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Combined and interactive effects of interference fit and preloads on composite joints 总被引:3,自引:3,他引:0
The combined and interactive effects of the bolt-hole fit conditions and the preloads of the fasteners on the load carrying capacity of single-lap composite-to-titanium bolted joints have been investigated both experimentally and numerically. Quasi-static tests of the hybrid joints with different fit conditions are implemented, and a three dimensional finite element progressive failure analysis model is proposed to predict the influences of the bolt-hole fit conditions and fastener's pre- loads on the mechanical behaviors of the joints. Based on the experimental validated simulation method, a multi-factor, mixed levels orthogonal design table and the analysis of variance method are used to arrange the simulation conditions and to further study the interactive effects of preloads and fit conditions. Through the analysis of the results, for the researched double bolt, single-lap composite-titanium joints, it is found that: the effects of both the interference fit and the preloads change from positive into negative mode with the increase of the interference fit values or preload values; appropriate bolt-hole fit conditions and preloads can improve the bolt-hole contact conditions of the loaded joints, and then retard the fiber failures around the fastener holes, and increase the load carrying capacity of the joints eventually; the interactive effect of the bolt-hole interference fit conditions and preloads cannot be ignored and the parameters need to be considered together and synthetically as the joints are being optimized. 相似文献
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针对现实中用户依据自身经验选择采样条件的不确定性,提出了一种能够客观判定最佳采样条件的方法.基于二维功率频谱分析,考虑奈奎斯特采样定理与混叠效应,提出一个归一近似因子来确定合适采样条件.经实验验证其适用于碳纤维复合材料表面形貌测量,研究证明用较大采样间距多次测量加工后工件的表面形貌,取粗糙度值的平均值或最大值来评定其表面质量更合理. 相似文献
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深入了解高能固体推进剂在低温条件下燃烧性能,获得燃烧波阵面变化规律,对评估推进剂在低温条件下的适应性能力具有重要指导意义。本文设计了燃烧波狭缝观测实验装置,采用高速摄影观测技术,对三组元HTPB固体推进剂在常温和低温条件下的燃烧过程进行了观测,获得了燃烧过程中波阵面的图像。结果表明,相比于在常温条件下,固体推进剂在低温条件下出现了燃烧波不稳定的情况。根据燃烧波图像计算出了推进剂的燃速,并与靶线法燃速测量结果进行比较。结果表明,两种方法测量的结果差异较小,推进剂在低温条件下的燃烧速度明显低于在常温条件下,常温条件的燃速在1.717~2.127mm/s,低温条件下的燃速在1.252~1.583mm/s。 相似文献
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进气条件对压气机中介机匣流场影响的试验研究 总被引:6,自引:1,他引:5
以某压气机中介机匣为试验研究对象,通过改变来流径向分布与马赫数,建立了评估中介机匣气动性能的进口约束条件。在同步测量轴向流路离散压力参数的基础上,分析了中介机匣内部流场对进气条件的稳态响应。研究结果表明:进气条件对中介机匣流动损失影响较大,与均匀进气相比,进气畸变会增大弯曲流道内部径向压力梯度,影响流道曲率与流向压力梯度对附面层的控制效果;支板尾流对通道主流的干扰导致下游平直流道上部区域流场恶化,而进气畸变会加剧支板尾迹的影响;随着进口马赫数的增大,中介机匣总压损失系数与总压畸变强度呈现出不同的增长趋势,其出口流场径向分布对马赫数变化的气动敏感性较高。 相似文献
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《中国航空学报》2020,33(4):1192-1205
Over the last few decades, the research on the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals is not sufficient. To this end, two kinds of brush-labyrinth seals for the bristle pack element installed upstream of the labyrinth teeth named BSU and installed downstream of the labyrinth teeth called BSD were used to investigate the effect of bristle pack position on the rotordynamic characteristics of the brush-labyrinth seals. Using the numerical model combining the porous medium model and the whirling rotor method, the rotordynamic characteristics of the BSU and BSD at various operating conditions including four kinds of pressure ratios, five kinds of inlet preswirl speeds and four kinds of rotor spinning speeds were conducted. The obtained results show that the effects of operating conditions on rotordynamic coefficients for the different seal configurations are different. The direct stiffness, cross-coupled stiffness and direct damping of the BSU are lower than those of the BSD. The rotordynamic coefficients of the BSU are more insensitive to the operating conditions variation. From the perspective of the seal stability, the BSU is a better brush-labyrinth seal configuration at high pressure ratio, high positive preswirl or high rotor spinning speed conditions. While in the case of low pressure ratio, low positive preswirl or low rotor spinning speed conditions, the BSD is a better choice. 相似文献
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针对中国商业银行表外业务与国际相比发展落后的现状,从两个方面,即商业银行自身是否具有发展表外业务的主观感望和我国现阶段是否具备开展此项业务的客观条件,分析其原因。研究认为,由于目前主客观两方面条件尚未充分具备,导致了表外业务的发展滞后。同时,依据对主客观两方面条件变化的预期,得出了我国银行业有必要也有能力加强表外业务发展的结论。 相似文献
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纺织复合材料细观力学分析的一般性周期性边界条件及其有限元实现 总被引:5,自引:0,他引:5
针对纺织复合材料细观有限元分析中单胞网格的快速生成与顺利施加周期性边界条件之间的矛盾,提出了非周期性网格划分条件下,一般性周期性边界条件的数学表达形式.基于ABAQUS有限元软件平台,通过在单胞模型的相对面、相对边及相对角点施加多点约束(MPC)方程,实现了一般性周期性边界条件的施加.结合三维四向编织复合材料单胞模型,对比分析了周期性网格划分和非周期性网格划分情况下,单胞模型受载下的变形状态、应力分布及弹性性能的预测结果,验证了一般性周期性边界条件的正确性和有效性.研究表明:一般性周期性边界条件可以实现复杂细观结构单胞模型的自由网格划分,降低网格划分的难度,提高网格生成的质量. 相似文献
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末段突防击水概率是反舰导弹设计和使用人员必须解决的一个问题。文章综合考虑了击水概率影响因素,从掠海飞行导弹背景建模、反舰导弹高度控制系统和弹体纵向运动方程等方面人手,对给定海情下反舰导弹高度输出进行仿真研究,并利用统计试验的方法对击水概率进行计算。仿真结果证实了不同海情下飞行高度对击水概率的影响。 相似文献
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从 k-ε湍流模型控制方程入手,对两类满足平衡大气边界层理论要求的入口边界条件进行了详细分析,比较了二者的理论差异。然后以我国公路桥梁抗风规范中建议的 A 类风场为来流条件,定义了相应的 k-ε模型常数与壁面条件,使用两类边界条件进行数值模拟。计算结果表明:两类边界条件结合相应的模型常数与壁面条件,均能在数值模拟中构建基本满足规范要求的平衡大气边界层,但各有其适用范围。在此基础上,对模型常数 C 1和湍动能耗散率与数值模拟结果之间的关系进行了研究,采用修改模型常数与边界条件的方法,改善了数值模拟结果。 相似文献
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We present an algorithm for calculating the shells of revolution with the branching meridian using the triangular finite elements, the rigidity matrices of which are formed based on the vector method of displacement interpolation [1]. The correct kinematic and static conditions of shell conjugation on the line of their coupling have been developed. The shell structure consisting of a cylinder and adjacent shells is calculated under various conditions of support. 相似文献
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Flow separation,as an aerodynamic phenomenon,occurs in specific conditions.The conditions are studied in a wind tunnel on different airfoils.The phenomenon can be delayed or suppressed by exerting an external momentum to the flow.Dielectric barrier discharge actuators arranged in a row of 8 and perpendicular to the flow direction can delay flow separation by exerting the momentum.In this study,a mathematical model is developed to predict a parameter,which is utilized to represent flow separation on an NACA0012 airfoil.The model is based on the neurofuzzy method applied to experimental datasets.The neuro model is trained in different flow conditions and the parameter is measured by pressure sensors. 相似文献
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Perhinschi M.G. Napolitano M.R. Campa G. Seanor B. Burken J. Larson R. 《IEEE transactions on aerospace and electronic systems》2006,42(2):562-571
For a research aircraft, "conventional" control laws (CLs) are implemented on a "baseline" flight computer (FC) while research CLs are typically housed on a dedicated research computer. Therefore, for an experimental aircraft used to test specific fault tolerant flight control systems, a safety logic scheme is needed to ensure a safe transition from conventional to research CLs (while at nominal conditions) as well as from research CLs at nominal conditions to conditions with "simulated" failures on specific control surfaces. This paper describes the design of such a safety scheme for the NASA Intelligent Flight Control System (IFCS) F-15 Program. The goals of the IFCS F-15 program are to investigate the performance of a set of fault tolerant CLs based on the use of dynamic inversion with neural augmentation. The different transitions are monitored using information relative to flight conditions and controller-related performance criteria. The testing of the scheme is performed with a Simulink-based flight simulation code and interface developed at West Virginia University for the NASA IFCS F-15 aircraft. 相似文献
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针对太阳能无人机在飞行状态下可能出现的太阳能电池局部遮挡情况,开展相应的太阳能电池最大功率点追踪算法和能源控制研究。通过将发光亮度引入相对吸引力计算过程对萤火虫算法进行改进,实现了局部阴影情况下太阳能电池最大功率点的高效追踪。以此为基础,设计了考虑局部遮挡情况下太阳能无人机的太阳能电池/蓄电池混合能源状态机控制规则。以"蒲公英I"无人机为例,建立了太阳能电池阵列模型,开展了考虑局部遮挡情况下太阳能电池最大功率点追踪仿真实验;基于"蒲公英I"飞行剖面,开展了考虑局部遮挡情况的混合能源控制仿真试验。研究结果表明:改进的萤火虫算法可以实现在局部阴影情况下太阳能电池最大功率点的有效跟踪,与萤火虫算法相比收敛时间更短、且功率波动幅度更小;采用改进萤火虫算法和状态机能源管理策略,在考虑局部遮挡的飞行状态下可以实现太阳能电池/蓄电池之间的合理功率分配与控制。 相似文献
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利用差值定理降低飞行器速度和加速度拟合的截断误差 总被引:1,自引:1,他引:0
推导了差值定理及其推论,并以此作为数据拟合的有效点判据,显著降低了飞行器速度和加速度拟合的截断误差;探讨了该判据条件下滤波参数对拟合结果的影响及截断误差的判断条件,并采用实测数据对拟合效果进行了检验。 相似文献