一种线性化圆平板挤压膜力模型

提出一种形式简单的线性化圆平板挤压膜力模型,用最小均方差方法得到等效的线性化挤压膜力的系数,用数值法研究了系统的响应。通过计算不同间隙时线性化系统和非线性系统的响应及其误差,对线性化模型在描述挤压膜系统时的可行性及近似程度做了分析研究。     

一种线性圆平板挤压膜力模型

提出一种形式简单的线性化圆平板挤压膜力模型,用最小均方差方法得到等效的线性化挤压膜力的系数,用数值法研究了系统的响应。通过计算不同间隙时线性化系统和非线性系统的响应及其误差,对线性化模型在描述挤压膜系统时的可行性及近似程度做了分析研究。     

2自由度滞迟振动系统简谐激励响应的等效线性化计算方法研究

研究了2自由度含有粘性阻尼双线性滞迟恢复力振动系统简谐激励下的响应计算问题,将等效线性化计算方法推广至含有滞迟环节的多自由度非线性振动系统,并证明了在首次近似意义上,等效线性化方法与Krybov-Bogoliubov慢变参数法、Fourier级数展开法是等价的,具有相同的计算精度。     

钢丝绳隔振器系统随机响应统计线性化分析

针对钢丝绳隔振器非线性系统随机响应运动方程求解困难、计算效率低的问题,提出钢丝绳隔振器-质量块非线性系统随机响应特性的统计线性化分析方法,并通过等效前后数值仿真进行了有效性验证,同时计算位移传递率评估钢丝绳隔振器的隔振效果.结果表明,统计线性化分析方法和数值仿真所得系统的随机响应曲线一致,验证了统计线性化分析钢丝绳隔振器系统随机响应特性的有效性和准确性,且分析速度远远高于数值仿真,显著提高了非线性隔振系统的设计效率.     

基于Shaw不变流形的双层金属橡胶隔振系统振动响应分析

多自由度非线性系统求解是困扰其推广使用的难题,为解决多自由度金属橡胶非线性隔振系统特性分析与响应计算问题,采用基于Shaw不变流行定义的非线性模态理论来求解双层金属橡胶隔振系统的振动响应。首先基于金属橡胶双折线本构关系模型建立了双层金属橡胶隔振系统的力学模型,并对金属橡胶迟滞环节进行了等效线性化,推导了隔振系统的运动微分方程;然后依据Shaw不变流行的定义,提出了能使非线性模态理论成立的基本假设,推导了该系统的非线性模态方程,并指出了用非线性模态叠加法求解的过程;最后分别用该方法与Runge-Kutta数值计算方法求解了算例,并将结果进行对比,说明了以非线性模态叠加法求解两自由度金属橡胶隔振系统响应的可行性,尽管该方法尚不能十分精确,但在多自由度非线性系统求解没有较好的办法的现状下,为解决多自由度金属橡胶振动系统响应计算问题打下了基础,该方法对多自由度非线性系统的求解具有重要的意义。     

共振运输机与共振筛的动力学特性及改善其工作性能的措施(续)

(三)非线性共振机械的精确计算及最大速度与加速度的求法非线性共振机械的几种近似计算方法,如等效一次谐波法、最小平方矩法、卡辽金法等等效线性化方法,它们都不能反应振动曲线的实际形状。为了计算机件上的动应力,用等效线性化所求得的振幅来计算加速度,进而计算机件的动应力,往往会有较大的误差。下面讨论用分段积分法来计算弹性力为折线变化的非线性振动机。     

含金属橡胶的双层隔振系统简谐激励响应计算方法研究

针对目前含金属橡胶的双层隔振系统简谐激励响应算法推导过程复杂、求解困难的现状,提出了基于多项式动态模型的等效线性化方法。首先引入多项式模型对金属橡胶的动态力学特性进行了描述,并对不同频率下隔振系统运动方程中的非线性刚度、阻尼进行等效线性化处理,然后求解方程获得系统在相应频率下的振幅,最后由不同频率的振幅组成幅频特性曲线。通过算例,将利用上述方法得到的结果与试验数据进行了对比,证明了多项式模型等效线性化方法对于含金属橡胶的双层隔振系统简谐激励响应计算问题的适用性、简便性和准确性。     

基于恒位移测试的转子系统非线性支承刚度参数辨识研究

采用基于正弦扫频技术的恒位移测试方法来获取转子支承系统在一系列恒定位移幅值响应下的频响函数,并辨识转子支承的非线性刚度参数。首先对转子支承系统进行两端支承状态下的模态分析,得到转子系统在线性支承条件下的模态;然后采用正弦激励进行仿真测试,对转子支承进行不同水平的恒位移测试,通过模态分析得到不同响应水平下的模态参数,建立等效非线性参数与响应之间的关系,再结合等效线性化理论,识别非线性刚度参数。     

五自由度随机参数结构车辆的振动响应分析

为了研究路面不平度产生的随机激励对随机结构参数非线性车辆系统的振动响应的影响,建立了随机结构参数的五自由度非线性车辆模型,将模型参数均认为是随机变量,在模型轮胎和车身之间存在非线性弹簧的前提下,来研究模型在随机激励下的随机振动响应。将路面的不平整度引起的对车辆的激励看作是白噪声过程来建立力学模型。先以能量差法等效线性化处理非线性车辆系统,然后求解李雅普诺夫方程来获得平稳随机振动响应协方差矩阵,通过多次迭代得到稳定的等效线性车辆系统参数。算例计算结果表明,方法可以高效和高精度的求解非线性系统在随机过程激励下的响应。     

直线式压缩机用谐振弹簧的刚度设计

谐振弹簧刚度是直线式压缩机高效运行的关键技术参数,不仅与压缩机驱动系统的激励频率有关,而且还与缸内气体的弹性有关.本文提出了一种非线性气体作用力线性化新方法--描述函数法,推导了缸内气体等效刚度、气体等效阻尼以及气体等效静作用力等表达式,并在此基础上设计谐振弹簧的刚度.理论研究表明:与传统的简单线性化方法对非线性气体作用力进行线性化相比较,描述函数法具有很高的精度.     

Statistical Linearization on 2 DOFs Hydropneumatic Suspension with Asymmetric Non-linear Stiffness

Most references on hydropneumatic suspension analysis regard it as harden Duffing spring and take the white noise as the system input, which is quite different from real physical model. It will introdu...     

Optimization of a structure with contact conditions using equivalent loads

Engineering structures consist of various components, and the components interact with each other through contact. Engineers tend to consider the interaction in analysis and design. Interactions of the components have nonlinearity because of the friction force and boundary conditions. Nonlinear analysis has been developed to accommodate the contact condition. However, structural optimization using nonlinear analysis is fairly expensive, and sensitivity information is difficult to calculate. Therefore, an efficient optimization method using nonlinear analysis is needed to consider the contact condition in design. Nonlinear Response Optimization using Equivalent Loads (NROEL) has been proposed for nonlinear response structural optimization. The method was originally developed for optimization problems considering geometric/material nonlinearities. The method is modified to consider the contact nonlinearity in this research. Equivalent loads are defined as the loads for linear analysis, which generate the same response field as that of nonlinear analysis. A nonlinear response optimization problem is converted to linear response optimization with equivalent loads. The modified NROEL is verified through three examples with contact conditions. Three structural examples using the finite element method are demonstrated. They are shape optimization with stress constraints, size optimization with stress/displacement constraints and topology optimization. Reasonable results are obtained in the optimization process.     

A new digital background calibration for redundant radix-4 pipelined ADCs by modeling of adaptive filter for linear and nonlinear errors

In this paper a new digital background correction and calibration technique for redundant multi-bit pipeline stages is presented. In this method output voltage of each stage in converter is defined as sum of the ideal product and error signal, which error voltage include of linear non-ideal section or first order error and nonlinearity undesired signal or third order error. Linear error is formed by capacitor mismatch, op-amp offset, comparator offset and finite op-amp gain effects. Nonlinear error is deformed the output voltage depend on the nonlinear results of open loop residue amplifier. Correction begins with separately calculation and cancelation of the nonlinear and linear errors respectively. For calibration of each stage at first step, the nonlinear effects in digital output of backend ADC is eliminated and then by digital modeling of first order analog error the influence of this unfavorable signal is diminished from digital equivalent of input voltage. Therefore for cancelation of non-ideal impairment in each stage a digital filter consist of linear and nonlinear channel in digital domain is designed. The first order and third order coefficients of designed digital function are unknown and should by a pertinent method be estimated simultaneously. Adaptive filter are best choose for this method. Simulation results show that INL/DNL parameters of 14-bit radix-4 pipelined converter are improved from 17LSB/3LSB to 0.45LSB/0.41LSB after calibration. The SNDR/SFDR parameters are increased from 30 dB/36 dB to 83 dB/90 dB.     

Optimization of the End Effect of Hilbert-Huang transform (HHT)

In fault diagnosis of rotating machinery, Hilbert-Huang transform(HHT) is often used to extract the fault characteristic signal and analyze decomposition results in time-frequency domain. However, end effect occurs in HHT, which leads to a series of problems such as modal aliasing and false IMF(Intrinsic Mode Function). To counter such problems in HHT, a new method is put forward to process signal by combining the generalized regression neural network(GRNN) with the boundary local characteristic-scale continuation(BLCC).Firstly, the improved EMD(Empirical Mode Decomposition) method is used to inhibit the end effect problem that appeared in conventional EMD. Secondly, the generated IMF components are used in HHT. Simulation and measurement experiment for the cases of time domain,frequency domain and related parameters of HilbertHuang spectrum show that the method described here can restrain the end effect compared with the results obtained through mirror continuation, as the absolute percentage of the maximum mean of the beginning end point offset and the terminal point offset are reduced from 30.113% and27.603% to 0.510% and 6.039% respectively, thus reducing the modal aliasing, and eliminating the false IMF components of HHT. The proposed method can effectively inhibit end effect, reduce modal aliasing and false IMF components, and show the real structure of signal components accurately.     

解非线性方程组的一元化方法

提出一种求解非线性且的一元化方法,该方法可以将ｍ元非线性方程组转化为之有相同解的ｍ个一元方程,从而使难以求解的非一方程组变成很求解地一元方程。该方法收敛速度快,计算精度高,且不易发散。经过大量表明,许多用拟牛顿迭代示、梯度法、下降法等传统方法难以求解且易发散或收敛速度是的非线性方程组,采用本文方法都可以容易持求得它们的解。在此基础上平常还提出了多元二分法,它作为一元化方法的一个特例,非常适用于求解     

Nonlinear ultrasonic techniques for nondestructive assessment of micro damage in material: A review

The nondestructive assessment of the damage that occurs in components during service plays a key role for condition monitoring and residual life estimation of in-service components/structures. Ultrasound has been widely utilized for this; however most of these conventional methods using ultrasonic characteristics in the linear elastic region are only sensitive to gross defects but much less sensitive to micro-damage. Recently, the nonlinear ultrasonic technique, which uses nonlinear ultrasonic behavior such as higher-harmonic generation, subharmonic generation, nonlinear resonance, or mixed frequency response, has been studied as a positive method for overcoming this limitation. In this paper, overall progress in this technique is reviewed with the brief introduction of basic principle in the application of each nonlinear ultrasonic phenomenon.     

外载荷作用下火箭发动机法兰连接系统的受力与变形分析

法兰连接系统在火箭发动机上得到了广泛的使用。将螺栓、O型圈和法兰环作为一个整体,应用弹性理论,提出了在外载荷作用下各元件的受力与变形的计算方法。算例的计算结果表明,本文提出的计算方法比等效压力法更接近真实情况。     

2D curve offset algorithm for pockets with islands using a vertex offset

An offset edge algorithm is a common method of creating contour-parallel paths that has been widely studied. The method includes approaches such as pair-wise intersection and Voronoi diagrams. The method proposed in this paper is unlike these approaches in that it determines an offset algorithm via the offset vertex. In addition, the proposed method differs from common approaches because: (1) the offset vertices are computed based on bisectors, (2) the validity of combining the direction and position checking for each offset edge is the main point of the proposed method; (3) an efficient algorithm is constructed to connect all offset edges simultaneously to generate raw offset lines without local invalid loops, and (4) an offset-distance check is performed to remove the global invalid loops from the raw offset lines as well as the interference loops in joining boundaries and multiple islands. The proposed method was verified with various slice contour shapes, with or without islands, and good results were obtained with significant reductions in the calculation time.     

反射法测量固体材料的非线性系数研究

基于准线性近似理论研究有限幅值波的反射基波和二次谐波声场特性,采用多元高斯声束将其表征为平面波解、衍射项和衰减项组合的形式,推导出超声反射法测量固体纵波非线性系数的计算模型。对经垂直入射自由界面的反射二次谐波进行模拟分析,结果显示,尽管入射二次谐波的反射波与新产生的二次谐波相位相反导致总的反射二次谐波减弱,但当试块厚度大于1/2倍瑞利距离时,探头接受到的反射二次谐波可用于固体材料纵波非线性系数的有效测量。设计并开展了6061铝的纵波非线性系数测量试验,结果表明当考虑反射、衍射修正和衰减补偿后,反射法测得的纵波非线性系数值与透射法的测量结果相近,但相比透射法,反射法具有试验要求低、限制条件少等优势,为固体材料纵波非线性系数测量的实际应用提供了一种有效方法。