Hydrodynamic Load Associated with the Oscillations of a Cylinder at the Interface in a Two-Layer Fluid of Finite Depth

The results of numerically solving the linear problem of the small steady-state oscillations of a horizontal cylinder located at the interface between two fluids of different densities are presented. The hybrid element method is used. In this method the velocity potentials are represented by means of the finite element method in a narrow zone in the neighborhood of the body and by means of the boundary integral equations in the outer domain. The Green’s functions for an oscillating source in a two-layer fluid bounded from above by a free boundary and from below by an even horizontal bottom are derived. Numerical calculations of the apparent mass and damping coefficients are carried out for an elliptic cylinder beneath a free surface and for a cylinder with the cross-section in the form of a Lewis rib contour which floats on the free surface.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 122–131Original Russian Text Copyright © 2005 by Sturova and Syui.     

非线性单稳态系统中基于内禀振荡的随机共振

通过考察具有内禀振荡的单稳态非线性系统的随机振荡行为,研究了内禀振荡对噪声背景中微弱信号检测性能的影响.结果表明,输出信噪比和系统信噪比增益都表现出随机共振行为;该随机共振现象依赖于系统的选频特性,而系统的选频特性源于内禀振荡.该单稳态非线性系统表现出的这种源于内禀振荡的随机共振,可能为微弱信号检测系统的设计提供新思路.     

热声振荡的格子气模拟

采用二维九速的格子气模型模拟热声振荡,建立了完备的多体碰撞规则,提供了粘性和热边界的处理方法.对不同热源温度的热声振荡起振特性进行了模拟,同时也数值模拟研究了板叠两端温度随时间的响应过程.研究结果显示,碰撞规则完善与否会影响格子气的模拟结果,系统中的温度场对板叠温差的扰动存在响应滞后,温差直接影响热声振荡的起振特性.此外,低温热源对格子气模型噪声的影响更为敏感.     

二阶非线性具时滞脉冲微分方程振动性

主要就二阶非线性具时滞脉冲微分方程振动性进行了讨论,得到一些充分判据,并给出例子以说明脉冲及时滞对振动性态所起的作用。     

Numerical Simulation of a Liquid Drop Freely Oscillating

Free oscillations of a viscous liquid drop surrounded by a dynamically inactive ambient gas, in zero gravity, are investigated numerically using FIDAP^TM package in the axisymmetrical case. The full Navier‐Stokes equations with appropriate interfacial conditions are solved by using Galerkin/Finite element technique along with the spine method for the advection of the free boundary are used. The aim of this preliminary study is to demonstrate the ability of the package to accurately solve nonlinear free surface problems. Oscillations of viscous drops released from an initial static deformation of small‐ to large‐amplitude proportional to the second spherical harmonic, without initial internal circulation, are considered. Accuracy is attested by demonstrating that (i) the drop volume remains constant, (ii) dynamic response to small and moderate amplitudes agrees well with linear and weakly non‐linear perturbation theories, (iii) large amplitude oscillations compare well with some numerical and experimental published results.     

Excitation of Forbidden Electronic Transitions in Atoms by Hermite–Gaussian Modes

Photoexcitation of trapped ions by Hermite–Gaussian (HG) modes from guided beam structures is proposed and investigated theoretically. In particular, simple analytical expressions for the matrix elements of induced atomic transitions are derived that depend both on the parameters of HG beams and on the geometry of an experiment. By using these general expressions, the ${}^2{S}_{1/2}\to {}^2{F}_{7/2}$ electric octupole (E3) transition is investigated in an Yb⁺ ion, localized in the low–intensity center of the HG₁₀ and HG₀₁ beams. It is shown how the corresponding Rabi frequency can be enhanced by properly choosing the polarization of incident light and the orientation of an external magnetic field, which defines the quantization axis of a target ion. The calculations, performed for experimentally feasible beam parameters, indicate that the achieved Rabi frequencies can be comparable or even higher than those observed for the conventional Laguerre–Gaussian (LG) modes. Since HG-like modes can be relatively straightforwardly generated with high purity and stability from integrated photonics, these results suggest that they may form a novel tool for investigating highly-forbidden atomic transitions.