Structural health monitoring of beams with moving oscillator: theory and laboratory

In this paper, a new intelligent portable mechanical system is introduced experimentally and theoretically to detect damage employing the fuzzy-genetic algorithm and EMD. For this purpose, the acceleration-time history is obtained from three points of a simply-supported beam utilizing accelerometer sensors. The gained signal is decomposed into small components by using an EMD method. Each decomposed component contains a specific frequency range. Finally, the proposed algorithm is designed to find the location and severity of damage through the frequency variation pattern among the safe and the damaged beam.

Investigating coupled train-bridge-bearing system under earthquake and train-induced excitations

The dynamic interaction between a bridge and a moving train has been widely studied. However, there is a significant gap in our understanding of how the presence of isolation bearings influences the dynamic response, especially when an earthquake occurs. Here we formulate a coupled model of a train-bridge-bearing system to examine the bearings' dynamic effects on the system responses. In the analysis, the train is modeled as a moving oscillator, the bridge is a one span simply-supported beam and one isolation bearing is installed under each support of the bridge. A mathematical model using fractional derivatives is used to capture the viscoelastic properties of the bearings. Vertical response is the focus of this investigation. Dynamic substructuring is used in the modeling to efficiently capture the coupled dynamics of the entire system. Illustrative numerical simulations are carried out to examine the effects of the bearings. The results demonstrate that although the presence of bearings typically decreases the bridge seismic responses, there is potential to increase the bridge response induced by the moving train.

An acceleration-based approach for crack localisation in beams subjected to moving oscillators

In this study, an output-only crack localisation method based on the Hilbert–Huang transform is proposed for crack localisation in bridge-type structures subjected to a moving vehicle simulated by a moving oscillator. The proposed method can accurately identify the location of cracks without using the conventional computationally expensive model updating techniques. The new crack localisation method can be adopted using fixed sensor and moving sensor approaches. In the fixed sensor approach, an acceleration sensor is located on an arbitrary point of the bridge, whereas in the moving sensor approach, an acceleration sensor is attached to a moving vehicle. The efficiency of the fixed sensor and moving sensor approaches is assessed through several numerical examples. A comprehensive analytical study is also conducted to investigate the impacts of crack depth and moving vehicle characteristics (such as damping coefficient, natural frequency, and velocity) on the accuracy of the predictions. It is shown that the proposed crack localisation method using fixed sensor and moving sensor approaches could efficiently identify the location and localisation of the cracks in all cases. However, the results indicate that the accuracy of the fixed sensor approach is generally better than that of the moving sensor approach in the localisation of cracks with small depth.

Dynamic Analysis of Sandwich Auxetic Honeycomb Plates Subjected to Moving Oscillator Load on Elastic Foundation

Based on Mindlin plate theory and finite element method (FEM), dynamic response analysis of sandwich composite plates with auxetic honeycomb core resting on the elastic foundation (EF) under moving oscillator load is investigated in this work. Moving oscillator load includes spring-elastic k and damper c. The EF with two coefficients was modelled by Winkler and Pasternak. The system of equations of motion of the sandwich composite plate can be solved by Newmark’s direct integration method. The reliability of the present method is verified through comparison with the results other methods available in the literature. In addition, the effects of structural parameters, material properties, and moving oscillator loads to the dynamic response of the auxetic honeycomb plate are studied.

Parametric Vibration of a Flexible Structure Excited by Periodic Passage of Moving Oscillators

Flexible structures carrying moving subsystems are found in various engineering applications. Periodic passage of subsystems over a supporting structure can induce parametric resonance, causing vibration with ever-increasing amplitude in the structure. Instead of its engineering implications, parametric excitation of a structure with sequentially passing oscillators has not been well addressed. The dynamic stability in such a moving-oscillator problem, due to viscoelastic coupling between the supporting structure and moving oscillators, is different from that in a moving-mass problem. In this paper, parametric resonance of coupled structure-moving oscillator systems is thoroughly examined, and a new stability analysis method is proposed. In the development, a set of sequential state equations is first derived, leading to a model for structures carrying a sequence of moving oscillators. Through the introduction of a mapping matrix, a set of stability criteria on parametric resonance is then established. Being of analytical form, these criteria can accurately and efficiently predict the dynamic stability of a coupled structure-moving oscillator system. In addition, by the spectral radius of the mapping matrix, the global stability of a coupled system can be conveniently investigated in a parameter space. The system model and stability criteria are illustrated and validated in numerical examples.