Uncertainty Quantification and Management in Ambient Modal Identification

结构的模态特性主要包括其固有频率、阻尼比和模态振型。它们的信息对于抗风、地震和人为激励等动荷载的设计是必不可少的。由于缺乏知识和建模限制而产生不确定性，这通常会增加项目风险。模态识别一直被认为是缓解结构动力学不确定性的有效手段。理论上，在不知道输入激励的情况下，仅根据结构的“输出”振动响应来识别模态特性是可能的。这种类型的测试，称为“环境振动测试”，由于其高实施可行性，稳健性和经济性，现已成为主要和最可持续的手段。然而，在没有加载信息和采集数据的非受控野外环境下，识别结果具有显著的变异性和低重复性。这限制了环境振动试验的经济效益，破坏了环境振动试验识别结果的科学意义。这一点已经得到了广泛的认可，但对于其起源或如何控制它，还没有定量的解释。该项目旨在开发一种全面的基本方法，用于量化和管理土木工程结构从环境振动数据中识别出的模态特性的不确定性。科学的核心是一套“不确定性定律”，类似于经典概率中大量数据的定律，从根本上明确和定量地表达了模态特性在测试配置方面的识别不确定性，如测量噪声、环境负载强度和传感器的数量和位置。由于问题的复杂性，对于一般情况，不太可能得到有见地的结果。该项目旨在通过对现实情况下剩余识别不确定性的主导行为的见解来基本表达。该项目的目标是通过一个综合方案来实现的，该方案包括基础理论发展、综合、实验室和现场数据的广泛核查以及与工业的知识转移。应编制一份规划和执行环境振动试验的实用指南，将项目的科学发现、团队成员的经验和工业伙伴的意见结合起来。

The modal properties of a structure include primarily its natural frequencies, damping ratios and mode shapes. Their information is indispensable for design against dynamic loads such as wind, earthquake and human excitation. Uncertainty arises due to the lack of knowledge and modelling limitations and this generally increases project risk. Modal identification has long been recognised as an effective means for uncertainty mitigation in structural dynamics. Theoretically it is possible to identify the modal properties based on only the 'output' vibration response of structures without knowing the 'input' excitation. This type of test, called 'ambient vibration test', has now become the primary and most sustainable means for its high implementation feasibility, robustness and economy. In the absence of loading information and with data collected under uncontrolled field environment, however, the identification results have significant variability and low repeatability. This has limited the economic benefit of ambient vibration tests and undermined the scientific significance of their identification results. This has been well-recognised but there has been no quantitative account for its origin or how to control it.This project aims at developing a comprehensive fundamental methodology for quantifying and managing the uncertainties of the modal properties of civil engineering structures identified from ambient vibration data. At the scientific core is a set of 'uncertainty laws', analogous to the laws of large numbers of data in classical probability, that expresses fundamentally the identification uncertainty of modal properties explicitly and quantitatively in terms of test configurations such as measurement noise, environmental load intensity and the number and location of sensors. Due to complexity of the problem, it is unlikely to obtain insightful results for general situations. The project aims at fundamental expressions with insights governing the dominant behaviour of the remaining identification uncertainty under realistic situations. The project objective is achieved through a comprehensive programme comprising fundamental theory development, extensive verification with synthetic, laboratory and field data, and knowledge transfer with industry. A practical guide for planning and performing ambient vibration test shall be produced incorporating scientific findings of the project and experience of the team members with input from industry partners.