扭转振动超声变幅杆计算及其等效电路

在平面波近似条件下,对几种常用的扭转振动半坡变幅杆(截面极惯性矩变化规律为圆锥、指数及悬链线型)进行了系统的理论分析。导出了变幅杆的等效电路,得出了变幅杆的输入机械阻抗、共振频率方程及振幅放大倍数的数学表达式。文中理论分析及所得结果可作为设计或计算扭转变幅杆的理论基础和依据。     

一种适用于声化学的新型复合超声变幅杆

提出一种新型复合超声变幅杆,该变幅杆总长为一个波长,由五段组成,其中三段为等截面圆柱杆,两段为变截面圆柱杆。给出了该类复合变幅杆的设计方法,并计算了两个实例。结果表明,和普通使用的半波长复合变幅杆相比,该类复合变幅杆具有在不减少甚至增大辐射面积的情况下放大振幅的特点,这对提高整个超声系统的辐射声功率和辐射效率具有积极意义。此类复合变幅杆特别适合在声化学等超声液体处理领域使用。     

A2弯曲振动变幅杆的设计

按照一般的变幅杆设计理论，超声弯曲振动变幅杆的设计将会非常复杂，为满足工程上的需要，我们在本文中给出一种简单的近似有效的弯曲振动变幅杆的设计方法，并以纯弯曲理论来分析其放大倍数，在考虑了转动惯性及剪切形变的影响后，还阐述了更精确的设计理论，通过实验发现实测的变幅杆谐振频率很接近于理论设计值     

A2 弯曲振动变幅杆的设计

按照一般的变幅杆设计理论，超声弯曲振动变幅杆的设计将会非常复杂，为满足工程上的需要，我们在本文中给出一种简单的近似有效的弯曲振动变幅杆的设计方法，并以弯曲理论来分析其放大倍数，在考虑了转动及剪切形变的影响后，还阐述了更精确的设计理论，通过实验发现实测的变幅杆谐振频率很接近于理论设计值。     

超声弯曲振动变幅杆的特性

根据文献 [1]提出的弯曲振动变幅杆的分析方法 ,通过大量数值计算 ,对圆截面指数形、锥形和悬链线形变幅杆弯曲振动的特性进行了研究。研究结果表明 ,变幅杆弯曲振动的频率随其长度增加而降低 ,随其直径增大而升高 ;进一步研究表明 ,尽管变幅杆谐振频率与其直径大小有关 ,但只要变幅杆两端直径比值一定 ,则其谐振频率与尺寸参数间存在一定关系 ,本文用谐振曲线描述了这一关系 ,谐振曲线对变幅杆设计以及复合振动的研究是一个非常重要的工具。最后对几种变幅杆的放大能力进行了比较 ,按从大到小的顺序依次是 :悬链线形、指数形和锥形     

QDFM-125型超声波软管封尾机变幅杆的改进设计

对QDFM-125型超声波封尾机的变幅杆进行研究,发现了其设计缺陷。改进了原有变幅杆的结构,并与原变幅杆进行封口比较。结果表明,改进后的变幅杆传递超声,能量损失减少,工作效率提高。     

矩形横截面耦合振动复合变幅杆的设计

本文研究由一部分变截面杆和一部分定截面杆构成的大尺寸矩形横截面复合变幅杆。文章中引进了变幅杆各轴向的等效弹性常数，并推出了具体表达式，利用表观弹性法探讨了大尺寸矩形变幅杆的耦合振动，得出了变幅杆的共振条件，即频率方程。实验表明，与一维理论的计算结果相比，利用耦合振动理论得出的变幅杆的共振频率更加接近于实测值。     

微超声振动细胞切割系统中变幅杆的分析与设计

针对细胞微超声振动切割系统对超声变幅杆的要求,将等截面圆柱形阶梯变幅杆的一端替换成圆锥形变幅杆构成一种复合圆锥阶梯形变幅杆。由任意变截面杆纵向振动的波动方程出发,推导了复合圆锥阶梯形变幅杆的基本理论参量,设计了超声变幅杆的基本结构,给出其制造尺寸。并应用有限元法对变幅杆进行了模态分析,得到了共振频率和位移节点等重要参数。     

大尺寸矩形截面幂函数复合变幅杆的研究

利用传输矩阵法,计算得到了幂函数复合变幅杆一维纵振动的频率方程,并在此基础上运用表观弹性法分析了大尺寸矩形截面幂函数复合变幅杆,得到了考虑横向耦合振动后的谐振频率方程,最后利用有限元软件ANSYS对三组变幅杆进行了模态分析。结果表明：变幅杆谐振频率的计算值与模拟值符合得很好,与一维理论相比,考虑横向耦合振动的二维理论具有更高的精确度。     

考虑负载影响的阶梯形超声变幅杆动力特性

考虑与加工工件表面高频重复撞击对结构动力特性的影响,基于瞬态波传播理论,研究周期激励下阶梯形超声变幅杆重复撞击加工工件的瞬态动力响应,及负载对变幅杆放大特性的影响。首先,建立阶梯形变幅杆力学模型,采用瞬态波响应法分别对接触过程和分离过程动力控制方程进行求解,得到适用于任意级数的阶梯形变幅杆的特征项传递函数,和重复撞击系统的瞬态响应理论解。以工程中常用的三级阶梯形变幅杆为算例,分析了不同外载频率下变幅杆重复撞击动力特性和负载工件对变幅杆聚能效果的影响,得出考虑加工件撞击产生的瞬态响应下的变幅杆放大系数,小于自由振动空载的设计值。可为精细超声加工变幅杆的设计提供更为精确的理论依据     

阻性负载超声变幅杆振动特性研究

在纵振型变幅杆等效电路的基础上,研究了三类负载超声变幅杆的共振频率与放大系数。得到了阻性负载时,变幅杆频率方程与放大系数的计算式;分别绘制了共振频率及放大系数随负载变化的曲线图,并给出了分析。这将有助于超声变幅杆的研究和设计。     

余弦型扭转振动超声变幅杆的研究

从波动方程出发,对余弦型变幅杆的扭转振动进行了系统探讨。利用传统方法,推导出了"余弦型变幅杆"扭转振动的频率方程和各特性参数表达式,为余弦型扭转振动变幅杆的设计提供了一定的理论依据,对巳有阶梯型、锥型、指数型杆的结果是一个完善。     

余弦形负载超声变幅杆输入阻抗特性的研究

研究余弦形负载超声变幅杆输入阻抗特性。求解了加负载时四种超声变幅杆的输入阻抗,得到加负载时输入阻抗和M"obius变换参数的统一算式。当变幅杆的输入抗分量为零时,计算了余弦形负载变幅杆的纵向振动共振频率方程和放大系数。由输入阻抗的表达式讨论了此类变幅杆的工作稳定性条件和相对阻抗相等点,对余弦形变幅杆的实际应用有一定的参考意义。     

Calculations of Sobol indices for the Gaussian process metamodel

Global sensitivity analysis of complex numerical models can be performed by calculating variance-based importance measures of the input variables, such as the Sobol indices. However, these techniques, requiring a large number of model evaluations, are often unacceptable for time expensive computer codes. A well-known and widely used decision consists in replacing the computer code by a metamodel, predicting the model responses with a negligible computation time and rending straightforward the estimation of Sobol indices. In this paper, we discuss about the Gaussian process model which gives analytical expressions of Sobol indices. Two approaches are studied to compute the Sobol indices: the first based on the predictor of the Gaussian process model and the second based on the global stochastic process model. Comparisons between the two estimates, made on analytical examples, show the superiority of the second approach in terms of convergence and robustness. Moreover, the second approach allows to integrate the modeling error of the Gaussian process model by directly giving some confidence intervals on the Sobol indices. These techniques are finally applied to a real case of hydrogeological modeling.     

Bandwidth from a large excursion of Gaussian noise

Some statistics properties of large excursions of Gaussian processes are presented, along with exact asymptotic formulas for calculating the root-mean-square (RMS) bandwidths of the underlying wideband or narrowband Gaussian processes in terms of the excursion level, height, and duration. The measured trajectory of a large excursion is used to illustrate the method. A somewhat similar phenomenon occurs for the envelope of a narrowband Gaussian process     

Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator

We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.     

Numerical Modelling of 3D Braiding Machine with Variable Paths of the Carriers

This paper presents latest development of a modelling algorithms and simulation results, related to 3D braiding machines with individually driven switches and horn gears. The early developed 3D braiding machines and the current software from the braiding producer covers only rectangular sets of horn gears. Based on complete emulation of the braiding process with the carrier motion, a generalized method for the simulation of any configuration of horn gears with different sizes was developed and reported earlier by the author. In this work, an extension of the algorithms with individually controlled switches is presented. These switches allow production of profiles for textiles reinforced composites with complex cross section, changing during the production. The machine emulation can be coupled with FEM based braiding process simulation and the complete product can be virtually produced and analyzed.     

Vision though afocal instruments: generalized magnification and eye-instrument interaction

In Gaussian optics all observers experience the same magnification, the instrument’s angular magnification, when viewing distant objects though a telescope or other afocal instruments. However, analysis in linear optics shows that this is not necessarily so in the presence of astigmatism. Because astigmatism may distort and rotate images it is appropriate to work with generalized angular magnification represented by a 2 × 2 matrix. An expression is derived for the generalized magnification for an arbitrary eye looking through an arbitrary afocal instrument. With afocal instruments containing astigmatic refracting elements not all eyes experience the same generalized magnification; there is interaction between eye and instrument. Eye-instrument interaction may change as the instrument is rotated about its longitudinal axis, there being no interaction in particular orientations. A simple numerical example is given. For sake of completeness, expressions for generalized magnification are also presented in the case of instruments that are not afocal and objects that are not distant.     

Crossing rate statistics of quadratic transformations of Gaussian processes

The main focus of this paper is the development of a numerical procedure for calculating the average crossing rates of a stochastic process that can be expressed as a sum of a linear and a nonlinear, quadratic transformation of a Gaussian process. Such a representation applies for instance to the motion response of a linear structure subjected to wind loading, when the loading model is proportional to the square of a Gaussian wind velocity process. It is also the standard model for expressing the total wave forces or horizontal excursion responses of a moored floating offshore platform in a random sea way. Knowledge of the crossing rate is a key to many important quantities related to response statistics and reliability applications. It is demonstrated how the proposed numerical procedure can be used for calculating the average crossing rate of the type of response processes considered.