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811.
Investigation of the infrared characteristics of a rocket nozzle is very important for the study of infrared initiating technology. The Narrow-Band Zone model is developed for that purpose. The spectral transmission and absorption factors are introduced, and the equations between radiative heat flux and the temperature of waill surfaces and gas are developed. The radiative heat transfer in one axisymmetric cylindrical enclosure filled with homogeneous radiative participating medium is computed with the Narrow-Band Zone model and compared with those in the reference documents. The comparison shows good agreement. The radiative heat transfer to the nozzle of one rocket engine is also calculated with the Narrow-Band Zone model, and the outgoing radiative energy flux and energy rate integrated in a mid-wave infrared band 2-6 pm, a long-wave infrared band 8-14 pm and the full wave band are analyzed. The following conclusions can be derived: the spectral radiation from the inlet and outlet of the nozzle show apparent spectral discontinuity, which appears greater in the 2.7-2.95 pm than in the neighboring wave band. The spectral outgoing radiative energy flux of nozzle wail is similar to that of gray body, which decreases with wavelength in 2-14 pm. The outgoing radiative energy flux on the nozzle wall is greater in the cylindrical and contracting section of nozzle, but smaller in the divergent section, which is determined by temperature. The nozzle of the rocket engine radiates most energy in the mid-wave surfaces by absorption. The most important feature of gas radiation is the strong selection of the waveband, so the detailed study of the infrared characteristics of nozzle of the rocket engine should be carried out on narrow-band computation. 相似文献
812.
航天飞机系统两体分离问题的探讨 总被引:1,自引:0,他引:1
本文简要地叙述了美国研究轨道器与外挂贮油箱,轨道器与载机分离问题的概况。对垂直起飞两级入轨的并联两机的分离问题,提出了研究模型并作了具体分析,着重提出了实现两机安全分离需要解决的技术难点。 二级航天飞机的两机分离问题,是未来航天高技术领域的关键技术之一,本文阐述了解决两体并联分离问题我国现有的技术水平,并提出了解决该问题的技术方案。 相似文献
813.
CAD技术及其在卫星工程中的应用 总被引:1,自引:0,他引:1
CAD 技术作为一种高效率、高质量、高精度的设计技术,正在包括航天技术在内的多个领域中广泛应用,发挥其效益。尤其是在机械(MCAD)与电子(ECAD)两方面的应用,更是令人瞩目。本文就CAD 技术的范畸、功能、组成、主要技术等并结合卫星研制的具体应用前景,作一介绍,目的在于推动CAD技术的开展,并为CAD/CAM 一体化做好思想准备。 相似文献
814.
This article presents the microstructure and hardness variation of an Al–8.5Fe–1.3V–1.7Si(wt%, FVS0812) alloy after selective laser melting(SLM) modification. Three zones were distinguished across the melting pool of the SLM-processed FVS0812 alloy: the laser melted zone(LMZ), the melting pool border, and the heat affected zone(HAZ) in the previously deposited area around the melting pool. Inside the LMZ, either an extremely fine cellular-dendritic structure or a mixture zone of the a-Al matrix and nanoscale Al_(12)(Fe,V)_3Si particles appeared. With a decreased laser beam scanning speed, the cellular-dendritic structure zone within the LMZ shrank significantly while the mixture zone expanded. The a-Al and Al_(12)(Fe,V)_3Si mixture zone was also observed in the HAZ, but another phase, submicron h-Al_(13)Fe_4 particles with rectangular or hexagonal shapes,formed along the melting pool border. Microhardness tests indicated that the hardness of the SLM-processed FVS0812 samples far exceeded that of the as-cast FVS0812 alloy. 相似文献
815.
A method combining rotor actuator disk model and embedded grid technique is presented in this paper, aimed at predicting the flow fields and aerodynamic characteristics of tilt rotor aircraft in conversion mode more efficiently and effectively. In this method, rotor's influence is considered in terms of the momentum it impacts to the fluid around it; transformation matrixes among different coordinate systems are deduced to extend actuator method's utility to conversion mode flow fields' calculation. Meanwhile, an embedded grid system is designed, in which grids generated around fuselage and actuator disk are regarded as background grid and minor grid respectively, and a new method is presented for ‘donor searching' and ‘hole cutting' during grid assembling. Based on the above methods, flow fields of tilt rotor aircraft in conversion mode are simulated, with threedimensional Navier–Stokes equations discretized by a second-order upwind finite-volume scheme and an implicit lower–upper symmetric Gauss–Seidel(LU-SGS) time-stepping scheme. Numerical results demonstrate that the proposed CFD method is very effective in simulating the conversion mode flow fields of tilt rotor aircraft. 相似文献
816.
Conflict avoidance (CA) plays a crucial role in guaranteeing the airspace safety. The cur- rent approaches, mostly focusing on a short-term situation which eliminates conflicts via local adjust- ment, cannot provide a global solution. Recently, long-term conflict avoidance approaches, which are proposed to provide solutions via strategically planning traffic flow from a global view, have attracted more attentions. With consideration of the situation in China, there are thousands of flights per day and the air route network is large and complex, which makes the long-term problem to be a large-scale combinatorial optimization problem with complex constraints. To minimize the risk of premature convergence being faced by current approaches and obtain higher quality solutions, in this work, we present an effective strategic framework based on a memetic algorithm (MA), which can markedly improve search capability via a combination of population-based global search and local improve- ments made by individuals. In addition, a specially designed local search operator and an adaptive local search frequency strategy are proposed to improve the solution quality. Furthermore, a fast genetic algorithm (GA) is presented as the global optimization method. Empirical studies using real traffic data of the Chinese air route network and daily flight plans show that our approach outper- formed the existing approaches including the GA .based approach and the cooperative coevolution based approach as well as some well-known memetic algorithm based approaches. 相似文献
817.
Gray bootstrap method for estimating frequency-varying random vibration signals with small samples 总被引:2,自引:0,他引:2
During environment testing, the estimation of random vibration signals (RVS) is an important technique for the airborne platform safety and reliability. However, the available meth- ods including extreme value envelope method (EVEM), statistical tolerances method (STM) and improved statistical tolerance method (ISTM) require large samples and typical probability distri- bution. Moreover, the frequency-varying characteristic of RVS is usually not taken into account. Gray bootstrap method (GBM) is proposed to solve the problem of estimating frequency-varying RVS with small samples. Firstly, the estimated indexes are obtained including the estimated inter- val, the estimated uncertainty, the estimated value, the estimated error and estimated reliability. In addition, GBM is applied to estimating the single flight testing of certain aircraft. At last, in order to evaluate the estimated performance, GBM is compared with bootstrap method (BM) and gray method (GM) in testing analysis. The result shows that GBM has superiority for estimating dynamic signals with small samples and estimated reliability is proved to be 100% at the given confidence level. 相似文献
818.
This paper presents a two-level geometric calibration method for the permanent magnet (PM) spherical actuator to improve its motion control accuracy. The proposed actuator is com- posed of a stator with circumferential coils and a rotor with multiple PM poles. Due to the assembly and fabrication errors, the real geometric parameters of the actuator will deviate from their design values. Hence, the identification of such errors is critical for the motion control tasks. A two-level geometric calibration approach is proposed to identify such errors. In the first level, the calibration model is formulated based on the differential form of the kinematic equation, which is to identify the geometric errors in the spherical joint. In the second level, the calibration model is formulated based on the differential form of torque formula, which is to calibrate the geometric parameters of the magnetization axes of PM poles and coils axes. To demonstrate the robustness and availability of the calibration algorithm, simulations are conducted. The results have shown that the proposed two-level calibration method can effectively compensate the geometric parameter errors and improve the positioning accuracy of the spherical actuator. 相似文献
819.
To overcome the influence of the nonlinear friction on the gimbaled servo-system of an inertial stabilized platforms(ISPs) with DC motor direct-drive, the methods of modeling and compensation of the nonlinear friction are proposed. Firstly, the inapplicability of LuGre model when trying to interpret the backward angular displacement in the prestiction regime is observed experimentally and the reason is deduced theoretically. Then, based on the dynamic model of direct-drive ISPs, a modified LuGre model is proposed to describe the characteristic of the friction in the prestiction regime. Furthermore, the state switch condition of the three friction regimes including presliding, gross sliding and prestiction is presented. Finally, a composite compensation controller including a nonlinear friction observer and a feedforward compensator based on the novel LuGre model is designed to restrain the nonlinear friction and to improve the control precision. Experimental results indicate that compared with those of the conventional proportion–integration–differentiation(PID) control method and the PID plus LuGre model-based friction compensation method, the dwell-time has decreased from 0.2 s to almost 0 s, the position error decreased to 86.7%and the peak-to-peak value of position error decreased to 80% after the novel compensation controller is added. It concludes that the composite compensation controller can greatly improve the control precision of the dynamic sealed ISPs. 相似文献
820.
总量控制与排污权交易的理论分析 总被引:3,自引:0,他引:3
本文从总量控制与排污权交易的概念出发,论述了排污权交易的基本理论和市场机制模型,分析了总量控制与排污权交易的经济、环境和社会效益,阐述了排污权的初始分配方式及交易方式。 相似文献