A fast Chebyshev polynomial method for calculating asteroid gravitational fields using space partitioning and cosine sampling

This paper presents a computationally fast method for solving gravitational accelerations near irregularly-shaped asteroids. This method is based on analytical three-dimensional Chebyshev polynomial approximation of the polyhedral gravity. For the purpose of improving the approximation accuracy, space partitioning schemes based on practical flight zones is used to avoid interpolation the whole space around the target asteroid. Specifically, a minimum ellipsoid close to the asteroid surface is defined to select the space for surrounding trajectories with safe distance and a cone connected to the surface is defined to select the space for descent trajectories. Moreover, interpolation points are sampled in a cosine sampling fashion according to the Chebyshev-Gauss-Lobatto nodes and a radial adaption technique. The performance of different space partitioning schemes is analyzed. The effectiveness of the proposed method is validated through simulations of solving gravitational accelerations at the test points near different shaped asteroids 1996 HW1, 433 Eros, 25143 Itokawa and 101955 Bennu.     

Coating deposition regularity depended on orientation difference in PS-PVD plasma jet

The YSZ coatings are prepared by the plasma spray-physical vapor deposition (PS-PVD) technology based on a specific experimental design. The structure, thickness and growth angle of YSZ coatings on the entire circumferential surface of the cylindrical sample are studied. The results indicated that the structure, thickness and deflection growth angle of YSZ coatings are related to the orientation of deposition location. The numerical simulation of the multiphase mixed fluid near the substrate is carried out and the deposition regularity and mechanism of YSZ coatings prepared by PS-PVD is deduced. The growth rate is related to the local characteristics of the plasma flow field, and is directly proportional to the field pressure and inversely proportional to the field velocity. The growth angle of the coating is generally affected by the flow direction of the plasma jet. Especially, the normal component of velocity vector, V_norm, mainly affects the speed at which the coating grows vertically upwards. The tangential component of velocity vector, V_tan, determines the degree that the coating growth direction deviates from the vertical direction. When V_tan ≠ 0, the coating forms a fine column with a certain deflection angle and finally develops into an oblique columnar structure.     

Ground-based and satellite DC-ULF electric field anomalies around Wenchuan M8.0 earthquake

The ground-based and satellite DC-ULF electric field data were analyzed around Wenchuan M8.0 earthquake on May 12, 2008 in China. The results show that ground electric field anomalies occurred at 3 stations located to the north and south of the epicenter with the amplitude of 3–100 mV/km. The change shapes and their amplitude of ground electric field anomalies are different largely due to their individual underground layer conductivity, water level and so on. The analysis of long time series illustrates that the abnormal geoelectric field started since March 2008. Onboard the DEMETER satellite, the ULF waveforms of electric field were collected and processed by wavelet transform method. The disturbances in the ionosphere were about 3–5 mV/m at a frequency band lower than 0.5 Hz. When the ground and space electric field anomalies were compared, their occurrence time and spatial distribution points are consistent with each other, including the long time anomalies from March 2008 and the short term ones 1–2 days before the Wenchuan earthquake. Finally, the coupling mechanism was discussed.     

Cosmic ray modulation with a Fisk-type heliospheric magnetic field and a latitude-dependent solar wind speed

The effect of a latitude-dependent solar wind speed on a Fisk heliospheric magnetic field [Fisk, L. A. Motion of the footpoints of heliospheric magnetic field lines at the Sun: implications for recurrent energetic particle events at high heliographic latitudes. J. Geophys. Res. 101, 15547–15553, 1996] was first discussed by Schwadron and Schwadron and McComas [Schwadron, N.A. An explanation for strongly underwound magnetic field in co-rotating rarefaction regions and its relationship to footpoint motion on the the sun. Geophys. Res. Lett. 29, 1–8, 2002. and Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003]. Burger and Sello [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005] found a significant effect for a simplified 2D version of a latitude-dependent Fisk-type field while Miyake and Yanagita [Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, 445–448, 2007] found a smaller effect. The current report improves on a previous attempt Hitge and Burger [Hitge, M., Burger, R.A. The effect of a latitude-dependent solar wind speed on cosmic-ray modulation in a Fisk-type heliospheric magnetic field. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 449–450, 2007] where the global change in the solar wind speed and not the local speed gradient was emphasized. The sheared Fisk field of Schwadron and McComas [Schwadron, N.A., McComas, D.J. Heliospheric “FALTS”: Favored acceleration locations at the termination shock. Geophys. Res. Lett. 30, 41–1, 2003.) is similar to the current Schwadron–Parker hybrid field. Little difference is found between the effects of a Parker field and a Schwadron–Parker hybrid field on cosmic-ray modulation, in contrast to the results of Burger and Sello and Miyake and Yanagita [Burger, R.A., Sello, P.C. The effect on cosmic ray modulation of a Parker field modified by a latitudinal-dependent solar wind speed. Adv. Space Res. 35, 643–646, 2005 and Miyake, S., Yanagita, S. The effect of a modified Parker field on the modulation of the galactic cosmic rays. In: Proceedings of 30th International Cosmic Ray Conference. Merida, Mexico, vol. 1, pp. 445–448, 2007]. The two-dimensional approximation used by these authors is therefore inadequate to model the complexities of the actual three-dimensional field. We also show that a Fisk-type field with a latitude-dependent solar wind speed (Schwadron–Parker hybrid field) decreases both the relative amplitude of recurrent cosmic ray intensity variations and latitude gradients and yields similar constants of proportionality for these quantities as for the constant solar wind speed case.     

基于协议变换的图像采集系统设计

介绍了一个基于高速协议变换的实时图像采集系统,该系统实现了从IEEE1394协议到千兆以太网协议的实时变换,将基于IEEE 1394协议的数字相机发出的图像数据转发到以太网上.系统设计使用了SOPC(System On a Programmable Chip)技术,通过Avalon总线将Nios Ⅱ处理器,千兆网MAC核和自定义的1394芯片接口逻辑等IP组件连接在一起形成主要的硬件电路,结合系统软件设计实现了对高速图像数据的实时转发.系统达到了较好的性能,同时具有集成度高,结构简单和扩展性好的特点,展示了利用SOPC技术解决此类问题的优势.     

一种点扫描形貌测量系统的现场标定方法

针对三角法点扫描形貌测量系统结构参数标定的非线性问题,提出并实现了一种简单易行的系统结构参数现场标定方法.利用二维靶标在测量空间内自由摆放,根据靶标上特征点及其像点间的位置关系,基于坐标系转换实现了点扫描形貌测量系统结构参数的精确标定.通过对平面及已知直径圆柱面进行测量,利用测量点到拟合平面或圆柱面的距离评价了系统标定的精度.所提标定方法无需精密调整靶标位置,具有较高的可靠性与实用性;也可用于其它基于三角法原理的三维形貌测量系统结构参数的标定.     

准静态电磁热弹性体第二类H-R型广义变分原理

应用变积方法建立了准静态电磁热弹性体的势能原理和第二类H-R型广义变分原理,并检验了变分原理的正确性,为电磁热弹多场问题的近似计算提供理论基础。     

星载铯钟C场设计及磁场分析

为了提高星载铯钟的频率准确度,依据星载铯钟C场系统的设计要求,运用毕奥—莎伐尔定律计算线圈磁场,设计并分析了C场磁场系统。通过数值计算证明了设计的合理性,得到了最佳的主C和副C线圈匝数等参数,改善了原子束流轨迹上磁场强度的均匀性并得到试验验证,可将信号的频率准确度提高一个量级。
     

基于现场总线和智能变送器的风洞气流参数测量系统研制

准确测量来流雷诺数对于研究一些对雷诺数变化敏感的流动现象十分重要,为了得到较为准确雷诺数需要测量来流速度、温度和环境大气压等气流参数。本研究基于带Hart通信协议的智能变送器以及数字式振筒气压仪,在低速风洞中实现了一套简单实用的气流参数采集系统。其中,主机和差压、温度变送器之间通过Hart适配器相连接,并通过串口以Hart协议实现通信;而数字式振筒气压仪与计算机之间则直接通过串口实现通信。在系统开发过程中对Hart协议进行了解析和测试。在该系统气流参数采集的基础上,实现了来流雷诺数实时精确的计算,并对比了因温度和气压波动导致的雷诺数计算差异对旋成体大迎角雷诺数效应研究的影响,从而进一步说明了发展该系统的重要性。     

导弹多喷流干扰特性数值计算分析

给出一种直接力/气动力复合控制的空空导弹计算模型,应用CFD软件对其侧向多喷流干扰流场进行了数值模拟;选择四种代表情况,重点研究分析了不同侧多喷流对导弹气动特性的影响。研究结果表明,喷流干扰使得升力系数和俯仰力矩系数减小,并产生较大的偏航干扰力矩,同时喷流的间距也影响俯仰力矩系数和偏航力矩系数。所得结论具有一定的参考价值。