Exploiting High-Spatial Density Vibration Measurements and Fe Models for Damage Identification (original) (raw)
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Improvement of damage-assessment results using high-spatial density measurements
Mechanical Systems and Signal Processing, 2005
Model-based damage assessment is based on measuring the distance between experimental and analytical results. In practice, measurements yield only partial mode shapes with respect to the total degrees of freedom present in the corresponding finite element model. Thus, before any damage detection method is implemented, the experimental mode shape has to be expanded to the same dimension of the numerical mode shape. Mode shapes expansion is a key point in the damage localisation process, since actual defects of the structure may be hidden by expansion errors. This paper introduces a new general procedure to the expansion/damage assessment process using an optimised choice for: the size of the expansion basis, the number of experimental degrees of freedom and the sensor placement. We introduce a new indicator to evaluate the problems inherent to the expansion/damage detection process using the minimisation of error on constitutive equations (MECE) technique. It provides insight of the inherent limitations of MECE and helps the decision making process on how many degrees of freedom should be measured and how many mode shapes should be used in the expansion basis. The procedure is illustrated using a finite element model of a plate-like structure, where the damage state is simulated as a reduction of the local stiffness.
Assessment of vibration-based damage identification techniques
Journal of Sound and Vibration, 2006
In this paper some usual vibration-based damage identification techniques (VBDIT) will be reviewed and used for structural damage evaluation. With the help of a simple supported beam with different damage levels the reliability of these techniques will be investigated. The techniques reviewed herein are based on measured modal parameters which use only few mode shapes and/or modal frequencies of the structure that can be easily obtained by dynamic tests. In other words, by realizing two sets of dynamic measurements, corresponding to two moments of the structure lifetime, the dynamic modal parameters can be obtained. In order to assess properly the performance of these techniques different noise levels are randomly introduced to the response signals of a simulated beam which is exited by a random force. For different levels of damage and noise, the probabilities of damage detection and the probabilities of false alarm for the total number of simulations is evaluated. It can be concluded that among the evaluated techniques the strain energy method presents the best stability regarding noisy signals; however, the detection judgement depends on a threshold level which is discussed in this paper. The change in mode shape curvature, change in flexibility and change in flexibility curvature methods are also capable to detect and localise damaged elements but in the case of complex and simultaneous damages these techniques show less efficiency. r
Improved Damage Location Accuracy Using Strain Energy-Based Mode Selection Criteria
AIAA Journal, 1997
A method is presented for selecting the subset of identified structural vibration modes to be used in finite element model correlation for structural damage detection. The method is based on a ranking of the modes using measured modal strain energy, and is a function of only the measured modal parameters. It is shown that a mode selection strategy based on maximum modal strain energy produces more accurate update results than a strategy based on minimum frequency. Strategies that use the strain energy stored by modes in both the undamaged and damaged structural configuration are considered. It is demonstrated that more accurate results are obtained when the modes are selected using the maximum strain energy stored in the damaged structural configuration. The mode selection techniques are applied to the results of a damage detection experiment on a suspended truss structure that has a large amount of localized modal behavior.
Damage identification in plate-like structure using mode shape derivatives
In this paper, a newdamage indicator based onmodal data, such as mode shapes and its derivatives, is presented for damage identification in plate-like structures. The proposed indicator is determined using modal analysis information extracted from a finite element code in MATLAB. After obtaining the mode shapes, the slope and curvature of the plate in each mode are calculated based on central finite difference methods. A numerical example with and without noise is considered to evaluate the exact location of different damage scenarios. In order to validate the proposed indicator for structural damage detection, the obtained results have been compared with another study which was based on experimental data. Moreover, in order to better assess the performance of the proposed indicator, a comparison has been made between the proposed indicator and two well-known indicators found in the literature. The results indicate that the proposed damaged indicator is able to detect precisely the location of single and multiple damage cases having different characteristics in plate-like structures.
Journal of Structural …, 2004
The paper reports on relative performance of inverse eigensensitivity and response function methods for structural damage detection, location and quantification using vibration data. In implementing each of these methods, a validated baseline finite element (FE) model for the structure, in its undamaged state, is assumed to be available. Depending on this, a matrix of sensitivity of structural dynamic characteristics, in frequency or modal domains, to changes in values of structural parameters, is constructed. An inverse procedure, based on pseudoinverse theory of matrices, is subsequently applied to identify structural damages based on observed changes in vibration response of the structure. Issues arising out of mismatch between degrees of freedom of the FE model and number of measured degrees of freedom are dealt with by using alternative model reduction/expansion schemes. Illustrative examples on synthetically and experimentally generated vibration data on cantilever beams and a three-storied building frame are presented.
Fundamental mode shape and its derivatives in structural damage localization
Various techniques for structural damage detection involving modal parameters have widely been used over the past few decades. This is because the modal parameters of a structure can easily be obtained from forced, free or ambient vibration measurements. In many of these techniques, mode shape curvature has been used for localization of damage. In this paper, a mathematical basis is provided to show the correlation between a structural damage and a change in the fundamental mode shape and its derivatives. This has been achieved by deriving the expression of a damaged mode shape utilizing a perturbation approach. For a cantilever shear beam, discretized into a large number of elements, this approach demonstrates that the change in the fundamental mode shape due to any damage is an excellent indicator of damage localization as it is found to be discontinuous at the location of damage. Further, the change in higher derivatives (i.e., slope and curvature) of the fundamental mode shape is shown to be sensitive enough in damage localization. A numerical study involving a shear building and a steel moment-resisting frame is conducted to show the effectiveness of the proposed approach in damage localization. It has been found from this study that spline fitting of mode shapes in case of a limited number of degrees-of-freedom, which is generally adopted for plotting mode shapes and their derivatives, may lead to false detection of damage.
Computer-Aided Civil and Infrastructure Engineering, 2011
ABSTRACT This article presents damage locating indices based on normalized modal macrostrain (MMS) as improvement on the typical curvature-dependent methods. Vulnerability to noise and the use of numerical differentiation procedures are the key factors for the poor performance of many curvature-dependent methods using displacement mode shapes. Whereas dynamic distributed strain measurement data from long-gauge FBG sensors have significantly improved the performance of many damage identification methods, the sensitivity to local damage diminishes as the gauge length increases. The proposed model-free damage identification techniques based on normalized MMS vectors are successfully implemented to locate damage in beam-like structures through numerical simulations and experimental verifications. The unique advantages of the techniques are their simplicity, robustness to noise, ability to precisely identify small damage extents, and localize single and multiple damage states using limited measurable modes from few sensors.
Damage localization and quantification by direct structural dynamic parameters updating method
2013
The objective of this paper is detecting the location and extent of structural damage from measured vibration test data based on direct structural finite element model updating. The method is based upon a mathematical model representing the undamaged vibrating structure and a local description of the damage and introduces a new finite element model updating approach for damage detection. The problem of modeling errors and their influence to damage localization accuracy is discussed and an approach to obtain reliable results in this case is presented. The concept of direct updating of individual dynamic parameters is used and according to that algorithms the mathematical function for damage assessment are defined. Then, error matrix of dynamic properties of healthy and damaged structures is established to detect the damage location and severity. For validation of damage detection approaches, two numerical examples are utilized. At the all examples, consider the modal data are incomplete and inverse of rectangular matrices is accomplished by Moore-Penrose inverse matrix without using any multipliers. It will be shown that the proposed procedure is simple to implement and may be useful for structural damage identification.
Studies on methodological developments in structural damage identification
Structural Durability and …, 2009
Many advances have taken place in the area of structural damage detection and localization using several approaches. Availability of cost-effective computing memory and speed, improvement in sensor technology including remotely monitored sensors, advancements in the finite element method, adaptation of modal testing and development of non-linear system identification methods bring out immense technical advancements that have contributed to the advancement of modal-based damage detection methods. Advances in modal-based damage detection methods over the last 20-30 years have produced new techniques for examining vibration data for identification of structural damage. In this paper, studies carried out on damage identification methods using model-and nonmodel-based approaches have been presented describing their effectiveness in identification, localisation and quantification of damage. Usefulness of different parameters such as change in frequency, mode shape, modal curvature and strain energy for detection of damage has been studied. Further, advanced nonmodel based techniques have also been studied for damage identification. But, most of these techniques are found to have limitation thereby restricting their usage. Moreover, majority of the approaches need a prior knowledge on the vibration characteristics of undamaged structure which is quite difficult to get in most of the cases. It has been noted that majority of the methodologies show good results in laboratory or analytical investigations and special care is needed in choosing the methodology for damage detection of real structures in field condition.
A probabilistic damage detection approach using vibration-based nondestructive testing
Structural Safety, 2012
With the aim of improving the accuracy of the assessment of existing structures, damage detection using vibration-based nondestructive testing (NDT) has been extensively studied. It has been recognized that a considerable amount of uncertainties exist in the damage detection process. This paper proposes a novel probabilistic damage detection approach that accounts for the underlying uncertainties. The proposed approach combines two techniques: A Bayesian model updating and a vibration-based damage identification technique (VBDIT). The model updating uses modal frequencies from a damaged structure to build a baseline finite element model (FEM). VBDIT uses mode shapes from the baseline model and the damaged structure to detect damage at local level. The proposed framework makes use of the advantages of the Bayesian model updating and the VBDIT, and compensates for their drawbacks. The sources and types of errors that may occur in the damage detection process are discussed and considered in the proposed formulation. In particular, the proposed approach considers the measurement errors in the vibration tests, the modeling errors in the damage detection process, and the statistical uncertainties in the unknown model parameters. As an application, a finite element model simulating a two-span aluminum beam is used to illustrate the proposed framework. The effects of the measurement and modeling errors on the performance of the proposed damage detection are studied. Modal data can be easily extracted from output only responses on an existing structure, making the proposed methodology of practical value.