Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is de...Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.展开更多
This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environmen...This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.展开更多
Negative stiffness mechanisms can improve low-frequency vibration isolation performance and have been widely used in the vibration isolation of precision equipment. However, the negative stiffness mechanism usually in...Negative stiffness mechanisms can improve low-frequency vibration isolation performance and have been widely used in the vibration isolation of precision equipment. However, the negative stiffness mechanism usually introduces a nonlinear stiffness,resulting in a nonlinear response and worsening the vibration isolation performance, especially under large amplitude vibration.In this paper, an electromagnetic spring with linear negative stiffness(ESLNS) is proposed, in which the antagonistic ampere forces of the energized coils are used to generate negative stiffness within a long linear stroke. The magnetic field distribution is improved through the design of the magnetic circuit, thereby increasing the stiffness generation efficiency. The stiffness can be adjusted bidirectionally by current within the range of positive and negative stiffness. An electromagnetic stiffness model was established based on the equivalent magnetic circuit method. Experimental measurements verified the accuracy of the model and proved the linearity of the electromagnetic spring. A vibration isolator with high static and low dynamic stiffness(HSLDS) based on the ESLNS is designed and tested. The experimental results prove that the introduction of the ESLNS can effectively expand the isolation frequency band without changing the equilibrium position. Moreover, the vibration isolator with ESLNS does not produce nonlinear response. The proposed electromagnetic spring with linear negative stiffness extends the application range of HSLDS isolators to a large amplitude vibration environment.展开更多
基金Supported by the Specialized Research Fund of the Transient Physics Laboratory under Grant No KX21373
文摘Pulsed discharge utilized to achieve large current density in the electromagnetic flow control is numerically studied. A mathematic discharge model is established to calculate the plasma channel, and an actuator is designed to generate the Lorentz force in the micro plasma channel. During the discharge process, the resistance in the channel decreases rapidly and a large current density appears between the discharge electrodes. After the actuator is applied in the leading edge of a flat plate, the separation region and downstream turbulent boundary layer on the plate disappear. Meanwhile, a skin-friction drag force reduction is achieved.
基金sponsored by the Alpha Foundation for the Improvement of Mine Safety and Health, Inc. (Alpha Foundation)
文摘This work proposes a vibrating mesh screen as an alternative to the static mesh screen currently used in conventional flooded-bed dust scrubbers for removing airborne coal mine dust in the continuous mining environment.Fundamental assessments suggest that a vibrating screen may improve the dust collection efficiency of scrubber systems and mitigate the clogging issues associated with the conventional design.To evaluate this hypothesis,computational fluid dynamics(CFD)simulations were carried out to assess the effects of vibration conditions(i.e.,frequency and amplitude)on the dust particle-mesh interaction and mesh wetting conditions,which are the two decisive factors in determining the dust collection efficiency.The results suggest that the vibrating mesh screen can enhance dust particle collision opportunities on the mesh and increase mesh wetted area as compared to the static mesh screen.The effects of mesh screen aperture,coal dust concentration,and spray nozzle flow rate on the performance of the vibrating mesh are also evaluated.Finally,a simplified three-phase flow simulation including airflow,dust particles,and water droplet spray is performed,and the results reflect a significant improvement of dust collection efficiency in the liquid-coated vibrating mesh screen.
基金supported by the National Natural Science Foundation of China(Grant Nos. 62325302, 62203076, 62103065)the China Postdoctoral Science Foundation(Grant No. 2021M700584)+1 种基金the Program of Shanghai Academic/Technology Research Leader(Grant No. 21XD1421400)the Natural Science Foundation of Chongqing, China(Grant No.cstc2020jcyj-zdxmX0014)。
文摘Negative stiffness mechanisms can improve low-frequency vibration isolation performance and have been widely used in the vibration isolation of precision equipment. However, the negative stiffness mechanism usually introduces a nonlinear stiffness,resulting in a nonlinear response and worsening the vibration isolation performance, especially under large amplitude vibration.In this paper, an electromagnetic spring with linear negative stiffness(ESLNS) is proposed, in which the antagonistic ampere forces of the energized coils are used to generate negative stiffness within a long linear stroke. The magnetic field distribution is improved through the design of the magnetic circuit, thereby increasing the stiffness generation efficiency. The stiffness can be adjusted bidirectionally by current within the range of positive and negative stiffness. An electromagnetic stiffness model was established based on the equivalent magnetic circuit method. Experimental measurements verified the accuracy of the model and proved the linearity of the electromagnetic spring. A vibration isolator with high static and low dynamic stiffness(HSLDS) based on the ESLNS is designed and tested. The experimental results prove that the introduction of the ESLNS can effectively expand the isolation frequency band without changing the equilibrium position. Moreover, the vibration isolator with ESLNS does not produce nonlinear response. The proposed electromagnetic spring with linear negative stiffness extends the application range of HSLDS isolators to a large amplitude vibration environment.
