基于Modelica和Dymola的压气机系统的建模与仿真方法

基于压气机性能方程推导出一种新的压气机级的数学模型，并在这一模型基础上用Modelica语言和Dymola编译器建立了计算机仿真模型，编成了压气机系统仿真程序。还描述了压气机仿真程序建模系统和面向对象的体系结构，介绍了压气机系统特性分析的应用例子，并进行了仿真验证。结果表明，采用建立的仿真模型能够用来模拟压气机性能。     

基于Modelica和Dymola的航空发动机燃气发生器的建模与性能仿真

基于对压气机、涡轮与燃烧室共同工作条件的分析,建立了1种快速简便的单轴燃气发生器性能仿真模型;用Modelica语言和Dymola编译器实现了单轴燃气发生器的性能仿真,验证了该模型的有效性。结果表明:该模型能够模拟单轴燃气发生器的性能,并能实现非设计转速小流量工况下的性能仿真。     

The Burst Alert Telescope (BAT) on the SWIFT Midex Mission

he burst alert telescope (BAT) is one of three instruments on the Swift MIDEX spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and localizes the burst direction to an accuracy of 1–4 arcmin within 20 s after the start of the event. The GRB trigger initiates an autonomous spacecraft slew to point the two narrow field-of-view (FOV) instruments at the burst location within 20–70 s so to make follow-up X-ray and optical observations. The BAT is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The detector plane is composed of 32,768 pieces of CdZnTe (4×4×2 mm), and the coded-aperture mask is composed of ∼52,000 pieces of lead (5×5×1 mm) with a 1-m separation between mask and detector plane. The BAT operates over the 15–150 keV energy range with ∼7 keV resolution, a sensitivity of ∼10⁻⁸ erg s⁻¹ cm⁻², and a 1.4 sr (half-coded) FOV. We expect to detect > 100 GRBs/year for a 2-year mission. The BAT also performs an all-sky hard X-ray survey with a sensitivity of ∼2 m Crab (systematic limit) and it serves as a hard X-ray transient monitor.     

基于Modelica和Dymola的航空发动机建模与性能仿真

本文介绍了Modelica/Dymola软件的主要特点,航空发动机模块划分的原则和方法,以及利用Modelica/Dymola软件开发的航空发动机通用模型库中主要部件的建模方法,并采用己建立的部件模型,搭建了双轴涡扇发动机的系统级模型,对其起动过程进行了仿真.结果表明,仿真结果符合实际情况,该模型库对于航空发动机的概念设计和初步设计具有重要意义和实用价值.     

Auroral Substorms: Search for Processes Causing the Expansion Phase in Terms of the Electric Current Approach

Auroral substorms are mostly manifestations of dissipative processes of electromagnetic energy. Thus, we consider a sequence of processes consisting of the power supply (dynamo), transmission (currents/circuits) and dissipations (auroral substorms-the end product), namely the electric current line approach. This work confirms quantitatively that after accumulating magnetic energy during the growth phase, the magnetosphere unloads the stored magnetic energy impulsively in order to stabilize itself. This work is based on our result that substorms are caused by two current systems, the directly driven (DD) current system and the unloading system (UL). The most crucial finding in this work is the identification of the UL (unloading) current system which is responsible for the expansion phase. A very tentative sequence of the processes leading to the expansion phase (the generation of the UL current system) is suggested for future discussions.

1. (1)
   The solar wind-magnetosphere dynamo enhances significantly the plasma sheet current when its power is increased above \(10^{18}~\mbox{erg}/\mbox{s}\) (\(10^{11}\) w).
    
2. (2)
   The magnetosphere accumulates magnetic energy during the growth phase, because the ionosphere cannot dissipate the increasing power because of a low conductivity. As a result, the magnetosphere is inflated, accumulating magnetic energy.
    
3. (3)
   When the power reaches \(3\mbox{--}5\times 10^{18}~\mbox{erg}/\mbox{s}\) (\(3\mbox{--}5\times 10^{11}\) w) for about one hour and the stored magnetic energy reaches \(3\mbox{--}5\times10^{22}\) ergs (\(10^{15}\) J), the magnetosphere begins to develop perturbations caused by current instabilities (the current density \({\approx}3\times 10^{-12}~\mbox{A}/\mbox{cm}^{2}\) and the total current \({\approx}10^{6}~\mbox{A}\) at 6 Re). As a result, the plasma sheet current is reduced.
    
4. (4)
   The magnetosphere is thus deflated. The current reduction causes \(\partial B/\partial t > 0\) in the main body of the magnetosphere, producing an earthward electric field. As it is transmitted to the ionosphere, it becomes equatorward-directed electric field which drives both Pedersen and Hall currents and thus generates the UL current system.
    
5. (5)
   A significant part of the magnetic energy is accumulated in the main body of the magnetosphere (the inner plasma sheet) between 4 Re and 10 Re, because the power (Poynting flux \([ \boldsymbol{E} \times \boldsymbol{B} ])\) is mainly directed toward this region which can hold the substorm energy.
    
6. (6)
   The substorm intensity depends on the location of the energy accumulation (between 4 Re and 10 Re), the closer the location to the earth, the more intense substorms becomes, because the capacity of holding the energy is higher at closer distances. The convective flow toward the earth brings both the ring current and the plasma sheet current closer when the dynamo power becomes higher.
    

This proposed sequence is not necessarily new. Individual processes involved have been considered by many, but the electric current approach can bring them together systematically and provide some new quantitative insights.

     

Meter-Scale Slopes of Candidate InSight Landing Sites from Point Photoclinometry

Photoclinometry was used to analyze the small-scale roughness of areas within the proposed Mars InSight landing ellipse. The landing ellipse presented in this study is in Elysium Planitia.This study was able to constrain surface slopes on length scales comparable to the HiRISE image resolution (0.25 meters/pixel and coarser). The InSight mission has various engineering constraints that each candidate landing ellipse must satisfy. These constraints indicate that the statistical value of the slopes at one, two, and five meter baselines are an important criterion. This technique estimates surface slopes across large swaths of each image, and builds up slope statistics for the images in the landing ellipse. The slopes I derived for the InSight landing site ellipse in this study are within the small-scale roughness constraints put forth by the InSight project. These results have provided input into the landing hazard assessment process.     

Thermosphere-Ionosphere-Electrodynamics General Circulation Model for the Ionospheric Connection Explorer: TIEGCM-ICON

The NASA Ionospheric Connection explorer (ICON) will study the coupling between the thermosphere and ionosphere at low- and mid-latitudes by measuring the key parameters. The ICON mission will also employ numerical modeling to support the interpretation of the observations, and examine the importance of different vertical coupling mechanisms by conducting numerical experiments. One of these models is the Thermosphere-Ionosphere-Electrodynamics General Circulation Model-ICON (TIEGCM-ICON) which will be driven by tidal perturbations derived from ICON observations using the Hough Mode Extension method (HME) and at high latitude by ion convection and auroral particle precipitation patterns from the Assimilative Mapping of Ionospheric Electrodynamics (AMIE). The TIEGCM-ICON will simulate the thermosphere-ionosphere (TI) system during the period of the ICON mission. In this report the TIEGCM-ICON is introduced, and the focus is on examining the effect of the lower boundary on the TI-system to provide some guidance for interpreting future ICON model results.     

Old-Aged Primary Distance Indicators

Old-aged stellar distance indicators are present in all Galactic structures (halo, bulge, disk) and in galaxies of all Hubble types and, thus, are immensely powerful tools for understanding our Universe. Here we present a comprehensive review for three primary standard candles from Population II: (i) RR Lyrae type variables (RRL), (ii) type II Cepheid variables (T2C), and (iii) the tip of the red giant branch (TRGB). The discovery and use of these distance indicators is placed in historical context before describing their theoretical foundations and demonstrating their observational applications across multiple wavelengths. The methods used to establish the absolute scale for each standard candle is described with a discussion of the observational systematics. We conclude by looking forward to the suite of new observational facilities anticipated over the next decade; these have both a broader wavelength coverage and larger apertures than current facilities. We anticipate future advancements in our theoretical understanding and observational application of these stellar populations as they apply to the Galactic and extragalactic distance scale.     

X-Ray Spectroscopy of Galaxy Clusters: Beyond the CIE Modeling

X-ray spectra of galaxy clusters are dominated by the thermal emission from the hot intracluster medium. In some cases, besides the thermal component, spectral models require additional components associated, e.g., with resonant scattering and charge exchange. The latter produces mostly underluminous fine spectral features. Detection of the extra components therefore requires high spectral resolution. The upcoming X-ray missions will provide such high resolution, and will allow spectroscopic diagnostics of clusters beyond the current simple thermal modeling. A representative science case is resonant scattering, which produces spectral distortions of the emission lines from the dominant thermal component. Accounting for the resonant scattering is essential for accurate abundance and gas motion measurements of the ICM. The high resolution spectroscopy might also reveal/corroborate a number of new spectral components, including the excitation by non-thermal electrons, the deviation from ionization equilibrium, and charge exchange from surface of cold gas clouds in clusters. Apart from detecting new features, future high resolution spectroscopy will also enable a much better measurement of the thermal component. Accurate atomic database and appropriate modeling of the thermal spectrum are therefore needed for interpreting the data.     

Experimental study of the aerodynamics of a wing with various configurations of wingtip triangular extension

In this paper, we discuss the main ways of improving the aircraft aerodynamics. The results of a physical experiment are presented that is aimed to verify the theoretical results obtained earlier on the possible improvement in a seaplane wing model lift-to-drag ratio, by using a deflectable triangular extension along the wing leading edge near the wingtip. We confirm the slight effectiveness of using the wingtip leading edge triangular extensions on the nature of flow around the wing.