Guirong Yan

Cyber-Physical Codesign of Distributed Structural Health Monitoring with Wireless Sensor Networks

Our deteriorating civil infrastructure faces the critical challenge of long-term structural health monitoring for damage detection and localization. In contrast to existing research that often separates the designs of wireless sensor networks and structural engineering algorithms, this paper proposes a cyber-physical codesign approach to structural health monitoring based on wireless sensor networks. Our approach closely integrates 1) flexibility-based damage localization methods that allow a tradeoff between the number of sensors and the resolution of damage localization, and 2) an energy-efficient, multilevel computing architecture specifically designed to leverage the multiresolution feature of the flexibility-based approach. The proposed approach has been implemented on the Intel Imote2 platform. Experiments on a simulated truss structure and a real full-scale truss structure demonstrate the systems efficacy in damage localization and energy efficiency.

Cyber-physical codesign of distributed structural health monitoring with wireless sensor networks

Our deteriorating civil infrastructure faces the critical challenge of long-term structural health monitoring for damage detection and localization. In contrast to existing research that often separates the designs of wireless sensor networks and structural engineering algorithms, this paper proposes a cyber-physical codesign approach to structural health monitoring based on wireless sensor networks. Our approach closely integrates 1) flexibility-based damage localization methods that allow a tradeoff between the number of sensors and the resolution of damage localization, and 2) an energy-efficient, multilevel computing architecture specifically designed to leverage the multiresolution feature of the flexibility-based approach. The proposed approach has been implemented on the Intel Imote2 platform. Experiments on a simulated truss structure and a real full-scale truss structure demonstrate the systems efficacy in damage localization and energy efficiency.

Review of Benchmark Studies and Guidelines for Structural Health Monitoring

In the past three decades, Structural Health Monitoring (SHM) has attracted considerable attention. The great achievements in theoretical study and the engineering applications of SHM are very encouraging and promising. Numerous approaches and techniques have been proposed and applied to different structures, making it difficult to compare and contrast the merits of the various methodologies. An SHM benchmark study provides a platform for comparing and evaluating the performance of SHM approaches and techniques on a consistent basis. This paper reviews the SHM benchmark studies. For each case, the physical structure, the numerical study, the scaled laboratorial model experiment as well as the comparisons made between results obtained from the variety of approaches are reviewed. The latest developments in guidelines on the application of SHM techniques is also be reviewed.

Structural damage detection robust against time synchronization errors

Structural damage detection based on wireless sensor networks can be affected significantly by time synchronization errors among sensors. Precise time synchronization of sensor nodes has been viewed as crucial for addressing this issue. However, precise time synchronization over a long period of time is often impractical in large wireless sensor networks due to two inherent challenges. First, time synchronization needs to be performed periodically, requiring frequent wireless communication among sensors at significant energy cost. Second, significant time synchronization errors may result from node failures which are likely to occur during long-term deployment over civil infrastructures. In this paper, a damage detection approach is proposed that is robust against time synchronization errors in wireless sensor networks. The paper first examines the ways in which time synchronization errors distort identified mode shapes, and then proposes a strategy for reducing distortion in the identified mode shapes. Modified values for these identified mode shapes are then used in conjunction with flexibility-based damage detection methods to localize damage. This alternative approach relaxes the need for frequent sensor synchronization and can tolerate significant time synchronization errors caused by node failures. The proposed approach is successfully demonstrated through numerical simulations and experimental tests in a lab.

Numerical simulation of vortex-induced vibration of two circular cylinders of different diameters at low Reynolds number

Two-degree-of-freedom Vortex-Induced Vibration (VIV) of two rigidly coupled circular cylinders of different diameters at a low Reynolds number of 250 is investigated numerically. While the diameter ratio and the mass ratio are kept constant, the study is focused on the effect of the position angle of the small cylinder on the lock-in regime of the VIV. Simulations are carried out for position angles α of the small cylinder ranging from 0° to 180° with an interval of 22.5° and the reduced velocities ranging from 1 to 15 with an increment of 1. In order to find the effect of the gap between the two cylinders on the vibration, two gap-to-diameter ratios (0 and 0.2) are considered. It is found that compared with a single cylinder case, the lock-in regime of the reduced velocity is widened significantly when the position angle of the small cylinder is α = 0°, 22.5°, 90°, or 112.5°. Pulsed beating phenomenon characterized by regular vibration with occasional high-amplitude disturbances at regular or irregular intervals is observed at G = 0 and α = 90°. At α = 135°, more than one lock-in regimes are observed in the computed range of reduced velocity for both gaps (G = 0 and 0.2). Setting a small gap (gap-to-diameter ratio of 0.2) between the two cylinders mitigates the vibration by narrowing the lock-in regime and reducing the vibration amplitude.

Hysteretic analysis of steel plate shear walls (SPSWs) and a modified strip model for SPSWs

Steel plate shear walls (SPSWs) have become more and more popular in recent years because of their potential huge energy dissipation capacity and ductility under lateral loads. Due to their low cost and fast construction, SPSWs have potential application in practice. The finite element software ANSYS applied to the analysis of the hysteretic behavior of SPSWs is described in this paper first. It was found that compressive stress existed in SPSWs and the effects became more evident with decreasing height-to-thickness ratio. This was validated by comparing theoretical and experimental test results. Secondly, based on the analytical results, a modified strip model is proposed. In the modified model, the compressive effects in the panel were taken into account and it was then found that the load-carrying capacity and the energy dissipation capacity agreed well with the already carefully validated experimental results.

Structural damage detection using the polynomial annihilation edge detection method

It is well-known that damage in a structure may cause a discontinuity in mode shapes or their derivatives, which has been used as a basis for some damage detection approaches. However, if the severity of damage is small, the discontinuity will be difficult to be detected. The polynomial annihilation edge detection method improves the accuracy of localising discontinuity in a function by determining intervals of smoothness in the function. The feasibility of this edge detection method in localising and quantifying cracks in a cantilevered beam has been demonstrated (Surace et al, 2013). This study is to further validate this edge detection method on various types of structures and damages using numerical simulations. First, this method is performed on a cantilever aluminium bar under longitudinal vibrations to localise and quantify cracks; then, it is performed on a simply supported steel beam to detect cracks. Finally, this method is applied to a more complicated structure, a cable-stayed bridge model, to localise the damage occurring in girders.

Evaluating the performance of distributed approaches for modal identification

In this paper two modal identification approaches appropriate for use in a distributed computing environment are applied to a full-scale, complex structure. The natural excitation technique (NExT) is used in conjunction with a condensed eigensystem realization algorithm (ERA), and the frequency domain decomposition with peak-picking (FDD-PP) are both applied to sensor data acquired from a 57.5-ft, 10 bay highway sign truss structure. Monte-Carlo simulations are performed on a numerical example to investigate the statistical properties and sensitivity to noise of the two distributed algorithms. Experimental results are provided and discussed.

A General Nonlinear System Identification Method Based upon Time-Varying Trend of Instantaneous Frequencies and Amplitudes

Nonlinear phenomena are widely encountered in practical applications. The presence of nonlinearity makes a system exhibit different dynamic behaviours from its linear counterpart. A typical example is that free-vibration frequencies of nonlinear systems are amplitude-dependent, resulting in the variation of free-vibration frequencies with time. Therefore, Fourier spectrum which has been widely used in linear systems cannot completely represent dynamic characteristics of nonlinear systems. On the contrary, the time-varying trend of instantaneous frequencies and vibration amplitudes can completely capture dynamic characteristics of nonlinear systems. In this study, a general system identification method based on curving-fitting the time-varying trend of instantaneous frequencies and amplitudes is proposed for nonlinear systems. Herein Hilbert transform is employed to extract instantaneous frequencies and amplitudes from the measured responses. By taking the relationships between instantaneous vibration characteristics and structural physical parameters as regression models, structural physical parameters can be estimated by a least-squares estimation or an optimization method. The combination of the instantaneous information in time domain and frequency domain leads to high accuracy of identification results. The determination of model structure of nonlinearities is solved by assuming a generalized model which involves as many types of nonlinearities as possible. The proposed method has been demonstrated by numerical simulations.

Effects of high modes on the wind-induced response of super high-rise buildings

For super high-rise buildings, the vibration period of the basic mode is several seconds, and it is very close to the period of the fluctuating wind. The damping of super high-rise buildings is low, so super high-rise buildings are very sensitive to fluctuating wind. The wind load is one of the key loads in the design of super high-rise buildings. It is known that only the basic mode is needed in the wind-response analysis of tall buildings. However, for super high-rise buildings, especially for the acceleration response, because of the frequency amplification of the high modes, the high modes and the mode coupling may need to be considered. Three typical super high-rise projects with the SMPSS in wind tunnel tests and the random vibration theory method were used to analyze the effect of high modes on the wind-induced response. The conclusions can be drawn as follows. First, for the displacement response, the basic mode is dominant, and the high modes can be neglected. Second, for the acceleration response, the high modes and the mode coupling should be considered. Lastly, the strain energy of modes can only give the vibration energy distribution of the high-rise building, and it cannot describe the local wind-induced vibration of high-rise buildings, especially for the top acceleration response.