Weilian Qu

Design and Fabrication of 500-kN Large-scale MR Damper

This article presents a thorough investigation of a large-scale MR damper which can produce 500 kN damping force and is prepared for application in the vibration reduction of civil engineering. It is known that it is quite important to prepare a high-performance MR fluid for the large-scale MR damper. The high-performance MR fluid is developed and its essential performance characteristics are tested. Test results show that the sedimentation-proof stability, maximum yield shear stress, and response time of the MR fluid satisfy the requirements for applications of the MR damper in the vibration reduction of engineering structures. The designing process is introduced and several key techniques for the MR damper design, including built-in disk-spring accumulator, magnetic-flux leakage prevented design, leakage prevention of magnetorheological fluid, and stability enhancement of the controller for large-scale MR damper are proposed. Finally, the performance experiments of the MR damper are carried out.

Active/Robust Control of Longitudinal Vibration Response of Floating-Type Cable-Stayed Bridge Induced by Train Braking and Vertical Moving Loads

The active/robust control of the longitudinal vibration response of the deck of floating-type cable-stayed bridges induced by train braking and vertical moving loads has been investigated in this paper. Controlled objects of large structures such as long span bridges generally have high orders of controlled variables and this may lead to high costs and complications of controllers. Hence, a reduced controlled model of lower orders based on a modal reduction method has been proposed. Because the controller designed from the reduced model may influence the control effect of the original controlled system; the stability and error of the reduced model have been studied. The results indicate that when a sufficient number of modals are included in the model, the influence is very small. In view of parameter uncertainties in long span bridge structures, the active robust control equations based on frequency uncertainties have been derived, and the active robust control of longitudinal vibration responses of the deck, which are induced by train braking and vertical moving loads, has been simulated for Tian Xingzhou Yangtze River Bridge in China. Simulated results have been compared with results of the active control based on the linear quadratic regulator (LQR) algorithm. Comparisons have shown that the robust control is more effective and efficient than the active control based on the LQR algorithm.

Intelligent control for braking-induced longitudinal vibration responses of floating-type railway bridges

This paper presents an intelligent control method and its engineering application in the control of braking-induced longitudinal vibration of floating-type railway bridges. Equations of motion for the controlled floating-type railway bridges have been established based on the analysis of the longitudinal vibration responses of floating-type railway bridges to train braking and axle-loads of moving trains. For engineering applications of the developed theory, a full-scale 500 kN smart magnetorheologic (MR) damper has been designed, fabricated and used to carry out experiments on the intelligent control of braking-induced longitudinal vibration. The procedure for using the developed intelligent method in conjunction with the full-scale 500 kN MR dampers has been proposed and used to control the longitudinal vibration responses of the deck of floating-type railway bridges induced by train braking and axle-loads of moving trains. This procedure has been applied to the longitudinal vibration control of the Tian Xingzhou highway and railway cable-stayed bridge over the Yangtze River in China. The simulated results have shown that the intelligent control system using the smart MR dampers can effectively control the longitudinal response of the floating-type railway bridge under excitations of braking and axle-loads of moving trains.

Study on numerical simulation of fluctuating wind for thunderstorm microburst using harmony superposition method

Thunderstorm microburst is an outburst strong wind on or near the ground, and its field characteristics are significantly different from boundary layer winds. As a kind of high intensity winds, thunderstorm microburst have caused numerous structural failures around the world. The paper studied numerical simulation of fluctuating wind for microburst using harmony superposition method. The stochastic process of fluctuating wind speed was converted to a uniformly modulated stochastic process. The harmony superposition method with introducing fast Fourier transform (FFT) technique was applied to simulate the uniformly modulated stochastic process. As a numerical example, good agreement is achieved between data from the method and full-scale data from a high intensity downburst that occurred at Andrews Air Force Base in 1983.

Numerical study on formation and diffusion wind fields for thunderstorm microburst

As a type of high intensity winds, thunderstorm microbursts have caused numerous structural failures around the world. The numerical method was employed to investigate the formation and diffusion unsteady wind fields for thunderstorm microburst related high intensity winds. Unsteady simulations of formation and diffusion wind fields were conducted using time-filtered Reynolds Averaged Navier-Stokes (RANS) numerical simulation method. The numerical results indicate that the wind fields present quite different characteristics at different time during the whole formation and diffusion process. The magnitude of wind velocity changes greatly during the whole formation and diffusion process. The maximum wind velocity occurs at the moment when the downdraft impacts on the ground and the main vortex is acting separation-reattachment, the secondary vortex is arising. Unsteady simulations supply a promising solution to study the thunderstorm microburst wind characteristics under the current conditions with lack detailed full scale data.

Finite element model updating for space truss structure by fuzzy pattern identification

Taking the roof space truss structure of Shenzhen Citizen Center as the engineering background, a novel finite element model updating method for the large space steel truss structure is proposed in the paper. Among all the components, the numerical models accuracy depends on the joint rigidity of the nodes. Thus the main purpose of updating is to determine the proper joint rigidity of all nodes. The process is conducted as following: Firstly, nodes are classified according to their size and rigidity, and then by changing joint rigidity parameters of different types of nodes and utilizing finite element method, the database which reflects the relationship between joint rigidity parameters and natural vibration frequencies of model is established. Secondly, structural natural vibration frequencies are selected as the input, and joint rigidity parameters of classified nodes are the output data, the fuzzy pattern system is obtained. Finally, the measured natural vibration frequencies of the roof structure of Shenzhen Citizen Center are inputted into the fuzzy pattern identification system, and then rigidity parameters of three categories of joint are determined. Thus, accurate finite element model of the roof space truss structure of Shenzhen Citizen Center is achieved.

Longitudinal vibration analysis of floating-type railway cable-stayed bridge subjected to train braking

This paper investigates the longitudinal vibration behavior of the deck of a floating-type cable-stayed bridge that is subjected to train braking and axle-loads of moving trains. A dynamic model for train braking and axle-loads of moving trains has been established based on the vehicle dynamics. The longitudinal forces induced by train braking and axle-loads of moving trains have been obtained. Meanwhile the developed theory has been applied to the Tian Xingzhou Yangtze River Bridge in China, the longest highway and railway floating-type cabled-stayed bridge in the world. The longitudinal vibration responses of the deck to train braking and axle-loads of moving trains have been calculated, and the characteristics of the dynamical response of the bridge are summarized.

Fuzzy mode identification method for propagation of three dimension straight through crack of ear plate of mast structure

This paper introduced the procedures of modeling a 3-D straight through crack at weld of ear plate of mast with ANSYS solid modeling method. Established the crack model separately from the overall model and then combine them with command of Boolean. Control the order of meshing by creating the transitional area around the crack which makes it flexible and convenient to create the model. And using fuzzy mode identification method to establish fuzzy sets of mapping between length of crack and stress field of the surface node of ear plate under the different conditions and obtain the crack length by identifying the sample of stress field of the surface node of ear plate.

Solid modeling method and calculation of stress intensity factor for structure with 3-D Surface Crack

This paper introduced the detailed procedures of modeling a 3-D Surface Crack with ANSYS solid modeling method. The method adopted the idea of break up the whole into parts. The crack part was established on the entire bridge model. To separate the entire model into two main parts by Boolean operation, mesh the crack part with particular method and the non-crack part with routinely free mapped method and pay attention to the transition of different meshing method. A comparison with direct modeling method of nodes by nodes had also been made. The results showed that the solid modeling method was simple and efficient and could be carried on easily, it was suitable to establish complicated configured model and had a high precision guarantee of stress intensity factor.

Damage diagnosis by static response of underwater shell structures based on improved genetic algorithms

Taking an underwater shell structure as engineering background, the Improved Genetic Algorithms (IGAs) is applied to detect the structural damage by static response data acquisition in the paper. Firstly, region water-level and finite point strains of the underwater shell structure are measured. Then, the Genetic Algorithms (GAs) are optimized. Finally, the structural damage location and degree are identified by comparison between measurement strains and calculation ones. When the measured strains are approached most close to the one among all the calculation strains, the structural damage condition is determined. In order to diagnose the large-scale structural damage by GAs, the decoding the damage location and damage index at same time is proposed, as well as, fine-tuning of variables and niche technique are also introduced to improve the convergence efficiency of GAs.