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991.
992.
针对具有快时变性、不确定性、强非线性和系统初始状态远离平衡点等特点的敏捷导弹的直接力/气动力复合控制律设计问题,提出了一种新型非奇异终端滑模控制方法。为缩短到达平衡态的时间,设计了一种组合非奇异终端滑模面,提高了系统状态在滑模面上的收敛速度,设计了改进的变系数双幂次趋近律,提高了系统状态到达滑模面的速度,并利用扩张状态观测器实时估计系统内外扰动,消除了观测误差对系统造成的干扰,抑制了抖振。最后,证明了所提方法的有限时间收敛特性,通过仿真对比校验了所提方法的有效性。 相似文献
993.
针对小型薄片结构零件切削过程中的变形问题,以薄片"一"字电极高速铣削加工试验为例,从编程方式、切削参数选用、工序安排、走刀路线等方面展开研究。控制其变形量达到最小,以满足产品设计要求。 相似文献
994.
This work aims to investigate local stress distribution, damage evolution and failure of notched composite laminates under in-plane loads. An analytic method containing uniformed boundary equations using a complex variable approach is developed to present layer-by-layer stresses around the notch. The uniformed boundary equations established in series together with conformal mapping functions are capable of dealing with irregular boundary issues around the notch and at infinity. Stress results are employed to evaluate the damage initiation and propagation of notched composites by progressive damage analysis(PDA). A user-defined subroutine is developed in the finite element(FE) model based on coupling theories for mixed failure criteria and damage mechanics to efficiently investigate damage evolution as well as failure modes. Carbon/epoxy laminates with a stacking sequence of [45°/0°/ 60°/90°]sare used to investigate surface strains, in-plane load capacity and microstructure of failure zones to provide analytic and FE methods with strong validation. Good agreement is observed between the analytic method, the FE model and experiments in terms of the stress(strain) distributions, damage evaluation and ultimate strength, and the layerby-layer stress components vary according to a combination effect of fiber orientation and loading type, causing diverse failure modes in individuals. 相似文献
995.
Composite-metal joints with a metal insert are one kind of connecting structure.In this paper,tensile experimental tests were carried out to investigate tensile properties of a composite metal joint with a novel metal insert design.Finite element models of the joint were established,and strain distribution and tensile strength were analyzed.The numerical results are in good agree ment with the experimental results.Results show that the joint failure is dominated by shear properties of the resin layer.Increasing the resin layer thickness in a certain range will improve the tensile strength of the joint,while increasing the radius of the fillet on the ending side of the metal insert will decrease the joint strength.Increasing the resin layer plasticity will improve the joint strength.The effect of the embedded depth of the metal insert can be ignored. 相似文献
996.
徐广 《沈阳航空工业学院学报》2011,(6):81-84
通过对足球与校园文化的研究,探索符合高校大学生体育学习的新的足球教学模式,为解决足球在高校的发展问题提供策略。三级足球教学的新模式,能够丰富校园体育文化内容,满足学生提高足球技战术水平的需要,最大限度地把学生吸引到足球运动中来,努力营造踊跃参与的校园足球文化氛围,实现足球与校园体育文化的完美结合,促进足球在高校校园的和谐发展。 相似文献
997.
在现行航空工程机务维修考核评分标准的基础上,应用CDIO的工程教育理念,结合航空维修的特点,提出了对训练的全过程进行指导、记录、考核、评估的航空维修工程训练全程考核评估标准模式,应用于维修基础实习、系统实习、维修工程实习中,取得了良好的成效。 相似文献
998.
As a key assembly in the 5-axis CNC machine tools, positioning precision of the A-axis directly affects the machining accuracy and surface quality of the parts. First of all, mechanical structure and control system of the A-axis are designed. Then, considering the influence of nonlin- ear friction, backlash, unmodeled dynamics, uncertain cutting force and other external disturbance on the control precision of the A-axis, an adaptive sliding mode control (ASMC) based on extended state observer (ESO) is proposed. ESO is employed to estimate the state variables of the unknown system and an adaptive law is adopted to compensate for the input dead-zone caused by friction, backlash and other nonlinear characteristics. Finally, stability of the closed-loop system is guaran- teed by the Lyapunov theory. Positioning experiments illustrate the perfect estimation of ESO and the stronger anti-interference and robustness of ASMC, which can improve the control precision of the A-axis by about 40 times. Processing experiments show that the ASMC can reduce the waviness, averaKe error and roughness of the nrocessed surface by 35.63%, 31.31% and 30.35%, respectively. 相似文献
999.
1000.