Field-based landcover classification using TerraSAR-X texture analysis

The present study aims to evaluate the field-based approach for the classification of landcover using high-resolution SAR data. TerraSAR-X (TSX) strip mode imagery, coupled with digital ortho-photos (DOPs) with 20 cm spatial resolution was used for landcover classification and parcel mapping respectively. Different filtering and analysis techniques were applied to extract textural information from the TSX image in order to assess the enhancement of the classification accuracy. Several attributes of parcels were derived from the available TSX images in order to define the most suitable parameters discriminating between different landcover types. Then, these attributes were further statistically analysed in order to define separability and thresholds between different landcover types. The results showed that textural analysis resulted in high classification accuracy. Hence, this paper confirms that integrated landcover classification using the textural information of TerraSAR-X has a high potential for landcover mapping.     

Oxidation Properties in CO2 of Inconel Alloy 600 Coated by Simultaneous Aluminizing-Chromizing Process

IN 600 alloy was coated with two different types of coatings, Cr-modified aluminide coating this is called aluminizing-chromizing and Y-doped chromium modified aluminide coating this is called aluminizing-chromizing-yttriumizing. Diffusion coating was carried at 1 050 ℃ for 8 h under Ar atmosphere by simultaneous aluminizing-chromizing process and by simultaneous aluminizing-chromizing- yttriumizing. Cyclic oxidation tests were conducted on the uncoated and on the coated Inconel 600 alloy in the temperature range 800- 1 000 ℃ in CO2 for 100 h at 10 h cycle.The results showed that the oxidation kinetics for uncoated Inconel 600 alloy in CO2 is parabolic and the phases present are NiO, (Fe, Cr)2O3 , NiFe2O4 and NiCrO4. The oxidation kinetics for both coated systems in CO2 was found to be parabolic and the value of kP for both coated systems were found to be lower than that for uncoated Inconel 600 alloy. Oxide phases that formed on coated systems are Al2O3 and NiCrO4. The role of yttrium can be attributed to its ability to improve the adherence of the oxide scale.     

Parameter extraction for the extended cantilever model of magneticcomponent windings

The extended cantilever model (ECM) for transformer or inductor windings is convenient from the parameter extraction standpoint since, theoretically, each model parameter can be extracted from a single measurement of an open-circuit voltage or a short-circuit current. The impedance of the sensor used to measure a short-circuit current, however, makes the “short” less ideal, and it has been believed that each parameter in the ECM cannot be directly measured unless the impedance of the current sensor is negligible. It is shown that as long as the ECM parameters are reactive (inductive or capacitive) and the current sensor resistive, the current-sense resistance does not have to be restrictively small for the ECM parameters to be directly measurable. A linear, broadband formulation is also presented for extraction of the model admittances using current sensors with significant impedances     

A heuristic design method for attitude stabilization of magnetic actuated satellites

In this paper a heuristic design strategy for stabilizing the satellite attitude has been proposed. It is assumed that the satellite is actuated by a set of mutually perpendicular magnetic coils. Using well-known Lyapunov direct stability method it is shown that the proposed controller causes to a global asymptotic stable system for all near polar orbits. The design procedure is based on analyzing of the conceptual effects of magnetic coils on the satellite attitude motion. Considering these effects lead to some intuitive results which determine the global stabilizing control law. The performance and robustness of the designed controller against actuators saturation and quantization error have been verified using a real-time-hardware–software in-loop (RTHSIL) simulation results. These results show that the global stability can be achieved although some disturbances and restrictions exist. This stabilizing controller can be simply combined with a linear explicit model predictive controller (EMPC) to achieve a full three-axis control law.     

MEMS中气体运动的若干微尺度效应

宏观流动到微流动不单是"量"的变化,而且有"质"的不同[1].在微流动中,由于微尺度效应,主导流动的作用力发生变化,惯性力不再占主导地位;在宏观尺度流动中可以忽略的表面效应和壁面滑移等现象,开始凸现出来,这就导致了微流动中出现了与宏观流动不同的现象和规律.本文研究微流动问题中的若干微尺度效应:包括微喷管中气体流动的特性、微槽道中的稀薄气体效应和分子泵内的流动问题.这些研究对于设计和开发新的微机械机电设备是非常重要的.     

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.     

Optimization of aerodynamic efficiency for twist morphing MAV wing

Twist morphing(TM) is a practical control technique in micro air vehicle(MAV) flight.However, TM wing has a lower aerodynamic efficiency(CL/CD) compared to membrane and rigid wing. This is due to massive drag penalty created on TM wing, which had overwhelmed the successive increase in its lift generation. Therefore, further CL/CDmaxoptimization on TM wing is needed to obtain the optimal condition for the morphing wing configuration. In this paper, two-way fluid–structure interaction(FSI) simulation and wind tunnel testing method are used to solve and study the basic wing aerodynamic performance over(non-optimal) TM, membrane and rigid wings. Then,a multifidelity data metamodel based design optimization(MBDO) process is adopted based on the Ansys-DesignXplorer frameworks. In the adaptive MBDO process, Kriging metamodel is used to construct the final multifidelity CL/CDresponses by utilizing 23 multi-fidelity sample points from the FSI simulation and experimental data. The optimization results show that the optimal TM wing configuration is able to produce better CL/CDmaxmagnitude by at least 2% than the non-optimal TM wings. The flow structure formation reveals that low TV strength on the optimal TM wing induces low CDgeneration which in turn improves its overall CL/CDmaxperformance.     

Evaluation of mixed mode-I/II criteria for fatigue crack propagation using experiments and modeling

In this study, in-plane mixed mode-I/II fatigue crack growth simulations and experiments are performed for the Al 7075-T651 aluminum alloy which is widely used in the aerospace industry. Tests are carried out under different mode mixity ratios to evaluate the applicability of a fracture criterion developed in a previous study to mixed mode-I/II fatigue crack growth tests. Results obtained from the analyses and experiments are compared with existing and developed criteria in terms of crack growth lives. Compact Tension Shear (CTS) specimens, which enable mixed mode loading with loading devices under different loading angles, are used in the simulations and experiments. In an effort to model and simulate the actual conditions in the experiments, crack surfaces of fractured specimens are scanned, crack paths are modeled exactly, and contacts are defined between the contact surfaces of a specimen and the loading device for each crack propagation step in the analyses. Having computed the mixed mode stress intensity factors from the numerical analyses, propagation life cycles are predicted by existing and the developed mixed mode-I/II criteria and then compared with experimental results.     

Design and optimization of solid rocket motor Finocyl grain using simulated annealing

The research effort outlined the application of a computer aided design(CAD)-centric technique to the design and optimization of solid rocket motor Finocyl(fin in cylinder) grain using simulated annealing.The proper method for constructing the grain configuration model,ballistic performance and optimizer integration for analysis was presented.Finocyl is a complex grain configuration,requiring thirteen variables to define the geometry.The large number of variables not only complicates the geometrical construction but also optimization process.CAD representation encapsulates all of the geometric entities pertinent to the grain design in a parametric way,allowing manipulation of grain entity(web),performing regression and automating geometrical data calculations.Robustness to avoid local minima and efficient capacity to explore design space makes simulated annealing an attractive choice as optimizer.It is demonstrated with a constrained optimization of Finocyl grain geometry for homogeneous,isotropic propellant,uniform regression,and a quasi-steady,bulk mode internal ballistics model that maximizes average thrust for required deviations from neutrality.     

低温推进剂在轨贮存与管理技术研究

低温推进剂由于其比冲高、无毒无污染,是载人和深空探测的首选推进剂。为解决空间恶劣的热环境和微重力环境下推进剂大量蒸发损耗及推进剂的气液两相混合等问题,以低温推进剂的在轨贮存与管理技术为研究对象,给出低温推进剂绝热的贮存方案和微重力气液分离的管理方案。并对其中的适用中短期任务的方案进行日蒸发率等指标核算,然后对方案中的热力学参数变化对系统方案中的蒸发量控制等影响进行讨论。最终给出针对载人登月等短期项目的低温推进剂在轨贮存与管理的推荐方案。