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MHD Natural Convection in a Nanofluid-filled Enclosure with Non-uniform Heating on Both Side Walls
Get PDFThis study examines natural convection in a square enclosure filled with a water-Al2O3 nanofluid and subjected to a magnetic field. The side walls of the cavity have spatially varying sinusoidal temperature distributions. The horizontal walls are adiabatic. A Lattice Boltzmann method (LBM) is applied to solve the governing equations for fluid velocity and temperature. The following parameters and related ranges are considered: Rayleigh number of the base fluid, from Ra=103 to 106, Hartmann number from Ha=0 to 90, phase deviation (γ =0, π/4, π/2, 3π/4 and π) and solid volume fraction of the nanoparticles between ø = 0 and 6%. The results show that the heat transfer rate increases with an increase in the Rayleigh number but it decreases with an increase in the Hartmann number. For γ =π/2 and Ra=105 the magnetic field strengthens the effect produced by the presence of nanoparticles. For Ha=0, the most evident influence of nanoparticles is achieved at γ = 0 and π/4 for Ra=104 and 105 respectively
Electronic Structure and Magnetic Properties of New Rare-earth Half-metallic Materials AcFe<sub>2</sub>O<sub>4</sub> and ThFe<sub>2</sub>O<sub>4</sub>: Ab Initio Investigation
No full textElectronic structure and magnetism of the rare-earth metals Ac and Th doped Fe3O4 Fe1-xRexFe2-yReyO4(Re=Ac, Th; x=0, 0.5, 1; y=0, 0.5, 1.0, 1.5, 2.0) are investigated by first-principle calculations. AcFe2O4, FeAc2O4 and ThFe2O4 are found to be II B-type half-metals. The large bonding-antibonding splitting is believed to be the origin of the gap for AcFe2O4, FeAc2O4 and ThFe2O4, resulting in a net magnetic moment of 9.0μB, 4.0μB and 8.1μB, respectively, compared with 4.0μB of Fe3O4. Also, the conductance of AcFe2O4 and ThFe2O4 are both slightly larger than that of Fe3O4. It can be predicted that the new rare-earth half-metals AcFe2O4 and ThFe2O4 have wider application ground in spin electronic devices due to their larger magnetoresistance and higher conductivity than that of Fe3O4. The half-metallic feature can be maintained up to the lattice contraction of 8%, 3% and 4% for Fe3O4, AcFe2O4 and ThFe2O4, respectively
Polarization Independent Dual-band Metamaterial Based Radar Absorbing Structure (RAS) for MillimeterWave Applications
Get PDFThe EM analysis of multi-layered metamaterial based radar absorbing structure (RAS) with dual-band characteristics in millimeter wave frequency regime has been carried out in this paper using transmission line transfer matrix (TLTM) method for TE and TM polarizations. The proposed metamaterial-based RAS exhibits dual-band characteristics at centre frequencies 120 GHz and 175 GHz with very low power reflection. It absorbs more than 90% power of incidence wave over the frequency range from 111-131 GHz at first resonance and from 164.5-185 GHz at second resonance without metal backing plate, which is desirable for stealth applications. It also showed very low (< 1.6%) transmission over the frequency of interest for both TE and TM polarizations. The proposed metamaterial-RAS has potential applications in the design of multi-band sensor systems and RCS reduction in millimeter wave frequency regime
Optimal Analysis for Shakedown of Functionally Graded (FG) Bree Plate with Genetic Algorithm
Get PDFThe Shakedown of a functionally graded (FG) Bree plate subjected to coupled constant mechanical loading and cyclically varying temperature is analyzed with more accurate approaches and optimized with the genetic algorithm method. The shakedown theorem takes into account material hardening. The variation of the material properties in the thickness of a FG Bree plate is characterized with a piecewise exponential distribution, which can replicate the actual distribution with sufficient accuracy. In order to obtain the best distribution of the mechanical properties in the FG plate, the distribution of the reinforcement particle volume fraction is optimized with the genetic algorithm (GA). Two numerical examples are presented, which demonstrate the validity of the developed method in the analysis of the shakedown of the FG Bree plate
Wrinkling Analysis in a Film Bonded to a Compressible Compliant Substrate in Large Deformation
Get PDFThe buckling of a thin film on a compressible compliant substrate in large deformation is studied. A finite-deformation theory is developed to model the film and the substrate under different original strain-free configurations. The neo-Hookean constitutive relation is applied to describe the substrate. Through the perturbation analysis, the analytical solution for this highly nonlinear system is obtained. The buckling wave number, amplitude and critical condition are obtained. Comparing with the traditional linear model, the buckling amplitude decreases. The wave number increases and relates to the prestrain. With the increment of Poisson’s ratio of the substrate, the buckling wave number increases, but the amplitude decreases. The displacements near the interface are different in two models
Experimental Evaluation of Fiber Orientation Based Material Properties of Skeletal Muscle in Tension
Get PDFBiomechanical researches are essential to develop new techniques to improve the clinical relevance. Skeletal muscle generates the force which results in the motion of human body, so it is essential to study the mechanical and structural properties of skeletal muscle. Many researchers have carried out mechanical study of skeletal muscle with in-vivo testing. This work aims to examine anisotropic mechanical behavior of skeletal muscle with in vitro test (tensile test). It is important to understand the mechanical and structural behavior of skeletal muscle when it is subjected to external loading; the research aims to determine the structural properties of skeletal muscle by tensile testing. Tensile testing is performed on 5 samples of skeletal muscle of a goat at the rate of 1mm/min with fiber orientation along the length and 45° inclined to the length. It is found that muscle is stiffer in the direction parallel to the muscle fiber than at 45° to the muscle fibers. The tensile strength of the skeletal muscle along the fiber direction is 0.44 MPa at maximum load of 110 N and for direction 45° inclined to the muscle fibers, the strength is 0.234 MPa at max load 43 N. The displacement of Muscle sample against the maximum load is small along the length of the muscle fiber i.e. under longitudinal elongation [15.257 mm] as compared to 45° inclined to the length of skeletal muscle [17.775 mm] and under cross fiber elongation [19.7291mm by FEA]. The testing is not performed for 90° fiber orientation due to unavailability of soft tissue in cross fiber direction of the required specification, but finite element analysis is done on the skeletal muscle for the cross fiber orientation. As the fiber orientation within skeletal muscle differs with respect to the length of the muscle, the stiffness of skeletal muscle is also changing effectively. Hence skeletal muscle exhibits the anisotropic mechanical behavior
Simulation of Thermal Fluid-structure Interaction Phenomena in a Liquid Sodium Porous System
Get PDFSingle-unit and multi-unit models of porous media (metal felts) have been used to investigate thermal fluid-structure interaction phenomena in a liquid sodium system. Micro-scale aspects have been studied via numerical simulations. The permeability of metal felts has been measured experimentally to verify the reliability of the models used. This integrated approach has allowed a proper evaluation of the interdependencies among phenomena on different scales (including relevant information on skeleton deformation and pressure drop as a function of different parameters). Pressure drop generally increases with velocity and heat flux for both laminar and turbulent flows. The final deformation is greater when turbulence is considered. When the flow is laminar and its rate changes linearly with time, the deformation amount also varies linearly
Numerical Study of Melting Coupled Natural Convection Around Localized Heat Sources
Get PDFA study is reported of heat transfer and melting in a fan-less thermal management system consisting of an insulated horizontal cavity filled with a phase change material (PCM) and heated from below by a conducting plate supporting three identical protruding heat sources. Such a PCM enclosure can be used as a heat sink for the cooling of electronic components. The advantage of this cooling strategy is that PCMs characterized by high energy storage density and small transition temperature interval, are able to store a high amount of heat (thereby providing efficient passive cooling). A two-dimensional simulation model is developed that accounts for heat transfer by conduction, convection in the molten region and phase change. In particular, numerical investigations are conducted using an enthalpy-porosity method in order to examine the impact of the considered geometry on the temperature distribution and evolution in the enclosure. A wide range of values of the enclosure aspect ratio is considered
Effect of Porosity and Magnetic Field Dependent Viscosity on Revolving Ferrofluid Flow in the Presence of Stationary Disk
Get PDFThe purpose of this paper is to study the flow characteristics of a ferrofluid revolving through a porous medium with a magnetic-field-dependent viscosity in the presence of a stationary disk. A Finite Difference Method is employed to discretize the set of nonlinear coupled differential equations involved in the problem. The discretized nonlinear equations, in turn, are solved by a Newton method (using MATLAB) taking the initial guess with the help of a PDE Solver. Results displayed in graphical form are used to assess the effect of the variable viscosity and porosity parameters on the velocity components. The displacement thickness of the boundary layer is also calculated for different values of these parameters by the Simpson’s three-eight’s rule of numerical integration. Further, the skin friction coefficients in the tangential and radial direction are determined
Rayleigh-Taylor Instability of a Two-fluid Layer Subjected to Rotation and a Periodic Tangential Magnetic Field
Get PDFThe Rayleigh-Taylor instability (RTI) of two superposed ferrofluids subjected to rotation and a periodic tangential magnetic field is considered. Relevant solutions and related dispersion relations are obtained by using the method of multiple scales