【作者】 王真；

【导师】 程远胜；

【作者基本信息】 华中科技大学 ， 船舶与海洋结构物设计制造， 2007， 博士

【摘要】 随着航空、航天、海洋、桥梁和军事装备等领域的重要大型工程结构的不断修建及已建结构的大批老化,从上个世纪70年代开始,无损检测技术的研究受到国内外学术和工程界越来越多的关注,并已进行了一些工程实践探索。其中,基于振动的结构损伤识别技术具有信号便于提取、易于实现自动化等优点,其工程应用前景良好,已成为研究的核心内容之一。然而,随着研究的深入和实际工程应用的需求,许多基于振动的损伤识别方法显露出了一些不足。本文首先对基于振动的结构损伤识别技术的基本理论和研究方法进行了总结和分析,在此基础上重点对如何提高噪声环境下损伤指标对损伤的灵敏度与采用结构振动的时域响应数据进行损伤识别进行了研究。主要研究工作包括:(1)从理论上证明了反馈控制能够提高频率对刚度的灵敏度。在此基础上,采用基于模态空间控制的反馈控制合理配置系统极点,提高了多自由度耦合系统的特征频率对结构刚度变化的灵敏度。以损伤前后闭环系统特征频率构造损伤识别指标,采用假设检验法判断损伤是否发生。假设检验法能够克服随机噪声对识别准确性的影响,并且由于采用反馈控制提高了频率对损伤的灵敏度,该方法对于噪声环境下较小程度损伤的存在性识别具有一定的优势。(2)在提高频率对损伤灵敏度的基础上,采用统计模式识别方法进行损伤定位的研究。采用基于模态空间控制的反馈控制法合理配置系统极点;然后以损伤前后闭环系统特征频率构造特征向量;通过矩阵摄动理论,推导了对该特征量进行归一化的方法,最后采用多元统计分析的Mahalanobis距离作为判别函数来识别损伤位置。(3)提出了一种采用随机载荷作用下的结构时域响应数据进行损伤识别的新方法。其主要原理是建立基于自回归参数的损伤灵敏度矩阵,该矩阵建立了由单元损伤导致的自回归参数的变化与损伤系数变化之间的关系;通过求解损伤系数向量来识别损伤位置和损伤程度。该方法与其它基于时域响应的损伤识别方法相比,其最大优势在于能够仅利用单个传感器的响应信号进行损伤识别,因此对于传感器位置和数量的选择上有较大的灵活性,尤其对于大型的复杂结构如海洋平台结构,该方法能够降低损伤识别的难度和测试成本。(4)推导了自回归参数对单元刚度损伤系数的灵敏度表达式。提出通过合理配置系统极点能够在一定程度上提高自回归参数对结构刚度变化的灵敏度,从而提高损伤识别正确率的新思路。其基本过程为,建立闭环系统加速度响应的时序模型,以自回归参数建立均值控制图,通过监测自回归参数的统计性变化判断结构是否发生损伤。该方法仅需结构的时域响应数据,并且由于反馈控制使得自回归参数灵敏度的提高,因此对于早期损伤能够及时诊断,适用于结构的健康监测系统。(5)以一梁结构为实验对象,测量了完好梁和损伤梁的传递函数和模态频率,并分析了损伤前后系统特性的变化。实验验证了采用控制图进行损伤存在性识别的有效性和可行性。本文将控制理论和统计方法综合运用于结构的损伤识别,从理论和方法上进行了较深入地研究。其研究成果为提高损伤识别方法的抗噪声能力、提高损伤识别指标对损伤的灵敏度以及基于时域响应的损伤识别方法的研究提供了新的研究思路和途径。更多还原

【Abstract】 With the continuous construction of large engineering structures in aerospace, civil, ocean, and mechanical engineering communities and the aging of existing structures in these communities, development of technology to monitor a structure and detect damage is becoming increasingly important. During the last 30 years, non-destructive examination (NDE)method has received considerable attention both in the academic and engineering communities. As the one kind of NDE vibration-based structural damage detection has become a hot research area because of its simplicity and minimum interaction with users and has promising applicability. However, with the development of research and acquirement of its practical application, many techniques of the vibration-based damage identification have shown some limitations.This thesis first presents a comprehensive summary and the state-of-the-art review on development of vibration-based structural damage detection. In the study, emphases are placed on how to enhance sensitivity of the damage indicator to damage and how to utilize time-domain response data of structure for detecting damage. The main works presented in the thesis are as follows:(1)The principle and feasibility of the sensitivity-enhancing feedback control for damage detection is further explored. Feedback control based on independent modal space control is first used to assign the pole of the system under detection intentionally. Then the prescribed characteristic frequencies of closed-loop system, which are more sensitive to damage, are obtained and further employed to constitute a sensitivity-enhanced damage indicator (SEDI). To overcome the effect of measurement noise on modal frequencies, a hypothesis test involving the t-test that utilizes the SEDI is employed to estimate the occurrence of damage. The combination of sensitivity-enhancing feedback control and statistical analysis is expected to improve the capability of the frequencies of the closed-loop system for identifying small damage and to lower the sensitivity to measurement noise.(2)A statistical pattern recognition technique is used for locating damage with the characteristic frequencies of the closed-loop system. Feedback control based on independent modal space control is used to assign the pole of the system under detection intentionally, and then the frequencies of the closed-loop system are used to construct feature vector. Based on perturbation theory, the feature vectors are normalized in order to eliminate the effect of damage extent on damage localization. Finally, mahalanobis distance of multivariate statistical analysis is used for locating damage.(3)A novel method using time-domain response data under random loading for detecting structural damage is proposed. A time series model with a fitting order is first constructed using the time domain response data with measurement noise. A sensitivity matrix consisting of the first differential of the autoregressive coefficients of the time series models with respect to the stiffness of the structural elements is then obtained. The locations and severities of the damage may be finally estimated by solving for the damage vector whose components are the damage degrees of the structural elements. A unique aspect of this method is that acceleration history data obtained from only one or a few sensors are required for detection and more feasibility for sensor arrangement is obtained accordingly. This advantage is helpful to reduce the difficulty and cost of testing of damage detection especially for large-scale complex engineering structures such as offshore platform structures.(4)The sensitivity of autoregressive coefficient to element stiffness is deduced, and it is concluded that assignment of pole of system under detection can be employed to enhance the sensitivity of autoregressive coefficient to element stiffness to improve the accuracy of damage detection. Principal component analysis is first carried out on all response time series of closed-loop system for data compression. A time series model with a fitting order is then constructed using the fist principal component. Finally, an X-bar control chart is constructed based on the mean value of autoregressive coefficient. The identification of damage occurrence is performed by monitoring the statically significant change of the control chart. Because only time-domain responses data are demanded and the sensitivity of autoregressive coefficient is enhanced by feedback control, the presented approach is efficient for the identification of early small damage and is very attractive for online structural monitoring system.(5)In order to demonstrate the effectiveness and feasibility of using control chart for damage detection, a beam structure with damage is tested in laboratory. Transfer function and modal frequencies of the damage and undamaged beams are measured. An analysis about the change of vibration characteristics of structures is carried out according to the measurement data. The process using control chart for the identification of damage occurrence is performed based on acceleration samples of the beam. High success rates are obtained.In this thesis, statistical approach combined with control theory are utilized for structural damage detection in an effort to enhance the sensitivity of damage feature indicator with measurement noise, and several key techniques and basic theories are studied. These research findings can be employed to supply novel ideas and approaches for improvement of robust ability of vibration-based damage identification, enhancement of the sensitivity of damage feature indicator to damage and the use of time-domain response data applied to damage detection.更多还原