Vibration of circular plate with multiple eccentric circular perforations by the Rayleigh-Ritz method

The free vibration of a circular plate with multiple perforations is analyzed by using the Rayleigh-Ritz method. Admissible functions are assumed to be separable functions of radial and tangential coordinates. Trigonometric functions are assumed in the circumferential direction. The radial shape functions are the boundary characteristic orthogonal polynomials generated following the Gram-Schmidt recurrence scheme. The assumed functions are used to estimate the kinetic and the potential energies of the plate depending on the number and the position of the perforations. The eigenvalues, representing the dimensionless natural frequencies, are compared with the results obtained using Bessel functions, where the exact solution is available. Moreover, the eigenvectors, which are the unknown coefficients of the Rayleigh-Ritz method, are used to present the mode shapes of the plate. To validate the analytical results of the plates with multiple perforations, experimental investigations are also performed. Two unique case studies that are not addressed in the existing literature are considered. The results of the Rayleigh-Ritz method are found to be in good agreement with those from the experiments. Although the method presented can be employed in the vibration analysis of plates with different boundary conditions and shapes of the perforations, circular perforations that are free on the edges are studied in this paper. The results are presented in terms of dimensionless frequencies and mode shapes.     

Mathematical modeling of fluxgate magnetic gradiometers

Issues of designing fluxgate magnetic gradiometers are considered. The areas of application of fluxgate magnetic gradiometers are determined. The structure and layout of a two-component fluxgate magnetic gradiometer are presented. It is assumed that the fluxgates are strictly coaxial in the gradiometer body. Elements of the classical approach to the mathematical modeling of the spatial arrangement of solids are considered. The bases of the gradiometer body and their transformations during spatial displacement of the gradiometer are given. The problems of mathematical modeling of gradiometers are formulated, basic mathematical models of a two-component fluxgate gradiometer are developed, and the mathematical models are analyzed. A computer experiment was performed. Difference signals from the gradiometer fluxgates for the vertical and horizontal position of the gradiometer body are shown graphically as functions of the magnitude and direction of the geomagnetic field strength vector.     

焊接电弧光谱的分布特征

在试验的基础上,给出了焊接电弧光谱的频域及空间分布的测试结果,分析了焊接电弧光谱的结构。通过分析得出了ＴＩＧ焊电弧光谱空间分布的差异性和ＭＩＧ焊电弧光谱空间分布的相似性,着重指出ＭＩＧ焊电弧光谱与熔滴过渡之间存在密切关系。此外,还对焊接电弧光谱特征的应用提出了方向。     

制造加工约束下连续体拓扑优化的数值实现

针对两类常见的制造加工约束即对称性和重复性下的连续体拓扑优化问题,提出了将敏度值在每轮优化前的修正方法,该方法简单且易于编程实现,实现了对称性或重复性约束条件下连续体拓扑优化设计,通过数值算例对不同制造加工约束下的拓扑结果进行了分析对比,结果表明,研究方法具有可行性和有效性。     

工程设计的发展趋势和未来

论述了工程设计的发展趋势。介绍了未来社会环境与需求，现代设计概念与方法学和工程设计管理。     

应用于油气钻采的磨料水射流喷嘴优化设计与试验研究

为了优化总长度和出口直径被限制的喷嘴的内部结构,进行喷嘴内外流场数值模拟、喷嘴流量系数测试以及喷嘴对砂岩冲蚀深度的试验。对试验结果进行分析表明,各喷嘴射流轴心线上的速度在喷嘴的内部达到最大后开始减小;数值模拟结果和流量系数测试结果相吻合,即喷嘴外部射流速度最大的喷嘴流量系数也最大,该喷嘴的工作性能最好;在设计试验的喷嘴范围内,进口收缩角为30°,出口圆柱段长度为11mm的喷嘴性能最好,其对砂岩的冲蚀深度高出其他喷嘴的200mm~300mm。     

Problems of engineering diagnostics of electron-beam welding

Features of electron-beam welding (EBW), various types of flaws arising in welded joints during EBW, and the factors causing these flaws’ appearance are considered. The effects of beam focusing and the thickness of the welded metals on the shape of a seam are demonstrated. EBW flaws are classified. The difficulties associated with obtaining informative parameters during EBW are analyzed. Radiation and acoustic methods for engineering diagnostics of EBW are considered. New approaches to the construction of systems for diagnostics of EBW are proposed. Experimental results are presented.     

基于活动标架法的二自由度机器人操作性能分析

用活动标架法研究了二自由度机器人机构的运动学 ,得出了机器人机构的一些不变量 ,并根据它们定义了机器人的平移体积、旋转体积、可操作性指标和灵活度 ,用这些指标评价机器人的操作性能。并由此得出了机器人产生奇异的条件 ,研究了工作空间曲面和奇异曲面的几何性质 ,计算了它们的法曲率和高斯曲率     

功能梯度硬质合金与金属陶瓷制备技术的研究进展

硬质合金与金属陶瓷的功能梯度化是现代切削加工材料的一个重要发展方向.介绍了制备功能梯度硬质合金与金属陶瓷的若干工艺,阐述了其制备原理,概述了国内外研发与应用现状,提出了目前所需要解决的关键问题.     

现代航空发动机健康管理技术与应用

介绍当前航空发动机健康管理系统的发展背景以及现状,讨论航空发动机健康管理系统所采用的几种常用的,如流道分析法,滑油以及碎屑分析法、振动分析等方法,并对每种方法都进行了较为详细的讨论。在流道分析法（GPA）中重点介绍了算法实现以及其优缺点,讨论了其局限性。最后,指出了当前航空发动机健康管理系统所应面对的问题和挑战。     

Resonance methods for microwave studies of dielectrics (Review)

The general properties of microwave resonators with dielectric inclusions, which are important in dielectric measurements, are described. The methods for measuring the permittivity and dielectric losses in isotropic and uniaxial dielectrics with the use of cavity, open, and dielectric resonators are considered. Approximations that are often used in the theory and practice of measurements and limit accuracy are analyzed. The formulas used in calculations and results of measurements of the dielectric parameters of various samples, including films, coatings, and substrates, in the range 1.5–75.0 GHz are presented. The possibilities of local measurements and measurements of parameters of media are discussed.     

The classification of flaws of metal materials synthesized by the selective laser melting method and the capabilities of nondestructive testing methods for their detection

Flaws in metal parts that are typical for the selective laser melting technique are considered. The flaws are divided into four groups by the degree of their danger. The quantitative and qualitative indices of the flaws are given and the causes of their formation are described.     

铜合金表面激光熔覆研究现状

为了提高铜合金的表面耐磨性能,激光熔覆技术已被用于铜合金的表面处理;总结了铜合金表面激光熔覆的特点,评述了铜合金表面熔覆材料体系的研究现状和激光熔覆技术工艺,分析了熔覆层的表面性能,阐明了铜合金表面激光熔覆存在的主要问题和相应改进途径,并提出了今后的研究方向。     

开敞式混流泵内流的数值模拟与出水机构选择

为了给新型开敞式混流泵的设计积累经验并为特殊出水流道结构设计提供方法,对具有不同出水机构的开敞式混流泵进行数值模拟,分析从小流量到最大流量下的内部流动和水力性能,提出适应特殊液压动力需求的开敞式出水机构方案。给出内部流动数值模拟和性能预测的方法,通过外特性预测结果与模型试验数据的比较,验证数值计算的可靠性。在模型分析基础上,针对轴向有导叶、轴向无导叶和径向无导叶等不同的开敞式出水结构形式,进行整机内部流动分析和外特性预测,对不同结果进行比较分析,给出不同出水机构对于特定结构和动力需求的适应性。     

纳米级超精密切削表面粗糙度若干影响因素分析

介绍了W-M函数和分形分维数的结构函数法求法,采用分形理论对影响纳米级超精密切削表面质量的若干因素进行了初步分析,并进行了相关的试验和统计分析,特别是对其中主要的影响因素及其影响程度进行了分析,得出并验证了集合与子集的分维数求法及其影响关系,并对将上述理论应用于设计实际的相关问题进行了探讨。     

卷到卷制造中基板横向振动研究进展

运动基板的横向振动问题已经成为严重限制卷到卷制造效率和质量的关键。详细介绍了卷到卷制造中运动基板横向振动问题的研究概况。讨论了运动基板横向振动的建模方法,以Hamilton原则为例,推导了基板横向振动的控制方程,结合解析求解和数值求解方法,计算横向振动的频率和模态。分析了基板张力、速度、材料特性、中间支撑和外界环境等因素对基板自由振动特性及动态稳定性的影响。研究了基板参数振动特性,考虑基板张力和速度两个主要参数的波动,阐述了基板横向振动被动控制和主动控制方法。联合基板纵向张力控制和侧向纠偏控制,讨论了横向振动控制在卷到卷制造中的工程应用。最后,展望卷到卷制造工程应用中基板横向振动研究的关键问题。     

Hydrodynamic lubrication of a circular thread

This paper presents a theoretical study of the hydrodynamic lubrication of a circular thread passing along a rotating drum. The effects of hydrodynamic friction and the influence of cavitation upon the bearing characteristics are included in the analysis. Differential equations governing the problem, derived from the Reynolds equation and the thread equilibrium equations, are established. Analytical solutions and numerical solutions are obtained for all the operating characteristics. Influences of friction and cavitation are discussed. Comparisons with the results of previously studied flat thread lubrication are also made. The effects of shape are evaluated. Some numerical examples in the field of sizing (coating) fibres are described.     

Models of vibrational transfer and filtration of vibroimpact processes

Examples of the appearance of vibrational motion modes, which lead to excess noise and premature wear of machine parts and mechanisms are presented. Models of mechanical filters of various types are considered, and the problems of the nonlinear and linear filtration of wave-vibrational processes are discussed. The models of the vibration-conducting media, involving the nonlinear vibrational guides of a complex structure, are presented. The analytical studies of the problems associated with the passage of periodically strongly nonlinear (vibroimpact) processes through the multidimensional machine designs, which are modeled by means of discrete 2D mechanical systems with regular structures, or multidimensional mechanical filters for low frequencies, are performed. The physical sense of the derived solutions is obtained, the computational formulas are derived, and the main dynamic effects are discussed. The notion of filter metrics is introduced.     

电动轮技术在电动汽车中的应用及发展趋势

介绍了电动轮的结构、技术优势,电动轮电动汽车的布置方式以及控制策略。对目前电动轮技术中的关键技术问题和电动轮电动汽车的发展趋势进行讨论,提出了相应的发展建议。     

闭孔泡沫铝力学特性及其在汽车碰撞吸能中的应用研究进展

汽车低能耗、安全和轻量化已经成为汽车领域研究的热点问题,闭孔泡沫铝作为一种轻质吸能金属材料,在低密度下具有良好的比刚度和比强度,同时具有良好的抗冲击性和能量吸收性,已逐渐引起汽车产业界地重视。简述泡沫铝单轴压缩试验中弹性模量、抗压强度、屈服强度、平台应力、致密化应变等参数的定义和试验标准;综述闭孔泡沫铝的本构方程的研究现状,重点讨论屈服面模型;总结泡沫铝的微观结构有限元建模方法,比较商业软件中集成的宏观材料模型。归纳吸能材料的特点,分析闭孔泡沫铝的吸能能力和抗冲击能力;综述应变率和冲击速度对泡沫铝吸能特性有无影响的研究进展,并对可能存在的影响进行解释。总结闭孔泡沫铝在汽车轻量化和碰撞安全性领域的应用,具体分析典型的案例。指出当前闭孔泡沫铝的力学特性及其在汽车结构中应用存在的问题与难点,总结并提出本研究领域可以借鉴的研究方向。