International Journal of Engineering
Volume:26 Issue: 7, Jul 2013

More than 90% of Malaysian roads are constructed using asphaltic concrete. However, previous investigations of asphaltic concrete have mainly concentrated on the macroscopic properties of the composite materials based on the assumption that the mixtures are homogeneous and isotropic. This paper applies a digital image processing technique to compare the orientations of coarse aggregate particles in asphaltic concrete compacted using Marshall, Servopac and Presbox compactors. Aggregate orientation was measured in terms of a vector magnitude and the average major axis angle. The average major axis angle of all compactors are less than 45° indicating that aggregate orientation in all of the prepared specimens have the preferential orientation along the horizontal plane. The vector magnitude results of the Presbox compacted sample is the least, indicating the presence of the most randomly oriented aggregate. However, the Servopac specimens have more randomly oriented aggregate compared to Marshall specimens. An ANOVA analysis for vector magnitude indicates that only compaction method, not Geometrically Cubical Shaped (GCS) proportion, has a significant impact on aggregate orientation randomness.

Progressive collapse is a situation where local failure of a primary structural component leads to the collapse of adjoining members which, in turn, leads to additional collapse. Hence, the total damage is disproportionate to the original cause. The most common local failure in framed structure is assumed tobe column failure. In this paper, a new approach for dynamic column removal in framed structures wasproposed. Using this approach, the structural response of a 5-story steel frame building under the sudden loss of columns for different scenarios of column removal was numerically assessed. Both material and geometric nonlinearities were taken into account in the analysis. The modeling techniques were described in details. Special emphasis was focused on the evolution of vertical displacements of column removal point. According to the results progressive collapse potential are strongly dependent on location of column loss. It could be concluded that the proposed approach offers the advantages of computational simplicity and practicality for dynamic column removal of framed structures.

In this paper, based on maximizing the outrigger-belt truss system’s strain energy, a methodology for determining the optimum location of an outrigger-belt truss system is presented. Tall building structures with combined systems of framed tube, shear core and outrigger-belt truss system are modeled using continuum approach. In this approach, the framed tube system is modeled as a cantilevered beam with box cross section. The effect of outrigger-belt truss and shear core system on framed tube’s response under lateral loading is modeled by a rotational spring at the outrigger-belt truss location. Optimum location of this spring is obtained when energy absorbed by the spring is maximized. For this purpose, first derivative of the energy equation with respect to spring location as measured from base of the structure, is set to zero. Optimum location for outrigger-belt truss system is calculated for three types of lateral loadings, i.e. uniformly and triangularly distributed loads along structure’s height, and concentrated load at top of the structure. Accuracy of the proposed method is verified through numerical examples. The results show that the proposed method is reasonably accurate.

Control of microstructure features that affect the Al-Ti-C master alloys grain refining efficiency is leading to improve the aluminum grain refinement. This study has been done to find the solute effect theory to produce new Al-Ti-C master alloys to get more possibility to control these features. The produced master alloys were examined by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD); also, the influence of them on pure aluminum was studied. Produced Al-6Ti-1C master alloy contained Ti and TiC particles in the aluminum matrix andAl-4Ti-1C contained TiC particles in the aluminum matrix. As the result, the produced Al-6Ti-1C master alloy is a more efficient grain refiner for pure aluminum as compared to the Al-4Ti-1C. This confirms the influence of Ti particles for grain refinement. The results showed that Al-6Ti-1C master alloy had maximum grain refining performance with 2 minutes holding time, at 983 oK temperature, and 1% wt master alloy addition. Finally, a new Al-Ti-C master alloy with excellent refinement has been prepared successfully.

The aim of the present research is to convert bioinert surface of NiTi to bioactive and biocompatible surface. In order to develop a bioactive and corrosion resistant film on NiTi, electrophoretic deposition process was done and TiO2 particles were deposited on the NiTi surface. Suspensions including TiO2 particles were prepared using a mixture of acetone and n-butanol (0%, 30%, 60%, 80% and 100% acetone) without using any dispersant. Sedimentation test was used to characterize the suspensions. SEM investigations on surface morphology of coatings shows deposition within 0% acetone cause to crack free and dense coating with relatively coarse grains and high corrosion resistance.

This study focused on the effect of electroslag remelting process (ESR) on microstructure and composition of as-cast Cu-Cr-Zr alloy. The results revealed that applying ESR process resulted in a more uniform distribution of alloying elements. However, slight aggregation of large precipitates and inclusions existed in as-cast ingot. It was observed that impurities like P, S and Mg which had significant effect on electrical property were eliminated after ESR process. Moreover, further optimization of alloy composition which in turn would affect its mechanical and electrical properties was obtained through using ESR technique, successfully.

Image analysis is used to study the effect of sintering atmosphere and sintering time on the pores morphology of Astaloy CrM. The pores morphology was described by means of some parameters, Circular Diameter (DC)- which shows the diameter of equivalent circle for comparing the pore size, FElongation and FShape- which have different geometrical meanings. The results were interpreted with reference to an elliptical geometry which represents the theoretical shape to which pores tend. Effect of different sintering atmospheres (N2, Cracked Ammonia (NH3), Ar, Vacuum and air) at 1200ºC was investigated. The results showed 20% decrease of maximum DC in vacuum and cracked ammonia in comparison with other atmospheres. The pore size measurement by image analyses confirmed the variation of density measured by Archimedes method. Dc was affected by atmosphere more than Fshape and FElongation. Furthermore, Fshape was more sensitive than Felongation to different sintering atmospheres. Mechanical properties of specimens have a significant relation with percentage of pores (porosity) and morphology. Vacuum atmosphere led to more spherical and finer pores. Sintering atmosphere has significant effect on pores size and pore distribution in comparison with other morphological parameters in Astaloy CrM. Differences in FShape and FElongation factors are more observable in large pores (over 75μm2 area) in comparison with smaller ones. Fshape seems to be more suitable than Felongation for evaluating the effect of sintering variables on the evolution of pores morphology.

In this paper, we develop a mathematical model to examine the transmission dynamics of curable malaria, curable mTB and non-curable HIV/AIDS and their co-infection. The size of population has been taken as varying due to the emigration of susceptible population. The total population is divided into five subclasses as susceptible, malaria infected, mTB infected, HIV infection and AIDS by assuming co-infection among them. The model has two basic parts, qualitative and numerical. In qualitative part, we analyze the transmission dynamics of this co-infection by using equilibrium and stability analysis. In numerical part, the computational simulation is used to transmission flow of disease among various classes. The sensitive analysis is also performed.

In this paper we study the steady state availability of main k-out-of-n: F and secondary subsystems. When more than k units of main subsystem fail, then the main subsystem shuts off the secondary subsystem. The life time distributions of the main units and that of secondary subsystem are exponentially distributed. A repair facility having single repairman is facilitated to restore the failed unit. The repair time is assumed to be i.i.d. general distributed. The failure of the main unit shuts off the operation of secondary subsystem, but not the other way around. The steady state availability is obtained by solving the linear ordinary differential equations governing the model by using supplementary variable technique. Four special cases of the repair distribution namely exponential, Gamma, Weibull and Pareto have been examined numerically for the illustration purposes

The effect of magnetic field on an incompressible (Kuvshiniski-type) viscoelastic rotating fluid heated from below in porous medium is considered. For the case of stationary convection, magnetic field and medium permeability have both stabilizing and destabilizing effect on the thermal convection under some conditions whereas rotation has a stabilizing effect on the thermal convection. In the absence of rotation, medium permeability has a destabilizing effect while magnetic field has a stabilizing effect on the thermal convection in a Kuvshiniski viscoelastic rotating fluid. It is also found that presence of magnetic field and rotation introduce oscillatory modes in the system, whereas in their absence principle of exchange of stabilities is satisfied in the system. Graphs also have been plotted by giving some numerical values to the parameters.

In the present work, the air-injection as an active flow stabilizing techniques were numerically examined during the aerodynamic behavior and the characteristics of an axial compressor. First, in design condition, the characteristic curve was numerically captured for a specified test compressor. The computed results showed good agreements with those obtained from the experiments. They validate the finite-volume solver which was developed based on Van Leer’s flux splitting algorithm in conjunction with TVD limiters and the κ-e turbulence model. At the second step, to examine the performance of the air injection technique unstable condition, the operating points were set for the unstable condition upon the operating map, and the expected unstable flow patterns were captured. At the final step, the numerical simulation was completed with the air injection, and surprisingly, the unstable flow patterns became highly re-stabilized. Consequently, a significant recovery of the performance was augmented. The study could successfully demonstrate the capability of the numerical studies for simulating the active flow controls specifically the inlet air-injection technique using a 2-D finite volume approach.

Changes in rib-height to channel-height ratio (e/H) has a significant effect on the heat transfer and pressure drop characteristics inside corrugated channels. In current paper, the variation of (e/H) was investigated numerically as well as a deep concern for finding the adequate turbulent model. In this regards, the governing equations were solved by a finite volume approach in a wide range of rib height to channel-height ratio (0.06 < e/H < 0.26) and the Reynolds numbers (5400 < Re < 23000). The predicted results reveal that the RNG k - ε turbulence model provides better agreement with available experimental data than other turbulence models. The computed results not only confirm the noticeable effects of (e/H) on the heat transfer performance and pressure drop but also, demonstrate the optimum corrugation design limits

In this paper interparticle potential model of the lattice Boltzmann method (LBM) is used to simulate the deformation and breakup of a falling droplet under the gravity force. First, this model is applied to ensure that the surface tension effect is properly implemented in this model. Two tests have been considered. First, it has been checked an initial square drop in a 2D domain can freely deform to a circular drop and secondly the coalescence of two static drops that merge to become a single circular drop is simulated. In order to further verify the model, Laplace law for static drops is performed. In the next step, wall effects on the droplet shape and its average velocity have been studied. It is seen that the average velocity of droplet at different times is independent of wall effects when the ratio of the width of the channel to droplet diameter (W/D) is more than 6. In the final section of the paper, deformation and breakup of a falling droplet for some range of Eotvos and Ohnesorge numbers are investigated. It is seen that at very low Eotvos numbers, where the surface tension force is dominant, the droplet deforms slowly and reaches a steady state without breakup. At higher Eotvos numbers gravitational force overcome the surface tension force and the droplet deforms more. For breakup modes at the small Ohnesorge number, if Eotvos number be increased to an intermediate value, the droplet deforms more than from a state of low Eotvos number value and eventually forms a backward-facing bag. Finally, for high Eotvos numbers, fragments of droplet are sheared from the edges and the shear breakup mechanism is seen. On the other hand, the stabilizing effect of the Ohnesorge number, (the ratio of viscous stresses and surface tension) is shown. At higher Ohnesorge number, the simulations show that the main effect of increasing Ohnesorge number is to move the boundary between the different breakup modes to higher Eotvos number.

In this article, element free Galerkin method is used for static analysis of thin orthotropic micro/nanoscale plates based on the nonlocal plate theory. Equilibrium equation is obtained based on the nonlocal Kirchoff plate theory. Weak form of the equilibrium equation is discretized based on the moving least square (MLS) approximation functions. Since MLS approximation functions do not satisfy the Kronecker’s delta property, the penalty method is used to impose the essential boundary conditions. Discrete form of the weak form is then solved and the plate deflection is obtained. Numerical results show that the number of nodes scattered in the plate domain, support domain radius and the number of Gauss quadrature points affect the results. Therefore, before presentation of the final results, the method is calibrated using some exact results. Finally, the plate deflection is obtained for various boundary conditions and the small scale effect is studied. In addition, as an example bending problem of nano graphene sheets is solved for different boundary conditions.