International Journal of Engineering
Volume:29 Issue: 6, Jun 2016

The purpose of this paper is to consider the problem of scheduling a set of start time-dependent jobs in a two-machine flow shop, in which the actual processing times of jobs increase linearly according to their starting time. The objective of this problem is to minimize the makespan. The problem is known to be NP-hardness; therefore, there is no polynomial-time algorithm to solve it optimally in a reasonable time. So, a branch-and-bound algorithm is proposed to find the optimal solution by means of dominance rules, upper and lower bounds. Several easy heuristic procedures are also proposed to derive near-optimal solutions. To evaluate the performance of the proposed algorithms, the computational experiments are extracted based on the recent literature. Deteriorating jobs lead to an increase in the makespan of the problems; therefore, it is important to obtain the optimal or near optimal solution. Considering the complexity of the problem, the branch-and-bound algorithm is capable of solving problems of up to 26 jobs. Additionally, the average error percentage of heuristic algorithms is less than 1.37%; therefore, the best one is recommended to obtain a near-optimal solution for large-scale problems.

In this paper, we want to improve association rules in order to be used in recommenders. Recommender systems present a method to create personalized offers. One of the most important types of recommender systems is the collaborative filtering that deals with data mining in user information and offering them the appropriate item. Among the data mining methods, finding frequent item sets and creating association rules are included in dataset. In this method, through separating the data of more active users, those who are interested in more items, we make sample from the training set and continue finding the association rules on the selected sample. Therefore, while the training set gets smaller, the production speed of rules increases. At the same time, we will show that the quality of the produced rules has been improved. Among the advantages of the proposed method, it can be referred to its simplicity and rapid implementation. Moreover, through a sampling from training set, the speed of association rules will be increased.

The goals of hub location problems are finding the location of hub facilities and determining the allocation of non-hub nodes to these located hubs. In this work, we discuss the multi-modal single allocation capacitated p-hub covering problem over fully interconnected hub networks. Therefore, we provide a formulation to this end. The purpose of our model is to find the location of hubs and the hub links between them at a selected combination of modes for each origin-destination. Furthermore, it determines the allocation of non-hub nodes to the located hubs at the best mode for each allocation such that the travel time between any origin–destination pair is not greater than a given time bound. In addition, the capacity of hub nodes is considered. Six valid inequalities are presented to tighten the linear programming lower bound. We present a heuristic tabu search based algorithm and test the performance of it on the Australian Post (AP) data set.

The purpose of this paper is to analyze the flow field structure in transient state and performance of secondary injection system for thrust vectoring in divergent section of a two-dimensional nozzle. Secondary injection for thrust vectoring in a two-dimensional nozzle is studied by solving three-dimensional Reynolds-averaged equations by means of fluent solver. Spalart-Allmaras model was used to model the fluid behavior near the walls. Density-based solver and explicit formulation are employed in the computational model. Results show that the solution of interfered field in the transient-state is more accurate than steady-state, especially in the initial injection. In addition, various testing showed that the maximum side force would be in the injection angle of twenty degrees and with increasing pressure ratio, we have more side force. At the end it was observed that by sketching the exit gases deviation according to time, we could be informed of desired secondary injection time in order to achieve required deviation around pitch axis, and the required force to achieve desired deviation angle. The innovation of this paper is the solution of interfered field in transient state, and of course the injection from the optimal point.

The bifurcation analysis of a symmetrically composite beam subjected to harmonic flapwise base excitation is studied when the ratio of flapwise and chordwise internal resonances is 1:2. Results are obtained by the numerical solution of modulation equations. In previous works, the modulation equations did not exhibit any symmetric properties. Therefore, modified equations with symmetric properties are studied in this paper. Chracteristics of the response are investigated in terms of time history, phase portraits diagrams and bifurcation diagram of poincare maps. It is observed that periodic and multi-periodic motions, jump and stable motion are appeared near the internal and external tunnig frequency parameters.

The aim of this paper is to focus on the effect of cryogenic treatment on the microstructure, mechanical and wear properties of Al 6061 and Al 8011. The first objective was to understand the degree to which hardness of these aluminium grades have been enhanced by giving cryogenic on the specimens. The second objective is to check the wear resistance property of these two aluminium specimens if coated with NiCoW and then treating it cryogenically. To conduct hardness tests specimens were fabricated from aluminium plates from both these grades and cryogenically treated. To conduct wear test, both the grades of aluminium were coated with NiCoW, and experimental investigation were carried out with cryogenic coolants. The hardness and wear removal rate were studied for both specimens. The cryogenic coolant enhanced the hardenability of aluminium alloys resulting in increased hardness of nearly 15%. The cryogenic coolant has increased the wear resistance properties of aluminium coated with NiCoW by nearly 25% when compared to wear of the non-treated aluminium with the coating materials. The cryogenic treatment was carried out under three different timings of 8, 24 and 48 hours for three different rpm‟s 300, 600, 800 under varying loads. The paper also studies the microstructural changes under these varying conditions.

In this research, dynamic analysis of the rotational slender axially moving string is investigated. String is assumed as Euler Bernoulli beam. The axial motion of the string, gyroscopic force and mass eccentricity were considered in the study. Equations of motion are derived using Hamilton’s principle, resulting in two partial differential equations for the transverse motions. The equations are changed to non-dimensional form and are discretized via Galerkin’ method. The bifurcation diagrams and Poincare'' portraits are represented in the case that the mean axial speed, the fluctuating speed and the mass eccentricity are respectively varied. The dynamical behaviors are numerically identified based on the Poincare'' portraits. Numerical simulations indicate that quasi-periodic motion occurs in the transverse vibrations of the string by variation of axial speed and mass eccentricity.

Exoskeletons are utilized extensively in robotic rehabilitation and power augmentation purposes. One of the most recognised control algorithms utilized in this field is the impedance controller. Impedance control approach provides the capability of realizing different rehabilitation exercises by tuning the target impedance gains. Trial and error experimental approach is one of the most common methods reported in the literature used to tune the target impedance. In this research, a general framework is proposed to study the effect of the target impedance selection on the exoskeleton performance and generation of the human gait profile. The dynamic model of the human-exoskeleton in the sagittal plane is derived for gait simulation study. In addition, a novel human-exoskeleton interaction model is introduced. The simulation study was carried out to illustrate that how the target impedance gains should be selected to minimize several criterias such as energy consumption, interaction forces and position tracking errors during walking. As a result, the proposed method provides better insight into the effective selection methods of the impedance control gains.

Micro/nanocantilevers have been employed as sensors in many applications including chemical and biosensing. Due to their high sensitivity and potential for scalability, miniature sensing systems are in wide use and will likely become more prevalent in micro/nano-electromechanical systems (M-NEMSs). This paper is mainly focused on the use of sensing systems that employ micro/nano-size cantilever beams for sensing gaseous molecules. Micro/nanocantilever-based gas sensing is concerned with determining the micro/nanocantilever resonance shift or detecting the micro/nanocantilever deflection due to adsorption event. This paper has considered the former approach, i.e., determining the resonance shift. In order to explain these changes more clearly, a micro/nanobeam has to be modeled by considering some micro/nanoscale parameters. A model based on classic elasticity theory potentially is unable to consider micro/nanoscale parameters which have considerable effects on the behavior of the micro/nanobeams. The effect of couple stress on the stiffness of cantilever beams remains an outstanding problem in the physical sciences. So in this paper, a modeling based on couple stress theory has been applied to explore the behavior of a micro/nanobeam due to the adsorption of gaseous molecules. This work has attempted to advance the field of micro/nanocantilever based gas sensing by shedding more light on the mechanical behavior of micro/nanocantilever.

Typically, viscous liquid explosives are injected into the warhead . The injection device consists of a piston which moves downward and leads the viscous fluid through a cylindrical duct towards the end of the duct. Then the viscous fluid entered into a converging nozzle and injected into the warhead or other ammunitions. This article is an analysis of heat transfer of fluid flow of the liquid explosive in the converging nozzle, as a part of the injection device under exposer of heat flux from the walls. Also, viscous dissipation phenomenon is considered, which is due to the viscosity of the fluid. It will raise the fluid temperature. Forced convection heat transfer is investigated analytically. Fully developed laminar flow is assumed. This analysis is done by considering wall heating and wall cooling. By comparing the effect of viscous dissipation and heat flux, it is investigated that effect of which of them is more significant. Axial heat conduction is neglected. Physical properties are assumed to be constant. The theoretical analysis of the steady heat transfer in nozzle flow for non-Newtonian fluid with considering viscous dissipation term in energy equation is performed by an analytical method. An important feature of this approach is obtaining steady temperature distribution of explosive fluid in converging pipe flow with viscous dissipation. Effects of the inlet velocity and density of liquid explosive on the distribution of temperature are presented. Also, the effect of changing the convergence angle on heat transfer is investigated.

In this study, nonlinear bending of solid and annular functionally graded (FG) sector plates subjected to transverse mechanical loading and thermal gradient along the thickness direction is investigated. Material properties are varied continuously along the plate thickness according to power-law distribution of the volume fraction of the constituents. According to von-Karman relation for large deflections,the two set of highly coupled nonlinear equilibrium equations are derived based on both first order shear deformation theory (FSDT) and classical plate theory (CPT). The dynamic relaxation (DR) method in conjunction with the finite difference discretization technique is used to solve the nonlinear equilibrium equations. To demonstrate the efficiency and accuracy of the present solution, some comparison studies are carried out. Effects of material grading index, boundary conditions, sector angles, thickness-to-radius ratio and thermal gradient are studied in detail. Also, to consider the effect of shear deformation and nonlinearity on the results, some linear and nonlinear analyses are carried out based on both CPT and FSDT for different thickness-to-radius ratios and boundary conditions.