Peng Xu’s research while affiliated with Jinan University (Guangzhou, China) and other places

This paper proposes a theoretical model for the forced vibration of time-varying elevator traction systems caused by eccentric excitation of the traction machine. Based on the Hamilton principle and a variational principle with variable boundaries, the equations of motion and the complex boundary condition of a time-varying elevator traction system are established. A quantitative formula between the angular velocity of the traction machine, the diameter of the traction wheel, the elevator running distance and the running time is put forward. It is found that when the maximum values of acceleration and deceleration exceed 1.5 m/s², the elevator traction system may undergo resonance.

Elevators used in ultra-high buildings are prone to vibrating due to their ultra-long traction ropes, which significantly affects the comfort and safety of high-speed elevators. Therefore, vibration of the elevator has always been a topic of research interest. This paper presents a theoretical model for analyzing the tension–torsion coupling vibration of the time-varying elevator traction system. The constitutive relations with the tension–torsion coupling effect of the wire rope are reduced by analyzing the deformation mechanism of the spiral winding wire rope. Based on Hamilton’s principle, the equations of motion and corresponding boundary conditions for the tension–torsion coupling vibration of the elevator traction system are derived. The Galerkin method is employed to account for the influence of nonlinear boundary conditions and to transform the equations of motion into discrete ones with variable coefficients of time, which are solved using the Newmark-β method. The accuracy of the proposed model is justified by the good agreement between theoretical predictions and experimental results, following which, the influence of the operation status and structural parameters of the elevator traction system on its vibration performance is discussed in detail.

This paper proposes a novel approach to scrutinize the creep buckling of the super-heating pipes in boilers subjected to external pressure in high temperature environment. It is well known that once buckling occurs, cylindrical shells will collapse instantly. As the load carrying capability of the cylindrical shell decreases sharply upon the occurrence of the buckling, the proposed analysis is based on the consideration that the creep will have a significant influence on the material properties only in the pre-buckling stage. According to the creep aging theory, the influence of the creep deformation on the mechanical response of the super-heating pipes is defined by introducing two parameters--the reduced Young's modulus and the reduced Poisson's ratio. The nonlinear constitutive relation for creep deformation of the super-heating pipes in high-temperature environment is established based on the deformation theory in mechanics of plasticity. Governing equations for creep buckling of super-heating pipes in boilers are derived by considering the extra change of curvature due to the initial curvature of the super-heating pipes. MATLAB programs are developed based on the analytical expression for super-heating pipes with simply supported boundary conditions at the two ends and are tested against the available experimental results and the finite element prediction from ABAQUS software. It is found that the components of the creep strain caused by the stress at high temperature far exceeds those of the elastic strain. As a results of that, the creep buckling load of the super-heating pipes is much lower than its elastic buckling load. From this study, an explicit expression to compute the creep buckling load is provided which facilitates engineer to easily predict the residual life of the super-heating pipes at different servo temperature and servo time.

In order to analyze emergency stop vibration of the friction vertical lifting system under different loads, a loading experiment was carried out, and the longitudinal vibration characteristics of the carriage, frame, and steel rope were measured during the emergency braking process of an elevator. Accordingly, it is found that the load mass does not affect the peak deceleration value of the car frame and the wire rope during downwards emergency stop. Then, vertical vibration is explored using the time-varying vibration analysis theory. The obtained results show that when analyzing the vibration of objects on both sides of the traction wheel, the deceleration of the wire rope on both sides of the traction wheel are not equal, and the influence of the pressure change during the traction-wheel friction should be considered in calculations. This article may provide a reference to calculate the steel rope tension of the elevator and mine hoist.

An elevator traction system is simplified as a damped vibration system. In order to study the damping characteristics of an elevator traction system, this paper tests the vibration characteristics of a car frame on an in-service elevator with a traction ratio of 2:1. The results show that the natural frequency and stiffness of the system decrease with the increase of the elevator load; the attenuation coefficient and damping increase with the increase of the elevator load; Furthermore, the damping of the traction system is related to the initial running direction. Under the same load, the damping value of downward is greater than that of upward. This research establishes the relationship between vibration parameters, load and elevator running direction and provides an approach to solve the problem of quantitative measurement of damping in the process of elevator operation. Results from this study can provide reference for elevator vibration analysis.

This paper presents a theoretical approach to analyze the eccentric bending and buckling of laminated cantilever beams actuated by embedded pre-stretched SMA wires. Two mechanisms are involved: phase transition of the SMA wires and the nonlinear bending of the laminated beam. On the basis of material model for shape memory alloy during the phase transition in thermal field proposed by Brison, constitutive relations of the SMA hybrid laminated beams are established to interpret the relationship among the recovery stress, the internal stress, the thermal temperature and the thermal expansion. Governing equations in terms of the slope function and the horizontal displacement are derived according to von-Kaman geometrically nonlinear relationships. The nonlinear bending deformation of the SMA hybrid laminated beams is analyzed by considering the deflection due to eccentric bending moment as an initial imperfection and is solved using perturbation approach. A compatible condition is proposed to ensure consistent deformation between the SMA wires and the laminated beams. By developing Matlab program, parametric studies are carried out to investigate the effect of the pre-strain, the volume fraction and the location of the SMA wires on the deflection, the critical temperature, the recovery stress and the internal stress of the SMA hybrid laminated beams. The efficiency and accuracy of the analytical solutions were expounded by comparing with the results from finite element analysis. It is found that buckling may or may not occur in the SMA hybrid laminated beam relying on the value of the pre-strain of the SMA wires.

An elevator is a typical flexible lifting machine. In order to monitor the vibration of elevator structure, the vibration characteristics of an elevator with a traction ratio of 1:1 has been tested experimentally. Sensors were arranged on the platform frame, car roof, and hoist rope to test the vibrations of the elevator in both ascending and descending conditions. The transverse, longitudinal, and coupled transverse-longitudinal vibrations were compared and analyzed. Further, the short-time Fourier transform (STFT) method was used to examine the power spectral density (PSD) of the test results, and the main frequency distribution and influencing factors of the vibration of elevator components were investigated. The results revealed that the transverse and longitudinal vibrations of the platform frame were low-frequency vibrations, which was attributed to the elastic interaction between the platform frame and the car frame. The form and amplitude of longitudinal vibration of the car frame were basically consistent with those of the platform frame, but PSD of the transverse vibration had an obvious peak in the high-frequency region. The transverse and longitudinal vibration frequencies of the hoist rope were higher. Furthermore, the peak PSD value of transverse vibration of the hoist rope was 421 times larger than that of the car frame, so a small disturbance at the end of the rope could lead to a huge disturbance in the center of the rope. Overall, this study provides useful insights on designing an elevator monitoring sensor and relevant data processing.

In order to study the relationship between the braking distance and the load of escalator and realize the prediction of the rated load braking distance with a little load, the method of combining theoretical analysis and experimental research is used. First, the dynamic characteristics of the escalator during emergency braking are analyzed, and the prediction model of the braking distance of the escalator under different loads is derived based on the law of conservation of energy. Furthermore, the influence coefficients under different loads were determined through experimental studies, the model was revised, and the concept of equivalent no-load kinetic energy (ENKE) was proposed. The research shows that the braking distance of the escalator increases nonlinearly with the increase in load. When the no-load braking distance and the 25% rated load braking distance change greatly, the braking distance increases faster as the load increases; the escalators with large brake force have a small ENKE and are easy to stop. Otherwise, it is difficult to stop. The test results show that the comparison between the predicted value of the prediction model and the measured value has a maximum error of 2.7%, and the maximum error at rated load is only 2.0%, which fully meets the needs of engineering measurement. And the prediction method reduces test costs, enhances test security, and improves test coverage.