Numerical evaluation of zirconium reinforced aluminium matrix composites for sustainable environment

Due to the momentous advantages of composite materials, recent years many studies focused on reinforcing different new materials to the existing ones to improve their conventional strength and life time within the concern of application status. In the row, reinforcements on Al6061 become a fancy topic among researchers due to its wide applications including automobiles, yachts, electrical fittings and so on. This study continues this innovation by reinforcing three different reinforcement materials including zirconia (ZrO₂), zirconia + aluminium oxide (ZrO₂ +Al₂O₃) and fused zirconia aluminum (40FZA). These three reinforcing materials are included with the proposition of varying particle reinforcements as 5, 10 and 15%. The testing specimens were experimented to explore its mechanical, wear and corrosion behavior. Further the experimental results are given as inputs to the numerical analysis, PROMETHEE. By combining the experimental and numerical methodologies the reliability of the results were improved. However, from this study it can be evident that inclusion of 15% particle reinforcement of zirconia fused alumina in Al6061 provides greater strength, toughness, high resistance to wear and corrosion on both experimental and numerical analysis. There is ample room that this proposed material inclusion be a better option for the reinforcement of Al6061 among available alternatives for sustainable development.

     

Transition waves and nonlinear interactions in the near wake of a circular cylinder

Transition waves and interactions between two kinds of instability—vortex shedding and transition wave in the near wake of a circular cylinder in the Reynolds number range 3 000–10 000 are studied by a domain decomposition hybrid numerical method. Based on high resolution power spectral analyses for velocity new results on the Reynolds-number dependence of the transition wave frequency, i.e.f _t /f_s∼Re^0.87 are obtained. The new predictions are in good agreement with the experimental results of Wei and Smith but different from Braza s prediction and some early experimental resultsf _t/f_s∼Re ^0.5 given by Blooret al. The multi-interactions between two kinds of vortex are clearly visualized numerically. The strong nonlinear interactions between the two independent frequencies (f _t,f _s ) leading to spectra broadening to form the couplingmf _s +nf _t are predicted and analyzed numerically, and the characteristics of the transition are described. Longitudinal variations of the transition wave and its coupling are reported. Detailed mechanism of the flow transition in the near wake before occurrence of the thedimensional evolution is provided. Project supported by the National Natural Science Foundation of China, the LNM of Institute of Mechanics, and partially by the National Basic Research Project.     

Artificial Intelligence in numerical modeling of nano sized ceramic particulates reinforced metal matrix composites

Artificial neural network models have the capacity to eliminate the need for expensive experimental investigation in various areas of manufacturing processes, including the casting methods. An understanding of the inter-relationships between input variables is essential for interpreting the sensitivity data and optimizing the design parameters. Aluminum is the best metal for producing metal matrix composites which are known as one of the most useful and high-tech composites in our world. Combining aluminum and nano Al₂O₃ particles will yield a material with high mechanical and tribological properties. In this investigation, the accuracy of various artificial neural network training algorithms in FEM modeling of Al₂O₃ nano particles reinforced A356 matrix composites has been studied.     

Some sufficient conditions for the E- and MV-optimality of block designs having blocks of unequal size

Summary In this paper we consider experimental situations in which ν treatments are to be tested inb blocks whereb _i blocks containk _i experimental units,i=1,...,p, k ₁<k ₂<...<k _p . The idea of a group divisible (GD) design is extended to that of a group divisible design with unequal block sizes (GDUB design) and then a number of results concerning the E- and MV-optimality of GD designs are generalized to the case of GDUB designs.     

Magnetic properties and microstructure of HDDR isotropic Nd-Dy-Fe-Co-B bonded magnets with high coercivity

The effect of small amount of Co and Dy addition on the magnetic properties of HDDR isotropic Nd-Dy-Fe-Co-B bonded magnets was investigated. The experimental results show that the intrinsic coercivity H_cj and the reversible temperature coefficient of remanence of (Nd_0.65 Dy_0.35)_12.5-(Fe_0.9Co_0.1)₈₁B_6.5 magnet were 1.53 MA·m^-1(19.3 kOe) and -0.059%/°C (25–155°C), respectively. The high coercivity and low temperature coefficient of the magnet are due to the enhanced anisotropy field, increased Curie temperature and improved microstructure by Dy and Co addition.     

CFD of turbulent transport of particles behind a backward-facing step using a new model—k-ε-Sp

The k-ε-S_p model, describing two-dimensional gas–solid two-phase turbulent flow, has been developed. In this model, the diffusion flux and slip velocity of solid particles are introduced to represent the particle motion in two-phase flow. Based on this model, the gas–solid two-phase turbulent flow behind a vertical backward-facing step is simulated numerically and the turbulent transport velocities of solid particles with high density behind the step are predicted. The numerical simulation is validated by comparing the results of the numerical calculation with two other two-phase turbulent flow models (k-ε-A_p, k-ε-k_p) by Laslandes and the experimental measurements. This model, not only has the same virtues of predicting the longitudinal transport of the solid particles as the present practical two-phase flow models, but also can predict the lateral transport of the solid particles correctly.     

Extracting energy from Vortex-Induced Vibrations: A parametric study

Here, Vortex-Induced Vibrations (VIVs) of a circular cylinder are analyzed as a potential source for energy harvesting. To this end, VIV is described by a one-degree-of-freedom model where fluid forces are introduced from experimental data from forced vibration tests. The influence of some influencing parameters, like the mass ratio m^∗ or the mechanical damping ζ in the energy conversion factor is investigated. The analysis reveals that: (i) the maximum efficiency η_M is principally influenced by the mass-damping parameter m^∗ζ and there is an optimum value of m^∗ζ where η_M presents a maximum; (ii) the range of reduced velocities with significant efficiency is mainly governed by m^∗, and (iii) it seems that encouraging high efficiency values can be achieved for high Reynolds numbers.     

A 3-D coupled Smoothed Particle Hydrodynamics and Coarse-Grained model to simulate drying mechanisms of small cell aggregates

Recently, meshfree-based computational modelling approaches have become popular in modelling biological phenomena due to their superior ability to simulate large deformations, multiphase phenomena and complex physics compared to the conventional grid-based methods. In this article, small plant cell aggregates were simulated using a three dimensional (3-D) Smoothed Particle Hydrodynamics (SPH) and Coarse-Grained (CG) coupled computational approach to predict the morphological behaviour during drying. The model predictions of these cell aggregate models have been compared qualitatively and quantitatively through comparisons with experimental findings. The results show that the shrinkage and wrinkling behaviour of cell cluster models are in fairly good agreement with real cellular structures. The agreement between the cell aggregate model predictions and the experimental findings are closer in the high and medium moisture content values (X/X₀ ≥ 0.3), than highly dried stages (X/X₀ < 0.3). Further, optimisation and sensitivity studies have been conducted on model parameters such as particle resolution, smoothing length, mass transfer characteristics and wall forces. Overall, the 3-D nature of this model allows it to predict real 3-D morphological changes more realistically compared to the previous meshfree based 2-D cellular drying models. The proposed 3-D modelling approach has a higher potential to be used to model larger plant tissues with complicated physical and mechanical interactions as well as their multiscale interactions.     

CONSTRUCTION OF CONCEPTUAL KNOWLEDGE: THE CASE OF COMPUTER-AIDED EXPLORATION OF PERIOD DOUBLING

This research focuses on students using an experimental approach with computer software to give visual meaning to symbolic ideas and to provide a basis for further generalisation. They use computer software that draws orbits of x=f(x) iteration and are encouraged to investigate the iterations of f_λ(x)=λx(1-x) as λ increases. The iterations pass through successive acts of period-doubling as λ=λ₀, λ₁, λ₂, …,. students are invited to estimate the values of λ and to compare their experimental results with the theory of geometric convergence. The supervisor acts as a mentor, using various styles of questioning to provoke links between different ideas. A variety of data is collected to give evidence for the ways in which students develop conceptual links between symbolic theory and the visual and numeric aspects of computer experiment.     

Acoustic estimation of suspended sediment concentration

In this paper, the acoustic estimation of suspended sediment concentration is discussed and two estimation methods of suspended sediment concentration are presented. The first method is curve fitting method, in which, according to the acoustic backscattering theory we assume that the fitting factor K₁ (r) between the concentration M(r) obtained by acoustic observation and the concentration M₀ ( r) obtained by sampling water is a high order power function of distancer. Using least-square algorithm, we can determine the coefficients of the high order power function by minimizing the difference betweenM( r) and M₀ ( r) in the whole water profile. To the absorption coefficient of sound due to the suspension in water we do not give constraint in the first method. The second method is recursive fitting method, in which we take M₀ ( r) as the conditions of initialization and decision and give rational constraints to some parameters. The recursive process is stable. We analyzed the two methods with a lot of experimental data. The analytical results show that the estimate error of the first method is less than that of the second method and the latter can not only estimate the concentration of suspended sediment but also give the absorption coefficient of sound. Good results have been obtained with the two methods.     

Synthesis and characterization of C3N4 crystal (II)

Single C₃N₄ crystals with 1–3 μ in length and 300 nm in cross area was obtained on nickel substrate. The results rule out the uncertainty of the experimental lattice parameters caused by C-Si-N phase when the growth was on silicon. The X-ray diffraction and transmission electron microscopy with selective-area electron diffraction give the lattice constantsa = 0.624 nm andc = 0.236 nm for β-C₃N₄, and α=0. 638 nm andc = 0.464 8 nm for α-C₃N₄, which are respectively 2.5% and 1.3% lower than those of the latest first-principle calculations. An N:C ratio of 1.30–1.40 was determined by energy dispersive X-ray. Based on the experimental lattice constants, the bulk modulus of the obtained β-C₃N₄ are in the region of 425–445 GPa.     

First-principles calculations on electronic, chemical bonding and optical properties of tetragonal SrHfO3

Electronic, chemical bonding and optical properties of tetragonal SrHfO₃ were investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The optimized equilibrium lattice parameters of tetragonal SrHfO₃ are in good agreement with experimental values. Band structure, densities of states (DOS), charge densities and molecular-orbital bonding structure of tetragonal SrHfO₃ have been obtained. The band structure shows that tetragonal SrHfO₃ has direct band gap. The DOS and charge densities indicate that bonding between Hf and O is mainly covalent due to Hf 5d and O 2p hybridization and that bonding between Sr and O is mainly ionic. The complex dielectric function, absorption coefficient, energy-loss spectrum, complex conductivity function and reflectivity of tetragonal SrHfO₃ have been predicted. The imaginary and real parts of the calculated complex dielectric functions are consistent with the experimental observations.     

Field theoretical effects in X-ray spectra

The L_I-L_II screening doublet separation in the relativistic approximation up to Z²⁰ has been compared with that obtained experimentally by the transitions M_IVL_II (Lβ ₁) and M_IVL_I (Lβ ₁₀). The experimental and theoretical values deviate considerably. If one retains terms up to Z⁴, an apparently close fit with the experimental values is obtained. It is shown that such a fit disappears on applying the field theoretical corrections and this stresses the need of retaining the terms up to Z²⁰. The justification of neglecting the still higher powers of Z lies in the smallness of their magnitude when compared to the experimental errors. The field theoretical corrections modify the relativistic curve that contains terms up to Z²⁰ in such a way that one again gets a good fit with the experimental values. This shows how the various field theoretical corrections and the contributions from relativistic terms with powers of Z greater than four compensate each other.     

Multifractality in relativistic charged particles produced at SPS energies

The multifractal analysis of relativistic shower particles produced in ³²S–emulsion interactions at 200 AGeV has been investigated using the method of modified multifractal moments, G_q, in pseudo-rapidity space. The anomalous fractal dimension, d_q, and generalized fractal dimensions, D_q, are determined for the present data for different order of moment. The experimental data reflects multifractal geometry in a multipion production process. The downward concave shape of the multifractal spectral function, f(α_q), gives an evidence for self-similar cascade mechanism. The multifractal specific heat has also been evaluated for the present data using the generalized fractal dimensions, D_q. We compared our experimental results with those obtained from simulated events of the Lund Monte Carlo Code FRITIOF and uncorrelated Monte Carlo events, (MC-RAND) generated randomly in pseudorapidity space based on the assumption of independent emission of particles. The experimental data on multifractality has been found to exhibit a remarkable proximity to the analogous data obtained from the FRITIOF code and the uncorrelated Monte Carlo events.     

Estimation of large domain Al foam permeability by Finite Difference methods

Classical methods to calculate permeability of porous media have been proposed mainly for high density (e.g. granular) materials. These methods present shortcomings in high porosity, i.e. high permeability media (e.g. metallic foams). While for dense materials permeability seems to be a function of bulk properties and occupancy averaged over the volume, for highly porous materials these parameters fail to predict it. Several authors have attacked the problem by solving the Navier-Stokes equations for the pressure and velocity of a liquid flowing through a small domain (Ω_s) of aluminium foam and by comparing the numerical results with experimental values (prediction error approx. 9%). In this article, we present calculations for much larger domains (Ω_L) using the Finite Difference (FD) method, solving also for the pressure and velocity of a viscous liquid flowing through the Packed Spheres scenario. The ratio Vol(Ω_L)/Vol(Ω_s) is around 10³. The comparison of our results with the Packed Spheres example yields a prediction error of 5% for the intrinsic permeability. Additionally, numerical permeability calculations have been performed for Al foam samples. Our geometric modelling of the porous domain stems from 3D X-ray tomography, yielding voxel information, which is particularly appropriate for FD. Ongoing work concerns the reduction in computing times of the FD method, consideration of other materials and fluids, and comparison with experimental data. (© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The inverse problem of estimating the film structure from X-ray reflection data

A new model of an X-ray reflection experiment is proposed for studying the structure of a film on a substrate. The experimental data are processed to yield the density distribution across the film, and an appropriate approximation produces numerical values of the parameters { δ_i, β_i, σ_i, d ₁} for each of the n layers in a multilayer film model. So far there has been no method for determining the film structure from experimental data and the problem has been usually solved by trial and error. __________ Translated from Prikladnaya Matematika i Informatika, No. 21, pp. 19–29, 2005.     

Cyclic and simultaneous iterative methods to matrix equations of the form A i X B i = F i

This paper deals with a general type of linear matrix equation problem. It presents new iterative algorithms to solve the matrix equations of the form A _i X?B _i = F _i . These algorithms are based on the incremental subgradient and the parallel subgradient methods. The convergence region of these algorithms are larger than other existing iterative algorithms. Finally, some experimental results are presented to show the efficiency of the proposed algorithms.     

Numerical solution of transonic and subsonic flow of compressible inviscid and viscous fluid

The work presents two numerical solutions of compressible flows problems with high and very low Mach numbers. Both problems are numerically solved by finite volume method and the explicit MacCormack scheme using a grid of quadrilateral cells. Moved grid of quadrilateral cells is considered in the form of conservation laws using Arbitrary Lagrangian–Eulerian method. In the first case, inviscid transonic flow through cascade DCA 8% is presented and the numerical results are compared to experimental data. The second case, numerical solution of unsteady viscous flow in the channel for upstream Mach number M_∞=0.012 and frequency of the wall motions 100 Hz is presented. The unsteady case can represent a simplified model of airflow coming from the trachea, through the glottal region with periodically vibrating vocal folds to the human vocal tract. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Regression and ANN models for estimating minimum value of machining performance

Surface roughness is one of the most common performance measurements in machining process and an effective parameter in representing the quality of machined surface. The minimization of the machining performance measurement such as surface roughness (R_a) must be formulated in the standard mathematical model. To predict the minimum R_a value, the process of modeling is taken in this study. The developed model deals with real experimental data of the R_a in the end milling machining process. Two modeling approaches, regression and Artificial Neural Network (ANN), are applied to predict the minimum R_a value. The results show that regression and ANN models have reduced the minimum R_a value of real experimental data by about 1.57% and 1.05%, respectively.