We investigate single-axis acoustic levitation using standing waves to levitate particles freely in a medium bounded by a driver and a reflector. The acoustic pressure at the pressure antinode of the standing wave cou...We investigate single-axis acoustic levitation using standing waves to levitate particles freely in a medium bounded by a driver and a reflector. The acoustic pressure at the pressure antinode of the standing wave counteracts the downward gravitational force of the levitating object. The optimal relationship between the air gap and the driving frequency leads to resonance and hence maximization of the levitating force. Slight deviation from the exact resonance condition causes a reduction in acoustic pressure at the pressure antinodes. This results in a significant reduction of the levitating force. The driving frequency is kept constant while the air gap is varied for different conditions. The optimal air gap for maximizing the levitation force is studied for first three resonance modes. Furthermore, a levitating particle is introduced between the driver and the reflector. The dependence of the resonance condition on the size of the levitating particle as well as the position of the particle between the driver and the reflector has also been studied. As the size of the levitating particle increases, the resonance condition also gets modified. Finite element results show a good agreement with the validated results available in the literature. Furthermore, the finite element approach is also used to study the variation of acoustic pressure at the pressure antinode with respect to the size of the reflector. The optimum diameter of the reflector is calculated for maximizing the levitating force for three resonance modes.展开更多
This paper discusses the design of the propulsion system of the UAQ4 （University of L＇Aquila, model 4） magnetic levitating train which is used for transportation applications in urban environments. UAQ4 is the only...This paper discusses the design of the propulsion system of the UAQ4 （University of L＇Aquila, model 4） magnetic levitating train which is used for transportation applications in urban environments. UAQ4 is the only magnetic levitating vehicle with resistance motion, except for aerodynamic drag and with energy consumption near zero at low speed. The feasibility of the system has been successfully verified and tested in the laboratory. Propulsion and braking are provided by a novel direct-current linear stepper motor, with the primary formed by permanent magnets distributed on central beam of the track, and the secondary by coils on board the vehicle, instead of the present alternate current linear motors that have well-known disadvantages. The motor working principles are described, and its performances are analyzed, by a finite element numerical model which allows modifying the most important parameters of the system. The main components of a full scale motor for urban transportation are measured and discussed.展开更多
New experimental results,which are important for the potential use of small levitating droplets as biochemical microreactors,are reported.It is shown that the combination of infrared heating and reduced evaporation of...New experimental results,which are important for the potential use of small levitating droplets as biochemical microreactors,are reported.It is shown that the combination of infrared heating and reduced evaporation of saline water under the droplet cluster is sufficient to produce equilibriumsaltwater droplets over a wide temperature range.The resulting universal dependence of droplet size on temperature simplifies the choice of optimal conditions for generating stable droplet clusters with droplets of the desired size.A physical analysis of the experimental results on the equilibrium size of saltwater droplets makes it possible to separate the effects related to the salinity of the water layer under the droplet cluster from the effects related to the reduction of water evaporation from the water droplets.This is expected to be important for further studies of heat transfer and diffusion in layers of evaporating solutions and condensed droplets.展开更多
The optically levitated mechanical system in vacuum is a powerful platform in physics.It has been displaying more extensive application prospects.This paper presents an experimental study of optical levitation,identif...The optically levitated mechanical system in vacuum is a powerful platform in physics.It has been displaying more extensive application prospects.This paper presents an experimental study of optical levitation,identification,motion measurement,and assembly of two-species photoluminescence nanoparticles.A laser trapping array simultaneously levitates nitrogen-vacancy(NV)nanodiamonds and Yb^(3+)/Er^(3+):NaYF_(4)nanoparticles.The species of each nanoparticle can be individually identified by measuring the photoluminescence spectrum.We choose the single NV nanodiamond and Yb^(3+)/Er^(3+):NaYF_(4)nanoparticle and assemble them into a Janus composite nanoparticle,which integrates the merits of the two components.This work demonstrates the potential advantages of a hybrid optically levitated system.It provides a practicable scheme for the study of macroscopic quantum phenomena and precision measurement,thanks to the spin manipulation or spin-mechanical coupling of an NV diamond and by simultaneously implementing laser refrigeration to the Yb^(3+)/Er^(3+):NaYF_(4)nanoparticle in an optically levitated composite nanoparticle.展开更多
The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr...The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys present only one recalescence during liquid/solid phase transition,while the Zr_(70)V_(30) alloy presents a transformation from two recalescence to one recalescence phenomenon with a critical undercooling of approximately 300 K.According to the LKT/BCT model,the calculated results of the primary β-Zr dendrite growth velocity in undercooled liquid Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys agree well with the experiments.The velocity inflection points at 119 K of Zr_(91.4)V_(8.6) alloy and 201 K of Zr_(83.5)V_(16.5) alloy could be explained by the competition between solutal undercooling control and thermal undercooling control modes.For Zr_(70)V_(30) alloy solidified in the P1 with twice recalescence,a critical second undercooling of 253 K and corresponding undercooling of 65 and 244 K are obtained.When the un-dercooling is in the range of 65-244 K,the second undercooling would be greater than 253 K,and the residual liquid phase would solidify into anomalous eutectic microstructure for Zr_(70)V_(30) alloy.The Vickers hardness of Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys all show a quadratic relationship with undercooling.Under electrostatic levitation condition,the mechanical property of Zr-V alloys could be significantly regulated through solidifying the alloys at different undercoolings.展开更多
The electromagnetic levitation system(EMLS)serves as the most important part of any magnetic levitation system.However,its characteristics are defined by its highly nonlinear dynamics and instability.Furthermore,the u...The electromagnetic levitation system(EMLS)serves as the most important part of any magnetic levitation system.However,its characteristics are defined by its highly nonlinear dynamics and instability.Furthermore,the uncertainties in the dynamics of an electromagnetic levitation system make the controller design more difficult.Therefore,it is necessary to design a robust control law that will ensure the system’s stability in the presence of these uncertainties.In this framework,the dynamics of an electromagnetic levitation system are addressed in terms of matched and unmatched uncertainties.The robust control problem is translated into the optimal control problem,where the uncertainties of the electromagnetic levitation system are directly reflected in the cost function.The optimal control method is used to solve the robust control problem.The solution to the optimal control problem for the electromagnetic levitation system is indeed a solution to the robust control problem of the electromagnetic levitation system under matched and unmatched uncertainties.The simulation and experimental results demonstrate the performance of the designed control scheme.The performance indices such as integral absolute error(IAE),integral square error(ISE),integral time absolute error(ITAE),and integral time square error(ITSE)are compared for both uncertainties to showcase the robustness of the designed control scheme.展开更多
Alkanes are present in the atmosphere,commonly in the form of aerosols,and can thus interact with water droplets,leading to the formation of new interfaces.Yet,in the study of these interactions,traditional experiment...Alkanes are present in the atmosphere,commonly in the form of aerosols,and can thus interact with water droplets,leading to the formation of new interfaces.Yet,in the study of these interactions,traditional experimental methods often rely on the presence of sample containers,which can interfere with the observations.Acoustic levitation is a technique which allows the manipulation of samples in the microliter regime in a contact-free manner.Hence,interfacial phenomena can be studied without the presence of external surfaces,mimicking atmospheric conditions.Herein,we acoustically levitated a droplet of water in contact with a droplet of hexadecane and observed interfacial crystallization at the hexadecane/water interface that propagated to the entire droplet of hexadecane.It was found that the crystallization occurred up to 3 K above the melting temperature of hexadecane,and at a relative humidity below 30%.Moreover,the volume ratio between water and hexadecane influenced the fraction of crystallized surface area;for a hexadecane:water ratio above 1:2 full surface crystallization occurred.Combining acoustic levitation with Raman spectroscopy allowed the characterization of the phase transition in real time,demonstrating the existence of a solid crystal of alkane upon water evaporation.This study provides insights into the process of interfacial crystallization of hexadecane and demonstrates the suitability of acoustic levitation to study contact-free interfacial phenomena between two immiscible liquids.展开更多
Vat photopolymerization 3D printing creates structures by projecting patterns onto a photosensitive resin within a vat.However,the presence of resin vats limits the printing of multiscale multimaterial structures.In t...Vat photopolymerization 3D printing creates structures by projecting patterns onto a photosensitive resin within a vat.However,the presence of resin vats limits the printing of multiscale multimaterial structures.In this context,a novel 3D printing process is presented in which a cured structure is produced from acoustically levitated droplets without a physical vat.This enables the printing process to achieve high flexibility in the printing orientation and material supply.In pursuit of the envisioned 3D acoustic levitation printing strategy,acoustic levitation technology was utilized to suspend a photosensitive resin.Objects with small features were successfully produced by projecting patterns onto levitated resin droplets.Transforming printing orientations allows the fabrication of multiscale structures.Levitating resin droplets on-demand enables the rapid replacement of materials,thereby realizing effortless multimaterial 3D printing.By exploiting the flexibility of printing on levitation resin droplets,the capability of 3D printing on existing objects was established.Finally,an interesting example was illustrated,in which an object integrating liquid,gas,and solid materials was fabricated using the proposed 3D printing strategy.The results show that 3D printing on levitated droplets is feasible for fabricating multiscale and multimaterial objects,which contributes to the development of new 3D printing methods and potential applications.展开更多
In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end op...In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end optical components need to meet the extremely stringent requirements of the full-frequency band error,which poses significant challenge to the control of the aerostatic spindle error.In this research,we put forward an active control method for the frequency domain error of the aerostatic spindle based on acoustic levitation,in which the acousticmagnetism-fluid-solid multi-field coupling rotor dynamics modeling method of the aerostatic spindle was proposed and the corresponding multi-field coupling model was established.Through the numerical simulation and preliminary experiments,the influence law of acoustic levitation on the frequency domain error of the aerostatic spindle is obtained.The results showed that acoustic levitation can be used to control the frequency domain error of the aerostatic spindle to some extent,which verified the effectiveness of the proposed method.展开更多
A novel parameter identification method for magnetic levitation bearing rotor systems is proposed,based on the modulation function method.The fundamental principle of the modulation function method for parameter ident...A novel parameter identification method for magnetic levitation bearing rotor systems is proposed,based on the modulation function method.The fundamental principle of the modulation function method for parameter identification is derived on the basis of the characteristics of the modulation function.The transformation of the differential equation model of a continuous system into a general algebraic equation model is effectively achieved,thereby avoiding the influence of errors introduced by the initial value and differential derivation of the system.Modulation function method parameter identification models have been established for single-degree-of-freedom and multi-degree-of-freedom magnetic levitation bearing rotor systems.The influence of different parameters of Hartley modulation function on the accuracy of system parameter identification has been investigated,thus providing a basis for the design of Hartley modulation function parameters.Simulation and experimental results demonstrate that the modulation function method can effectively identify system parameters despite the presence of system noise.展开更多
Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu60Co30Cr10 alloy by using the electromagnetic levitation and splat-quenching.It is found that the ...Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu60Co30Cr10 alloy by using the electromagnetic levitation and splat-quenching.It is found that the alloy generally has a microstructure consisting of a（Co,Cr）-rich phase embedded in a Cu-rich matrix,and the morphology and size of the（Co,Cr）-rich phase vary drastically with cooling rate.During the electromagnetic levitation solidification processing the cooling rate is lower,resulting in an obvious coalescence tendency of the（Co,Cr）-rich spheroids.The（Co,Cr）-rich phase shows dendrites and coarse spheroids at lower cooling rates.In the splat quenched samples the（Co,Cr）-rich phase spheres were refined significantly and no dendrites were observed.This is probably due to the higher cooling rate,undercooling and interface tension.展开更多
The rapid solidification processes of undercooled Ti-(47,50,54)at.%Al alloys were investigated by electromagnetic levitation(EML)method combined with a high-speed photoelectric detector.The maximum undercoolings of th...The rapid solidification processes of undercooled Ti-(47,50,54)at.%Al alloys were investigated by electromagnetic levitation(EML)method combined with a high-speed photoelectric detector.The maximum undercoolings of the three liquid alloys were 376 K,352 K and 316 K,respectively.Recalescence processes corresponding to the primary dendrite growth and subsequent phase transition were recorded at various undercoolings.The primary dendrite growth velocity V meets a double exponential relationship with the undercooling T.Besides,a novel formula with physical meaning is proposed to explain that the more ordered liquid metal atoms accelerate the primary dendrite growth.Three recalescences are found at all undercoolings for Ti-47 at.%Al alloy and at high undercoolings for Ti-50 at.%Al alloy.The microstructures of solidified Ti-47 at.%Al alloys successively appear as coarse lamellar dendrites and finally evolve to refined parallel lamellar dendrites with the increasing undercooling.When T rises,the microstructures of solidified Ti-50 at.%Al alloys appear from coarse primary dendrites and interdendritic dendrites to refined lamellar dendrites.In the process from low undercooling to high undercooling,the primary phase of undercooled Ti-54 at.%Al alloys changes from r-Ti(r)to r-TiAl(r)and the microstructures of solidified alloys evolve from spherical primary dendrites and matrix phases to cellular dendrite phases.Meanwhile,for the Ti-(47,50)at.%Al,the transformation temperature of metastable intermediateγphase decreases with the increase of undercooling.Moreover,the microhardness of the three solidified alloys reaches the maximum when the undercoolings are 185 K,270 K and 316 K,respectively.展开更多
This paper presents a new device integrating a nonlinear vibration absorber with a levitation magnetoelectric energy harvester for whole-spacecraft systems. This device effectively reduces vibration and has a stronger...This paper presents a new device integrating a nonlinear vibration absorber with a levitation magnetoelectric energy harvester for whole-spacecraft systems. This device effectively reduces vibration and has a stronger energy harvesting capability than the existing systems. It harvests energy from a wide frequency range and has a high output voltage. The harvested energy is determined by magnetic field strength, excitation frequency, and resistive load. The change in the magnetic field strength has the least impact on the output voltage. The vibration reduction effects and harvested energy of the system are analyzed with an approximate analytical method that combines the harmonic balance approach and the pseudo-arclength continuation algorithm. The results of the Runge-Kutta method are nearly consistent with those of the approximate analytical method. Moreover, the effects of the excitation frequency, resistive load, and parameters of the nonlinear energy sink on the system vibration response and energy harvesting are analyzed.展开更多
In order to explore the precise dynamic response of the maglev train and verify the validity of proposed controller,a maglev guideway-electromagnet-air spring-cabin coupled model is developed in the first step.Based o...In order to explore the precise dynamic response of the maglev train and verify the validity of proposed controller,a maglev guideway-electromagnet-air spring-cabin coupled model is developed in the first step.Based on the coupled model,the stresses of the modules are analyzed,and it is pointed out that the inherent nonlinearity,the inner coupling,misalignments between the sensors and actuators,and external disturbances are the main issues that should be considered for the maglev engineering.Furthermore,a feedback linearization controller based on the mathematical model of a maglev module is derived,in which the nonlinearity,coupling and misalignments are taken into account.Then,to attenuate the effect of external disturbances,a disturbance observer is proposed and the dynamics of the estimation error is analyzed using the input-to-state stability theory.It shows that the error is negligible under a low-frequency disturbance.However,at the high-frequency range,the error is unacceptable and the disturbances can not be compensated in time,which lead to over designed fluctuations of levitation gap,even a clash between the upper surface of electromagnet and lower surface of guideway.To solve this problem,a novel nonlinear acceleration feedback is put forward to enhancing the attenuation ability of fast varying disturbances.Finally,numerical comparisons show that the proposed controller outperforms the traditional feedback linearization controller and maintains good robustness under disturbances.展开更多
This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedba...This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedback are analyzed when compared with the current feedback. Then, a backstepping controller with magnetic flux feedback based on the mathematical model of levitation module is developed. To obtain magnetic flux signals for full-size maglev system, a physical method with induction coils installed to winding of the electromagnet is developed. Furthermore, to avoid its hardware addition, a novel conception of virtual magnetic flux feedback is proposed. To demonstrate the feasibility of the proposed controller, the nonlinear dynamic model of full-size maglev train with quintessential details is developed. Based on the nonlinear model, the numerical comparisons and related experimental validations are carried out. Finally, results illustrating closed-loop performance are provided.展开更多
This work addresses the saturation influence of control voltage on the occurring of self-excited vibration of maglev vehicle-bridge interaction system, which greatly degrades the stability of the levitation control, d...This work addresses the saturation influence of control voltage on the occurring of self-excited vibration of maglev vehicle-bridge interaction system, which greatly degrades the stability of the levitation control, decreases the ride comfort, and restricts the cost of the whole system. Firstly, the interaction model of vehicle-bridge system is developed. Based on the interaction model, the relationship between the control voltage and vibration frequency is solved. Then, the variation of the effective direct component and fundamental harmonic are discussed. Furthermore, from the perspective of energy transmission between the levitation system and bridge, the principle underlying the self-excited vibration is explored, and the influence on the stability is discussed. Finally, in terms of the variation of the characteristic roots, the influence is analyzed further and some conclusions are obtained. This study provides a theoretical guidance for mastering the self-excited vibration problems.展开更多
A novel maglev transportation system was proposed for large travel range ultra precision motion.The system consists of a levitation subsystem and a propulsion subsystem.During the propulsion subsystem driving the movi...A novel maglev transportation system was proposed for large travel range ultra precision motion.The system consists of a levitation subsystem and a propulsion subsystem.During the propulsion subsystem driving the moving platform along the guideway,the levitation subsystem uses six pairs of electromagnets to steadily suspend the moving platform over the guideway.The model of the levitation system,which is a typical nonlinear multi-input multi-output coupling system and has many inner nonlinear coupling characteristics,was deduced.For testifying the model,the levitation mechanism was firstly controlled by proportional-integral-differential(PID) control,and then a lot of input-output data were collected for model parameter identification.The least-square parameter identification method was used.The identification results prove that the model is feasible and suitable for the real system.展开更多
A novel magnetic levitation support method is proposed, which can relieve the perturbation caused by traditional support methods andprovide more accurate position control of the capsule. This method can keep the perfe...A novel magnetic levitation support method is proposed, which can relieve the perturbation caused by traditional support methods andprovide more accurate position control of the capsule. This method can keep the perfect symmetry of the octahedral spherical hohlraum and hasthe characteristics in stability, tunability and simplicity. It is also favorable that all the results, such as supporting forces acting on the super-conducting capsule, are calculated analytically, and numerical simulations are performed to verify these results. A typical realistic design isproposed and discussed in detail. The superconducting coating material is suggested, and the required superconducting properties are listed.Damped oscillation of the floating capsule in thin helium gas is discussed, and the restoring time is estimated.展开更多
基金Supported by the Science and Engineering Research Board under Grant No YSS/2015/001245
文摘We investigate single-axis acoustic levitation using standing waves to levitate particles freely in a medium bounded by a driver and a reflector. The acoustic pressure at the pressure antinode of the standing wave counteracts the downward gravitational force of the levitating object. The optimal relationship between the air gap and the driving frequency leads to resonance and hence maximization of the levitating force. Slight deviation from the exact resonance condition causes a reduction in acoustic pressure at the pressure antinodes. This results in a significant reduction of the levitating force. The driving frequency is kept constant while the air gap is varied for different conditions. The optimal air gap for maximizing the levitation force is studied for first three resonance modes. Furthermore, a levitating particle is introduced between the driver and the reflector. The dependence of the resonance condition on the size of the levitating particle as well as the position of the particle between the driver and the reflector has also been studied. As the size of the levitating particle increases, the resonance condition also gets modified. Finite element results show a good agreement with the validated results available in the literature. Furthermore, the finite element approach is also used to study the variation of acoustic pressure at the pressure antinode with respect to the size of the reflector. The optimum diameter of the reflector is calculated for maximizing the levitating force for three resonance modes.
文摘This paper discusses the design of the propulsion system of the UAQ4 （University of L＇Aquila, model 4） magnetic levitating train which is used for transportation applications in urban environments. UAQ4 is the only magnetic levitating vehicle with resistance motion, except for aerodynamic drag and with energy consumption near zero at low speed. The feasibility of the system has been successfully verified and tested in the laboratory. Propulsion and braking are provided by a novel direct-current linear stepper motor, with the primary formed by permanent magnets distributed on central beam of the track, and the secondary by coils on board the vehicle, instead of the present alternate current linear motors that have well-known disadvantages. The motor working principles are described, and its performances are analyzed, by a finite element numerical model which allows modifying the most important parameters of the system. The main components of a full scale motor for urban transportation are measured and discussed.
基金the Russian Science Foundation(Project No.24-29-00303)for the financial support of the present study.
文摘New experimental results,which are important for the potential use of small levitating droplets as biochemical microreactors,are reported.It is shown that the combination of infrared heating and reduced evaporation of saline water under the droplet cluster is sufficient to produce equilibriumsaltwater droplets over a wide temperature range.The resulting universal dependence of droplet size on temperature simplifies the choice of optimal conditions for generating stable droplet clusters with droplets of the desired size.A physical analysis of the experimental results on the equilibrium size of saltwater droplets makes it possible to separate the effects related to the salinity of the water layer under the droplet cluster from the effects related to the reduction of water evaporation from the water droplets.This is expected to be important for further studies of heat transfer and diffusion in layers of evaporating solutions and condensed droplets.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.61975101,11234008,11361161002,and 6157-1276)。
文摘The optically levitated mechanical system in vacuum is a powerful platform in physics.It has been displaying more extensive application prospects.This paper presents an experimental study of optical levitation,identification,motion measurement,and assembly of two-species photoluminescence nanoparticles.A laser trapping array simultaneously levitates nitrogen-vacancy(NV)nanodiamonds and Yb^(3+)/Er^(3+):NaYF_(4)nanoparticles.The species of each nanoparticle can be individually identified by measuring the photoluminescence spectrum.We choose the single NV nanodiamond and Yb^(3+)/Er^(3+):NaYF_(4)nanoparticle and assemble them into a Janus composite nanoparticle,which integrates the merits of the two components.This work demonstrates the potential advantages of a hybrid optically levitated system.It provides a practicable scheme for the study of macroscopic quantum phenomena and precision measurement,thanks to the spin manipulation or spin-mechanical coupling of an NV diamond and by simultaneously implementing laser refrigeration to the Yb^(3+)/Er^(3+):NaYF_(4)nanoparticle in an optically levitated composite nanoparticle.
基金supported by the National Natural Science Foundation of China(Grant No.52088101)the Space Utilization System of China Manned Space Engineering(Grant No.KJZ-YY-NCL02)+1 种基金the National Key R&D Program of China(Grant No.2021YFA0716301)the Shannxi Key Science and Technology Program(Grant Nos.2023-ZDLGY-36,2024JC-ZDXM-24).
文摘The liquid Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys were undercooled to the maximum undercooling of 364 K(0.18 T_(L)),405 K(0.21 T_(L)),and 375 K(0.21 T_(L)),respectively,by using electrostatic levitation technique.The Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys present only one recalescence during liquid/solid phase transition,while the Zr_(70)V_(30) alloy presents a transformation from two recalescence to one recalescence phenomenon with a critical undercooling of approximately 300 K.According to the LKT/BCT model,the calculated results of the primary β-Zr dendrite growth velocity in undercooled liquid Zr_(91.4)V_(8.6) and Zr_(83.5)V_(16.5) alloys agree well with the experiments.The velocity inflection points at 119 K of Zr_(91.4)V_(8.6) alloy and 201 K of Zr_(83.5)V_(16.5) alloy could be explained by the competition between solutal undercooling control and thermal undercooling control modes.For Zr_(70)V_(30) alloy solidified in the P1 with twice recalescence,a critical second undercooling of 253 K and corresponding undercooling of 65 and 244 K are obtained.When the un-dercooling is in the range of 65-244 K,the second undercooling would be greater than 253 K,and the residual liquid phase would solidify into anomalous eutectic microstructure for Zr_(70)V_(30) alloy.The Vickers hardness of Zr_(100-x)V_(x)(x=8.6,16.5,30)alloys all show a quadratic relationship with undercooling.Under electrostatic levitation condition,the mechanical property of Zr-V alloys could be significantly regulated through solidifying the alloys at different undercoolings.
文摘The electromagnetic levitation system(EMLS)serves as the most important part of any magnetic levitation system.However,its characteristics are defined by its highly nonlinear dynamics and instability.Furthermore,the uncertainties in the dynamics of an electromagnetic levitation system make the controller design more difficult.Therefore,it is necessary to design a robust control law that will ensure the system’s stability in the presence of these uncertainties.In this framework,the dynamics of an electromagnetic levitation system are addressed in terms of matched and unmatched uncertainties.The robust control problem is translated into the optimal control problem,where the uncertainties of the electromagnetic levitation system are directly reflected in the cost function.The optimal control method is used to solve the robust control problem.The solution to the optimal control problem for the electromagnetic levitation system is indeed a solution to the robust control problem of the electromagnetic levitation system under matched and unmatched uncertainties.The simulation and experimental results demonstrate the performance of the designed control scheme.The performance indices such as integral absolute error(IAE),integral square error(ISE),integral time absolute error(ITAE),and integral time square error(ITSE)are compared for both uncertainties to showcase the robustness of the designed control scheme.
基金the financial support from the Swedish Research Council(VR)(Public,Sweden)the Swedish Foundation for Strategic Research(SSF)(Non-Profit,Sweden)。
文摘Alkanes are present in the atmosphere,commonly in the form of aerosols,and can thus interact with water droplets,leading to the formation of new interfaces.Yet,in the study of these interactions,traditional experimental methods often rely on the presence of sample containers,which can interfere with the observations.Acoustic levitation is a technique which allows the manipulation of samples in the microliter regime in a contact-free manner.Hence,interfacial phenomena can be studied without the presence of external surfaces,mimicking atmospheric conditions.Herein,we acoustically levitated a droplet of water in contact with a droplet of hexadecane and observed interfacial crystallization at the hexadecane/water interface that propagated to the entire droplet of hexadecane.It was found that the crystallization occurred up to 3 K above the melting temperature of hexadecane,and at a relative humidity below 30%.Moreover,the volume ratio between water and hexadecane influenced the fraction of crystallized surface area;for a hexadecane:water ratio above 1:2 full surface crystallization occurred.Combining acoustic levitation with Raman spectroscopy allowed the characterization of the phase transition in real time,demonstrating the existence of a solid crystal of alkane upon water evaporation.This study provides insights into the process of interfacial crystallization of hexadecane and demonstrates the suitability of acoustic levitation to study contact-free interfacial phenomena between two immiscible liquids.
基金supported by National Natural Science Foundation of China(Grant No.52305398)Chengdu University of Information Technology Project(Grant No.KYTZ202145).
文摘Vat photopolymerization 3D printing creates structures by projecting patterns onto a photosensitive resin within a vat.However,the presence of resin vats limits the printing of multiscale multimaterial structures.In this context,a novel 3D printing process is presented in which a cured structure is produced from acoustically levitated droplets without a physical vat.This enables the printing process to achieve high flexibility in the printing orientation and material supply.In pursuit of the envisioned 3D acoustic levitation printing strategy,acoustic levitation technology was utilized to suspend a photosensitive resin.Objects with small features were successfully produced by projecting patterns onto levitated resin droplets.Transforming printing orientations allows the fabrication of multiscale structures.Levitating resin droplets on-demand enables the rapid replacement of materials,thereby realizing effortless multimaterial 3D printing.By exploiting the flexibility of printing on levitation resin droplets,the capability of 3D printing on existing objects was established.Finally,an interesting example was illustrated,in which an object integrating liquid,gas,and solid materials was fabricated using the proposed 3D printing strategy.The results show that 3D printing on levitated droplets is feasible for fabricating multiscale and multimaterial objects,which contributes to the development of new 3D printing methods and potential applications.
基金Supported by National Natural Science Foundation of China(Grant No.52475494)Zhejiang Provincial Natural Science Foundation of China(Grant No.LY22E050003)Fundamental Research Funds for the Provincial Universities of Zhejiang(Grant No.RF-A2020005).
文摘In the machining of high-end optical components,the aerostatic spindle error of an ultra-precision machine tool has a significant impact on the surface quality of the machined surfaces.The surfaces of many high-end optical components need to meet the extremely stringent requirements of the full-frequency band error,which poses significant challenge to the control of the aerostatic spindle error.In this research,we put forward an active control method for the frequency domain error of the aerostatic spindle based on acoustic levitation,in which the acousticmagnetism-fluid-solid multi-field coupling rotor dynamics modeling method of the aerostatic spindle was proposed and the corresponding multi-field coupling model was established.Through the numerical simulation and preliminary experiments,the influence law of acoustic levitation on the frequency domain error of the aerostatic spindle is obtained.The results showed that acoustic levitation can be used to control the frequency domain error of the aerostatic spindle to some extent,which verified the effectiveness of the proposed method.
基金supported by the National Science and Technology Major Project(Grant No.J2019-Ⅳ-0003-0070).
文摘A novel parameter identification method for magnetic levitation bearing rotor systems is proposed,based on the modulation function method.The fundamental principle of the modulation function method for parameter identification is derived on the basis of the characteristics of the modulation function.The transformation of the differential equation model of a continuous system into a general algebraic equation model is effectively achieved,thereby avoiding the influence of errors introduced by the initial value and differential derivation of the system.Modulation function method parameter identification models have been established for single-degree-of-freedom and multi-degree-of-freedom magnetic levitation bearing rotor systems.The influence of different parameters of Hartley modulation function on the accuracy of system parameter identification has been investigated,thus providing a basis for the design of Hartley modulation function parameters.Simulation and experimental results demonstrate that the modulation function method can effectively identify system parameters despite the presence of system noise.
基金the National Natural Science Foundation of China (50861003)the Natural Science Foundation of Guangxi (2010GXNSFD013004)+2 种基金the Foundation of Key Laboratory of National Education Ministry for Nonferrous Metals and Materials Processing Technology (GXKFJ09-15)the Foundation of Guangxi Department of Education (200911MS07)the Foundation of Guangxi University (X081056)
基金Projects(51171152,50871088) supported by the National Natural Science Foundation of ChinaProject(20126102110048) supported by Doctoral Fund of Ministry of Education of China+2 种基金Project(SKLSP201202) supported by Foundation of State Key Laboratory of Solidification,ChinaProject(2012JC2-02) supported by Natural Science Basic Research Plan in Shaanxi Province,ChinaProject (JC201268) supported by the NPU Foundation for Fundamental Research,China
文摘Metastable liquid phase separation and rapid solidification in a metastable miscibility gap were investigated on the Cu60Co30Cr10 alloy by using the electromagnetic levitation and splat-quenching.It is found that the alloy generally has a microstructure consisting of a（Co,Cr）-rich phase embedded in a Cu-rich matrix,and the morphology and size of the（Co,Cr）-rich phase vary drastically with cooling rate.During the electromagnetic levitation solidification processing the cooling rate is lower,resulting in an obvious coalescence tendency of the（Co,Cr）-rich spheroids.The（Co,Cr）-rich phase shows dendrites and coarse spheroids at lower cooling rates.In the splat quenched samples the（Co,Cr）-rich phase spheres were refined significantly and no dendrites were observed.This is probably due to the higher cooling rate,undercooling and interface tension.
基金financially supported by the National Natural Science Foundation of China(Nos.51734008,51522102 and 51474175).
文摘The rapid solidification processes of undercooled Ti-(47,50,54)at.%Al alloys were investigated by electromagnetic levitation(EML)method combined with a high-speed photoelectric detector.The maximum undercoolings of the three liquid alloys were 376 K,352 K and 316 K,respectively.Recalescence processes corresponding to the primary dendrite growth and subsequent phase transition were recorded at various undercoolings.The primary dendrite growth velocity V meets a double exponential relationship with the undercooling T.Besides,a novel formula with physical meaning is proposed to explain that the more ordered liquid metal atoms accelerate the primary dendrite growth.Three recalescences are found at all undercoolings for Ti-47 at.%Al alloy and at high undercoolings for Ti-50 at.%Al alloy.The microstructures of solidified Ti-47 at.%Al alloys successively appear as coarse lamellar dendrites and finally evolve to refined parallel lamellar dendrites with the increasing undercooling.When T rises,the microstructures of solidified Ti-50 at.%Al alloys appear from coarse primary dendrites and interdendritic dendrites to refined lamellar dendrites.In the process from low undercooling to high undercooling,the primary phase of undercooled Ti-54 at.%Al alloys changes from r-Ti(r)to r-TiAl(r)and the microstructures of solidified alloys evolve from spherical primary dendrites and matrix phases to cellular dendrite phases.Meanwhile,for the Ti-(47,50)at.%Al,the transformation temperature of metastable intermediateγphase decreases with the increase of undercooling.Moreover,the microhardness of the three solidified alloys reaches the maximum when the undercoolings are 185 K,270 K and 316 K,respectively.
基金the National Natural Science Foundation of China (Project No. 11772205)the Training Project of Liaoning Provincial Higher Education Institutions in Domestic and Overseas (Project No. 2018LNGXGJWPY-YB008)the Scientific Research Fund of Liaoning Provincial Education Department (Project No. L201703).
文摘This paper presents a new device integrating a nonlinear vibration absorber with a levitation magnetoelectric energy harvester for whole-spacecraft systems. This device effectively reduces vibration and has a stronger energy harvesting capability than the existing systems. It harvests energy from a wide frequency range and has a high output voltage. The harvested energy is determined by magnetic field strength, excitation frequency, and resistive load. The change in the magnetic field strength has the least impact on the output voltage. The vibration reduction effects and harvested energy of the system are analyzed with an approximate analytical method that combines the harmonic balance approach and the pseudo-arclength continuation algorithm. The results of the Runge-Kutta method are nearly consistent with those of the approximate analytical method. Moreover, the effects of the excitation frequency, resistive load, and parameters of the nonlinear energy sink on the system vibration response and energy harvesting are analyzed.
基金Project(60404003)supported by the National Natural Science Foundation of China
文摘In order to explore the precise dynamic response of the maglev train and verify the validity of proposed controller,a maglev guideway-electromagnet-air spring-cabin coupled model is developed in the first step.Based on the coupled model,the stresses of the modules are analyzed,and it is pointed out that the inherent nonlinearity,the inner coupling,misalignments between the sensors and actuators,and external disturbances are the main issues that should be considered for the maglev engineering.Furthermore,a feedback linearization controller based on the mathematical model of a maglev module is derived,in which the nonlinearity,coupling and misalignments are taken into account.Then,to attenuate the effect of external disturbances,a disturbance observer is proposed and the dynamics of the estimation error is analyzed using the input-to-state stability theory.It shows that the error is negligible under a low-frequency disturbance.However,at the high-frequency range,the error is unacceptable and the disturbances can not be compensated in time,which lead to over designed fluctuations of levitation gap,even a clash between the upper surface of electromagnet and lower surface of guideway.To solve this problem,a novel nonlinear acceleration feedback is put forward to enhancing the attenuation ability of fast varying disturbances.Finally,numerical comparisons show that the proposed controller outperforms the traditional feedback linearization controller and maintains good robustness under disturbances.
基金Projects(11302252,11202230)supported by the National Natural Science Foundation of China
文摘This work proposes a practical nonlinear controller for the MIMO levitation system. Firstly, the mathematical model of levitation modules is developed and the advantages of the control scheme with magnetic flux feedback are analyzed when compared with the current feedback. Then, a backstepping controller with magnetic flux feedback based on the mathematical model of levitation module is developed. To obtain magnetic flux signals for full-size maglev system, a physical method with induction coils installed to winding of the electromagnet is developed. Furthermore, to avoid its hardware addition, a novel conception of virtual magnetic flux feedback is proposed. To demonstrate the feasibility of the proposed controller, the nonlinear dynamic model of full-size maglev train with quintessential details is developed. Based on the nonlinear model, the numerical comparisons and related experimental validations are carried out. Finally, results illustrating closed-loop performance are provided.
基金Projects(11302252,11202230)supported by the National Natural Science Foundation of China
文摘This work addresses the saturation influence of control voltage on the occurring of self-excited vibration of maglev vehicle-bridge interaction system, which greatly degrades the stability of the levitation control, decreases the ride comfort, and restricts the cost of the whole system. Firstly, the interaction model of vehicle-bridge system is developed. Based on the interaction model, the relationship between the control voltage and vibration frequency is solved. Then, the variation of the effective direct component and fundamental harmonic are discussed. Furthermore, from the perspective of energy transmission between the levitation system and bridge, the principle underlying the self-excited vibration is explored, and the influence on the stability is discussed. Finally, in terms of the variation of the characteristic roots, the influence is analyzed further and some conclusions are obtained. This study provides a theoretical guidance for mastering the self-excited vibration problems.
基金Projects(50735007,51005253) supported by the National Natural Science Foundation of ChinaProject(2007AA04Z344) supported by the National High-Tech Research and Development Program of China
文摘A novel maglev transportation system was proposed for large travel range ultra precision motion.The system consists of a levitation subsystem and a propulsion subsystem.During the propulsion subsystem driving the moving platform along the guideway,the levitation subsystem uses six pairs of electromagnets to steadily suspend the moving platform over the guideway.The model of the levitation system,which is a typical nonlinear multi-input multi-output coupling system and has many inner nonlinear coupling characteristics,was deduced.For testifying the model,the levitation mechanism was firstly controlled by proportional-integral-differential(PID) control,and then a lot of input-output data were collected for model parameter identification.The least-square parameter identification method was used.The identification results prove that the model is feasible and suitable for the real system.
文摘A novel magnetic levitation support method is proposed, which can relieve the perturbation caused by traditional support methods andprovide more accurate position control of the capsule. This method can keep the perfect symmetry of the octahedral spherical hohlraum and hasthe characteristics in stability, tunability and simplicity. It is also favorable that all the results, such as supporting forces acting on the super-conducting capsule, are calculated analytically, and numerical simulations are performed to verify these results. A typical realistic design isproposed and discussed in detail. The superconducting coating material is suggested, and the required superconducting properties are listed.Damped oscillation of the floating capsule in thin helium gas is discussed, and the restoring time is estimated.
