Convective Heat Transfer Characteristics of the Elliptic Cylinder with Axis Ratio 4∶1 in Crossflow

The heat transfer features around the elliptic cylinder of axis ratio 4∶1 in crossflow were investigated experimentally within a wide range of Reynolds number. By means of heat-mass transfer analogy and the naphthalene sublimation technique, the local heat transfer distribution and the mean heat transfer coefficient are clarified. The result shows that the mean heat transfer coefficient is higher than that of a circular cylinder in most Reynolds number range regarded, and this superiority turns to be more significant with the increase of flow speed. Moreover, the effect of axis ratio on mean heat transfer coefficient was investigated tentatively. The oil-lampblack technique was employed to enable visualization of the flow pattern around the cylinder and on the cylinder wall.

Active control of flow past an elliptic cylinder using an artificial neural network trained by deep reinforcement learning

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.

INTERACTION OF A FLOATING ELLIPTIC CYLINDER WITH A VIBRATING CIRCULAR CYLINDER

The nonlinear hydrodynamic interaction between a floating elliptic cylinder and a vibrating circular cylinder immersed in an infinite fluid was investigated. By taking the added masses of the two-cylinder system into account, the dynamical equations of motion were formulated from the Lagrange equations of motion. The dynamical behaviors of these two cylinders were analyzed numerically for some typical situations, and the results show that the presence of a vibrating circular cylinder has a significant influence on the planar motion of a floating elliptic cylinder. The hydrodynamic interaction between them results in complicated nonlinear behaviors of the floating cylinder. It is found that oscillatory motion of the elliptic cylinder takes place in response to the vibrating mode of the circular one.

Effective electroelastic constants for three-phase confocal elliptical cylinder model in piezoelectric quasicrystal composites

A three-phase confocal elliptical cylinder model is proposed to analyze micromechanics of one-dimensional hexagonal piezoelectric quasicrystal （PQC） compos- ites. Exact solutions of the phonon, phason, and electric fields are obtained by using the conformal mapping combined with the Laurent expansion technique when the model is subject to far-field anti-plane mechanical and in-plane electric loadings. The effective elec- troelastic constants of several different composites made up of PQC, quasicrystal （QC）, and piezoelectric （PE） materials are predicted by the generalized self-consistent method. Numerical examples are conducted to show the effects of the volume fraction and the cross-sectional shape of inclusion （or fiber） on the effective electroelastic constants of these composites. Compared with other micromechanical methods, the generalized self- consistent and Mori-Tanaka methods can predict the effective electroelastic constants of the composites consistently.

A semi-analytical solution for electric double layers near an elliptical cylinder

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.

Optical properties of the electromagnetic waves propagating in an elliptical cylinder multilayer structure

Theoretical description of the wave propagation in an elliptical cylinder multilayer structure under the conditions of H polarization and E polarization is presented. A transfer matrix method has been developed for elliptical cylinder waves. The formulas of reflection and transmission coefficients for an elliptical cylinder multilayer structure are driven. Reflection and transmission coefficients of elliptical cylinder waves by a single elliptical cylinder interface is presented. The obtained formulas can be generalized to the cold plasma filled structures and thus the obtained results in the limit of circular cylinder structures are investigated.

Surface effects on the indentation of a soft layer on a rigid substrate with an elliptical cylinder indenter

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.

Band structure calculations of in-plane waves in two-dimensional phononic crystals based on generalized multipole technique

A numerical method, the so-called multiple monopole（MMoP） method,based on the generalized multipole technique（GMT） is proposed to calculate the band structures of in-plane waves in two-dimensional phononic crystals, which are composed of arbitrarily shaped cylinders embedded in a solid host medium. To find the eigenvalues（eigenfrequencies） of the problem, besides the sources used to expand the wave fields, an extra monopole source is introduced which acts as the external excitation. By varying the excitation frequency, the eigenvalues can be localized as the extreme points of an appropriately chosen function. By sweeping the frequency range of interest and the boundary of the irreducible first Brillouin zone（FBZ）, the band structures can be obtained. Some typical numerical examples with different acoustic impedance ratios and with inclusions of various shapes are presented to validate the proposed method.