International Journal of Engineering
Volume:28 Issue: 5, May 2015

In this paper the earth’s magnetic field is simulated precisely while the intensity and direction of the field are verified with one of the standard references for selected points on the earth and the results are compared with some low-order models. In another simulation, the complete model is compared with a common approximate model. The magnetic field in orbital frame is described and to employ earth’s magnetic field in spacecraft attitude control applications, it is transferred into the spacecraft body frame. Transformation between orbital frame and body frame can be linear or nonlinear; the validity of linear transformation is investigated regarding various attitude angles. The divergence plots and the plot and table of error percentage illustrate the result based on the defined acceptable error.

Polypyrrole–hydroxyethylcellulose/TitaniumDioxide (PPy-HEC/TiO2) nanocomposite was synthesized via in situ chemical oxidative polymerization method at room temperature in water and water/ethyl acetate solution in the presence of ferric chloride (FeCl3). The effect of TiO2 nanoparticles and HEC on the characteristics of products such as thermal stability and morphology was investigated. The fabricated composite and nanocomposite morphology and structure were analyzed by atomic forced microscopy (AFM), Scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and Thermogravimetric analysis (TGA). The AFM images of products indicated that hydroxyethylcellulose decreased the surface roughness of nanocomposite. Also, hydroxyethylcellulose decreased particle size. The molecular structure of product was determined by FTIR spectroscopy. The results of XRD confirmed crystalline structure of TiO2 nanoparticles and partly crystalline structure of PPy-HEC/TiO2 nanocomposite. TGA was used to study the thermal behavior of nanocomposite. The TGA curves indicated that TiO2 and HEC enhanced thermal stability of products.

Tuned mass dampers (TMDs) could be used to absorb the input energy of the applied load, and reduce the response of the building frames. However, the effectiveness of TMD in reducing the response of the building frames could be affected by inherited uncertainties in the structural characteristics of the frames. In this study, in order to investigate the probabilistic response of steel moment resisting frames equipped with TMDs, variation in the failure probability of the structure has been studied through cumulative damage representative for the stories of the structure. The damage representative of each story has been calculated from the cumulative damage index of the structural elements, based on the weighted average approach. Although the response of the deterministic model of the structure could be reduced by installing TMD, the results of the numerical simulations on the probabilistic response of the structures indicate that for the records that cause excessive damage in the stories of the structures, the effect of the TMD on failure probability of the structure could be detrimental.

Carbon fiber reinforced polymer (CFRP) sheets are externally bonded to reinforced concrete (RC) members to provide additional strength such as flexural and shear strength. It has been widely accepted that carbon fiber reinforced polymers (CFRPs) can be used effectively to strengthen reinforced concrete (RC) members. This paper is intended to study and use externally bonded CFRP strips to repair and strengthen RC continuous T-beams, as well as investigating the influence of material (CFRP) on repair of shear defect on RC continuous T-beams. This defect will be repaired using different CFRP strips under sustained loading. Total of three RC continuous T-beams with identical sizes of 150x320x3650 mm, flange width of 400 mm and flange thickness of 120 mm were used, and the orientation involved 0/90 degree and 45/135 degree in 3 sides wrap schemes. All beams were tested under sustained loading. Tests result showed the effectiveness and shear capacity of the CFRP strengthened specimens. The shear enhancement of the CFRP strengthened beams varied between 26.57% and 38.56% over the control beam. This study confirms that the CFRP strip technique significantly enhances the shear capacity of reinforced concrete shear beams.

Lateral spreading is one of the most destructive effects of liquefaction. Liquefaction is known as one of the major causes of ground failure related to earthquake. This phenomenon is likely to occur when the rate of earthquake-induced excess pore water pressure buildup exceeds the rate of drainage. Estimation of the hazard of lateral spreading requires characterization of subsurface conditions. In this study, neuro-fuzzy group method of data handling (NF-GMDH) is utilized for assessment of lateral displacement in both ground slope and free face conditions. The NF-GMDH approach is improved using particle swarm optimization (PSO) algorithm. The comprehensive database used for the development of the model was obtained from different earthquakes. Contributions of the variables influencing the lateral displacement of soil are evaluated through a sensitivity analysis. Performance of the NF-GMDH-PSO models are compared with those yielded using empirical equations in terms of error indicators parameters and the advantages of the proposed models over the conventional method are discussed.

In this paper, two linear arrays including a linear 1×4 and a planar 2×2 of microstrip patch and halfmode substrate integrated waveguide (SIW) cavity hybrid antenna are introduced and investigated. These are simply implemented using low cost single layer printed circuit board (PCB) process. The array element consists of a rectangular microstrip patch with appropriate dimensions in the vicinity of a semi-circular SIW resonator provide a wideband hysbrid antenna. In both antenna arrays a microstrip feeding network including a quarter-wave transformer matching circuit has been used to feed the array elements. The size of 1×4 linear array is 1.58λ0×2.87λ0 and planar 2×2 array size is 1.57 0×1.37λ0. Array structures are numerically and experimentally investigated. The measured and simulated results including reflection coefficient, radiation patterns and gain of the both arrays are reported.

In this paper, the digital controller design for compensating the dc-dc buck converter output voltage has been analyzed in the digital domain. The main idea of this paper is patterning the samples of high order ideal controller and using integral square error in determining digital PID coefficients. This approach provides higher precision of digital controller design and eliminates the need for manipulating the coefficients, which in turn will lead to stringent design parameters in response to the system output. The proposed scheme has been simulated in MATLAB software and the results have been presented. The digital controller has been designed based on the proposed method for the buck converter and has been implemented on a TMS320LF2812 DSP core.

Measurement of the solar radiance requires utilization of expensive devices. To address this issue, estimator models are used to facilitate the measurement process. In this paper, a new method based on the empirical equations is introduced to estimate the monthly average of daily global solar radiation on a horizontal surface. The proposed method takes advantages of an intelligent water drops algorithm as a swarm-based nature-inspired optimization technique. This algorithm has been implemented in the MATLAB software. The best obtained coefficients of linear and nonlinear empirical models and global solar radiation are employed for the measurement of the six different climate regions of Iran. Performance of this approach has been compared to the other existing techniques. The result reveals the superiority of the proposed method in term of accuracy for estimating the monthly average daily global solar radiation.

Torque control strategy is a common strategy to control robotic manipulators. However, it becomes complex duo to manipulator dynamics. In addition, position control of permanent magnet synchronous motors (PMSMs) is a complicated control. Therefore, tracking control of robots driven by PMSMs is a challenging problem. This article presents a novel tracking control of electrically driven robots which is simple and free from manipulator model. The novelty is the developing of voltage control strategy for the direct-drive robots driven by PMSMs. In addition, a state-space model is obtained for the robotic system including the direct-drive robot manipulator and the PMSMs. Then, the proposed approach is verified by stability analysis. A comparative study through simulations shows the superiority of the voltage control strategy to the torque control strategy.

In the facility location problem usually reducing total transferring cost and time are common objectives. In the p-hub covering problem it is attempted to locate hubs and allocate customers to established hubs while allocated nodes to hubs are inside of related hubs covering radius. In this paper, we attempt to consider capability of established hubs to achieve a more reliable network. Also, the proposed model try to construct a network with more covering reliability by determining operating covering radius inside of nominal radius. Then, a sensitivity analysis is performed to analyze effect of parameters in the model. The proposed multi objective model is solved by ε-constraint algorithm for small size instances. For large scale instances a non-dominated sorting genetic algorithm (NSGA-II) is presented to obtain Pareto solutions and its performance is compared with results of ε constraint algorithm. The model and solution algorithm were analyzed by more numerical examples such as Turkish network dataset. The sensitivity analysis confirms that the network extracted by the proposed model is more efficient than classic networks.

Designing highly reliable and economical systems is of interest in today’s competitive world. In this paper, enhancing system reliability through redundancy allocation is investigated, where the supplier selection is taken into account and redundant components are provided from appropriate suppliers with the most suitable offers such as discount on purchasing price of components, warranty length of components, things like that, so that the system reliability, profit and the warranty length proposed by suppliers are simultaneously maximized. The resulting multi-objective model is then solved with the well-known compromise programming approach and the performance of the proposed approach is investigated through a numerical example.

In this paper, we propose a new model for designing integrated forward/reverse logistics based on pricing policy in direct and indirect sales channel. The proposed model includes producers, disposal center, distributers and final customers. We assumed that the location of final customers is fixed. First, a deterministic mixed integer linear programming model is developed for integrated logistics network design. Then, the stochastic counterpart of the proposed mixed integer linear programming model is developed by using scenario-based stochastic approach. We use the value of the stochastic solution (VSS) as a measure to evaluate the accuracy of stochastic programming approach. VSS value showed that using stochastic approach for solving the proposed model is sufficient. Moreover, we could obtain optimal values of sale prices in direct and indirect sale channel and service level by considering forward and reverse flow together.

This paper presents a new mathematical model for integrated dynamic cellular manufacturing systems and production planning that minimizes machine purchasing, intra-cell material handling, cell reconfiguration and setup costs. The proposed model forms the manufacturing cells and determines the quantity of machine and movements during each period of time. This problem is NP-hard, so a metaheuristic algorithm based on genetic algorithm (GA) is developed to solve it. Experimental results confirm the efficiency and the effectiveness of the proposed GA to provide good solutions, especially for medium and large-sized problems.

In the present paper, general equations governing the beam vibration are derived in its three sub dimensions under the influence of system dynamics by using the Euler-Bernoulli beam theory and by utilizing Hamiltonian method. Then, two fundamental cases of a cantilever beam and a rotating beam are considered. Regarding the difficulty and the costliness of applying control commands to suppress the beam vibrations on its domain and regarding the difficulties of designing the controller based on the reduced and the discretized equations such as the control spillover and the boundary control method is both proposed and utilized. Thus, in order to suppress the beam vibration, control forces and moments placed on the system boundary are used. The controller which is designed based on the boundary control method and Lyapunov method guarantees the asymptotic stability of vibrations. The simulation results illustrate the high efficiency of the proposed method in suppressing the longitudinal and transversal vibrations of both states of cantilever and rotating beam with and without the boundary controller.

This paper deals with state estimation of micro tunable capacitor subjected to nonlinear electrostatic force. To this end, a nonlinear observer has been designed for state estimation of the structure. Necessary and sufficient conditions for construction of the observer are presented. Stability of the observer is checked using Lyapunov theorem. Observer design is based on converting differential equation of dynamic error from heterogeneous to homogenous. Thereby, non-linear electrostatic term is presented as coefficient of error which is done using decomposition of Taylor expansion of nonlinear term. By stabilizing of homogenous differential equation, gains of observer can be obtained. Ability of the observer in state estimation of micro tunable capacitor is checked and related results are presented.

In this paper, the problem of unsteady mixed convection boundary layer flow of a viscous incompressible fluid near the stagnation-point on a vertical permeable plate with both cases of prescribed wall temperature and prescribed wall heat flux is investigated numerically. Here, both assisting and opposing buoyancy forces are considered and studied. The nonlinear coupled partial differential equations governing the flow, thermal and concentration fields are first transformed into a set of nonlinear coupled ordinary differential equations by a set of suitable similarity transformations. The resulting system of coupled nonlinear ordinary differential equations is solved numerically using the Runge–Kutta scheme coupled with a conventional shooting procedure.Numerical results are obtained for the skin-friction coefficient, Nusselt number and Sherwood number as well as for the velocity, temperature and concentration profiles for some values of the governing parameters, namely, the unsteadiness parameter A, permeability parameter f0 and mixed convection parameter λ. It is found that dual solutions exist for both assisting and opposing flows, and the range of the mixed convection parameter for which the solution exists, increases with suction and unsteadiness parameters.

Due to long life of steam power plants in Iran, transformation of steam cycles to combined cycles is under consideration. Bandar-Abbas steam power plant with capacity of 320 MW has been analyzed in this work. This old plant is located near the harbor city of Bandar-Abbas in south of Iran. Exergy analysis method is used to study the current and the repowered systems. Optimum state of the repowered cycle is also obtained using exergy analysis. In this work, a point by point analysis of Bandar-Abbas steam power plant is performed for different modes of full repowering, using exergy analysis method. For this purpose, V94.2 and V94.3A gas turbines are used and effect of duct burner is investigated for each case. The results show that at the best repowering mode, power plant efficiency is 34.5% higher than the design efficiency of the current steam plant. Minimum rate of exergy destruction rate is 6711 MW at this mode and the heat rate reduces by 26.6%. According to our results, increasing fuel consumption in duct burner and use of V94.2 gas turbine are not recommended for repowering of Bandar-Abbas power plant.

The purpose of present study is to investigate the dynamic response of two conventional types of solid oxide fuel cells to the inlet air mass flow rate variation. A dynamic compartmental model based on CFD principles is developed for two typical planar and tubular SOFC designs. The model accounts for transport processes (heat and mass transfer), diffusion processes, electrochemical processes, anode and cathode activation and ohmic polarizations, among others. Using developed model the dynamic response of the cell to the step change of the air feed stream conditions is investigated. The results show an almost slow electrical response of the cell to the air mass flow rate step variation that is estimated to be about one hour. Moreover, it can be concluded that the effect of the inlet air flow conditions on a tubular solid oxide fuel cell performance is more noticeable than its effects on a planar SOFC. However, the electrical response time of the tubular type SOFC is calculated about ten times more than the planar type.

The nonlinear bending behavior of sector graphene sheets is studied subjected to uniform transverse loads resting on a Winkler-Pasternak elastic foundation using the nonlocal elasticity theory. Considering the nonlocal differential constitutive relations of Eringen theory based on first order shear deformation theory and using the von-Karman strain field, the equilibrium partial differential equations are derived. the nonlinear partial differential equations system is solved using the differential quadrature method (DQM) and a new semi analytical polynomial method (SAPM). By using the DQM or SAPM, the partial differential equations are converted to nonlinear algebraic equations, then the Newton–Raphson iterative scheme is applied to solve the resulting nonlinear algebraic equations system. The obtained results from DQM and SAPM are compared and observed the SAPM results are so close to DQM. Whereas, the SAPM’s formulations are considerably simpler than the DQM. Different boundary conditions including clamped, simply supported and free edges are considered. The obtained results are validated with available researches, then the small scale effects is investigated on the results due to various conditions such as outer radius to thickness ratio, boundary conditions, linear to nonlinear analysis, nonlocal to local analysis ratio, angle of the sector and stiffness value of elastic foundation.

In this study, a mathematical model is introduced to simulate the coupled heat transfer equation and Stefan condition occurring in moving boundary problems such as the solidification process in the continuous casting machines. In the continuous casting process, there exists a two phase Stefan problem with moving boundary. The control-volume finite difference approach together with the boundary immobilization method is selected to predict the position of moving interface and the temperature distribution. The approach is validated by some available models and the agreement is found to be satisfactory. Effects of the governing parameters such as Stefan number and casting speed on the evolution of the freezing front and temperature distributions are investigated. It is found that the variation of Stefan number has a strong influence on the growth of the shell thickness and the temperature distributions. For the same values of heat transferred from the mold, increasing Stefan number has significant results such as: accelerating the solidification process and increasing the solid thickness, enhancing the local heat flux in the liquid, and broadening the liquid zone affected by the cooling water jacket. As the casting speed becomes higher, the molten flow leaves the mold faster and the solid thickness entering the secondary cooling stage is decreased; meanwhile, the central liquid region has less time to be affected by the cooling water. Reducing casting speed results in decreasing the solid temperature; in other words, the solid layer becomes cooler.