Construction of fast dynamos using unsteady flows and maps in three dimensions
Construction of fast dynamos using unsteady flows and maps in three dimensions
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DOI：
10.1080/03091928808208887
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发表时间：
1988-12
影响因子：
1.3
通讯作者：
B. Bayly;S. Childress
中科院分区：
文献类型：
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作者：
B. Bayly;S. Childress
非定常快速发电机是利用一系列由磁场扩散周期分隔的快速运动来构造的。受Ze'dovich和Soward描述的物理机制的启发，我们研究了顺序施加的单模Beltrami波的效果，并表明它们可以近似为一个简单的“拉伸-折叠-剪切”（SFS）映射的单位立方体到自身。在SFS映射中，场点在固定方向上，并且扩散很容易计算。数值结果表明，快速发电机行动发生足够大的剪切，该过程主要是一个连贯的功能较大的磁尺度。光滑流也得到了类似的结果。一些初步分析的SFS地图使用的分解方法进行说明。
Unsteady fast dynamos are constructed using a sequence of rapid movements separated by periods of diffusion of the magnetic field. Motivated by the physical mechanism described by Ze'dovich and by Soward, we examine the effect of single-mode Beltrami waves applied sequentially, and show that they can be approximated by a simple “stretch-fold-shear” (SFS) map of the unit cube onto itself. In the SFS map, the field points in a fixed direction and diffusion is easily computed. The numerical results indicate that fast dynamo action occurs for sufficiently large shear, and that the process is primarily a coherent feature of the larger magnetic scales. Similar results are obtained for smooth flows. Some preliminary analysis of the SFS map using a decomposition method is described.