非线性阻尼动力方程的复合积分法

非线性动力方程直接积分法的基础是构造$t$时刻与t+\Delta t时刻状态量间的关系, 由此形成基本量的非线性方程组, 再在每个时间步内采用 Newton-Raphson或BFGS等迭代方法求解. 该文基于Bathe复合积分法(composite implicit time integration), 提出了非线性阻尼系统基于速度变量的复合时间 积分迭代格式. 以非线性黏滞阻尼Sdof系统为例, 按上述方法以及基于BFGS迭代 的Newmark-\beta法编制Fortran程序, 结果与Adina软件对比, 验证了该文方法的有效性.     

用MATLAB进行单自由度系统机械振动试验

分析单自由度阻尼系统受迫机械振动特性,建立数学模型,利用MATLAB对其进行仿真试验,进行定量分析,试验结果得出振动方程解析解,并用几何方式描述了振动方程和幅频特性.     

车架结构动力修改与力响应模拟技术研究

以某轻型越野汽车车架为研究对象,通过对该型车辆特定路面行驶工况下路面激励响应特性的研究,构造了模拟载荷谱. 结合车架结构试验模态模型,采用力响应模拟分析技术,对基于舒适性准则进行结构修改后的车架动态特性进行了模拟力响应对比分析,结果表明,力响应模拟分析技术是进行结构动态优化设计的高效手段.     

虚拟仪器在振动分析教学实验中的应用

介绍一个由学生自己定义、自己设计的虚拟仪器实验方法,既能培养学生实验动手能力,又能解决一般学校实验仪器套数少的问题.     

用振动方法测量流体密度

介绍了用振动方法则量流体密度的实验原理、实验装置和实验方法, 这是振动力学的一个教学实验,具有实际应用价值。     

解析法计算高剪切均质机转子的变形

用解析法分析了高剪切均质机转子的变形,推导了计算径向位移的有关公式. 所得结果为此类转子结构参数优化提供了依据.     

理论力学的教学实践

探讨了理论力学教学中, 不同教学内容的讲授方式、教师个人素质的作用以及扬长避短采用多媒体教学手段的问题.     

走钢丝的力学

分析走钢丝的动力学原理. 解释演员为保持在钢丝上直立行走的稳定性, 对平衡棒所起的控制作用.     

关于铅球最佳出手角的数值分析

考虑铅球运动员的推力随出手角的变化, 利用Matlab软件计算出手角的最佳值. 在此基础上讨论了运动员的身高、推力、角度衰减系数以及铅球质量对最佳出手角的影响.     

计算含大位移动边界非定常流动的无网格算法

研究了可以计算处理包含大位移动边界非定常流动的无网格算法. 创建了无网格方法中由于大位移边界运动造成的不合要求点的判断标准, 采用高效的填充方法实现点云重构, 运用线性插值方法得到新点参数, 实现了局部重构处理大位移动点. 流场计算方面, 在计算域自动布点基础上, 采用曲线逼近计算导数及HLLC格式计算数值通量, 发展了求解基于无网格的ALE方程组的算法. 最后, 对活塞问题进行了模拟, 结果与解析解相吻合, 验证了算法的准确性; 另外, 计算比较了气流流过静止圆柱以及圆柱在静止流场运动流场, 结果表明方法是成功的.     

A vibration absorber for motorcycle handles

This paper describes the application of a vibration absorber to ameliorate the comfort of motorcycle handles. The concept of dynamical absorber is briefly summarised and a frequency response function is expressed as the ratio of vibration amplitudes (transmissibility). Some practical hints on the tuning strategy are also suggested in order to correctly define the absorber and then achieve the most effective vibration reduction. A specifically designed item is presented, with the peculiar characteristic of taking advantage of the damping properties of viscoelastic material undergoing shear deformations. An experimental verification of the good performances of the absorber is eventually given on the basis of both a modal analysis of a motorbike and the testing of its handle on an electrodynamical shaker.     

An analytic solution to asymmetrical bending problem of diaphragm coupling

Because rigidity of either hub or rim of diaphragm coupling is much greater than that of the disk, and asymmetrical bending is under the condition of high speed revolution, an assumption is made that each circle in the middle plane before deforma- tion keeps its radius unchanged after deformation, but the plane on which the circle lies has a varying deflecting angle. Based on this assumption, and according to the principle of energy variation, the corresponding Euler＇s equation can be obtained, which has the primary integral. By neglecting some subsidiary factors, an analytic solution is obtained. Applying these formulas to a hyperbolic model of diaphragm, the results show that the octahedral shear stress varies less along either radial or thickness direction, but fluctuates greatly and periodically along circumferential direction. Thus asymmetrical bending significantly affects the material＇s fatigue.     

Natural convection in a rectangular cavity. An analytic solution

Summary An analytic solution is given to a problem of natural convection in a rectangular cavity, by means of a Papkovich-Fadle series. The convergence of the method is numerically proven and the results are compared with those obtained by several other methods. The considered solution procedure shows definite advantages with respect to the other techniques.

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Sommario Si fornisce, per mezzo della serie di Papkovich-Fadle, una soluzione analitica per un problema di convezione naturale in una cavità rettangolare. La convergenza del metodo è numericamente provata e i risultati sono confrontati con quelli ottenuti con altri metodi. La soluzione proposta tramite la serie è in tal caso vantaggiosa rispetto alle altre tecniche.

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This work has been partially supported by C.N.R. through grant n. 81.01501.11.     

An analytic solution of dense two-phase flow in a vertical pipeline

According to a mathematical model for dense two-phase flows presented in theprevious paper,a dense two-phase flow in a vertical pipeline is analytically solved,and theanalytic expressions of velocity of each continuous phase and dispersed phase arerespectively derived The results show that when the drag force between two phases dependslinearly on their relative velocity,the relative velocity profile in the pipeline coincides withDarcy’s law except for the thin layer region near the pipeline wall,and that the theoreticalassumptions in the dense two-phase flow theory mentioned are reasonable.     

Interaction of elastic system with snap-through vibration absorber

Interaction of essentially non-linear vibration absorber (snap-through truss) with primary 1DOF linear oscillator is investigated. The study covers both free and forced (external excitation applied to the linear oscillator) responses of the system. The analysis is performed by complexification-averaging technique, describing a slow variation of amplitudes of principal harmonic components. Periodic and quasiperiodic oscillations are revealed and investigated. It turns out that for realistic parameters of the system vast majority of the responses, including those suitable for the vibration absorption, is quasiperiodic. The results are verified by means of a direct numeric simulation.     

Some analytic solutions for a simple model of microwave absorber

An absorber, whose permittivity is a continuous function of the wave propagation direction z only, is placed between two planes, z = 0 and z = L, in a straight waveguide with a uniform cross section and perfectly conducting walls. Solutions of Maxwell's equations for the region occupied by the absorber, are given as transverse electric and transverse magnetic waves, and expressed in terms of known functions for certain choices of permittivity. Expressions for reflection and transmission coefficients are deduced.     

An analytic solution of the static problem of inclined risers conveying fluid

Meccanica - We use the method of matched asymptotic expansion to develop an analytic solution to the static problem of clamped–clamped inclined risers conveying fluid. The inclined riser is...     

Chatter mitigation using the nonlinear tuned vibration absorber

A passive vibration absorber, termed the nonlinear tuned vibration absorber (NLTVA), is designed for the suppression of chatter vibrations. Unlike most passive vibration absorbers proposed in the literature for suppressing machine tool vibrations, the NLTVA comprises both a linear and a nonlinear restoring force. Its linear characteristics are tuned in order to optimize the stability properties of the machining operation, while its nonlinear properties are chosen in order to control the bifurcation behavior of the system and guarantee robustness of stable operation. In this study, the NLTVA is applied to turning machining.