Influence Of Rayleigh Research Articles

Numerical investigation of convective cooling in a rectangular vented cavity with two inlets and a hot obstacle

The current numerical study analyzes an air-filled vented cavity of AR 1.5 with two inlets and one outlet under laminar convective flow. Rayleigh’s number is varied between 103 and 106. The inlets are located at the bottom of the vertical walls, whereas the outlet is placed in the middle of the top wall. The vertical walls are hot, and the influence of Rayleigh’s number is studied in this configuration. With each rise in Ra, the thermal recirculation increased, which increased the temperature in that region. The influence of the presence of a hot block is analyzed by placing a hot block at the center of the bottom wall. The impact of the block’s dimensionless width and depth is studied by varying each value from 0.2H to 0.8H, keeping the other perpendicular dimension as 0.3H. The flow field, thermal field, velocity components, and heat transfer rates were analyzed. The presence of a hot block creates a hydrodynamic blockage and shifts the streamlines. The findings show that when the block’s size is increased parallel to the hot wall, the heat transfer rate is higher than the other direction variation. Correlation relationships for the overall Nusselt number with other variables are attained with two power models.

The Influence of Rayleigh and Brillouin Backscattering on the Performance of a 10 Gb EPON System

In order to improve the performance of 10 Gb Ethernet passive optical network (EPON). This paper builds a single channel bi-directional 10Gb EPON simulation system on the VPI simulation platform. By changing the system parameters such as Brillouin Scattering, Rayleigh back-scattering and AmplitudeRF, observed and analyzed the waveform, spectrum, eye diagram and bit error rate of uplink optical line terminal (OLT) received signal. Experimental results show that both Rayleigh and Brillouin backscattering have an impact on the performance of the system, but the Brillouin scattering effect is more affected when the two effects are simultaneously existed. In addition, the effect of Brillouin backscattering can be reduced by phase modulation of the optical uplink carrier.

The Influence of Rayleigh and Brillouin Backscattering on the Performance of a 10 Gb EPON System

The Influence of Rayleigh and Brillouin Backscattering on the Performance of a 10 Gb EPON System

Bifurcations in two‐dimensional differentially heated cavity

In this work, we propose a numerical analysis of a bidimensional instationary naturalconvection in a square cavity filled with air and inclined 45 degree versus to horizontal. The verticalwalls are subjected to non‐uniform temperatures while the horizontal walls are adiabatic. Theequations based on the formulation vorticity‐stream function are solved using the AlternatingDirections Implicit scheme (ADI) and Gauss elimination method. We analyze the influence ofRayleigh number on the roads to chaos borrowed by the natural convection developed in thiscavity, and we are looking for stable solutions representing the nonlinear dynamic system. Acorrelation between the Nusselt number and the Rayleigh number is proposed. We have analyzedthe vicinity of the critical point. The transition of the point attractor to another limit cycleattractor is characterized by the Hopf bifurcation.

Study of Fe3O4-water nanofluid with convective heat transfer in the presence of magnetic source

Influence of external magnetic source on ferrofluid convection in an enclosure with elliptic hot cylinder is studied. Governing formulae are first made dimensionless form along with the associated boundary conditions and then solved by powerful numerical method namely CVFEM. Influences of Rayleigh and Hartmann numbers and Fe3O4 volume fraction on hydrothermal behavior are presented. Results indicated that temperature gradient is an enhancing function of volume fraction of Fe3O4 and Rayleigh number but it is a reducing function of Lorentz forces. Lorentz forces cause the nanofluid velocity to reduce and augment the thermal boundary layer thickness. The role of effective parameters is illustrated through graphs and tables. Comparison of the present work is also made with the existing literature.

Numerical modeling of nanofluid natural convection in a semi annulus in existence of Lorentz force

Influence of external magnetic source on Fe3O4-water heat transfer in a cavity with circular hot cylinder is studied. New numerical method is chosen namely CVFEM. Influences of Rayleigh, Hartmann numbers and volume fraction of Fe3O4 on hydrothermal characteristics are presented. Results illustrate that Lorentz forces cause the nanofluid velocity to reduce and augment the thermal boundary layer thickness. The heat transfer improvement enhances with augment of Lorentz forces. Nusselt number augments with rise of buoyancy forces but it reduces with augment of Lorentz forces.

Free convection of Fe 3 O 4 -water nanofluid under the influence of an external magnetic source

Abstract Influence of external magnetic source on free convection of ferrofluid is reported in this paper. Obtaining systems have been solved through Control volume based finite element method. Influences of Rayleigh, Hartmann numbers, size of inner cylinder and volume fraction of Fe 3 O 4 on hydrothermal characteristics are presented. Results indicate that both temperature gradient and nanofluid velocity decease with augment of Hartmann number. Thermal boundary layer thickness reduces with augment of r in . Nusselt number decreases with rise of Lorentz forces while it enhances with rise of buoyancy forces.

Ferrofluid convective heat transfer under the influence of external magnetic source

Ferrofluid convective heat transfer in a cavity with sinusoidal cold wall is examined under the influence of external magnetic source. The working fluid is Fe3O4-water nanofluid. Single phase model is used to estimate the behavior of nanofluid. Vorticity stream function formulation is utilized to eliminate pressure gradient source terms. New numerical method is chosen namely Control volume base finite element method. Influences of Rayleigh, Hartmann numbers, amplitude of the sinusoidal wall and volume fraction of Fe3O4 on hydrothermal characteristics are presented. Results indicate that temperature gradient enhances as space between cold and hot walls reduces at low buoyancy force. Lorentz forces cause the nanofluid velocity to reduce and augment the thermal boundary layer thickness. Nusselt number augments with rise of buoyancy forces but it decreases with augment of Lorentz forces.

Parametrically Induced Damping in a Cracked Rotor

A transverse shaft crack in a rotor is usually modeled as a local change in shaft stiffness. This local stiffness change is not constant and varies as a result of a so-called breathing mechanism, explained with periodical opening and closing of crack faces under the load of external forces applied to the rotor. The rotor with a periodically varied stiffness can be modeled as a parametrically excited linear system. In the presence of a parametric excitation, the vibrations of the system can be amplified or damped at specific excitation frequencies. Usually, the frequencies at which the vibrations are amplified are important, since they can affect stability of the system. However, the increased damping at specific frequencies is a significant feature of a parametrically excited system that can have some potentially useful applications. One of such applications can be an early detection of a shaft crack. This paper presents results of numerical analysis of the influence of Rayleigh's damping and gyroscopic effects on the increase in damping in a parametrically excited rotor with a cracked shaft. It is shown that the increase in damping in a parametrically excited system is rather a rare phenomenon that can be observed only at properly selected values of the excitation frequency and Rayleigh's damping. Furthermore, gyroscopic effects influence the exact values of antiresonance frequencies at which the phenomenon appears.

Improved Large Spring / Stiffness Technique for Dynamic Response Analysis of Structures Subjected to Base Excitations

Based on the large spring/stiffness method (LSM), this paper develops an improved technique (I-LSM) applicable to structural dynamic analysis with the assumption of Rayleigh damping. To estimate the accuracy of the technique, the dynamic response is analyzed for a 2-DOFs model respectively subjected to uniform/nonuniform seismic excitations. It indicates that the traditional LSM is inapplicable when Rayleigh damping is adopted. And the errors increase monotonously with the aggrandizement of damping. It’s also validated that the I-LSM based on the modification of displacement considering the influences of Rayleigh damping presented in this paper is able to effectively yield results almost identical to those of theoretical methods with errors beneath 4%.

Improved Large Mass Method for Structural Base Excitation Analysis

To verify the precision and possible applicability of the large mass method (LMM) widely used in multiple-supported structures subjected to non-uniform base excitations, numerical simulations of a two-degrees-of-freedom (2-DOF) finite element model using the Rayleigh damping assumption are performed respectively according to the LMM and the relative motion method (RMM). Through comparisons with the RMM, the error origins and the applicability of the LMM are discussed. Then the improved LMM is presented herein based on the modification of ground motions considering the influences of Rayleigh damping coefficient α. It indicates that the LMM is not applicable to multi-support excitation analysis in the case of Rayleigh damping, which can cause significant errors. And the errors depend on the damping coefficient α. It’s also proved that the improved LMM is able to yield results that are identical to those of the RMM.

Spectral Numerical Study of a Problem Governed by Navier-Stokes Equations, Influence of Rayleigh and Prandtl Numbers

We present in this work a numerical study of a problem governed by Navier-Stokes equations and heat equation. The mathematical problem under consideration is obtained by modelling the natural convection of an incompressible fluid, in laminar flow between two horizontal concentric coaxial cylinders, the temperature of the inner cylinder is supposed to be greater than the outer one. The numerical simulation of the flow is carried out by collocation-Legendre method. The influence of Prandtl and Rayleigh numbers is investigated

Rayleigh and Mie scattering in polymer optical fibers

In this article, the influence of Rayleigh and Mie scattering, which are the main causes of mode mixing in polymer optical fibers (POFs), is investigated. Measurement results obtained from a variety of different POF types ranging from standard POF, high-temperature POF, up to custom-made POF are presented. These measurements are compared to theoretical results obtained from a simplified scattering model. By comparing both results, the contribution of the different scattering sources and mechanisms is characterized independently

A Two-Temperature Model for Solid-Liquid Phase Change in Metal Foams

Transient solid-liquid phase change occurring in a phase-change material (PCM) embedded in a metal foam is investigated. Natural convection in the melt is considered. Volume-averaged mass and momentum equations are employed, with the Brinkman-Forchheimer extension to the Darcy law to model the porous resistance. Owing to the difference in the thermal diffusivities between the metal foam and the PCM, local thermal equilibrium between the two is not assured. Assuming equilibrium melting at the pore scale, separate volume-averaged energy equations are written for the solid metal foam and the PCM and are closed using an interstitial heat transfer coefficient. The enthalpy method is employed to account for phase change. The governing equations are solved implicitly using the finite volume method on a fixed grid. The influence of Rayleigh, Stefan, and interstitial Nusselt numbers on the temporal evolution of the melt front location, wall Nusselt number, temperature differentials between the solid and fluid, and the melting rate is documented and discussed. The merits of incorporating metal foam for improving the effective thermal conductivity of thermal storage systems are discussed.

Influence of Rayleigh scattering on the ion feature of Thomson scattering spectrum from a partially stripped plasma

Studied in this paper is the influence of Rayleigh scattering on the ion feature of the Thomson scattering spectrum from a partially stripped plasma. The result shows that the profile of the scattering spectrum is nearly the same as that of Thomson scattering with inclusion of Rayleigh scattering, but the intensity of the scattering signal may be remarkably different from that of Thomson scattering.

Unsteady Abyssal Circulation Driven by a Discrete Buoyancy Source in a Continuously Stratified Ocean

Abstract Analytical and numerical models are presented for linear quasigeostrophic buoyancy-driven flow forced bya time periodic pulsating point mass source in a continuously stratified, incompressible β-plane ocean withconstant Brunt–Vaisala frequency. The source represents the seasonal introduction of dense water into the abyssalocean and is located on a linear sloping bottom of arbitrary orientation. The ocean domain is horizontallyunbounded and of infinite depth. Rayleigh friction is incorporated into the horizontal momentum equations andappears at order Rossby number in the quasigeostrophic expansions. In the density equation the influence ofRayleigh friction and Laplacian friction are each considered in turn. Analytical solutions are obtained in the case of 1) a midlatitude β plane with no bottom slope and 2) an fplane with a bottom slope. In both of these problems the fluid is initially at rest and the mass source is switchedon and maintained. A three-dimensional radiating field of baroclinic Rossb...