The gap effect is a key factor in the design of the heat sealing in super- sonic vehicles subjected to an aerodynamic heat load. Built on S-A turbulence model and Roe discrete format, the aerodynamic environment aroun...The gap effect is a key factor in the design of the heat sealing in super- sonic vehicles subjected to an aerodynamic heat load. Built on S-A turbulence model and Roe discrete format, the aerodynamic environment around a gap on the surface of a supersonic aircraft was simulated by the finite volume method. As the presented results indicate, the gap effect depends not only on the attack angle, but also on the Mach number.展开更多
The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are ...The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are shown and the dispersion relation is calculated. The results show that, by introducing the inter-coupling between the different piezoelectric segments, which is accomplished by serially connecting every n piezoelectric segment into supercells, some tunable Bragg band gaps can accordingly be opened in the low frequency region. The investigation could provide a new guideline for the tunable phononic crystal under passive control.展开更多
The spin-dependent Andreev reflection is investigated theoretically by analyzing the electronic transport in a thin-film topological insulator(TI)ferromagnet/superconductor(FM/SC)junction.The tunneling conductance and...The spin-dependent Andreev reflection is investigated theoretically by analyzing the electronic transport in a thin-film topological insulator(TI)ferromagnet/superconductor(FM/SC)junction.The tunneling conductance and shot noise are calculated based on the Dirac-Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk theory.It is found that the magnetic gap in ferromagnet can enhance the Andreev retro-reflection but suppress the specular Andreev reflection.The gate potential applied to the electrode on top of superconductor can enhance the two types of reflections.There is a transition between the two types of reflections at which both the tunneling conductance and differential shot noise become zero.These results provide a method to realize and detect experimentally the intra-band specular Andreev reflection in thin film TI-based FM/SC structures.展开更多
To explore the influence of the meso-mechanical behaviors of the wet coal dust layers on the contact stiffness of mechanical bonding surfaces,a three-body contact model incorporating an interface with wet coal dust wa...To explore the influence of the meso-mechanical behaviors of the wet coal dust layers on the contact stiffness of mechanical bonding surfaces,a three-body contact model incorporating an interface with wet coal dust was constructed based on breakage theory.The model considered the mechanical surface morphology and contact characteristics of the wet coal dust.The force chain evolution laws of the wet coal dust layer were elucidated under the effects of gap filling and the cover layer,and the bearing characteristics of the three-body contact bonding surfaces were revealed by quantitative analyses of the number,length,collimation coefficient,and coordination number of the force chains within the wet coal dust layer.Finally,the three-body normal contact stiffness under various preload forces was computed and experimentally validated.The results demonstrate that the external load transfer path of the three-body contact bonding surfaces was from mechanical surface(macroscopic stress)to wet coal dust layer(mesoscopic force chains)and then to mechanical surface(peaks and valleys).The interactions among these three elements contributed to transforming the distributions of the macroscopic stresses and mesoscopic force chains to the locations at the peaks and valleys of the mechanical surface.Among them,the proportion of short force chains in the wet coal dust layer increased from approximately 0.8%–91%,while the proportion of long force chains exhibited an opposite changing trend.The force chain collimation coefficient initially increased and subsequently stabilized,reaching a maximum value of 0.93.A large number of broken,small particles in the wet coal dust layer mainly served to fill the gaps among large particles.The maximum relative error between the experimental and simulated values on the three-body contact stiffness is 7.26%,indicating that the simulation results can be an approximate substitute for the experimental results with a certain degree of accuracy and practicality.The research results are of great significance for understanding the contact characteristics of mechanical surfaces containing particulate media.展开更多
This work used a modified direct shear apparatus, created newly by the authors, to explore effects of the gap between shear box halves and specimen size on the shear resistance of coarse-grained soil. The shear boxes ...This work used a modified direct shear apparatus, created newly by the authors, to explore effects of the gap between shear box halves and specimen size on the shear resistance of coarse-grained soil. The shear boxes of this apparatus were assembled from a series of steel structures capable of superimposition and nesting. Such characteristics facilitated variation of specimen size in both diameter and height. The new device can also maintain a constant gap during shearing. We performed a series of gap-effect and size-effect tests for two uniformly graded, coarse^grained soil samples. The test results showed that both the gap space and specimen size bad significant influences on shear resistance of the coarse-grained soil. Further, analysis of variations in shear strength indices led to a reasonable gap dimension and specimen size of the two soil samples.展开更多
In underwater applications of contactless power transmission(CLPT) systems,high pressure and noncoaxial operations will change the parameters of electromagnetic(EM) couplers.As a result,the system will divert from its...In underwater applications of contactless power transmission(CLPT) systems,high pressure and noncoaxial operations will change the parameters of electromagnetic(EM) couplers.As a result,the system will divert from its optimum performance.Using a reluctance modeling method,we investigated the gap effects on the EM coupler in deep-sea environment.Calculations and measurements were performed to analyze the influence of high pressure and noncoaxial alignments on the coupler.It was shown that it is useful to set a relatively large gap between cores to reduce the influence of pressure.Experiments were carried out to verify the transferring capacity of the designed coupler and system for a fixed frequency.The results showed that an EM coupler with a large gap can serve a stable and efficient power transmission for the CLPT system.The designed system can transfer more than 400 W electrical power with a 2-mm gap in the EM coupler,and the efficiency was up to 90% coaxially and 87% non-coaxially in 40 MPa salt water.Finally,a mechanical layout of a 400 W EM coupler for the underwater application in 4000-m deep sea was proposed.展开更多
Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many coun...Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.展开更多
基金supported by the National Natural Sciences Foundation of China(11272042)the Fundamental Research Funds for the Central Universities(2014YJS088)
文摘The gap effect is a key factor in the design of the heat sealing in super- sonic vehicles subjected to an aerodynamic heat load. Built on S-A turbulence model and Roe discrete format, the aerodynamic environment around a gap on the surface of a supersonic aircraft was simulated by the finite volume method. As the presented results indicate, the gap effect depends not only on the attack angle, but also on the Mach number.
基金Supported by the National Natural Science Foundation of China under Grant No 11274121
文摘The longitudinal wave propagating in one-dimensional periodic piezoelectric composite rod with inter-coupling between different piezoelectric segments is investigated. The analytical formulae for such a structure are shown and the dispersion relation is calculated. The results show that, by introducing the inter-coupling between the different piezoelectric segments, which is accomplished by serially connecting every n piezoelectric segment into supercells, some tunable Bragg band gaps can accordingly be opened in the low frequency region. The investigation could provide a new guideline for the tunable phononic crystal under passive control.
文摘The spin-dependent Andreev reflection is investigated theoretically by analyzing the electronic transport in a thin-film topological insulator(TI)ferromagnet/superconductor(FM/SC)junction.The tunneling conductance and shot noise are calculated based on the Dirac-Bogoliubov-de Gennes equation and Blonder-Tinkham-Klapwijk theory.It is found that the magnetic gap in ferromagnet can enhance the Andreev retro-reflection but suppress the specular Andreev reflection.The gate potential applied to the electrode on top of superconductor can enhance the two types of reflections.There is a transition between the two types of reflections at which both the tunneling conductance and differential shot noise become zero.These results provide a method to realize and detect experimentally the intra-band specular Andreev reflection in thin film TI-based FM/SC structures.
基金the National Natural Science Foundation of China(grant No.52204214)the China Postdoctoral Science Foundation(grant No.2023M741502)the University-local government scientific and technical cooperation cultivation project of Ordos Institute-LNTU(grant No.YJY-XD-2023-009).
文摘To explore the influence of the meso-mechanical behaviors of the wet coal dust layers on the contact stiffness of mechanical bonding surfaces,a three-body contact model incorporating an interface with wet coal dust was constructed based on breakage theory.The model considered the mechanical surface morphology and contact characteristics of the wet coal dust.The force chain evolution laws of the wet coal dust layer were elucidated under the effects of gap filling and the cover layer,and the bearing characteristics of the three-body contact bonding surfaces were revealed by quantitative analyses of the number,length,collimation coefficient,and coordination number of the force chains within the wet coal dust layer.Finally,the three-body normal contact stiffness under various preload forces was computed and experimentally validated.The results demonstrate that the external load transfer path of the three-body contact bonding surfaces was from mechanical surface(macroscopic stress)to wet coal dust layer(mesoscopic force chains)and then to mechanical surface(peaks and valleys).The interactions among these three elements contributed to transforming the distributions of the macroscopic stresses and mesoscopic force chains to the locations at the peaks and valleys of the mechanical surface.Among them,the proportion of short force chains in the wet coal dust layer increased from approximately 0.8%–91%,while the proportion of long force chains exhibited an opposite changing trend.The force chain collimation coefficient initially increased and subsequently stabilized,reaching a maximum value of 0.93.A large number of broken,small particles in the wet coal dust layer mainly served to fill the gaps among large particles.The maximum relative error between the experimental and simulated values on the three-body contact stiffness is 7.26%,indicating that the simulation results can be an approximate substitute for the experimental results with a certain degree of accuracy and practicality.The research results are of great significance for understanding the contact characteristics of mechanical surfaces containing particulate media.
文摘This work used a modified direct shear apparatus, created newly by the authors, to explore effects of the gap between shear box halves and specimen size on the shear resistance of coarse-grained soil. The shear boxes of this apparatus were assembled from a series of steel structures capable of superimposition and nesting. Such characteristics facilitated variation of specimen size in both diameter and height. The new device can also maintain a constant gap during shearing. We performed a series of gap-effect and size-effect tests for two uniformly graded, coarse^grained soil samples. The test results showed that both the gap space and specimen size bad significant influences on shear resistance of the coarse-grained soil. Further, analysis of variations in shear strength indices led to a reasonable gap dimension and specimen size of the two soil samples.
基金supported by the National High-Tech R & D Program (863) of China (No 2007AA091201)the Natural Science Foundation of Zhejiang Province, China (No Y5090117)the Qianjiang Excellence Project of Zhejiang Province, China (No 2009R10036)
文摘In underwater applications of contactless power transmission(CLPT) systems,high pressure and noncoaxial operations will change the parameters of electromagnetic(EM) couplers.As a result,the system will divert from its optimum performance.Using a reluctance modeling method,we investigated the gap effects on the EM coupler in deep-sea environment.Calculations and measurements were performed to analyze the influence of high pressure and noncoaxial alignments on the coupler.It was shown that it is useful to set a relatively large gap between cores to reduce the influence of pressure.Experiments were carried out to verify the transferring capacity of the designed coupler and system for a fixed frequency.The results showed that an EM coupler with a large gap can serve a stable and efficient power transmission for the CLPT system.The designed system can transfer more than 400 W electrical power with a 2-mm gap in the EM coupler,and the efficiency was up to 90% coaxially and 87% non-coaxially in 40 MPa salt water.Finally,a mechanical layout of a 400 W EM coupler for the underwater application in 4000-m deep sea was proposed.
基金supported by the National Natural Science Foundation of China (Grant no. 11472262)the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant no. XDB22040502)+1 种基金the Collaborative Innovation Center of Suzhou Nano Science and Technologythe Fundamental Research Funds for the Central Universities
文摘Development of high-performance phase transformation electrodes in lithium ion batteries requires comprehensive studies on stress-mediated lithiation involving migration of the phase interface. It brings out many counter-intuitive phenomena, especially in nanoscale electrodes, such as the slowing down migration of phase interface, the vanishing of miscibility gap under high charge rate, and the formation of surface crack during lithiation. However, it is still a challenge to simulate the evolution of stress in arbitrarily-shaped nanoscale electrodes, accompanied with phase transformation and concurrent plastic deformation. This article gives a brief review of our efforts devoted to address these issues by developing phase field model and simulation. We demonstrate that the miscibility gap of two-phase state is affected not only by stress but also by surface reaction rate and particle size. In addition, the migration of phase interface slows down due to stress. It reveals that the plastic deformation generates large radial expansion, which is responsible for the transition from surface hoop compression to surface hoop tension that may induce surface crack during lithiation. We hope our effort can make a contribution to the understanding of stress-coupled kinetics in phase transformation electrodes.