管内气液螺旋环状流动可以通过设置固定叶片的旋流器形成,旋流器的结构极大地影响了形成的螺旋环状流动的稳定性。对此,选取了四种典型旋流器结构开展三个典型来流工况下螺旋环状流形成的实验研究。通过图像处理结合概率密度函数(probab...管内气液螺旋环状流动可以通过设置固定叶片的旋流器形成,旋流器的结构极大地影响了形成的螺旋环状流动的稳定性。对此,选取了四种典型旋流器结构开展三个典型来流工况下螺旋环状流形成的实验研究。通过图像处理结合概率密度函数(probability density function,PDF)拟合的方法分析了形成螺旋环状流的稳定性,同时结合液膜波动特性与旋流器内部作用过程分析发现:平板式及平板有中心柱式旋流器在不同来流工况下产生的液膜相较于螺旋叶片式A/B旋流器都更加稳定,相同工况下的失稳距离也更长,而螺旋叶片式A/B旋流器产生的螺旋环状流的稳定性较差,在更短的距离内即发生了螺旋环状流失稳现象;不同工况下液相折算速度的上升有助于提高液膜稳定性与螺旋环状流失稳距离,从而形成更稳定的螺旋环状流;叶片作用下流体内部压力梯度和气液相分布规律高度相关,压力梯度和周向速度是形成螺旋环状流动的主要因素,并且压力梯度和周向速度的大小一定程度决定了螺旋环状流动气液交界面的稳定性。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
In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the l...In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.展开更多
Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be de...Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be defined, with special reference to Hall/Anti-Hall bar configurations. In part II, we focus on topologies where no conventional stream function can be defined, like Corbino disks. If current is injected and extracted at different boundaries of a multiply-connected conductive region, the current density shows spiral streamlines at strong magnetic field. Spiral streamlines also appear in simply-connected Hall plates when current contacts are located in their interior instead of their boundary, particularly if the contacts are very small. Spiral streamlines and circulating current are studied for two complementary planar device geometries: either all boundaries are conducting or all boundaries are insulating. The latter case means point current contacts and it can be treated similarly to singly connected Hall plates with peripheral contacts through the definition of a so-called loop stream function. This function also establishes a relation between Hall plates with complementary boundary conditions. The theory is explained by examples.展开更多
文摘管内气液螺旋环状流动可以通过设置固定叶片的旋流器形成,旋流器的结构极大地影响了形成的螺旋环状流动的稳定性。对此,选取了四种典型旋流器结构开展三个典型来流工况下螺旋环状流形成的实验研究。通过图像处理结合概率密度函数(probability density function,PDF)拟合的方法分析了形成螺旋环状流的稳定性,同时结合液膜波动特性与旋流器内部作用过程分析发现:平板式及平板有中心柱式旋流器在不同来流工况下产生的液膜相较于螺旋叶片式A/B旋流器都更加稳定,相同工况下的失稳距离也更长,而螺旋叶片式A/B旋流器产生的螺旋环状流的稳定性较差,在更短的距离内即发生了螺旋环状流失稳现象;不同工况下液相折算速度的上升有助于提高液膜稳定性与螺旋环状流失稳距离,从而形成更稳定的螺旋环状流;叶片作用下流体内部压力梯度和气液相分布规律高度相关,压力梯度和周向速度是形成螺旋环状流动的主要因素,并且压力梯度和周向速度的大小一定程度决定了螺旋环状流动气液交界面的稳定性。
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.
基金Supported by National Natural Science Foundation of China(Grant No.51276125)National Key Basic Research Development Program of China(973 Program,Grant No.2012CB720101)
文摘In working state, the dynamic performance of dry gas seal, generated by the rotating end face with spiral grooves, is determined by the open force of gas film and leakage flow rate. Generally, the open force and the leakage flow rate can be obtained by finite element method, computational fluid dynamics method and experimental measurement method. However, it will take much time to carry out the above measurements and calculations. In this paper, the approximate model of parallel grooves based on the narrow groove theory is used to establish the dynamic equations of the gas film for the purpose of obtaining the dynamic parameters of gas film. The nonlinear differential equations of gas film model are solved by Runge-Kutta method and shooting method. The numerical values of the pressure profiles, leakage flux and opening force on the seal surface are integrated, and then compared to experimental data for the reliability of the numerical simulation. The results show that the numerical simulation curves are in good agreement with experimental values. Furthermore, the opening force and the leakage flux are proved to be strongly correlated with the operating parameters. Then, the function-coupling method is introduced to analyze the numerical results to obtain the correlation formulae of the opening force and leakage flux respectively with the operating parameters, i.e., the inlet pressure and the rotating speed. This study intends to provide an effective way to predict the aerodynamic performance for designing and optimizing the groove styles in dry gas seal rapidly and accurately.
文摘Multiply-connected Hall plates show different phenomena than singly connected Hall plates. In part I (published in Journal of Applied Physics and Mathematics), we discussed topologies where a stream function can be defined, with special reference to Hall/Anti-Hall bar configurations. In part II, we focus on topologies where no conventional stream function can be defined, like Corbino disks. If current is injected and extracted at different boundaries of a multiply-connected conductive region, the current density shows spiral streamlines at strong magnetic field. Spiral streamlines also appear in simply-connected Hall plates when current contacts are located in their interior instead of their boundary, particularly if the contacts are very small. Spiral streamlines and circulating current are studied for two complementary planar device geometries: either all boundaries are conducting or all boundaries are insulating. The latter case means point current contacts and it can be treated similarly to singly connected Hall plates with peripheral contacts through the definition of a so-called loop stream function. This function also establishes a relation between Hall plates with complementary boundary conditions. The theory is explained by examples.
