Transverse free vibration analysis of a tapered Timoshenko beam on visco-Pasternak foundations using the interpolating matrix method

The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the eff ects of the Winkler coeffi cient, Pasternak coeffi cient and damping coeffi cient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary diff erential equations with variable coeffi cients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verifi ed through two numerical examples. The infl uences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with diff erent taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam.

Study on tapered crossed subwavelength gratings by Fourier modal method

Fourier modal method incorporating staircase approximation is used to study tapered crossed subwavelength gratings in this paper. Three intuitive formulations of eigenvalue functions originating from the prototype are presented, and their convergences are compared through numerical calculation. One of them is found to be suitable in modeling the diffraction efficiency of the circular tapered crossed subwavelength gratings without high absorption, and staircase approximation is further proven valid for non-highly-absorptive tapered gratings. This approach is used to simulate the ＂moth-eye＂ antireflection surface on silicon, and the numerical result agrees well with the experimental one.

基于Slepian序列信号字典的目标频段瞬态信号检测方法

提出一种基于Slepian序列信号字典的目标频段瞬态信号检测方法,该方法只关注目标频段的能量信息,是一种高效率的检测方式。首先,选取标准正交的Slepian序列组成信号字典,该字典能够表征目标频段内信号特征;然后,通过判断被观测信号样点与字典的匹配程度实现检测。对比实验表明,该方法的计算效率比短时傅里叶变换提升92%以上,比离散小波变换提升71%以上,比加窗Wigner-Ville分布提升35%以上。仿真实验使用时域稀疏的脉冲调制信号进行验证,结果表明了该检测方法的有效性。

圆锥滚子轴承套圈辗扩成形有限元模拟

环件辗扩是轴承套圈的主要成形方法,加工质量直接影响轴承的使用性能。以圆锥滚子轴承为例,基于DEFORM建立套圈径向辗扩有限元模型,通过试验验证了模型的正确性,并分析了初始辗扩温度、芯辊进给速度和主动辊转速对套圈等效应变和温度的影响,结果表明:初始辗扩温度、芯辊进给速度增大,套圈等效应变减小;主动辊转速增大会使套圈等效应变增加;芯辊进给速度和主动辊转速增大,套圈温度升高且温度分布更均匀。

考虑风载特征的风电机组主轴承载荷谱编制方法

针对风电机组主轴承载荷波动大且随机性强,传统雨流外推法得到的载荷谱精度不能保证的问题,提出了一种考虑风载特征的风电机组主轴承载荷谱编制方法,采用小波包分解及长短期记忆网络进行考虑风载特征的载荷外推。与雨流外推法得到的载荷谱以及载荷趋势进行对比发现,在雨流外推法得到的幅值极大值范围内,2种方法结果基本一致,且该方法可以考虑风载特征,可更好地实现载荷外推,优化载荷谱的编制。

基于激光测量的螺纹廓形数据降噪处理方法

石油锥管螺纹在石油行业不仅起到传递扭矩的作用,还有良好的密封性,因此对加工完成的石油锥管螺纹的测量精度要求也越来越高。提出以SCK230型数控石油锥管螺纹修复车床为载体,搭载NC50型石油锥管螺纹廓形参数在机测量系统,由线激光位移传感器获取石油锥管螺纹的廓形数据。为了准确提取线激光位移传感器采集数据的有效特征,充分发挥变分模态分解算法在信号降噪中的优势,利用蜣螂优化算法优化变分模态分解算法对采集的数据进行降噪处理。实验数据表明,本方法具有良好的降噪效果,能够有效地采集石油锥管螺纹廓形的真实信息。

基于色散转折点处的高灵敏度锥形七芯光纤折射率传感器

基于色散转折点的锥形光纤折射率传感器由于依赖色散转折点(Dispersion Turning Point,DTP)的独有特性,可获得超高的传感灵敏度,在生物溶液检测和物质分析等领域展现了广阔的应用前景。提出了一种基于色散转折点处的锥形七芯光纤(Saven-core-fiber,SCF)液体折射率传感器,该传感器通过二次拉锥法制作而成,通过理论和实验证明,该传感器在色散转折点附近具有超高的折射率灵敏度,折射率在1.33附近区域时,折射率灵敏度的最大值为23262.30 nm·RIU^(-1);折射率在1.35附近区域时,折射率灵敏度的最大值为23658.23 nm·RIU^(-1),此外,该传感器具有良好的复现性,使其在微生物溶液检测和血浆检测等领域显示出巨大的潜力。

Axial response and material efficiency of tapered helical piles

Different techniques have been proposed to increase the bearing capacity of open-ended piles.Welding helices to the shaft and tapering the pile shaft could be used simultaneously to enhance the static and dynamic behaviors of these piles.This paper subjects the bearing capacity,stiffness,frictional behavior,and material efficiency of the tapered helical piles to scrutiny.Tapered helical piles are introduced herein as an alternative option to improve the material efficiency of hollow piles.Based on the Taguchi method,a series of experiments was designed and conducted.The axial responses of tapered helical piles are also investigated using finite element analyses.The results derived from loadedisplacement curves and strain gages are used to characterize the axial compression responses of tapered helical piles.The effects of tapered angle,helices diameter and helices distance are examined using dimensionless parameters,and the degree of contribution of these factors is calculated on each of the enumerated variables individually.Experimental results show that the shaft friction resistance of tapered helical piles increases continuously with the pile head settlement.Furthermore,the effect of tapered wall on the shaft friction resistance is more tangible at low stress levels.The results showed that the relative material efficiency factor of the optimum pile could be 2.5 times that of unoptimized pile with a similar quantity of material.

CFD-DEM simulation of fluid-solid flow of a tapered column separation bed

Research on recycling waste Printed Circuit Boards(PCB) is at the forefront of preventing environmental pollution and finding ways to recycle resources.The Tapered Column Separation Bed(TCSB) is invented aiming at disposing the problem that fine particles of waste printed circuit boards cannot be separated efficiently so as to obtain further insight about the underlying mechanisms and demonstrate the separation feasibility in the tapered column separation bed.In this work,a Computational Fluid Dynamics(CFD) coupled with Discrete Element Method(DEM) model for two-phase flow has been extended to simulate the fluid-solid flow in the tapered column separation bed.Its validity is demonstrated by its successful capturing the key features of particles' flow pattern,velocity,the pressure distribution,the axial position with time and axial force for particles with different densities.Simulation results show that the plastic particles and resin particles become overflow,while copper particles,iron particles and aluminum particles successively become underflow,with a discharge water flow rate of 1 m^3/h,an obliquity of 30°.The simulated results agree reasonably well with the experimental observation.Using this equipment to separate waste PCBs is feasible,theoretically.

An RKDG finite element method for the one-dimensional inviscid compressible gas dynamics equations in a Lagrangian coordinate

In this paper,Runge-Kutta Discontinuous Galerkin（RKDG） finite element method is presented to solve the onedimensional inviscid compressible gas dynamic equations in a Lagrangian coordinate.The equations are discretized by the DG method in space and the temporal discretization is accomplished by the total variation diminishing Runge-Kutta method.A limiter based on the characteristic field decomposition is applied to maintain stability and non-oscillatory property of the RKDG method.For multi-medium fluid simulation,the two cells adjacent to the interface are treated differently from other cells.At first,a linear Riemann solver is applied to calculate the numerical ？ux at the interface.Numerical examples show that there is some oscillation in the vicinity of the interface.Then a nonlinear Riemann solver based on the characteristic formulation of the equation and the discontinuity relations is adopted to calculate the numerical ？ux at the interface,which suppresses the oscillation successfully.Several single-medium and multi-medium fluid examples are given to demonstrate the reliability and efficiency of the algorithm.

平面波导微型光谱仪系统芯片中Taper耦合结构的研究

设计了一种专用于平面波导微型光谱仪的Taper耦合器。推导了基于三维有限差分光束传播法的标量方程,并利用光束传播法和透明边界条件对耦合器的耦合效率进行了模拟计算和分析。结果表明,Taper耦合器结构稳定,耦合效率高,可满足微型光谱仪的应用要求。

Analysis and design of the taper in metal-grating periodic slow-wave structures for rectangular Cerenkov masers

The hybrid-mode dispersion equation of the metal-grating periodic slow-wave structure for a rectangular Cerenkov maser is derived by using the Borgnis function and field-matching methods.An equivalent-circuit model for the taper of the groove depth that matches the smooth waveguide to the metal-grating structure is proposed.By using the equivalentcircuit method,as well as the Ansoft high frequency structure simulator（HFSS） code,an appropriate electromagnetic mode for beam-wave interaction is selected and the equivalent-circuit analysis on the taper is given.The calculated results show that a cumulative reflection coefficient of 0.025 for the beam-wave interaction structure at a working frequency of 78.1 GHz can be reached by designing the exponential taper with a TE z10 rectangular waveguide mode as the input and the desired TE x10 mode as the output.It is worth pointing out that by using the equivalent-circuit method,the complex field-matching problems from the traditional field-theory method for taper design can be avoided,so the taper analysis process is markedly simplified.

Buckling Analysis of Tapered Continuous Columns by Using Modified Buckling Mode Shapes

Elastic critical buckling load of a column depends on various parameters,such as boundary conditions,material,and crosssection geometry.The main purpose of this work is to present a new method for investigating the buckling load of tapered columns subjected to axial force.The proposed method is based on modified buckling mode shape of tapered structure and perturbation theory.The mode shape of the damaged structure can be expressed as a linear combination of mode shapes of the intact structure.Variations in length in piecewise form can be positive or negative.The method can be used for single-span and continuous columns.Comparison of results with those of finite element and Timoshenko methods shows the high accuracy and efficiency of the proposed method for detecting buckling load.

Natural frequency of tapered high pier considering pile-soil interaction

In seismic design of tapered high pier, the analysis of natural vibration frequency is of great importance. According to the engineering features of tapered high pier in mountainous area, a vibration calculation model was set up considering the tapered pier characteristics and pile-soil interaction. Based on Southwell frequency composition theory, it consists of elastic deformation of bridge pier and the rigid deformation of group piles, which are respectively solved by the finite-element method and energy method, and then the natural frequency is derived. The comparison between the measured and calculated results shows that the calculation errors with and without considering pile-soil interaction are 4.9% and 14.7%, respectively. Additionally, the main parameters (pier height, section variation coefficient and lateral foundation horizontal proportional coefficient) affecting natural frequency were investigated. The result shows that natural frequency ascends with the increase of the lateral foundation horizontal proportional coefficient; and it is quite necessary to consider the pile-soil interaction in natural frequency calculation of tapered high pier.

扭矩-竖向荷载联合作用下楔形端承摩擦桩承载性能分析

为了讨论楔形端承摩擦桩在扭矩T-竖向荷载V联合作用下的承载性能,考虑地基土剪切模量在地面处为非零值且随深度呈幂函数的分布形式,根据能量法和变分原理,分别得出基桩在桩顶竖向荷载和扭矩作用下的桩身竖向位移以及扭转角微分控制方程。采用MATLAB编制程序求解楔形端承摩擦桩的极限竖向荷载、极限扭矩,得到相应的承载力包络图。在T→V加载顺序下,通过改变初始扭矩值,分析了初始扭矩对楔形端承摩擦桩竖向承载特性的影响。对T-V联合受荷楔形端承摩擦桩进行了参数影响分析。研究结果表明:与等截面桩相比,纯压和纯扭作用下楔形端承摩擦桩的极限竖向荷载和极限扭矩有所提高。在T→V加载顺序下,楔形端承摩擦桩承载力包络线相比等截面桩有所外扩。随着桩径变化率的增大,楔形端承摩擦桩的承载力包络线也随之向外扩张。当初始扭矩与极限扭矩之比超过一定值时,楔形端承摩擦桩极限竖向荷载开始显著降低,需注意T-V组合效应。对于大直径长桩而言,需要重视初始扭矩对基桩竖向承载性能的影响。一味提高混凝土标号并不能极大的改善基桩在T→V受荷模式下的竖向承载性能。

双列圆锥滚子轴承拟静力学建模和刚度计算分析

针对双列圆锥滚子轴承建模及求解过程复杂的问题,以切片法为基础,建立了双列圆锥滚子轴承的拟静力学模型,结合同伦-牛顿法,实现了对上述模型的求解,并针对不同工况条件下双列圆锥滚子轴承的刚度特性展开分析。分析结果表明:所建模型一定程度上克服了传统非线性迭代算法对初值的高依赖性;双列圆锥滚子轴承的刚度特性受轴承转速和预紧位移影响,在仅有预紧力的工况下,当转速从0增加到4 000 r/min时,轴承的径向、轴向刚度减小,当预紧位移从0.005 mm增加到0.015 mm时,径向、轴向刚度增加;当受轴向力且轴向力从10 kN增加到14 kN时,轴承径向、轴向刚度减小,当轴向力从14 kN增加到19 kN时,其径向、轴向刚度增加,转折点为第二列滚子与内滚道脱离点;增加转速时,出现脱离点所需的轴向力减小;增加预紧位移时,出现脱离点所需轴向力增加。

凹槽织构化圆锥滚子轴承静力学特性研究

为了解织构化圆锥滚子轴承在运转过程中的载荷特性,建立了轴承外滚道的径向凹槽织构化模型,再利用Newton-Raphson迭代法求解织构化圆锥滚子轴承的静力学平衡方程。凹槽深度为50μm,宽度为0~500μm(对应周向角度为0~1.08°)。结果表明,与光滑轴承相比,织构化圆锥滚子轴承的滚动体与外滚道的接触载荷有明显增大的趋势。当凹槽宽度小于或等于54.59μm(周向角度为0.117°)时,滚动体与轴承外滚道接触稳定,不会发生解应力现象。当其超过该临界值时,滚动体与外滚道的接触力将发生明显变化,使得轴承各滚子受力不均,运行状况不一,从而出现轴承运行不稳定的现象。

基于状态空间法的阶梯型变截面水平受荷桩分析方法

为研究阶梯型变截面桩的水平承载特性,基于Timoshenko梁理论,建立了综合考虑桩基尺寸效应、剪切变形和桩基材料非线性效应的四弹簧模型及其状态方程,获得了非线性桩土相互作用下任意长细比的桩截面内力与变形解析解。通过与已有文献中现场试验结果对比分析,验证该方法的适用性和有效性,并讨论了变径位置、桩径比和弹性模量比对桩基受荷特性的影响。研究结果表明:(1)桩基水平承载力对三者的敏感性为:桩径比>变径位置>弹性模量比;(2)综合考虑桩承载能力和经济性,建议变径位置、桩径比和弹性模量比取0.6。

风电轴承保持架冲压工艺参数优化

采用Dynaform数值模拟技术和正交试验相结合的方法,对风电主轴用圆锥滚子轴承保持架冲压工艺参数进行优化设计,以板料厚度变化量作为优化判断指标,研究了不同工艺参数组合对保持架成形质量的影响。结果表明冲压工艺参数的相对最优组合为压边力110 kN,摩擦因数0.12,冲压速度5000 mm/s,并针对优化后的工艺参数进行数值模拟研究,验证了基于Dynaform数值模拟技术和正交试验相结合方法进行保持架冲压成形工艺参数优化的有效性。