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Author

Charles R. Farrar

Other affiliations: Analysis Group
Bio: Charles R. Farrar is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Structural health monitoring & Sensor node. The author has an hindex of 70, co-authored 357 publications receiving 26338 citations. Previous affiliations of Charles R. Farrar include Analysis Group.


Papers
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Proceedings ArticleDOI
18 Jun 2002
TL;DR: In this application of the statistical pattern recognition paradigm, a prediction model of a chosen feature is developed from the time domain response of a baseline structure and the SPRT algorithm is utilized to decide if the test structure is undamaged or damaged and which joint is exhibiting the change.
Abstract: In this application of the statistical pattern recognition paradigm, a prediction model of a chosen feature is developed from the time domain response of a baseline structure. After the model is developed, subsequent feature sets are tested against the model to determine if a change in the feature has occurred. In the proposed statistical inference for damage identification there are two basic hypotheses; (1) the model can predict the feature, in which case the structure is undamaged or (2) the model can not accurately predict the feature, suggesting that the structure is damaged. The Sequential Probability Ratio Test (SPRT) develops a statistical method that quickly arrives at a decision between these two hypotheses and is applicable to continuous monitoring. In the original formulation of the SPRT algorithm, the feature is assumed to be Gaussian and thresholds are set accordingly. It is likely, however, that the feature used for damage identification is sensitive to the tails of the distribution and that the tails may not necessarily be governed by Gaussian characteristics. By modeling the tails using the technique of Extreme Value Statistics, the hypothesis decision thresholds for the SPRT algorithm may be set avoiding the normality assumption. The SPRT algorithm is utilized to decide if the test structure is undamaged or damaged and which joint is exhibiting the change.

12 citations

Journal ArticleDOI
TL;DR: In this article, the results of a series of experimental modal analyses that were performed to examine the similitude of the dynamic parameters of reinforced concrete replica models were reported, showing that both material properties and system geometry must be considered when scaling the damping forces.
Abstract: This paper reports the results of a series of experimental modal analyses that were performed to examine the similitude of the dynamic parameters of reinforced concrete replica models. Also reported are the similitude requirements for damping forces that were developed as part of this study. The similitude analysis shows that both material properties and system geometry must be considered when scaling the damping forces. Results of the experiments show that the modal frequencies and the mode shapes of a prototype structure can be accurately predicted from tests on scale-model structures. Variations in equivalent viscous damping ratios identified on models and prototype were greater than variations for the other measured dynamic parameters. However, all damping ratios were less than 2 percent of critical, and the observed variations would not significantly alter the dynamic response of the structures.

12 citations

01 Mar 1999
TL;DR: In this paper, the authors summarized current methods that are employed to develop accelerated testing criteria and highlighted the attributes and limitations of these methods, highlighting the confounding factors associated with developing acceleration criteria for nonlinear vibration response (e.g., rattling of components).
Abstract: Accelerated vibration testing seeks to compress long service exposures to vibration into a reduced length laboratory test by increasing the amplitude and/or frequency of the applied inputs during the laboratory test relative to the amplitude and/or frequency experienced during service This testing procedure provides an important tool that can reduce testing time associated with a new design and reduce time to market This paper will summarize current methods that are employed to develop accelerated testing criteria and will highlight the attributes and limitations of these methods Typically there are two ways of accelerating vibration testing The first method involves testing at fewer cycles but at higher amplitude levels; and the second method involves testing at higher frequencies (rates) A combination of the two is also an option Development of an accelerated test based on either of these methods requires a priori knowledge of the controlling failure mechanisms The review will begin with a discussion of Miner's Rule for developing accelerated testing criteria This rule, which is based on a linear damage accumulation assumption, was first proposed in the 1940's for fatigue failures of ductile metals loaded repetitively in bending Confounding factors associated with developing accelerated testing criteria for nonlinear vibration response (eg, rattling of components) will be illustrated with an example

12 citations

Book ChapterDOI
01 Jan 2016
TL;DR: A novel phase-based video motion magnification and Blind Source Separation based method to perform operational modal analysis in a relatively efficient and automated manner is proposed.
Abstract: Traditionally, experimental and operational modal analysis requires wired sensors that are physically attached to the structure of interest for vibration measurements. The instrumentation of these sensors on structures for long-term applications (e.g., structural health monitoring) is costly, time-consuming, and requires significant maintenance. Even if a wireless sensor network is used, there still exist substantial challenges associated with security, available bandwidth, and providing energy to the network. As a non-contact method, optics measurements from digital cameras combined with vision based algorithms have been successfully used for experimental vibration measurement and analysis. This opens the door to replacing physical sensors with remote sensing techniques, which could eliminate many of the problems associated with conventional distributed sensor networks. However, research to date has focused on simple structures that can be represented using a single edge. In this work, we propose a novel phase-based video motion magnification and Blind Source Separation (BSS) based method to perform operational modal analysis in a relatively efficient and automated manner.

12 citations


Cited by
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Christopher M. Bishop1
01 Jan 2006
TL;DR: Probability distributions of linear models for regression and classification are given in this article, along with a discussion of combining models and combining models in the context of machine learning and classification.
Abstract: Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

10,141 citations

Journal ArticleDOI
TL;DR: This survey tries to provide a structured and comprehensive overview of the research on anomaly detection by grouping existing techniques into different categories based on the underlying approach adopted by each technique.
Abstract: Anomaly detection is an important problem that has been researched within diverse research areas and application domains. Many anomaly detection techniques have been specifically developed for certain application domains, while others are more generic. This survey tries to provide a structured and comprehensive overview of the research on anomaly detection. We have grouped existing techniques into different categories based on the underlying approach adopted by each technique. For each category we have identified key assumptions, which are used by the techniques to differentiate between normal and anomalous behavior. When applying a given technique to a particular domain, these assumptions can be used as guidelines to assess the effectiveness of the technique in that domain. For each category, we provide a basic anomaly detection technique, and then show how the different existing techniques in that category are variants of the basic technique. This template provides an easier and more succinct understanding of the techniques belonging to each category. Further, for each category, we identify the advantages and disadvantages of the techniques in that category. We also provide a discussion on the computational complexity of the techniques since it is an important issue in real application domains. We hope that this survey will provide a better understanding of the different directions in which research has been done on this topic, and how techniques developed in one area can be applied in domains for which they were not intended to begin with.

9,627 citations

Journal ArticleDOI
TL;DR: This paper attempts to summarise and review the recent research and developments in diagnostics and prognostics of mechanical systems implementing CBM with emphasis on models, algorithms and technologies for data processing and maintenance decision-making.

3,848 citations

ReportDOI
01 May 1996
TL;DR: A review of the technical literature concerning the detection, location, and characterization of structural damage via techniques that examine changes in measured structural vibration response is presented in this article, where the authors categorize the methods according to required measured data and analysis technique.
Abstract: This report contains a review of the technical literature concerning the detection, location, and characterization of structural damage via techniques that examine changes in measured structural vibration response. The report first categorizes the methods according to required measured data and analysis technique. The analysis categories include changes in modal frequencies, changes in measured mode shapes (and their derivatives), and changes in measured flexibility coefficients. Methods that use property (stiffness, mass, damping) matrix updating, detection of nonlinear response, and damage detection via neural networks are also summarized. The applications of the various methods to different types of engineering problems are categorized by type of structure and are summarized. The types of structures include beams, trusses, plates, shells, bridges, offshore platforms, other large civil structures, aerospace structures, and composite structures. The report describes the development of the damage-identification methods and applications and summarizes the current state-of-the-art of the technology. The critical issues for future research in the area of damage identification are also discussed.

2,916 citations