Boundary Effects in Flow in Annular Porous Media

An analytical method for flow calculations in an annular porous media bounded by a solid outer wall and subject to a countercurrent flow in its inner boundary is presented. The analysis is rigorous and makes it possible to evaluate the effect of the boundaries in the transport capacity of porous channels. The mathematical model is applicable to wicks, such as those found in heat pipes. The paper explores the conditions, that is. the value of critical parameters, under which boundary effects are not negligible and should be taken into account in wick design.     

A sub-grid air entrainment model for breaking bow waves and naval surface ships

Direct numerical simulations (DNS) of air entrainment by the breaking bow waves of naval surface ships are outside of the computational reach of the most powerful computers in the foreseeable future. This creates a need for physically-based models of air entrainment for applications in numerical simulations for ship design. Due to the non-linear dependence of the terminal bubble velocity with diameter most air entrainment flows have a high void fraction region immediately below the free surface. We present a model that locates this region employing the local liquid velocity and the distance to the interface. Using this model and the bubble size distributions measured by Deane and Stokes [Deane BD, Stokes MD. Scale dependence of bubble creation mechanisms in breaking waves. Nature 2002;418:839-44] we have simulated the air entrainment in the breaking wave experiments of Wanieski et al. [Waniewski TA, Brennen CE, Raichlen F. Measurement of air entrainment by bow waves. J Fluids Eng 2001;123:57-63]. Comparison against these experimental data is good. We then apply this model to simulate the flow around naval combatant DTMB 5415 and the research vessel Athena. The model predicts air entrainment in regions where it was actually observed at sea, namely the breaking bow wave, along the water/air/hull contact line and in the near-wake. To the best of our knowledge this is the first model of air entrainment that compares favorably with data at laboratory scale and also presents the right trends at full-scale.     

The electrical conductivity of inhomogeneous thin metallic films

This paper reports the following results: (i) an explicit for the electrical conductivity of a thin metal film where the electron mean free path is not constant through its thickness, and (ii) calculations showing how in this case an illusory fit to the Fuchs-Sondheimer result can be obtained with a dependence of the specularity parameter on thickness or angle. A survey of experimental results is also presented.     

Fatigue and damage accumulation in open cell aluminium foams

Open‐cell aluminium foams are a relatively new material with interesting uses in different engineering applications. This study investigates the fatigue behaviour and damage accumulation of metal foams via a fatigue analysis (Weibull E‐N model), a failure criterion (the relation among the prepeak compressive and tensile slopes, the reduction in the tensile stress, or the reduction in the compressive stress), and a mathematical approach (linear, quadratic, or exponential). As a result of combining the 3 mathematical approaches and 3 failure criteria, different approaches are obtained, analysed, and validated by using experimental data. Finally, the proposed approaches can be used to directly obtain the damage accumulation level for open‐cell metal foams under fully reversed cyclic loading as a function of the number of cycles applied, the total strain amplitude, and the initial damage accumulation condition.     

Numerical conjugate air mixed convection/non-Newtonian liquid solidification for various cavity configurations and rheological models

Unsteady 2D natural convection/phase change of a non-Newtonian liquid inside a square container caused by external mixed convection of a Newtonian fluid with various cavity configurations has been studied numerically. Air was chosen as external cooling fluid and modified non-Newtonian water as the internal solidifying fluid. Conjugate convective fluid and heat transport, described in terms of non-linear coupled continuity, momentum, and energy equations, were solved by using the finite volume method with the SIMPLE algorithm. Effects of four external fluid inlet/outlet locations and four non-Newtonian rheological models were studied. Results for the time evolution of streamlines, isotherms and freezing curves are analyzed. The effect of the cavity inlet/outlet configuration on streamlines of the external fluid is remarkable, near the region close to the non-Newtonian liquid filled container.     

Unsteady conjugate mixed convection phase change of a power law non-Newtonian fluid in a square cavity

Transient phase change of a power law non-Newtonian fluid inside an inner thin walled container caused by external mixed convection in a square cavity has been analyzed numerically. Air was chosen as external cooling fluid and modified non-Newtonian water as the phase change fluid. Fluid mechanics and conjugate convective heat transfer, described in terms of continuity, linear momentum and energy equations, were predicted by using the finite volume method. Solidification was treated in terms of a phase change function varying linearly with temperature. The effect of the external Reynolds number, for Re = 200 and 1000 on solidification was studied along the influence of the non-Newtonian power law index (n = 0.5, n = 1.0). Results for the time evolution of streamlines, isotherms and freezing curves are analyzed. The effect of the Reynolds number on streamlines of the external fluid is remarkable, principally near the region close to the internal water filled container. Differences between cooling and freezing times are found for Newtonian (n = 1.0) and non-Newtonian modified (n = 0.5) water.     

Experimental and theoretical study of thermodynamics and transport properties of multilayer polymeric food packaging

The specific migration of Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate (I-1076) from three-layer low-density polyethylene plastic films into a fatty food simulant was studied. The film samples, having a symmetrical structure with a contaminated core layer and virgin outer layers, were developed with a known amount of a selected migrant in the inner layer. A phenomenological model based on a resistances-in-series was resolved through the regula falsi algorithm according to a routine that considers the income of the structural parameters of the system and experimental conditions in which migration testing was performed. The model’s accuracy in predicting migration was demonstrated successfully by comparing simulated results to experimental data. The computer program, developed as a total solution package for migration problems, can be applied not only to multilayer structures made with the same type of plastics but also to structures with different plastics.     

Unsteady fluid mechanics and heat transfer study in a double-tube air–combustor heat exchanger with porous medium

Fluid mechanics and heat transfer are studied in a double-tube heat exchanger that uses the combustion gases from natural gas in a porous medium located in a cylindrical tube to warm up air that flows through a cylindrical annular space. The mathematical model is constructed based on the equations of continuity, linear momentum, energy and chemical species. Unsteady fluid mechanics and heat transfer by forced gas convection in the porous media, with combustion in the inner tube, coupled to the forced convection of air in the annular cylindrical space are predicted by use of finite volumes method. Numerical simulations are made for four values of the annular air flow Reynolds number in the range 100 ? Re ? 2000, keeping constant the excess air ψ = 4.88, the porosity ε = 0.4, and the air–fuel mixture inlet speed Uo = 0.43 m/s. The results obtained allow the characterization of the velocity and temperature distributions in the inner tube and in the annular space, and at the same time to describe the displacement of the moving combustion zone and the annular porous media heat exchanger thermal efficiency. It is concluded that the temperature increase is directly related to the outer Reynolds number.     

From Fourier Expansions to Arithmetic-Haar Expressions on Quaternion Groups

Arithmetic expressions for switching functions are introduced through the replacement of Boolean operations with arithmetic equivalents. In this setting, they can be regarded as the integer counterpart of Reed-Muller expressions for switching functions. However, arithmetic expressions can be interpreted as series expansions in the space of complex valued functions on finite dyadic groups in terms of a particular set of basic functions. In this case, arithmetic expressions can be derived from the Walsh series expansions, which are the Fourier expansions on finite dyadic groups. In this paper, we extend the arithmetic expressions to non-Abelian groups by the example of quaternion groups. Similar to the case of finite dyadic groups, the arithmetic expressions on quaternion groups are derived from the Fourier expansions. Attempts are done to get the related transform matrices with a structure similar to that of the Haar transform matrices, which ensures efficiency of computation of arithmetic coefficients. Received: October 5, 1999; revised version: June 14, 2000     

LocalBoost: A Parallelizable Approach to Boosting Classifiers

Neural Processing Letters - We are introducing a new type of membrane, called neuro-skin or neuro-membrane. It is comprised of neurons embedded in a plastic membrane. The skin is smart and adaptive...