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61.
A low frequency, small signal model, valid for all types of converters, both in the heavy and the light mode of conduction, is developed in block diagram form. The model provides a clear insight into the behavior of such converters and enhances the respective contributions of input and output filters. 相似文献
62.
We present a general overview of the structure and evolution of massive stars of masses ≥12 M ⊙ during their pre-supernova stages. We think it is worth reviewing this topic owing to the crucial role of massive stars in astrophysics, especially in the evolution of galaxies and the universe. We have performed several test computations with the aim to analyze and discuss many physical uncertainties still encountered in massive-star evolution. In particular, we explore the effects of mass loss, convection, rotation, 12C(α,γ)16O reaction and initial metallicity. We also compare and analyze the similarities and differences among various works and ours. Finally, we present useful comments on the nucleosynthesis from massive stars concerning the s-process and the yields for 26Al and 60Fe. 相似文献
63.
低速液体射流在高速湍流气体作用下的气液同轴射流雾化流场是瞬态密集型喷雾场,高速湍流中影响和控制雾化的因素很多。针对空气雾化流场液核分布与特征进行分析,开发了模拟液核的随机浸入体模型,结合大涡模拟方法对同轴射流空气雾化喷嘴下游流场进行数值模拟。模拟结果与实验结果对比表明:随机浸入体模型可快速捕捉液核的长度和位置信息。当气液动量比M为3~10000时,能够较准确地预测液核长度,当M>10时,其预测结果远优于唯象模型;该模型能够捕捉回流区、大尺度涡等流场结构。同时,可以准确地预测喷嘴附近的液滴粒径,特别是在气流速度较大(>60m/s)时,液滴平均直径预测误差<10%。 相似文献
64.
Response of Hainan GPS ionospheric scintillations to the different strong magnetic storm conditions 总被引:2,自引:0,他引:2
S.P. Shang J.K. Shi P.M. Kintner W.M. Zhen X.G. Luo S.Z. Wu G.J. Wang 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(4):579-586
Using the GPS ionospheric scintillation data at Hainan station (19.5°N, 109.1°E) in the eastern Asia equatorial regions and relevant ionospheric and geomagnetic data from July 2003 to June 2005, we investigate the response of L-band ionospheric scintillation activity over this region to different strong magnetic storm conditions (Dst < −100 nT) during the descending phase of the solar cycle. These strong storms and corresponding scintillations mainly took place in winter and summer seasons. When the main phase developed rapidly and reached the maximum near 20–21 LT (LT = UT + 8) after sunset, scintillations might occur in the following recovery phase. When the main phase maximum occurred shortly after midnight near 01–02 LT, following the strong scintillations in the pre-midnight main phase, scintillations might also occur in the post-midnight recovery phase. When the main phase maximum took place after 03 LT to the early morning hours no any scintillation could be observed in the latter of the night. Moreover, when the main phase maximum occurred during the daytime hours, scintillations could also hardly be observed in the following nighttime recovery phase, which might last until the end of recovery phase. Occasionally, scintillations also took place in the initial phase of the storm. During those scintillations associated with the nighttime magnetic storms, the height of F layer base (h’F) was evidently increased. However, the increase of F layer base height does not always cause the occurrence of scintillations, which indicates the complex interaction of various disturbance processes in ionosphere and thermosphere systems during the storms. 相似文献
65.
N. I. Akishev I. I. Zakirov V. A. Ivanov V. N. Paimushin M. A. Shishov 《Russian Aeronautics (Iz VUZ)》2011,54(2):115-124
The known analytical solutions of the linearized stability problems for rectangular hinged plates under the combined loading
are generalized to the similar problems for skew plates, the deformation mechanics of which is described by the equations
of the classical theory formed in the oblique Cartesian coordinates. 相似文献
66.
In this paper, we examine experimentally some devices the principle of action of which is based on using the dynamic pressure
of air extracted to engine cooling and which are meant for reducing the radial temperature gradient in GTE rotor disks. We
established that the devices equipped with the ejector channels make it possible to accelerate the process of the disk hub
heating by hot air suction from the cavity periphery towards the rotor axis of rotation. Using the data of visualization studies,
we show the possibility for efficient operation of ejector devices in the conditions of real GTE rotor circumferential velocities. 相似文献
67.
A technique of optimizing the electrode system of the differential recorder for the aircraft time-of-flight ion-marking airspeed
and aircraft angle of attack sensor by the criterion of ion-marking recording error variance minimum is considered. The technique
is based on analyzing the function of spatial distribution for the ion-marking and recorder electrode interaction field potential
and determining a point for which this function reaches the maximum slope. The relations making it possible to synthesize
the sensor electrode system by the complex criterion as a ratio of error variance to transformation channel response are obtained. 相似文献
68.
M. V. Usanin A. A. Siner A. M. Sipatov L. Yu. Gomzikov V. G. Avgustinovich 《Russian Aeronautics (Iz VUZ)》2011,54(1):34-42
The application of the low dissipative high-order accurate scheme for numerical solution of the Euler and Navier-Stokes equations
in the two-dimensional statement is considered. The scheme of calculating space derivatives is the seven-point central-difference
approximation of the fourth order with the coefficients optimized to reduce the dispersion errors. The optimized six-step
Runge-Kutta method is used for evaluating the time derivatives. By means of filtration, spurious pulsations are suppressed
and shocks are processed. The results of verifying the calculation scheme realized on the stationary problem of flow around
the model turbine blades are presented. 相似文献
69.
N. M. Bodunov 《Russian Aeronautics (Iz VUZ)》2011,54(1):89-94
A mathematical model of the process of bending and rolling the thin-walled components is presented taking into account the
geometrical nonlinearity. Also presented is the technique for calculating the setup variables of bending equipment, which
is based on reduction of the initial differential boundary-value problem to the discrete one with the use of the finite difference
method. 相似文献
70.