截锥壳颤振分析的微分求积法

引入微分求积法(Differential Quadrature Method,简称DQM)对截锥壳气动弹性方程离散,采用一阶活塞理论气动力,运用特征值分析方法求解系统的颤振临界动压。研究了半顶角、径厚比、长径比等几何参数对颤振临界动压的影响。结果表明,DQM求解截锥壳气动弹性方程具有良好的精度和计算效率,结构产生1阶~2阶耦合型颤振的最低临界动压对应的周向波数较大,并因几何参数而异;颤振临界动压参数随半顶角的增大而减小,随着径厚比的增大而增大,随长径比的增大而减小。     

钢铝结构连接耦合损耗因子计算方法研究

统计能量法已广泛用于解决高频振动与噪声问题,耦合损耗因子是其关键参数之一。研究基于统计能量法、有限元法和功率输入法,提出一种钢铝连接耦合损耗因子数值计算方法,并运用MATLAB编写了计算软件。通过对含过渡接头的T型连接结构进行数值和实验研究,验证了该法的可靠性。这对提高钢铝混合结构的噪声预报精度及指导其结构声学设计具有重要意义。     

有限元仿真方法评价护栏安全性能的可行性

建立多种车辆和护栏有限元仿真模型,运用多次碰撞试验数据对仿真模型计算结果进行比对,对采用有限元仿真方法评价护栏安全性能的可行性进行分析。研究结果表明,仿真计算可以得到车辆行驶轨迹、结构防护导向、乘员风险和动态变形等护栏安全评价的各项指标,仿真结果与试验结果一致,误差在10%以内,验证了建模方法的正确性,运用有限元仿真方法评价护栏安全性能具有较高可行性。强调运用评价护栏安全性能的仿真模型须通过碰撞试验校核,同时建议通过法规和准则对从事护栏评价CAE工程师进行职业管理。     

用Normal Form直接法研究壁板的热颤振与控制

建立了二维受热壁板在超音速气流中的颤振方程。运用分岔理论求得了系统的Hopf分岔点,应用Normal Form直接法计算得到系统Hopf分岔Normal Form系数。引入wash-out滤波器技术对壁板热颤振进行了主动控制,延迟系统Hopf分岔的产生而不改变分岔类型。最后采用数值模拟验证了理论分析。     

混杂边界轴向运动Timoshenko梁固有频率数值解

运用微分求积方法求解两端带有扭转弹簧且弹簧系数均可任意变化的非对称下的轴向运动Timoshenko梁的固有频率。以权系数修改法处理轴向运动Timoshenko梁的混杂边界。研究系统的前两阶固有频率随轴向速度、刚度系数以及弹簧弹性系数变化的情况,并将数值计算结果与半解析半数值的研究结果进行比较,结果表明,数值计算结果与半解析半数值结果基本吻合。     

基于离散单元法和物理引擎的结构连续倒塌可视化模拟

目前强离散性、大位移、大变形的倒塌全过程求解是结构计算分析的瓶颈,而离散单元法以理论力学为基础,基于刚体运动学和动力学方程,可有效实现结构全过程倒塌可视化模拟。运用Blender平台实现建筑结构的三维可视化建模及倒塌场景的可视化渲染;BCB(Bullet Constraints Builder)完成结构梁板柱构件的离散及刚体间约束的建立;物理引擎计算刚体间碰撞过程并"实时"更新刚体运动轨迹,三者协同作用实现倒塌全过程可视化模拟。模拟结果表明:所用方法适用于结构大变形模拟,可实现结构从弹性、弹塑性直至倒塌破坏的全过程可视化模拟,后续研究可为结构连续倒塌破坏机理的分析及人员逃生路径和搜救人员营救路线的选择提供科学指导。     

高速列车作用下简支梁车桥耦合振动随机响应分析

以三跨简支梁为例,进行车桥系统空间非平稳随机分析。将系统在确定性荷载作用下得到的响应作为均值,采用虚拟激励法将轨道高低、方向和左右轨高差不平顺转化为一系列简谐荷载,将系统在虚拟荷载作用下的响应的自功率谱密度积分得到均方差,运用3 准则确定系统响应的最大、最小值,取其绝对值的较大值做为响应的代表值,讨论系统响应在不同车速下的变化趋势。研究表明：车体加速度、桥梁跨中横向响应和轮对受到横向轮轨力的随机性较大,轨道不平顺是其主要影响因素,桥梁跨中垂向响应及垂向轮轨力主要由确定性荷载引起。桥梁响应并不随车速的增加而单调增加,车体响应以及轮轨力随车速的增加而单调增加     

不平衡-碰摩-松动耦合故障的转子动力学建模与盲分离研究

建立了不平衡-碰摩-基础松动耦合故障的转子动力学模型。在模型中,轴承简化为线性弹簧,转子考虑为两端无约束的等截面自由欧拉梁,同时,建立了不平衡、碰摩和松动耦合转子动力学运动方程,运用模态截断法,利用数值积分方法获取转子系统的振动响应。显然,系统响应是多个耦合故障信号的混合,因此借助盲源分离方法进行了转子系统耦合故障信号分离研究,并运用ZT-3型多功能转子试验台进行了实验验证,仿真和实验结果表明了所建立故障动力学模型的正确性以及利用盲分离方法实施耦合故障分离的有效性     

基于FEM和TM方法的轨道-隧道-土层振动耦合响应分析

针对地铁隧道中日益增多的振动问题,基于FEM(有限元)和TMM(传递矩阵方法)技术,以上海轨道交通四号线为研究背景,探讨在移动荷载作用下轨道-隧道-土层系统的振动响应及荷载传播问题。其中在频率波数域内运用FEM模拟轨道系统响应,运用TM技术模拟土层运动,并将隧道简化为欧拉梁,利用应力应变关系将轨道系统、土层与隧道梁进行耦合。模拟数据与实测数据对比表明,该模型能较好地模拟地铁隧道中振动的传播。基于该理论模型,运用频散曲线对轨道及土层特性进行分析,从理论上讨论轨道系统与土层耦合条件下振动波传播的特殊规律,并以地表位移及土层应力为研究对象,分析不同频率条件下振动响应的差异。     

基于动态规划的动载荷时域识别方法研究

提出一种基于动态规划方程的动态载荷时域方法。首先从系统的状态空间方程出发,利用最小二乘法建立系统响应的实际测量值与识别值之间的目标函数。将Bellman最优化原理运用到目标函数的最小化当中,推导出动态优化载荷识别公式。通过一个多自由度数值算例对本方法进行验证,表明方法对含有噪声的动态载荷识别问题适应性强,具有较高的识别精度。     

Using the synthetic aperture focusing technique with velocity responses to detect the defects inside reinforced concrete structures

In civil engineering, imaging can be a useful non-destructive testing (NDT) tool for revealing defects in a concrete structure. To date, there is no effective method for imaging the defects inside in situ concrete structures. In this study, a new elastic wave-based NDT method has been developed and then applied to reveal the defects inside concrete specimens using an imaging method. This method integrates the point-source/point-receiver method with the synthetic aperture focusing technique (SAFT) to achieve a scanning effect when using a phase array system. This method operates with a large functioning depth because the transient elastic wave method possesses a high-energy feature, whereas the traditional ultrasonic method does not. As an alternative to using displacement responses, this method uses velocity responses to construct the SAFT image. Based on the numerical simulation and the experimental results, using the proposed method allowed a high image quality to be produced and successfully revealed defects underneath a layer of rebars. The results of this study indicate the great potential for using the elastic wave-based imaging method to inspect defects in situ concrete structures.     

A study on setting standard time using work achievement quotient

A method is proposed for setting standard time using a work achievement quotient approach. As an example, the vehicle safety inspection service for fork-lift trucks is considered. Conventionally, standard time has been set using a Predetermined Time System (PTS) method such as the Work Factor (WF) and Method-Time Measurement (MTM) methods or using a stopwatch method. The PTS method sometimes may be inappropriate because the analysis is too much trouble when the method is used for a work of a small manufacturing volume or of a long cycle time. Although simpler WF methods like the Ready Work Factor (RWF) method, etc., have been developed, users of these methods are expected to be trained and have completed hands-on analytical practice through a formal training course and to acquire the necessary skills in order to obtain accurate time measurements. When the stopwatch method is used to conduct the rating, subjective impressions can influence the results. To obtain accurate time measurements, a thorough training using films, etc., is necessary. In contrast, the method for setting standard time using the work achievement quotient approach can grasp individual variation of workers in time sequence and evaluate it dynamically. Thus, calculation is possible using a small statistical sample.     

A new method for solving single and multi-objective fuzzy minimum cost flow problems with different membership functions

Several authors have proposed different methods for solving fuzzy minimum cost flow (MCF) problems. In this paper, some single and multi-objective fuzzy MCF problems are chosen which cannot be solved by using any of the existing methods and a new method is proposed for solving such type of problems. The main advantage of the proposed method over existing methods is that the fuzzy MCF problems which can be solved by using the existing methods can also be solved by the proposed method. But, there exist several fuzzy MCF problems which can be solved only by using the proposed method i.e., it is not possible to solve these problems by using the existing methods. To illustrate the proposed method and also to show the advantages of the proposed method over existing methods some single and multi-objective fuzzy MCF problems which cannot be solved by using the existing methods are solved by using the proposed method and the obtained results are discussed.     

Multidimensional interpolation and numerical integration by boundary element method

This paper presents a multidimensional interpolation method and a numerical integration for a bounded region using boundary integral equations and a polyharmonic function. In the method using B-spline, points must be assigned in a gridiron layout for two-dimensional cases. In the method presented in this paper, using the polyharmonic function, arbitrary points can be assigned instead of using a gridiron layout, making interpolation an easy process. This method requires the use of boundary geometry of the region and arbitrary internal points. Values at an arbitrary point and the integral value are calculated after solving the discretized boundary integral equations. Numerical integration is performed using this interpolation. In order to investigate the efficiency of this method, several examples are given.     

Fringe analysis method for electronic speckle pattern interferometry using only speckle patterns before and after deformation

Electronic speckle pattern interferometry is employed in many industrial fields as a useful deformation measurement method. However, two speckle patterns obtained before and after the deformation are necessary for measurement. Furthermore, at least three speckle patterns are required for high resolution measurement using ordinary fringe scanning technologies. In this paper, a novel method that can measure high speed deformations using a limited number of speckle patterns without using high speed cameras is proposed. The method enables application to dynamic deformation analysis because the method involves analysis using only two speckle patterns obtained before and after the deformation. A novel optical system that can record some spatial information into each speckle is set up for the method. In experimental results, it is confirmed that the out-of-plane deformation measurement can be precisely performed by the method and that the resolution power is almost equivalent to that of the ordinary method.     

Micro-three dimensional shape measurement method based on shadow Moiré using scanning electron microscopy

A novel, precise, three-dimensional shape measurement method using scanning electron microscopy (SEM) and Moiré topography has been proposed. The possibility for measurement of wavelength order using this method is discussed based on results of experiments to confirm the principle. In these experiments, a high-resolution method based on the new measurement method is proposed, employing fringe scanning technology for the shadow Moiré. The optical system is constructed with a SEM using backscattering electrons, a grating holder that can shift the position of the grating, and a grating having a pitch of 120?µm. Measured results using a bearing ball as a sample show that high resolution measurements of around one micrometre can be performed using the fringe scanning method and the new measurement arrangement. An error analysis of the method is performed to enable improvement of the measuring accuracy.     

运用振动反分析方法计算振动荷载

本文研究运用振动反问题理论求解振动荷载时程的问题。在Newmark法求解运动平衡方程的基础上，推导了求解振动荷载的公式。采用最小二乘法估计最可置信的荷载系数。提出了由结构对振动荷载的反应求振动荷载时程的有限元方法。通过算例验证了方法的有效性。本文为计算振动荷载提供了一种新的方法。     

响应表面法在结构噪声优化中的应用研究

针对结构噪声有限元直接优化的非线性和复杂性,利用传统的声固耦合有限元法,结合响应表面法计算结构噪声值,以结构参数为设计变量,建立设计变量与结构噪声值的映射模型,避免了有限元灵敏度分析,提高了优化速度。以封闭箱体的结构噪声优化为例,验证了该方法的有效性。     

Performance comparison between on-line sensors and control charts in manufacturing process monitoring

The rapid evolution of sensor technology, using techniques such as lasers, machine vision and pattern recognition, provides the potential to greatly improve the Statistical Process Control (SPC) method for monitoring manufacturing processes. This paper studies the method of using on-line sensors to monitor manufacturing processes and compares that method with the control chart method, a widely used SPC tool. Two separate economic models are formulated for using either a sensor or a control chart to monitor a manufacturing process. Then, the two models are compared in a sensitivity analysis with lespect to several process parameters.     

A semi-analytic boundary element method for parabolic problems

A new semi-analytic solution method is proposed for solving linear parabolic problems using the boundary element method. This method constructs a solution as an eigenfunction expansion using separation of variables. The eigenfunctions are determined using the dual reciprocity boundary element method. This separation of variables-dual reciprocity method (SOV-DRM) allows a solution to be determined without requiring either time-stepping or domain discretisation. The accuracy and computational efficiency of the SOV-DRM is found to improve as time increases. These properties make the SOV-DRM an attractive technique for solving parabolic problems.