When air is pumped in, a tubular balloon initially inflates slightly and homogeneously. A short section of the balloon then forms a bulge, which coexists with the unbulged section of the balloon. As more air is pumped...When air is pumped in, a tubular balloon initially inflates slightly and homogeneously. A short section of the balloon then forms a bulge, which coexists with the unbulged section of the balloon. As more air is pumped in, the bulged section elongates at the expense of the unbulged section, until the entire balloon is bulged. The phenomenon is analogous to the liquid-to-vapor phase transition. Here we study the bulging transition in a dielectric elastomer tube as air is pumped into the balloon and a voltage is applied through the thickness of the membrane. We formulate the condition for coexistent budged and unbulged sections, and identify allowable states set by electrical breakdown and mechanical rupture. We find that the bulging transition dramatically amplifies electromechanical energy conversion. Energy converted in an electromechanical cycle consisting of unbulged and bulged states is thousands of times that in an electromechanical cycle consisting of only unbulged states.展开更多
A superconducting magnet(SM)can produce high magnetic fields up to a dozen times stronger than those generated by an electromagnet made of normal conductors or a permanent magnet(PM),and thus has attracted increasing ...A superconducting magnet(SM)can produce high magnetic fields up to a dozen times stronger than those generated by an electromagnet made of normal conductors or a permanent magnet(PM),and thus has attracted increasing research efforts in many domains including medical devices,large scientific equipment,transport,energy storage,power systems,and electric machines.Wireless energisers,e.g.,high temperature superconducting(HTS)flux pumps,can eliminate the thermal load from current leads and arc erosion of slip rings,and are thus considered a promising energisation tool for SMs.However,the time‐averaged DC output voltage in existing HTS flux pumps is generated by dynamic resistance:the dynamic loss is unavoidable,and the total AC loss will become significant at high frequencies.This study introduces a highly efficient superconducting wireless energizer(SWE)designed specifically for SMs.The SWE takes advantage of the inherent properties of a superconducting loop,including flux conservation and zero DC resistivity.Extensive theoretical analysis,numerical modelling exploiting the H‐ϕformulation,and experimental measurements were conducted to demonstrate the efficiency and efficacy of the novel SWE design.The electromechanical performance and loss characteristics of the SWE system have also been investigated.Compared to conventional HTS flux pumps,the proposed SWE has lower excitation loss,in the order of 10−1 mW,and thus can achieve a high system efficiency of no less than 95%.Furthermore,it has a simpler structure with higher reliability,considered ready for further industrial development.In addition to deepening the understating of the intricate electromechanical dynamics between magnetic dipoles and superconducting circuits,this article provides a novel wireless energisation technique for SMs and opens the way to step changes in future electric transport and energy sectors.展开更多
Along with intense rock strain and rock bursting processes at the late stage of earthquake preparation, mechanical-electrical energy conversion appears in the seismogenic region and its nearby rock formations, which c...Along with intense rock strain and rock bursting processes at the late stage of earthquake preparation, mechanical-electrical energy conversion appears in the seismogenic region and its nearby rock formations, which correspondingly stimulate certain electromagnetic effects. The paper mainly analyzes the pre-seismic electromagnetic effect of the ionosphere and proposes a method of monitoring VLF radio waves over the additional ionized region and so on. It is deemed that the method is of significance for short and imminent term prediction of strong earthquakes.展开更多
From the principles of electromechanical energy conversion and electromagnetic torque generation, our study evaluatedthe mathematical model of the electromagnetic torque and the vector control method of motors. An ana...From the principles of electromechanical energy conversion and electromagnetic torque generation, our study evaluatedthe mathematical model of the electromagnetic torque and the vector control method of motors. An analysis of motor typesindicates that the electromechanical energy conversion component is interchangeable. Three distinct types of motor structures,namely DC, induction, and synchronous, are possible, all three being commonly used in pure electric vehicles. For each motortype, simulation models were developed using Modelica, a modeling language for object-oriented multi-domain physicalsystem. A test model of each motor type was configured in the MWorks simulation platform. With a representative motor,specifically the permanent-magnet DC motor, the asynchronous induction motor, and the permanent-magnet synchronousmotor, mechanical properties were simulated and analyzed. The simulation results show that the characteristics of each motormodel are consistent with the theoretical and engineering performance of the representative motor. Therefore, modeling,motor control, and performance testing of a unified multi-pole-field motor, which is used in pure electric vehicles, have beenachieved.展开更多
基金supported by ARO(W911NF-09-1-0476)DARPA (W911NF-10-1-0113)+2 种基金MRSECsupported by China Scholarship Council as a visiting scholar for two years at Harvard Universitythe Alexander von Humboldt Foundation for the Humboldt Award
文摘When air is pumped in, a tubular balloon initially inflates slightly and homogeneously. A short section of the balloon then forms a bulge, which coexists with the unbulged section of the balloon. As more air is pumped in, the bulged section elongates at the expense of the unbulged section, until the entire balloon is bulged. The phenomenon is analogous to the liquid-to-vapor phase transition. Here we study the bulging transition in a dielectric elastomer tube as air is pumped into the balloon and a voltage is applied through the thickness of the membrane. We formulate the condition for coexistent budged and unbulged sections, and identify allowable states set by electrical breakdown and mechanical rupture. We find that the bulging transition dramatically amplifies electromechanical energy conversion. Energy converted in an electromechanical cycle consisting of unbulged and bulged states is thousands of times that in an electromechanical cycle consisting of only unbulged states.
文摘A superconducting magnet(SM)can produce high magnetic fields up to a dozen times stronger than those generated by an electromagnet made of normal conductors or a permanent magnet(PM),and thus has attracted increasing research efforts in many domains including medical devices,large scientific equipment,transport,energy storage,power systems,and electric machines.Wireless energisers,e.g.,high temperature superconducting(HTS)flux pumps,can eliminate the thermal load from current leads and arc erosion of slip rings,and are thus considered a promising energisation tool for SMs.However,the time‐averaged DC output voltage in existing HTS flux pumps is generated by dynamic resistance:the dynamic loss is unavoidable,and the total AC loss will become significant at high frequencies.This study introduces a highly efficient superconducting wireless energizer(SWE)designed specifically for SMs.The SWE takes advantage of the inherent properties of a superconducting loop,including flux conservation and zero DC resistivity.Extensive theoretical analysis,numerical modelling exploiting the H‐ϕformulation,and experimental measurements were conducted to demonstrate the efficiency and efficacy of the novel SWE design.The electromechanical performance and loss characteristics of the SWE system have also been investigated.Compared to conventional HTS flux pumps,the proposed SWE has lower excitation loss,in the order of 10−1 mW,and thus can achieve a high system efficiency of no less than 95%.Furthermore,it has a simpler structure with higher reliability,considered ready for further industrial development.In addition to deepening the understating of the intricate electromechanical dynamics between magnetic dipoles and superconducting circuits,this article provides a novel wireless energisation technique for SMs and opens the way to step changes in future electric transport and energy sectors.
文摘Along with intense rock strain and rock bursting processes at the late stage of earthquake preparation, mechanical-electrical energy conversion appears in the seismogenic region and its nearby rock formations, which correspondingly stimulate certain electromagnetic effects. The paper mainly analyzes the pre-seismic electromagnetic effect of the ionosphere and proposes a method of monitoring VLF radio waves over the additional ionized region and so on. It is deemed that the method is of significance for short and imminent term prediction of strong earthquakes.
文摘From the principles of electromechanical energy conversion and electromagnetic torque generation, our study evaluatedthe mathematical model of the electromagnetic torque and the vector control method of motors. An analysis of motor typesindicates that the electromechanical energy conversion component is interchangeable. Three distinct types of motor structures,namely DC, induction, and synchronous, are possible, all three being commonly used in pure electric vehicles. For each motortype, simulation models were developed using Modelica, a modeling language for object-oriented multi-domain physicalsystem. A test model of each motor type was configured in the MWorks simulation platform. With a representative motor,specifically the permanent-magnet DC motor, the asynchronous induction motor, and the permanent-magnet synchronousmotor, mechanical properties were simulated and analyzed. The simulation results show that the characteristics of each motormodel are consistent with the theoretical and engineering performance of the representative motor. Therefore, modeling,motor control, and performance testing of a unified multi-pole-field motor, which is used in pure electric vehicles, have beenachieved.
