Damage detection of bridge structures under unknown seismic excitations using support vector machine based on transmissibility function and wavelet packet energy

Lijun Liu,Jianan Mi,Yixiao Zhang,Ying Lei 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.2

Since it may be hard to obtain the exact external load in practice, damage identification of bridge structures using only structural responses under unknown seismic excitations is an important but challenging task. Since structural responses are determined by both structural properties and seismic excitation, it is necessary to remove the effects of external excitation and only retain the structural information for structural damage identification. In this paper, a data-driven approach using structural responses only is proposed for structural damage alarming and localization of bridge structures. The transmissibility functions (TF) of structural responses are used to eliminate the influence of unknown seismic excitations. Moreover, the inverse Fourier transform of TFs and wavelet packet transform are used to reduce the influence of frequency bands and to extract the damagesensitive feature, respectively. Based on Support vector machines (SVM), structural responses under ambient excitations are used for training SVM. Then, structural responses under unknown seismic excitations are also processed accordingly and used for damage alarming and localization by the trained SMV. The numerical simulation examples of beam-type bridge and a cablestayed bridge under unknown seismic excitations are studied to illustrate the performance of the proposed approach.

Disturbance Observer-based LQR Tracking Control for Unmanned Autonomous Helicopter Slung-load System

Lijun Liu,Mou Chen,Tao Li 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.4

This work investigates the optimal tracking control for unmanned autonomous helicopter (UAH) slungload system under external disturbance. Firstly, the linearized UAH slung-load system model is obtained by using the small perturbation linearization method, in which parameter uncertainty and disturbance are considered. Secondly, the control objective is described via a reference model, and the tracking controller is designed for the UAH slung-load system by using the reference model control approach, disturbance observer based-control (DOBC) scheme, and LQR control method. Thirdly, under the proposed tracking controller, the stability of the closed-loop system is analyzed on the basis of Lyapunov stability theory and linear matrix inequality (LMI) technique. Finally, some simulations and comparisons are presented to illustrate the proposed control method.

Locating and identifying model-free structural nonlinearities and systems using incomplete measured structural responses

Liu, Lijun,Lei, Ying,He, Mingyu Techno-Press 2015 Smart Structures and Systems, An International Jou Vol.15 No.2

Structural nonlinearity is a common phenomenon encountered in engineering structures under severe dynamic loading. It is necessary to localize and identify structural nonlinearities using structural dynamic measurements for damage detection and performance evaluation of structures. However, identification of nonlinear structural systems is a difficult task, especially when proper mathematical models for structural nonlinear behaviors are not available. In prior studies on nonparametric identification of nonlinear structures, the locations of structural nonlinearities are usually assumed known and all structural responses are measured. In this paper, an identification algorithm is proposed for locating and identifying model-free structural nonlinearities and systems using incomplete measurements of structural responses. First, equivalent linear structural systems are established and identified by the extended Kalman filter (EKF). The locations of structural nonlinearities are identified. Then, the model-free structural nonlinear restoring forces are approximated by power series polynomial models. The unscented Kalman filter (UKF) is utilized to identify structural nonlinear restoring forces and structural systems. Both numerical simulation examples and experimental test of a multi-story shear building with a MR damper are used to validate the proposed algorithm.

Synthesis, Antioxidant Activity and Fluorescence Properties of Novel Europium Complexes with (E)-2- or 4-hydroxy-N'-[(2-hydroxynaphthalen-1- yl)methylene]benzohydrazide Schiff Base

Lijun Liu,Mohammad Sayed Alam,Dong Ung Lee 대한화학회 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

Two novel Eu(III) complexes with notable properties have been successfully prepared with hydrazone Schiff base ligands, (E)-2-hydroxy-N'-[(2-hydroxynaphthalen-1-yl)methylene]benzohydrazide (3a) and (E)-4-hydroxy- N'-[(2-hydroxynaphthalen-1-yl)methylene]benzohydrazide (3b). DFT, FMO energy and Mulliken charge distribution studies of the ligands allowed us to hypothesize that their HC=N, >C=O and -OH (naphthyl) groups were involved in coordinating with the Eu3+ ion. The eight coordination sites of the Eu3+ ion were occupied by the three functional groups of the two ligands (3a or 3b) mentioned above and two water molecules. Similar UV, IR and fluorescence spectra indicated the presence of comparable coordination environments for the Eu3+ ion in both complexes. Both the ligands and their complexes exhibited moderate DPPH radical scavenging activity. Moreover, it was found that the Eu(III) complexes exhibited fluorescence properties.

Novel Detection Method for MIMO System with Polarization Multiplexing and Transmit Diversity

Lijun Liu,Myoung-Seob Lim 대한전자공학회 2008 ICEIC:International Conference on Electronics, Inf Vol.1 No.1

A novel detection method was devised using the characteristic of polarization for multiple-input multiple - output (MIMO) system with polarizations multiplexing and transmit diversity in mobile communication. Using this detection method the MIMO system can increase the transmission rate twice while maintaining almost same bit error rate (BER) performance.

Locating and identifying model-free structural nonlinearities and systems using incomplete measured structural responses

Lijun Liu,Ying Lei,Mingyu He 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.2

Structural nonlinearity is a common phenomenon encountered in engineering structures under severe dynamic loading. It is necessary to localize and identify structural nonlinearities using structural dynamic measurements for damage detection and performance evaluation of structures. However, identification of nonlinear structural systems is a difficult task, especially when proper mathematical models for structural nonlinear behaviors are not available. In prior studies on nonparametric identification of nonlinear structures, the locations of structural nonlinearities are usually assumed known and all structural responses are measured. In this paper, an identification algorithm is proposed for locating and identifying model-free structural nonlinearities and systems using incomplete measurements of structural responses. First, equivalent linear structural systems are established and identified by the extended Kalman filter (EKF). The locations of structural nonlinearities are identified. Then, the model-free structural nonlinear restoring forces are approximated by power series polynomial models. The unscented Kalman filter (UKF) is utilized to identify structural nonlinear restoring forces and structural systems. Both numerical simulation examples and experimental test of a multi-story shear building with a MR damper are used to validate the proposed algorithm.

Improved Kalman filter with unknown inputs based on data fusion of partial acceleration and displacement measurements

Lijun Liu,Jiajia Zhu,Ying Su,Ying Lei 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.17 No.6

The classical Kalman filter (KF) provides a practical and efficient state estimation approach for structural identification and vibration control. However, the classical KF approach is applicable only when external inputs are assumed known. Over the years, some approaches based on Kalman filter with unknown inputs (KF-UI) have been presented. However, these approaches based solely on acceleration measurements are inherently unstable which leads poor tracking and so-called drifts in the estimated unknown inputs and structural displacement in the presence of measurement noises. Either on-line regularization schemes or post signal processing is required to treat the drifts in the identification results, which prohibits the real-time identification of joint structural state and unknown inputs. In this paper, it is aimed to extend the classical KF approach to circumvent the above limitation for real time joint estimation of structural states and the unknown inputs. Based on the scheme of the classical KF, analytical recursive solutions of an improved Kalman filter with unknown excitations (KF-UI) are derived and presented. Moreover, data fusion of partially measured displacement and acceleration responses is used to prevent in real time the so-called drifts in the estimated structural state vector and unknown external inputs. The effectiveness and performance of the proposed approach are demonstrated by some numerical examples.

Probabilistic damage detection of structures with uncertainties under unknown excitations based on Parametric Kalman filter with unknown Input

Lijun Liu,Han Su,Ying Lei 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.6

System identification and damage detection for structural health monitoring have received considerable attention. Various time domain analysis methodologies based on measured vibration data of structures have been proposed. Among them, recursive least-squares estimation of structural parameters which is also known as parametric Kalman filter (PKF) approach has been studied. However, the conventional PKF requires that all the external excitations (inputs) be available. On the other hand, structural uncertainties are inevitable for civil infrastructures, it is necessary to develop approaches for probabilistic damage detection of structures. In this paper, a parametric Kalman filter with unknown inputs (PKF-UI) is proposed for the simultaneous identification of structural parameters and the unmeasured external inputs. Analytical recursive formulations of the proposed PKF-UI are derived based on the conventional PKF. Two scenarios of linear observation equations and nonlinear observation equations are discussed, respectively. Such a straightforward derivation of PKF-UI is not available in the literature. Then, the proposed PKF-UI is utilized for probabilistic damage detection of structures by considering the uncertainties of structural parameters. Structural damage index and the damage probability are derived from the statistical values of the identified structural parameters of intact and damaged structure. Some numerical examples are used to validate the proposed method

Synthesis, Antioxidant Activity and Fluorescence Properties of Novel Europium Complexes with (E)-2- or 4-hydroxy-N'-[(2-hydroxynaphthalen-1-yl)methylene]benzohydrazide Schiff Base

Liu, Lijun,Alam, Mohammad Sayed,Lee, Dong-Ung Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

Two novel Eu(III) complexes with notable properties have been successfully prepared with hydrazone Schiff base ligands, (E)-2-hydroxy-N'-[(2-hydroxynaphthalen-1-yl)methylene]benzohydrazide (3a) and (E)-4-hydroxy-N'-[(2-hydroxynaphthalen-1-yl)methylene]benzohydrazide (3b). DFT, FMO energy and Mulliken charge distribution studies of the ligands allowed us to hypothesize that their HC=N, > C=O and -OH (naphthyl) groups were involved in coordinating with the $Eu^{3+}$ ion. The eight coordination sites of the $Eu^{3+}$ ion were occupied by the three functional groups of the two ligands (3a or 3b) mentioned above and two water molecules. Similar UV, IR and fluorescence spectra indicated the presence of comparable coordination environments for the $Eu^{3+}$ ion in both complexes. Both the ligands and their complexes exhibited moderate DPPH radical scavenging activity. Moreover, it was found that the Eu(III) complexes exhibited fluorescence properties.

Active Fault-tolerant Control Design for a Submarine Semi-physical Simulation System

Lijun Liu,Wei Yu,Zhen Yu 제어·로봇·시스템학회 2018 International Journal of Control, Automation, and Vol.16 No.5

In this paper, an integrated design of fault diagnosis and active fault-tolerant control is proposed for a submarine semi-physical simulation system in the presence of unknown faults of rudder systems. The semi-physical simulation system is constructed by combining two real rudder control systems and a virtual mathematical model for the vertical movement control of a submarine. The separate modules of the semi-physical simulation system are connected by industrial communication technologies. Then, an active fault-tolerant controller is designed for unknown rudder system faults. Finally, the results of the semi-physical simulation experiments verify the effectiveness of the proposed fault-tolerant control method, and make a solid foundation for designing an active fault-tolerant control system for a real submarine.