液膜密封振动及冲击动力学特性

液膜密封运行过程因工况瞬时变化、系统振动及润滑不足等因素易引发端面接触冲击,严重影响密封寿命。建立考虑端面接触的液膜密封动力学模型,采用直接数值求解方法对运动方程、质量守恒空化边界雷诺方程、微凸体接触方程在全时间域内耦合求解,研究了液膜空化、轴向扰动及运行工况瞬变对密封稳定性与冲击特性的影响。结果表明:液膜空化有效提高了系统抗干扰能力,膜厚越小,受扰动后震荡频率越大且恢复至稳定状态的时间越长;发生端面冲击时膜厚振动频率显著大于全液膜状态下所受扰动情况。随转速及密封腔压力变化值的不断扩大,接触载荷值及冲击频率均不断增大,冲力响应越显著,在端面接触发生瞬间有明显的速度方向突变。     

启动振动与海浪冲击耦合时变UHMWPE轴承润滑分析

建立了启动过程超高分子量聚乙烯(UHMWPE)轴承的弹流润滑模型。综合考虑加速过程伴随振动与冲击载荷耦合时变效应,数值模拟了UHMWPE轴承不同工况下启动时的润滑情况,以期为实际工况中UHMWPE轴承的安全运转提供参考。结果表明:冲击对压力的影响较大,而振动对膜厚的影响较大。轴法向振动与海浪冲击同周期下,当两者变化一致时,将产生叠加的协同作用,反之则相互削弱。其中负正弦振动对压力和膜厚的影响更为明显。随着加速度的增大,压力随之降低,膜厚随之增大,膜厚增幅变大,振动对压力和膜厚的影响变小。     

载荷脉宽对圆柱壳瞬态响应的影响分析

为认识载荷脉宽对圆柱壳瞬态响应及其对X射线冲击响应模拟等效性的影响规律,定义了等效性评价指标即平均应变差异。以四种不同尺寸的典型圆柱壳为对象,分别加载六种冲量相同、脉宽不同的三角形脉冲载荷,通过数值模拟,获得了平均应变差异Δε随脉宽变化的关系,从结构特性角度分析了变化的原因。发现Δε主要受t/τ(脉宽占比)控制,t/τ≤0.45时,平均应变差异在20%以内。所得结果可为模拟X射线冲击环境的试验设计、结果评估和数值模拟提供参考。     

基于弹流润滑理论的非对称齿轮胶合强度多目标优化

为提高双压力角非对称齿廓齿轮的设计质量,缩短设计周期,依据弹性流体动力润滑理论,通过范例,以齿间最小油膜厚度最大和齿轮传动总体积最小为目标函数,按照粒子群优化算法,利用MATLAB编制优化程序,进行约束多目标优化设计.在此基础上,根据齿轮啮合原理和现代摩擦学原理从数学逻辑关系和物理机理上分析了目标函数对各个设计变量的灵敏度.研究结果表明:非对称齿轮的体积随模数和齿宽的增加而增加,对模数的敏感程度大于齿宽;齿间最小油膜厚度随模数、齿宽、压力角及变位系数的增加而增加,其敏感程度依次为压力角、模数、齿宽和变位系数;压力角是影响弹流润滑齿间最小油膜厚度最重要的因素,在工作齿侧适度增大压力角可以显著增大最小膜厚;大、小齿轮的变位系数对最小油膜厚度具有同等的影响程度.     

滤波减速器润滑特性研究

为了研究啮合位置、载荷、转速等因素对滤波减速器润滑特性的影响, 建立了滤波减速器的内啮合润滑模型,将牛顿(有限元)法应用到弹流润滑方程组的求解中,利用Matlab软件,采用数值计算方法,实现了弹流润滑方程组的完全数值解,得到了滤波减速器轮齿在不同啮合位置、不同载荷以及不同转速下啮合轮齿表面油膜压力和油膜厚度值,分析了不同啮合位置、不同载荷以及不同转速下轮齿所处的润滑状态,得到了啮合位置、载荷以及转速等因素对轮齿润滑特性的影响规律.结果表明：在轮齿的啮入、啮出及节点处,润滑薄膜厚度值不一样,节点处的润滑膜厚值最小;载荷增大时,轮齿表面油膜压力会变大,而油膜厚度会变小;转速增高时,油膜厚度会变大,而油膜压力变化不大.     

摆线针轮传动线接触弹流润滑分析

对摆线针轮线接触弹流润滑进行数值分析,得出啮合过程中最小膜厚,与经验公式对比,验证模型的正确性。以摆线轮θ=arccos K1处润滑状态作为判断依据,研究载荷、转速和流变指数对摆线针轮传动润滑状态的影响规律。结果表明:随着转速提高,二次压力峰高度降低并向入口区移动,膜厚相应增加;而随着载荷增加,接触区变宽,二次压力峰增加且向出口区移动,膜厚略微减小;流变指数n增加,二次压力峰先增加后减小,最后趋近于Hertz压力,并向出口区移动,膜厚相应减小。讨论了短幅系数k1对润滑的影响,表明在满足设计要求情况下,短幅系数k1减小,有利于提高润滑性能。     

基于多参数耦合的滚动轴承油膜刚度分析

针对传统经验公式难以准确反映滚动轴承正常工作时油膜刚度动态变化的问题,根据滚动轴承运行时油膜状态分布,基于非Newton流体弹流润滑理论,考虑表面粗糙形貌、热效应、时变效应等因素,建立滚动轴承油膜刚度计算模型。通过数值计算,得到一个完整工作周期内油膜压力、膜厚、温度和刚度变化规律。结果表明:油膜刚度在一个周期内呈非线性变化,并随载荷、黏度、表面粗糙度幅值的增大而增大,随卷吸速度的增大而有所减小;油膜刚度的振荡频率随表面粗糙度波长和粗糙表面纹理走向与轴承滚动方向夹角增大而增大;滚动轴承正常工作时,油膜的温升最大,内圈次之,滚动体最小且不可忽略。     

GCr15钢在4种润滑状态下的冲击损伤行为

为了了解GCr15钢的冲击损伤状态,采用自制的冲击磨损试验机、扫描电镜(SEM)及Taylor Hobson粗糙度轮廓分析仪研究了5 kg电磁杆和13.2 N冲击载荷下GCr15钢在干接触,CKD220油、海水和海水/CKD220油(1∶1)混合润滑下的表面损伤行为。结果表明:冲击使GCr15钢表面发生了塑性变形和磨损,塑性变形存在于冲击的每一阶段;冲击凹坑深度及体积随冲击次数的增加呈增大趋势,干接触时凹坑最浅,海水润滑时最深,CKD220油润滑时凹坑深度略大于海水/CKD220油混合润滑时;海水/CKD220油混合润滑的凹坑内部形貌既不同于干接触,也不同于CKD220油或海水润滑下的凹坑内部形貌。     

装药落锤冲击实验载荷特性研究

在装药发射安全性试验中,只有落锤的冲击载荷与膛压曲线较为相近时,落锤冲击试验结果才有意义。落锤冲击载荷特性与多种因素有关,通过对各种因素的调整,使落锤冲击载荷与膛压曲线吻合是落锤法进行装药发射安全性试验的前提,也具有一定难度。采用ANSYS/LS-DYNA非线性有限元软件对落锤冲击载荷作用下炸药装药内部压力的变化过程进行数值模拟,通过改变落锤的高度、落锤的质量以及炸药装药的高度,来研究炸药装药内部的动态响应特征(压力变化的过程)。模拟实验的结果表明:落锤的高度、落锤的质量以及炸药装药的高度对炸药装药内部压力都有影响;落锤的质量和炸药装药高度对压力脉冲作用时间宽度有影响,而落锤的高度对压力脉冲作用时间没影响。     

正交面齿轮传动非线性振动特性分析

以正交面齿轮传动系统为研究对象,建立了包含时变啮合刚度、啮合阻尼、齿面误差、齿面摩擦、齿侧间隙、轴承间隙等因素的弯-扭耦合非线性动力学模型,采用4-5阶变步长Runge-Kutta法对系统的无量纲动力学微分方程组进行求解。计算结果表明：在不同转速时系统会出现单周期非谐响应、多周期次谐响应、拟周期响应及混沌响应,并伴随着跳跃现象;随着负载转矩的增大,系统响应呈现混沌-多周期次谐-单周期非谐的变化趋势,轻载时齿轮副易出现单边和双边冲击现象,当载荷增大到一定程度后齿轮副处于无冲击状态;摩擦系数较小时,对系统非线性振动特性影响不大,当其逐渐增大时,系统运动状态由单周期经倍周期分叉进入混沌运动     

Hybrid spectral/finite element analysis of dynamic delamination of patterned thin films

A combined spectral and finite element analysis is performed to investigate the dynamic edge delamination of patterned thin films from a substrate. The analysis is motivated by an emerging experimental technique in which high-amplitude laser-induced stress waves initiate progressive interfacial debonding of thin film interfaces. The numerical method relies on the spectral representation of the elastodynamic solutions for the substrate and the finite element model for the thin film. A cohesive model is introduced along the interface of the bimaterial system to capture the decohesion process. The important role of the film inertia on the crack extension and the appearance of the mixed-mode failure are demonstrated by observing the traction stress evolution at various points along the bond line. Parametric studies on the effect of film thickness, interface fracture toughness, loading pulse shape and amplitude on the debonding process are performed. A semi-analytical investigation on the inertial effect is carried out to predict the final crack length as a function of the film thickness and pulse amplitude.     

An efficient method for nonlinear analysis of layered shells

Finite element formulation based on explicit through-thickness integration scheme assumes importance when applied to multilayered shells, as it is numerically accurate and computationally efficient. Explicit integration becomes possible on assuming the variation of the inverse Jacobian through the thickness. The element stiffness matrices are discussed for (i) large rotation, and (ii) small rotation. Relative efficiencies of the explicit through-thickness integration schemes are compared with that of the conventional formulation involving numerical integration in three directions in each layer and summation over the layers. The small rotation formulation assuming linear variation of the Jacobian inverse across the thickness and based on further approximation regarding certain submatrices is seen to be computationally efficient. The geometric nonlinear behaviours of laminated composite cylindrical panels subjected to external pressure are discussed. The parameters considered are: number of layers, symmetric/antisymmetric, cross-ply/angleply, boundary conditions and central angle. The strength of shallow panels with longitudinal edges hinged and curved edges free is controlled by the limit point load, while for deep panels it is controlled by the bifurcation load. The boundary conditions have significant influence on load carrying capacities. A list of symbols is given at the end of the paper     

大型水轮机组推力轴承油膜厚度在线监测研究

油膜厚度是反映推力轴承运行状态的重要参数,对油膜厚度进行实时在线监测有助于实现推力轴承的稳定运行。以某大型水轮机组推力轴承为例,结合其润滑流体的雷诺方程和油膜厚度方程,利用有限差分法分析了不同载荷和不同转速下推力轴承油膜厚度和压力分布的变化规律,并设计了一种油膜厚度实时在线监测方法。理论分析结果表明,当转速一定时,推力轴承油膜厚度先随着载荷的增大而增大,达到峰值后,随着载荷的增大而减小;当载荷一定时,油膜厚度随着转速的增大而增大。理论分析结果与该水轮机组推力轴承油膜厚度的在线监测数据完全吻合,验证了提出的油膜厚度在线监测方法的可靠性,为推力轴承运行状态的诊断提供了科学依据。     

Analytical study on the buckling of cylindrical shells with stepwise variable thickness subjected to uniform external pressure

This article focuses on the buckling of cylindrical shells with stepwise variable thickness subjected to uniform external pressure. First, combining the method of separation of variables, perturbation method, and Fourier series expansion, an analytical method for the buckling analysis of cylindrical shells with axisymmetric thickness variation subjected to external pressure is established. The method is verified by comparing with the previous results. Then, the stepwise variable thickness of cylindrical shells is described exactly by the arc tangent function. Finally, using the presented method, a general formula for the critical buckling load of cylindrical shells with stepwise variable thickness subjected to uniform external pressure is derived. This general formula is compared and discussed with some empirical formulae in the current design standards. This study lays a theoretical foundation for the calculation of the buckling load of cylindrical shells with stepwise variable thickness subjected to uniform external pressure. Moreover, it provides a reference and guidance for the further revision of related standards.     

Numerical solution of the point contact problem using the finite element method

The elastohydrodynamic lubrication problem, in which the lubricant pressure and film thickness are sensitive to surface deformation, is solved by using a finite element procedure and the Newton method. The numerical procedure is applied to the point contact problem, in which a thin lubricant film is maintained between two balls loaded together by a high load under conditions of pure rolling. The present analysis shows that pressure spikes are formed near the outlet region, a result which has been found in the line contact problem and which has been conjectured in the present problem.     

Galton型高强气流声源的发声特性

文章介绍了一款带中心杆的Galton型气流声源,通过试验和数值模拟方法,研究了该声源发声特性、进气压力对声场分布的影响以及流体介质对发声特性的影响.研究发现,该声源稳定发声时,共鸣腔内压力场与流场均呈周期性变化;不同进气压力下,声场空间分布基本一致,具有较强的声指向性.共鸣腔后侧轴线处,声压级达到最大值,为153 dB...     

Improvement of minimum paint film thickness for THz paint meters by multiple-regression analysis

We propose a numerical parameter fitting method to determine the time delay between two temporally overlapped echo pulses in terahertz (THz) tomography measurements. The method is based on multiple-regression analysis with the least-squares method and is applied to decrease the minimum paint film thickness for THz paint meters. Applying multiple-regression analysis to paint thickness measurements is five times more sensitive with regard to the minimum thickness than numerical Fourier deconvolution. We apply the proposed method to determine the optical thickness, geometrical thickness, and group refractive index of dry paint film and wet paint film. The proposed method is useful for decreasing the minimum thickness for a THz paint meter and other THz tomography measurements.     

A novel numerical scheme for the analysis of effects of surface roughness on EHL line contact with couple stress fluid as lubricant

In this article, a Jacobian-free Newton Multigrid (JFNMG) method is used for obtaining the solution of isothermal, steady and compressible elastohydrodynamic lubrication (EHL) line contact problem with surface roughness. The lubricant is a couple stress fluid. A finite difference scheme is used for the solution of EHL equations. The proposed JFNMG method, for the solution of resulting nonlinear system of algebraic equations, comprises nonlinear Newton iterations on the outer loop and linear multigrid iterations on the inner loop. It overcomes the limitations of conventional schemes for the investigation of the problems covering wide range of physical parameters of interest. For increasing values of couple stress parameter, there is an increase in minimum film thickness and considerable decrease (in height as well as spread) of pressure spike. Also, the sensitivity of height and spread of pressure spike as a function of load, couple stress parameter and other parameters are investigated.     

对转圆柱滚子轴承动态特性分析

针对内外圈对转圆柱滚子轴承内部复杂的运动特性及相互作用力,通过分析轴承径向游隙的影响因素以及考虑滚子与滚道的接触变形和热效应对油膜厚度的影响,利用拟静力学法建立了轴承的分析模型,并采用NewtonRaphson法进行求解;同时,利用该模型对滚子打滑率进行计算,以验证所采用分析方法的正确性和可靠性。然后,进一步探讨了不同工况下对转圆柱滚子轴承内部组件的转速变化规律与接触特性。结果表明：滚子的自转转速、滚子与滚道的接触载荷均随径向载荷的增大而增大;内、外圈转速变化会使受载区滚子与滚道的接触载荷以一定的规律重新分配,且转速对最小油膜厚度的影响较径向载荷更为明显。研究结果可为对转圆柱滚子轴承的结构优化和生热机理分析提供理论依据。