射体和待测样本的反射信号分别进行逆滤波处理,恢复未经传递系统"污染"的反射信号,计算待测样品的反射系数和吸声系数。仿真实验分析了"后置"逆滤波相对于传统"前置"逆滤波的在低频测试方面优势。对橡胶材料样品进行了实验测试,无论在低频段还是中高频段,宽带脉冲法和CW (Continuous Wave)脉冲法测试结果均吻合较好。宽带脉冲法是一种有效的测试方法,其低频测试能达到350 Hz,能有效拓展低频测试范围。      

由磁测量确定环流器等离子体截面形状的方法

一、引言在环流器实验中,等离子体柱截面形状和位置是位形基本参数。尤其对非圆截面和放电期间截面变化的装置,为调节、控制成形、分析等离子体内外电流分布变化引起的位形和稳定性改变,边界磁面形状位置是不可缺少的信息。本文用给定极向磁场,由拟合计算的方法来确定等离子体边界。     

非圆截面环流器硬X射线剂量测量

本文给出了硬X射线剂量测量的原理和方法,并在非圆截面环流器装置上测量了硬X射线的吸收剂量,约为10~(-10)Gy/每次放电。     

非圆截面环流器等离子体对于高n理想磁流体气球模的最佳压强分布

本文假定等离子体局部压强梯度由理想磁流体高n气球模所限定,讨论了非圆截面环流器的最佳压强剖面。分析了椭圆及三角变形的效应,发现三角变形对提高稳定性很有利;q剖面对平均比压值及中心比压值都有强烈影响,而沿半径下降的q剖面对提高比压值很有利。     

The attenuation of the higher-order cross-section modes in a duct with a thin porous layer

A numerical method for sound propagation of higher-order cross-sectional modes in a duct of arbitrary cross-section and boundary conditions with nonzero, complex acoustic admittance has been considered. This method assumes that the cross-section of the duct is uniform and that the duct is of a considerable length so that the longitudinal modes can be neglected. The problem is reduced to a two-dimensional (2D) finite element (FE) solution, from which a set of cross-sectional eigen-values and eigen-functions are determined. This result is used to obtain the modal frequencies, velocities and the attenuation coefficients. The 2D FE solution is then extended to three-dimensional via the normal mode decomposition technique. The numerical solution is validated against experimental data for sound propagation in a pipe with inner walls partially covered by coarse sand or granulated rubber. The values of the eigen-frequencies calculated from the proposed numerical model are validated against those predicted by the standard analytical solution for both a circular and rectangular pipe with rigid walls. It is shown that the considered numerical method is useful for predicting the sound pressure distribution, attenuation, and eigen-frequencies in a duct with acoustically nonrigid boundary conditions. The purpose of this work is to pave the way for the development of an efficient inverse problem solution for the remote characterization of the acoustic boundary conditions in natural and artificial waveguides.     

非圆截面等离子体平衡外部流函数的步进滤波解法

本文将滤波方法与步进计算相结合,从而得到求解不适定的等离子体流函数方程Cauchy问题的一种数值方法。此新方法克服了普通步进计算解流函数方程Cauchy问题时出现的不稳定现象,取得了稳定解的较好结果。     

Index to volume 72

A numerical analysis of wave propagation in one dimensional inhomogeneous media is presented in this paper, the first (Part I) of two companion papers. The aim is to provide a natural and physical basis for the solution of the inverse scattering problem in one dimension. The paper includes (i) a discussion of some aspects of the numerical solution of the direct problem, (ii) typical results of calculation and (iii) a comparison between exact solutions and forward scattering approximation (FSA) solutions of the direct problem. It is shown that the FSA allows accurate calculations of the reflected wave and thus constitutes a sound basis for the solution of the inverse problem treated in Part II.     

三维时变等离子体目标的电磁散射特性研究

基于电流密度拉普拉斯变换方法改进的时域有限差分(LTJEC-FDTD)算法, 研究时变等离子体目标的电磁散射特性.由Maxwell方程和等离子体本构方程出发, 利用拉普拉斯变换和拉普拉斯逆变换, 推导出计算三维时变问题的时域有限差分(FDTD)算法的迭代式. 采用模式匹配方法验证了FDTD迭代式的正确性, 并通过计算等离子体球的雷达散射截面(RCS)验证了算法相关边界的正确性. 最后用LTJEC-FDTD算法分析了涂覆时变等离子体的战斧式巡航导弹的RCS. 关键词： 时变等离子体 雷达散射截面 模式匹配方法 时域有限差分方法     

A review on the solution of Grad–Shafranov equation in the cylindrical coordinates based on the Chebyshev collocation technique

Equilibrium reconstruction consists of identifying, from experimental measurements, a distribution of the plasma current density that satisfies the pressure balance constraint. Numerous methods exist to solve the Grad–Shafranov equation, describing the equilibrium of plasma confined by an axisymmetric magnetic field. In this paper, we have proposed a new numerical solution to the Grad–Shafranov equation (an axisymmetric, magnetic field transformed in cylindrical coordinates solved with the Chebyshev collocation method) when the source term (current density function) on the right-hand side is linear. The Chebyshev collocation method is a method for computing highly accurate numerical solutions of differential equations. We describe a circular cross-section of the tokamak and present numerical result of magnetic surfaces on the IR-T1 tokamak and then compare the results with an analytical solution.     

快加热环流器等离子体的位形演变

本文讨论了环流器等离子体在快加热过程中位形演变的近似描述问题。对两类重要的通量守恒演变系列,即绝热压缩和非压缩快加热,具体计算了平衡解。假定等离子体截面形状有任意的小变形,但初态位形只有一个椭圆磁轴,所用近似方法基于对反环径比展开。结果表明,这一方法可以成功地描述绝热压缩演变系列;对非压缩快加热,在磁轴位移不很大时,所得结果与严格的二维通量守恒解是相符的。 关键词：     

A Meshless Regularization Method for a Two-Dimensional Two-Phase Linear Inverse Stefan Problem

In this paper, a meshless regularization method of fundamental solutions is proposed for a two-dimensional, two-phase linear inverse Stefan problem. The numerical implementation and analysis are challenging since one needs to handle composite materials in higher dimensions. Furthermore, the inverse Stefan problem is ill-posed since small errors in the input data cause large errors in the desired output solution. Therefore, regularization is necessary in order to obtain a stable solution. Numerical results for several benchmark test examples are presented and discussed.     

共轭梯度法求解双曲传热多宗量反问题

提出双曲传热反问题热物性参数和边界条件多宗量联合反演的一般数值求解模式,考虑了非均质和分布参数的影响,时域上采用时域精细算法进行离散,建立了便于敏度分析的有限元正演模型.由最小二乘原理建立反演模型,应用共轭梯度法进行求解.探讨了时间步长和测量误差对反演结果的影响,并进行了数值验证.     

Noniterative analytical formula for inverse scattering of multiply scattering point targets

This paper derives, in the exact framework of multiple scattering theory for point targets, a noniterative analytical formula for the nonlinear inversion of the target scattering strengths from the scattering or response matrix that can be applied after the target positions have been estimated in a previous step via, e.g., time-reversal multiple signal classification or another approach. The new formula provides a noniterative analytical alternative to the iterative numerical solution approach for the same problem presented in a recent paper [A. J. Devaney, E. A. Marengo, and F. K. Gruber, "Time-reversal-based imaging and inverse scattering of multiply scattering point targets," J. Acoust. Soc. Am. 118, 3129-3138 (2005)]. The two methods (noniterative versus iterative) are comparatively investigated with two numerical examples.