Dynamic coefficients and stability analysis of a water-lubricated hydrostatic bearing by solving the uncoupled Reynolds equation

This paper concerns the dynamic characteristics of incompressible laminar flow hydrostatic bearings. An improved method based on the mathematical perturbation technique for calculating the stiffness and damping coefficients of hydrostatic bearings is presented; it raises the calculation efficiency by uncoupling the recess flow continuity equations from the solving of the Reynolds equation. The dynamic coefficients of a water-lubricated four-recess hydrostatic bearing are calculated with both the improved method and the conventional method. The comparisons between these two methods validate the effectiveness and correctness of the improved method. Furthermore, the dynamic response and stability characteristics of a rotor supported by the hydrostatic bearing are calculated and compared with experimental results. First, the dynamic responses calculated with the linear and nonlinear bearing dynamic coefficients models show that the linear model is inaccurate if the rotor whirls in a large eccentricity ratio range, owing to the nonlinearity of stiffness and damping. Second, according to the numerical and experimental results, the nonlinearity of bearing stiffness and damping coefficients could induce double rotational frequency component in the unbalance response frequency spectrum. Finally, the numerical results indicate that the stability threshold speed of the bearing increases with eccentricity ratio. The improved method proposed can be used to evaluate the dynamic performance of hydrostatic bearings efficiently, and the bearing characteristics presented could contribute to a better understanding of the performance of water-lubricated hydrostatic bearings.     

垂直于叶片弦线方向喷气对转子稳定性的影响研究

以NASA Rotor37为研究对象,采用数值模拟的方法进行叶顶喷气对转子稳定性的影响研究。研究表明,在叶顶垂直于叶片弦线方向喷气可以达到扩稳效果,其扩稳机理在于通过喷口喷射出的高速射流把叶顶泄漏流吹向转子吸力面,减弱了叶顶泄漏流对主流的影响,使得转子叶顶堵塞区域减小,改善了叶顶区域的流通状况,从而得到扩稳效果。在喷气流量对转子稳定性的研究中,喷气流量越大,对增强稳定性越有利。在所选取的1%,1.5%和2%三种喷气流量水平下,2%的喷气流量可以使转子的流量裕度提高4.24%,综合裕度改进量提高5.16%。此外,不同喷气流量对转子的流场影响不同,随着喷气流量的增大,除了可以降低叶顶前缘负荷外,还可以通过将激波位置推向下游,从而有利于减弱流动分离,对转子稳定性的提升更为有利。     

武装直升机横航向增控增稳系统鲁棒性研究

武装直升机横航向增控增稳系统可看作是２输入５输出的多变量控制系统,多变量控制系统的鲁棒性可用稳定裕度作为衡量标准。利用矩阵奇异值分解的方法,计算武装直升机横航向ＳＣＡＳ的稳定裕度,来评判所设计系统的鲁棒性。该方法获得的满足鲁棒性所要求的裕度指标,为我国军用直升机飞行品质规范的修订提供了依据。     

试飞确定电传飞控系统稳定裕度

根据飞控系统稳定裕度的要求,给出了几种求取稳定裕度的方法,尤其是提出的基于返回误差阵奇异值的稳定裕度判定方法,可解决多通道多回路复杂交联系统的稳定裕度评价问题。     

HEV型静态混合器优化设计分析

为提高混合器的优化设计水平和工程应用的速度,采用计算流体力学商业软件Fluent,对HEV型静态混合器内置翼片顺排、错排两种结构方式下内部的浓度场、速度场、湍流场等参数进行模拟计算,分析比较两种翼片排列方式的混合效果,为HEV型静态混合器优化设计提供依据。     

某新型相控阵雷达抗有源压制性干扰建模与仿真

现代战争有针对性地对干扰进行研究来提高雷达系统的抗干扰能力是很必要的.本文建立了3种典型的有源压制性干扰的数学模型,并以此作为抗干扰系统模型的干扰输入进行了建模,仿真结果与实际相符,该雷达具有较强的抗有源压制性干扰的能力.     

基于海浪谱的东中国海海浪二维仿真

基于海浪谱的海浪仿真理论,对东中国海海浪进行二维仿真,并对传统的模型进行了简化,提高了对波高的敏感性和加快了运算速度。文章的目的就是建立精度较高的快速仿真模型,以适应复杂多变的海面环境。一方面,对多种海浪谱的综合运用,克服了传统的模型以单一海浪谱为核心所导致的频带范围局限性;另一方面,嵌入式模块设想的提出,解决了使用循环嵌套程序造成的运算量过大的问题。最终,使得模型的实用价值得到了较大的提升。     

遥测数据仿真系统的设计和实现

针对遥测数据种类的多样性和处理方法的复杂性给软件测试带来的问题,对遥测系统基本工作原理、遥测格式、遥测处理方法进行了深入研究,设计和实现了一个适合不同遥测系统评测的遥测数据仿真模型。该模型的设计和实现使测试软件具备良好的可扩展性和可重用性,缩短了软件测试周期。     

Stability and chaos of a damped satellite partially filled with liquid

The stability and chaotic motions of a damped satellite partially filled with liquid which is subjected to external disturbance are investigated in this paper. With linearization analysis, the stability of the two non-trivial equilibrium points is studied. The homoclinic and heteroclinic orbits are found by using the undetermined coefficient method, and the convergence of the series expansions of these two types of orbits is proved. It analytically demonstrates that there exist homoclinic orbits of the Si’lnikov type that join the two non-trivial equilibrium points to themselves, and therefore smale horseshoes and the horseshoe chaos occur for this system via the Si’lnikov criterion. In addition, there also exists a heteroclinic orbit connecting the two non-trivial equilibrium points. Numerical simulations are also given, which verify the analytical results. The system can be chaotic through period-doubling bifurcations as the amplitude of the external disturbance varies, and backward period-doubling bifurcations as the angular momentum of the rotor varies.     

Effect of ultrasonic vibration on finished quality in ultrasonic vibration assisted micromilling of Inconel718

Inconel718 was machined with the traditional micromilling (TMM) and ultrasonic vibration assisted micromilling (UVAMM) with the different technology parameters, whose surface quality and burrs formation were studied. The results show that TMM often forms pits, bumps and gullies in the size effect range. UVAMM effectively improves the surface quality compared with TMM. The surface defects are significantly reduced with the increase of feed per tooth (ƒ_z). When ƒ_z exceeds 4 μm, the effect of ultrasonic vibration on the surface quality is no longer obvious. The minimum burr size on the down milling side and the up milling side are 50.23 μm and 36.57 μm, respectively. The feasibility of vibration cutting in improving surface quality and suppressing burr size was verified. UVAMM effectively suppresses the formation of built-up edge, which can significantly improve the micromilling process. The cutting force is obtained through simulation and experiment. They are agreement in the change trend. The finite element simulation can be used to predict the cutting force. Compared with TMM, feeding force (F_x), radial force (F_y) and axial force (F_z) of UVAMM decrease by 7.6%, 11.5% and 1.3%, respectively.