Due to the high viscosity of magnetorheological(MR)fluid,eliminating air pockets dissolved in the fluid is very difficult,which results in a force lag phenomenon.In order to evaluate the performance of a semi-active c...Due to the high viscosity of magnetorheological(MR)fluid,eliminating air pockets dissolved in the fluid is very difficult,which results in a force lag phenomenon.In order to evaluate the performance of a semi-active control system based on the MR damper considering the trapped air effect,a performance test on a MR damper is carried out under different loading cases,and the influence of the input current,excitation amplitude and frequency on the force lag phenomenon is analyzed.A concise and efficient parametric model,combining the simple Bouc-Wen model and a spring with small stiffness,is proposed to portray the experimental characteristics of the MR damper with force lag,and then the response analysis of the semi-active controlled single-degree-of-freedom(SDOF)structure is performed using the classic clipped-optimal control strategy based on acceleration feedback.Numerical results show that the trapped air in the MR fluid can weaken the control effect of the MR damper,and the performance of the semi-active control system will be reduced more obviously and become close to the passive-off control with the increasing content of air trapped in the MR fluid.展开更多
Visual and pressurized pipeline systems with single- and multi-undulation layouts were used to study experimentally and analyze theoretically the transient characteristics of water-air two-phase flow during water fill...Visual and pressurized pipeline systems with single- and multi-undulation layouts were used to study experimentally and analyze theoretically the transient characteristics of water-air two-phase flow during water fillings in undulation pipelines based on the combination action analyses of both the communicating pipe and the gravity of the water-air two-phase flows in the descending pipe. For the single undulation pipeline, the complex two-phase flow-pattern evolutions including full pipe flow and stratified flow for low, medium, high water-filling velocity cases, respectively, lead to a great difference in transient pressure, flow pattern and the water-filling duration. Especially for low and medium water-filling velocity cases, the hydraulic theories related to hydraulic drop and hydraulic jump were employed to investigate the entrapped air pocket evolutions in the descending pipe, and the mechanism of negative pressure at the top of the undulation pipes was analyzed. For the same multi-undulation pipeline, due to the different elevations of the three undulation points along flow direction, namely three different types of pipeline layout, high-medium-low case (high elevation undulation point, medium one, and low one), low-medium-high and high-low-medium ones, their water-filling durations are significantly different, i.e., approximately 80.02 s, 227.34 s and 617.78 s. Meanwhile, there are significant differences in flow patterns in water filling, namely larger entrapped air pockets in three descending pipes for the high-medium-low case, entrapped air pockets in the first two descending pipes and open channel stratified flow in the last one for low-medium-high case, some bubbles in three descending pipes for the high-low-medium case.展开更多
基金The National Science Fund for Distinguished Young Scholars(No.51625803)China and Korea International Cooperation Project of the National Key Research and Development Program(No.2016YEE0119700)+3 种基金the Fundamental Research Funds for the Central Universities(No.3205008102)the Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(No.CE02-2-33)Research and Innovation Project for College Graduates of Jiangsu Province(No.KYLX15_0088,KYLX16_0255)the State Foundation for Studying Abroad,China
文摘Due to the high viscosity of magnetorheological(MR)fluid,eliminating air pockets dissolved in the fluid is very difficult,which results in a force lag phenomenon.In order to evaluate the performance of a semi-active control system based on the MR damper considering the trapped air effect,a performance test on a MR damper is carried out under different loading cases,and the influence of the input current,excitation amplitude and frequency on the force lag phenomenon is analyzed.A concise and efficient parametric model,combining the simple Bouc-Wen model and a spring with small stiffness,is proposed to portray the experimental characteristics of the MR damper with force lag,and then the response analysis of the semi-active controlled single-degree-of-freedom(SDOF)structure is performed using the classic clipped-optimal control strategy based on acceleration feedback.Numerical results show that the trapped air in the MR fluid can weaken the control effect of the MR damper,and the performance of the semi-active control system will be reduced more obviously and become close to the passive-off control with the increasing content of air trapped in the MR fluid.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.52079140,51779257).
文摘Visual and pressurized pipeline systems with single- and multi-undulation layouts were used to study experimentally and analyze theoretically the transient characteristics of water-air two-phase flow during water fillings in undulation pipelines based on the combination action analyses of both the communicating pipe and the gravity of the water-air two-phase flows in the descending pipe. For the single undulation pipeline, the complex two-phase flow-pattern evolutions including full pipe flow and stratified flow for low, medium, high water-filling velocity cases, respectively, lead to a great difference in transient pressure, flow pattern and the water-filling duration. Especially for low and medium water-filling velocity cases, the hydraulic theories related to hydraulic drop and hydraulic jump were employed to investigate the entrapped air pocket evolutions in the descending pipe, and the mechanism of negative pressure at the top of the undulation pipes was analyzed. For the same multi-undulation pipeline, due to the different elevations of the three undulation points along flow direction, namely three different types of pipeline layout, high-medium-low case (high elevation undulation point, medium one, and low one), low-medium-high and high-low-medium ones, their water-filling durations are significantly different, i.e., approximately 80.02 s, 227.34 s and 617.78 s. Meanwhile, there are significant differences in flow patterns in water filling, namely larger entrapped air pockets in three descending pipes for the high-medium-low case, entrapped air pockets in the first two descending pipes and open channel stratified flow in the last one for low-medium-high case, some bubbles in three descending pipes for the high-low-medium case.
