共查询到14条相似文献,搜索用时 62 毫秒
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推广完备正交函数系(OFSE)展开方法,应用它研究冕环中无耗散扭转Alfven波和快波耦合的时变过程.采用这种方法,从数学上描述了总体波模的固有角频率,从理论和数值计算结果两方面分析了Alfven波和快波耦合时冕环中磁力线Alfven波固有角频率.采用这种方法,分析了耦合驱动项和Alfven波共振的关系.计算结果给出了耦合共振出现位置Alfven波和快波的波幅特征,发现如果足点驱动角频率不等于冕环总体波模的固有角频率,在耦合共振位置当扭转Alfven波幅出现δ断面时,快波振幅沿径向梯度很大,有时近似为一个间断,非常有利于快波耗散;如果足点驱动角频率等于总有体波模的固有角频率,Alfvn波振幅出现δ断面时在径向出现丰富的小尺度结构,共振位置近似为一个间断,非常有利于Alfven波耗散. 相似文献
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《空间科学学报》2003,23(4):241-247
提出完备正交函数基(OFSE)展开方法,求解冕环中无耗散扭转Alfvén波.每个基函数对应冕环中每根磁力线的一个固有角频率ωn,当冕环足点驱动频率等于磁力线的固有频率时,Alfvén波将在这根磁力线处发生共振.采用OFSE方法求解了双足点驱动时冕环Alfvén波的时变演化问题,给出了时变解析解的新形式,其中包含共振项,从共振项可以发现,在共振角频率为ω的共振磁力线附近,在时间t为π/ω的整数倍时,出现δ型间断;在t为π/(2ω)的奇数倍时,出现1/x间断.共振磁力线振幅随时间线性增加,增加的斜率正比于Alfvén波速,反比于冕环长度,与驱动频率无关. 相似文献
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提出完备正交函数基(OFSE)展开方法,求解冕环中无耗散扭转Alfvn波。每个基函数对应冕环中每根磁力线的一个固有角频率ω_n,当冕环足点驱动频率等于磁力线的固有频率时,Alfvn波将在这根磁力线处发生共振。采用OFSE方法求解了双足点驱动时冕环Alfvn波的时变演化问题,给出了时变解析解的新形式,其中包含共振项,从共振项可以发现,在共振角频率为ω的共振磁力线附近,在时间t为π/ω的整数倍时,出现δ型间断;在t为π/(2ω)的奇数倍时,出现1/x间断。共振磁力线振幅随时间线性增加,增加的斜率正比于Alfvn波速,反比于冕环长度,与驱动频率无关。 相似文献
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磁流体斜激波的碰撞 总被引:1,自引:0,他引:1
讨论了磁流体斜激波之间的碰撞及其与接触间断的相互作用规律,主要结论如下:(1)两个快激波碰撞后交换位置,同时出现一接触间断和一慢稀疏波对。(2)两个慢激波碰撞后交换位置且强度减弱,同时出现一接触间断和一块激波对。(3)一前向快激波与一后向慢激波碰撞后交换位置,快激波强度增加,慢激波强度减弱,同时出现一后向快激波、一负接触间断和一前向慢稀疏波。(4)一前向快激波与一正(负)接触间断相互作用后交换位置,快激波减弱,同时出现一后向快稀疏波(快激波)、一后向慢激波和一前向慢激波(慢稀疏波).(5)一前向慢激波与一正(负)接触间断相互作用后交换位置,慢激波减弱,同时出现一后向慢稀疏波(慢激波)和一快稀疏波(快激波)对。 相似文献
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Snyoll Oghim Henzeh Leeghim Donghoon Kim 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2019,63(2):1007-1016
A real-time intercept strategy for spacecraft under the non-uniform gravitational perturbation of Earth is addressed in this paper. To intercept a target spacecraft on general conic sections, an interceptor considered in this work makes use of a thruster propelling the constant thrust which is comparable to unrealistic impulse-type thrust. The perturbation introduces critical dynamic variations of spacecraft orbiting the Earth, which results in a considerable amount of position error of the interceptor at the final intercept point. In order to release the burden of disturbance and make the miss distance between the target and interceptor small, a real-time intercept technique with an optimal intercept algorithm is suggested. The strategy proposed is to obtain an optimized output iteratively for a given time interval with previously obtained optimal values. These parameters are evaluated by the optimal intercept algorithm suggested. Once the optimal velocity change is obtained to satisfy intercept requirements, although the orbital system is perturbed, it is easy to regenerate a new solution by setting the previous solution as new initial guesses. This strategy is employed iteratively until the interceptor meets the target. Several numerical simulations are performed to highlight the proposed real-time strategy for spacecraft intercept missions. 相似文献
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Erika Gularte Daniel D. Carpintero Juliana Jaen 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2018,61(7):1790-1802
We have developed a new approach towards a new database of the ionospheric parameter . This parameter, being the frequency of the maximum of the ionospheric electronic density profile and its main modeller, is of great interest not only in atmospheric studies but also in the realm of radio propagation. The current databases, generated by CCIR (Committee Consultative for Ionospheric Radiowave propagation) and URSI (International Union of Radio Science), and used by the IRI (International Reference Ionosphere) model, are based on Fourier expansions and have been built in the 60s from the available ionosondes at that time. The main goal of this work is to upgrade the databases by using new available ionosonde data. To this end we used the IRI diurnal/spherical expansions to represent the variability, and computed its coefficients by means of a genetic algorithm (GA). In order to test the performance of the proposed methodology, we applied it to the South American region with data obtained by RAPEAS (Red Argentina para el Estudio de la Atmósfera Superior, i.e. Argentine Network for the Study of the Upper Atmosphere) during the years 1958–2009. The new GA coefficients provide a global better fit of the IRI model to the observed than the CCIR coefficients. Since the same formulae and the same number of coefficients were used, the overall integrity of IRI’s typical ionospheric feature representation was preserved. The best improvements with respect to CCIR are obtained at low solar activities, at large (in absolute value) modip latitudes, and at night-time. The new method is flexible in the sense that can be applied either globally or regionally. It is also very easy to recompute the coefficients when new data is available. The computation of a third set of coefficients corresponding to days of medium solar activity in order to avoid the interpolation between low and high activities is suggested. The same procedure as for can be perfomed to obtain the ionospheric parameter M(3000)F2. 相似文献
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本文讨论了单色平面引力波对宇宙飞船轨道的影响。着重指出ω/n=2和ω/n=1,3这三种主共振态是二类不同的共振态,前者直接影响系统的能量,而后者则主要使轨道在空间转动和改变形状。 相似文献
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B Baican E Schopper T h Wendnagel J U Schott C Heilman 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》1992,12(2-3):355-358
The aim of the experiment "Seeds" on the Sowjetic satellite Biokosmos 9 was the observation of mutagenic effects caused at special loci of seeds of Arabidopsis thaliana and assigned to particles of the Cosmic radiation. Two types of exposure units were flown: A low-shielding unit Type I, mounted at the surface of the satellite (1.4 g/cm2 shielding) and, for comparison, an identical item inside (16 g/cm2 shielding), using nuclear emulsion as track detectors. A Type II unit, flown inside (18g/cm2 shielding) was mounted with AgCl track detectors. The layout will be briefly described. A first set of dosimetric data from the physical evaluation of the experiment will be presented. The subdivision into charge- and LET-groups shows a rather high contribution of the intermediate LET-group (350-1000 MeV/cm) due to medium heavy particles (Z = 6-10) and to enders of light (p, alpha) particles. 相似文献
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本文研究了中层大气受迫Rossby波包非线性三波相互作用问题。理论分析得出,如果仅有最大波长或最小波长的波包受外源作用,系统仅能维持受迫波包的运动,平衡状态下外源能量不向另两个波包传递;仅有中等波长波包受外源作用时,随着外源强度的增加,系统的平衡态会发生分岔,并且在分岔点以后,中等波长波包的波幅不再增大,但大气高度愈高该振幅饱和值愈大,外源增大的能量全部通过非线性相互作用馈送给其他两个波包,从而外源可以维持三个波包的长期等幅运动。本文还给出了系统中有两个受迫Rossby波包时系统的平衡态和稳定性条件,这时无论三个波包的尺度关系如何,外源能量均能在三个波包之间传递,因此外源也可以维持三个波包的运动。进一步的结果和波包的演化过程将通过数值计算给出。 相似文献
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电离层的运动与电波频率的变化 总被引:1,自引:0,他引:1
本文对从空间缓慢变化电离层反射的回波的多卜勒频移进行了讨论,认为反射面的运动和媒质的运动可以分开,等效镜反射面不一定在偏区.提出了利用寻常波和非寻常波多卜勒频移反演等值面运动速度剖面的方法. 相似文献
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非线性磁声波和动力Alfven波的稀疏孤子解及其在低极尖区的应用 总被引:1,自引:0,他引:1
详细研究非线性磁声波和动力Alfven波稀疏型孤子解的性质,发现激发的电磁场在方向和形态上有明显区别,并和低极尖区Freja卫星观测资料作比较,说明低频流密度下凹型更可能是非线性动力Alfven波所引起。 相似文献