汽车悬置以上结构模态参数对转向轮摆振的影响

对整车的实验研究表明,整车悬置以上结构模态参数对前轮摆振有重要影响.本文利用了模态分析和模态综合技术建立了十二阶的分析汽车转向轮摆振的数学模型.利用该模型对我国存在前轮摆振问题的CA-10解放牌汽车、以及其变型油罐车进行了仿真计算,计算结果与实车存在的情况相吻合.故此模型可以用于指导前轮摆振的研究工作和有关的设计工作.     

某新型直升机“地面共振”初步分析

对某新型直升机垂直起落状态“地面共振”初步分析,采用经典的空间动力模型进行计算.文中给出了该机“地面共振”初步计算的计算方法和计算结果,并得出初步计算结论.根据现有条件,该机暂时无法做起落架刚度、阻尼试验,在初步计算中,起落架的全部动力学参数都是根据理论计算或经验公式得出的,包括起落架传递系数,缓冲器和机轮的静压曲线、刚度阻尼特性等.本文推导了这些参数的计算方法以及全机平衡状态计算的计算方法.     

着陆冲击力对起落架摆振的影响

为了分析着陆冲击力对起落架摆振特性的影响，考虑支柱缓冲器的负油孔面积，在ADAMS中建立了某飞机起落架的虚拟样机模型，并对该模型进行了动力学分析，得到了起落架缓冲系统负油孔面积对轮胎与地面之间接触力的影响曲线、对前轮摆角的影响曲线、在不同垂直降落速度下摆幅的对比曲线，并结合摆振基本理论进行分析。结果表明：负油液阻尼孔面积减小或飞机触地垂直降落速度增大时，对应的着陆冲击力增大，使摆幅增大；当负油孔面积小于50.5mm2或飞机着陆时的垂直降落速度大于1773mm/s时，由于着陆冲击力过大，使摆振极不稳定。     

起落架落震试验机轮瞬态冲击转速的测试方法

飞机起落架落震试验中,机轮触台时的瞬态转速变化的测试数据对起落架安全设计和强度研究有着重要的意义.本文针对机轮在高速旋转冲击下,震动强烈并且瞬态转速变化范围大的特点,设计了非接触式机轮转速测试系统.采用M/T转速测量方法,实现了机轮在触台全过程中瞬态转速的准确测量.     

特性拦阻材料的台架实验装置研制

本文建立了单轮负载、平台拖动式的台架实验装置,并开展了验证实验。该装置主要包括固定框架、吊篮、活动平台、机轮夹持组件和传感器。将拦阻材料安装在活动平台上,通过牵引活动平台实现机轮对拦阻材料的碾压。该装置可以更换不同机轮、安装不同性能的拦阻材料;实验条件包括机轮胎压、机轮承重等参数;传感器可以测量实验过程中机轮受到的拦阻力、机轮压入深度等参数。该装置可以为研究机轮规格、胎压、承重、拦阻材料性能等对拦阻力的影响提供实验手段。验证实验结果表明,所建立的装置可以满足机轮与特性拦阻材料力学模型研究的需要。     

大型固定翼民用飞机系留载荷非线性计算分析

采用有限元法,充分考虑了固定翼民用飞机机体结构刚度分布对超静定问题求解的影响、起落架缓冲支柱"行程-载荷"之间的非线性关系、系留绳索单向承力特性以及起落架与地面之间的接触非线性,建立了大型固定翼民用飞机系留载荷计算模型并给出了相应计算流程;计算分析了风载作用方向、飞机重量、起落架机轮与地面摩擦系数、系留绳索刚度对飞机系留载荷的影响规律。分析发现:风载方向与航向平行(不平行)时,系留载荷较小(较大);由摩擦系数和飞机重量变化所引起最大系留载荷的差异分别为9%和35%,摩擦系数对最大系留载荷存在一定影响,而飞机重量对其影响显著;飞机重量越小,则最大系留载荷越大,在计算系留载荷时需要考虑可能的最小飞机重量;系留绳索刚度越大,则系留载荷越大,但飞机最大位移越小,在选取系留绳索材料时应同时考虑系留载荷和系留作用下飞机最大位移。     

一种含负刚度元件的新型动力吸振器的参数优化

提出了一种含有负刚度弹簧元件的新型动力吸振器模型,对该模型的最优参数进行了详细研究. 通过拉氏变换得到了系统的解析解,发现该系统存在着两个固定点,利用固定点理论得到了动力吸振器的最优阻尼比和最优频率比. 进一步研究发现接地刚度取负值时能够得到更好的减振效果,根据负刚度的特性得到了在保证系统稳定情况下的最优负刚度比. 通过数值解与解析解的对比证明了解析解的正确性. 通过与两种已有的典型动力吸振器模型在简谐激励和随机激励情况下的对比,说明了负刚度模型在主系统减振方面具有很大的优势,减振效果远优于两种已有动力吸振器模型,从而为设计新型动力吸振器模型提出了理论上的依据.     

机载电子设备耐振试验时间的确定与合格判据

根据新研飞机研制过程中提出的问题,论证了机载电子设备仍需进行耐振环境试验的必要性,提出了机载电子设备耐振试验时间的确定方法,并对耐振试验的合格判据进行了研究,结果表明耐振试验中,如机载设备仅发生由“一次通过破坏”或“峰值破坏”引起的功能故障,仍应判为合格通过.     

不同类型水平弹簧组合刚度非线性吸振器的性能分析及稳定性研究

动力吸振器作为一种振动控制单元被广泛运用于各种工程场合,但传统的线性吸振器只能实现窄带振动控制.文章在线性吸振器的基础上引入对称水平弹簧构建线性刚度与非线性刚度相结合的组合刚度非线性吸振器,以提升吸振器的吸振性能.考虑实际工程中可能的安装方式,分别建立水平弹簧接地安装和不接地安装的组合刚度非线性吸振器模型,利用谐波平衡法结合弧长延拓法解析求解动力学响应,并与数值结果相互验证,证明了求解结果的准确性.随后分析比较两种组合刚度非线性吸振器与线性吸振器以及非线性能量阱之间的吸振性能,发现水平弹簧接地安装类型的组合刚度非线性吸振器在保留线性吸振器优势的同时又改善其吸振频带窄的缺点,且与非线性能量阱相比在主共振频率附近的较宽频内吸振性能更优.在此基础上,讨论了水平弹簧参数以及吸振器阻尼对主结构振动幅频响应和稳定性的影响,最后观察分析主结构幅频响应曲线不稳定区内的复杂动力学行为.研究结果表明合适的设计参数能够使得主结构振动峰值较低的同时,频响曲线不稳定运动区域的范围也较小.     

DYNAMIC LOAD CHARACTERISTICS OF ARRESTING HOOK SWINGING ALONG ARRESTING CABLE IN CARRIER-BASED AIRCRAFT

针对舰载机钩偏着舰时拦阻钩沿拦阻索侧向滑摆运动,运用仿真与理论分析结合的方法,通过调整拦阻钩侧向动载荷的振动频率范围,具体研究了飞机机身动载荷特性。结果表明,在2 Hz, 10 Hz,20 Hz 等振动频率附近,机身会受到严重的载荷情况。结论可供机体结构刚度、钩头减摆等性能优化设计参考。     

Interaction of torsion and lateral bending in aircraft nose landing gear shimmy

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcation analysis in terms of the forward velocity and the vertical force on the gear reveals routes to different types of shimmy oscillations. In particular, we find regions of stable torsional and stable lateral shimmy oscillations, as well as transient quasiperiodic shimmy where both modes are excited.     

Theory of the shimmy phenomenon

The shimmy phenomenon is the appearance of angular self-excited vibrations of the carriage wheels. Such self-excited vibrations provide a serious safety hazard for motion, which explains the great interest of scientists in this phenomenon [1–6]. This problem is most serious for the aircraft fore wheels.     

Multi-parameter bifurcation study of shimmy oscillations in a dual-wheel aircraft nose landing gear

We develop and investigate a mathematical model of an aircraft nose landing gear with a dual-wheel configuration. The main aim here is to study the influence of a dual-wheel configuration on the existence of shimmy oscillations. To this end, we consider a model that describes the torsional and lateral vibrational modes and the non-linear interaction between them via the tyre-ground contact. More specifically, we perform a bifurcation analysis (with the software package auto) of the model in the two-parameter plane of forward velocity of the aircraft and vertical load on the nose landing gear. This two-parameter bifurcation diagram allows one to identify regions of different dynamics, and the question addressed here is how it depends on two key parameters of the dual-wheel configuration. Namely, we consider the influence of, first, the separation distance between the two wheels and, second, of gyroscopic effects arising from the inertia of the wheels. For both cases, we find that with increasing separation distance and wheel inertia, respectively, the lateral mode becomes more stable and the torsional mode becomes less stable. More specifically, we present associated bifurcation scenarios that explain the transitions between qualitatively different two-parameter bifurcation diagrams. Overall, we find that the separation distance and gyroscopic effects due to wheel inertia may have a significant influence on the quantitative and qualitative nature of shimmy oscillations in aircraft nose landing gears. In particular, the torsional and the lateral modes of a dual-wheel nose landing gear may interact in a quite complicated fashion.     

汽车摆振动力学机理研究——位移延时反馈及能量传递分析

主要分析了汽车摆振的动力学机理。通过使用解析法从理论上证明了摆振是由位移延时反馈引起的自激振动现象。利用数值分析方法揭示摆振系统的动力学机制及响应行为，验证了解析分析的相关结论。并进一步计算能量输入与能量传递的值，结果表明能量输入可以用来评价汽车摆振的动力学响应。最后根据能量传递规律提出汽车摆振的抑制措施。     

OPTIMIZATION OF FUSELAGE OPENING ZONE OF CIVIL AIRCRAFT

在民用飞机机身上通常布置较多舱门开口,导致机身结构刚度发生急剧变化。为了保证飞机结构刚度以及载荷的传递,本文对机身开口结构的刚度及强度进行了深入研究,明确了开口结构刚度的影响因素,并对开口角度大小及加强结构尺寸进行了优化。以上研究对机身开口结构设计及加强提供了方向和方法,可以用于飞机机身开口结构初步设计阶段。     

An Eigenvalue Method for Calculation of Stability and Limit Cycles in Nonlinear Systems

In the calculation of periodic oscillations of nonlinear systems –so-called limit cycles – approximative and systematic engineeringmethods of linear system analysis are known. The techniques, working inthe frequency domain, perform a quasi-linearization of the nonlinear system,replacing nonlinearities by amplitude-dependent describing functions.Frequently, the resulting equations for the amplitude and frequency ofpresumed limit cycles are solved directly by a graphical procedure in aNyquist plane or by solving the nonlinear equations or a parameteroptimization problem. In this paper, an indirect numerical approach isdescribed which shows that, for a system of nonlinear differentialequations, the eigenvalues of the quasi-linear system simply indicateall limit cycles and, additionally, yield stability regions for thelinearized case. The method is applicable to systems with multiplenonlinearities which may be static or dynamic. It is demonstrated foran example of aircraft nose gear shimmy dynamics in the presence ofdifferent nonlinearities and the results are compared with those fromsimulation.     

基于可变形蜂窝的柔性蒙皮力学性能分析与结构设计

变体飞机可以在飞行中充分改变外形获得最佳气动效率以适应变化的任务环境.覆盖在结构表面的蒙皮不仅要具有良好的面内方向柔性,产生满足设计变形量的光滑连续变形,同时要提供足够的垂直平面方向刚度,维持气动构型,并将气动载荷传递到下层结构.论文提出一种在十字形可变形蜂窝表面覆盖硅胶表层的结构作为柔性蒙皮,理论分析了该柔性蒙皮在面内方向的变形机理以及十字形可变形蜂窝的形状参数对其力学性能的影响,并与仿真和试验结果进行了比较.根据后缘变弯度机翼的设计要求,给出了柔性蒙皮的设计参数范围.结果表明该柔性蒙皮具有足够的面内方向变形能力和垂直平面方向承载能力,满足变弯度机翼后缘设计要求.     

Equivalent models of corrugated panels

The design of corrugated panels has wide application in engineering. For example corrugated panels are often used in roof structures in civil engineering. More recently corrugated laminates have been suggested as a good solution for morphing aircraft skins due to their extremely anisotropic behaviour. The optimal design of these structures requires simple models of the panels or skins that may be incorporated into multi-disciplinary system models. Thus equivalent material models are required that retain the dependence on the geometric parameters of the corrugated skins or panels. An homogenisation-based analytical model, which could be used for any corrugation shape, is suggested in this paper. This method is based on a simplified geometry for a unit-cell and the stiffness properties of original sheet. This paper outlines such a modelling strategy, gives explicit expressions to calculate the equivalent material properties, and demonstrates the performance of the approach using two popular corrugation shapes.     

任意分布参数的梁结构刚度可靠性灵敏度分析

在刚度可靠性设计理论与灵敏度分析方法的基础上,研究了任意分布参数的梁结构刚度可靠性灵敏度分析问题,提出了刚度可靠性灵敏度分析的计算方法,给出了可靠性灵敏度的变化规律,研究了设计参数的改变对梁结构刚度可靠性的影响,为任意分布参数的梁结构刚度可靠性设计提供了理论依据。