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781.
自然层流机翼是最简单而有效的减阻技术。本文结合作者新近的工作,着重论述了后掠翼上自然层流边界层转捩的估算方法和转捩准则的选择并讨论了压力分布对转捩的影响。最后还提出了若干建议供读者参考。 相似文献
782.
为了解决小不对称再入体滚转气动力测量问题 ,北京空气动力研究所研制开发了以空气轴承为核心的滚转气动力测量技术 ,利用空气轴承自身旋转阻尼非常小的特点 ,使模型做自由滚转运动 ,一个特殊设计的非接触的光学测量系统测出模型的转角随时间的历程 ,用参数拟合的方法得到滚转力矩的大小和方向。为验证该项实验技术的正确性与可靠性 ,在5 0 0高超声速风洞中对 4个模型进行了吹风实验 ,吹风马赫数为 5 ,测量滚转力矩系数Cl0 和滚转阻力矩系数Clp。实验结果表明 ,该文方法数据合理 ,并较其它方法更具有鲁棒性。 相似文献
783.
氢涡轮泵转子轴向振动 总被引:1,自引:0,他引:1
若氢涡轮泵转子轴向固有频率低于工作转速,可能发生轴向共振与自激振动。报告研究轴向振动的机理和消除方法。 相似文献
784.
785.
Hancheol Cho 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(5):1454-1467
In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances. 相似文献
786.
Behrad Vatankhahghadim Christopher J. Damaren 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):2746-2756
The deployment dynamics of a solar sail consisting of four flexible booms and four membrane quadrants are studied. First, previous work on modelling only one membrane quadrant attached to two axially moving beams using time-varying quasi-modal expansion is extended to be applicable to the complete four-quadrant system. This is achieved via “lifting” the quadrant-level matrices into system-level forms by mapping the former’s constituent blocks to the correct partitions in the latter. After the quadrant-to-system conversion of the matrices, the equations of motion from the authors’ previous work readily apply to the complete system. Modal analysis is performed on a constant-length sail to validate the model’s basic foundations against the results obtained by finite element methods in the past literature. Deployment simulation results are presented, numerical parameter studies that show possibility of instability are performed using the system’s eigenvalues, and the stability results are discussed. 相似文献
787.
Casing treatment is a mature stabilization technique which has been widely applied on aero-engines for modern aircrafts and turbo-chargers for automobiles. After the investigations of half century since the 1960s, this technique has been well developed for various configurations with different effectiveness. From the perspective of stabilization mechanism, this paper roughly categorizes the configurations of casing treatment into two types: traditional ones which work by affecting the flow structure of blade tip region; a novel one named as Stall Precursor-Suppressed (SPS) casing treatment. The effectiveness of both types will be demonstrated for their applications on axial compressors and centrifugal compressors with uniform or distorted inlet. And the stabilization mechanism of casing treatments for regular types and SPS one will also be explained respectively. In addition, this review will summarize the methodologies of casing treatments with the numerical simulations for regular grooved configurations and the eigenvalue approach for SPS casing treatment. Looking forward to the future of compressor stabilization, casing treatment technique will still exist as a general and inexpensive option, and the exploration for its effectiveness and mechanism will be deeper with the development of computational fluid dynamics and advanced measurement techniques. 相似文献
788.
通过对液浮陀螺电机轴向预紧力调整情况及声音异常现象的分析,归纳和完善了电机轴向预紧力调整过程中的经验调法,并对电机轴向预紧力的量化调整进行了摸索和探讨,提出了较为可行的解决措施,从一定程度上保证了电机装调质量,提高了小型化精密电机装调合格率。 相似文献
789.
大型飞机电缆网络结构复杂,点数多,接头分布分散,导通关系复杂,对测试设备提出了整机测试、扩展方便、测试速度快的要求。本文提出了一种基于CAN总线的分布式柔性电缆测试仪模型。该模型采用多点激励、模块化分布机矩阵开关、矩阵开关标准转接接口、转接电缆特征识别等方法,可以满足整机电缆快速测试要求,具有较高的理论价值和实用价值。 相似文献
790.
文章研究了学习活动中的一些问题,归纳总结出了非线性阈值效应,建立非线性动力学模型,进行了分岔与稳定性分析,做了仿真模拟并结合经验进行了解释。 相似文献