Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerical...Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.展开更多
In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micro...In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.展开更多
The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the L...The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the Landau phase transition theory. The dependency of velocity on current density is square root which degenerates into linear if the current is much higher than the critical value. The theory result is consistent with several previous experiments and also can explain the change of critical current in the presence of temperature. The role of temperature playing in the dynamics of domain wall motion is also discussed. The phase transition theory in terms of current density is employed to explain the critical behavior of domain wall motion.展开更多
The unsteady magnehydrodynamics （MHD） Couette flow of an electrically conducting fluid in a rotating system is investigated by taking the Hall and ion-slip currents into consideration. The derived fundamental equati...The unsteady magnehydrodynamics （MHD） Couette flow of an electrically conducting fluid in a rotating system is investigated by taking the Hall and ion-slip currents into consideration. The derived fundamental equations on the assumption of a small magnetic Reynolds number are solved analytically with the well-known Laplace transform technique. The unified closed-form expressions axe obtained for the velocity and the skin friction in the two different cases of the magnetic field being fixed to either the fluid or the moving plate. The effects of various parameters on the velocity and the skin friction axe discussed by graphs. The results reveal that the primary and secondary velocities increase with the Hall current. An increase in the ion-slip paxameter also leads to an increase in the primary velocity but a decrease in the secondary velocity. It is also shown that the combined effect of the rotation, Hall, and ion-slip parameters determines the contribution of the secondary motion in the fluid flow.展开更多
In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves...In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves can present three types of motion, i. e. significant stratification, fragile stratification and strong mixing. The motion gf turbid;,ater presents significant stratification when (H/D)/root Delta rho/rho less than or equal to 4.5, generally this state is known as density current. The formulas of motion velocity, thickness, and discharge of density current moving on horizontal bottom are derived by use of basic equations such as momemtum equation, equation of energy conservation and continuity equation of fluid. The time-average velocity and the thickness of density current under the action of waves have a relationship with such parameters as relative density (Delta rho/rho), wave height (H), and water depth (D). When these parameters are determined, the time-average thickness and motion velocity of density current are also determined. The relative thickness of density current (D-t/D) decreases with the increase of Delta rho/rho and increases with the increase of H/D. On the other hand, the motion velocity of density current increases with the increase of Delta rho/rho and decreases with the increase of the relative thickness (D-t/D) of density current. It is shown that the calculated results are in agreement with those of the flume experiment.展开更多
In this paper, we present a new idea to study the stochastic current within the canonical framework of white noise analysis. We define Wick-type stochastic current by using Wick integral with respect to Brownian motio...In this paper, we present a new idea to study the stochastic current within the canonical framework of white noise analysis. We define Wick-type stochastic current by using Wick integral with respect to Brownian motion, firstly. Moreover, we prove that the Brownian stochastic current is considered as a Hida distribution in terms of white noise approach and S-transform.展开更多
A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Ha...A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.展开更多
We discuss the transport of an underdamped particle driven by an external fluctuation force in a spatially periodic asymmetric potential with correlated noises. The corresponding mathematical model is established. The...We discuss the transport of an underdamped particle driven by an external fluctuation force in a spatially periodic asymmetric potential with correlated noises. The corresponding mathematical model is established. The movement of the steady current of an underdamped particle is presented by the method of the numerical simulation. It is indicated that the value of the current may be negative, zero, or positive. The external fluctuation force and correlated noises can effect the current direction. Under the appropriate parameters, the correlated noises intensity may even raise a reversal of the current. Besides, we have noticed a phenomenon that particles with different weight have different directions during movement by the impact of the correlated noises and external fluctuation force. Therefore, the Brownian particles can be effectively separated according to their masses.展开更多
To develop a control system of cantilever arm for barrels welding, a motion controller has been developed to fit the welding procedure. The main research fields of the controller are: (1) finding effective measures to...To develop a control system of cantilever arm for barrels welding, a motion controller has been developed to fit the welding procedure. The main research fields of the controller are: (1) finding effective measures to protect the controller against interferences; (2) decreasing welding current gradually in order to alleviate arc craters which are harmful to seam forming and welding quality; (3) planning the arm velocity to minimize the influence of the arm swing on arc length regulator; (4) adopting adaptive control algorithm with PD feedback and velocity feed-forward to reduce the influence of system inertia and velocity planning on the system transient performance.展开更多
In this paper,a method is proposed to improve the energy efficiency of the vertical axis turbine.First of all,a single disk multiple stream-tube model is used to calculate individual fitness.Genetic algorithm is adopt...In this paper,a method is proposed to improve the energy efficiency of the vertical axis turbine.First of all,a single disk multiple stream-tube model is used to calculate individual fitness.Genetic algorithm is adopted to optimize blade pitch motion of vertical axis turbine with the maximum energy efficiency being selected as the optimization objective.Then,a particular data processing method is proposed,fitting the result data into a cosine-like curve.After that,a general formula calculating the blade motion is developed.Finally,CFD simulation is used to validate the blade pitch motion formula.The results show that the turbine＇s energy efficiency becomes higher after the optimization of blade pitch motion;compared with the fixed pitch turbine,the efficiency of variable-pitch turbine is significantly improved by the active blade pitch control;the energy efficiency declines gradually with the growth of speed ratio;besides,compactness has lager effect on the blade motion while the number of blades has little effect on it.展开更多
以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线...以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线测量结果表明,采用小地板能够获得更均匀的流剖面。通过风洞试验对4种不同型式的运动抑制结构流载荷进行测量,进一步采用数值模拟方法对不同型式运动抑制结构的尾流场进行分析。结果表明:运动抑制结构通过对尾涡的限制,减少能量损耗,实现减阻效果。研究结果可为运动抑制结构的设计提供一定的参考。展开更多
基金funded by by the National Science Fund for Distinguished Young Scholars(Grant No.51425901)the National Natural Science Foundation of China(Grant Nos.51479053 and 51137002)+4 种基金the Natural Science Foundation of Jiangsu Province(Grant No.BK2011026)the 111 Project(Grant No.B2012032)the Specialized Research Funding for the Doctoral Program of Higher Education(Grant No.20130094110014)the Marine Renewable Energy Research Project of State Oceanic Administration(Grant No.GHME2013GC03)the Fundamental Research Funds for the Central University(Hohai University,Grant Nos.2013B31614 and 2014B04114)
文摘Horizontal axis tidal turbines have attracted more and more attentions nowadays, because of their convenience and low expense in construction and high efficiency in extracting tidal energy. The present study numerically investigates the flow motion and performance of a horizontal axis tidal turbine with a supporting vertical cylinder under steady current. In the numerical model, the continuous equation and incompressible Reynolds-averaged Navier-Stokes equations are solved, and the volume of fluid method is employed to track free surface motion. The RNG k-ε model is adopted to calculate turbulence transport while the fractional area/volume obstacle representation method is used to describe turbine characteristics and movement. The effects of installation elevation of tidal turbine and inlet velocity on the water elevation, and current velocity, rotating speed and resultant force on turbine are discussed. Based on the comparison of the numerical results, a better understanding of flow structure around horizontal axis tidal turbine and turbine performance is achieved.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11247026 and 11374253)
文摘In a magnetic nanostripe, the effects of perpendicular magnetic anisotropy（PMA） on the current-driven horizontal motion of vortex wall along the stripe and the vertical motion of the vortex core are studied by micromagnetic simulations.The results show that the horizontal and vertical motion can generally be monotonously enhanced by PMA. However, when the current is small, a nonmonotonic phenomenon for the horizontal motion is found. Namely, the velocity of the horizontal motion firstly decreases and then increases with the increase of the PMA. We find that the reason for this is that the PMA can firstly increase and then decrease the confining force induced by the confining potential energy. In addition, the PMA always enhances the driving force induced by the current.
文摘The relation between domain wall motion and intensity of driven current is examined in a phenomenological theory where the kinetic energy is expanded as a series of polynomial function of current density just as the Landau phase transition theory. The dependency of velocity on current density is square root which degenerates into linear if the current is much higher than the critical value. The theory result is consistent with several previous experiments and also can explain the change of critical current in the presence of temperature. The role of temperature playing in the dynamics of domain wall motion is also discussed. The phase transition theory in terms of current density is employed to explain the critical behavior of domain wall motion.
文摘The unsteady magnehydrodynamics （MHD） Couette flow of an electrically conducting fluid in a rotating system is investigated by taking the Hall and ion-slip currents into consideration. The derived fundamental equations on the assumption of a small magnetic Reynolds number are solved analytically with the well-known Laplace transform technique. The unified closed-form expressions axe obtained for the velocity and the skin friction in the two different cases of the magnetic field being fixed to either the fluid or the moving plate. The effects of various parameters on the velocity and the skin friction axe discussed by graphs. The results reveal that the primary and secondary velocities increase with the Hall current. An increase in the ion-slip paxameter also leads to an increase in the primary velocity but a decrease in the secondary velocity. It is also shown that the combined effect of the rotation, Hall, and ion-slip parameters determines the contribution of the secondary motion in the fluid flow.
文摘In this paper, the characteristics of density current under the action of waves are described with the help of flume experiment and theoretical analysis. The study shows that turbid water under the action of the waves can present three types of motion, i. e. significant stratification, fragile stratification and strong mixing. The motion gf turbid;,ater presents significant stratification when (H/D)/root Delta rho/rho less than or equal to 4.5, generally this state is known as density current. The formulas of motion velocity, thickness, and discharge of density current moving on horizontal bottom are derived by use of basic equations such as momemtum equation, equation of energy conservation and continuity equation of fluid. The time-average velocity and the thickness of density current under the action of waves have a relationship with such parameters as relative density (Delta rho/rho), wave height (H), and water depth (D). When these parameters are determined, the time-average thickness and motion velocity of density current are also determined. The relative thickness of density current (D-t/D) decreases with the increase of Delta rho/rho and increases with the increase of H/D. On the other hand, the motion velocity of density current increases with the increase of Delta rho/rho and decreases with the increase of the relative thickness (D-t/D) of density current. It is shown that the calculated results are in agreement with those of the flume experiment.
基金Supported by National Natural Science Foundation of China(Grant No.11061032)Colleges and Universities Scientific Research Funds Project Plan of Gansu Province for Postgraduate Tutor(Grant No.1205-07)Colleges and Universities Fundamental Research Funds Project of Gansu Province(2012)
文摘In this paper, we present a new idea to study the stochastic current within the canonical framework of white noise analysis. We define Wick-type stochastic current by using Wick integral with respect to Brownian motion, firstly. Moreover, we prove that the Brownian stochastic current is considered as a Hida distribution in terms of white noise approach and S-transform.
基金This project was supported by the National Outstanding Youth Science Foundation of China under contract! No. 49825161.
文摘A time-dependent mild-slope equation for the extension of the classic mild-slope equation of Berkhoff is developed for the interactions of large ambient currents and waves propagating over an uneven bottom, using a Hamiltonian formulation for irrotational motions. The bottom topography consists of two components the slowly varying component which satisfies the mild-slope approximation, and the fast varying component with wavelengths on the order of the surface wavelength but amplitudes which scale as a small parameter describing the mild-slope condition. The theory is more widely applicable and contains as special cases the following famous mild-slope type equations: the classical mild-Slope equation, Kirby's extended mild-slope equation with current, and Dingemans's mild-slope equation for rippled bed. Finally, good agreement between the classic experimental data concerning Bragg reflection and the present numerical results is observed.
基金Projected supported by the National Natural Science Foundation of China(Grant No.11202120)the Fundamental Research Funds for the Central Universities of China(Grant Nos.GK201502007 and GK201701001)
文摘We discuss the transport of an underdamped particle driven by an external fluctuation force in a spatially periodic asymmetric potential with correlated noises. The corresponding mathematical model is established. The movement of the steady current of an underdamped particle is presented by the method of the numerical simulation. It is indicated that the value of the current may be negative, zero, or positive. The external fluctuation force and correlated noises can effect the current direction. Under the appropriate parameters, the correlated noises intensity may even raise a reversal of the current. Besides, we have noticed a phenomenon that particles with different weight have different directions during movement by the impact of the correlated noises and external fluctuation force. Therefore, the Brownian particles can be effectively separated according to their masses.
文摘To develop a control system of cantilever arm for barrels welding, a motion controller has been developed to fit the welding procedure. The main research fields of the controller are: (1) finding effective measures to protect the controller against interferences; (2) decreasing welding current gradually in order to alleviate arc craters which are harmful to seam forming and welding quality; (3) planning the arm velocity to minimize the influence of the arm swing on arc length regulator; (4) adopting adaptive control algorithm with PD feedback and velocity feed-forward to reduce the influence of system inertia and velocity planning on the system transient performance.
基金financially supported by the National Natural Science Foundation of China(Grant No.51309069)the Special Funded of Innovational Talents of Science and Technology in Harbin(Grant No.RC2014QN001008)+1 种基金the China Postdoctoral Science Foundation(Grant No.2014M561334)the Heilongjiang Postdoctoral Science Foundation(Grant No.LBH-Z14060)
文摘In this paper,a method is proposed to improve the energy efficiency of the vertical axis turbine.First of all,a single disk multiple stream-tube model is used to calculate individual fitness.Genetic algorithm is adopted to optimize blade pitch motion of vertical axis turbine with the maximum energy efficiency being selected as the optimization objective.Then,a particular data processing method is proposed,fitting the result data into a cosine-like curve.After that,a general formula calculating the blade motion is developed.Finally,CFD simulation is used to validate the blade pitch motion formula.The results show that the turbine＇s energy efficiency becomes higher after the optimization of blade pitch motion;compared with the fixed pitch turbine,the efficiency of variable-pitch turbine is significantly improved by the active blade pitch control;the energy efficiency declines gradually with the growth of speed ratio;besides,compactness has lager effect on the blade motion while the number of blades has little effect on it.
文摘以带运动抑制结构的圆筒型浮式生产储卸油装置(Cylindrical Floating Production Storage and Offloading,CFPSO)为研究对象,在低速风洞中对CFPSO流载荷进行测量。为获得均匀流并减少边界层的影响,采用距离地面一定高度的小地板。热线测量结果表明,采用小地板能够获得更均匀的流剖面。通过风洞试验对4种不同型式的运动抑制结构流载荷进行测量,进一步采用数值模拟方法对不同型式运动抑制结构的尾流场进行分析。结果表明:运动抑制结构通过对尾涡的限制,减少能量损耗,实现减阻效果。研究结果可为运动抑制结构的设计提供一定的参考。
