弹性支承滑动轴承－转子系统稳定性的研究

本文研究弹性支承滑动轴承－转子系统的动力稳定性问题，建立了弹性支承滑动轴承－Ｊｅｆｆｃｏｔｔ转子系统的力学模型，采用牛顿延拓法从理论上对该转子轴承系统的动力稳定性进行了分析，讨论弹性支承的刚度对系统稳定性的影响，从而提出提高系统稳定性的有关措施。最后，依据理论分析，利用Ｊｅｆｆｃｏｔｔ转于实验台，作者设计和加工了一副弹性支承器，通过刚性支承和弹性支承两个对比实验，对理论分析的结果进行了验证。实验结果表明，弹性支承能提高转子动力稳定性。     

弹性支承滑动轴承—转子系统稳定性的研究

本文研究弹性支承滑动轴承－转子系统的动力稳定性问题，建立了弹性支承滑动轴承－Ｊｅｆｆｃｏｔｔ转子系统的力学模型，采用牛顿延拓法从理论上对该转子轴承系统的动力稳定性进行了分析，讨论弹性支承的刚度对系统稳定的影响，从而提出提高系统稳定性的有关措施。最后，依据理论分析，利用Ｊｅｆｆｃｏｔｔ转子实验台，作者设计和加工了一副弹性支承器，通过刚性支承和弹性支承两个对比实验，对理论分析的结果进行了验证。实验结果     

考虑刷丝支承刚度的高速引电器转子动力学特性研究

为研究多通道刷丝–滑环接触副中刷丝支承刚度对系统动力学特性的影响，将刷丝简化为欧拉–伯努利悬臂梁，推导了刷丝支承刚度计算的理论公式。建立了滑环胶合细长轴的高速引电器转子系统有限元模型，考虑多通道刷丝支承刚度影响，开展了转子系统动模态数值仿真分析，得到了系统振型图、坎贝尔图及临界转速偏离裕度。研究结果表明，刷丝支承刚度对引电器转子细长轴结构一阶弯曲模态的影响不可忽略。     

关于位移法计算有侧移斜梁的研究

针对用位移法计算有侧移斜梁时遇到的几个问题进行了研究，利用运动学原理对斜 梁位移进行分析，采用力法对几种常见载荷作用下的斜梁进行理论推导，得到了几 个重要结论: 一是斜梁的侧移计算公式，二是一端固定、一端定向支承(支杆与斜梁斜交时)的有侧移单 跨斜梁的转角位移方程、固端弯矩分别与两端固定支承的水平梁的相同，所以计算此类斜梁 时可以按两端固定支承的单跨水平梁处理.     

具有域内支承的中厚板的边界元法分析

本文借助简化的Reissner理论,利用边界元法对具有域内支承的中厚板进行了分析。建立了相应的边界积分方程,导出了各基本解,讨论了域内支承柱对板的支承情况,编制了计算程序并给出部分算例。     

无网格法在点弹性支承矩形薄板横向振动中的应用

基于薄板理论和弹性动力学Hamilton原理的推广,采用无网格伽辽金法,建立了具有有限多个点弹性支承的弹性矩形薄板横向振动的无量纲量运动微分方程,给出了其特征方程。通过求解特征方程,得出了四边简支板的无量纲固有频率随点弹性支承的刚性系数和支承位置的变化曲线,分析了点弹性支承的刚性系数和支承位置对矩形薄板横向振动特性的影响。数值计算结果表明,无网格法求解点弹性支承板横向振动问题是切实可行的。     

大型多支承变刚度回转窑支承载荷分配问题

回转窑是冶金、水泥、耐火材料生产中的核心设备，是一种重载、大扭矩、多支点、静不定运行系统，由于其载荷和刚度分布复杂、各支承存在偏移，作用在它托轮上的支承载荷分配严重不均。本文针对回转窑载荷和刚度分布的特点，建立支承载荷求解的力学模型和线性方程组，导出支承载荷分配与支承偏差的关系式；用该方法对现场回转窑进行计算，得出该窑支承载荷分配的线性公式和一些分析结论，为生产中回转窑的状态分析、优化调控提供依据。     

任意支承条件下连续板系结构的有限板块解法

本文基于薄板小挠度弯曲理论，构造出板元内部解析，边界挠度和边界法向弯矩以带补充项的付氏级数逼近，同时考虑域内多点支承作用的板元位移函数，给出了一处适用于任意支承条件下连续板系结构的有限板块法求解格式。数值计算结果表明：本文的方法具有良好的计算精度和计算效率，适于工程应用。     

浮筏隔振系统功率流特性分析

针对工程实际中浮筏隔振装置，建立了柔性基础上机组多支承弹性浮筏耦合隔振系统动力学普遍模型，提出了子系统动态特性综合分析法，给出了耦合系统动态传递方程及功率流表达式。根据工程中两机组浮筏隔振系统功率流理论计算结果，着重探讨安装频率与支承结构柔性耦合作用及其对隔振效果影响。研究结果表明：合理设计安装频率，可有效控制振动能量传输。     

多跨换热器传热管在静水中的阻尼特性

本文对多跨换热器传热管在静水中的结构阻尼与粘滞阻尼作了分析。通过求解带N—1个同心支承板的管子运动方程,导出计算挤压膜阻尼的公式. 为了验证理论分析结果,对四跨传热管在静水中的挤压膜阻尼进行了实验研究.得出挤压膜阻尼与支承板数、支承板厚度、管子—支承板管孔偏心率、以及管子—支承板间隙之间的关系.在分析实验结果的基础上,得出了计算传热管挤压膜阻尼的改进公式.     

Ultrasonic-shear-wave measurement of known residual stress in aluminum

Ultrasonic-shear-wave time-of-flight measurements were made at a nominal frequency of 4 MHz on both stressed and nonstressed sample disks of 2024 aluminum alloy. The stressed state of the first sample was produced by shrink-fitting a plug and ring to produce a calculated 130-MPa region of uniform compression in the plug, and a concomitant nonuniform tension and compression in the ring. Time-of-flight measurement scans across sample diameters were made using a piezoelectric-shear transducer with a viscous couplant, and repeated using a contactless electromagnetic-acoustic transducer. The ultrasonic results were then compared with elasticity theory, assuming the acoustoelastic relationship between sound velocity and material strain.     

Beam generating and sound field modeling of flexible phased arrays for inspecting complex geometric components

The flexible phased array ultrasonic technology has been developed to tackle the long-term challenge of damage inspection in complex-profiled components. However, due to the influences of curved interfaces, it is sometimes difficult to control the transmission signal of the sound field, thereby creating unreliable transducer performances. This paper proposes the time delay laws for generating steering or focusing beams on curved surfaces (concave, convex, concave/convex) based on the ray acoustics theory. Then, we derive the analytic expression of the entire flexible array ultrasonic field based on the multiple line source model and the time delay laws. Finally, the acoustic pressure distribution of curved structures is simulated to verify the feasibility of the derived principles. The numerical results show that the beams can realize dynamic steering and focusing without distortions or disorientations even when the steering angle reaches 45 degrees. Furthermore, the influences of the specimen surface profile, steering angle and focusing distance on the acoustic field are also analyzed by the axial sound pressure plots. These preliminary results represent an essential step in the development of a nondestructive testing (NDT) system for inspecting components with complex surfaces.     

Nondestructive evaluation of the carbon content in steel

The aim of this work is to propose an experimental method to evaluate the steel carbon content by ultrasound. The sample is immersed in a water tank in order to analyze it under various incidences of sound waves. Longitudinal wave velocities are measured by immersion by using a 5-MHz frequency probe. Transverse wave velocities are measured in a contact mode by using a 4-MHz transverse wave transducer. The attenuation coefficients of ultrasonic longitudinal and transverse waves are deduced from three successive basic echoes through the sample. The effects of some heat treatments on ultrasonic parameters are also studied. The measurement of ultrasonic parameters in steel offers an interesting possibility of tracing the carbon content and, at the same time, provides information on the steel structure and its elasticity.     

THEORETICAL INVESTIGATION ON THE DYNAMIC PERFORMANCE OF CMUT FOR DESIGN OPTIMIZATION

Although many modeling approaches exist for analyzing the behavior of capacitive micro-machined ultrasonic transducers(CMUTs),the relation equation between the design parameters with input and output is still lacking.What there is can only be used to analyze the dynamic performance of CMUT indirectly and qualitatively,such as stiffness and sound pressure.A lumped-parameter theoretical model based on the dynamic theory is proposed in this paper.The relation equations between the design parameters with inputs and outputs are given.The results obtained by the proposed model agree well with those by finite element method(FEM)simulation.The dynamic and static behavior of CMUT can be clearly depicted,which is helpful for design and optimization iterations.This shows that the proposed model makes it easier to optimize the parameters of a CMUT with respect to output and bandwidth directly and to better understand the influence of each parameter.     

Analysis of eigenmodes in a relativistic gas

The eigenmodes of a relativistic gas within a five-, thirteen- and fourteen-field theories are analyzed in the ultra-relativistic, relativistic and non-relativistic regimes. The five-field theory furnishes one non-propagating and two propagating hydrodynamic modes and there appear sound propagation gaps caused by a coupling of thermal and pressure fluctuations at large wavenumbers. Apart from the three hydrodynamic modes of the five-field theory in the fourteen-field theory emerge more three kinetic sound modes, which at small wavenumbers are purely non-propagating diffusive modes. In the thirteen-field theory, there appear the three hydrodynamic of the five-field theory and two kinetic sound modes, which do not propagate for small values of the wavenumber. It is shown that the fourteen- and the thirteen-field theories exhibit no sound propagation gaps, so that these gaps are shortcomings that arise from the five-field theory.     

Determination of correlation functions of turbulent velocity and sound speed fluctuations by means of ultrasonic technique

An experimental study of the propagation of high-frequency acoustic waves through grid-generated turbulence by means of an ultrasound technique is discussed. Experimental data were obtained for ultrasonic wave propagation downstream of heated and non-heated grids in a wind tunnel. A semi-analytical acoustic propagation model that allows the determination of the spatial correlation functions of the flow field is developed based on the classical flowmeter equation and the statistics of the travel time of acoustic waves traveling through the kinematic and thermal turbulence. The basic flowmeter equation is reconsidered in order to take into account sound speed fluctuations and turbulent velocity fluctuations. It allows deriving an integral equation that relates the correlation functions of travel time, sound speed fluctuations and turbulent velocity fluctuations. Experimentally measured travel time statistics of data with and without grid heating are approximated by an exponential function and used to analytically solve the integral equation. The reconstructed correlation functions of the turbulent velocity and sound speed fluctuations are presented. The power spectral density of the turbulent velocity and sound speed fluctuations are calculated.     

The effect of boundary conditions on sound loudness radiated from rectangular plates

This paper describes the effect of boundary conditions on sound loudness radiated from rectangular plates. Based on the Rayleigh integral, the Zwicker’s loudness model and the dynamic response of the plates, the sound loudness radiated from vibrating plates and the effects of simple support, clamped support and free support on sound loudness are separately studied. The effects of boundary conditions on sound intensity level, sound intensity density and critical-band level are also studied, taking the frequency selectivity of human hearing into account. The transformation from sound intensity level to sound loudness radiated from rectangular plates, due to the frequency-selectivity characteristics of human hearing, is also illustrated.     

Study on aerosol agglomeration using the airborne ultrasonic transducer

Acoustic agglomeration technology use high-intensity acoustic field to make aerosol particles collide and condense rapidly. Existing studies have shown that 70%–90% of fine particles can be eliminated within minutes using compression drives and air-jet generators. Currently, there are limitations to the sound sources used. In this paper, an airborne ultrasonic transducer with a resonant frequency of 15 kHz is designed, followed by the corresponding numerical simulation and experiments for the evaluation of the vibration modal and sound pressure field. The sound pressure levels (SPL) of the open space and the agglomeration chamber can reach 150 dB and 156 dB, respectively. The agglomeration effect of water droplets, liquid phase smoke, solid phase smoke and mixed smoke is experimentally investigated, and the light transmittance rapidly increases from 8% to 60% within 4 s, 8 s, 5 s and 6 s, respectively. Agglomeration is also effective in the high-frequency range, and we infer that the acoustic wake effect is the predominant mechanism. The elimination effect is promoted with the increasing of SPL until the corresponding secondary acoustic effect is enhanced. Moreover, the agglomeration rate of higher concentration aerosol is significantly better than that of diluted aerosols in ultrasonic agglomeration process.     

A novel ultrasonic strain gauge for single-sided measurement of a local 3D strain field

A novel method is introduced for the measurement of a 3D strain field by exploiting the interaction between ultrasound waves and geometrical characteristics of the insonified specimen. First, the response of obliquely incident harmonic waves to a deterministic surface roughness is utilized. Analysis of backscattered amplitudes in Bragg diffraction geometry then yields a measure for the in-plane strain field by mapping any shift in angular dependency. Secondly, the analysis of the reflection characteristics of normal incident pulsed waves in frequency domain provides a measure of the out-of-plane normal strain field component, simply by tracking any change in the stimulation condition for a thickness resonance. As such, the developed ultrasonic strain gauge yields an absolute, contactless and single-sided mapping of a local 3D strain field, in which both sample preparation and alignment procedure are needless. Results are presented for cold-rolled DC06 steel samples onto which skin passing of the work rolls is applied. The samples have been mechanically loaded, introducing plastic strain levels ranging from 2 % up to 35 %. The ultrasonically measured strains have been validated with various other strain measurement techniques, including manual micrometer, longitudinal and transverse mechanical extensometer and optical mono- and stereovision digital image correlation. Good agreement has been obtained between the ultrasonically determined strain values and the results of the conventional methods. As the ultrasonic strain gauge provides all three normal strain field components, it has been employed for the extraction of Lankford ratios at different applied longitudinal plastic strain levels, revealing a strain dependent plastic anisotropy of the investigated DC06 steel sheet.     

超声波作用下气泡的非线性振动

Flynn方程在引入泡内气体的压缩性修正后能够更好地描述超声波作用下液体内气泡的非线性振动。我们以此为基础通过数值分析得到了不同初始半径的气泡在同一声场中的振动位移时间图像和相轨迹,发现气泡的运动行为对其初始状态有很强的依赖关系,在频率为26.5 kHz,幅度为1.35 atm的声波作用下,初始半径小于1 μm的气泡作小幅受迫振动,大于200 μm的气泡作小幅准本征振动,不具备空化气泡特征。声场中的小气泡对声波强度变化的反应更为激烈,当增加声强度时,可将一定范围内的小幅受迫振动气泡转化为空化气泡,并且,当驱动声波压力幅值增加时,初始半径越小的气泡的最大位移增加幅度越大。驱动声波频率同样影响气泡的振动。随着声波频率的升高,空化气泡的初始半径取值区间越来越小,空化振荡也越来越弱。本文还通过高速摄影系统对换能器作用于未除气的自来水所引起的变化进行了实验研究,结果表明,超声波作用下液体内的气泡场是一个混合场,场内气泡尺寸呈一定的分布状态,不仅有空化气泡,还有毫米级的大气泡。气泡的运动行为直接影响空化效果。超声空化场是一个复杂的物理场,场内除了有气泡的振动外,还有气泡间的相互吸引、碰撞和结合。