An optimal cam profile design considering dynamic characteristics of a cam-valve system

In this work, an optimal cam profile design method for an OHV-type cam-valve train is studied considering the dynamic characteristics of the valve system. When designing a cam profile for an internal combustion engine, it is desirable to make the valve lift area be as large as possible and the valve peak acceleration and seating velocity be as low as those can be within the cam-event angle. But, as we know, those features conflict with one another. An optimal design must strike a compromise between the two. Another important factor in valve train design is avoiding abnormal valve motions such as jump and bounce. It is known that jump and bounce are closely related to valve train dynamic characteristics.In this paper, a two-step optimization technique to design an optimal cam profile is proposed. In the first step, an attempt was made to maximize valve lift area without causing abnormal valve motions while satisfying all the given constraints such as cam-event angle, maximum valve acceleration, and cam displacements at both ends of the cam-event angle. Then, in the second step, minor modifications of the cam developed in the first step were made in order to reduce the cam acceleration while maintaining the maximized valve lift area and satisfying constrains obtained in the first step.In order to prove the effectiveness of the optimization method, the valve motion driven by the optimized cam was not only simulated with a four degree of freedom model but was also tested experimentally. It was found that the measured valve motions agree quite well with the simulation results. Comparing the valve motions of the optimized cam with those of the original cam, it was found that the optimized cam can increase the valve-lift area by 8.6 percent while reducing the peak cam acceleration by 28.7 percent. Also, it was noted that the optimized cam increases the cam-valve train operating speed at which jump and bounce occur.Paper was presented at the 1988 SEM Spring Conference on Experimental Mechanics held in Portland, OR on June 5–10.     

氧乙炔焰喷焊挺杆抗点蚀性能的试验研究

作者以45号钢为基材,对其施行表面喷焊覆层强化处理的工艺,试验研究了氧乙炔焰喷焊斯太尔挺杆与国产斯太尔凸轮配副的抗点蚀性能。结果表明,在相同工况下,氧乙炔焰喷焊挺杆的优点蚀寿命比212堆焊合金铸铁挺杆的长一倍,比按国外原图纸工艺要求试制的20Cr气体软氮化斯太尔挺杆的长4培。文章还就喷焊挺杆的点蚀失效机理、挺杆表面喷焊覆层的抗点蚀性能和喷焊工艺对挺杆抗点蚀性能的影响等进行了比较系统而深入的分析和讨论,指出这种喷焊上艺可以应用于斯太尔挺杆的国产化批量生产。     

Local and global bifurcations of valve mechanism

In this paper we study in detail problems of nonlinear oscillations of valve mechanism at internal combustion engine. The practical measurement indicates that stiffness of valve mechanism is not constant but is a function of the rotational angle of the cam. For simplicity of analysis we replace valve mechanism of internal combustion engine with a nonlinear oscillator of single degree of freedom under combined parametric and forcing excitation. We use the method of multiple scales and normal form theory to study local and global bifurcations of valve mechanism at internal combustion engine.     

新型立式动平衡机的设计与分析

在分析传统的双面立式动平衡机的振动结构的基础上，设计了一种新的立式动平衡机的振动结构(即摆架)，采用新摆架结构的动平衡机可以实现静不平衡和偶不平衡的有效分离。文中详细分析了新摆架结构的特点，并在ANSYS7．0平台上对摆架进行了有限元模态分析和谐响应分析。由于新的摆架结构采用多块簧板，在多个部位刚度匹配，且采用多个传感器安装于测量点处，这样新的动平衡机可以直接测量静不平衡和偶不平衡，且相互影响极小。实践证明：采用新摆架结构的动平衡机特别适合于飞行物体的惯性测量，且克服了传统的双面立式动平衡机长期以来平面分离不佳的缺点，具有很高的推广价值。     

船用凸轮-挺柱副摩擦润滑性能研究

随着船舶柴油机功率密度和转速等性能参数的不断提升,配气凸轮-挺柱副面临着更加严苛的工作环境,尤其是界面微观接触区的摩擦学特性,在瞬态载荷冲击、速度冲击、曲率变化及局部粗糙峰接触条件下,界面摩擦及闪温迅速突变,带来磨损和胶合等表面失效问题. 本研究中基于先进三维线接触混合润滑模型,考虑凸轮-挺柱副瞬态突变工况及几何变化、瞬态表面粗糙度影响以及润滑油非牛顿流体作用,采用稳定性好、收敛速度快的准系统数值分析方法开展凸轮-挺柱副摩擦闪温分析,揭示粗糙度参数、工况改变及几何结构对其润滑状态和摩擦闪温特性的影响规律,为船舶柴油机配气凸轮-挺柱副摩擦学优化设计及磨损胶合失效预测提供理论指导.      

Non-linear parametric modelling of a high-speed rail hydraulic yaw damper with series clearance and stiffness

At high operational speeds, the train system becomes very sensitive to parameter variations of components. Therefore, it is imperative to incorporate more accurate component models in the vehicle dynamics studies. This study addresses a more subtle and comprehensive non-linear parametric model of a high-speed rail hydraulic yaw damper. A new concept of a hydraulic yaw damper model is suggested, in which the small mounting clearance, the series stiffness, and the viscous damping are built in. The series stiffness is the tandem result of the dynamic oil stiffness, the rubber attachment stiffness, and the mounting seat stiffness. A dynamic oil property model is established and coupled to the entire modelling process, in which the density, the dynamic viscosity, the volumetric elastic modulus, and the stiffness of the oil are all changeable in terms of the instantaneous working pressure, the oil temperature, and the entrapped air ratio of the oil. The dynamic flow loss and the valve system dynamics are also incorporated. Experiments validated that the established non-linear parametric model is accurate and robust in predicting the damping characteristics within an extremely wide speed range. The validated damper model was then successfully applied to a thorough parameter sensitivity analysis and damping nature prediction under practical, in-service conditions. The established damper model couples all the main influential factors that are not or are insufficiently considered in normal-speed problems; thus, it will be more accurate and appropriate for furthering high-speed problem studies.     

基于逆迭代法的结构动力缩聚技术

有限元模型的动力缩聚法已被广泛地应用到大阶系统的特征分析、试验－分析模型的相关分析等领域中。本文从逆迭代法出发,导出了一种有限元模型动力缩聚迭代方法。该方法具有三个显著的优点：其一是收敛速度远远超过现有的动力缩聚迭代法;若干是该迭代法收敛的可以从理论上得到保证,其三是由于没有必要的在每次迭代中都去计算降阶系数的刚度矩阵、质量矩阵和特征问题,因而可减少计算工作量,尤其在主自由度数较大的情况下。     

高速列车引起的地基振动半解析解

随着列车速度的提高,地基振动的反应越来越大。根据有限元理论、轨道动力学及地基土振动Green函数,建立了轨道-无限地基土相互作用理论分析模型。为了组装系统的动力方程,通过引入静态自由度凝聚模式来消除梁存在转动自由度。借助文献[12]的柔度矩阵定义并通过Hankel变换获得了系统的刚度矩阵,进而采用Newmark法求出了系统动力反应。最后,以瑞典X2000高速旅客列车为对象进行仿真,通过与试验结果的比较来说明本文方法的可行性。     

Identification of stiffness properties of composite tubes from dynamic tests

The identification of the stiffness properties of typical laminated composite tubes from dynamic tests is presented. Unknown coefficients are identified by a technique of model updating. The fomulation is based on the minimization of the eigensolution residuals (sensitivity method). Errors of generalized masses are considered. The technique allows for the simultaneous identification of several properties from a single test. Stiffness properties of extension, bending/twisting and transverse shear are identified. Important points of the model updating of tubes in dynamics are addressed: potential energy evaluation, placement of sensors and the problem of multiple eigenvalues. Results obtained by numerical simulation show the efficiency of the proposed method.     

Tensile Test Machine for Unsymmetrical Materials

A novel solution to overcome the shortcoming of conventional tensile test machines in dealing with unsymmetrical materials and off-axis testing of composites is presented. Conventional testing machines are designed on the basis of subjecting a specimen to axial load to determine the stiffness and strength of the material. For specimens with unsymmetrical cross-section this method is no longer valid due to induced additional bending stresses. To overcome this problem a novel tensile test machine was designed, which allows bending deformation, thus subjecting the specimen to pure tension instead of axial loading. To validate the design, the machine was fabricated and employed for tensile testing of an aluminum specimen with unsymmetrical cross-section. The comparison of test results from a conventional machine and from analytically calculations, based on pure tension, reveals that conventional machine generates significant errors, while the results from new machine are in good agreement. The machine was then used to test a functionally graded beam.     

基于局部插值的结构动力模型降阶方法

提出了一种基于局部插值对大型结构有限元模型的特征值问题进行降阶的方法. 该方法通过局部插值将复杂结构的有限元模型中节点的位移用凝聚点的位移插值来表示, 从而得到用插值函数表示的简化基向量, 实现对结构广义特征值问题的降阶. 为了提高降阶模型的精度, 采用非协调元的插值函数作为局部插值函数来弱化凝聚后的结构刚度, 并且在有限元模型上进行逆迭代, 对得到的降阶后的广义特征值问题的特征值和特征向量进行改善. 为了提高模型降阶的效率, 采用规整网格包围整个结构生成均匀的凝聚点, 高效地确定了有限元模型中节点所依附的凝聚点. 最后, 对 3 个机床部件的模态分析验证了提出的简化方法的高效性和可行性.      

DEM speedup: Stiffness effects on behavior of bulk material

A number of techniques exist for minimizing the computational cost of discrete element simulations (DEMs). One such method is a reduction of particle stiffness, which allows for bigger time steps and therefore fewer iterations in a simulation. However, the limits and drawbacks of this approach are still unclear, and may lead to invalid results. This paper investigates the effect of a stiffness reduction on bulk behavior by examining three case studies. Two cases demonstrate that particle stiffness can be reduced without affecting the bulk material behavior, whereas the third test shows that a stiffness reduction influences the bulk behavior.     

DEM speedup： Stiffness effects on behavior of bulk material

A number of techniques exist for minimizing the computational cost of discrete element simulations （DEMs）. One such method is a reduction of particle stiffness, which allows for bigger time steps and therefore fewer iterations in a simulation. However, the limits and drawbacks of this approach are still unclear, and may lead to invalid results. This paper investigates the effect of a stiffness reduction on bulk behavior by examining three case studies. Two cases demonstrate that particle stiffness can be reduced without affecting the bulk material behavior, whereas the third test shows that a stiffness reduction influences the bulk behavior.     

Design of nonlinear springs for attaining a linear response in gap-closing electrostatic actuators

Gap-closing electrostatic actuators are inherently nonlinear and their dynamic range is often limited by the pull-in instability. To overcome this, we propose a nonlinear spring that counteracts the nonlinear effects of electrostatic attraction. The nonlinear spring is designed to extend the stable range of the actuator and to enforce a linear electromechanical response. We present a method for designing elastic springs with monotonically increasing stiffness. The mechanism we propose is effective shortening of a straight clamed-guided beam flexure, by wrapping it over a cam. We consider two specific cases. The first case assumes the wrapped section of the beam flexure fully conforms to the cam shape. The second case assumes that there is a single contact point between the beam flexure and the cam. To validate the concept we have designed and measured the response of a nonlinear spring with a prescribed force–displacement law. Experimental measurements of a macro-scale spring are in good agreement with the model predictions.     

Determination of the critical loads of shells by nondestructive methods

Two methods for determining the location of and load level to produce instability of compressed cylindrical shells are presented. The first relates the variation in the wall normal stiffness as a function of applied compressive force to the critical load. It uses the distribution of stiffness over the surface of the shell as a guide to buckle location. The second method associates the local dynamic mass with instability behavior. The test data presented show that either method will give excellent prediction capability from low-load-level data for shells of orthodox form. Neither method appears to apply to spirally stiffened shells. This is thought to be due to the fact that there is a substantial difference between the buckle pattern under axial compression and the imperfection shape induced by the normal displacement which is used to ascertain the wall stiffness and the dynamic mass.     

Bifurcation and chaos analysis of multistage planetary gear train

A nonlinear time-varying dynamic model for a multistage planetary gear train, considering time-varying meshing stiffness, nonlinear error excitation, and piece-wise backlash nonlinearities, is formulated. Varying dynamic motions are obtained by solving the dimensionless equations of motion in general coordinates by using the varying-step Gill numerical integration method. The influences of damping coefficient, excitation frequency, and backlash on bifurcation and chaos properties of the system are analyzed through dynamic bifurcation diagram, time history, phase trajectory, Poincaré map, and power spectrum. It shows that the multi-stage planetary gear train system has various inner nonlinear dynamic behaviors because of the coupling of gear backlash and time-varying meshing stiffness. As the damping coefficient increases, the dynamic behavior of the system transits to an increasingly stable periodic motion, which demonstrates that a higher damping coefficient can suppress a nonperiodic motion and thereby improve its dynamic response. The motion state of the system changes into chaos in different ways of period doubling bifurcation, and Hopf bifurcation.     

纤维杆元模型在框架结构非线性分析中的应用

本文基于Fiber模型,结合分段变刚度概念,推导建立了便于框架结构非线性分析应用的纤维杆元模型,即由杆件两端弹塑性区的纤维子单元及杆件中部弹性区的弹性子单元组成。弹塑性区由于受力较大,采用精细的纤维子单元模拟,中间弹性区受力相对较小,直接采用弹性子单元代替;同时,应用增分理论,分别推导了三维纤维子单元及弹性子单元的单刚矩阵,并采用静力凝聚方法,集成了三维纤维杆元模型的刚度矩阵。另外,直接应用混凝土及钢筋的本构关系,利用该计算模型对一栋12层框架结构进行了时程非线性分析,计算结果与振动台试验结果进行了比较,比较结果表明两者在结构动力特性,位移响应方面等均吻合较好,验证了该模型的有效性,可为推广使用提供参考。     

A novel beam finite element with singularities for the dynamic analysis of discontinuous frames

In this work, a model of the stepped Timoshenko beam in presence of deflection and rotation discontinuities along the span is presented. The proposed model relies on the adoption of Heaviside’s and Dirac’s delta distributions to model abrupt and concentrated, both flexural and shear, stiffness discontinuities of the beam that lead to exact closed-form solutions of the elastic response in presence of static loads. Based on the latter solutions, a novel beam element for the analysis of frame structures with an arbitrary distribution of singularities is here proposed. In particular, the presented closed-form solutions are exploited to formulate the displacement shape functions of the beam element and the relevant explicit form of the stiffness matrix. The proposed beam element is adopted for a finite element discretization of discontinuous framed structures. In particular, by means of the introduction of a mass matrix consistent with the adopted shape functions, the presented model allows also the dynamic analysis of framed structures in presence of deflection and rotation discontinuities and abrupt variations of the cross-section. The presented formulation can also be easily employed to conduct a dynamic analysis of damaged frame structures in which the distributed and concentrated damage distributions are modelled by means of equivalent discontinuities. As an example, a simple portal frame, under different damage scenarios, has been analysed and the results in terms of frequency and vibration modes have been compared with exact results to show the accuracy of the presented discontinuous beam element.     

Effects of the dynamic wheel–rail interaction on the ground vibration generated by a moving train

Based on Biot’s fully dynamic poroelastic theory, the dynamic responses of the poroelastic half-space soil medium due to quasi-static and dynamic loads from a moving train are investigated semi-analytically. The dynamic loads are assumed to be generated from the rail surface irregularities. The vehicle dynamics model is used to simulate the axle loads (quasi-static loads) and the dynamic loads from a moving train. The compatibility of the displacements at wheel–rail contact points couple the vehicle and the track–ground subsystem, and yield equations for the dynamic wheel–rail loads. A linearized Hertzian contact spring between the wheel and rail is introduced to calculate the dynamic loads. Using the Fourier transform, the governing equations for the poroelastic half-space are then solved in the frequency–wavenumber domain. The time domain responses are evaluated by the fast inverse Fourier transform. Numerical results show that the dynamic loads can make important contribution to dynamic response of the poroelastic half-space for different train speed, and the dynamically induced responses lie in a higher frequency range. The ground vibrations caused by the moving train can be intensified as the primary suspension stiffness of the vehicle increases.     

Finite element study of dynamic characteristics of main components of machine tools

Dynamic characteristics have been studied for main components of machine tools by finite element method. The multi-element static and dynamic structural analysis program makes possible the analysis of main components in various computing models.The eigen pairs are solved by the transfer subspace iterative method with the advantages of high efficiency and precision. The program can be executed on the China-made computer TQ-16 and arbitrary sets of eigen pairs for the treatment of dynamic characteristics of complex structures of various kinds are thus obtained.