A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation(NFAL) is presented.In this article,the transient response characteristics,including the levitated heigh...A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation(NFAL) is presented.In this article,the transient response characteristics,including the levitated height of an object with radius of 24 mm and thickness of 5 mm,the radial velocity and pressure difference of gas at the boundary of clearance between the levitated object and radiating surface(squeeze film),is calculated according to several velocity amplitudes of radiating surface.First,the basic equations in fluid areas on Arbitrary Lagrange-Euler(ALE) form are numerically solved by using streamline upwind petrov galerkin(SUPG) finite elements method.Second,the formed algebraic equations and solid control equations are solved by using synchronous alternating method to gain the transient messages of the levitated object and gas in the squeeze film.Through theoretical and numerical analyses,it is found that there is a oscillation time in the transient process and that the response time does not simply increase with the increasing of velocity amplitudes of radiating surface.More investigations in this paper are helpful for the understanding of the transient properties of levitated object in NFAL,which are in favor of enhancing stabilities and responsiveness of levitated object.展开更多
The importance to industry of non-contact bearings is growing rapidly as the demand for highspeed and high-precision manufacturing equipment increases.As a recently developed non-contact technology,near-field acoustic...The importance to industry of non-contact bearings is growing rapidly as the demand for highspeed and high-precision manufacturing equipment increases.As a recently developed non-contact technology,near-field acoustic levitation(NFAL)has drawn much attention for the advantages it offers,including no requirement for an external pressurized air supply,its compact structure,and its ability to adapt to its environment.In this paper,the working mechanism of NFAL is introduced in detail and compared to all existing non-contact technologies to demonstrate its versatility and potential for practical applications in industry.The fundamental theory of NFAL,including gas film lubrication theory and acoustic radiation pressure theory is presented.Then,the current stateof-the-art of the design and development of squeeze film air bearings based on NFAL is reviewed.Finally,future trends and obstacles to more widespread use are discussed.展开更多
The dynamic characteristics of acoustic levitation were investigated for the purpose of containerless processing of materials. Experimental measurements were accomplished on the variations of sound pressure level with...The dynamic characteristics of acoustic levitation were investigated for the purpose of containerless processing of materials. Experimental measurements were accomplished on the variations of sound pressure level with both axial position z (6.5mm≤ z ≤27.5mm) and radial position r (1mm≤ r ≤16mm) in a cylindrical resonant tube(34mm×45mm) of a single axis acoustic levitator. The results showed that the minimum sound pressure levels in both axial and radial directions occur at the centres of two transverse intercepting planes with z =8.5mm and z =21.5mm, which were identified as the sound pressure nodes not only of the axial direction but also of the radial direction, and hence were expected to have good levitation stability. This was further proved by experimental observations.展开更多
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
In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts: The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and alg...In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts: The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and algorithms request that there is only the direct acoustic pressure contained in the pressure at any point on the hologram surface, consequently, they cannot be used to reconstruct acoustic source and predict acoustic field directly. To take the reflected pressure into consideration, near-field acoustic holography for semi-free acoustic field based on wave superposition approach is proposed to realize the holographic reconstruction and prediction of the semi-free acoustic field, and the wave superposition approach is adopted as a holographic transform algorithm. The proposed theory and algorithm are realized and verified with a numerical example, and the drawbacks of the general theories and algorithms in the holographic reconstruction and prediction of the semi-free acoustic field are also demonstrated by this numerical example.展开更多
We present a design of an acoustic levitator consisting of three pairs of opposite transducer arrays.Three orthogonal standing waves create a large number of acoustic traps at which the particles are levitated in mid-...We present a design of an acoustic levitator consisting of three pairs of opposite transducer arrays.Three orthogonal standing waves create a large number of acoustic traps at which the particles are levitated in mid-air.By changing the phase difference of transducer arrays,three-dimensional manipulation of particles is successfully realized.Moreover,the relationship between the translation of particles and the phase difference is experimentally investigated,and the result is in agreement with the theoretical calculation.This design can expand the application of acoustic levitation in many fields,such as biomedicine,ultrasonic motor and new materials processing.展开更多
Because of the ill-posedness of the near-field acoustic holography(NAH),the regularization method is required to stabilize the computational process of NAH.The regularization effect is related to how to select the p...Because of the ill-posedness of the near-field acoustic holography(NAH),the regularization method is required to stabilize the computational process of NAH.The regularization effect is related to how to select the parameter correctly and effectively.However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection,which influences the application of NAH.For the purpose of solving the problems existed in the L-curve method,the (?)-curve method is introduced into the field of NAH,and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH.However,it is found out via investigations that the(?)-curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly.In order to select the parameter correctly and effectively,a novel method for selecting regularization parameters is proposed based on the original(?)-curve method,which can be called improved (?)-curve method.In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value,and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate,which are the two main differences compared with the L-curve and with the original(?)-curve method.In linear coordinate and using the linearly discretized regularization parameters,the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter,moreover the curve is convex everywhere.So the regularization parameters can be selected correctly and effectively based on the improved(?)-curve method.Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method.Experiments with two actual sources,a clamped plate and the double speakers,are carried out to do a further demonstration.The simulation result as well as the experimental result shows that the improved(?)-curve method is efficacious and has some advantages over the L-curve method and the original(?)-curve method.The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.展开更多
The aerodynamic breakup of the droplet has been intensely studied in this paper.We aim to establish a unified relationship between dimensionless kinematic parameters such as displacement,spreading diameter,Weber num-b...The aerodynamic breakup of the droplet has been intensely studied in this paper.We aim to establish a unified relationship between dimensionless kinematic parameters such as displacement,spreading diameter,Weber num-ber,time,and so on.The breakup characteristics of the acoustic levitated ethanol droplet are experimentally inves-tigated when exposed to an air jetflow.The breakup phenomenons were recorded with a high-speed camera.The breakup characteristics were analyzed,and the physical models of the moving and transforming behaviors were established to explain the breakup mechanisms.We found that the displacement of the windward side of the dro-plet follows free acceleration rule,with the displacement,acceleration,and time in the dimensionless form.The spreading of the diameter during deformation can also be written in a simple equation as a function of Weber number and displacement.We also discussed more details.展开更多
In order to develop the acoustic keyboard for Personal Computer(PC),it is necessary to seek high-precision near-field source localization algorithm for identifying the keyboard characters.First of all,the focusing pro...In order to develop the acoustic keyboard for Personal Computer(PC),it is necessary to seek high-precision near-field source localization algorithm for identifying the keyboard characters.First of all,the focusing property of Time Reversal Mirror(TRM) is introduced,and then a mathe-matical model of microphone array receiving typing sound is established according to the realization of acoustic keyboard from which the TRM localization algorithm is carried out.The results through computer simulation show that the localization Root Mean Square Error(RMSE) performance of the algorithm can reach 10-3,which demonstrates that the algorithm possesses a high accuracy for the actual near-field acoustic source localization,with potential of developing the computer acoustic keyboard.Furthermore,for the purpose of testing its effect on actual near-field source localization,we organize three experiments for acoustic keyboard characters localization.The experiment results show that the positioning error of TRM algorithm is less than 1 cm within a provided acoustic keyboard region.This will provide theoretical guidance for the further research of computer acoustic keyboard.展开更多
The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influenc...The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influencing the undercoolability of water under acoustic levitation are synthetically analyzed. The experimental results indicate that impurities tend to decrease the undercooling level, whereas the dominant factor is the effect of ultrasound. The stirring and cavitation effects of ultrasound tend to stimulate the nucleation of water and prevent further bulk undercooling in experiments. The stirring effect provides some extra energy fluctuation to overcome the thermodynamic barrier for nucleation. The local high pressure caused by cavitation effect increases the local undercooling in water and stimulates nucleation before the achievement of a large bulk undercooling. According to the cooling curves, the dendrite growth velocity of ice is estimated, which is in good agreement with the theoretical prediction at the lower undercooling. The theoretical calculation predicts a dendrite growth velocity of 0.23 m/s corresponding to the maximum undercooling of 24 K, at which the rapid solidification of ice occurs.展开更多
Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously i...Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously in solidification sample,opposite to macrosegregation in solidification sample under conventional condition. Stokes motion of the second liquid droplet (Ga) is significantly restrained un-der acoustic levitation condition. The analyses indicate that the melt vibration in the gravity direction forced by acoustic field can induce steady flow around the second liquid droplet,which influences droplet shape during its moving upward and consequently restrains Stokes motion velocity of the second liquid droplet.展开更多
The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on t...The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on the research of PVS, pressure-particle velocity (P-U) probe, and its application in noise source identification. Firstly, the principle and characteristics of PVS are presented. Secondly, a P-U probe is designed on the basis of PVS development. Finally, the noise measurement experiment for a single source is arranged and conducted. The result shows that the proposed P-U probe performs well in near-field noise source identification and localization.展开更多
基金Supported by the National Basic Research Program of China(973 Program)(2011CB707602)the China Natural Science Fond under Grant No.11174149the Funding of Jiangsu Innovation Program for Graduate Education under Grant No.CXl0B_092Z
文摘A new approach to the study on the transient properties of the levitated object in near-field acoustic levitation(NFAL) is presented.In this article,the transient response characteristics,including the levitated height of an object with radius of 24 mm and thickness of 5 mm,the radial velocity and pressure difference of gas at the boundary of clearance between the levitated object and radiating surface(squeeze film),is calculated according to several velocity amplitudes of radiating surface.First,the basic equations in fluid areas on Arbitrary Lagrange-Euler(ALE) form are numerically solved by using streamline upwind petrov galerkin(SUPG) finite elements method.Second,the formed algebraic equations and solid control equations are solved by using synchronous alternating method to gain the transient messages of the levitated object and gas in the squeeze film.Through theoretical and numerical analyses,it is found that there is a oscillation time in the transient process and that the response time does not simply increase with the increasing of velocity amplitudes of radiating surface.More investigations in this paper are helpful for the understanding of the transient properties of levitated object in NFAL,which are in favor of enhancing stabilities and responsiveness of levitated object.
基金the financial support from the National Natural Science Foundation of China(Nos.51575170 and 51875185)the National Key R&D Program of China(2018YFB2000100)the Foundation of Hunan Province(2018JJ1006).
文摘The importance to industry of non-contact bearings is growing rapidly as the demand for highspeed and high-precision manufacturing equipment increases.As a recently developed non-contact technology,near-field acoustic levitation(NFAL)has drawn much attention for the advantages it offers,including no requirement for an external pressurized air supply,its compact structure,and its ability to adapt to its environment.In this paper,the working mechanism of NFAL is introduced in detail and compared to all existing non-contact technologies to demonstrate its versatility and potential for practical applications in industry.The fundamental theory of NFAL,including gas film lubrication theory and acoustic radiation pressure theory is presented.Then,the current stateof-the-art of the design and development of squeeze film air bearings based on NFAL is reviewed.Finally,future trends and obstacles to more widespread use are discussed.
文摘The dynamic characteristics of acoustic levitation were investigated for the purpose of containerless processing of materials. Experimental measurements were accomplished on the variations of sound pressure level with both axial position z (6.5mm≤ z ≤27.5mm) and radial position r (1mm≤ r ≤16mm) in a cylindrical resonant tube(34mm×45mm) of a single axis acoustic levitator. The results showed that the minimum sound pressure levels in both axial and radial directions occur at the centres of two transverse intercepting planes with z =8.5mm and z =21.5mm, which were identified as the sound pressure nodes not only of the axial direction but also of the radial direction, and hence were expected to have good levitation stability. This was further proved by experimental observations.
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.
基金This project is supported by National Natural Science Foundation of China (No.10504006, No.50575063).
文摘In the semi-free acoustic field, the actual acoustic pressure at any point is composed of two parts: The direct acoustic pressure and the reflected acoustic pressure. The general acoustic holographic theories and algorithms request that there is only the direct acoustic pressure contained in the pressure at any point on the hologram surface, consequently, they cannot be used to reconstruct acoustic source and predict acoustic field directly. To take the reflected pressure into consideration, near-field acoustic holography for semi-free acoustic field based on wave superposition approach is proposed to realize the holographic reconstruction and prediction of the semi-free acoustic field, and the wave superposition approach is adopted as a holographic transform algorithm. The proposed theory and algorithm are realized and verified with a numerical example, and the drawbacks of the general theories and algorithms in the holographic reconstruction and prediction of the semi-free acoustic field are also demonstrated by this numerical example.
基金Supported by the Beijing College Students’Innovation and Entrepreneurship Training Program under Grant No BJ17040
文摘We present a design of an acoustic levitator consisting of three pairs of opposite transducer arrays.Three orthogonal standing waves create a large number of acoustic traps at which the particles are levitated in mid-air.By changing the phase difference of transducer arrays,three-dimensional manipulation of particles is successfully realized.Moreover,the relationship between the translation of particles and the phase difference is experimentally investigated,and the result is in agreement with the theoretical calculation.This design can expand the application of acoustic levitation in many fields,such as biomedicine,ultrasonic motor and new materials processing.
基金supported by National Natural Science Foundation of China(Grant No.11004045,No.10974040)Fok Ying Tung Education Foundation of China(Grant No.111058)Program for New Century Excellent Talents in University of China(Grant No.NCET-08-0767)
文摘Because of the ill-posedness of the near-field acoustic holography(NAH),the regularization method is required to stabilize the computational process of NAH.The regularization effect is related to how to select the parameter correctly and effectively.However the L-curve method commonly used for the selection of regularization parameters has the disadvantages of wrong selection and incorrect selection,which influences the application of NAH.For the purpose of solving the problems existed in the L-curve method,the (?)-curve method is introduced into the field of NAH,and the performance applied to NAH directly is analyzed on the basis of equivalent source method-based NAH.However,it is found out via investigations that the(?)-curve method in NAH also has the problem of wrong selection and is unable to choose the regularization parameter correctly.In order to select the parameter correctly and effectively,a novel method for selecting regularization parameters is proposed based on the original(?)-curve method,which can be called improved (?)-curve method.In the proposed method the regularization parameters are discretized linearly between the largest singular value and the smallest singular value,and the solution norm and the residual norm corresponding to these regularization parameters are also described in a linear coordinate instead of in a lg-lg coordinate,which are the two main differences compared with the L-curve and with the original(?)-curve method.In linear coordinate and using the linearly discretized regularization parameters,the solution norm is a monotonically decreasing function of the residual norm as the increase of the regularization parameter,moreover the curve is convex everywhere.So the regularization parameters can be selected correctly and effectively based on the improved(?)-curve method.Then a numerical simulation is done with a simply supported plate to verify the validity of the proposed method.Experiments with two actual sources,a clamped plate and the double speakers,are carried out to do a further demonstration.The simulation result as well as the experimental result shows that the improved(?)-curve method is efficacious and has some advantages over the L-curve method and the original(?)-curve method.The proposed novel method is able to avoid the problem of wrong selection and to select the regularization parameter correctly even if the curve is smooth.
基金supported by the National Natural Science Foundation China(Nos.51576159 and 91741110)the Shaanxi Provincial Key R&D Plan(Grant Nos.2019ZDLGY15-10 and 2019ZDLGY15-07).
文摘The aerodynamic breakup of the droplet has been intensely studied in this paper.We aim to establish a unified relationship between dimensionless kinematic parameters such as displacement,spreading diameter,Weber num-ber,time,and so on.The breakup characteristics of the acoustic levitated ethanol droplet are experimentally inves-tigated when exposed to an air jetflow.The breakup phenomenons were recorded with a high-speed camera.The breakup characteristics were analyzed,and the physical models of the moving and transforming behaviors were established to explain the breakup mechanisms.We found that the displacement of the windward side of the dro-plet follows free acceleration rule,with the displacement,acceleration,and time in the dimensionless form.The spreading of the diameter during deformation can also be written in a simple equation as a function of Weber number and displacement.We also discussed more details.
文摘In order to develop the acoustic keyboard for Personal Computer(PC),it is necessary to seek high-precision near-field source localization algorithm for identifying the keyboard characters.First of all,the focusing property of Time Reversal Mirror(TRM) is introduced,and then a mathe-matical model of microphone array receiving typing sound is established according to the realization of acoustic keyboard from which the TRM localization algorithm is carried out.The results through computer simulation show that the localization Root Mean Square Error(RMSE) performance of the algorithm can reach 10-3,which demonstrates that the algorithm possesses a high accuracy for the actual near-field acoustic source localization,with potential of developing the computer acoustic keyboard.Furthermore,for the purpose of testing its effect on actual near-field source localization,we organize three experiments for acoustic keyboard characters localization.The experiment results show that the positioning error of TRM algorithm is less than 1 cm within a provided acoustic keyboard region.This will provide theoretical guidance for the further research of computer acoustic keyboard.
基金the National Natural Science Foundation of China(Grant Nos.50101010&502211011)Fok Ying Tung Education Foundation(Grant No.71044)
文摘The experiments on undercooling of acoustically levitated water drops with the radius of 5-8 mm are carried out, and the maximum undercooling of 24 K is obtained in such a containerless state. Various factors influencing the undercoolability of water under acoustic levitation are synthetically analyzed. The experimental results indicate that impurities tend to decrease the undercooling level, whereas the dominant factor is the effect of ultrasound. The stirring and cavitation effects of ultrasound tend to stimulate the nucleation of water and prevent further bulk undercooling in experiments. The stirring effect provides some extra energy fluctuation to overcome the thermodynamic barrier for nucleation. The local high pressure caused by cavitation effect increases the local undercooling in water and stimulates nucleation before the achievement of a large bulk undercooling. According to the cooling curves, the dendrite growth velocity of ice is estimated, which is in good agreement with the theoretical prediction at the lower undercooling. The theoretical calculation predicts a dendrite growth velocity of 0.23 m/s corresponding to the maximum undercooling of 24 K, at which the rapid solidification of ice occurs.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50121101, 50271058, 50395105 and 50301012)
文摘Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously in solidification sample,opposite to macrosegregation in solidification sample under conventional condition. Stokes motion of the second liquid droplet (Ga) is significantly restrained un-der acoustic levitation condition. The analyses indicate that the melt vibration in the gravity direction forced by acoustic field can induce steady flow around the second liquid droplet,which influences droplet shape during its moving upward and consequently restrains Stokes motion velocity of the second liquid droplet.
文摘The Particle Velocity Sensor (PVS) is a kind of acoustic transducer which measures the particle velocity directly with figure-of-eight directivity. This paper proposes a near-field noise scanning technology based on the research of PVS, pressure-particle velocity (P-U) probe, and its application in noise source identification. Firstly, the principle and characteristics of PVS are presented. Secondly, a P-U probe is designed on the basis of PVS development. Finally, the noise measurement experiment for a single source is arranged and conducted. The result shows that the proposed P-U probe performs well in near-field noise source identification and localization.