微型梁杨氏模量与内应力的固有频率法测量

为实现对硅微机械与光纤组合式阵列传感器的核心敏感元件———微型硅梁的杨氏模量和内应力进行测试 ,提出了利用光纤耦合机理来测量微型硅梁的横向固有振动频率 ,进而推导梁构件杨氏模量和内应力的方法 ,原理简洁 ,具体实现也较为可行 ,从而为机械构件的机械性能测试分析提供了方法 ,具有实用意义 .

基于随机子空间法和固有频率法的线路故障定位

输电线路发生故障后,进行准确快速的故障距离判断在实际生产运行中具有很大的意义。线路故障后,将产生一系列的故障暂态行波,且从频域的角度看,行波可看作为谐波形式。提出基于随机子空间法和行波固有频率法相结合的方法进行线路故障定位。首先通过相模变换得到输电线路中的模电流分量,然后基于随机子空间算法进行辨识得到行波固有频率,进而计算此频率下的行波波速和模阻抗导纳矩阵,最后可求得故障距离。在PSCAD中搭建两端系统仿真模型,经过仿真验证表明,此方法可有效进行线路故障定位,且准确度较高。

边坡稳定性判别新理念—固有频率判别法

从结构动力学基本理论可知,频率与刚度是直接相关的,边坡的基本固有频率与边坡的稳定性有着密切的关系,它会随着边坡体的支承刚度的变化而变化。可利用这种变化进行边坡滑体的稳定性判据研究,与现行的变形监测相比,是一种新的理念,即固有频率判别法,它的主要理论依据是频率、刚度、质量三者之间的关系——当质量一定时,频率仅与刚度有关。工程地震研究表明,边坡固有频率是场地的基本特性,通过实测或数值模型计算,均可得到可信的结果。

高压直流输电线路故障测距研究综述

高压直流输电线路的距离长、跨越的地区地形地貌和环境气候差别很大,故障概率高。对故障测距的准确度要求也高。因此,提出了描述分布参数线路电气特征的波动方程作为故障测距原理的基础,针对时间、频率和空间三个角度,分别对提出的行波法、固有频率法和故障分析法进行了技术梳理与总结,明确了以行波法为主、固有频率法和故障分析法协助提高测距可靠性的整体技术方案,并就高阻接地弱故障启动、波头振荡、反射系数频变等行波测距法现存的问题给出了后续的改进思路和方案。

形状记忆合金梁的建模及混沌阈值计算

从形状记忆合金(SMA)的等应变拉压实验数据出发,利用van-der-pol环模型模拟了形状记忆合金在加载和卸载过程中的应力应变迟滞环特性。并根据弹性理论和Galerkin方法建立了形状记忆合金简支梁在受轴向激励时的振动模型。随后得出了自由振动系统的分岔特性。在利用待定固有频率法研究了模型的非线性参数对系统固有频率的影响后,根据待定固有频率法的计算结果和时间尺度变化提出了系统Melnikov函数的改进表达式,提高了计算形状记忆合金梁模型在参数激励下发生混沌的阈值的精度。数值模拟的结果证明了该途径的有效性。

非对称截面环状Kirchhoff弹性细杆的拓扑构型分析

为了揭示非对称截面环状Kirchhoff弹性细杆受到外力(矩)作用时其拓扑状态的变化情况,引入了等效初始扭矩的概念,利用势能密度函数与哈密顿函数形式上的相似性,建立了其与系统哈密顿函数、初始自连接数之间的定量关系.以环状DNA分子为背景,对扭矩模型进行了非线性动力学分析,并利用解析方法中的待定固有频率法,分析了主要参数对扭矩模型稳定构型的影响.最后,利用等效刚度得到相应状态下曲率的表达式,为进一步认识和描述DNA环受到生物酶作用下的稳定构型提供了新的理论途径.

高压直流输电线路故障定位研究综述

高压直流输电是我国的重点发展方向之一。快速、准确的高压直流输电线路故障定位对保障高压直流系统运行可靠性、减少停运时间具有重要意义。对目前应用于高压直流输电线路以及柔性直流配电网故障定位的主要技术,包括行波测距法、固有频率法、故障分析法和非精确同步测距法,进行了详细的分析和综述。探讨了不同故障定位技术在高压直流输电线路故障定位应用中的优缺点。结合传感器技术、计算机技术与人工智能技术的发展趋势,对高压直流输电线路故障定位技术的未来发展进行了展望。该研究给高压直流线路故障定位方法的研究者提供了良好的参考。

FREE VIBRATION ANALYSIS AND PHYSICAL PARAMETER IDENTIFICATION OF NON-UNIFORM BEAM CARRYING SPRING-MASS SYSTEMS

To analyze a multibody system composed of non-uniform beam and spring-mass subsystems, the model discretization is carried on by utilizing the finite element method（FEM）, the dynamic model of non-uniform beam is developed by using the transfer matrix method of multibody system（MS-TMM）, the transfer matrix of non-u- niform beam is derived, and the natural frequencies are computed. Compared with the numerical assembly method （NAM）, the results by MS-TMM have good agreement with the results by FEM, and are better than the results by NAM. When using the high precision method, the global dynamic equations of the complex multibody system are not needed and the orders of involved system matrices are decreased greatly. For the investigation on the re- verse problem of the physical parameter identification of multibody system, MS-TMM and the optimization tech- nology based on genetic algorithms（GAs） are combined and extended. The identification problem is exchanged for an optimization problem, and it is formulated as a global minimum solution of the objective function with respect to natural frequencies of multibody system. At last, the numerical example of non-uniform beam with attach- ments is discussed, and the identification results indicate the feasibility and the effectivity of the proposed aop- proach.

Thermal Modal Analysis of Doubly Curved Shell Based on Rayleigh⁃Ritz Method

The doubly curved shell(DCS)is a common structure in the engineering field.In a thermal environment,the vibration characteristics of the DCS will be affected by the thermal effect.The research on the vibration characteristics of DCS in thermal environment is relatively limited.In this paper,the thermal strain and the change of Young’s modulus caused by the changing of temperature are studied,and the DCS energy equation is established systematically.The displacement tolerance function of the DCS is constructed by the spectral geometry method,and the natural frequencies and mode shapes of the DCS with different structural parameters,such as thicknesses,ratios of R_(a)/R_(b) and a/b,at different temperatures are solved by the Rayleigh-Ritz method.The results show that the natural frequency of the DCS decreases with the increasing temperature,R_(a)/R_(b) and a/b ratios,and increases with the increasing thickness.

Vibration analysis of wind tunnel support

In order to enable a wind tunnel support to have a high enough natural frequency to prevent experiencing mechanical resonance and excessive vibration displacement, five kinds of wind tunnel support structures have been simulated and analyzed individually under five different load conditions by means of a nonlinear finite element numerical method. With natural frequency and three directions vibration displacement given, simulation and analyses indicated that additional supports is more beneficial than heightening the rigidity of steel reinforced concrete in support pillars and adopting steel wrappers on the pillars to increase natural frequency of support structure. Increasing the rigidity of steel reinforced concrete, adopting steel wrappers and providing additional supports are all helpful in reducing three directions vibration Max displacement. and additional supports are comparatively more effective. Therefore, a structure scheme with steel reinforced concrete support pillars, steel wrappers and additional supports should be adopted in practical wind tunnel support construction.

Method for optimizing manipulator's geometrical parameters and selecting reducers

A geometrical parameters optimization and reducers selection method was proposed for robotic manipulators design. The Lagrangian approach was employed in deriving the dynamic model of a two-DOF manipulator. The flexibility of links and joints was taken into account in the mechanical structure dimensions optimization and reducers selection, in which Timoshenko model was used to discretize the hollow links. Two criteria, i.e. maximization of fundamental frequency and minimization of self-mass/load ratio, were utilized to optimize the manipulators. The NSGA-II (fast elitist nondominated sorting genetic algorithms) was employed to solve the multi-objective optimization problem. How the joints flexibility affects the manipulators design was analyzed and shown in the numerical analysis example. The results indicate that simultaneous consideration of the joints and the links flexibility is very necessary for manipulators optimal design. Finally, several optimal combinations were provided. The effectiveness of the optimization method was proved by comparing with ADAMS simulation results. The self-mass/load ratio error of the two methods is within 10%. The maximum error of the natural frequency by the two methods is 23.74%. The method proposed in this work provides a fast and effective pathway for manipulator design and reducers selection.

Determination of Natural Frequencies of Multilayered Plates by Mixed Finite Elements

Natural frequencies for multilayer plates are calculated by mixed finite element method. The main object of this paper is to use the mixed model for multilayer plates, analyzing each layer as an isolated plate, where the continuity of displacements is achieved by Lagrange multipliers （representing static variables）. This procedure allows us to work with any model for single plate （so as to ensure the proper behavior of each layer）, and the complexity of the multilayer system is avoided by ensuring the condition of displacements by the Lagrange multipliers （static variables）. The plate is discretized by finite element modeling based on a primary hybrid model, where the domain is divided by quadrilateral, both for the displacement field and static variables. This mixed element for plates was implemented and several examples of vibrations have been verified successfully by the results obtained by other methods in the literature.

Numerical investigation of liquid sloshing in FLNG membrane tanks with various bottom slopes

To analyze the bottom slope's effect on the sloshing liquid in floating liquefied natural gas(FLNG)membrane tanks,a simulation model is built and applied to describe the liquid behavior in a sloshing container.The free surface motion is simulated by the volume-of-fluid method and the standard k-εturbulence model.Experimental data and numerical results from references are used to validate the accuracy of the proposed simulation model.To study the influence of the sloped bottom on the liquid sloshing,different slope sizes and filling ratios are numerically simulated at the lowest natural frequency.The results reveal that the natural frequency can be determined by the average peak values of hydrodynamic parameters.The natural frequency and pressure loading on the tank walls decrease with the increase in the slope size.The peak pressure on the wall decreases by 5.45 kPa with the increase in the slope ratio from 5%to 20%.However,the relationship between the peak pressure and slope ratio is more significant with lower filling rates.Liquid behavior is more stable and independent with the change of the slope structure at a high filling rate(60%).The results of numerical simulation and modeling are expected to provide reference data for the design and operation of the FLNG system.

遥感相机实验室静态MTF测量误差分析

应用于航空航天等军工技术领域的高分辨率遥感相机在轨图像处理过程中,需要用到相机实验室静态MTF测量结果进行补偿复原,因此对其测量的准确性提出了较高的要求。针对目前遥感相机实验室静态MTF测量常用的固有频率目标法,进行了各相关误差源的深入量化分析,并结合某航天遥感相机的MTF测量计算出各误差源的影响程度,其中系统总误差和随机总误差分别为0.021 32和0.003 04,最后给出了提高测量精度的建议。在实际工程中,可根据测量条件估算出误差值,并对影响较严重的误差因素采取相应措施,从而提高测量的准确性,对遥感相机在轨图像处理有指导意义。

A novel method of dynamic characteristics analysis of machine tool based on unit structure

A novel approach,which can be used for dynamic characteristics analysis of machine tools based on unit structure(US),is reported in this paper.The concepts of unit structures for design of machine tools are defined.In order to satisfy the dynamic characteristics requirement of high natural frequency and light-weight of US,a design method of multi-disciplinary optimization of NSGA-II about unit structures driven by natural frequency and mass is developed.Through analyzing the unit structures,key factors affecting the natural frequency and mass are extracted,and the mathematical models of natural frequency and mass about unit structures are also established by using central composite design and response surface model.The goal of high natural frequency and light-weight is reached by using the multi-objective genetic algorithms.The Pareto optimal set is also obtained.The dynamic behavior of US is investigated by the experimental modal analysis.To show the efficiency of the proposed novel method,the example of YKW51250 gear shaping machine bed is used.Through optimization of NSGA-II about US of YKW51250 machine bed,the natural frequency of YKW51250 gear shaping machine bed is increased by 30.4%and its mass decreased by 5.2%comparing with the original design.By studying the dynamic characteristics of the simplified machine tools bed,useful laws are obtained,and these laws can be used in primary design of NC machine tools structures.The optimal method based on US can be also applied to the dynamic optimal design of machine tools and other similar equipments.

A hybrid multiple damages detection method for plate structures

A hybrid method is proposed to properly identify multiple damages for plate structures in this work. In the stage of damage localization, singular value decomposition （SVD） is applied to reveal singularities in modal shapes, and hence to detect the damage locations. In the stage of damage quantification, based on the detected location information ant colony optimization （ACO） algorithm is introduced to estimate damage severity by searching for damage evaluation database, which reveals the relationship between the natural frequencies and the damage severity. The modal shapes and the natural frequencies required in damage localization and quantification are obtained via the wavelet finite element method. The numerical simulation and experimental investigation are carried out to test the performance of the hybrid method for free aluminum plates with multiple damages. And the results indicate that the proposed method is effective to identify multiple damages of plate structures with reasonable precision.

A two-level method for sparse time-frequency representation of multiscale data Dedicated to Professor LI TaTsien on the Occasion of His 80th Birthday

Based on the recently developed data-driven time-frequency analysis(Hou and Shi, 2013), we propose a two-level method to look for the sparse time-frequency decomposition of multiscale data. In the two-level method, we first run a local algorithm to get a good approximation of the instantaneous frequency. We then pass this instantaneous frequency to the global algorithm to get an accurate global intrinsic mode function(IMF)and instantaneous frequency. The two-level method alleviates the difficulty of the mode mixing to some extent.We also present a method to reduce the end effects.