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潘媛 《西安航空技术高等专科学校学报》2009,27(4)
随着经济全球化的发展,企业环境变得越来越复杂,所面临的风险也日趋增加,风险管理受到前所未有的重视,对于内部审计参与企业风险管理也成为了一种趋势,通过分析内部审计参与企业风险管理的动因,揭示其必要性,并且得出内部审计参与企业风险管理的具体措施. 相似文献
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对于二元高超声速进气道内压缩通道及隔离段设计,提出了进气道下壁弧形曲面构型方案。在一系列不同收缩比、不同波系配置的平面构型进气道基础上,通过基于N-S方程的数值模拟研究了不同半径的弧形过渡曲面对进气道性能的影响。发现采用弧形曲面过渡可以削弱平面构型方案对气流不必要的膨胀,减小隔离段进口处上侧壁面高压,改善隔离段进口气流均匀性。新构型有助于降低起动马赫数,且弧形过渡半径越大,收缩比越大,降低的程度越明显;还可以大大提高进气道的总压恢复,无须最后一道内压激波打在下壁面肩点上即可获得较高的性能。 相似文献
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精密单点定位(PPP)模糊度固定(AR)能够显著提升精密定位的收敛速度和精度。通过在BDS-2和BDS-3之间添加系统间偏差的方法实现BDS-3的模糊度固定,并基于全球MGEX测站静态、仿动态数据和车载实验数据全面评估了BDS-3模糊度固定的效果。结果表明,相对于浮点解,BDS-3 PPP模糊度固定能够显著提升PPP的精度,在东北天3个方向上静态解算精度提升依次为37.4%、26.2%和20.1%;仿动态解算精度提升依次为38.3%、27.2%和11.1%;车载动态实验BDS-3模糊度固定精度在三维方向上综合提升为40.4%。此外,模糊度固定后,以浮点解稳定后的两倍定位精度为基准,在东北天方向上,静态定位时间提升程度依次为63.5%、64.0%和40.3%;仿动态定位时间提升程度依次为58.7%、56.8%和25.4%;车载实验在三维方向的收敛时间为30.0 min。以上结果证明了所提方法的有效性及BDS-3模糊度固定的性能提升。 相似文献
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The start-up current control of the high-speed brushless DC (HS-BLDC) motor is a chal-lenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is proposed based on the adaptive neural network (ANN) inverse system and the two degrees of freedom (2-DOF) internal model controller (IMC). The HS-BLDC motor is identified by the online least squares support vector machine (OLS-SVM) algo-rithm to regulate the ANN inverse controller parameters in real time. A pseudo linear system is developed by introducing the constructed real-time inverse system into the original HS-BLDC motor system. Based on the characteristics of the pseudo linear system, an extra closed-loop feed-back control strategy based on the 2-DOF IMC is proposed to improve the transient response per-formance and enhance the stability of the control system. The simulation and experimental results show that the proposed control method is effective and perfect start-up current tracking perfor-mance is achieved. 相似文献
58.
M.V. Klimenko V.V. Klimenko I.E. Zakharenkova S.A. Pulinets B. Zhao M.N. Tsidilina 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2011
The problems of physical explanation and possible mechanisms of the seismo-ionospheric effects formation are under discussion now. There are proposed different mechanisms of such effects, for example, large- and small-scale internal gravity waves (IGWs), atmospheric electric field, electromagnetic fields and emissions. However, the appearance of local large-scale seismo-ionospheric anomalies in Total Electron Content (TEC) is possible to explain only by two mechanisms: an atmospheric electric field and/or small-scale IGWs. In this paper, the simulation results for reproduction of the observed seismo-ionospheric great positive effects in TEC prior to strong Wenchuan earthquake are presented. The obtained results confirm the proposed mechanism of seismo-ionospheric effects formation by the penetration of the seismogenic electric field from the atmosphere into the ionosphere. It is suggested that so great TEC enhancement observed 3 days prior to Wenchuan earthquake could be explained by combined action of seismogenic vertical electric field and IGWs generated by the solar terminator. 相似文献
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This paper considers a spinning rigid body and a particle with internal motion under axial thrust. This model is helpful for gaining insights into the nutation anomalies that occurred near the end of orbit injections performed by STAR-48 rocket motors. The stability of this system is investigated by means of linearized equations about a uniform spin reference state. In this model, a double root does not necessarily imply instability. The resulting stability condition defines a manifold in the parameter space. A detailed study of this manifold and the parameter space shows that the envelope of the constant solutions is in fact the stability boundary. Only part of the manifold defines a physical system and the range of frequency values that make the system unstable is restricted. Also it turns out that an increase of the spring stiffness, which restrains the internal motion, does not necessarily increase the stability margin. The application of the model is demonstrated using the orbit injection data of ESA's Ulysses satellite in 1990. 相似文献