基于正交试验和神经网络的液压杆稳定性研究

以Euler公式为基础,发现动力猫道液压杆的稳定性与其缺陷的形状、面积、深度及位置有关.通过对液压杆屈曲载荷的模拟计算,运用正交试验法分析缺陷的形状、面积、深度及位置对液压杆屈曲载荷的影响.研究结果表明:缺陷的面积、位置和深度对液压杆稳定性具有显著影响,其发生不显著情况的概率分别为0.007,0.021,0.008;缺...     

连杆衬套内表面磨损的正交试验研究

在连杆衬套内表面磨损的试验研究中,分别选取间隙值、载荷和转速作为试验因子。用正交试验法进行摩擦磨损试验,并用极差分析法分析了试验结果。结果表明：对连杆衬套内表面磨损影响主次顺序为转速、载荷、间隙值。从中得到了连杆衬套内表面最大磨损量和最小磨损量的工况。     

曲柄轴净扭矩趋近直线形态的抽油机传动机构研究

普通电动机输出扭矩基本恒定,而抽油机曲柄轴净扭矩是交变载荷,两者的载荷特性无法达到"柔性"匹配,导致抽油机运行效率低下、能耗增高。利用游梁结构和导杆机构设计的游梁式六杆机构,实现了曲柄轴净扭矩曲线趋近于直线形态,提高了电动机的功率利用率,实现了抽油机节能降耗。根据设计方案,建立游梁式六杆机构运动和动力学模型,分析影响曲柄轴净扭矩曲线形态的主要因素,并以MATLAB优化工具箱为平台,对设计方案进行全参数优化设计,以实际载荷工况对游梁式六杆机构抽油机节能效果进行对比分析。     

The influence of the magnetoelastic effect on the hysteretic properties of medium-carbon steel during uniaxial loading

Hysteretic magnetic properties and longitudinal magnetostriction of planar specimens of air-hardened 45 steel were measured as functions of elastic tensile stresses along and perpendicular to the applied loading using a closed magnetic circuit and attachable transducers. Parameters that exhibit monotonic variations with increasing elastic tensile stresses, were found. It was shown that the maxima that were observed in the dependences of residual inductance and relative maximum magnetic permeability on applied stresses, as well as the minima that were observed in the dependences of the coercive force and demagnetizing current of an attachable electromagnet as measured with a sensor arranged along the tension axis on applied stresses, are related to the behavior of the magnetostriction curves of the steel under study.     

A dark-line two-dimensional magneto-optical trap of (85)Rb atoms with high optical depth

We describe the apparatus of a dark-line two-dimensional (2D) magneto-optical trap (MOT) of (85)Rb cold atoms with high optical depth (OD). Different from the conventional configuration, two (of three) pairs of trapping laser beams in our 2D MOT setup do not follow the symmetry axes of the quadrupole magnetic field: they are aligned with 45° angles to the longitudinal axis. Two orthogonal repumping laser beams have a dark-line volume in the longitudinal axis at their cross over. With a total trapping laser power of 40 mW and repumping laser power of 18 mW, we obtain an atomic OD up to 160 in an electromagnetically induced transparency (EIT) scheme, which corresponds to an atomic-density-length product NL = 2.05 × 10(15) m(-2). In a closed two-state system, the OD can become as large as more than 600. Our 2D MOT configuration allows full optical access of the atoms in its longitudinal direction without interfering with the trapping and repumping laser beams spatially. Moreover, the zero magnetic field along the longitudinal axis allows the cold atoms maintain a long ground-state coherence time without switching off the MOT magnetic field, which makes it possible to operate the MOT at a high repetition rate and a high duty cycle. Our 2D MOT is ideal for atomic-ensemble-based quantum optics applications, such as EIT, entangled photon pair generation, optical quantum memory, and quantum information processing.     

Mid-infrared scanning near-field optical microscope resolves 30 nm

We explore the performance of a scanning near-field infrared microscope, which works by scattering tightly focused CO2 laser radiation (lambda = 10 microm) from the apex of a metallized atomic force microscope tip. The infrared images of test samples prove a spatial resolution of 30 nm and are free of topographical and inertial artefacts, thus they should be of great interest for practical applications. We also observe that the infrared contrast vanishes when the input beam polarization is orthogonal to the tip axis, in accordance with theoretical expectations for a mechanism of longitudinal field interaction.     

Facile characterization of ripple domains on exfoliated graphene

Ripples in graphene monolayers deposited on SiO(2)∕Si wafer substrates were recently shown to give rise to friction anisotropy. High friction appears when the AFM tip slides in a direction perpendicular to the ripple crests and low friction when parallel. The direction of the ripple crest is, however, hard to determine as it is not visible in topographic images and requires elaborate measurements of friction as a function of angle. Here we report a simple method to characterize ripple crests by measuring the cantilever torsion signal while scanning in the non-conventional longitudinal direction (i.e., along the cantilever axis, as opposed to the usual friction measurement). The longitudinal torsion signal provides a much clearer ripple domain contrast than the conventional friction signal, while both signals show respective rotation angle dependences that can be explained using the torsion component of the normal reaction force exerted by the graphene ripples. We can also determine the ripple direction by comparing the contrast in torsion images obtained in longitudinal and lateral scans without sample rotation or complicated normalization.     

On the load distribution of thin-walled beams subjected to bending with respect to the cross-section distortion

The paper deals with the estimation of the load distribution under which distortion of the cross-sections of thin-walled beams subjected to bending cannot occur. It is assumed that beam walls are hinged along their longitudinal edges. Beams with closed and open rectangular cross-sections, with three or two cells, with two or one axis of symmetry are considered. It is shown that the problem can be treated by two equivalent beams, defined by the shear flow zero points of the beam with rigid cross-section. The beam load must be distributed in the plane of beam walls, proportionally to the cross-section moments of inertia of the equivalent beams. Some illustrative examples are given.     

Three-dimensional measurement of intervertebral kinematics in vitro using optical motion analysis

Measurement of the stiffness of spinal motion segments is widely used for evaluating the stability of spinal implant constructs. A three-dimensional motion analysis technique has been developed that allows accurate measurement of the relative movement of the vertebral bodies about a well-defined anatomical axis system. The position of marker clusters on each vertebra is tracked using digital infrared cameras (Qualisys AB, Gothenburg). Landmarks are identified using a marked pointer, and an anatomical coordinate system is defined for each vertebra. The transformation relating the upper and lower vertebrae is calculated, using the joint coordinate system approach of Grood and Suntay to find the rotations and translations in each anatomical plane. The stiffness of vertebrectomy constructs was investigated using a Synex vertebral body replacement and an anterior rod with one or two screws in each vertebral body, with or without damage to the posterior longitudinal ligament (PLL). A moment of 2 N m was applied about each anatomical axis, and the range of motion about each axis was calculated. The range of motion in flexion-extension and lateral bending was significantly greater with only one screw. When the PLL was cut, there was no significant increase in the range of motion.     

Dynamic behavior analysis of reciprocating compressor with subsidence fault considering flexible piston rod

Subsidence wear is inevitable in a reciprocating compressor system, but how to induce body vibration is not clear. We investigated the dynamic behavior of a reciprocating compressor system with subsidence fault considering a flexible piston rod. The flexible piston rod was modeled as a cantilever beam. The dynamic model, in which the influence of the subsidence size, variational cylinder pressure, impact effects and piston rod flexibility are taken into account, was established. Influences of the four parameters including subsidence size, vertical force of flexible piston rod, cylinder pressure and crankshaft speed were analyzed in the dynamic response. Numerical results reveal that with the change of the four parameters, the existence of subsidence fault has a significant effect on the displacement, velocity and acceleration of the crosshead in the transverse direction, but only conspicuously affects the acceleration in the longitudinal direction. In addition to cylinder pressure, the larger the values of the other three parameters, the greater the influences. The cylinder pressure is a time-varying working load. Not only the cylinder pressure but also the open/close time of the valves and change rate of the pressure all affect the dynamic behavior of the system with subsidence. Meanwhile, the change in the vertical force of the flexible piston rod has a remarkable effect on the jump position of the crosshead, but the effect of other parameters is not obvious. In addition, the changes of parameters produce obvious influences on the impact force and the impact range of the crosshead. The stability of the reciprocating compressor system was studied using Poincaré portraits method. The result shows that the system with subsidence fault has chaotic behavior.     

高频纵向超声导波在埋于无限大介质中钢杆的传播特性

从理论上分析高频纵向超声导波在埋于无限大介质中钢杆传播的特性.根据在杆状波导中传播的超声波具有频散现象及多模态特征,选择特定频率下的单音频信号激励超声导波,使其衰减最小,能传播较长距离;能量速度最大,最先到达,从而可与其他速度较慢的模态相区别.说明此频率下的纵向模态可用来对埋于介质中的钢杆进行检测.同时建立试验系统,对直径22 mm、长度1 m的埋于水泥中的钢杆进行检测,并对结果进行时频分析,试验结果与理论分析相吻合.     

变频游梁式抽油系统运行参数的优化设计与性能仿真*

综合考虑电动机端电压频率的实时变化以及电动机负载扭矩波动对电动机瞬时转速的影响,建立了变频控制游梁式抽油系统曲柄运动规律、抽油杆柱纵向振动规律与系统动态参数的仿真模型。将抽汲参数、平衡装置参数、频率函数、电动机输出轴皮带轮转动惯量等系统运行参数作为优化设计变量,在保证油井产量不变、抽油机承载能力、抽油杆柱强度、平衡度和上下冲程时间分配等约束条件的基础上,以系统输入功率最低作为优化设计的目标函数,建立了变频游梁式抽油系统运行参数优化设计的数学模型。仿真与优化结果表明：① 在抽汲参数一定的条件下,优化实时频率可以显著改善游梁式抽油系统的动力性,具有明显的节电效果;② 优化电动机输出轴皮带轮转动惯量可以降低电动机输出功率的幅值与波动程度,进一步提高变频控制游梁式抽油系统的节电效果;③ 综合优化抽汲参数、平衡装置参数、频率函数与电动机输出轴皮带轮转动惯量可以显著改善系统的动力性能,降低系统能耗。     

The three-point bending of Y-frame and corrugated core sandwich beams

Sandwich beams comprising Y-frame and corrugated cores have been manufactured by assembling and brazing together pre-folded AISI type 304 stainless steel sheets. The longitudinal axis of the cores coincides with the axis of the beams. The quasi-static three-point bending response of both simply supported and clamped beams is measured along with the indentation response of the beams placed on a rigid foundation. The investigation reveals that the initial collapse strength of the beams is governed by the indentation of the Y-frame or corrugated core for all beam geometries considered here. The simply supported beams have a softening response beyond the initial peak load while the clamped beams display a hardening response due to the longitudinal stretching of the face-sheets. The experimental investigation reveals that sandwich beams with Y-frame or corrugated cores have comparable responses for each of the loading situations considered. Additional insight into the deformation modes is obtained by three-dimensional finite element (FE) calculations.     

Mid-infrared scanning near-field optical microscope resolves 30 nm

We explore the performance of a scanning near-field infrared microscope, which works by scattering tightly focused CO₂ laser radiation (λ = 10  μ m) from the apex of a metallized atomic force microscope tip. The infrared images of test samples prove a spatial resolution of 30 nm and are free of topographical and inertial artefacts, thus they should be of great interest for practical applications. We also observe that the infrared contrast vanishes when the input beam polarization is orthogonal to the tip axis, in accordance with theoretical expectations for a mechanism of longitudinal field interaction.     

The elastic stability of a thin cantilever beam under an articulated tip force—I: Statics analysis

Previous work on the buckling of thin elastic cantilever beams when subjected to tip forces applied by means of an articulated rod is here extended to cases when the axis of the rod is directed at any angle to the beam axis. The system is typical of engineering situations in which mechanical control circuits involve a bellcrank lever connected to an articulated rod, the remote end of which is loaded by a tube directionally guided in rollers. The function of the articulated rod is to permit geometric changes to take place in the mechanical system.A numerical solution is provided to the differential equation system by finite-difference approximations. The resulting equations are of a sufficiently simple form as to permit evaluation of buckling forces by desk calculation; alternatively a computer adaptation can be made.The results of the analysis are verified by an experimental investigation.     

Vibration from a shaft-bearing-plate system due to an axial excitation of helical gears

In this paper, a simplified model is studied to predict analytically the vibration from the helical gear system due to an axial excitation of helical gears. The simplified model describes gear, shaft, bearing, and housing. In order to obtain the axial force of helical gears, the mesh stiffness is calculated in the load deflection relation. The axial force is obtained from the solution of the equation of motion, using the mesh stiffness. It is used as a longitudinal excitation of the shaft, which in turn drives the gear housing through the bearing. In this study, the shaft is modeled as a rod, while the bearing is modeled as a parallel spring and damper only supporting longitudinal forces. The gear housing is modeled as a clamped circular plate with viscous damping. For the modeling of this system, transfer matrices for the rod and bearing are used, using a spectral method with four pole parameters. The model is validated by finite element analysis. Using the model, parameter studies are carried out. As a result, the linearized dynamic shaft force due to the gear excitation in the frequency domain was proposed. Out-of-plan displacement from the forced vibrating circular plate and the renewed mode normalization constant of the circular plate were also proposed. In order to control the axial vibration of the helical gear system, the plate was more important than the shaft and the bearing. Finally, the effect of the dominant design parameters for the gear system can be investigated by this model.     

The elastic stability of a thin cantilever beam under an articulated tip force—II: Kinetic analysis

Previous work on the buckling of thin elastic cantilever beams when subjected to tip forces applied by means of an articulated rod is here extended to cases when the axis of the rod is directed at any angle to the beam axis. The system is typical of engineering situations in which mechanical control circuits involve a bellcrank lever connected to an articulated rod, the remote end of which is loaded by a tube directionally guided in rollers. The function of the articulated rod is to permit geometric changes to take place in the mechanical system.A numerical solution is provided to the differential equation system by finite-difference approximations. The resulting equations are of a sufficiently simple form as to permit evaluation of buckling forces by desk calculation; alternatively a computer adaptation can be made.The results of the analysis are verified by an experimental investigation.     

线性缓冲材料对质量块撞击下的弹性杆动态屈曲影响研究

针对刚性质量块撞击情况,对弹性直杆在线性缓冲材料防护下的动态屈曲进行分析,得到撞击条件下杆体屈曲发生的临界弹簧刚度。以杆体整个长度发生轴向应变的最小弹性屈曲载荷为判据,分析了临界弹簧刚度与载荷作用时间、载荷幅值、缓冲材料及杆体长度的关系,以及缓冲材料位置对于杆体屈曲防护的影响等。结果表明：撞击初速和刚性块质量是引起临界弹簧刚度改变的两个因素,缓冲材料的安放位置在一定条件下影响着弹性杆屈曲防护。所得结论对于在刚性质量块作用下弹性直杆的动态屈曲防护问题提供了一定的理论依据。     

基于有限元法的柴油机连杆强度分析研究

采用有限元接触分析的方法,利用ANSYS有限元分析软件对某型柴油机连杆进行了疲劳强度分析。根据连杆的实际工作状况,建立了按多体接触的三维模型,模拟了连杆零部件之间的接触;根据连杆的受载情况,分别就连杆承受的最大压力和最大拉力两种工况计算了连杆工作载荷,并利用APDL语言编程,将载荷以油膜压力分布的方式施加到连杆的轴瓦和衬套上。通过有限元的方法,基于接触理论对连杆进行了结构强度计算分析。实践证明,该方法能有效地指导连杆的设计工作。     

High-load, squeeze action linear bearings with beam deflection

The literature provides little information on high-speed, high-normal-load, plain linear bearings, although the case for two rigid surfaces in relative linear motion can readily be solved by assuming squeeze action resistance. A new genus of internal combustion engines based on the Stiller-Smith mechanism incorporates connecting rods constrained by linear bearings, with the central normal load on the rod restricted by an oil film. A general analysis takes into account the bending of the rod, when the distributed oil film pressure resists the distributed load on the elastic rod. Design charts result that yield the dimensionless velocity at which the rod sinks in the oil as a function of the dimensionless load and the bearing clearance, and predict the deflection of the beam. The rod clearance history simulations for the Stiller-Smith engine compare favourably with computations for the rigid beam, confirming the analysis technique.