钛合金铣削刀具/工件接触区域温度预测

钛合金（Ti-6Al-4V）因其优良的综合性能广泛应用于航空航天领域中,然而由于其导热系数低、弹性模量低等特性,铣削加工过程中刀具/工件接触区域温度过高,从而导致刀具磨损严重,影响已加工表面质量。因此研究切削过程中刀具/工件接触区域温度具有重要意义。从切削机理出发,将切削区域的3个热源等效为螺旋线热源,其中热流密度计算类比铣削力预测模型中铣削力计算方法,提出包含铣削热系数的热流密度计算模型,并通过实验标定铣削热系数,结果表明热流密度随切削厚度增加接近于线性增加。建立刀具/工件接触区域温度预测模型,通过半人工热电偶测温实验对模型的可行性与准确性进行了验证,实验值与预测值的相对误差在10%之内。提高了刀具/工件接触区域温度的计算精度,并为切削参数的合理选择提供理论基础。     

整数槽同步电机低振动噪声定子结构设计

针对电机电磁振动噪声问题,依据电磁振动噪声的基础理论,采用电磁和结构弱耦合的有限元仿真方法,以1台12极72槽车用永磁同步牵引电机为例,分析在不同长宽比、槽口宽度以及结构综合变化的条件下,径向电磁力密度的情况;同时对整个电机进行电磁-结构耦合场分析,研究结构振动位移在不同定子长宽比、槽口宽度以及结构综合变化时的响应情况。综合比较分析两种仿真结果,给出了电磁振动噪声关于定子结构长宽比和槽口宽度的变化规律。最后在额定负载工况下对实物样机进行振动检测和频谱分析,与仿真数值进行对比分析,以验证仿真试验的准确性。     

对流传热场协同原理在高速可压缩边界层流动中的推广

应用理论分析方法对适用于不可压缩层流与湍流流动的对流传热场协同原理进行了可压缩层流与湍流流动上的推广。分析结果表明,与不可压缩流动的对流传热场协同原理不同,可压缩层流与湍流的对流传热取决于流动当地单位体积的动量与总焓梯度的协同。用当地单位体积的动量与总焓梯度的协同研究可压缩流动的壁面传热问题,对层流热流,不但计及了高速流动的密度变化对热流的作用,而且包括了静焓梯度、压力梯度、壁面分子黏性剪切效应对热流的影响;对湍流问题,除了高速流动的密度变化、压力梯度、壁面分子黏性剪切效应对热流的影响外,还计及了雷诺剪切应力对热流的作用。另外,对黏性影响不能忽略的不可压缩流动的对流传热问题,用速度向量与总温（总焓）梯度协同更精确。     

卫星产品多轴随机振动试验条件制定方法初探

卫星产品多轴随机振动试验技术的难点之一是试验条件的制定。文章分析了多轴随机振动试验条件制定的理论基础,并就多轴随机振动试验条件的工程处理方法从模型使用、简化处理、互谱设计、时域信号等4个方面进行了探讨,最后从简化处理、遥测数据分析、仿真计算和现有试验数据分析对比4个角度对卫星产品多轴随机振动试验条件的制定思路提出了建议。     

Multi-resolution Analysis of Density Fluctuation of Coherent Structures About Supersonic Flow over VG

The density field around a vortex generator (VG) in supersonic flow is studied with a nanoparticle-based planar laser scattering (NPLS) method. Based on the calibration, i.e., the density distribution of the supersonic flow around a wedge, the density field of a supersonic VG is measured. According to movement characteristics of coherent structure in VG’s flow fields and the basic concepts of wavelet, the density fluctuating signals and multi-resolution characteristics of density field images are studied. The multi-resolution characteristics of density fluctuation can be analyzed with wavelet transformation of NPLS images. The wavelet approximate coefficients of density fluctuating signals exhibit their characteristics at different scales, and the corresponding detail coefficients show the difference of diverse layer smooth approximation in some way. Based on 2D wavelet decomposition and reconstruction of density field images, the approximate and detail signals at different scales are studied, and the coherent structures at different scales are extracted and analyzed.     

Modeling of sub-ionospheric VLF signal perturbations associated with total solar eclipse, 2009 in Indian subcontinent

During the total solar eclipse of 2009, a week-long campaign was conducted in the Indian sub-continent to study the low-latitude D-region ionosphere using the very low frequency (VLF) signal from the Indian Navy transmitter (call sign: VTX3) operating at 18.2 kHz. It was observed that in several places, the signal amplitude is enhanced while in other places the amplitude is reduced. We simulated the observational results using the well known Long Wavelength Propagation Capability (LWPC) code. As a first order approximation, the ionospheric parameters were assumed to vary according to the degree of solar obscuration on the way to the receivers. This automatically brought in non-uniformity of the ionospheric parameters along the propagation paths. We find that an assumption of 4 km increase of lower ionospheric height for places going through totality in the propagation path simulate the observations very well at Kathmandu and Raiganj. We find an increase of the height parameter by h^′=+3.0$h^{\prime }=+3.0$ km for the VTX-Malda path and h^′=+1.8$h^{\prime }=+1.8$ km for the VTX-Kolkata path. We also present, as an example, the altitude variation of electron number density throughout the eclipse time at Raiganj.     

Harmonic analysis of the ionospheric electron densities retrieved from FORMOSAT-3/COSMIC radio occultation measurements

In order to investigate the regular variations of the ionosphere, the least-squares harmonic estimation is applied to the time series of ionospheric electron densities derived from about five years of Global Positioning System radio occultation observations by FORMOSAT-3/COSMIC satellites. The analysis is done for different latitudes and altitudes in the region of Iran. The least-squares harmonic estimation is found to be a powerful tool for the frequency analysis of the completely unevenly spaced time series of radio occultation measurements. Although the obtained results are slightly different from the exact expected cycles (i.e. annual and diurnal components with their Fourier decompositions, and the 27-day period) due to the low horizontal resolution of radio occultation measurements, high vertical resolution of the observations enables us to detect not only the total electron content variations but also periodic patterns of electron densities at different altitudes of the ionosphere. The dominant diurnal and annual signals together with their Fourier series decompositions are obtained, which are consistent with the previous analyses on the total electron content. In the equatorial anomaly band, the annual component is weaker than its Fourier decomposition periods. In particular, the semiannual period dominates the annual component, indicating the relationship between the semiannual variation of the electron densities and the ionospheric equatorial anomaly. From detection of the phases of the components, it is revealed that the annual signal generally has its maximum value in summers at high altitudes, and in the winters at low altitudes. This is probably due to the higher [O/N₂] ratios in winter than in the summer in the lower ionosphere. Furthermore, the semiannual component mostly peaks around solstices or about a month before/after them.     

高精度航天器微振动力学环境分析

高精度航天器由于其指向精度和分辨率水平极高,需要考虑微振动的影响。文章给出了微振动的定义,分析了微振动特性、国外研究现状、建模特点及方法,总结归纳了高精度航天器星体内部的主要扰动源。给出了反作用轮、斯特林低温制冷器、星载敏感器以及太阳翼等典型扰动源扰动的时域或频域模型及微振动隔离模型,并进行了相应的仿真,从系统层面评估了微振动对高精度航天器性能的影响,可供高精度航天器设计时参考。     

陀螺电动机磁滞材料磁化状态的研究

陀螺磁滞电动机在工作状态下存在磁通密度和比磁滞损耗无法直接测试得到的问题。本文根据电机向量图和等效电路图,通过计算方法得到这两个参数,然后将交流磁化状态和直流磁化状态下这两个参数进行对比分析。本文的研究有利于我们更深入的了解磁滞材料性能,进而达到更精确计算和正确设计磁滞电动机的目的。     

Regional 4-D modeling of the ionospheric electron density

The knowledge of the electron density is the key point in correcting ionospheric delays of electromagnetic measurements and in studying the ionosphere. During the last decade GNSS, in particular GPS, has become a promising tool for monitoring the total electron content (TEC), i.e., the integral of the electron density along the ray-path between the transmitting satellite and the receiver. Hence, geometry-free GNSS measurements provide informations on the electron density, which is basically a four-dimensional function depending on spatial position and time. In addition, these GNSS measurements can be combined with other available data including nadir, over-ocean TEC observations from dual-frequency radar altimetry (T/P, JASON, ENVISAT), and TECs from GPS-LEO occultation systems (e.g., FORMOSAT-3/COSMIC, CHAMP) with heterogeneous sampling and accuracy.