超音速下热壁板的颤振分析

首先研究了热效应对壁板结构动力学特性的影响.将基于超音速活塞理论的非定常气动力模型与壁板的结构动力学方程相结合,得到了热壁板的颤振方程.利用p-k法进行了热壁板的颤振计算,讨论了气流偏角对颤振速度的影响.数值结果表明,热效应对壁板的固有特性有较大影响,进而影响壁板的颤振特性.     

基于复模态方法的二维夹层壁板颤振分析

本文研究二维夹层壁板在一侧受超音速气动力的情况下的颤振现象.利用复模态方法和伽辽金方法分析颤振临界马赫数以及夹芯粘性阻尼对颤振的影响.结果发现考虑前四阶模态时,由于一二阶频率重合而使振动能量积聚发生颤振.考虑中间层的粘弹性时,发现随着粘性阻尼的增加,颤振临界马赫数和临界颤振频率均呈现先降低后升高的现象,其原因是粘弹性一方面降低系统固有频率使得临界马赫数降低,另一方面又使能量耗散使得临界马赫数升高,在这两种作用的影响下出现了上述复杂的现象.本文的研究结果有利于颤振抑制时的设计优化.     

超声速气流中复合材料壁板的动力学分析及其控制

超声速飞行器外表具有大量的蒙皮壁板结构,其在巡航过程中会受到气动、热、声及机械等载荷的联合作用.本文针对超声速气流中的复合材料壁板结构,基于一阶剪切变形理论(First-Order Shear Deformation Theory,FSDT)和超声速活塞理论,推导得到了复合材料壁板的气热弹动力学的能量泛函,并运用Hamilton原理变分求得系统的控制方程,利用牛顿迭代法结合Newmark法,求解获得了壁板的临界颤振动压和时域动力学响应.通过变参数计算,分析了不同参数对于壁板动力学响应的影响.最后,应用非线性能量阱(Nonlinear Energy Sink,NES)对复合材料壁板的动力学响应进行颤振控制,结果表明,NES可以有效降低壁板的颤振极限环振幅,从而极大提高超声速飞行器的可靠性和寿命.     

基于H无穷范数的颤振分析方法

颤振是一种典型的气动弹性动不稳定现象, 求解颤振临界点是气动弹性稳定性分析的重要任务之一.从H_∞控制理论观点出发, 将气动弹性系统视为多输入多输出系统, 并导出其传递函数矩阵. 在颤振临界点附近, 根据系统传递函数矩阵的H_∞–范数趋于无穷大的特点, 发展了相应的颤振临界点搜索方法. 与传统的颤振分析方法相比, 该方法属于完全频域方法, 算法更为简洁, 且具有更高的自动化程度. 数值算例表明, 该方法可以获得正确的颤振临界点.     

基于有限元的输电塔架稳定性研究

输电塔架作为输电系统的重要构件,其稳定性直接关系到输电系统的安全,进而影响到人民的生产建设和生活秩序.本文对塔架系统进行了简化,简化后变为固支梁力学系统,并建立了它的力学模型.以简化的塔架力学模型为基础,借助有限元软件ANSYS,模拟分析塔架结构在荷载作用下发生失稳的问题.     

考虑舵机动力学的舵回路系统颤振特性分析

针对液压舵机动刚度特性,研究了舵回路系统(舵机系统和舵面耦合系统)的颤振特性.利用分支模态法建立了基于舵机系统动力学方程的时域和频域颤振计算模型,提出了2种考虑舵机动态特性的颤振求解方法,第1种方法思想是对舵回路系统模型在各种来流速度下进行状态矩阵的稳定性判断;第2种方法是将舵机复刚度特性包含在频域颤振方程中,使用迭代法求解该方程得到舵系统颤振特性,并验证了两种方法的可行性.分析结果显示舵机动态特性对颤振特性有着很大的影响,说明舵机动态特性使得颤振边界提高,为飞机系统设计和结构振动分析提供有用的边界支持和设计依据.     

低速轴向气流中曲壁板的稳定性及分岔分析

本文研究了带有初始曲率的二维曲壁板在低速轴向气流中的稳定性及分岔问题.基于薄翼理论获得了作用在曲壁板上的气动力,并设计了风洞实验以验证该理论气动力的准确性.采用Galerkin方法将非线性运动方程离散成常微分方程组;利用牛顿迭代法求解壁板的静变形;在参数区间内分析了系统的分叉结构.结果表明：本文给出的气动力理论计算结果与实验吻合良好;静态气动力会破坏系统的对称性;在来流动压超过临界值后,曲壁板会发生非对称的静态分岔并出现新的稳定及不稳定的平衡态;系统临界来流动压随面内拉力(压力)的增加而增加(减小),而随初始曲率的增加呈现先增大后减小的规律;系统在不同参数区域内存在四种典型的分岔行为;系统的响应与来流动压及初值有关.     

颤振试飞测试系统的设计与实现

颤振是飞机结构最危险的振动形式;飞机颤振飞行试验属于防颤振研究的最终环节,它是验证新机颤振安全性必不可少的关键试飞课题;为完成颤振飞行试验,设计了一套高可靠性综合机载测试系统,完成模拟量、飞控数据、总线数据采集,并可实现实时数据处理;该测试系统硬件具有接口简洁、实时性强、抗干扰特性好,适用于航空试飞领域;根据试验数据分析暴露的问题,进行了深入研究,提出了合理解决方案,解决了颤振飞行试验过程中出现的问题,对于今后的颤振试飞测试具有指导意义。     

压电加筋壁板结构的多模态自抗扰振动控制

针对压电加筋壁板结构多模态主动控制时存在振动模型和外界干扰难以确定等问题, 提出一种不依赖结构数学模型的多模态自抗扰振动控制方法. 首先,采用多回路的扩张状态观测器实时估计其他模态的输出叠加、输入耦合、高次谐波以及外界激励等组成的集总干扰, 并将估计值通过前馈补偿的方式消除干扰对整个控制系统的影响. 然后, 针对每个控制模态设计独立的PD反馈控制器. 为了提高整个控制系统的振动抑制性能, 结合多模态振动控制的特点, 引入一种具有实际意义的性能指标函数. 并基于此性能函数, 提出基于logistic映射的自抗扰振动控制器参数自动优化方法. 最后, 利用dSPACE半实物仿真平台, 搭建了四面固支壁板结构的压电振动控制实验系统.最后, 多模态干扰激励的实验结果表明了所提的多模态自抗扰振动主动控制方法的有效性.     

静电驱动微梁谐振器的厚度形态误差特性分析

本文研究了一类双极板静电驱动两端固支微梁谐振器.考虑中性面拉伸和厚度形态误差,建立了微谐振器连续体模型.厚度形态误差通过设置参数方程实现,方程中包含误差参数λ,用于调整误差影响程度.利用伽辽金法和Newton-Cotes法将系统化简为单自由度模型.首先,通过COMSOL Multiphysics有限元软件对理论求得的静电力进行了仿真验证.然后,推导了不考虑厚度形态误差时系统的吸合情况,发现系统在特定情况下可以出现二次吸合现象.通过改变误差参数,分析了厚度形态误差对吸合情况的影响.最后,利用多尺度法求出系统小幅振动下的响应,研究了厚度形态误差对等效固有频率和系统软硬特性的影响.     

Supporting Business Intelligence Usage: An Integrated Framework with Automatic Weighting

This paper presents an integrated framework that comprises an automatic weighting method for assessing data quality (DQ) of the framework so as to better support the business intelligence (BI) usage. Specifically, we utilize business process modeling (BPM) notation and information product map and frame them into a hierarchical mapping structure. Furthermore, we develop and demonstrate an automatic weight-assignment method for evaluating critical dimensions (i.e., completeness and accuracy) of DQ of the integrated framework. Through a design science paradigm, the effectiveness of the framework and the associated DQ weighting method has been rigorously validated by faculty management users of a university. The framework together with the DQ weighting method builds user confidence by enhancing the traceability of a BI product. The automatic DQ weight assignment also provides better time efficiency because the weight of each data attribute is determined automatically based on its usage on the BI dashboard.     

Size-dependent effects on critical flow velocity of a SWCNT conveying viscous fluid based on nonlocal strain gradient cylindrical shell model

This article investigates vibration and instability analysis of a single-walled carbon nanotube (SWCNT) conveying viscous fluid flow. For this purpose, the first-order shear deformation shell model is developed in the framework of nonlocal strain gradient theory (NSGT) for the first time. The proposed model is a conveying viscous fluid in which the external force of fluid flow is applied by the modified Navier–Stokes relation and considering slip boundary condition and Knudsen number. The NSGT can be reduced to the nonlocal elasticity theory, strain gradient theory or the classical elasticity theory by inserting their specific nonlocal parameters and material length scale parameters into the governing equations. Comparison of above-mentioned theories suggests that the NSGT predicts the greatest critical fluid flow velocity and stability region. The governing equations of motion and corresponding boundary conditions are discretized using the generalized differential quadrature method. Furthermore, the effects of the material length scale, nonlocal parameter, Winkler elastic foundation and Pasternak elastic foundation on vibration behavior and instability of a SWCNT conveying viscous fluid flow with simply supported and clamped–clamped boundary conditions are investigated.     

高速列车转向架的主动稳定性研究

提出了基于构架横向振动的高速列车稳定性主动控制方法,讨论了采用惯性作动器控制构架横向振动,以及对动力转向架驱动系统采用主动弹性悬挂这两种实施方式.以车辆蛇行稳定性指标和控制力作为两个目标函数,利用遗传算法(NSGA-II)来优化控制参数和驱动系统悬挂参数.研究表明构架横向振动控制可以有效地提高转向架蛇行稳定性.同时发现当直接反馈构架状态实现构架振动控制时,控制系统时滞易导致系统失稳,因此提出一种通过反馈附加振子状态的方法来减小时滞的影响,合理的附加振子悬挂参数有利于提高车辆系统稳定性.较硬的附加振子可提高转向架控制系统的蛇行临界速度裕度,但会导致控制系统在一定的时滞内出现不稳定的现象.因此,在优化附加振子悬挂参数时,必须同时兼顾转向架蛇行稳定性和控制系统稳定性.本文对于涉及的350 km/h高速列车转向架,得出了附加振子的最佳固有频率和阻尼比.     

Parametric instability of a non-prismatic bar with localized damage subjected to an intermediate periodic axial load

The dynamic instability behaviour of a tapered beam with localized zones of damage and subjected to concentrated periodic loads applied at some intermediate point has been studied by using a finite element analysis. The effects of parameters such as extent and position of damage, position of load, the static and dynamic load factors on the vibration and instability behaviour are discussed. The influence of damage on natural frequency is observed to be most intense at some critical position on the beam. The parametric instability regions are influenced by the combined effects of the position of damage and the position of intermediate load on the beam.     

Head Orientation Prediction: Delta Quaternions Versus Quaternions

Display lag in simulation environments with helmet-mounted displays causes a loss of immersion that degrades the value of virtual/augmented reality training simulators. Simulators use predictive tracking to compensate for display lag, preparing display updates based on the anticipated head motion. This paper proposes a new method for predicting head orientation using a delta quaternion (DQ)-based extended Kalman filter (EKF) and compares the performance to a quaternion EKF. The proposed framework operates on the change in quaternion between consecutive data frames (the DQ), which avoids the heavy computational burden of the quaternion motion equation. Head velocity is estimated from the DQ by an EKF and then used to predict future head orientation. We have tested the new framework with captured head motion data and compared it with the computationally expensive quaternion filter. Experimental results indicate that the proposed DQ method provides the accuracy of the quaternion method without the heavy computational burden.     

A multidimensional analysis of data quality for credit risk management: New insights and challenges

Recent studies have indicated that companies are increasingly experiencing Data Quality (DQ) related problems as more complex data are being collected. To address such problems, the literature suggests the implementation of a Total Data Quality Management Program (TDQM) that should consist of the following phases: DQ definition, measurement, analysis and improvement. As such, this paper performs an empirical study using a questionnaire that was distributed to financial institutions worldwide to identify the most important DQ dimensions, to assess the DQ level of credit risk databases using the identified DQ dimensions, to analyze DQ issues and to suggest improvement actions in a credit risk assessment context. This questionnaire is structured according to the framework of Wang and Strong and incorporates three additional DQ dimensions that were found to be important to the current context (i.e., actionable, alignment and traceable). Additionally, this paper contributes to the literature by developing a scorecard index to assess the DQ level of credit risk databases using the DQ dimensions that were identified as most important. Finally, this study explores the key DQ challenges and causes of DQ problems and suggests improvement actions. The findings from the statistical analysis of the empirical study delineate the nine most important DQ dimensions, which include accuracy and security for assessing the DQ level.     

Appropriate number of unit cells in a representative volume element for micro-structural bifurcation encountered in a multi-scale modeling

The paper proposes a method to determine the number of unit cells (basic structural elements) to be employed for a representative volume element (RVE) of the multi-scale modeling for a solid with periodic micro-structures undergoing bifurcation. Main difficulties for the multi-scale modeling implementing instability are twofold: loss of convexity of the total potential energy that should be homogenized and determination of a pertinent RVE that contains multiple unit cells. In order to resolve these difficulties, variational formulation is achieved with the help of Γ-convergence theory within the framework of non-convex homogenization method, while the number of unit cells in an RVE is determined by the block-diagonalization method of group-theoretic bifurcation theory. The latter method enables us to identify the most critical bifurcation mode among possible bifurcation patterns for an assembly of arbitrary number of periodic micro-structures. Thus, the appropriate number of unit cells to be employed in the RVE can be determined in a systematic manner. Representative numerical examples for a cellular solid show the feasibility of the proposed method and illustrate material instability at a macroscopic point due to geometrical instability in a micro-scale.     

氯乙烯精馏工艺中的低塔控制优化方案

该文是作者在氯乙烯精馏装置的生产操作、工艺改进、参数控制的长期实践基础上写成的。作者阐述了经过工艺和控制系统优化后,形成的新的控制方案和操作方法。生产实践证明了该方案操作简单、控制有效,解决了精馏生产过程中长期存在的控制不稳和氯乙烯含量不稳的问题,使产品质量达到了工艺要求。     

应用于低性能单片机的拼音输入法设计与实现

Aiming at the research on the detection system of the camera hole of mobile phone’s glass panel, this paper introduces a design method of the helium-neon(He-Ne) laser driving circuit. The He-Ne laser is selected as the detecting light source, and interfer- ence is generated after the laser being projected to the camera hole of the glass panel. According to the quality of the interference fringes, the detection purpose can be achieved. The importance of He-Ne laser as the light source of this system is proposed. And combining with the actual application, the reasons for the instability of interference fringes produced by He-Ne laser are analyzed. Next, a technical method for the temperature control of the He-Ne laser driving circuit is proposed. Finally, the principle and design method of the He-Ne laser driving circuit are given. Experimental result shows that the driving circuit module can stably control the He-Ne laser light source, and the light source can fully satisfy the system’s requirements.     

基于数字图像处理技术实现人造板孔穴评价的研究*

利用计算机数字图像处理技术对人造板板材断面的图像进行分析,提取人造板孔穴率、孔穴率均匀程度、孔穴大小和孔穴形态四个参数,作为对板材物理性能进行综合评价的参数.通过对50个样本进行实验对比,验证了该方法的可行性.