The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the K...The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.展开更多
The study reveals analytically on the 3-dimensional viscous time-dependent gyrotactic bioconvection in swirling nanofluid flow past from a rotating disk.It is known that the deformation of the disk is along the radial...The study reveals analytically on the 3-dimensional viscous time-dependent gyrotactic bioconvection in swirling nanofluid flow past from a rotating disk.It is known that the deformation of the disk is along the radial direction.In addition to that Stefan blowing is considered.The Buongiorno nanofluid model is taken care of assuming the fluid to be dilute and we find Brownian motion and thermophoresis have dominant role on nanoscale unit.The primitive mass conservation equation,radial,tangential and axial momentum,heat,nano-particle concentration and micro-organism density function are developed in a cylindrical polar coordinate system with appropriate wall(disk surface)and free stream boundary conditions.This highly nonlinear,strongly coupled system of unsteady partial differential equations is normalized with the classical von Kármán and other transformations to render the boundary value problem into an ordinary differential system.The emerging 11th order system features an extensive range of dimensionless flow parameters,i.e.,disk stretching rate,Brownian motion,thermophoresis,bioconvection Lewis number,unsteadiness parameter,ordinary Lewis number,Prandtl number,mass convective Biot number,Péclet number and Stefan blowing parameter.Solutions of the system are obtained with developed semi-analytical technique,i.e.,Adomian decomposition method.Validation of the said problem is also conducted with earlier literature computed by Runge-Kutta shooting technique.展开更多
Kármán Vortex Street, a fascinating phenomenon of fluid dynamics, has intrigued the scientific community for a long time. Many researchers have dedicated their efforts to unraveling the essence of this intri...Kármán Vortex Street, a fascinating phenomenon of fluid dynamics, has intrigued the scientific community for a long time. Many researchers have dedicated their efforts to unraveling the essence of this intriguing flow pattern. Here, we apply the lattice Boltzmann method with curved boundary conditions to simulate flows around a circular cylinder and study the emergence of Kármán Vortex Street using the eigen microstate approach, which can identify phase transition and its order-parameter. At low Reynolds number, there is only one dominant eigen microstate W_(1) of laminar flow. At Re_(c)^(1)= 53.6, there is a phase transition with the emergence of an eigen microstate pair W^(2,3) of pressure and velocity fields. Further at Re_(c)^(2)= 56, there is another phase transition with the emergence of two eigen microstate pairs W^(4,5) and W^(6,7). Using the renormalization group theory of eigen microstate,both phase transitions are determined to be first-order. The two-dimensional energy spectrum of eigen microstate for W^(1), W^(2,3) after Re_(c)^(1), W^(4-7) after Re_(c)^(2) exhibit-5/3 power-law behavior of Kolnogorov's K41 theory. These results reveal the complexity and provide an analysis of the Kármán Vortex Street from the perspective of phase transitions.展开更多
Based on the Boltzmann’s superposition principles of linear viscoelastic materials and the von K*-rm*-n’s hypotheses of thin plates with large deflections, a mathematical model for quasi-static problems of viscoelas...Based on the Boltzmann’s superposition principles of linear viscoelastic materials and the von K*-rm*-n’s hypotheses of thin plates with large deflections, a mathematical model for quasi-static problems of viscoelastic thin plates was given. By the Galerkin method in spatial domain, the original integro-partial-differential system could be transformed into an integral system. The latter further was reduced to a differential system by using the new method for temporal domain presented in this paper. Numerical results show that compared with the ordinary finite difference method, the new method in this paper is simpler to operate and has some advantages, such as, no storage and quicker computational speed etc.展开更多
By studying the characteristics of the flow field around a swimming fish,useful insights can be obtained into the superior swimming capabilities developed by nature over millions of years,in comparison to what can be ...By studying the characteristics of the flow field around a swimming fish,useful insights can be obtained into the superior swimming capabilities developed by nature over millions of years,in comparison to what can be achieved using the standard engineering principles traditionally employed in naval and ocean engineering.In the present study,the flow field related to a single joint fish model is simulated in the framework of a commercial computational fluid dynamics software(ANSYS Fluent 18.0).The principle of the anti-Kármán vortex street is analyzed and the relationship between the direction of the tail vortex and the direction of the fin swing is determined according to the vortex structures and the pressure distribution.A parametric investigation is finally conducted to analyze in particular how the Strouhal number(St)can affect the fish propulsive performance and efficiency。展开更多
The asymptotic behaviour of solutions of three-dimensional nonlinear elastodynamics in a thin shell is considered,as the thickness h of the shell tends to zero.Given the appropriate scalings of the applied force and o...The asymptotic behaviour of solutions of three-dimensional nonlinear elastodynamics in a thin shell is considered,as the thickness h of the shell tends to zero.Given the appropriate scalings of the applied force and of the initial data in terms of h,it’s verified that three-dimesional solutions of the nonlinear elastodynamic equations converge to solutions of the time-dependent von Kármán equations or dynamic linear equations for shell of arbitrary geometry.展开更多
The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the d...The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the downstream centerline of the bluff cylinder at a distance of 4 diameters away from the center of the cylinder. To simulate the fish body undulation and movement, the moving mesh is generated by a coupling approach based on the radial basis function and the overset grid technology. The Navier-Stokes equation in the arbitrary Lagrangian-Eulerian form is solved by coupling with the kinematics equation. Three cases are investigated: in a stationary position without deformation, a passive locomotion without deformation, and an active deformation based on the Kármán gait model. The results indicate that the fish body is acted by an alternating force and moment when it is located in the centerline of the vortex street. Furthermore, the fish could extract sufficient kinetic energy to overcome the drag under suitable conditions even when it keeps rigid and out of the suction zone. When the fish body undulates based on the Kármán gait model, the interaction is evidently shown between the fish body and the vortices. The theoretical analysis demonstrates that the lateral force and the moment acting on the fish body vary in a cosine formula, with the lateral translation and the body rotation as a result. This study focuses on the behavior of the fish body in the bluff cylinder wake and reproduces some phenomena observed in the experiments. Besides, the Kármán gait model is also theoretically analyzed, for the further exploration of the FSI mechanism in case of fish swimming.展开更多
In this paper,a newly developed second order temporally and spatially accurate finite difference scheme for biharmonic semi linear equations has been employed in simulating the time evolution of viscous flows past an ...In this paper,a newly developed second order temporally and spatially accurate finite difference scheme for biharmonic semi linear equations has been employed in simulating the time evolution of viscous flows past an impulsively started circular cylinder for Reynolds number(Re)up to 9,500.The robustness of the scheme and the effectiveness of the formulation can be gauged by the fact that it very accurately captures complex flow structures such as the von Kármán vortex street through streakline simulation and the a and b-phenomena in the range 3,000≤Re≤9,500 among others.The main focus here is the application of the technique which enables the use of the discretized version of a single semi linear biharmonic equation in order to efficiently simulate different fluid structures associated with flows around a bluff body.We compare our results,both qualitatively and quantitatively,with established numerical and more so with experimental results.Excellent comparison is obtained in all the cases.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 12065022 and 12147213)。
文摘The dynamics of spin–orbit-coupled Bose–Einstein condensate with parity-time symmetry through a moving obstacle potential is simulated numerically. In the miscible two-component condensate, the formation of the Kármán vortex street is observed in one component, while ‘the half-quantum vortex street' is observed in the other component. Other patterns of vortex shedding, such as oblique vortex dipoles, V-shaped vortex pairs, irregular turbulence, and combined modes of various wakes, can also be found. The ratio of inter-vortex spacing in one row to the distance between vortex rows is approximately0.18, which is less than the stability condition 0.28 of classical fluid. The drag force acting on the obstacle potential is simulated. The parametric regions of Kármán vortex street and other vortex patterns are calculated. The range of Kármán vortex street is surrounded by the region of combined modes. In addition, spin–orbit coupling disrupts the symmetry of the system and the gain-loss affects the local particle distribution of the system, which leads to the local symmetry breaking of the system, and finally influences the stability of the Kármán vortex street. Finally, we propose an experimental protocol to realize the Kármán vortex street in a system.
文摘The study reveals analytically on the 3-dimensional viscous time-dependent gyrotactic bioconvection in swirling nanofluid flow past from a rotating disk.It is known that the deformation of the disk is along the radial direction.In addition to that Stefan blowing is considered.The Buongiorno nanofluid model is taken care of assuming the fluid to be dilute and we find Brownian motion and thermophoresis have dominant role on nanoscale unit.The primitive mass conservation equation,radial,tangential and axial momentum,heat,nano-particle concentration and micro-organism density function are developed in a cylindrical polar coordinate system with appropriate wall(disk surface)and free stream boundary conditions.This highly nonlinear,strongly coupled system of unsteady partial differential equations is normalized with the classical von Kármán and other transformations to render the boundary value problem into an ordinary differential system.The emerging 11th order system features an extensive range of dimensionless flow parameters,i.e.,disk stretching rate,Brownian motion,thermophoresis,bioconvection Lewis number,unsteadiness parameter,ordinary Lewis number,Prandtl number,mass convective Biot number,Péclet number and Stefan blowing parameter.Solutions of the system are obtained with developed semi-analytical technique,i.e.,Adomian decomposition method.Validation of the said problem is also conducted with earlier literature computed by Runge-Kutta shooting technique.
基金supported by the National Natural Science Foundation of China (Grant No.12135003)。
文摘Kármán Vortex Street, a fascinating phenomenon of fluid dynamics, has intrigued the scientific community for a long time. Many researchers have dedicated their efforts to unraveling the essence of this intriguing flow pattern. Here, we apply the lattice Boltzmann method with curved boundary conditions to simulate flows around a circular cylinder and study the emergence of Kármán Vortex Street using the eigen microstate approach, which can identify phase transition and its order-parameter. At low Reynolds number, there is only one dominant eigen microstate W_(1) of laminar flow. At Re_(c)^(1)= 53.6, there is a phase transition with the emergence of an eigen microstate pair W^(2,3) of pressure and velocity fields. Further at Re_(c)^(2)= 56, there is another phase transition with the emergence of two eigen microstate pairs W^(4,5) and W^(6,7). Using the renormalization group theory of eigen microstate,both phase transitions are determined to be first-order. The two-dimensional energy spectrum of eigen microstate for W^(1), W^(2,3) after Re_(c)^(1), W^(4-7) after Re_(c)^(2) exhibit-5/3 power-law behavior of Kolnogorov's K41 theory. These results reveal the complexity and provide an analysis of the Kármán Vortex Street from the perspective of phase transitions.
文摘Based on the Boltzmann’s superposition principles of linear viscoelastic materials and the von K*-rm*-n’s hypotheses of thin plates with large deflections, a mathematical model for quasi-static problems of viscoelastic thin plates was given. By the Galerkin method in spatial domain, the original integro-partial-differential system could be transformed into an integral system. The latter further was reduced to a differential system by using the new method for temporal domain presented in this paper. Numerical results show that compared with the ordinary finite difference method, the new method in this paper is simpler to operate and has some advantages, such as, no storage and quicker computational speed etc.
基金the National Natural Science Foundation of China,Grant Nos.51906224 and 51976200.
文摘By studying the characteristics of the flow field around a swimming fish,useful insights can be obtained into the superior swimming capabilities developed by nature over millions of years,in comparison to what can be achieved using the standard engineering principles traditionally employed in naval and ocean engineering.In the present study,the flow field related to a single joint fish model is simulated in the framework of a commercial computational fluid dynamics software(ANSYS Fluent 18.0).The principle of the anti-Kármán vortex street is analyzed and the relationship between the direction of the tail vortex and the direction of the fin swing is determined according to the vortex structures and the pressure distribution.A parametric investigation is finally conducted to analyze in particular how the Strouhal number(St)can affect the fish propulsive performance and efficiency。
基金the National Science Foundation of China under Grant Nos.61473126 and61573342Key Research Program of Frontier Sciences+1 种基金CASunder Grant No.QYZDJ-SSW-SYS011。
文摘The asymptotic behaviour of solutions of three-dimensional nonlinear elastodynamics in a thin shell is considered,as the thickness h of the shell tends to zero.Given the appropriate scalings of the applied force and of the initial data in terms of h,it’s verified that three-dimesional solutions of the nonlinear elastodynamic equations converge to solutions of the time-dependent von Kármán equations or dynamic linear equations for shell of arbitrary geometry.
基金Project supported by the National Key Research and Development Program of China (Grant No.2016YFB0200701)the National Natural Science Foundation of China (Grant Nos.11532016, 11672324)the National Key Project (Grant No.GJXM92579).
文摘The fluid-structure interaction (FSI) in case of fish swimming in the vortex street is investigated by numerical simulations. The vortex street is generated by a D-section cylinder. A 2-D fish model is placed on the downstream centerline of the bluff cylinder at a distance of 4 diameters away from the center of the cylinder. To simulate the fish body undulation and movement, the moving mesh is generated by a coupling approach based on the radial basis function and the overset grid technology. The Navier-Stokes equation in the arbitrary Lagrangian-Eulerian form is solved by coupling with the kinematics equation. Three cases are investigated: in a stationary position without deformation, a passive locomotion without deformation, and an active deformation based on the Kármán gait model. The results indicate that the fish body is acted by an alternating force and moment when it is located in the centerline of the vortex street. Furthermore, the fish could extract sufficient kinetic energy to overcome the drag under suitable conditions even when it keeps rigid and out of the suction zone. When the fish body undulates based on the Kármán gait model, the interaction is evidently shown between the fish body and the vortices. The theoretical analysis demonstrates that the lateral force and the moment acting on the fish body vary in a cosine formula, with the lateral translation and the body rotation as a result. This study focuses on the behavior of the fish body in the bluff cylinder wake and reproduces some phenomena observed in the experiments. Besides, the Kármán gait model is also theoretically analyzed, for the further exploration of the FSI mechanism in case of fish swimming.
基金The first author would like to express his thanks to the DST,India for supporting his research work under Project No.SR/S4/MS:468/07The second author is thankful to the University Grants Commission,India for supporting a part of the work by providing financial support in the form of a minor project(Project No.F.No.37-537/2009(SR)).
文摘In this paper,a newly developed second order temporally and spatially accurate finite difference scheme for biharmonic semi linear equations has been employed in simulating the time evolution of viscous flows past an impulsively started circular cylinder for Reynolds number(Re)up to 9,500.The robustness of the scheme and the effectiveness of the formulation can be gauged by the fact that it very accurately captures complex flow structures such as the von Kármán vortex street through streakline simulation and the a and b-phenomena in the range 3,000≤Re≤9,500 among others.The main focus here is the application of the technique which enables the use of the discretized version of a single semi linear biharmonic equation in order to efficiently simulate different fluid structures associated with flows around a bluff body.We compare our results,both qualitatively and quantitatively,with established numerical and more so with experimental results.Excellent comparison is obtained in all the cases.
