Scientia Iranica
Volume:22 Issue: 5, 2015

this paper wants to apply a multi-objective optimization method for optimizing truss design problem. This method is named as Multi-Objectives Bees Algorithm (MOBA). In the first problem, objective functions are minimizing stress in the two members and minimizing volume of truss, and on each of other three problems, the objectives which should be optimized are value of total weight of structure and also total displacement of nodes with considering limits on cross section of elements. The bees algorithm is developed based on principle of multi-objective problems. A clustering algorithm is applied for multi-objective bees algorithm in order to manage the size of the Pareto-optimal set. The results are good evidence for robustness and effectiveness of multi-objective bees algorithm in solving multi-objective optimal truss design.

The analysis of unsteady-state thermo-mechanical problem of functionally graded thick-walled spheres is presented in this paper. The material properties, except Poisson’s ratio, are assumed to be an arbitrary function of radial direction. Considering linearly increasing boundary temperature and employing Laplace transform techniques, the time-dependent temperature is obtained. In a special case, by assuming the material properties to follow a power-law function, the Navier equation is solved for an arbitrary time which led to radial displacement, radial stress, and hoop stress as a function of radial direction.In the numerical results calculated by FEM software ABAQUS is compared to the analytical results. The present results agree well with existing analytical results.

Electrical discharge machining is a non-contact process based on thermoelectric energy between the electrode and workpiece. It is an efficient machining process to machine an advanced difficult-to-machine material with high precision, complex shapes and high surface quality. Realizing the advantages and abilities of this machining method, electrical discharge machining research has drawn an interest of many researchers. This paper reviews on the electrical discharge machining process, recent research fields and inventions that have been developed in order to improve workpiece surface quality and integrity, machining time, tool wear and material removal rate. Then, electrical discharge machining apparatus and its servomechanism system including the mechanical structure developments using computer numerical control, lead-screw mechanism, linear motor driven and piezoelectric actuator are reviewed in this paper. Furthermore, control strategies that were applied in electrical discharge machining system including servo-drive control and optimization techniques such as fuzzy, genetic algorithm and artificial neural network are also discussed.

Considering the loss of direct visual and tactile information, surgeons require special training programs to obtain sufficient proficiency for laparoscopic surgery. Surgical training simulation systems provide an effective alternative to animal models for repetitive training practices. The purpose of this study was to develop a biomechanical model of large soft organs for simulation of the interactions of a surgical grasper and spleen in real-time. The mechanical behavior of the spleen was molded in detail, including its nonlinear hyper viscoelastic properties, using a mass-spring-damper model. A novel collision detection algorithm was used to determine the tool-tissue contact zones. Force-based and geometry-based boundary conditions were imposed at the contact nodes, respectively, to represent slippage-included and slippage-free grasping conditions. The model’s predictions were validated against the experimental results on a synthetic test sample. Results of simulation of interactions between the grasping tool and the spleen organ indicated that the non-linear rate dependent and stress relaxation behaviors of the tissue was well depicted by the model. Also, the model was capable of reflecting the effect of tool-tissue friction coefficient on the slippage-free or slippage-included grasping behaviors.

This paper aims to optimize the transmission and control strategy of a parallel hybrid electric vehicle in order to minimize Fuel Consumption (FC) and emissions, simultaneously. Vehicle transmission is a Power Split Continuously Variable Transmission (PS-CVT), while the employed Torque Coupler (TC) is a two-speed TC. Using this type of TC increases designer ability to create a more ecient transmission. In this vehicle, the electric assist control strategy is used as the control strategy. In this strategy, the engine operates at optimal operation points, obtained using the Global Criterion method (GC). A multi-objective optimization is implemented using GC to minimize vehicle FC and emissions without sacri cing dynamic performance. Finally, results of the conventional method of hybrid vehicle optimization and the results of using the Dynamic Programming method are compared.

In this paper, modelling and control of an elastic actuator are investigated. First, the required performance of the actuator is determined and then a model of the actuator is proposed. Further, a control algorithm is presented to meet the required performance specifications. A speed feedback and a PI controller are utilized. Moreover, a PID controller is used to control the actuator output torque. Experimental tests are performed on the actuator to validate the actuator performance. First, an accuracy evaluation test is performed on the actuator to calibrate the torque measured by the spring. The results exhibit the spring’s linear characteristics and the capability of torque measurement. Second, the bandwidth of the actuator is measured through sinusoidal input. The results show that the actuator is capable of delivering the required torque in the frequency range of rehabilitation. Third, an impedance measurement test is performed on the actuator indicating that it is capable of exerting the lowest and or highest resistance on patient movement if required. As a result, it is shown that the proposed actuator can satisfy the whole rehabilitation requirements appropriately.

The biomicro fluidic devices utilizing electroosmosis for flow actuation are usually encountered with non-Newtonian behavior of working uids. Hence, studying the flow of non-Newtonian fluids under an electroosmotic body force is of high importance for accurate design and active control of these devices. In this paper, mixed electroosmotically and pressure driven flow of two viscoelastic uids, namely PTT and FENE-P models, through a rectangular microchannel is examined. The governing equations in dimensionless form are numerically solved through a fi nite di erence procedure for a non-uniform grid. It is observed that although the Debye-Huckel linearization fails to predict the velocity pro le for viscoelasticuids, this approximation holds even at high zeta potentials, provided the velocity field is normalized with the mean velocity. It is also revealed that the dependency of the mean velocity on the level of elasticity in the fluid is linear. This functionality results in a Poiseuille number independent of the level of elasticity in the fluid. Moreover, the pressure e ects are pronounced for higher values of the channel aspect ratio. In addition, both the mean velocity and the Poiseuille number are increasing functions of the channel aspect ratio.

In this paper, deformation of an elastic spherical capsule suspended in a shear flow is studied in detail using Lattice Boltzmann method for fluid flow simulation, immersed boundary method for fluid-membrane interaction and finite element method for membrane force analysis. While Lattice Boltzmann method is capable of implementing inertia effects, computations were carried out for small Reynolds number in which inertia effects are negligible. Effect of three membrane constitutive equations on capsule deformation, including Neo-Hookean, zero-thickness shell approximation and Skalak’s law with different area-dilation modulus, are studied in detail. Results presented in the form of Taylor deformation parameter, inclination angle and period of tank-treading motion of capsule, show close agreement between those obtained from Neo-Hookean and zero-thickness shell approximation with previous published ones. Such agreement is partially observed for Skalak’s law implementing different area-dilation modulus. In general, behavior of all three constitutive laws are similar for nondimensional shear rates of less than 0.05 while some differences were observed for its values of 0.1 and 0.2. As an efficient computational framework, it is shown that combined Lattice Boltzmann, Immersed Boundary and Finite element method is a promising method for such flow configuration, implementing different membrane constitutive laws.

To improve the machining efficiency for the conventional five-axis numerically controlled (NC) machining of a centrifugal impeller, this paper presents an efficient simultaneous three-axis NC machining approach on five-axis machine instead of simultaneous five-axis NC machining technology. On the basis of the characteristic curves of an impeller and its projection graphs, a rough-cut surface of the blades is partitioned into several unit machining regions (UMRs). The rotating and tilting angles of a five-axis machine bed are calculated and fixed in advance to support the simultaneous three-axis NC machining of each UMR. The tool paths with the zigzag shape are generated to avoid interference and collision between the cutter and the impeller blades based on the simultaneous three-axis control approach on five-axis machine bed. A prototype model of an impeller with nine blades is established, and its final tool paths in each UMR are verified by means of a cutting simulation function on Vericut software. Simulation results demonstrate that the simultaneous three-axis machining approach on five-axis machine bed can significantly improve the machining efficiency compared to the conventional five-axis machining technology.

A pressure driven axisymmetric flow in a circular tube, having a non- Newtonian Oldroyd 8-constant fluid in the core, is considered in this paper. The Oldroyd 8-constant fluid is surrounded by a Newtonian fluid in the present study. The exact solution of the governing equation is obtained in the form of an integral which is evaluated using Gaussian quadrature. The expression for the apparent viscosity is obtained. The graphical results are presented for the pro les of apparent viscosity for different values of the material parameters plotted against tube radius. It is found that for all the values of the material parameters, the apparent viscosity decreases as the tube radius decreases which is the Fahraeus-Lindqvist eff ect. The results for the case, when there is no Newtonian fluid present in the periphery, are also deduced.

In this work, an adhesion system for wall climbing robots using vortex cup has been designed and numerically simulated. A small scale model of the system has been designed and the flow patterns including pressure and velocity fields are computed using CFD analysis. The results are verified using mesh independ­ency and validated through comparison with the available experimental data and show to have high correlation together. Then a large scale vortex cup based on an actual weight of a wall climbing robot has been designed and simulated. Furthermore, the effects of different parameters such as the number of nozzles, cup height and cup radius on the adhesion force have been studied. Finally, a new cup has been designed base on the optimum data obtained from the numerical results.

In this paper nonlinear vibration of transversely vibrated beam with large slenderness and immovable ends is analyzed using Variational Iteration Method (VIM). The nonlinear partial differential equation of motion is converted to a set of coupled ordinary differential equations using Galerkin technique. Two mode expansion for the system response is considered and second order analytical solution of the equations is obtained using VIM. Two algebraic coupled equations are also developed to find the nonlinear frequencies of the system. Numerical Simulations are performed for various initial conditions. Close agreement between the numerical and analytical results is achieved. Also the frequency analysis is performed for a range of initial amplitudes of vibration.

Marine propeller hydrodynamics and noise study is an important problem in the suitable performance of ships and submarines. In the first step of this paper, the hydrodynamics of two propellers was studied under different operating conditions.Thensheet cavitation inception and development conditions were obtained in order to understand the impact of varying rotational speed of the propeller and pressure drop on the propeller noise. In the second step overall sound pressure levels (SPLs) under non-cavitating and sheet cavitating conditions were extracted for each of these models. The overall SPLs were calculated from Ffowcs Williams and Hawkings(FW-H) equations and its integral solutions. In this work, the flow field was analysed with the FVM, and then flow data including; pressure fluctuations, sheet cavitation volume and velocity magnitude results of the flow solution were used as the input for the FW-H formulation to predict the overall SPLs. The results from flow analysis are significant since they are used as noise sources in the FW-H equations to obtainthe overall SPLs. Therefore, these results must be thoroughly analysed. The numerical hydrodynamics results were compared with experiment results for the two propellers and a good agreement was found.