Vortices that develop over intakes are a hazardous hydraulic phenomenon.In this study, a 3D model was developed to study the flow field in air-core vortices.This model is based on the spiral pattern of streamlines and...Vortices that develop over intakes are a hazardous hydraulic phenomenon.In this study, a 3D model was developed to study the flow field in air-core vortices.This model is based on the spiral pattern of streamlines and the analytical solution of the momentum and continuity equations for deriving the three components of velocity.The model provides equations for free surface profiles and 3D patterns of the streamlines.Moreover, a new relationship was suggested for calculating effective viscosity and its distribution across the vortex flow field.The performance of the proposed analytical model was compared with existing experimental data and the results of previous analytical models.The outcomes indicated that the proposed model could predict characteristics of the vortex flow with good accuracy.展开更多
When a spiral groove is formed using superplastic molding, precision casting, additive manufacturing, or other non?mechanical processing technology, it is diffcult to meet the molding precision required for direct use...When a spiral groove is formed using superplastic molding, precision casting, additive manufacturing, or other non?mechanical processing technology, it is diffcult to meet the molding precision required for direct use, and the surface quality and accuracy of the shape need to be improved through a finishing process. In view of the poor reachability of the current tool?based polishing process, a tool?less polishing method using free?abrasive grains for complex spiral grooves is proposed. With this method, by controlling the movement of the workpiece, the design basis and relative motion of the abrasive particles along a helical path remain consistent, resulting in a better polishing profile. A spiral groove of a revolving body is taken as the research object; the influence of the installation method and the position of the parts, as well as the effect of the rotational speed of the abrasive ball on its relative motion along a helical trajectory, are studied, and the polishing cutting process of an abrasive ball is reasonably simplified. A consistent math?ematical model of the trajectory of an abrasive ball relative to the design helix is constructed. The grooved drum parts are verified through a polishing experiment. The spiral groove of the revolving body is modified and polished. Experiments show that the process not only corrects the shape a spiral groove error, but also reduces the surface roughness of a spiral groove. This study provides a theoretical basis for achieving free?abrasive, tool?free polishing.展开更多
We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by th...We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by the corre- sponding spectrum analysis. For a large T, the external modulation leads to the occurrence of more frequency peaks and these frequencies change with the modulation period according to their specific rules, respectively. Some of the frequencies and a primary frequency fl determine the corresponding curvature periods, which are locked into rational multiplies of the modulation period. These frequency-locking behaviours and the limited life-span of the frequencies in their variations with the modulation period constitute many resonant entrainment bands in the T axis. In the main bands, which follow the relation T/T12 = m/n, the size variable Rx of the tip trajectory is a monotonic increasing function of T. The rest of the frequencies are linear combinations of the two ones. Due to the complex dynamics, many unique tip trajectories appear at some certain T. We find also that spiral waves are eliminated when T is chosen from the end of the main resonant bands. This offers a useful method of controling the spiral wave.展开更多
Cellular aging can result in deterioration of electrical coupling, the extension of the action potential duration, and lower excitability of the cell. Those factors are introduced into the Greenberg–Hastings cellular...Cellular aging can result in deterioration of electrical coupling, the extension of the action potential duration, and lower excitability of the cell. Those factors are introduced into the Greenberg–Hastings cellular automaton model and the effects of the cellular aging on the dynamics of spiral waves are studied. The numerical results show that a 50% reduction of the coupling strength of aging cells has a little influence on spiral waves. If the coupling strength of aging cells equals zero, the ability for the medium to maintain spiral waves will be reduced by approximately 50% when the aging cell ratio increases from 0 to 0.5, where the reduction of cell excitability plays a major role in inducing disappearance of spiral waves. When the relevant parameters are properly chosen, the cellular aging can lead to the meandering of spiral waves,the emergence of the binary spiral waves, and even the disappearance of spiral waves via the stopping rotation or shrinkage of wave. Physical mechanisms of the above phenomena are analyzed briefly.展开更多
In this article, the performance and applications of a Spiral Plate Heat Exchanger are demonstrated. Also, governing equation of heat transfer phenomena in such heat exchangers is discussed. Regarding the governing eq...In this article, the performance and applications of a Spiral Plate Heat Exchanger are demonstrated. Also, governing equation of heat transfer phenomena in such heat exchangers is discussed. Regarding the governing equations, a LAB-sized model of this type of heat exchanger was designed and constructed. Galvanized Iron sheets were used as the heat transfer surfaces. Two Galvanized Iron sheets were rolled together around a central core and, as a result, two separated channels were made. Also, a predesign simulation of the heat exchanger was done using the Fluent software to predict the performance of the heat exchanger. First the geometry was made using Gambit software environment then the model was analyzed through Fluent. Because of less fouling, easier cleaning and high heat transfer coefficient, Spiral Heat Exchanger is a good alternative to the other types of heat exchangers, especially when it’s going to handle high fouling flows or highly viscous fluids. Low fouling rate of the heat exchanger, reduces the need of cleaning and therefore the out of service will be decreased. In the constructed heat exchanger, Nusselt number increases as the mass flow rate increases. Average Nusselt number is about 100 that is very good.展开更多
In this paper, we studied the effect of Gaussian coloured noise on the formation and instability of spiral waves described by one class of modified FitzHugh Nagumo equation. It was found that Gaussian coloured noise p...In this paper, we studied the effect of Gaussian coloured noise on the formation and instability of spiral waves described by one class of modified FitzHugh Nagumo equation. It was found that Gaussian coloured noise plays a constructive role in the formation, transition and instability of spiral wave. Too weak or too strong noise may act against the formation of spiral waves. At a certain noise level, spiral wave is maintained in a medium, in which spiral wave cannot be observed in the absence of the noise. It is difficult to make a stable spiral wave into unstable state by Gaussian coloured noise, unless the noise level is very high. The parameter regions of Gaussian coloured noise for spiral forming and spiral instability were given and discussed with numerical simulations.展开更多
A complete mathematical model for logarithmic spiral type sprag one-way clutch design and analysis is given.It assumes that the motion of all clutch components can be expressed by a model of epicyclic gearing.It takes...A complete mathematical model for logarithmic spiral type sprag one-way clutch design and analysis is given.It assumes that the motion of all clutch components can be expressed by a model of epicyclic gearing.It takes advantage of Hunt-Crossley contact impact theory to calculate the contact forces between sprags and races,and it can be used for optimization of design and comparison with other types of sprag clutches.A good deal of analysis shows that the parameters of the steady windup angle,the steady contact force,the natural frequency and natural cycle of clutch have nothing to do with the initial velocity of outer race,while the parameters of the maximum transient windup angle,the maximum transient impact force and the steady engagement time increase linearly in the mode of engaging operation of clutch.It is also shown that the strut angle has great influence on the dynamic engagement performance of clutch.The parameters of the steady windup angle,the maximum transient windup angle,the steady engaging time,the steady contact force,the maximum transient impact force and the natural cycle of clutch decrease linearly nearly with the inner strut angle,while the natural frequency of the system increases linearly with the inner strut angle.展开更多
In this study, the damage-plasticity model for concrete that was verified by the model experiment was used to calculate the damage to a spiral case structure based on the damage mechanics theory. The concrete structur...In this study, the damage-plasticity model for concrete that was verified by the model experiment was used to calculate the damage to a spiral case structure based on the damage mechanics theory. The concrete structure surrounding the spiral case was simulated with a three-dimensional finite element model. Then, the distribution and evolution of the structural damage were studied. Based on investigation of the change of gap openings between the steel liner and concrete structure, the impact of the non-uniform variation of gaps on the load-beating ratio between the steel liner and concrete structure was analyzed. The comparison of calculated results of the simplified and simulation algorithms shows that the simulation algorithm is a feasible option for the calculation of spiral case structures. In addition, the shell-spring model was introduced for optimization analysis, and the results were reasonable.展开更多
A conservation equation for topological charges of phase singularities （scroll and spiral waves） in excitable media is given. It provides some topological properties of scroll （spiral） waves： for example, the top...A conservation equation for topological charges of phase singularities （scroll and spiral waves） in excitable media is given. It provides some topological properties of scroll （spiral） waves： for example, the topological charge of the generated or annihilated spiral pair must be opposite. Additionally, we obtain another equation on scroll waves, which shows that singular filaments of scroll waves occur on a set of one-dimensional curves which may be either closed loops or infinite lines.展开更多
In this paper, we propose the distributed predictive control strategies of spiral wave in cardiac excitable media. The modified FitzHugh-Nagumo model was used to express the cardiac excitable media approximately. Base...In this paper, we propose the distributed predictive control strategies of spiral wave in cardiac excitable media. The modified FitzHugh-Nagumo model was used to express the cardiac excitable media approximately. Based on the control-Lyapunov theory, we obtained the distributed control equation, which consists of a positive eontrol-Lyapunov function and a positive cost function. Using the equation, we investigate two kinds of robust control strategies： the time-dependent distributed control strategy and the space-time dependent distributed control strategy. The feasibility of the strategies was demonstrated via an illustrative example, in which the spiral wave was prevented to occur, and the possibility for inducing ventricular fibrillation was eliminated. The strategies are helpful in designing various cardiac devices. Since the second strategy is more efficient and robust than the first one, and the response time in the second strategy is far less than that in the first one, the former is suitable for the quick-response control systems. In addition, our spatiotemporal control strategies, especially the second strategy, can be applied to other cardiac models, even to other reaction-diffusion systems.展开更多
基金supported by the Iran National Science Foundation(INSF,Grant No.97008045)
文摘Vortices that develop over intakes are a hazardous hydraulic phenomenon.In this study, a 3D model was developed to study the flow field in air-core vortices.This model is based on the spiral pattern of streamlines and the analytical solution of the momentum and continuity equations for deriving the three components of velocity.The model provides equations for free surface profiles and 3D patterns of the streamlines.Moreover, a new relationship was suggested for calculating effective viscosity and its distribution across the vortex flow field.The performance of the proposed analytical model was compared with existing experimental data and the results of previous analytical models.The outcomes indicated that the proposed model could predict characteristics of the vortex flow with good accuracy.
基金Supported by Key Scientific&Technological Research Project of Henan Province,China(Grant No.102102210497)
文摘When a spiral groove is formed using superplastic molding, precision casting, additive manufacturing, or other non?mechanical processing technology, it is diffcult to meet the molding precision required for direct use, and the surface quality and accuracy of the shape need to be improved through a finishing process. In view of the poor reachability of the current tool?based polishing process, a tool?less polishing method using free?abrasive grains for complex spiral grooves is proposed. With this method, by controlling the movement of the workpiece, the design basis and relative motion of the abrasive particles along a helical path remain consistent, resulting in a better polishing profile. A spiral groove of a revolving body is taken as the research object; the influence of the installation method and the position of the parts, as well as the effect of the rotational speed of the abrasive ball on its relative motion along a helical trajectory, are studied, and the polishing cutting process of an abrasive ball is reasonably simplified. A consistent math?ematical model of the trajectory of an abrasive ball relative to the design helix is constructed. The grooved drum parts are verified through a polishing experiment. The spiral groove of the revolving body is modified and polished. Experiments show that the process not only corrects the shape a spiral groove error, but also reduces the surface roughness of a spiral groove. This study provides a theoretical basis for achieving free?abrasive, tool?free polishing.
基金supported by the National Natural Science Foundation of China (Grant No. 11005030)the Science Foundation of Hebei Education Department,China (Grant No. 2009135)+1 种基金the Science Foundation of Inner Mongolia Education Department,China(Grant No. NJ09178)the Science Foundation of Hebei Normal University,China
文摘We numerically study the dynamics of spiral waves in the excitable system with the excitability modulated by a rectangle wave. The tip trajectories and their variations with the modulation period T are explained by the corre- sponding spectrum analysis. For a large T, the external modulation leads to the occurrence of more frequency peaks and these frequencies change with the modulation period according to their specific rules, respectively. Some of the frequencies and a primary frequency fl determine the corresponding curvature periods, which are locked into rational multiplies of the modulation period. These frequency-locking behaviours and the limited life-span of the frequencies in their variations with the modulation period constitute many resonant entrainment bands in the T axis. In the main bands, which follow the relation T/T12 = m/n, the size variable Rx of the tip trajectory is a monotonic increasing function of T. The rest of the frequencies are linear combinations of the two ones. Due to the complex dynamics, many unique tip trajectories appear at some certain T. We find also that spiral waves are eliminated when T is chosen from the end of the main resonant bands. This offers a useful method of controling the spiral wave.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11165004 and 11365003)
文摘Cellular aging can result in deterioration of electrical coupling, the extension of the action potential duration, and lower excitability of the cell. Those factors are introduced into the Greenberg–Hastings cellular automaton model and the effects of the cellular aging on the dynamics of spiral waves are studied. The numerical results show that a 50% reduction of the coupling strength of aging cells has a little influence on spiral waves. If the coupling strength of aging cells equals zero, the ability for the medium to maintain spiral waves will be reduced by approximately 50% when the aging cell ratio increases from 0 to 0.5, where the reduction of cell excitability plays a major role in inducing disappearance of spiral waves. When the relevant parameters are properly chosen, the cellular aging can lead to the meandering of spiral waves,the emergence of the binary spiral waves, and even the disappearance of spiral waves via the stopping rotation or shrinkage of wave. Physical mechanisms of the above phenomena are analyzed briefly.
文摘In this article, the performance and applications of a Spiral Plate Heat Exchanger are demonstrated. Also, governing equation of heat transfer phenomena in such heat exchangers is discussed. Regarding the governing equations, a LAB-sized model of this type of heat exchanger was designed and constructed. Galvanized Iron sheets were used as the heat transfer surfaces. Two Galvanized Iron sheets were rolled together around a central core and, as a result, two separated channels were made. Also, a predesign simulation of the heat exchanger was done using the Fluent software to predict the performance of the heat exchanger. First the geometry was made using Gambit software environment then the model was analyzed through Fluent. Because of less fouling, easier cleaning and high heat transfer coefficient, Spiral Heat Exchanger is a good alternative to the other types of heat exchangers, especially when it’s going to handle high fouling flows or highly viscous fluids. Low fouling rate of the heat exchanger, reduces the need of cleaning and therefore the out of service will be decreased. In the constructed heat exchanger, Nusselt number increases as the mass flow rate increases. Average Nusselt number is about 100 that is very good.
基金Project supported partially by National Science Foundation of China (Grant No 10305005)the Fundamental Research Fund for Physics and Mathematic of Lanzhou University of China
文摘In this paper, we studied the effect of Gaussian coloured noise on the formation and instability of spiral waves described by one class of modified FitzHugh Nagumo equation. It was found that Gaussian coloured noise plays a constructive role in the formation, transition and instability of spiral wave. Too weak or too strong noise may act against the formation of spiral waves. At a certain noise level, spiral wave is maintained in a medium, in which spiral wave cannot be observed in the absence of the noise. It is difficult to make a stable spiral wave into unstable state by Gaussian coloured noise, unless the noise level is very high. The parameter regions of Gaussian coloured noise for spiral forming and spiral instability were given and discussed with numerical simulations.
基金Project(2011CB706800)supported by the National Basic Research Program of China
文摘A complete mathematical model for logarithmic spiral type sprag one-way clutch design and analysis is given.It assumes that the motion of all clutch components can be expressed by a model of epicyclic gearing.It takes advantage of Hunt-Crossley contact impact theory to calculate the contact forces between sprags and races,and it can be used for optimization of design and comparison with other types of sprag clutches.A good deal of analysis shows that the parameters of the steady windup angle,the steady contact force,the natural frequency and natural cycle of clutch have nothing to do with the initial velocity of outer race,while the parameters of the maximum transient windup angle,the maximum transient impact force and the steady engagement time increase linearly in the mode of engaging operation of clutch.It is also shown that the strut angle has great influence on the dynamic engagement performance of clutch.The parameters of the steady windup angle,the maximum transient windup angle,the steady engaging time,the steady contact force,the maximum transient impact force and the natural cycle of clutch decrease linearly nearly with the inner strut angle,while the natural frequency of the system increases linearly with the inner strut angle.
基金supported by the National Natural Science Foundation of China (Grant No. 51079020)the He'nan Provincial Research Foundation for Basic and Advanced Technology (Grant No. 122300410001)the Foundation of He'nan Educational Committee (Grant No. 13A570715)
文摘In this study, the damage-plasticity model for concrete that was verified by the model experiment was used to calculate the damage to a spiral case structure based on the damage mechanics theory. The concrete structure surrounding the spiral case was simulated with a three-dimensional finite element model. Then, the distribution and evolution of the structural damage were studied. Based on investigation of the change of gap openings between the steel liner and concrete structure, the impact of the non-uniform variation of gaps on the load-beating ratio between the steel liner and concrete structure was analyzed. The comparison of calculated results of the simplified and simulation algorithms shows that the simulation algorithm is a feasible option for the calculation of spiral case structures. In addition, the shell-spring model was introduced for optimization analysis, and the results were reasonable.
基金Supported by the National Natural Science Foundation of China under Grant No 10675099, the Hong Kong Research Council （RGC）, and the Hong Kong Baptist University Faculty Research Fund （FRG）.
文摘A conservation equation for topological charges of phase singularities （scroll and spiral waves） in excitable media is given. It provides some topological properties of scroll （spiral） waves： for example, the topological charge of the generated or annihilated spiral pair must be opposite. Additionally, we obtain another equation on scroll waves, which shows that singular filaments of scroll waves occur on a set of one-dimensional curves which may be either closed loops or infinite lines.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10305005)the Hunan Provincial Natural Science Foundation of China (Grant No. 07JJ6126)
文摘In this paper, we propose the distributed predictive control strategies of spiral wave in cardiac excitable media. The modified FitzHugh-Nagumo model was used to express the cardiac excitable media approximately. Based on the control-Lyapunov theory, we obtained the distributed control equation, which consists of a positive eontrol-Lyapunov function and a positive cost function. Using the equation, we investigate two kinds of robust control strategies： the time-dependent distributed control strategy and the space-time dependent distributed control strategy. The feasibility of the strategies was demonstrated via an illustrative example, in which the spiral wave was prevented to occur, and the possibility for inducing ventricular fibrillation was eliminated. The strategies are helpful in designing various cardiac devices. Since the second strategy is more efficient and robust than the first one, and the response time in the second strategy is far less than that in the first one, the former is suitable for the quick-response control systems. In addition, our spatiotemporal control strategies, especially the second strategy, can be applied to other cardiac models, even to other reaction-diffusion systems.
