International Journal of Engineering
Volume:28 Issue: 9, Sept 2015

In the Boudouard reaction, where CO2 is reacted with carbon (char) to produce CO, very high temperatures are required to shift the equilibrium towards CO production. This endothermic reaction is inherently slow and catalytic species are effective to speed up the reaction rate at temperatures below 900 °C. In this study, the catalytic effect of some alkali (K, Na), alkaline earth (Ca) and transition (Fe) metals on enhancing the CO2 gasification reactivity of pistachio shell (PS) char was investigated. The CO2 gasification studies were performed in a Thermogravimetric analyzer (TGA). Among the examined potassium species, K2CO3 showed the highest catalytic effect; wherein, complete carbon conversion was achieved 48.1% faster as compared to un-catalyzed PS char. The highest catalytic effect among the sodium salts was devoted to NaNO3 which showed 57.7% enhancement in the reactivity of char. CaCl2 and Fe(NO3)2 also showed the best catalytic performance among the examined calcium and iron species and improved the reaction rate by 64.6 and 46.1%, respectively.

Direct displacement based design (DDBD) is a conceptual framework that directly designs a structure to achieve an expected performance level under specified seismic intensity. In this study, two important issues relevant to torsional response of mass eccentric 8-story RC building designed with DDBD approach are investigated. These issues are including the effects of unbalanced mass distribution scenario on the torsional response parameters and the study of these parameters with reference to diagonal displacement. Diagonal displacement is the SRSS combination of the displacement demands along the direction of excitation and orthogonal direction. Three different unbalanced mass distribution scenarios which produce the same mass eccentricity were applied to the plan of the generic structural model to determine the general range of the mass moment of inertia (MMI) variation due to different unbalanced mass distribution scenarios. Expressions were established to correlate MMI and mass eccentricity in each scenario. Results show that for slight eccentricities the variation of the MMI is negligible but as eccentricity is increased the range of the variation is extended. Then, sensitivity analyses based on finite element method and inelastic time history analysis have been carried out on 8-story RC building frame designed with DDBD approach with different levels of mass eccentricity and different MMI. Torsional response parameters in terms of maximum displacement demands of edge elements, diaphragm rotation, nominal relative displacement and nominal rotation is compared with diagonal and horizontal displacement demands along seismic excitation.

Numerous problems in engineering and science can be transformed into optimization problems. Artificial bee colony (ABC) algorithm is a newly developed stochastic optimization algorithm and has been successfully used in many areas. However, due to the stochastic characteristics of the solution search equation, the traditional ABC algorithm often suffers from poor exploitation. Aiming at this weakness of the traditional ABC algorithm, in this paper, we propose an enhanced ABC algorithm with elite opposition-based learning strategy (EOABC). In the proposed EOABC, it executes the elite opposition-based learning strategy with a preset learning probability to enhance the exploitation capacity. In the experiments, EOABC is tested on a set of numerical benchmark test functions, and is compared with some other ABC algorithms. The comparisons indicate that EOABC can obtain competitive results on the majority of the test functions.

This paper presents the VHDL implementation of fault tolerant cellular genetic algorithm. The goal of paper is to harden the hardware implementation of the cGA against single error upset (SEU), when affecting the fitness registers in the target hardware. The proposed approach consists of two phases; Error monitoring and error recovery. Using innovative connectivity between processing elements and efficient correction policy, the PEs will prohibit spreading the faulty evaluated individual in the population. In the experiments, three metrics and four test functions are used to show the performance of the proposed structures. Two structures (2D and 3D) of proposed FT-cGAs are set to optimize various test functions. The experimental results illustrate the robustness of the proposed system. An outstanding outcome was that the implemented fault tolerant algorithm was able to reach the optimal solution when at least one processing element is healthy in population.

This paper explores and presents the analysis, design and implementation of a high voltage ratio topology of DC-DC converter. The DC-DC converter has high voltage ratio with reduced output voltage and output current ripple, also reduces the voltage and current rating of power electronic components compared with conventional boost converter. The voltage stress on the switches are reduced in this topology. Analysis, design and converter operating waveforms in the continuous conduction mode are provided along with design guidelines. The converter has been designed for rated power of 50W, input voltage of 24V, output voltage of 72V and switching frequency of 25 kHz. The floating output interleaved input high voltage gain converter is compared with conventional boost converter, hardware and simulation results are verified.

Some products like green vegetables, volatile liquids and others deteriorate continuously due to evaporation, spoilage etc. In this study, an inventory model is developed for deteriorating items with linearly time dependent demand rate under inflation and time discounting over a finite planning horizon. Shortages are allowed and linearly time dependent. Mathematical model is presented for the proposed model. We show that total profit is concave with respect fraction of scheduling period k. The results are discussed with the help of numerical example. A sensitivity analysis of the optimal solution with respect to the key parameters is also discussed.

In recent two decades, countries focused on extraction of the minimum amount of fossil fuels and utilization of the renewable energies based on their policies and environmental considerations. Thus, choosing the best renewable energy alternative plays a significant role on the investments. Among the classical decision approaches used in the literature, a hesitant fuzzy sets (HFSs) theory is an appropriate tool to deal with uncertain and imprecise conditions. The HFSs can help the decision makers or experts in an energy sector to consider some membership degrees for a renewable energy alternative regarding to the conflicted criteria under a set. The aim of this paper is to propose a hierarchical complex proportional assessment (COPRAS) method to consider subjective judgments and objective opinions based on the HFS theory for multi-criteria group decision making (MCGDM) problems. In addition, the hesitant fuzzy decision matrix and main criteria along with sub-criteria are defined based on linguistic variables and then are converted to hesitant fuzzy elements. In the proposed approach, weights of experts are different and computed by a proposed hesitant fuzzy entropy method. Also, the weights of main criteria are determined by a new relation in n levels of the hierarchy structure with experts'' risk preferences. Finally, a real case study in Iran on the renewable energy selection in the hierarchy structure is presented and a hesitant fuzzy hierarchical complex proportional assessment (HF-HCOPRAS) method is applied in order to show the applicability of the proposed approach.

Selecting an appropriate project is a main key for contractors to increase their profits. In practice, in this area the uncertainty and imprecise of the involved parameters is so high. Therefore, considering fuzzy sets theory to deal with uncertainty is more appreciate. The aim of this paper is to present a multi-criteria group decision-making model under an intuitionistic fuzzy set environment. The weight of each decision maker and each criterion are considered different. Indeed, decision maker's weights are determined based on a new intuitionistic fuzzy index, and criteria’ weights are specified by proposed decision method according to the concept of closer to ideal solution and farther from negative ideal solution. Then, the potential projects are ranked based on new intuitionistic fuzzy relative closeness coefficient. Thus, the proposed intuitionistic fuzzy group decision-making model is applied in an illustrative example about construction project selection from the recent literature. Finally, the ranking results are compared with a fuzzy TOPSIS method to indicate the applicability and efficiency of the proposed model.

The present study aims at developing A356/Al2O3(np) nano-composite with a novel and cost effective method for attaining homogeneous dispersion of Al2O3 nanoparticles in the Al matrix. In the current research, Al micro powders distributed on aluminum foil and then Al2O3 nanoparticles ultra-sounded in ethanol and sprayed on Al substrate. Subsequently, the sandwich foil was added to molten A356 during stirring. The nano-composite was characterized through scanning electron microscopy (SEM) for microstructural evaluations. Also, mechanical properties of A356/Al2O3(np) nano composite was measured through compression and hardness tests. By this novel method, an Al based (356) nanocomposite with 2 wt. % Al2O3 nanoparticles was obtained which shows 26.79%, 95.6 % and 43 % enhancement in yield stress, compression strength and hardness, respectively, as compared with the pure alloy processed under the same condition.

The mechanical alloying process was used to synthesize the Ni50Al50−xMox nanocrystalline intermetallic compound using pure Ni and Al elemental powder. This process was carried out in the presence of various Mo contents as a micro-alloying element for various milling times. Structural changes of powder particles during mechanical alloying were studied by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). Results showed that mechanical alloying in various combinations was completed after 48 h of milling time. Minimum crystallite size of the as milled powders (∼10 nm) was achieved after introducing Mo and milling for 128 h. Also, lattice strain decreased with increasing milling time up to 48 h and again increased after 48 h of milling time. On the other hand, the presence of Mo significantly affected variation intensity of the lattice parameter and morphology of the powder particles.

Due to the extensive use of composites in various industries, and the fact that defects reduce ultimate strength and efficiency during operation, detection of failures in composite parts is very important. The aim of this paper is to use Acoustic Emission (AE) non-destructive method in four-point bending test of carbon/epoxy composite to analyze and examine the failure mechanisms. This method is based on waves activated from defects in structures which are built during loading. Sensors collect acoustic signals which created by the separated layers. Each stage of failure is in specific frequency range and indicates a specific mechanism. Clustering of these signals is done with C-means and K-means algorithms then compared with the results of previous works. The failure process was shown to proceed through four stages. In both algorithms, each cluster coincides with one part of these stages.

The Coulomb force applied by an electric field on any charge present in a dielectric liquid may cause fluid motion. At high applied electric fields in an insulating liquid, electric charge carriers are created at metallic/liquid interfaces, a process referred to as ion injection, and result from complex electrochemical reactions. In this article we deal with the problem of electro-thermo convection in a dielectric liquid placed in a square cavity and subjected to the simultaneous action of a thermal gradient and an electric field. Thus, the aim is to analyze, from a numerical point of view, the evolution of flow structure, charge distribution and heat transfer in the case of a strong injection. The computational domain is as follow: the vertical walls are differentially heated; the horizontal walls are adiabatic except a part of the bottom wall (33% of the total length) is defined as the injecting electrodes. Three possible configurations are treated depending on the location of the injecting electrode: so we identify an injection from the left, from the middle and finally from the right. The results show that a partial injection can enhance heat transfer up to 24%. The flow structure in terms of streamlines, distribution of electric charge density and thermal field is highlighted. The effect of various system parameters in particular the injection zone locations, the electric Rayleigh number is investigated as well.

Squeeze film dampers (SFDs) are often used in machines with high rotational speed to reduce nonperiodic behavior by creating external damping. There are some structural parameters which are of great importance in designing these systems, such as oil film thickness and inner race mass of SFD. Moreover, there is a crucial parameter associated with manufacturing process, under the title of waviness. Geometric imperfections are often called waviness if its wavelength is much longer than Hertzian contact width. In this paper, a system of a flexible rotor and two ball bearings with squeeze film dampers and centralizing springs and also consideration of waviness has been modeled and solved by a numerical integration method to investigate the system dynamic response. Results show that by increasing the number of wave lobes, non-periodic and chaotic behavior increases. This reveals the importance of manufacturing accuracy and necessity of taking this term into account in simulations. Moreover, by changing the oil film thickness, it is revealed that there is an optimal value for this parameter to provide maximum damping. In addition, with increasing the inner race mass of SFD, the disc displacement amplitude increases. This reveals the importance of utilizing light materials in manufacturing the SFDs.

In this research, the effect of shape parameters such as number of magnet wire turns, spools, thickness of the gap, and pole length in a Magnetorheological (MR) fluid damper is analytically investigated and the optimization of these parameters is done with response surface method (RSM) which is combined Neuro-Fuzzy method and Particle Swarm Optimization (PSO) algorithm. Since the electromagnetic and mechanical components of a Magnetorheological (MR) fluid damper have a direct effect on the electrical power consumption, time delay, and damped force that are considered as objective functions. Because of the nonlinear behavior of the components, a robust approach is needed to predict their reactions; therefore, Neuro-Fuzzy is utilized to generate a high accurate surface and PSO finds the optimum solution base on the surface. The sensitive analysis is also performed to examine the variation of the objective functions with various input parameters. In this process, the best parameters are obtained by overtaking the appropriate value of the objective functions. The results demonstrate that the optimum MR damper has provided the best configurations, so that damps a maximum force in minimum time and lowest power consumption. On the other hand, the amplitude of vibrations is significantly decreased in the presence of the optimized MR damper.

To maintain the structural integrity of the engineering components, having an exact knowledge of residual stresses is important. Among all mechanical strain relief techniques to measure residual stresses, slitting is one of the youngest. This technique relies on the introduction of a narrow slot of increasing depth in a part containing residual stresses. Similar to other measurement techniques, slitting also employs simplifying assumptions. One of these assumptions is that the stress does not vary along the cut line. There are many sources of errors in the slitting method. However, the error caused by this assumption can be severe. In this research, residual stresses of quenched samples were measured experimentally using slitting technique. The results were then compared with those obtained from the finite element analyses. The cylindrical specimens were designed with different ratios of height to diameter to investigate the effect of stress variations in transverse direction along the cut plane. It was evident that the non-uniformity of stress can severely influence the residual stresses measurement. The experimental results confirmed the numerical findings.

This study presents a designing process for refurbishing of a 32 MW rotor-generator damaged coupling. The reason of rotor damage was being hit by the quivers of an explosion. The original coupling was union with the rotor formed after a machining process on a mono block forged rotor. In some areas imposed damages caused the breaking off and detachment of some parts in the coupling flange. Because of this accident, the coupling region was removed by machining completely and another coupling was made and mounted on the rotor-generator shaft by shrink fitting. Reverse engineering method was used with comparing a 145 MW rotor-generator. At first all of the mechanical loadings on the coupling were assessed. The calculations include analytical method by using ANSI standard and simulation of ANSYS software. The results showed that in spite of geometrical restrictions, it is possible to install a distinct coupling by shrink fitting on the rotor generator shaft.

Polymer-based nanocomposites due to good corrosion resistance, adequate mechanical properties and low cost are widely used in modern technologies. Because of the increasing application of these nanocomposites, their joining through welding processes seems unavoidable. In this paper, 5mm thick nanocomposite plates containing polypropylene, ethylene-propylene diene monomer with 0, 3 and 6% clay were butt welded using a novel hot tool in friction stir welding process. Response surface method is used to design experiments and determine the effect of process parameters such as tool rotational speed, welding speed, tool shoulder temperature and clay content on weld tensile strength. The results show that although increasing clay content in the base material increases its tensile strength, but decreases the tensile strength of the weld such that in specimens with 0, 3 and 6% clay content, the tensile strength of the weld equals 94, 80 and 61 percent of the respective base materials.

The ever increasing demand for minerals has forced the surface mines to consistently upgrade the mechanization, for extracting minerals and removing overburden (OB), as well. Also, loading and hauling machineries are highly capital intensive equipments to procure, operate and maintain in surface mining operation. These machineries perform tens of thousands of cycles annually. Therefore, a small improvement in their speed factor will definitely have a significant effect on their production and productivity. Speed factor is the ratio of the planned cycle time of the equipment to the actual cycle time. For an idealized situation, the speed factor should be equal to 1. The low range of speed factor can be defined as the increase in cycle time of operation and decrease in production of this equipment. In the case study mine, speed factor of dragline operation was computed as 0.8222 which amounts to a loss of 1039 work hours per year or an annual loss of 50,531 cycles of operation which is an equivalent loss of 844221 m3 in output. Therefore, a small improvement in speed factor will definitely have a significant effect on its performance and production. As such, it is imperative to critically analyze the cycle time operation of this machine in order to enhance the speed factor, overall effectiveness and production. In this light, the present paper is an endeavour to critically analyze actual cycle time of dragline operation. In this regard, field observations for cycle time of dragline operation were precisely recorded on the basis of time and motion study. This was done by capturing real-time motion pictures of dragline operation, under normal operating conditions, by robust field camera installed with a precise in-built watch. The influence of degree of fragmentation on the cycle time was also critically evaluated by image analysis of the blasted muck pile. Descriptive statistics of the cycle time data reveal that unloading time is more or less constant; also there is not much variation in swing time segment. But the digging time segment exhibits significant variations which are affected by numerous field conditions such as collar oversize of blasted rock and balancing diagram of cut geometries.