基于虚拟激励法的一种新型五轮车行驶性能研究

针对新型五轮侧面叉车的行驶平顺性能否满足使用要求而进行了数值分析及仿真研究.一方面引入虚拟激励函数,将非平稳的振动信号转化为确定载荷函数下的动力学响应分析,进一步用功率谱来描述随机信号的特征.另一方面,运用ADAMS搭建侧面叉车的多刚体模型,并仿真分析出不同载荷下的加速度与时间的响应函数和基于虚拟激励的数学模型的加速度功率谱密度函数曲线.数学模型和仿真分析结合完善了对系统振动的分析.     

飞行器结构噪声致振试验及声振耦合响应分析

以高超声速飞行器X-43A为研究对象,建立其有限元结构模型,在动力学实验室进行飞行器结构模型的固有频率测试,通过固有频率计算与试验结果对比,二者误差在1%左右,这表明所建立的结构有限元模型是比较准确的．在高声强混响室进行飞行器结构噪声致振试验,得到飞行器结构测点加速度功率谱密度(power spectral density, PSD)和舱内声场噪声声压级,通过声振耦合数值模拟计算结果与试验值对比,结果表明:数值模拟计算方法对振动噪声环境预测是比较可靠的,结构振动响应与舱内噪声响应的有限元分析与试验结果趋势上较为一致,低频段吻合较好;高频外噪声场引起的飞行器弹性腔体结构振动占据结构振动响应的主要成分,尤其是以结构低阶振动为主,而外噪声场传递到封闭腔体内的噪声也主要是通过结构腔体弹性壁板的低阶振动传播,即使外噪声激励是宽频的,封闭舱内响应噪声的频率主分量仍然是结构的低阶模态振动．     

粘弹性运动带动力响应分析

基于Kelvin粘弹性材料本构模型及带运动方程,建立了运动带非线性动力学分析模型.基于该模型和Lie群分析方法推导了匀速运动及简谐运动带线性问题的解析解;基于该非线性模型的数值仿真讨论了运动带材料参数、带稳态运动速度、扰动速度对系统动态响应的影响.结果表明:1)当带匀速运动时,无论系统是线性还是非线性,运动带横向振动"频率"都随着带运动稳态速度增加而减小.2)随着材料粘性增加,系统耗散能力逐渐增强,动态响应逐渐减小.3)当带运动速度简谐波动时,系统动态响应随扰动速度增大而增大.扰动频率对带横向振动影响较大.     

删失数据下的半参数变系数部分线性回归模型

为了分析删失数据,该文考虑变系数部分线性模型,此模型允许协变量对响应变量存在非线性影响.响应变量与协变量之间关系的统计模型通过线性结构来拟合是非常重要而且有益.对于删失数据,常用的统计方法不能直接应用于此模型.该文首先提出一类数据变换用以建立无偏条件期望.然后利用profile最小二乘方法,给出了模型中参数分量和非参数分量的profile最小二乘估计,并建立了这些估计的渐近正态性.最后通过数值例子来说明该文所提出的方法的有效性.     

柔性头颅模型撞击弹性板的动态响应分析

将柔性接触撞击过程处理为一个振动系统响应,采用机械网络图和求机械阻抗的方法解决了这一动态响应问题。柔性接触撞击模型考虑了头部的实际结构,把头部简化成撞击部位的头皮和头骨的质量、头部其它部分的头骨和脑液的质量、头部的刚度、头皮和脑液的阻尼系数组成的振动模型,弹性板也同样简化成由质量、刚度和阻尼构成的振动模型。采用求激振点速度阻抗的方法,得到了系统的动态撞击力、头部所受到的撞击加速度值,以及板的弹性变形、系统的固有频率等动态响应。实验数据与计算数据符合较好,证明方法是计算撞击作用下系统动态响应的实用方法,从而为头部撞击保护设计提供参考。     

典型弹药系统基础振动激励的IPRK法分析

运用IPRK法对典型弹药系统基础振动激励问题进行了研究.在阐述IPRK法基本原理的基础上,根据典型弹药系统包装形式构建了基于易损部件的三自由度弹药公路运输振动力学模型.结合实例对IPRK法和高斯白噪声模拟的有效性进行了验证,同时通过与传统Runge-Kutta法进行比较,验证了方法具有很高的计算精度和计算效率.最后运用IPRK法分析了包装箱质量、缓冲包装刚度和阻尼对引信振动加速度响应的影响规律.     

附加非线性振子的双稳态电磁式振动能量捕获器动力学特性研究

随着微机电科技的进步,利用环境振动进行系统自供电已经成为目前非线性动力学研究的热点.将质量-弹簧-阻尼系统与双稳态振动能量捕获系统相结合,提出了附加非线性振子的双稳态电磁式振动能量捕获器,建立系统的力学模型及控制方程.通过数值仿真研究了简谐激励下质量比和调频比发生变化时附加非线性振子的双稳态电磁式振动能量捕获器的动力学响应.通过与附加线性振子双稳态系统的对比,获得了上述参数对附加非线性振子的双稳态电磁式振动能量捕获器发生大幅运动的影响规律,显示出附加非线性振子的双稳态电磁式振动能量捕获器的优越性,并获得了附加非线性振子的双稳态电磁式振动能量捕获器发生连续大幅混沌运动的最优参数配合.上述研究结果为双稳态电磁式振动能量捕获系统的相关研究提供了理论基础.     

几种结构非概率可靠性模型的比较研究

相对概率可靠性模型和模糊可靠性模型,基于区间分析的结构非概率可靠性模型对数据的要求低,因此在实际工程中对非概率可靠性模型的研究越来越重要.近年来,非概率可靠性理论得到了很好的发展和完善.文中综述了已有的4种主要的非概率可靠性模型,针对线性结构功能函数,分别从度量原理、可靠性指标物理意义、适用范围和结果精度等方面对各可靠性模型进行比较与总结;针对非线性结构功能函数,对各可靠性模型的适用性进行了初步的讨论,从而对非概率可靠性模型有更加全面和深刻的理解,为实际工程中非概率可靠性模型的选取提供重要的理论依据.     

Landweber迭代正则化方法在动态载荷识别中的应用

在载荷识别过程中,由于结构矩阵的病态特性以及测量噪声的影响,常规最小二乘法往往失效,这就是反问题的不适定问题．Landweber迭代正则化方法可以用来解决载荷识别的不适定问题．线性系统的响应可以表示为载荷与单位脉冲响应函数的卷积分,将其在时域内离散后可得到结构振动响应的正问题模型．应用该方法,在一个桥梁模型上进行了仿真试验,仿真结果说明提出的识别方法是有效的,可以得到满足工程要求的稳定近似解.     

非均匀变厚度梁的动力响应的一般解

在本文中提出一个新方法——阶梯折算法来研究在任意载荷下任意非均匀和任意变厚度伯努利-欧拉梁的动力响应问题.研究了自由振动和强迫振动.新方法需要将区间离散为一定数目的元素,每个元素可看作是均匀和等厚度的.因此均匀、等厚度梁的一般解可在每个元素上应用.然后用初参数表示的整个梁的一般解使之满足相邻二元素间的物理和几何连续条件,这样就可以得到解析形式的自由振动的频率方程和解析形式的强迫振动的最终解,它化为求解二元线性代数方程,与离散元素的数目无关.现在的方法可推广应用至任意非均匀及任意变厚度有粘滞性和其他种类的梁以及其他结构元件问题上去.     

Predicting stochastic characteristics of generalized eigenvalues via a novel sensitivity-based probability density evolution method

This paper proposes a novel numerical method for predicting the probability density function of generalized eigenvalues in the mechanical vibration system with consideration of uncertainties in structural parameters. The eigenproblem of structural vibration is presented by first and the sensitivity of generalized eigenvalues with respect to structural parameters can be derived. The probability density evolution method is then developed to capture the probability density function of generalized eigenvalues considering uncertain material properties. Within the proposed method, the probability density evolution equation for the generalized eigenvalue problem is established accounting for the sensitivity of generalized eigenvalues with respect to structural parameters. A new variable which connects generalized eigenvalues to structural parameters is then introduced to simplify the original probability density evolution equation. Next, the simplified probability density evolution equation is solved by using the finite difference method with total variation diminishing schemes. Finally, the probability density function as well as the second-order statistical quantities of generalized eigenvalues can be predicted. Numerical examples demonstrate that the proposed method yields results consistent with Monte-Carlo simulation method within significantly less computation time and the coefficients of variation of uncertain parameters as well as the total number of them have remarkable effects on stochastic characteristics of generalized eigenvalues.     

Cyclic Creep of Polymers and Polymer-Matrix Composites

The paper provides a state-of-the-art review of the current understanding regarding the long-term response of polymer-matrix composites subjected to cyclic loading conditions. Typically, under such conditions, the behavior of polymeric systems is characterized by much higher creep rates than those observed in the cases of static loading. In this paper, research accomplishments in the subject area are discussed. New experimental results are presented regarding the cyclic-creep response of a composite system consisting of a thin-film piezoelectric polymer polyvinylidene fluoride (PVDF) with thin metallic layers deposited on both surfaces of the polymer. This composite was tested under the conditions of tensile static stresses with superimposed sinusoidal oscillations. As a result, considerable acceleration of creep rates has been recorded as the mean stresses, vibration amplitudes, and frequencies of oscillations tended to increase. These effects were observed even within the linear viscoelastic deformation range at room temperature; however, the acceleration of cyclic-creep rates tended to decrease below the freezing temperature. In general, as indicated in the conclusion, the problem of cyclic creep in polymeric systems is far from being well understood and requires further studies.     

A rapid granular chute avalanche impinging on a small fixed obstacle: DEM modeling,experimental validation and exploration of granular stress

Granular flows are constrained by applied stresses. When a granular flow moves rapidly and impinges on an obstacle, the stress is significantly increased along the contact force networks. Granular stresses are still incompletely understood. The aim of this study is to investigate a rapid avalanche of spherical glass beads in an inclined chute with a small fixed semi-cylindrical obstacle by using particle image velocimetry (PIV) technique and discrete element method (DEM). The proposed DEM model produces good agreement with the corresponding avalanche experiment in terms of the velocity profiles. The validated DEM results are then used to explore the internal flow characteristics of a granular avalanche that are not directly observable in experiments, such as the solid fraction, the average coordination number and the granular stress. Rectangular measurement cells, similar to representative volume elements, are developed to determine the spatial variation in stresses for the granular avalanche. The internal flow characteristics of a rapid granular avalanche with and without obstacles are compared. For the unobstructed flow, the normal and shear stresses decrease in the downstream direction because the solid fraction and the average coordination number decrease, resulting from the gravitational acceleration. On the other hand, granular jamming forms in front of the semi-cylindrical obstacle and results in a significant increase in the normal and shear stresses. The unobstructed flow shows slightly anisotropic stress states, giving an earth pressure coefficient of approximately 1.0, whereas the disturbed flow exhibits strongly anisotropic stress states. The simulation results show that the corresponding earth pressure coefficient can be much higher than unity and increases to a maximum value of roughly 5.0. A shear band develops at a distance of roughly twice the particle diameter above the basal surface and a stronger shear band forms in the upstream vicinity of the obstacle.     

Damping of water hammer oscillations – comparison of 3D CFD and 1D calculations using two selected models for pipe friction

Water hammer calculations are important for power plants, drinking water systems and procedural facilities. In most cases, the piping systems are very big and the probability of a resonance between a part of the piping system and a hydraulic oscillation resulting from water hammer is very high. The limiting factors for the amplitudes of the structural stresses and strains are the structural and hydraulic damping. In general, one-dimensional codes based on the method of characteristics with quasi-steady friction models are used to calculate the hydraulic system. This results in too small damping of the pressure oscillation and thus in an overestimation of the structural loads. Two models from the literature for a more physical reproduction of the fluid damping using one-dimensional codes are presented and compared with a quasi-steady pipe friction model. Additionally, a three-dimensional computational fluid dynamics simulation of a water hammer oscillation in a small pipe section including a 90°-bend was carried out. A comparison of the results of the three-dimensional simulation and the one-dimensional calculations with regard to the pressure and friction velocity distributions was performed, the performance of the models was evaluated and the limits of validity were identified. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Load share and finite element stress analysis for double circular-arc helical gears

The authors analyze the tooth surface contact and stresses for double circular-arc helical gear drives. The geometry of such gear drives has been represented by the authors in their previous paper [1]. The proposed approach is based on application of (i) computerized simulation of meshing and contact of loaded gear drives, and (ii) the finite element method. Load share between the neighboring pairs of teeth is based on the analysis of position errors caused by surface mismatch and elastic deformation of teeth. The authors have investigated the conditions of load share under a load and determined the real contact ratio for aligned and misaligned gear drives, respectively. Elastic deformation of teeth and the stress analysis of the double circular-arc helical gears are accomplished by using the finite element method. The finite element models for the pinion and gear are constructed, respectively. Contact pressure is spread over elliptical area. The stress analysis for aligned and misaligned gear drives, respectively, has been performed. The numerical results have been compared with those obtained by other approaches.     

Simulation and Measurements of Rolling Tire Dynamics

The simulation of rolling tires including stationary rolling, modal analysis, excitation with roughness of road surfaces and sound radiation is presented for state of the art industrial tire models. The target of this research, part of the german project “Leiser Straßenverkehr”, is the reduction of trafic noise, whereas the main source, namely the tire/road system, is investigated in contrast to other techniques like sound insulating walls. The needs and methods for the solution of the resulting large scale problems are discussed next to special properties of rotating structures, high frequency behavior of rubber material and approaches for the reduction of computational cost. For the validation of the model measurements of real tires and roads are used. These include shaker tests of the standing tire and acoustics of tires rolling on a drum. The same set–ups are applied to the simulation for the comparison of frequency response functions and sound pressure levels. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Modeling and analysis of distributed electromagnetic oscillators for broadband vibration attenuation and concurrent energy harvesting

Many energy harvesting devices employ dynamics ascribed to the classical vibration absorber. Conventional models suggest that when host structural motion excites the harvesters at resonance, maximum electrical power output is achieved. As the harvesters become inertially substantial relative to the structure, this condition no longer holds since the electro-elastic response of the harvester is coupled to the structural vibration. In this regime, the devices become true vibration absorbers that alter the structural oscillations which may consequently affect energy harvesting capability. Distributions of point oscillators have been considered as broadband vibration control treatments making it natural to consider the potential for energy harvesting devices to serve this end. This paper presents an analysis of distributed single- and two-degree-of-freedom, linear electromagnetic oscillators attached to a harmonically excited panel. The coupled Euler–Lagrange equations of motion are solved and the simultaneous goals of vibration attenuation of the host panel and harvested electrical power are computed for several scenarios. It is found that design parameters optimizing the individual goals occur in relative proximity such that small compromises need to be made in order to achieve both ends reasonably well, particularly in regards to the overall mass added to the structure.