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951.
952.
分析了通过窄缝隙耦俣的矩形波导H面T形接头对(以下简称HT对)的电气特性,利用等效原理和切向场连续性建立积分方程组,采用矩量法化积分方程为代数方程进行数值求解,获得散射场和等效散射参数,以X波段标准矩形波导HT接头对为例进行具体求解和计算,以及实验验证,得到良好结果。 相似文献
953.
客观准确的安全绩效评估,可以反映出空中交通管制系统运行的安全状况,并识别出安全管理存在的薄弱环节.从管制员、空中交通管制设备、环境、管理四方面找出影响系统安全运行的过程性指标,将过程性指标与结果性指标相结合构建空中交通管制系统安全绩效评估指标体系;在模糊物元分析法的基础上,对隶属度函数的确定方法进行改进,建立基于改进的模糊物元分析法的空中交通管制系统安全绩效评估模型;利用该模型对某空中交通管制单位的安全绩效进行评估,评估结果能够反映出该单位的安全状况,并指出应当改进的环节.结果表明:本模型可以对空中交通管制系统的安全绩效作出综合评判,并可以对空中交通管制系统的安全性进行量化描述. 相似文献
954.
955.
The flow control of hydraulic transformers is a great challenge.To meet this challenge,a new kind of hydraulic transformer,variable hydraulic transformer(VHT),is proposed in this work.This paper focuses on the power characteristics of the newly proposed VHT,including instantaneous power,average power,power pulsation,and efficiency.In the analyses,the concepts of efficiency,input power,output power,starting angle,and ceasing angle are defined or redefined.To investigate the power characteristics,their models are derived by considering the governing factors such as the control angle of the swash plate and the structure of the port plate.This work highlights that the load flow can be adjusted by adjusting the control angle of the swash plate,and the power characteristics at the B-port produce a remarkable change.In addition,the VHT has a starting angle and a ceasing angle,and these two angles can be adjusted by the influencing factors.The results reveal that the power pulsation and the jump points of the instantaneous power are the primary causes of a less smooth work.Then,it is shown that the control angle of the port plate,the control angle of the swash plate,and the pressures at the ports are the three key elements for a stable operation.The results also reveal that the adjustment of the influencing factors can improve the efficiency. 相似文献
956.
Robust Navier-Stokes method for predicting unsteady flowfield and aerodynamic characteristics of helicopter rotor 总被引:2,自引:0,他引:2
A robust unsteady rotor flowfield solver CLORNS code is established to predict the complex unsteady aerodynamic characteristics of rotor flowfield. In order to handle the difficult problem about grid generation around rotor with complex aerodynamic shape in this CFD code,a parameterized grid generated method is established, and the moving-embedded grids are constructed by several proposed universal methods. In this work, the unsteady Reynolds-Averaged Navier-Stokes(RANS) equations with Spalart-Allmaras are selected as the governing equations to predict the unsteady flowfield of helicopter rotor. The discretization of convective fluxes is accomplished by employing the second-order central difference scheme, third-order MUSCL-Roe scheme, and fifth-order WENO-Roe scheme. Aimed at simulating the unsteady aerodynamic characteristics of helicopter rotor, the dual-time scheme with implicit LU-SGS scheme is employed to accomplish the temporal discretization. In order to improve the computational efficiency of holecells and donor elements searching of the moving-embedded grid technology, the ‘‘disturbance diffraction method" and ‘‘minimum distance scheme of donor elements method" are established in this work. To improve the computational efficiency, Message Passing Interface(MPI) parallel method based on subdivision of grid, local preconditioning method and Full Approximation Storage(FAS) multi-grid method are combined in this code. By comparison of the numerical results simulated by CLORNS code with test data, it is illustrated that the present code could simulate the aerodynamic loads and aerodynamic noise characteristics of helicopter rotor accurately. 相似文献
957.
一种翼身融合飞行器的失速特性研究 总被引:1,自引:0,他引:1
翼身融合(BWB)布局飞行器作为下一代商用飞机的主要构型之一,越来越受到重视。对于翼身融合飞行器的研究主要针对其巡航状态的特性,而对其失速特性的研究较少。对一种翼身融合客机构型进行风洞试验研究,采用测力试验方法对其无增升装置的构型,以及具有翼梢小翼、前缘缝翼和机身上部双吊舱的组合部件构型下的纵向特性进行研究,特别是对其失速特性的分析,并通过二维粒子图像测试技术以及油流试验对其失速过程的流动机理进行研究。结果表明,无增升装置的基本构型下,翼身融合飞行器可以保持低速飞行,而各组合构型都具有提高最大升力系数的作用。对失速过程的分析表明,随着迎角的增大,飞机表面流场分离区域从翼梢开始逐渐向翼根以及机身发展,当外翼段完全处于分离区域时,飞机并不会马上失速,因为中心体同样具有提供升力的作用,且中心体的流动分离较外翼的流动分离更晚,所以当外翼在失速迎角出现升力损失时可以通过中心体的升力进行补偿,维持其低速飞行状态,真正的失速发生在中心体出现流动分离之后。 相似文献
958.
Main factors influencing the characteristics of the acoustic reverberation chamber are considered. Studies of mode density and calculation of required acoustic power are carried out from the relations of the RK-600 chamber dimensions depending on technical requirements for the ground-based experimental development of communication space vehicles (SV). 相似文献
959.
K.G. Ratovsky A.V. MedvedevM.V. Tolstikov D.S. Kushnarev 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(9):1454-1458
The height structure of TID characteristics is studied on the base of the electron density profiles measured by two beams of the incoherent scatter radar and DPS-4 ionosonde. The height profiles of the TID propagation characteristics are obtained by means of cross-correlation and spectrum analysis of the radar and ionosonde data. The noticeable height variability of the TID parameters is observed. The variability is explained by interference of several TIDs. The obtained TID propagation characteristics are compared with known results of the TID studies. 相似文献
960.
Lanfang H. Levine Patricia A. Bisbee Jeffrey T. Richards Michele N. Birmele Ronald L. Prior Michele Perchonok Mike Dixon Neil C. Yorio Gary W. Stutte Raymond M. Wheeler 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2008,41(5):754-762
This study addresses whether reduced atmospheric pressure (hypobaria) affects the quality traits of radish grown under such environments. Radish (Raphanus sativus L. cv. Cherry Bomb Hybrid II) plants were grown hydroponically in specially designed hypobaric plant growth chambers at three atmospheric pressures; 33, 66, and 96 kPa (control). Oxygen and carbon dioxide partial pressures were maintained constant at 21 and 0.12 kPa, respectively. Plants were harvested at 21 days after planting, with aerial shoots and swollen hypocotyls (edible portion of the radish referred to as the “root” hereafter) separated immediately upon removal from the chambers. Samples were subsequently evaluated for their sensory characteristics (color, taste, overall appearance, and texture), taste-determining factors (glucosinolate and soluble carbohydrate content and myrosinase activity), proximate nutrients (protein, dietary fiber, and carbohydrate) and potential health benefit attributes (antioxidant capacity). In roots of control plants, concentrations of glucosinolate, total soluble sugar, and nitrate, as well as myrosinase activity and total antioxidant capacity (measured as ORACFL), were 2.9, 20, 5.1, 9.4, and 1.9 times greater than the amount in leaves, respectively. There was no significant difference in total antioxidant capacity, sensory characteristics, carbohydrate composition, or proximate nutrient content among the three pressure treatments. However, glucosinolate content in the root and nitrate concentration in the leaf declined as the atmospheric pressure decreased, suggesting perturbation to some nitrogen-related metabolism. 相似文献