A complete conjugate conduction convection and radiation problem for a heated block in a vertical differentially heated square enclosure

The complete conjugate heat conduction, convection and radiation problem for a heated block in a differentially heated square enclosure is solved by an operator-splitting pseudo-time-stepping finite element method. The main feature of the solution procedure is that the multi-phases are treated as a single computational domain with unknown interfacial boundary conditions. The temperature distribution in the heated block and in the enclosure fluid, together with the convective flow pattern are obtained simultaneously by the solution technique. The heated block has a resistant effect to the heat transfer between the differentially heated walls. When more heat is generated in the block, its emissivity has significant influence on the global flow. With increasing emissivity, the global convective flow decreases and the fraction of thermal radiation can be more than 30% of the total heat transfer. Received: 4 January 1999     

Experimental investigation of heat transfer by natural convection in an enclosure

An experimental study has been made of heat transfer by natural convection from a thin wire in a cylindrical enclosure filled with liquid. The dependence of the convection coefficient on the parameter GrPr has been found with different lengths of measuring interval and for various inclinations of the measuring tube to the horizontal.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 15, No. 6, pp. 1124–1127, December, 1968.     

Effects of wall conduction on natural convection in a porous triangular enclosure

Conjugate natural convection in a two-dimensional triangular enclosure filled with a porous medium is examined in this article. It is assumed that the solid vertical wall is of finite conductivity and that the temperature of the inclined wall is lower than that of the vertical wall, while the horizontal wall is adiabatic. A finite difference method is used to solve the governing equations of convection and conduction for different parameters as Rayleigh number, width of the vertical solid wall, aspect ratio of the enclosure and thermal conductivity ratio between solid and porous media. It is found that heat transfer increases with increasing Rayleigh number and aspect ratio of the triangle, decreasing wall thickness and with the increase of the wall conductivity.     

Development of natural convection in a liquid heated by the front of self-propagating high-temperature synthesis (SHS)

The process of development of free convection in a liquid heated by a moving combustion front is considered. The emphasis is on the dynamics of development of the process.Moscow Power Institute, Kazan' Branch. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 63, No. 4, pp. 400–403, October, 1992.     

Free convection of hybrid Al2O3-Cu water nanofluid in a differentially heated porous cavity

Hybrid nanofluids are a new type of enhanced working fluids, engineered with enhanced thermo-physical properties. The hybrid nanofluids profit from the thermo-physical properties of more than one type of nanoparticles. The present study aims to address the free convective heat transfer of the Al₂O₃-Cu water hybrid nanofluid in a cavity filled with a porous medium. Two types of important porous media, glass ball and aluminum metal foam, are considered for the porous matrix. The experimental data show dramatic enhancement in the thermal conductivity and dynamic viscosity of the synthesized hybrid nanofluids, and hence, these thermophysical properties could not be modeled using available models of nanofluids. Thus, the actual available experimental data for the thermal conductivity and the dynamic viscosity of hybrid nanofluids are directly utilized in the present theoretical study. Various comparison with results published previously in the literature are performed and the results are found to be in excellent agreement. In most cases, the average Nusselt number Nu_l is decreasing function of the volume fraction of nanoparticles. The results show the reduction of heat transfer using nanoparticles in porous media. The observed reduction of the heat transfer rate is much higher for hybrid nanofluid compared to the single nanofluid.     

A holographic interferometry study of natural convection in a fully‐partitioned air‐filled enclosure

Abstract

The technique of real‐time holographic interferometry is used in the present study to study natural convection in a fully‐partitioned air‐filled square enclosure. Transient and steady‐state temperature distributions in separated subenclosures are visualized for a Rayleigh number between 2.5×10⁵ and 8.4×10⁵ with a centrally‐located conducting partitions. Steady‐state experimental results are found to be in reasonably good agreement with the numerical predictions. Moreover, the experimental observations during the transient one‐sided heating processes indicate that the presence of a conducting partition can provide a good buffer against a sudden external disturbance to the enclosure.     

Influence of a magnetic field on natural convection in a shallow porous enclosure saturated with a binary fluid

Summary An analytical and numerical investigation is conducted to study the effect of an electromagnetic field on natural convection in a horizontal shallow porous cavity filled with an electrically conducting binary mixture. A uniform heat flux is applied to the horizontal walls of the layer while the vertical walls are adiabatic. The solutal buoyancy forces are assumed to be induced either by the imposition of constant fluxes of mass on the horizontal boundaries (double diffusive convection) or by temperature gradients (Soret induced convection). Governing parameters of the problem under study are the thermal Rayleigh number, R _T , Hartmann number, Ha, Lewis number, Le, buoyancy ratio, ϕ, aspect ratio, A, and normalized porosity of the porous medium, ɛ. An analytical solution, valid for a shallow layer (A ≫ 1) is derived on the basis of the parallel flow approximation. In the range of the governing parameters considered in this study, a good agreement is found between the analytical predictions and the numerical results obtained by solving the full governing equations.     

Effect of a non-constant magnetic field on natural convection in a horizontal porous layer heated from the bottom

An analytical and numerical investigation is conducted to study the effect of an electromagnetic field on natural convection in a horizontal shallow porous cavity filled with an electrically conducting fluid. The magnetic field is assumed to be induced by two long wires, carrying current, parallel to the horizontal boundaries of the system. A uniform heat flux is applied to the horizontal walls of the layer while the vertical walls are adiabatic. The governing parameters of the problem under study are the thermal Rayleigh number, Ra, Hartmann number, Ha, position of the electrical wires, d, current intensity ratio, r, and aspect ratio of cavity, A. An analytical solution, valid for a shallow layer (A ? 1), is derived on the basis of the parallel flow approximation. The critical Rayleigh number, Ra _c , for the onset of motion is derived in closed form in terms of the parameters of the problem. For finite-amplitude convection the heat and flow characteristics predicted by the analytical model are found to agree well with a numerical study of the full governing equations.     

The effect of thermal boundary conditions on local features of low-intensity natural convection in a square enclosure

Local features are investigated of heat transfer and thermal stratification under conditions of weakened natural convection in a square enclosure. The dependence of local effects on the type of thermal conditions on horizontal boundaries is studied. Conditions of two types are employed, namely, a uniform heat flux (or efflux) and the general condition of heat transfer. Estimates are given of the limits of modes of convection, and the dependences of temperature fields and heat fluxes on criterional numbers are obtained.     

The temperature calculation for a plate and cylinder heated simultaneously by radiation and convection

A solution is derived for the Fourier equation by the method of averaging the functional correction factors in the case of convection-radiation heating. Tables are presented for the practical calculation of plate and cylinder temperatures.Translated from Inzhenerno-Fizicheskii Zhurnal Vol. 16, No. 6, pp. 1082–1086, June, 1969.     

基于提升小波变换的MFCC在目标识别中的应用

水下环境噪声对被动声呐目标的分类识别影响显著,为了提高水声信号识别系统对环境噪声的鲁棒性,采用提升小波变换方法提取MFCC特征,对水下被动声呐目标进行分类和识别。仿真实验表明,与传统MFCC和小波变换的MFCC相比,在信噪比相近的情况下,提升小波变换方法提取MFCC具有识别率较高、对噪声鲁棒性较好的显著优点。     

Finite element analysis of natural convection flows in a square cavity with non-uniformly heated wall(s)

A penalty finite element analysis with bi-quadratic rectangular elements is performed to investigate the influence of uniform and non-uniform heating of wall(s) on natural convection flows in a square cavity. In the present investigation, one vertical wall and the bottom wall are uniformly and non-uniformly heated while the other vertical wall is maintained at constant cold temperature and the top wall is well insulated. Parametric study for a wide range of Rayleigh number (Ra), 10³ ⩽ Ra ⩽ 10⁶ and Prandtl number (Pr), 0.2 ⩽ Pr ⩽ 100 shows consistent performance of the present numerical approach to obtain the solutions as stream functions and temperature profiles. Heat transfer rates at the heated walls are presented in terms of local Nusselt number.     

Damage identification based on ridges and maxima lines of the wavelet transform

The paper analyses the transient vibration behaviour of structures using the continuous wavelet transform (CWT), which provides effective tools for detecting changes in the structure of the material. The advantage of the CWT over commonly used time-frequency methods like the Wigner–Ville and the Gabor transform is its ability to decompose signals simultaneously both in time (or space) and frequency (or scale) with adaptive windows. The essential information is contained in the maxima of the wavelet transform. From the ridges, the modal parameters of the decoupled modes can be extracted and the signal can be reconstructed. From the maxima lines, defects can be localized. This paper presents a new approach for the calculation of wavelet transform ridges and maxima lines, which is based on a direct integration of differential equations. The potential of the method is demonstrated by the analysis of the impact vibration response of different bars.     

BEM–FEM coupling model for the dynamic analysis of piles and pile groups

This paper shows a BEM–FEM coupling model for the time harmonic dynamic analysis of piles and pile groups embedded in an elastic half-space. Piles are modelled using finite elements (FEM) as a beam according to the Bernoulli hypothesis, while the soil is modelled using boundary elements (BEM) as a continuum, semi-infinite, isotropic, homogeneous or zoned homogeneous, linear, viscoelastic medium. It is assumed that the soil continuity is not altered by the presence of the piles, and the tractions at the pile–soil interface are considered as a load applied within the half-space. The formulation is exposed in detail. In order to validate the model, selected numerical results of time harmonic impedances of different pile groups configurations are evaluated and contrasted with other reference values taken from the literature.     

基于小波变换的弱非线性阻尼和刚度辨识方法

利用脊上连续小波变换系数的幅度和相位,从结构系统的自由衰减响应中辨识了弱非线性阻尼和刚度.提出了一种检测小波脊的新方法以消除连续小波变换幅度极值的频移.为了抑制边界效应,提出利用最小二乘拟合误差选择小波函数参数的优化算法.使用数值仿真和实验检验了辨识方法的精度.实验装置是一台高精度转动惯量测试仪.结果表明提出的方法能够准确的辨识结构中的弱非线性阻尼及刚度参数.     

Impact of nonuniform heated plate on double-diffusive natural convection of micropolar fluid in a square cavity with Soret and Dufour effects

A numerical work has been carried out to study the effect of heated plate on double diffusive natural convection in a cavity with the presence of Soret and Dufour effects. The vertical left and right sidewalls of the cavity are maintained at constant cold temperatures while the lower and upper walls are considered insulated. The influence of pertinent parameters such as Rayleigh number, Schmidt number, vortex viscosity parameter, Soret and Dufour coefficients and plate non-uniformity parameter on the flow and heat transfer characteristics has been examined. Numerical results show that the heat and mass transfer rate increases with the rise of the Rayleigh number and Schmidt number. It is found that the heat and mass transfer rate are considerably suppressed by the vortex viscosity parameter. In addition, it is observed that the average Nusselt number increases and Sherwood number decreases with increasing Soret and Dufour effects.     

Effect of a magnetic field on natural convection in an inclined half-annulus enclosure filled with Cu–water nanofluid using CVFEM

In this paper, the effect of a magnetic field on natural convection in a half-annulus enclosure with one wall under constant heat flux using control volume based finite element method. The fluid in the enclosure is a water-based nanofluid containing Cu nanoparticles. The effective thermal conductivity and viscosity of nanofluid are calculated using the Maxwell–Garnetts (MG) and Brinkman models, respectively. Numerical simulations were performed for different governing parameters namely the Hartmann number, Rayleigh number and inclination angle of enclosure. The results indicate that Hartmann number and the inclination angle of the enclosure can be control parameters at different Rayleigh number. In presence of magnetic field velocity field retarded and hence convection and Nusselt number decreases.     

Finite-difference solution of the conjugate heat transfer,natural convection,and solidification problem

A mathematical model of the solidification of a binary melt under convection conditions with a two-phase zone taken into account is formulated on the basis of average transfer equations. Results of a numerical solution are presented.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 47, No. 2, pp. 286–293, August, 1984.