Qingjun Yang

Notice of Retraction Nonlinearity analyses of pneumatic vibration isolation system with simple harmonic excitations

Due to the volumetric compressibility of air, the usage of linear models as a mean to describe the behavior of pneumatic vibration isolators is often justified given the range of parameter settings of characteristic system properties. Outside this range, the nonlinear behavior may quickly prevail over the linear behavior. In this paper, a nonlinear model of pneumatic vibration isolator was established, considering the volumetric compressibility of air. Based on this, balance point of the system was analysed and simulation analyses were done using matlab/simulink software. The results show that the system has strong nonlinear characters. Single-frequency excitations can induce harmonic frequency response and offset response at the zero frequency. When the frequency is near to the the linearized natural frequency, the harmonic frequency response become stronger. Nonlinear characters have much to do with the drive amplitude. When the drive amplitude become large, the nonlinear characters are more obvious.

A study on motion and energy absorption characteristics of raft-type wave energy converter

This paper utilizes the method of adding a mass source and a damping term into the fluid governing equation for generating and absorbing the second order stokes wave. A nonlinear mathematic model for a raft-type wave energy converter with three floaters is proposed based on the Lagrange formulation. A number of simulations are accomplished in CFD software by numerically solving the non-linear mathematical model for investigating the motion and energy absorption characteristics of the raft-type wave energy converter. The simulation results show that the increasing of the hydraulic damping can decrease the root-mean-square angular velocity of the floater and increase the hydraulic moment. This indicates that there exists an optimal hydraulic damping for maximizing the absorbed energy.

Nonlinear primary resonances of a pneumatic spring under simple harmonic excitations

The nonlinear primary resonances of a pneumatic spring with simple harmonic excitations were studied by the method of nonlinear dynamics. Through testing, load curve of the pneumatic spring under a certain initial pressure was got. According to the test data, the relative elastic force was fitted to relative displacement by cube polynomial equation. The method of multiple scales was used to solve nonlinear dynamics equations. Nonlinear primary resonances were obtained and the effect of the parameters were studied. The results show that the frequency-response curve have much to do with the parameters. The nonlinearity becomes evidence with cube stiffness increasing. As the amplitude of the excitation increases, the frequency-response curves bend away from the linear axis. The peak amplitude decreases with damping coefficient increasing. These can be quite useful for the designing of a pneumatic vibration isolation system.

Numerical simulation on flow characteristics of PM2.5 in the indoor environment

The research of Particulate Matter (PM2.5) in the indoor environment is a significant research area in the indoor environmental technology. Unfortunately, this research area is in its infancy, and literatures relating to the study of the flow characteristics of PM2.5 in the indoor environment are rarely available. This paper aims to analyze the influence of ventilation mouth location, number, and ventilation speed on the flow characteristics of PM2.5 in the indoor environment by conducting CFD numerical simulations. The results show that locating the ventilation mouth in the side wall, increasing the number of the ventilation mouth in the top wall and selecting an appropriate ventilation speed can contribute to decrease the concentration of PM2.5 of the indoor environment. And it could provide guidance for dust removal technology in the indoor environment.

Latching control using optimal control method for a raft-type wave energy converter

ABSTRACT The method of efficient wave energy harvesting is a significant research field. As a kind of phase control strategy, latching control has been widely applied to point-absorption wave energy converters (WECs). However, the determination of latching duration is a difficult problem especially when the WEC is a multi-degree-of-freedom (DOF) system or includes multiple oscillators. This paper relates to latching control for a raft-type WEC with multiple DOFs and including two oscillators. The control law between latching and unlatching is decided by using the optimal control method, which avoids computing the latching duration directly. Simulations are performed to evaluate how large the benefit that latching control can bring to the raft-type WEC is. Results show that the benefit in terms of ratio between average captured power with latching control and that without control can reach 10.54 in regular waves, whereas it achieves 5.23 in random seas. Furthermore, the influence of wave parameters on the benefit is investigated.

Research on position control of pneumatic switch valves system based on PWM

The pneumatic system based on switch valves has many advantages, such as low cost, high performance, easy maintenance, and so on. The pressure fluctuation produced by open and close of the switch valve will impact on the accuracy of pneumatic position system. A new pneumatic system is established containing an asymmetric cylinder and four switch valves. The Pulse-Width Modulation (PWM) is used to control the system. Every two valves work together, the work time of valves in each PWM period is adjusted by controlling the duty cycle to control the position of the cylinders piston. The steady-state duty cycle is defined to improve the stability of the system when the position deviation is zero or less than the error range. The pressure fluctuation is simulated under different duty cycle and frequency, and the steady-state duty cycles are 47.5% and 52.5%. The model of the system is founded with AMESim, and the simulation results show that the stable time is less than 5 seconds, positional error is less than 5%, accordance with the results of experiments.

Research on elastic deformation compensation system for three axis air bearing platform

The three axis air bearing platform is an important equipment to perform full physical simulations to analogize non-damping movement of the satellite in outer space. The disturbance torque in the out space environment is very small, and this leads to the fact that the disturbance torque of the three axis air bearing platform should be limited in a small region. Previous studies show that the disturbance torque would be produced due to the displacement of the center of mass under the gravity, when the stiffness of the three axis air bearing platform is small. This paper is to investigate the law of the displacement of the center of the mass due to the deformation of the three axis air bearing platform under gravity. Then an elastic deformation compensation system is proposed to diminish the disturbance torque. For validating the reliability of the elastic deformation compensation system, a number of simulation models are achieved. The simulation results show that the disturbance torque can be decreased sharply by the elastic deformation compensation.