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71.
涡扇发动机早期退化性能的线性变参数估计 总被引:1,自引:1,他引:1
针对涡扇发动机线性变参数(Linear parameter varying,LPV)模型,给出了一种新的早期退化航空发动机部件性能LPV滤波器设计方法.该方法采用仿射依赖于参数的二次Lyapunov函数,在仿射二次稳定性的基础上,引入多凸性引理将滤波器求解问题转化为线性矩阵不等式(Linear matrix inequalities,LMI)约束下的凸优化问题,避免了求解参数化线性矩阵不等式(Parameterized linear matrix inequalities,PLMI)约束下的优化问题.针对某型早期退化涡扇发动机的仿真表明,该方法能以较高精度估计性能退化参数,且鲁棒性强,增益调度简单,具有一定的工程意义. 相似文献
72.
MESSENGER: Exploring Mercury’s Magnetosphere 总被引:1,自引:0,他引:1
James A. Slavin Stamatios M. Krimigis Mario H. Acuña Brian J. Anderson Daniel N. Baker Patrick L. Koehn Haje Korth Stefano Livi Barry H. Mauk Sean C. Solomon Thomas H. Zurbuchen 《Space Science Reviews》2007,131(1-4):133-160
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission to Mercury offers our first opportunity
to explore this planet’s miniature magnetosphere since the brief flybys of Mariner 10. Mercury’s magnetosphere is unique in
many respects. The magnetosphere of Mercury is among the smallest in the solar system; its magnetic field typically stands
off the solar wind only ∼1000 to 2000 km above the surface. For this reason there are no closed drift paths for energetic
particles and, hence, no radiation belts. Magnetic reconnection at the dayside magnetopause may erode the subsolar magnetosphere,
allowing solar wind ions to impact directly the regolith. Inductive currents in Mercury’s interior may act to modify the solar
wind interaction by resisting changes due to solar wind pressure variations. Indeed, observations of these induction effects
may be an important source of information on the state of Mercury’s interior. In addition, Mercury’s magnetosphere is the
only one with its defining magnetic flux tubes rooted beneath the solid surface as opposed to an atmosphere with a conductive
ionospheric layer. This lack of an ionosphere is probably the underlying reason for the brevity of the very intense, but short-lived,
∼1–2 min, substorm-like energetic particle events observed by Mariner 10 during its first traversal of Mercury’s magnetic
tail. Because of Mercury’s proximity to the sun, 0.3–0.5 AU, this magnetosphere experiences the most extreme driving forces
in the solar system. All of these factors are expected to produce complicated interactions involving the exchange and recycling
of neutrals and ions among the solar wind, magnetosphere, and regolith. The electrodynamics of Mercury’s magnetosphere are
expected to be equally complex, with strong forcing by the solar wind, magnetic reconnection, and pick-up of planetary ions
all playing roles in the generation of field-aligned electric currents. However, these field-aligned currents do not close
in an ionosphere, but in some other manner. In addition to the insights into magnetospheric physics offered by study of the
solar wind–Mercury system, quantitative specification of the “external” magnetic field generated by magnetospheric currents
is necessary for accurate determination of the strength and multi-polar decomposition of Mercury’s intrinsic magnetic field.
MESSENGER’s highly capable instrumentation and broad orbital coverage will greatly advance our understanding of both the origin
of Mercury’s magnetic field and the acceleration of charged particles in small magnetospheres. In this article, we review
what is known about Mercury’s magnetosphere and describe the MESSENGER science team’s strategy for obtaining answers to the
outstanding science questions surrounding the interaction of the solar wind with Mercury and its small, but dynamic, magnetosphere. 相似文献
73.
H. J. Völk 《Space Science Reviews》2007,130(1-4):431-438
The dynamical and chemical effects of the Galactic Wind are discussed. This wind is primarily driven by the pressure gradient
of the Cosmic Rays. Assuming the latter to be accelerated in the Supernova Remnants of the disk which at the same time produce
the Hot Interstellar Medium, it is argued that the gas removed by the wind is enriched in the nucleosynthesis products of
Supernova explosions. Therefore the moderate mass loss through this wind should still be able to remove a substantial amount
of metals, opening the way for stars to produce more metals than observed in the disk, by e.g. assuming a Salpeter-type stellar
initial mass function beyond a few Solar masses. The wind also allows a global, physically appealing interpretation of Cosmic
Ray propagation and escape from the Galaxy. In addition the spiral structure of the disk induces periodic pressure waves in
the expanding wind that become a sawtooth shock wave train at large distances which can re-accelerate “knee” particles coming
from the disk sources. This new Galactic Cosmic Ray component can reach energies of a few×1018 eV and may contribute to the juncture between the particles of Galactic and extragalactic origin in the observed overall
Cosmic Ray spectrum. 相似文献
74.
针对椭圆参考轨道的编队飞行控制系统,基于哈密尔顿 雅克比(Hamilton-Jacobi)方程,给出一种新的生成函数半解析近似解的计算方法,同时推导了编队飞行控制系统相对运动的线性状态转移矩阵,并且验证了模型的精度。在此基础上,结合一个具体的编队飞行任务,采用线性规划算法得到了队形保持的闭环控制器,该算法得到的是脉冲形式的控制序列,因此更具有实际意义。同时还提出了一种简单的避免生成函数奇异点的方法,从而减少了生成函数间相互转换所带来的计算量。最后的非线性仿真结果验证了控制方法的有效性。 相似文献
75.
76.
77.
介绍了某型发动机的RT-11燃油调节器加速性不稳定、起飞状态燃油供油量停滞的情况,分析了产生故障的原因和故障机理,并提出了修理中的改进措施。 相似文献
78.
79.
首先对民用飞机电源系统负加速度试飞进行简要说明,提出民用飞机电源系统负加速度试飞的原因和目的。其次对电源系统负加速度试飞条件、试飞方法和试飞程序进行说明。对电源系统负加速试飞结果进行分析评估,表明电源系统设计是满足设计要求和民用航空标准要求的。最后对负加速度试飞中注意事项进行了详细说明,为其它机型飞机进行负加速度试飞提供借鉴。 相似文献
80.
采用壁面马赫数呈线性分布的曲面压缩系统改进参考侧压式进气道的顶板,得到弯曲激波压缩侧压式进气道,并与参考侧压式进气道进行了比较.数值研究结果表明:设计状态无黏时曲面压缩顶板壁面马赫数分布与给定的马赫数分布基本一致,并且有黏时其壁面压力分布也与二维曲面的基本相同;同参考侧压式进气道相比,顶板采用曲面压缩能够一定程度地改善壁面压力分布,使其末端压力梯度变化平缓;并且非设计状态下的性能也得到有效地改善,特别是来流马赫数为4时,其流量系数提高6.0%、达到0.799,喉道截面总压恢复系数提高1.9%;来流马赫数为5时,其流量系数提高5.2%、达到0.909,喉道截面总压恢复系数提高3.2%.随着攻角增大,该进气道流量捕获能力增强、隔离段出口截面流场畸变减小,但喉道截面总压恢复系数下降剧烈. 相似文献