某型电动飞机螺旋桨振动特性实验研究

某型电动飞机采用螺旋桨产生拉力,为了防止螺旋桨工作时共振,利用ES-2-150振动实验系统进行了两叶木质螺旋桨和碳纤维螺旋桨的振动特性实验,采用谐振搜索与驻留方法测量出木质螺旋桨的第一阶固有频率为36.07Hz,碳纤维螺旋桨的第一阶固有频率为73.58Hz。螺旋桨爬升状态转频为39Hz,这与木质螺旋桨的第一阶固有频率非常接近,导致木质螺旋桨在爬升状态出现比较严重的振动故障。因此,某型电动飞机最终选择两叶碳纤维螺旋桨作为其拉力产生装置。     

某型航空发动机压气机叶片振动疲劳寿命研究

以某型航空发动机压气机叶片为研究对象,在室温条件下进行了一阶弯曲振动疲劳试验,确定了叶片1×107循环基数下的振动疲劳极限.疲劳寿命分析表明在低振动应力下,Basquin方程可以很好地预测叶片的振动疲劳寿命.但在较高振动应力下,Basquin方程预测叶片的疲劳寿命偏于危险,原因在于Basquin方程不能反映塑性滑移对疲劳损伤的影响.为解决这一问题,引入了一个新的应变比因子对Basquin方程进行了修正.对于较高振动应力770MPa和740MPa下叶片的振动疲劳寿命而言,修正后的方程寿命预测误差分别为78.7%和38.5%.与原始Basquin方程相比,修正后的方程寿命预测精度分别提高了66.0%和19.2%.     

某型水陆两栖飞机水面高速滑行振动研究

某型水陆两栖飞机在某次试飞过程中的水面高速滑行阶段出现海豚运动和机翼振动的异常现象,针对该现象展开原因分析研究。首先,建立飞机结构动力学有限元模型,研究弹性体飞机的固有动力特性;然后,建立双质量弹簧系统模型,结合水动力学研究飞机在水面滑行的运动特性;最后,结合飞机固有动力特性和水面高速滑行运动特性,分析飞机在水面高速滑行过程中机翼产生异常振动的原因。研究结果表明：飞机着水时因着水姿态以及自身静稳性等因素发生海豚运动;在某个运动时刻,当运动固有频率与机翼的一阶弹性模态频率耦合导致机翼振动。研究结果既为后续研究异常避免措施以及保证滑行试飞安全,提供了理论依据;也为水陆两栖飞机振动设计以及水面高速滑行振动分析提供了一种研究思路。     

金属连接导管振动疲劳极限测试方法研究

为确定滚压和焊接钛合金导管的振动疲劳极限寿命,采用HB5277-84规定的振动疲劳试验方法和失效准则。分别利用激光位移传感器和电阻应变片测定了试件的第一阶频率和规定加速度载荷激励下的试件悬臂端位移及试件根部的应变。试验发现：对于具有连接特性的试件在进行定频振动疲劳试验初期,试件第一阶响应频率快速下降,此时试件并未发生裸眼可见破坏和裂纹。为满足产品定寿要求,采用逐级增加试验载荷进行扫频振动试验,直至试件频率稳定以及根部应变和端部位移达到试验要求后,再进行正式定频振动疲劳试验,仍采用依据频率下降1%作为失效准则完成了所用规定试验。     

某型歼击机XX升机身副油箱尾锥振动故障分析研究

从分析、振动实测、地面故障再现、结构更改、耐振试验,直至领先试飞全过程较系统地介绍了成功解决外场结构振动故障的实例.可为解决类似结构振动故障问题提供借鉴.     

副翼铰链力矩脱机校准试验的简化方法及验证

飞机副翼铰链力矩飞行实测是新机定型的必要环节.采取传统的脱机载荷校准方法完成某新型民机副翼铰链力矩的校准试验需要自主研发专用实验台,难度大、成本高.本文提出了一种简化的副翼作动器脱机载荷校准试验方法,不需要研制专用实验台,仅使用一台拉压试验机,排空作动器中的液压油,将作动器直接安装在拉压试验机上进行拉压试验即可完成校准...     

跨音速湿空气非平衡凝结流动的数值研究

跨音速流动条件下湿空气中的水蒸气由于快速膨胀而发生非平衡凝结,凝结潜热对跨音速气流进行加热,会显著改变气流的流动特性。通过对商用计算流体动力学软件FLUENT进行二次开发,建立了湿空气非平衡凝结流动的数值求解方法。该方法可用于二维或三维、粘性或无粘、内流或外流的求解中。采用该方法分剐对缩放喷管、透平叶栅以及绕CA-0.1圆弧翼型的湿空气非平衡凝结流动进行了数值分析。计算结果表明：湿空气凝结手l起缩放喷管中的凝结激波、导致叶橱流动中总压降低;对于翼型周围的流动,在相对湿度分别为50％、57．1％、64.1％时,依次计算得到了单激波、五激波、双激波。     

飞行振动环境实验室模拟的有效性分析

本文在简要介绍了实验室模拟实际飞行环境的振动试验方法后,采用频响函数理论,以随机振动响应功率谱等效为目标,分析了该方法模拟有效的条件,指出了实际应用中应注意的几个关键环节以及尚需进一步研究的问题.     

三峡工程基岩爆破振动特性的试验研究

以三峡工程坝基岩体开挖爆破为背景 ,在弱风化花岗岩底板内进行了 6次现场爆破试验 ,测量出距爆源不等距离处的 36组地震波形。通过频域与统计分析发现 ,岩石质点振动主频率与药量、距离成反比关系 ;地震波作用时间与爆破药量成正比关系 ,而与距离成反比关系。应用神经网络理论建立的基于爆破地震效应先验知识的网络模型 (PKFN)能很好地描述爆破地震波的衰减规律 ,其计算平均相对误差仅为 3 .5 %。用地震层析成象方法 (CT)较准确地测定出了岩体爆破松裂区边界 ,并结合PKFN模型得到了三峡工程坝基岩体的临界质点振动速度范围 13 .816 .6cm/s。     

列车编组对桥梁振动响应影响的试验研究

通过对两座桥梁振动测试结果的分析，发现列车编组对桥梁振动响应很有影响，且这一现象过去常常被忽略。本文详细研究了列车编组与桥梁横向振动响应之间的关系，同时还就一座桥梁加固后的试验结果进行分析，指出用改善列车编组的方法提高桥梁动态性能的必要性和可行性。     

FURTHER STUDY ON LARGE AMPLITUDE VIBRATION OF CIRCULAR SANDWICH PLATES

ＦＵＲＴＨＥＲＳＴＵＤＹＯＮＬＡＲＧＥＡＭＰＬＩＴＵＤＥＶＩＢＲＡＴＩＯＮＯＦＣＩＲＣＵＬＡＲＳＡＮＤＷＩＣＨＰＬＡＴＥＳＤｕＧｕｏｊｕｎ（杜国君）ＣｈｅｎＹｉｎｇｊｉｅ（陈英杰）Ａｂｓｔｒａｃｔ：Ｉｎｔｈｉｓｐａｐｅｒ，ａｓｏｌｕｔｉｏｎｏｆａｘｉ...     

Computational aeroelastic investigation of a transonic limit-cycle-oscillation experiment at a transport aircraft wing model

Aeroelastic measurements of a three-dimensional wing model, the so-called Aerostabil wing, were conducted in the Transonic Windtunnel Göttingen. This clean, backward-swept wing allowed the experimental investigation of limit cycle oscillations in a certain transonic parameter range. In this paper, a detailed insight into the observed physical phenomena, especially the measured limit cycle oscillations, is presented by means of CFD–CSM coupled simulations. These simulations on the basis of a detailed structural finite element model reveal the specific properties of the Aerostabil wing and furthermore allow investigating the unstable behavior of this windtunnel model for transonic flow settings. The aerodynamic characteristics include a two-shock system and large flow separation areas, further increasing the complexity of the aeroelastic problem. A structural single degree-of-freedom system is used for the prediction of the experimental stability range and the limit cycle oscillation investigations. Due to the good agreement of simulation and experiment the limit cycle oscillations can be explained by means of nonlinear aerodynamic effects.     

PIV study on a shock-induced separation in a transonic flow

A transonic interaction between a steady shock wave and a turbulent boundary layer in a Mach 1.4 channel flow is experimentally investigated by means of particle image velocimetry (PIV). In the test section, the lower wall is equipped with a contour profile shaped as a bump allowing flow separation. The transonic interaction, characterized by the existence in the outer flow of a lambda shock pattern, causes the separation of the boundary layer, and a low-speed recirculating bubble is observed downstream of the shock foot. Two-component PIV velocity measurements have been performed using an iterative gradient-based cross-correlation algorithm, providing high-speed and flexible calculations, instead of the classic multi-pass processing with FFT-based cross-correlation. The experiments are performed discussing all the hypotheses linked to the experimental set-up and the technique of investigation such as the two-dimensionality assumption of the flow, the particle response assessment, the seeding system, and the PIV correlation uncertainty. Mean velocity fields are presented for the whole interaction with particular attention for the recirculating bubble downstream of the detachment, especially in the mixing layer zone where the effects of the shear stress are most relevant. Turbulence is discussed in details, the results are compared to previous study, and new results are given for the turbulent production term and the return to isotropy mechanism. Finally, using different camera lens, a zoom in the vicinity of the wall presents mean and turbulent velocity fields for the incoming boundary layer.     

Effects of damping on the speed of increase and amplitude of limit cycle for an aircraft braking system subjected to mode-coupling instability

A nonlinear model of an aircraft braking system is presented and used to investigate the effects of damping on the stability in Chevillot et al. (Arch Appl Mech 78(12):949–963, 2008). It has been shown that the addition of damping into the equations of motion does not lead systematically to the stabilization of the system. In the case of a mode-coupling instability, there is indeed an optimal ratio between the modal damping coefficients of the two modes in coalescence, that maximize the stable area. But the stable area is not a sufficient criterion. In dynamics, the amplitude of the vibrations and the transient behavior characterized by the speed of increase of the oscillations are best indicators. In this paper, the same nonlinear model of the aircraft braking system is used to compute time-history responses by integration of the full set of the nonlinear dynamic equations. The aim of the study is to evaluate the effects of damping on the nonlinear dynamics of the brake. It is shown that damping may be very efficient to significantly reduce and slow down the increase of the friction-induced vibrations. But, in the same way as for the stability area, there exists a value of the damping ratio that optimizes the effects of damping.     

Experiments on densifying packing of equal spheres by two-dimensional vibration

Densification of mono-sized sphere packings using two-dimensional （2D） vibration was experimentally studied. The effects of vibration mode, amplitude and frequency, feeding method, and container size on packing density were systematically analyzed. Useful results were obtained.     

Determination of the aerodynamic characteristics of aircraft in the transonic velocity range

The problem of determining the integral aerodynamic characteristics of aircraft as a whole in the transonic velocity range is considered. An approximate method of their calculation is developed using the nonlinear transonic theory of small perturbations for three-dimensional flow over a body. The method of investigation consists in separating the flow region into two subregions (outer and inner), applying numerical methods of integrating the equations in those regions, and joining the solutions. The Murman-Cole method of calculating the pressure drag of an isolated wing is generalized to the case of a combination of wing and fuselage. Central Aerohydrodynamics Institute, Zhukovskii 140160. Translated from Prikladnaya Mekhanika i Tekhnicheskaya fizika, Vol. 39, No. 4, pp. 91–101, July–August, 1998.     

对弹性弦非小振幅振动的初步分析

以弹性弦的长度变化不可忽略为条件，简要推导了一般振幅下的弦的振动方程。结果显示，弦的振动情形是复杂的，但在此条件下得到的弦振动方程比小振幅条件下的方程具有更真实的物理意义，且后者是前者的极限简单情形，指出了横振动可以向纵振动转化，此推导过程可以使人们更好的理解弦的振动。     

机载甚低频拖曳天线非线性振动分析

拖曳天线力学特征和控制是对飞机对潜通信系统进一步深入论证需要解决的关键问题之一,其中振动分析是其动力学特征研究的一个重要部分。本文通过对其运动状态及其受力进行分析,建立了机载甚低频拖曳天线动力学模型。针对模型复杂的非线性和耦合性,在考虑机载甚低频拖曳天线旋转平衡时构型的基础上,采用Galerkin法研究求解了甚低频天线末端锥袋的非线性振动。研究表明:在一阶模态截断下,利用多尺度摄动方法,当ω1:ω2:ω3近似等于2:2:1、1:1:2、1:1:1时,机载甚低频拖曳天线发生内共振;在特定的飞行状态下,其水平面面内的两个振动会发生内共振,而垂直方向则不会,因此不会对机载甚低频拖曳天线的垂直度产生显著的影响。