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Three-dimensional MHD dynamo simulation

三维 MHD 发电机模拟

基本信息

批准号：
10640404
负责人：
HONKURA Yoshimori
金额：
$ 1.98万
依托单位：
Tokyo Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1998
资助国家：
日本
起止时间：
1998 至 2000
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-10640404/
关键词：
MHD dynamo Magnetic field origin Boundary layer Earth and planetary magnetism Tangent cylinder 磁場凍結近似地球惑星ダイナモ

项目摘要

Aiming at solving a dynamo problem as a mechanism of the origin of Earth and planetary magnetism, we have performed three-dimensional MHD dynamo simulation. So far, we have found that boundary layers develop depending on the Ekman number and in the layer small-scale phenomena are dominant, when a non-slip boundary condition is given to the velocity field. Therefore, we must evaluate the effect of boundary layers if we want to obtain reliable results of MHD dynamo simulation. In 1998 and 1999, we developed a new computer code for dynamo simulation and compared its results with those derived from our previous code and showed that our new code is valid. Then we modified this code so as to cope with parallel computing. In 2000, we have participated the dynamo benchmark test as an international group attempt. As a result, our results were found to agree with the others and therefore our computer code is as effective as the other codes developed by oversea researchers. From our results, we could find that crude spatial resolution in the radial direction greatly affects the drift rate of the velocity filed pattern. In other words, it is the most important to assure enough resolution in the boundary layers when we examine the results of numerical computation. A hypothetical cylinder, which is tangent to the inner core at its equator and parallel to the rotation axis, is called a tangent cylinder, which is also a boundary layer. The effect of this layer becomes prominent for the non-slip boundary condition. Inside the tangent cylinder, the flow is not violent when the Rayleigh number is small, but for a high Rayleigh number, convective motion becomes active, Such a feature has a great influence on the mechanism of magnetic field creation and variation. As a future work, we should try to under stand the dependence of the Rayleigh number on dynamics inside the tangent cylinder

针对作为地球和行星磁性起源机制的发电机问题，我们进行了三维MHD发电机模拟。到目前为止，我们已经发现，边界层的发展取决于Ekman数和层中的小尺度现象是占主导地位的，当无滑移边界条件的速度场。因此，要获得可靠的磁流体发电机模拟结果，就必须考虑边界层的影响。在1998年和1999年，我们开发了一个新的计算机程序的发电机模拟和比较其结果来自我们以前的代码，表明我们的新代码是有效的。然后，我们修改了这个代码，以科普并行计算。2000年，我们作为国际团体尝试参加了发电机基准测试。结果表明，我们的计算结果与其他人的计算结果一致，因此我们的计算机程序与国外研究人员开发的其他程序一样有效。结果表明，径向粗空间分辨率对速度场的漂移率有很大的影响。换句话说，当我们检验数值计算的结果时，保证边界层有足够的分辨率是最重要的。一个假设的圆柱体，在赤道处与内核相切，并平行于旋转轴，称为切向圆柱体，它也是边界层。在无滑移边界条件下，这一层的影响变得突出。在切向圆柱内部，当Rayleigh数较小时，流动并不剧烈，但当Rayleigh数较高时，对流运动变得活跃，这一特征对磁场的产生和变化机制有很大影响。作为未来的工作，我们应该尝试理解瑞利数对切向圆柱内部动力学的依赖性