Hamed Kalhori

Spectral-based damage identification in structures under ambient vibration

AbstractThe motivation behind this paper is to develop a spectral-based damage detection and damage localization scheme using in-service ambient vibration in the context of non–model-based damage characterization. In this regard, a response parameter known as spectral moment is implemented for structural damage identification. The damage identification procedure starts with developing response power spectral density (PSD). The principal structural response features are then extracted from the frequency distribution of the spectrum using spectral moments. It is demonstrated that, although, spectral moment is a nonmodal characteristic of a process, it is related to modal parameters of a response signal since the spectral moment at each location is proportional to its corresponding modal vector. Hence, it is expected that due to damage occurrence spectral moment undergoes a variation. On this point, a damage sensitive feature is defined by comparing the spectral moments of two successive states of the struct...

Quantitative identification of delamination at different interfaces using guided wave signals in composite laminates

This article presents the development of a quantitative method for identifying interfacial delamination in composite laminates. Splitting and merging occur as Lamb waves pass through the delamination. It is demonstrated from the dispersion curve of Lamb waves that the group velocities of A0 and S0 modes in the sub-laminates above and below the delamination area are different when the delamination interface is not at the thickness center of a symmetrical layup laminate. Changes in the time of flight (ToF) of A0 and S0 modes are caused by the parallel propagation of Lamb waves. Based on those changes in the ToF, delamination size can be evaluated even though the delamination location through the thickness is not pregiven. Numerical and experimental studies are conducted to assess this method. Continuous wavelet transform is applied to extract the ToF of A0 mode waves from the overlapped signals. Mode conversion is illustrated for the interaction of Lamb waves and delamination. The sensitivity and applicability of the proposed method are validated numerically and experimentally in two asymmetric layup composite laminates. The limitation of this method for symmetric layup composite laminates is analyzed and a potential improvement approach is further discussed.

Inverse estimation of impact force on a composite panel using a single piezoelectric sensor

Identification of location and magnitude of impact forces on a rectangular carbon fibre–epoxy honeycomb composite panel has been experimentally investigated through an inverse approach. The dynamic signals captured by a single piezoelectric (PZT) sensor installed on the panel remotely from the impact locations are utilized to identify the impact forces generated by an instrumented hammer. A number of potential impact locations on the panel are assumed to be known a priori. An actual impact is then occurred at one or two of these locations. The objective is to simultaneously identify the location and magnitude of the impact forces using the PZT sensor. The problem is solved through minimization of an extended matrix form of the convolution integral incorporating linear superposition of the responses due to impact at different locations. The under-determined problem is ill-posed and is regularized by Tikhonov and generalized cross validation methods. It is revealed that impact forces occurred at any location among four possible locations can be well identified.

Automated Operational Modal Analysis of a Cable-Stayed Bridge

11 Automated techniques for analyzing the dynamic behavior of full-scale civil structures are becoming 12 increasingly important for continuous structural health monitoring applications. This paper aims to extract the 13 structural modal parameters of a full-scale cable-stayed bridge from the collected ‘output-only’ vibration data 14 without the need of any user interactions. The work focuses on the development of an automated and robust 15 operational modal analysis (OMA) algorithm, utilizing a multi-stage clustering approach. The main 16 contribution of the work is to define a novel way of automatically defining the hierarchical clustering threshold 17 to enable the accurate identification of a complete set of modal parameters. The proposed algorithm is 18 demonstrated to work with any parametric system identification algorithm that uses the system order ‘n’ as the 19 sole parameter. In particular the results from Covariance-driven Stochastic Subspace Identification (SSI-Cov) 20 methods are presented. 21

Identification of Location and Magnitude of Impact Force on a Composite Sandwich Structure With Lattice Truss Core

In this study, a new method was developed to estimate both the location and magnitude of an impact force applied to a composite sandwich panel with lattice truss core using an inverse algorithm based on dynamic characteristics of the structure. A method utilizing deconvolution with a transfer function in the time domain was employed to tackle the problem. The dynamics signals were captured using a Scanning Laser Doppler Vibrometer (SLDV) and the force is applied using a shaker. It is assumed that a set of impact forces be applied at a set of locations of the structure at the same time, but the magnitude of all impact forces except one is set to zero, implying that an impact event has occurred at only one of the possible locations. The aim is then to find the unknown impact location among the other possible ones as well as the magnitude of the impact force. The least-square approach is adopted, and the truncated singular value decomposition is then used to regularize and solve the problem.Copyright