The active control of flow past an elliptical cylinder using the deep reinforcement learning(DRL)method is conducted.The axis ratio of the elliptical cylinderΓvaries from 1.2 to 2.0,and four angles of attackα=0°...The active control of flow past an elliptical cylinder using the deep reinforcement learning(DRL)method is conducted.The axis ratio of the elliptical cylinderΓvaries from 1.2 to 2.0,and four angles of attackα=0°,15°,30°,and 45°are taken into consideration for a fixed Reynolds number Re=100.The mass flow rates of two synthetic jets imposed on different positions of the cylinderθ1andθ2are trained to control the flow.The optimal jet placement that achieves the highest drag reduction is determined for each case.For a low axis ratio ellipse,i.e.,Γ=1.2,the controlled results atα=0°are similar to those for a circular cylinder with control jets applied atθ1=90°andθ2=270°.It is found that either applying the jets asymmetrically or increasing the angle of attack can achieve a higher drag reduction rate,which,however,is accompanied by increased fluctuation.The control jets elongate the vortex shedding,and reduce the pressure drop.Meanwhile,the flow topology is modified at a high angle of attack.For an ellipse with a relatively higher axis ratio,i.e.,Γ1.6,the drag reduction is achieved for all the angles of attack studied.The larger the angle of attack is,the higher the drag reduction ratio is.The increased fluctuation in the drag coefficient under control is encountered,regardless of the position of the control jets.The control jets modify the flow topology by inducing an external vortex near the wall,causing the drag reduction.The results suggest that the DRL can learn an active control strategy for the present configuration.展开更多
Steady state plastic flow of the ideal plastic half-space surface by sliding elliptical cylinder is numerically calculated with account of contact friction effect. Numerical solution of the plane strain hyperbolic dif...Steady state plastic flow of the ideal plastic half-space surface by sliding elliptical cylinder is numerically calculated with account of contact friction effect. Numerical solution of the plane strain hyperbolic differential equations with unknown contact pressure distribution is treated as nonlinear vector equation for the steady state plastic flow condition. Pronounced effect of the ellipse boundary curvature on the plastic flow mode is shown. Engineering application of the computer model is surface plastic deformation technology to improve wear and fatigue resistance of metal parts.展开更多
A theoretical analysis on the electric double layer formed near the surface of an infinite cylinder with an elliptical cross section and a prescribed electric potential in an ionic conductor was performed using the li...A theoretical analysis on the electric double layer formed near the surface of an infinite cylinder with an elliptical cross section and a prescribed electric potential in an ionic conductor was performed using the linearized Gouy–Chapman theory. A semi-analytical solution in terms of the Mathieu functions was obtained. The distributions of the electric potential, cations, anions, and electric field were calculated. The effects of various physical and geometric parameters were examined. The fields vary rapidly near the elliptical boundary and are nearly uniform at far field. Electric field concentrations were found at the ends of the semi-major and semi-minor axes of the ellipse. These concentrations are sensitive to the physical and geometric parameters.展开更多
The non-Newtonian effect in the boundary layer flow over a horizontal elliptical cylinder is investigated numerically. A modified power-law viscosity model is used to correlate the non-Newtonian characteristics of the...The non-Newtonian effect in the boundary layer flow over a horizontal elliptical cylinder is investigated numerically. A modified power-law viscosity model is used to correlate the non-Newtonian characteristics of the fluid flow. For natural convectionflows, the surface of the cylinder is maintained by the uniform surface temperature(UST)or the uniform heat flux(UHF) condition. The governing equations corresponding to theflow are first transformed into a dimensionless non-similar form using suitable transformations. The resulting equations are solved numerically by an efficient finite difference scheme. The numerical results are presented for the skin friction coefficient and the local Nusselt number with the eccentric angle for different values of the power-law index n. The local skin friction coefficient and the local Nusselt number are found to be higher and lower, respectively, for the shear thickening fluids(n > 1) than the other fluids(n≤1).The effects of different elliptical configurations on the average Nusselt number are also presented and discussed for both conditions of the surface temperature.展开更多
Surface effects often play a significant role in the mechanical properties of soft materials such as hydrogels and biological tissues.In this paper,we investigate the plane-strain indentation of a soft elastic layer b...Surface effects often play a significant role in the mechanical properties of soft materials such as hydrogels and biological tissues.In this paper,we investigate the plane-strain indentation of a soft elastic layer bonded to a rigid substrate.The surface effects on the indentation behavior of the elastic layer-substrate system are theoretically analyzed.Indentation tests using indenters with different elliptical shapes are compared.Analytical expressions are derived for the indentation force-displacement relation using the Kerr model with the effect of surface tension.The theoretical solution is verified by finite element simulations.The dependence of surface effects on the ratio of the indenter’s major and minor elliptical axes is also examined.This work helps understand the size effects on the indentation behaviors of soft materials and guides the design of corresponding measurement tests.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos.11988102,92052201,11972220,12032016,11825204,91852202,and 11732010)the Key Research Projects of Shanghai Science and Technology Commission of China (Nos.19JC1412802 and 20ZR1419800)。
文摘The active control of flow past an elliptical cylinder using the deep reinforcement learning(DRL)method is conducted.The axis ratio of the elliptical cylinderΓvaries from 1.2 to 2.0,and four angles of attackα=0°,15°,30°,and 45°are taken into consideration for a fixed Reynolds number Re=100.The mass flow rates of two synthetic jets imposed on different positions of the cylinderθ1andθ2are trained to control the flow.The optimal jet placement that achieves the highest drag reduction is determined for each case.For a low axis ratio ellipse,i.e.,Γ=1.2,the controlled results atα=0°are similar to those for a circular cylinder with control jets applied atθ1=90°andθ2=270°.It is found that either applying the jets asymmetrically or increasing the angle of attack can achieve a higher drag reduction rate,which,however,is accompanied by increased fluctuation.The control jets elongate the vortex shedding,and reduce the pressure drop.Meanwhile,the flow topology is modified at a high angle of attack.For an ellipse with a relatively higher axis ratio,i.e.,Γ1.6,the drag reduction is achieved for all the angles of attack studied.The larger the angle of attack is,the higher the drag reduction ratio is.The increased fluctuation in the drag coefficient under control is encountered,regardless of the position of the control jets.The control jets modify the flow topology by inducing an external vortex near the wall,causing the drag reduction.The results suggest that the DRL can learn an active control strategy for the present configuration.
文摘Steady state plastic flow of the ideal plastic half-space surface by sliding elliptical cylinder is numerically calculated with account of contact friction effect. Numerical solution of the plane strain hyperbolic differential equations with unknown contact pressure distribution is treated as nonlinear vector equation for the steady state plastic flow condition. Pronounced effect of the ellipse boundary curvature on the plastic flow mode is shown. Engineering application of the computer model is surface plastic deformation technology to improve wear and fatigue resistance of metal parts.
基金supported by the National Natural Science Foundation of China (Grants 11502108 and 11232007)the Program for New Century Excellent Talents in Universities (Grant NCET-12-0625)+2 种基金the Natural Science Foundation of Jiangsu Province (Grant BK20140037)the Fundamental Research Funds for Central Universities (Grant NE2013101)Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)
文摘A theoretical analysis on the electric double layer formed near the surface of an infinite cylinder with an elliptical cross section and a prescribed electric potential in an ionic conductor was performed using the linearized Gouy–Chapman theory. A semi-analytical solution in terms of the Mathieu functions was obtained. The distributions of the electric potential, cations, anions, and electric field were calculated. The effects of various physical and geometric parameters were examined. The fields vary rapidly near the elliptical boundary and are nearly uniform at far field. Electric field concentrations were found at the ends of the semi-major and semi-minor axes of the ellipse. These concentrations are sensitive to the physical and geometric parameters.
基金Project supported by the North South University,Bangladesh(Nos.NSU-RP-18-067 and CTRG-19/SEPS/15)。
文摘The non-Newtonian effect in the boundary layer flow over a horizontal elliptical cylinder is investigated numerically. A modified power-law viscosity model is used to correlate the non-Newtonian characteristics of the fluid flow. For natural convectionflows, the surface of the cylinder is maintained by the uniform surface temperature(UST)or the uniform heat flux(UHF) condition. The governing equations corresponding to theflow are first transformed into a dimensionless non-similar form using suitable transformations. The resulting equations are solved numerically by an efficient finite difference scheme. The numerical results are presented for the skin friction coefficient and the local Nusselt number with the eccentric angle for different values of the power-law index n. The local skin friction coefficient and the local Nusselt number are found to be higher and lower, respectively, for the shear thickening fluids(n > 1) than the other fluids(n≤1).The effects of different elliptical configurations on the average Nusselt number are also presented and discussed for both conditions of the surface temperature.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.11802225 and 11921002).
文摘Surface effects often play a significant role in the mechanical properties of soft materials such as hydrogels and biological tissues.In this paper,we investigate the plane-strain indentation of a soft elastic layer bonded to a rigid substrate.The surface effects on the indentation behavior of the elastic layer-substrate system are theoretically analyzed.Indentation tests using indenters with different elliptical shapes are compared.Analytical expressions are derived for the indentation force-displacement relation using the Kerr model with the effect of surface tension.The theoretical solution is verified by finite element simulations.The dependence of surface effects on the ratio of the indenter’s major and minor elliptical axes is also examined.This work helps understand the size effects on the indentation behaviors of soft materials and guides the design of corresponding measurement tests.
