Z.R. Lu

A two-step approach for damage Identification in plates:

This paper presents a two-step approach based on modal strain energy and response sensitivity analysis to identify the local damages in isotropic plates with moderate thickness. The first step focuses on detection of damage location. The local damage is simulated by a reduction in the elemental Young’s modulus of the plate. It is determined from the modal strain energy change ratio approach. A method to weaken the “vicinity effect” is proposed to reduce the false alarms in the localization of damage. In the second step, an approach based on response sensitivity-based finite element model updating is used to further identify the locations and extents of the local damages in time domain. The identified results are obtained iteratively with Tikhonov regularization using the measured structural dynamic responses. Two numerical examples are investigated to illustrate the correctness and efficiency of the proposed method. Both single and multiple damages can be identified successfully and the effect of measurement noise on the identification results is investigated. Good identified results can be obtained from the short time histories of a few number of measurement points.

Structural damage identification based on cuckoo search algorithm

A method for structural damage identification based on cuckoo search algorithm is presented. The nonlinear objective function for the damage identification problem is established by utilizing modal assurance criteria and structural natural frequencies. Then, the cuckoo search algorithm is adopted to detect local damages by solving the objective function. Two numerical examples are studied to investigate the efficiency and correctness of the proposed method. Meanwhile, a laboratory work is conducted for further verification. The simulation and experiment results show that the present method can produce more accurate damage identification results even under measurement noise, comparing with genetic algorithm.

Parametrically excited vibrations of marine riser under random wave forces and earthquake

This article presents theoretical studies for parametrically excited vibrations of marine riser of the floating production, drilling, storage, and offloading system under random wave forces and earthquake excitation. The equation of motion of the riser is obtained by a mathematical method utilizing Euler beam theory and Galerkin method. The trigonometric series method is used to formulate random wave force and earthquake excitation in time domain. The dynamic analysis, spectral response analysis, and key parameters’ sensitivity analysis are conducted for the riser system. Parameter studies are conducted for the effects of wave and earthquake parameters and structural parameters on dynamics response of the riser system. The results from this study can provide valuable recommendations for the design and construction of the parametrically excited marine riser system under random wave forces and earthquake excitation and can promote widely practical application of the deep water riser in complicated environmental conditions.

Bird mating optimizer for structural damage detection using a hybrid objective function

Abstract A structural damage detection approach based on bird mating optimizer (BMO) in time-frequency domain is proposed in this paper. A hybrid objective function is introduced by minimizing the discrepancies between the measured and calculated natural frequencies and correlation function vector of acceleration of damaged and intact structures. Then the BMO algorithm with a disturbance procedure is developed to solve the objective function. Benefited from the hybrid objective function, only a few number of natural frequencies are needed in the detection process. And the disturbance procedure designed in this paper can enhance the precision of identification. The efficiency and robustness of the proposed method are verified by a planar truss and a frame, a three connected shear buildings and an experimental work. The studies in numerical simulations validate that the proposed objective function and disturbance procedure are helpful to improve the precision of identification. The experimental work shows that the proposed method has the potential of practical application. In addition, comparison among the proposed method and other optimization algorithms, i.e. GA, ABC, L-SHADE and HCLPSO, reveals the superiority of the proposed method in structural damage detection.

A Two-Step Approach for Structural Damage Localization and Quantification Using Static and Dynamic Response Data

A two-step approach based on coupled static and dynamic structural responses is proposed for local damage identification in this study. Firstly the suspicious damaged elements are predicted by calculating the residual force vector which is derived from the equation of static equilibrium. As the suspicious damaged elements are determined, a response sensitivity based model updating method is applied to quantify the damage extents. The proposed method is verified with both single and multiple damages identification from several numerical simulations. Local damages can be identified successfully from the proposed method and the damage extents are in good agreement with the true values. The results of the simulation also show that the proposed method is insensitive to the artificial measurement noise.

Bird Mating Optimizer in Structural Damage Identification

In this paper, a structural damage detection approach based on bird mating optimizer BMO is proposed. Local damage is represented by a perturbation in the elemental stiffness parameter of the structural finite element model. The damage parameters are determined by minimizing the error derived from modal data, and natural frequency and modal assurance criteria MAC of mode shape is employed to formulate the objective function. The BMO algorithm is adopted to optimize the objective and optimum set of stiffness reduction parameters are predicted. The results show that the BMO can identify the perturbation of the stiffness parameters effectively even under measurement noise.

Identification of distributed damage in bridges from vehicle-induced dynamic responses

This article presents a distributed damage identification approach based on dynamic response sensitivity of the moving vehicle. Numerical studies are carried out on a simply supported beam and a continuous two-span bridge under a vehicle with nonlinear springs for identification of distributed damage due to the cracks. Combined Newmark direct integration method and Runge–Kutta method are used to calculate the dynamic responses of the coupled bridge–vehicle system. The numerical results show that the distributed damage(s) can be identified accurately by the measured acceleration data of four virtual moving acceleration sensors and it is insensitive to the measurement noise.

Monitoring Dynamic Characteristics for a Supertall Structure under Different Loading Events

The Guangzhou New TV Tower (GNTVT), completed its construction in May 2009 in Guangzhou China, is a super tall tube-in-tube structure with a total height of 600m. A complicated structural health monitoring (SHM) system consisting of over 700 sensors has been implemented to the GNTVT for both in-construction and in-service real-time monitoring. This implemented SHM system has monitored the structural responses of the GNTVT after having completed its construction under different loading events (the typhoon, the earthquake and normal wind loading conditions). Firstly, the time history and PSD of the acceleration response under different loading events have been compared. Secondly, the modal properties (modal frequencies, mode shapes, and damping ratios) of the structure under different loading events have been identified. The results of this paper supply some references for better understanding the dynamic characteristics of supertall under different loadings.

Precise identification of moving vehicular parameters based on improved glowworm swarm optimization algorithm

Abstract This paper proposes an indirect method for the identification of moving vehicular parameters using the dynamic responses of the vehicle. The moving vehicle is modelled as 2-DOF system with 5 parameters and 4-DOF system with 12 parameters, respectively. Finite element method is used to establish the equation of the coupled bridge–vehicle system. The dynamic responses of the system are calculated by Newmark direct integration method. The parameter identification problem is transformed into an optimization problem by minimizing errors between the calculated dynamic responses of the moving vehicle and those of the simulated measured responses. Glowworm swarm optimization algorithm (GSO) is used to solve the objective function of the optimization problem. A local search method is introduced into the movement phase of GSO to enhance the accuracy and convergence rate of the algorithm. Several test cases are carried out to verify the efficiency of the proposed method and the results show that the vehicular parameters can be identified precisely with the present method and it is not sensitive to artificial measurement noise.

Analysis of Dynamic Characteristics of the Canton Tower under Different Earthquakes

This paper presents the experimental modal analysis of the Canton Tower from the ambient vibration measurements under different earthquake excitation conditions. Firstly, the time history and Power Spectral Density (PSD) of the acceleration response under different earthquake excitations have been compared. Secondly, two output-only modal identification techniques are applied to the field measurements under earthquake excitations to identify the dynamic properties of the tower, namely, the Frequency Domain Decomposition (FDD) and the Subspace Stochastic Identification (SSI). At last, the Hilbert-Huang transform (HHT) method is applied to obtain the instantaneous frequencies and energy distribution under different loadings in the time-frequency domain and the results are compared with those from wavelet transform. The modal properties of the Canton Tower presented in this paper can be used as baseline for structural health monitoring and the analysis of dynamic characteristic of the high-rise structures under different earthquake excitations in future.