Influence of interfacial friction and specimen configuration in Split Hopkinson Pressure Bar system

Influences of interface friction and specimen configuration on the material dynamic response using split Hopkinson pressure bar (SHPB) experiment are evaluated using nonlinear finite element (FE) analysis. The effect of various friction conditions between specimen and the transmitted/incident bars in SHPB system is investigated for different specimen geometries. Cylindrical and cuboid specimens with one- and four-layered configurations are adopted and the stress states along the specimen are analyzed. Results indicate that the transmitted signal decreases and the reflected signal increases with friction coefficient increasing. Interface friction brings great variation in stress triaxiality and Lode parameters in the SHPB specimen. Experimental tests are also conducted in this study to verify the conclusions made through FE simulations.     

Dynamic deformation behavior of aluminum alloys under high strain rate compressive/tensile loading

Mechanical properties of the materials used for transportations and industrial machinery under high strain rate loading conditions such as seismic loading are required to provide appropriate safety assessment to these mechanical structures. The Split Hopkinson Pressure Bar (SHPB) technique with a special experimental apparatus can be used to obtain the material behavior under high strain rate loading conditions. In this paper, dynamic deformation behaviors of the aluminum alloys such as A12024-T4, A16061T-6 and A17075-T6 under both high strain rate compressive and tensile loading conditions are determined using the SHPB technique.     

变厚度板中水平剪切波的传播特性分析

为研究超声导波在储罐壁板等变壁厚结构中的传播特性,建立了SH波在空间自由边界中的传播模型,基于各向同性弹性介质Navier-Stokes方程,推导了变厚度板中SH波的频散方程,分析了变厚度板中水平剪切波走时t与倾斜角θ间的相互作用关系;通过简谐点源的远场响应并引入板厚与传播位移的非线性关系,得出了变厚度板中SH波的远场响应方程。在此基础上,仿真分析和实验验证了水平剪切波在不同倾斜角变厚度板中的传播特性,结果表明:在变厚度板的薄端激励水平剪切波并沿结构表面传播时,无频散现象,且无波包分离现象;但随着变厚度板倾斜角θ增大,水平剪切波的走时和接收信号幅值均逐渐递减,且呈非线性关系。     

弹性波在高压输电线中的传播特性

采用压电陶瓷设计了一种适用于高压输电线结构健康监测的传感器,分析了该传感器在输电线表面激励弹性波,得到了弹性波在输电线中的传播特性。利用Gabor小波变换计算传感信号到达时间的原理,试验得到了弹性波在输电线中传播的群速度频散曲线。结果表明,在低频段(低于30kHz)时,弹性波在输电线中的传播模态比较简单,适合用于结构健康监测。通过弹性波在输电线中的衰减试验,得到了信号峰值随传播距离的衰减曲线以及激励信号频率与信号峰值之间的关系曲线,得到弹性波在输电线中按照指数规律衰减。     

The effect of deformation on the lateral resolution of atomic force microscopy

A computer model based on the elastic properties of rubber is introduced for the evaluation of the lateral resolution in atomic force microscopy of deformable specimens. The computational results show that, if the full width at half-height can be defined as the lateral resolution, it is continuously improved at greater probe forces, at the expense of a reduced molecular height. In fact, even for a probe that is bigger than the molecule, the real size of the molecule can be 'recovered' at about 25% compression. This result demonstrates that for a better lateral resolution, a greater probe force can be beneficial, provided that the molecule is not moved or damaged and the response remains elastic. Measurements on isolated low-density lipoproteins (LDL) show that with 26% vertical compression, the lateral size measured in atomic force microscopy is only about 72% of the value predicted by a simple convolution, and is only slightly larger (≈ 13%) than the known size of LDL. Therefore, the results on LDL provide a direct support for the conclusions of the computational model.     

Diagnosis of cryogenic pump-motor systems using vibration and current signature analysis

In general, to send out natural gas via a pipeline network across the nation in LNG terminal, high-pressure cryogenic pump supply highly compressed LNG to high-pressure vaporization facilities. The Number of cryogenic pumps determined the send-out amount in LNG receiving terminal. So it is main equipment at LNG production process and should be maintained on best conditions. In this paper, to find out the cause of high vibration at cryogenic pumps-motor system in LNG terminal, vibration spectrum analysis and motor current signature analysis have been performed together. Through the analysis, motor rotor bar problems are estimated by the vibration analysis and confirmed by the current analysis. So, it is demonstrated through the case study in this paper, how performing vibration analysis and current signature analysis together can reliable diagnosis rotor bar problems in pump-motor system.     

海上漂浮式风电机组风波载荷计算与分析

以海上大型漂浮式风电机组三浮桶式支撑结构为对象,考虑风波联合作用,借助叶素-动量理论和线性波理论,联合风载荷和波浪载荷模型构建了风波联合载荷模型。计算过程中,考虑了风电机组不同的运行工况,依据浮桶直径与波长的比值来确定波浪载荷适用的计算模型（Morison理论与绕射理论）;得到了不同工况、不同环境参数和结构参数条件下的载荷结果,分析了风波载荷的变化特征。     

行波超声马达传动机理的研究（一）——运动传递机理及定子中存在弯曲行波的条件

首先基于几何分析法研究了压电行波超声马达的运动传递机理，重点分析了驻波的产生和行波的合成原理，与转子相接触的定子表面质点的椭圆运动。然后基于弹性动力学方法研究了在定子中存在弯曲行波的条件，得出旋转型压电行波超声马达定子中弯曲行波的产生是基于同频和同节线的两个正交弯曲振型的叠加规律，提出了对圆形薄板圆形对称的基本结构要求     

Study of sample temperature compensation in the measurement of soil moisture content

Since the near-infrared (NIR) spectrum is susceptible to sample temperature fluctuations, we investigate the influence of sample temperature on the predictive power of calibration model for soil moisture content (MC) and propose the multi-source information fusion technology based on back propagation neural network (BPNN) to compensate for sample temperature effect. With the discrete wavelet transform (DWT) as the pre-processing method and the least squares support vector machine (LS-SVM) regression as the modeling method, a model at 20 °C to predict MC of the soil samples at other temperatures was established. The results show that except for 20 °C, the root mean square error of prediction (RMSEP) are large. We analyze the predicted results with the dual-factor analysis of variance without duplication and the result shows that the effect of sample temperature on the prediction model for soil MC is significant. A temperature compensation model was then established with combining of soil MC and sample temperature based on BPNN. The predicted results showed that the prediction precision of the model was improved significantly.     

导波雷达物位计在油脂填料式脱臭塔上的应用

本文介绍了导波雷达物位计的工作原理、性能特点以及在油脂填料式脱臭塔上的安装和调试的方法。     

Analysis of thick-walled cylindrical pressure vessels under the effect of cyclic internal pressure and cyclic temperature

A problem common to the pressure vessels' designer is the evaluation of stresses due to the effect of both cyclic temperature and pressure. This paper presents a complete analysis of stresses within the wall of a cylindrical pressure vessel subjected to cyclic internal pressure and temperature. The time-dependent stress distribution is obtained using a numerical model on the basis of the forward finite difference technique. The influence of the working parameters, such as mean pressure and mean temperature, pressure and temperature amplitudes, diameter ratio, etc. on the effective stress is studied. The relation between the mean stress and stress amplitude is obtained for different working conditions. The relation between the working parameters according to Soderberg criteria is presented. An approximate expression for the relation between the working parameters is introduced in a simple and direct form. The results of the approximate solution are found to fit well with the numerical findings.     

The Additive Action of Some Organic Chlorides and Sulfides in the Four-Ball Lubricant Test

When tested by the four-ball extreme-pressure procedure, oil solutions of t-octyl chloride at the 2 percent chlorine level rated approximately equal to oil solutions of di-t-octyl disulfide at the 2 percent sulfur level, and both of these additive blends rated better than n-octyl chloride in oil at the 2 percent chlorine level or di-n-octyl disulfide in oil at the 2 percent sulfur level. n-Octyl chloride and di-n-octyl disulfide in oil at corresponding concentrations of active element were approximately equivalent in additive action. t-Octyl chloride was almost as good at the 1 percent as at the 2 percent chlorine level. Mixtures of di-t-octyl disulfide and t-octyl chloride in oil at the level 1 percent S-1 percent Cl rated approximately twice as well as di-t-octyl disulfide (2 percent S) or t-octyl chloride (2 percent Cl). Some finer points of the action of these additives were investigated by studying time-connected behavior at 50-kg and 100-kg loads. The action of the additives cannot be explained on the basis of their chemical structures only; interactions with the rubbing process in the four-ball machine also must be considered.     

固-流掺杂结构声子晶体中弹性波的缺陷模

为了研究弹性波在固-流掺杂结构声子晶体中缺陷模的特性,推导出了弹性波斜入射固-流掺杂结构声子晶体的转移矩阵。研究了固-流掺杂结构声子晶体中弹性波的透射系数,得到了由于掺杂在禁带的中央出现了一条狭长的缺陷模透射峰的结论。当杂质厚度固定时,缺陷模随入射角的增加向高频方向移动。当入射角固定时,缺陷模的中心频率随杂质厚度的增加近似呈线性减小。     

低阶扭转模态电磁声阵列传感器研制及其在厚壁小径管中的试验研究

管道检测是发电厂热力设备安全的重要问题,由于高温以及检测区域的限制,常规无损检测方法很难满足电站管道检测要求。低阶扭转T(0,1)模态导波,由于其非频散特性,对管道缺陷大范围检测十分有效。为在管道中实现非接触激励T(0,1)模态,设计并研制了一种电磁声阵列传感器。利用所研制的电磁声阵列传感器,实现了厚壁小径管中T(0,1)模态激励和接收。通过优化电磁声阵列传感器各元件间不同连接方式可知,当各元件并联连接时,不仅提高了所激励信号的能量,还抑制了其它模态产生。同时测试了电磁声阵列传感器的频率特性,并对有周向人工缺陷的样管进行检测。试验结果表明,该电磁声阵列传感器可以实现对样管中周向缺陷的检测与准确定位,为在管道中激励接收T(0,1)模态并实现非接触检测缺陷奠定了基础。     

微速差双转子智能动平衡仪中拍振信号动态显示的意义及实现

简述拍振信号动态显示的意义，并从硬件和软件的角度详细讨论拍振信号动态显示的实现方法。     

化学机械抛光过程中护环对硅片表面接触压强分布和宏观轮廓的影响

为了获得单晶硅片化学机械抛光过程中护环对接触压强分布的影响规律,根据有护环化学机械抛光实际出发,建立了抛光过程的接触力学模型和边界条件,利用有限元的方法对有护环抛光接触状态接触压强分布进行了计算和分析,并利用抛光实验对计算获得结果进行了验证;获得了硅片与抛光垫间的接触表面压强分布形态,以及护环几何参数对压强分布的影响规律;结果表明护环抛光接触压强的分布也存在不均匀性,而且在硅片外径邻域内接触压强最大,这些也能导致被加工硅片产生平面度误差和塌边,选择合理地护环几何参量和负载比,可以改善接触压强场分布的均匀性。     

耦合梁中高频抖动的行波分析与主动控制

为研究中高频扰动下耦合梁结构的动力学响应与主动控制,基于Timoshenko梁理论,考虑梁中转动惯量和剪切变形的影响,采用行波方法分别建立梁结构纵向运动、弯曲运动的单元模型与结点散射模型,进而获得耦合梁的行波动力学模型及其精确的中高频抖动响应;引入“功率流”的分析思想,并以此为目标函数,优化得到了最优控制力的大小与相位,然后对结构施加最优控制力,实现耦合梁结构的功率流主动控制。在此基础上,进行数值仿真分析,并与Euler-Bernoulli梁理论计算结果进行对比。结果表明,采用行波方法计算耦合梁结构的动力学响应准确可靠;Timoshenko梁模型较Euler-Bernoulli梁模型在中、高频段更为精确,且更接近工程实际;功率流主动控制可以明显降低耦合梁结构全频域内的抖动,验证了基于行波方法功率流主动控制的正确性与有效性。     

An analysis of flow and screech tone from supersonic axisymmetric jet at the initial stage

The screech tone from jet Mach number 1.18 is numerically calculated from the initial stage. A fourth-order optimized compact scheme and fourth-order Runge-Kutta method are used to solve the 2D axisymmetric Euler equation. Pulse jet problem with Mach number 1.56 is solved to validate the present method. Not only two important components of generating screech tones, shock cell structure and vortices, but also the transient behavior of the screech tone are investigated at the initial stage. Additional time is necessary to generate periodic screech tone after formation of shock cell structures. As time goes on, the location of the vortex generation becomes fixed near the nozzle exit, which is farther downstream initially, and the screech tone becomes periodic. The FFT results of three different periods are compared. It is observed that the component of lower frequency is dominant at the beginning, and the component of the screech tone becomes dominant as time increases. It can be concluded that the screech tones can be also numerically reproduced at the initial stage with the present inviscid method.     

静电分离器中电场和电流体特性试验研究

利用静电分离技术从空气中分离平均直径为2μm的油滴,对小尺度的线—板式静电分离器的电晕放电特性和流型特征进行试验研究,放电电极接高压电源正极。测试在不同的气体流速、油滴浓度条件下分离器的伏安特性曲线。利用高速摄像机对其中的电流体流型特征进行可视化研究,试验测定进口流速为0.2 m/s、0.3 m/s、0.4 m/s,施加电压从0～16 kV条件下电流体流型的变化,得到在不同的施加电压和气体流速下的流型分布图。试验表明,进口流速对分离器的电场影响并不明显,而油滴浓度对电场有很大的影响,在相同的施加电压下电流密度随着油滴浓度的增大而降低。电流体流型的变化取决于进口流速和施加电压的相互作用。得到在不同的描述惯性力和电场力关系的量纲一参数雷诺数和电流体数下5种代表的电流体流型。     

A study of Si-L and O-K ELNES in plant material: SiO2, Ca- and Zn-silicate in Minuartia

The formation of vacuolar precipitates containing silicon and calcium, as well as the accumulation of metal-silicates in cell walls of Minuartia has been investigated by electron microscopy, energy-dispersive X-ray analysis and electron spectroscopic imaging. The bond state of the elements concerned is examined by analysing energy-loss near-edge structures (ELNES), particularly the Si-L_2,3 and the O-K ELNES. Experimental ELNES results are compared with local densities of unoccupied states calculated by molecular orbital methods and results of XANES calculations.