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951.
Qiumin Dai Xiande Fang Xiaojian Li Lili Tian 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012,49(6):1045-1052
The design and operation of a high altitude scientific balloon requires adequate knowledge of the thermal characteristics of the balloon to make it safe and reliable. The thermal models and dynamic models of altitude scientific balloons are established in this paper. Based on the models, a simulation program is developed. The thermal performances of a super pressure balloon are simulated. The influence of film radiation property and clouds on balloon thermal behaviors is discussed in detail. The results are helpful for the design and operate of safe and reliable high altitude scientific balloons. 相似文献
952.
953.
The start-up current control of the high-speed brushless DC (HS-BLDC) motor is a chal-lenging research topic. To effectively control the start-up current of the sensorless HS-BLDC motor, an adaptive control method is proposed based on the adaptive neural network (ANN) inverse system and the two degrees of freedom (2-DOF) internal model controller (IMC). The HS-BLDC motor is identified by the online least squares support vector machine (OLS-SVM) algo-rithm to regulate the ANN inverse controller parameters in real time. A pseudo linear system is developed by introducing the constructed real-time inverse system into the original HS-BLDC motor system. Based on the characteristics of the pseudo linear system, an extra closed-loop feed-back control strategy based on the 2-DOF IMC is proposed to improve the transient response per-formance and enhance the stability of the control system. The simulation and experimental results show that the proposed control method is effective and perfect start-up current tracking perfor-mance is achieved. 相似文献
954.
955.
Turbulence affects both combustion and NO formation. Fluctuation correlations are ideally used for quantitative analysis. From the instantaneous chemical reaction rate expression,ignoring the third-order correlation terms, the averaged reaction rate will have four terms, including the term of averaged-variable product, a concentration fluctuation correlation term, and temperature-concentration fluctuation correlation term. If the reaction-rate coefficient is denoted as K, the temperature fluctuation would be included in the K fluctuation. In order to quantitatively study the effect of turbulence on NO formation in methane-air swirling combustion, various turbulencechemistry models are tested. The magnitudes of various correlations and their effects on the time-averaged reaction rate are calculated and analyzed, and the simulation results are compared with the experimental measurement data. The results show that among various correlation moments, the correlation between the reaction-rate coefficient K fluctuation with the concentration fluctuation is most important and is a strong nonlinear term. 相似文献
956.
A study on turbulence transportation and modification of Spalart–Allmaras model for shock-wave/turbulent boundary layer interaction flow 总被引:1,自引:0,他引:1
It is of great significance to improve the accuracy of turbulence models in shock-wave/ boundary layer interaction flow. The relationship between the pressure gradient, as well as the shear layer, and the development of turbulent kinetic energy in impinging shock-wave/turbulent boundary layer interaction flow at Mach 2.25 is analyzed based on the data of direct numerical simulation(DNS). It is found that the turbulent kinetic energy is amplified by strong shear in the separation zone and the adverse pressure gradient near the separation point. The pressure gradient was non-dimensionalised with local density, velocity, and viscosity. Spalart–Allmaras(S–A) model is modified by introducing the non-dimensional pressure gradient into the production term of the eddy viscosity transportation equation. Simulation results show that the production and dissipation of eddy viscosity are strongly enhanced by the modification of S–A model. Compared with DNS and experimental data, the wall pressure and the wall skin friction coefficient as well as the velocity profile of the modified S–A model are obviously improved. Thus it can be concluded that the modification of S–A model with the pressure gradient can improve the predictive accuracy for simulating the shock-wave/turbulent boundary layer interaction. 相似文献
957.
燃油喷嘴内的液体流动在一定条件下会形成空化,进而影响喷嘴的雾化效果。应用高速摄像仪对圆形喷嘴内的空化以及喷口外的雾化进行了实验研究。实验所用喷嘴直径包括0.5mm,1.0mm,1.5mm和2.0mm,其中直径为1.5mm的喷嘴的长径比从2变化到9,实验工质为纯净水。实验发现,喷嘴内空化的形成是动态的,空化长度出现高频低幅脉动。对于喷嘴的收缩类型研究发现,急收型相比渐收型更易形成空化,并有增强雾化的效果。长径比相同的喷嘴,直径越大,达到超空化的喷射压力越大,雾化锥角也越大;直径相同的喷嘴,随长径比的增加,达到超空化的空化数逐渐减小,但射流的喷雾锥角没有明显的变化趋势,均在10°到20°之间。对比破碎模式规律,除了0.5mm的喷嘴外,所有喷嘴达到超空化后均为雾化模式。 相似文献
958.
应用精确线性化方法研究了永磁同步电动机的非线性控制问题.根据精确线性化理论,设计了永磁同步电动机状态反馈线性化控制器和相对阶为1的多指标输入输出反馈线性化控制器.多指标非线性控制器选择全状态量线性组合形式为输出函数,根据系统特征根配置方法,整定了输出函数中各状态量的反馈系数.比较2种控制器仿真结果发现,多指标非线性控制器可以实现对电动机转速的有效控制,且控制器结构简单,设计方便,动静态性能良好. 相似文献
959.
960.
以医疗器械应急物流配送为研究对象,以配送时间最短为研究目标,建立了医疗器械应急物流配送路径优化的数学模型,并将混沌蚁群算法用于模型求解,给出了求解步骤。经计算机仿真表明,与基本蚁群算法相比,混沌蚁群算法优化质量明显改善,有效缩短了应急配送时间,提高了医疗器械应急物流的配送效率。 相似文献