结构参数对无轴承旋翼悬停气弹稳定性的影响

为了准确分析结构参数在悬停状态下对无轴承旋翼气动弹性稳定性的影响,建立一种基于有限状态入流的直升机气弹稳定性分析的新模型。采用Green-Lagrange应变张量推导无轴承旋翼桨叶的非线性应变-位移关系,把桨叶作为多路传力系统进行处理并根据Hamilton原理建立桨叶运动的有限元方程,非定常气动力采用有限状态状态入流模型,旋翼的气弹稳定性根据桨叶摄动方程的特征值进行判断,研究结构参数对无轴承旋翼在悬停状态下气弹稳定性的影响。结果表明：（1）无轴承旋翼气弹稳定性分析采用模型比以往的动力入流模型或均匀入流模型与实验结果吻合更好;（2）桨毂预锥角、桨叶的摆振刚度及挥舞刚度对无轴承旋翼气弹稳定性的影响很大。     

弹性耦合对直升机复合材料桨叶稳定性的影响

研究了弹性耦合对复合材料桨叶动特性和气弹稳定性的影响, 所采用的结构模型考虑了剪切变形、剖面面外翘曲变形和复合材料弹性耦合。推导出同时考虑剪切和翘曲影响的小应变、中等变形梁的应变2位移关系,并构造出21 个自由度梁单元, 应用Hamilton 原理推导出桨叶运动的有限元方程。在此基础上, 对三种不同构型的复合材料桨叶进行固有频率计算和气弹稳定性分析。计算结果表明: 尽管复合材料弹性耦合对桨叶固有频率的影响非常小, 但却改变了固有振型分布, 使桨叶挥舞-摆振-扭转运动之间存在耦合; 弹性耦合对桨叶气弹稳定性有很大的影响; 正的挥舞2扭转耦合使得摆振一阶稳定性增加, 负的挥舞2扭转耦合却使摆振一阶稳定性下降。      

悬停状态带磁流变减摆器直升机的动稳定性分析

建立了适用于直升机悬停状态动稳定性的磁流变减摆器模型,悬停状态下动力入流模型采用动量理论模型,与直升机旋翼/机体耦合动力学方程组联立,采用Simulink时域仿真的方法计算得到磁流变减摆器对悬停状态下直升机动稳定的影响,对比了不同电压下磁流变减摆器对桨叶挥舞摆振运动的影响.结果表明:对于磁流变减摆器,施加不同电压可得到不同的阻尼力,该性质可以抑制直升机悬停状态动不稳定性.     

无轴承旋翼摆振模态阻尼识别技术研究及其应用

旋翼桨叶的一阶摆振后退型模态是影响直升机地面共振稳定性的主要模态。为了识别装机状态下桨叶一阶摆振模态阻尼,该研究发展了基于FFT分析的移动矩形窗法、基于Fourier级数的移动矩形窗法、基于希尔伯特变换法和基于Wavelet小波变换等四种方法的无轴承旋翼一阶摆振模态阻尼识别技术,针对试验中测得的信号出现的频率成分密集和信噪比差等情况在阻尼识别过程中增加了数字滤波器,数值仿真和基于装机试验数据的识别均表明,基于Fourier级数的移动矩形窗和基于Wavelet小波变换两种阻尼识别技术可有效分离无轴承旋翼摆振模态,数字滤波器可有效提高桨叶摆振阻尼识别精度。     

基于流固耦合的旋翼结构振动载荷计算分析

建立旋翼结构振动载荷的流固耦合分析方法,计算分析旋翼前飞状态下的结构振动载荷,其中旋翼动力学模型中采用大变形梁模型,旋翼气动模型采用CFD模型,利用多重滑移网格技术实现旋翼变距、旋转等运动,最后采取松耦合策略集成动力学、气动模型。在结构和气动模型分别验证的基础上,通过计算SA349/2直升机桨叶在前飞状态的挥舞、摆振剖面结构振动载荷并对比飞行实测数据,验证流固耦合计算方法的准确性,同时对比自由尾迹模型计算结果,证明在旋翼结构振动载荷计算当中引入CFD方法能有效提高载荷计算的预估精度。     

变距/摆振耦合对直升机空中共振稳定性的影响

采用多桨叶坐标转换和复数坐标 变换等方法,研究了变距/摆振耦合对直升 机空中共振的影响;推导出完全引入变距/ 摆振耦合的直升机空中共振分析公式,建立 了相应的分析模型和计算程序。利用系统的 特征值研究了直升机空中共振的动不稳定性, 得出变距/摆振耦合对直升机空中共振的影响 ;通过系统的特征向量与各自由度之间的相互 作用（能量关系）的研究,揭示了空中共振机理 ,以某型直升机为例进行了计算分析。研究表明 ：正的变距/摆振耦合可以抑制旋翼/机体耦合 系统的动不稳定性,在同时存在挥舞/摆振耦合 和正的变距/摆振耦合时,直升机的旋翼/机体 耦合系统为绝对稳定。     

大型水平轴风力发电机桨叶稳定性研究

大型水平轴风力发电机桨叶为流-刚-柔耦合的周期时变多体系统。本文暂未考虑风载荷,分析了重力载荷和桨叶预锥角、转速等因素的变化对稳定性的影响。力学建模中,考虑了桨叶挥舞、摆振、扭转和轴向运动以及根部铰的挥舞、摆振和变矩等刚体运动。利用有限元法形成5节点18自由度的刚-柔混合梁单元模型,应用Hamilton原理建立桨叶动力学方程,求得对应的摄动方程,采用Newmark隐式积分方法求解。根据Floquet理论判断运动稳定性,计算了相关转换矩阵的特征值。结果表明预锥角对桨叶运动稳定性影响不容忽视。在通常的工况下,桨叶能够稳定地运转。     

ABC 共轴直升机旋翼/机身耦合振动响应分析

前行桨叶概念（Advanced Blade Concept, ABC）共轴直升机具有较大的振动问题,为研究振动机理,建立了ABC 共轴旋翼/机身耦合气动弹性模型,其中桨叶采用有限元梁模型,机身采用精细有限元模型。为提高耦合模型的气动弹性响应分析精度,结合传统 CFD/CSD 耦合分析方法与自由尾迹,提出了 CFD/CSD/自由尾迹耦合计算方法,解决了传统方法的尾迹耗散问题,并保证了计算效率。基于此方法建立了 ABC 共轴直升机旋翼/机身耦合气弹响应分析方法。以样例 ABC 共轴直升机为研究对象,总结了重点位置振动响应随前进比和旋翼交叉角的变化规律,并得出了一些有意义的结论。     

大变形薄壁复合材料旋转梁静动态特性分析

该文研究了大变形薄壁复合材料旋转梁的静、动态特性以及复合材料旋转梁不同铺层角、转速对固有频率的影响变化规律。在梁截面上设立翘曲节点引入翘曲变形,假设应变沿薄壁厚度呈二次曲线形式变化;由Hamilton原理,推导了复合材料梁的大变形公式;建立了考虑剪切、翘曲薄壁复合材料大变形梁静、动态分析的有限元模型,并编写了相应的计算程序。分析了复合材料薄壁梁大变形状态下的静态变形行为;在旋转状态下,考虑哥氏力影响,不同转速、不同铺层角对复合材料梁动态特性的影响。计算结果表明:能够用该文建立的模型计算复合材料梁的静动态特性,与相关文献计算结果进行比较,说明了模型的优越性。     

大型水平轴风力发电机浆叶稳定性研究

大型水平轴风力发电机桨叶为流－刚－柔耦合的周期时变多体系统。本文暂未考虑风载荷，分析了重力载荷和桨叶预锥角、转速等因素的变化对稳定性的影响。力学建模中，考虑了桨叶挥舞、摆振、扭转和轴向运动以及根部铰的挥舞、摆振和变矩等刚体运动。利用有限元法形成5节点18自由度的刚－柔混合梁单元模型，应用Hamilton原理建立桨叶动力学方程，求得对应的摄动方程，采用Newmark隐式积分方法求解。根据Floquet理论判断运动稳定性，计算了相关转换矩阵的特征值。结果表明预锥角对桨叶运动稳定性影响不容忽视。在通常的工况下，桨叶能够 稳定地运转。     

Calculation of a transient in a two-pole network with a thermistor

An analytical expression is derived which describes the variation of the thermistor temperature during a relay-effect transient process following an instantaneous change in the supply voltage in an R — R_T two-pole network.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 38, No. 3, pp. 465–472, March, 1980.     

Stress analysis of a strip with a step and a crack

Stress analysis for a strip of which widths are different at the right and left handsides is carried out for before and after occurrence of a crack at a corner of a step. The strip is analyzed as a thin plate bending problem subject to transverse bending and torsion, and as a plane eleastic problem subject to bending in the plane and uniaxial tension. The rational mapping function of a sum of fractional expressions and complex variable method are used. Stress distribution and stress intensity factors are obtained.     

Interaction between a liquid and a cylindrical body touching a wall

An exact solution is obtained for the problem of interaction between the ideal liquid homogeneously moving at infinity and streamlining a round cylinder touching a solid wall.     

Imaging a point to a line with a single spherical mirror

Methods for imaging a single point source to a line image are discussed, and a design study of single spherical mirror systems that form aberration-free line images is presented. An expression forthe ray density along the line image is derived for such systems in the cases of (i) uniform beam profiles and (ii) Gaussian beam profiles. The resulting ray density profiles are illustrated for single spherical mirror systems over a wide range of design parameters.     

Influence lines for bending under a ring load of a free shell,a shell embedded in a soft medium and a shell containing a soft core

Summary Theoretical expressions for stresses and displacements have been derived for bending under a ring load of a free shell, a shell embedded in a soft medium, and a shell containing a soft core. Numerical work has been done for typical cases with anElliot 803 Digital Computer and influence lines are drawn therefrom.

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Einflußlinien für die Biegung einer freien Schale, einer Schale in einer weichen Bettung und einer Schale mit weichem Kern

Zusammenfassung Für die Biegung einer freien Schale, einer weich gebetteten Schale und einer Schale mit weichem Kern unter einer Ringlast werden Ausdrücke für die Spannungen und Verschiebungen hergeleitet. Die Ergebnisse wurden für einige typische Fälle mit einem DigitalrechnerElliot 803 numerisch ausgewertet. Die sich ergebenden Einflußlinien wurden graphisch dargestellt.

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Nomenclature A (),B () Functions of - a, t Mean radius and thickness of the shell - E _S , _S Young's modulus andPoisson's ratio of the shell - G _c , _c Shear modulus andPoisson's ratio of the casting or core - I ₀ (r),I ₁ (r) ModifiedBessel functions of the first kind and order zero and one respectively - K ₀ (r),K ₁ (r) ModifiedBessel functions of the second kind and order zero and one respectively - p Ring load, lb/in - U, W Displacement components in the casing or core in thez andr direction - u, w Displacement components of a middle surface point in the shell - _r , _rz Radial and shearing stress components - Independent variable of infinite integrals - k [3(1–S ²)a ²/t ²]^1/4 With 13 Figures     

Analysis of a Premature Failure of a Hub from a Diesel Generator of a High-Speed Motor Ship

Failure analysis is carried out on a fractured hub obtained from a diesel generator of a high-speed motor ship. Macrofractography, microfractography, standard optical metallography, material characterization techniques, and numerical modeling were used to verify the findings of the current investigation. Cracking initiation is attributed to fretting fatigue caused by a modification performed in the vicinity of the fractured hub. Operational vibrations contributed to the propagation of the cracks as typical fatigue cracks until final fracture.     

Linear heat transfer in a flow around a cylinder or a sphere

It is shown that the relation between the Nusselt and Reynolds numbers determined by the Reynolds analogy is linear with self-similarity of the hydrodynamic resistance coefficient.Special Design and Technology Office Element, Odessa, Ukraine. translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 68, No. 3, May–June, pp. 395–396, 1995.     

Interaction between a cylindrical shell in a fluid and a pulsating bubble

The dynamic behavior of a cylindrical fluid-immersed shell in a pressure wave initiated by a pulsating vapor-gas bubble that develops as a result of the action of laser radiation on the absorbing medium (metal) is examined experimentally and theoretically. The results of the experiments suggest that the amplitude of the shock wave that develops as a result of complete or partial vaporization of the absorbing medium is appreciably smaller than the amplitude of the waves due to pulsations of the bubble that is formed. Experimental data on the pattern of structural deformation are confirmed by calculations. The effect of load simulation on the behavior of the shell is established according to computational data.Translated from Problemy Prochnosti, No. 6, pp. 116–120, June, 1990.