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1.
On 14 July 1998 TRACE observed transverse oscillations of a coronal loop generated by an external disturbance most probably caused by a solar flare. These oscillations were interpreted as standing fast kink waves in a magnetic flux tube. Firstly, in this review we embark on the discussion of the theory of waves and oscillations in a homogeneous straight magnetic cylinder with the particular emphasis on fast kink waves. Next, we consider the effects of stratification, loop expansion, loop curvature, non-circular cross-section, loop shape and magnetic twist. An important property of observed transverse coronal loop oscillations is their fast damping. We briefly review the different mechanisms suggested for explaining the rapid damping phenomenon. After that we concentrate on damping due to resonant absorption. We describe the latest analytical results obtained with the use of thin transition layer approximation, and then compare these results with numerical findings obtained for arbitrary density variation inside the flux tube. Very often collective oscillations of an array of coronal magnetic loops are observed. It is natural to start studying this phenomenon from the system of two coronal loops. We describe very recent analytical and numerical results of studying collective oscillations of two parallel homogeneous coronal loops. The implication of the theoretical results for coronal seismology is briefly discussed. We describe the estimates of magnetic field magnitude obtained from the observed fundamental frequency of oscillations, and the estimates of the coronal scale height obtained using the simultaneous observations of the fundamental frequency and the frequency of the first overtone of kink oscillations. In the last part of the review we summarise the most outstanding and acute problems in the theory of the coronal loop transverse oscillations.  相似文献   

2.
根据间断有限元法的数据结构特点,基于METIS网格分区技术,设计并行计算策略,在非结构网格上实现了并行高阶间断有限元法。控制方程的数值通量项使用Local Lax-Friedrichs(LLF)格式计算。设计了并行的牛顿-块高斯赛德尔法(Newton-Block GS)来加速收敛,提高迭代效率。并行性能分析表明,所设计的并行算法能够得到较好的加速比和并行效率,有效地节省计算时间,合理分配内存。这使得采用高阶间断有限元法计算更为复杂的问题成为可能。  相似文献   

3.
基于PC-CLUSTER群机并行体系结构与消息传递库MPI并行环境,研究了二维非结构网格DSMC并行算法。提出一类非结构网格动态分区策略,保证各子区域的分子数量大致相等,实现计算进程间的动态负载平衡。利用MPI库函数构造了符合DSMC并行原理的单步通讯法。采用单控制多数据流(SPMD)以及Master/Slave并行模式,设计了二维非结构网格DSMC整体并行算法。在程序的编制过程中,充分展现了Fortran90高级语言的主要特性,引人动态数组、指针、链表及派生类型数据。最后对过渡流域高超声速绕流进行了并行计算,数值试验的结果表明本文设计的并行算法可以取得较为理想的加速比。  相似文献   

4.
针对大型计算流体力学(CFD)软件的验证与确认,为了减少人工成本,提高软件质量和开发效率,并适应于未来高性能计算发展的要求,基于云计算思想,提出了自动化测试云平台的解决方案。该方案采用模块化的浏览器/服务器(B/S)网络架构;利用LAMP(Linux+Apache+MySQL+PHP/Python)开发工具;建立了持续集成的专业数据库;构建了涵盖可靠集群监控、复杂作业调度及大规模并行计算功能的云端环境;实现了通过便捷的网络访问,自动加载测试算例、提交集群计算、监测实时进度、自动化后处理、输出分析结果,并提供丰富的实验对比图、误差分析报表和汇总报告等;完成了对大型CFD软件的自动化验证与确认。将该方案应用于某大规模并行计算的CFD软件,验证了该解决方案的可行性与实用性。  相似文献   

5.
为提高压气机内部复杂流动计算的收敛速度,发展了一种多块多重网格上的可压缩流动并行计算流体动力学(CFD)方法,数值模拟了跨声速转子NASA Rotor 35内部流动及气动性能,重点分析了对接分区方式和内界面通信模式对并行性能的影响。结果表明:对接分区方法和多块多重网格内界面数据处理方法能够保证串、并行CFD方法结果基本一致,且与实验数据吻合良好;并行精度基本不受分区数目和通信模式的影响,并行效率随着相对通信负载的增大而降低。所发展的并行计算方法对跨声速转子气动分析和设计具有一定的可靠性,为开发大型流体机械复杂流动的基础并行算法及软件提供了参考价值。  相似文献   

6.
The Coronal Mass Ejection (CME) is arguably the most important discovery of solar eruptive phenomena in the 20th century. It is now also recognized that CMEs have great impact on the Earth's environment by inducing geomagnetic storms. Thus, development of simulation models to understand the physical mechanisms of CME initiation and propagation has become a challenge in the solar MHD community. In this paper we shall summarize chronologically the development of the theoretical analyses, and the successes and failures of the numerical magnetohydrodynamic (MHD) simulations of coronal mass ejections (CMEs) during the past two decades. The chronological development of numerical simulation models and the evolution of the numerical methods to treat this class of problems are presented. The most appropriate way to model CMEs is to have (i) a realistic pre-event coronal atmosphere, and (ii) realistic driving mechanisms. Details of the progress and assessment of the theoretical and modeling efforts for the understanding of the physics of the CME initiation and propagation will be presented, and the numerical methods to construct these simulation models will be discussed.  相似文献   

7.
This paper presents a novel, fully parallel algorithm for robust linearly constrained minimum variance (LCMV) beamforming. The robustness results from the use of an adjustable constraint to compensate for the unavoidable small mismatch between the nominal and the actual steering vector of the signal-of-interest. The need for parallelism follows from the large computational demands of beamforming algorithms and by the high data rates which are typically present in communications applications. The algorithm exhibits good numerical properties as it is based on orthogonal transformations only. Two systolic architectures are presented on which the throughput is independent of the size of the beamformer  相似文献   

8.
The nonlinear evolution of a partially open coronal magnetic configuration is considered, assuming that corona responds to photospheric footpoint motions by small-scale reconnection events that produce a relaxed lower-energy state while conserving the global magnetic helicity of the system. The results of numerical calculations for such a relaxed equilibrium show an essential role of the amount of helicity injected to the closed-field region. If photospheric perturbations are incoherent (small-scale shearing with inefficient helicity injection), the relaxed state becomes close to an initial potential field. In this case reconnective relaxation does not result in a substantial global evolution, just providing heating of the corona (Vekstein et al, 1993). On the contrary, sufficient injection of the magnetic helicity can lead to a considerable restructuring of the coronal magnetic configuration, with possible change of its topology (formation of magnetic islands), and even catastrophic loss of equilibrium (Wolfson et al, 1994)  相似文献   

9.
王子航  吕宏强 《航空学报》2021,42(z1):726366-726366
雷电空间电磁场一直是电磁领域研究的热门,成熟的算法例如有限时域差分法(FDTD),传输线矩阵法(TLM)以及频域的矩量法(MoM)在计算雷电问题方面都有广泛的应用。由于计算流体力学(CFD)中的Euler方程与电磁学中的Maxwell方程有着相同的守恒形式,而且采用间断伽辽金方法(DG)已经在流场问题上得到广泛的尝试,因此引入了基于计算流体力学的DG方法来离散时域Maxwell方程,并采用网格分区并行技术加速计算,使用基于DG的圆球雷达散射截面积(RCS)算例进行测试,数值结果一致表明DG算法在求解电磁场问题上的可行性,之后通过计算一段近场雷电通道的电场分布并与解析解、某算法仿真解对比,数据基本吻合,说明该方法适合于雷电电磁场的计算。  相似文献   

10.
微推偏火箭喷管非对称内流场数值模拟   总被引:2,自引:2,他引:0  
研究了入流倾斜于喷管超音速段轴线的微推偏喷管内流场。数值方法是具有高分辨率高精度的三维隐式有限体积的TVD格式。针对一系列典型锥形喷管和钟型喷管,数值模拟结果得出非对称内流场的侧向力和侧向力矩随喷管几何结构以及入流条件变化的一些特征,并同有关实验结果符合良好,对微推偏喷管设计具有一定的指导意义。  相似文献   

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