Modares Mechanical Engineering
Year:2016 | Volume:16 | Issue:1|Papers Count:49

In this paper motion of some blood clots with different mechanical properties in the cerebrovascular arteries is investigated. Blood clots are mostly originated from heart or other cardiovascular arteries and by entering the cerebrovascular arteries trigger occlusion and deprive the brain’s tissue from proper perfusion. To study this phenomenon, we used patient-specific geometry of cerebrovascular arteries and due to obtaining the motion of clot and blood’s flow in cerebral arteries, algorithm of fluid-structure interactions was used. Although previous researches have not considered the effect of mechanical properties on the motion of clot, our results demonstrate the variation of the dynamic parameters of the clot’s motion by changing the mechanical properties. We show that by increasing the rigidity of the clot, their tendency for entering to the larger arteries is increased. Also, other dynamic parameters like clot’s average velocity is altered when the mechanical property of the clots changes. Mechanical parameters have the main role in the motion of clots and by investigating them, insight to the mechanism of pathologies would expand, moreover, strategies of the cerebrovascular treatments would be interesting to study in the future.

Due to the importance of autopilot systems in Micro Aerial Vehicles (MAVs), in this paper, first, parametric guidance and control systems are designed and are then implemented on simulated nonlinear six-DOF MAV. The control system is fuzzy-supervisory and its gains are optimized using genetic algorithm. For designing the guidance system, first, two-dimensional (constant height) path following algorithms of vector field and carrot-chasing are developed to 3D algorithms. Then, an optimized 3D fuzzy carrot-chasing guidance system is presented using combination of the carrot-chasing geometric algorithm, fuzzy logic, and genetic algorithm. Augmentation of the fuzzy logic to the carrot-chasing algorithm improves its performance significantly. In any autonomous flight maneuver, guidance and control systems affect the performance of the aircraft, simultaneously. So using similar control system, the performance of the 3D carrot-chasing algorithm, 3D vector yield method, and the proposed 3D fuzzy carrot chasing algorithms are compared with and without applying the wind external disturbance. Results have shown signifiicant superiority of the proposed 3D fuzzy carrot-chasing approach in the horizontal plane of motion and the 3D vector field method in the vertical plane of motion.

In this study, particulate nanocomposites with A356 aluminum alloy as a matrix reinforced with 1 and 1.5 wt.% SiC nanoparticles with 50 nm average grain size were fabricated by stir casting method and then the obtained composites were subjected to T6 heat treatment. The mechanical properties such as Hardness Test and Tensile Test of composites samples were investigated. Microstructures of the samples were also investigated by using optical microscope (OM) and scanning electron microscope (SEM). The results show that T6 heat treated nanocomposites have significantly higher hardness and tensile strength compared to the nanocomposites without heat treatment. The enhancement in the mechanical properties is due to the formation of Mg2Si phase and globular silicon particles. Also, increasing of concentration of SiC nanoparticles led to improvement in hardness and tensile strength, so that the highest tensile strength and hardness was obtained for the 1.5 wt.% SiC nanocomposite. Tensile strength and hardness of 1.5 wt% SiC nanocomposites before and after T6 heat treatment achieved 177 MPa and 236 MPa and 80 HBN and 123 HBN, respectively. Fracture surfaces studied using SEM show that failure of all samples is brittle fracture.

Cable-Driven Parallel Robot has many advantages. However, the problems of cable collision between each other and environment, the lack of proper structure and non-positive cable tension prevent the spread of them. Therefore, connecting a serial manipulator to mobile platform improves the ability of object manipulation. This paper investigates the multi-objective optimization structure design and comparative study of spatial constrained and suspended cable-driven parallel robot. Installed serial manipulators possess a full hybrid robot’s features. The workspace volume, kinematic stiffness and sensitivity are three sets of optimization criteria. The workspace volume is calculated by a novel approach of combination constraints to prevent cables colliding with each other, cable collision with moving platform, uncontrollability and singularity of the robot. First, the range of forces and torque reaction of the serial manipulator to moving platform is examined. Then, the evolutionary optimization genetic algorithm is used for the multi-objective optimization of constrained and suspended spatial cable-driven parallel robot structure to achieve proper Pareto front confrontation. The Pareto front reconciliation of these three criteria will be discussed. The constrained and suspended optimized by the same criteria will be compared in the same conditions. It is confirmed that the constrained structure significantly reduced actuation energy to manipulate a serial robot, supply greater workspace and manipulability. The result of this study used for manufacturing and development of a prototype spatial cable-driven parallel robot (RoboCab).

This paper presents a nonlinear predictive approach for Stewart platform (6 degrees of freedom). The optimal control is computed directly from the minimization of receding horizon cost function with offline optimization. The main purpose of this research is to design the predictive controller for Stewart platform. In this study, the kinematics and dynamics of Stewart robot are introduced, considering the dynamics of actuators. Following the introduction of nonlinear model predictive control will be discussed and according to robot dynamics, controller will be designed. In addition, given the various uncertainties, robot dynamic equation could be rewritten. The controller is designed according to these uncertainties and then stability control is confirmed using Lyapunov theory. Due to the limited engine power and the output torque electric drive in practice, the proposed controller manages Stewart platform in such a way that it could track the desired trajectory well. To review the proposed method at the end of the study, Stewart platform is simulated and the control method proposed in this paper was compared with computed torque control (CTC) method, sliding mode control and Proportional-Integrator- Differentiation (PID) controller.

In this study, optimization of a solar cooling system assisted ground source Heat Pump system (GSHP) is performed. The optimization process was carried out using a multi-objective evolutionary algorithm. Three optimization scenarios, including thermodynamic single objective, thermoeconomic single objective, and multi-objective optimizations, are performed. In the case of multi-objective optimization, an example of a decision-making process for selection of the final solution from the Pareto optimal frontier is presented. It was concluded that the multi-objective optimization considers two objectives of thermodynamic and economic, simultaneously. The results obtained using the various optimization approaches are compared and discussed. It is shown that the thermodynamic optimization is focused on provision for the limited source of energy, whereas the thermoeconomic optimization only focuses on monetary resources. In contrast, the multi-objective optimization considers both energy and money. The results showed that percentages of deviation from ideal values of thermodynamic and economic criteria for the thermodynamic optimized system were 0 % and 905 % respectively. These percentages for the economic optimized system were 104 % and 0 %, respectively. Deviation values from minimum ideal point for the multi-objective optimized design were obtained 10 % and 88 % for thermodynamic and economic criteria, respectively. It was concluded that the multi-objective design satisfies the thermodynamic and economic criteria better than two single-objective thermodynamic and economic optimized designs.

In this paper the coupled lattice Boltzmann model is developed for simulation of multi-step combustion mechanism of methane jet diffusion flame. The lattice Boltzmann scheme employs the double-distribution-function model, one distribution function for solving flow field and another for temperature and species concentration fields. The density and temperature fields are coupled through low Mach number flow field. The solution parameters such as species properties and rate of chemical reactions are adjusted in each time step according to temperature and concentration of species variations. Using combustion mechanisms instead of one step fast chemistry reaction and considering effect of temperature and species concentration on solution parameters are the main advantages of the developed model. For validation of the model, fourstep reduced mechanism with six species is used for simulation of combustion in methane jet diffusion flame configuration. Results show that the developed model predicts the concentration of chemical species and flame temperature with good accuracy. It is important to note that the relaxation time in lattice Boltzmann equation must be function of both temperature and space to gain these results. Variation of the relaxation time eventuate in divergence of solution in usual LB Models. To overcome this problem the time steps are adjusted according to temperature variation. Agreement between the present results and experimental data confirms that this scheme is also an efficient numerical method for more detailed combustion simulations.

CCTV cameras are the main sources of inspecting sewer pipeline conditions, although they do not provide decisive information in both developing and developed countries. Managing sewage installations requires reliable quantitative and geometrical data on the conditions of pipes both inservice and after installation. Measuring the rate of sewage blockage has always been challenging. Various attempts have been made to develop and apply different techniques for the determination of pipe blockage, but most of them were not practical or comprehensive. Pipe profiling could be a novel method in this regard. The method proposed in this paper would be able to measure both the crosssection and profile of sewer pipes. This includes two infrared sensors and a servomotor attached to a measurement device mechanism. The set enters a sewer pipe and measures the coordinates of pipe cross-section points. Then, the collected raw data are transferred outside in order to be processed and later saved in a text file format. The saved data will be depicted as pipe cross-section 2D profile using the suggested and developed API package at SOLIDWORKS environment, which in turn will result in the availability of a 3D model of under-inspection pipes. It should be mentioned that different parameters of every desired pipe cross-section will be measurable as well.

Conformational changes during protein -protein or ligand -protein docking play an important role in the biological processes. These changes involve low frequency collective motions, and normal mode analysis is generally used for finding the frequencies and mode shapes of the proteins. Many studies have focused on the prediction of these transitions using different protein models. Among them, elastic network models are popular, as they are simple and do not require energy minimization. However, so far no systematic study has been undertaken regarding the effect of different parameters in prediction of these conformational changes. In this study, 20 proteins with pre-determined conformational changes were selected and the success and validation of each elastic network model in predicting the bound state were tested. According to the results, the first three modes play the major role in predicting the conformational changes. Moreover, choosing the proper cutoff radius is more effective than the potential function. Results also show that non-exponential models with 10 angstrom cutoff are more accurate in predicting conformational changes, in spite of their simplicity and being less time consuming.

Gas turbine blades operate at high temperature under mechanical loads; hence creep failure is the major concern in their design. To increase blade creep lifetime, it is necessary to reduce the blade temperature. For this purpose, cooling flow passes through the inner channels of the blade. In this paper, coolant heat transfer along the channels has been modeled and the effects of wall roughness and coolant’s specific humidity have been investigated. The blade body and cooling channels are regarded as a heat exchanger with thermal barrier coating and convective film cooling. A computer code has been developed to calculate the physical properties of the coolant as a function of temperature and humidity. Then, by taking into account the effect of wall roughness, convection coefficient and temperature distribution on the blade have been obtained using an analytical solution method. The results show that in the rough channels, coolant receives more heat from the blade body and consequently its temperature decreases especially in the critical section. It has been shown that with increasing humidity; the coolant temperature decreases along the blade span and consequently, the blade metal temperature reduces with about 2.5 percent. Also the result show that by increasing coolant’s humidity and roughness of the channels within a reasonable range, blade’s creep lifetime can be increased by up to 3.18 times.

In this paper, the flow field and mass transfer characteristics were evaluated numerically via Large Eddy Simulation in the presence and absence of the electric field in flat channel that is includes cavity containing water. Comparison of the numerical results with the experimental data was in good agreement with experimental data for prediction of flow field and mass transfer. Then, the effect of the Reynolds number variations in the different applied voltage on the water evaporation rate is investigated. The results indicate that applying the high voltage at the wire electrode can generate vortex and produce perturbation on the water surface. It is shown that at constant Reynolds number with the presence of the electric field, the Sherwood number will be increased but in constant applied voltage the Sherwood number will increase to the Reynolds of 3391 and then will decrease due to reduction in the size of generated vortex. Also, a linear relationship was obtained and relationship exists between the Sherwood number factor and the EHD number at Reynolds numbers greater than 3391. Finally, a relationship between dimensionless numbers like the relative Sherwood number, the Reynolds number and the EHD number was obtained.

In this paper, multi objective genetic algorithm is applied to optimize one type of recuperator in a 200 kW microturbine by considering two key parameters such as recuperator efficiency and cost. e-NTU method is selected for the recuperator efficiency and pressure drop calculation. The recuperator total cost consists of capital cost, operational cost and maintenance cost. A plate-fin heat exchanger with offset strip fin for counter and cross flow arrangements is chosen for optimization. Fin pitch, fin height, fin offset length, cold stream flow length, non-flow stream length and hot stream flow length are considered as six design parameters. NSGA-II (Non-dominated Sorting Genetic Algorithm) is conducted to maximize recuperator efficiency and minimize its total cost. Results of the optimization are presented as a set of designs, called ‘Pareto-optimal solutions’. The results reveal the conflict between the two objective functions. It can be concluded that any change in the geometry of the recuperator increasing the efficiency also increases the total cost and vice versa. Finally, the optimal designs are compared together based on non-dominated sorting concept and the final optimal designs are obtained.

Adding particles and fibers to the adhesive layer is a method suggested to improve the stress distribution and to increase the strength and toughness of adhesive joints. In this paper, the effects of adding the metal fibers and also the reduction of fiber horizontal distance on distribution of peel stress and shear stress toward longitudinal and transverse directions were studied using finite element analysis. The obtained results showed that the reduction of the horizontal distance between the metal fibers in the longitudinal direction improves the distribution of the peel stress and shear stress and leads to a significant reduction in their maximum values in the joint length with respect to the non-reinforced adhesive. Meanwhile, reduction of the horizontal distance between the metal fibers in the transverse direction first degrades the peel stress and then improves it. Despite the trend observed for the peel stress with the transverse direction, the distribution of the shear stress with reduction of the horizontal distance between the metal fibers becomes more uniform and the maximum values of shear stress regularly decreases in the joint length due to considerable load sharing of the metal fibers in the adhesive layer. In addition to the analyses carried out on the distribution of stress in the joints length, the distribution of peel stress and shear stress were also investigated in joint width, which was indicative of the significant effect of the metal fibers in the transverse configuration.

Electromagnetic forming is a high energy rate forming process applied for manufacturing and assembly of many parts that are used in automobile and aerospace industries. In this process, the electromagnetic body forces (Lorentz forces) are used to produce metallic parts. Joining high electrical conductivity parts by using electromagnetic forming process is an innovative method. Therefore, it is very important to use a proper technique to ensure the quality of the Strength of Electromagnetic Joints. In this article, this process was simulated in ABAQUS. Then geometric, physical and mechanical specifications of the tube and coil are entered to subroutine and the magnetic pressure is obtained; by applying them on tube in ABAQUS software, agent analysis of the process and deformation of the work-piece is obtained. The effective process parameters such as discharge voltage, clearance between the tube and die, wall thickness and length of the tube on depth of bead were experimentally investigated by design of experiment technique based on Taguchi Method and signal to noise. Finally, very good agreement was found between simulation and experimental results. The depth of bead in sequential coupled algorithm compared to experimental result had about 4% error.

Use of Forming limit diagrams (FLD) in process design of metal forming is a conventional method. Therefore many experimental and theoretical efforts have been carried out in order to investigate the FLDs. Many ways to obtain this FLDs and their effective parameters have been studied. But the stress state at these studies is planar which lead to an untrue model for several metal forming process such as incremental sheet forming. With this technique, the forming limit curve (FLC) appears in a different pattern, revealing an enhanced formability, compared to conventional forming techniques. Therefore, in this study, the effect of through thickness shear stress has been examined on the prediction of the forming limit diagrams (FLDs). Determination of the FLD is based on the Marciniak and Kuczynski (M–K) model with some modifications on the stress states for consideration of the through thickness shear stress effects. Also, the effective range of this stress has been investigated. The results showed that if the through thickness shear stress has a 10 per cent of yield stress value, this stress component has no effect on the FLD.

Using molecular dynamics simulations, the structural properties and vibrational behavior of single- and double-walled carbon nanotubes (CNTs) under physical adsorption (functionalization) of Flavin Mononucleotide (FMN) biomolecule are analyzed and the effects of different boundary conditions, the weight percentage of FMN, radius and number of walls on the natural frequency are investigated. As the functionalized nanotubes mainly operate in aqueous environment, two different simulation environments, i.e. vacuum and aqueous environments, are considered. Considering the structural properties, increasing the weight percentage of FMN biomolecules results in linearly increasing the gyration radius. Also, it is observed that presence of water molecules expands the distribution of FMN molecules wrapped around CNTs compared to that of FMN molecules in vacuum. It is demonstrated that functionalization reduces the frequency of CNTs, depending on their boundary conditions in vacuum which is more considerable for fully clamped (CC) boundary conditions. Performing the simulations in aqueous environments demonstrates that, in the case of clamped-free (CF) boundary conditions, the frequency increases unlike that of CNTs with fully clamped and fully simply supported boundary conditions. The value of frequency shift increases by raising the weight percentage of FMN biomolecule. Moreover, it is observed that the frequency shifts of SWCNTs with bigger radius are more considerable, whereas the sensitivity of frequency shift to the weight percentage of FMN biomolecule reduces and this is more pronounced as the simulation environment is aqueous.

The flight dynamics of nine configurations of supersonic continuous deflectable nose guided missiles have been investigated. The studied configurations consist of a spherical nose tip, a tangent ogive, a set of stabilizing tail fins and a cylindrical body having mid-section flexible enough to form an arc of circle. So the cylindrical body consists of a fixed part in the vicinity of nose, middle flexible part and main body with stabilizers. The effects of fixed length and flexible length parameters on the flight dynamics of surface to surface, anti-aircraft and antimissile missiles have been studied. A code has been developed to solve full Navier-Stokes equations using finite volume and modified Baldwin-Lomax turbulence model. Further, a 3 degree of freedom code has been developed to compare planar flight dynamics of missiles. This code consists of a guidance subroutine based on pure pursuit law. The results show that even increase of fixed and flexible lengths enhance the maneuverability of the missile, but in some scenarios this can lead to increased flight time and more errors in the target engagement. Deflected nose relocates mass center away from the axis and a thrust vector torque is created. Study of surface to surface scenario shows that this torque improves accuracy of targeting and the ability of target dislocation. In air defense missiles, increase of Fix and Flex variables will extend the limits of allowable firing angle. However, a heavy nose increases the role of thrust torque and subsequently decreases the role of nose geometry.

In this paper, a numerical method to extract rate coefficients of multi-step global reactions for combustion of hydrocarbon fuels with air regarding combustor operating conditions is presented and implemented. The numerical procedure is based on simultaneous interactions of two solvers including a solver for combustive field and another solver as numerical optimizer. A simple reactor solver, namely Perfectly Stirred Reactor (PSR) is employed as a solver for reactive flow, and chemical kinetics such as detailed, skeletal or reduced can be considered as benchmark mechanism. Considering rate coefficients of predefined multi-step global reactions as design variables for Differential Evolution (DE) optimizer and the difference between product concentrations obtained from benchmark mechanism and multi-step mechanism as cost function gives optimized values of rate coefficients regarding desired conditions. To confirm reliability and applicability of the present method, three different five-step models are generated for methane-air combustion under three different operating pressures (1.0, 6.28, and 30.0 atm.) and equivalence ratio ranges between 0.4-1.0 for predicting NO and CO emissions. Product concentrations such as NO and CO and flame temperature obtained from the presented five-step mechanisms are in close agreement with results obtained from the full GRI-3.0 mechanism. A comparative numerical study by means of Computational Fluid Dynamics (CFD) code has been performed for a laboratory scale combustor employing the generated five-step model and an eight-step pressure-dependent global mechanism (suggested by Novosselov) under operating pressure of 6.28 (atm.).

In the present work, optimization of air-cooled heat exchanger using structural theory of Bejan using fluent software has been investigated. Two constraints are applied in the optimization process: the first one is to fix the overall area of heat exchanger, A and second, the ratio of fraction of total heat exchange surface in the fixed pipe, Using these two constraints and the aforementioned theories, the best geometry, which is symmetric geometry of the tube and the fins, was obtained. Furthermore, the effect of parameters such as pressure, Stanton number, ratio of fraction of the convective heat transfer coefficients, ratio of fraction of the conductivity, and the number of ins, etc. was investigated. The results show that for tubular length of 5.8 cm and 4.3 cm radius, the fraction of optimal ins diameter to pipe diameter is 1.88 and the optimal number of ins is 7. By using software such as Fluent and Matlab, the ins height and the distance between the fins were investigated. According to structural constraints, structure was selected such that heat transfer from all the fins are equal. It was observed that the amount of the heat transfer was optimized by 6.2%.

In this work, an analytical micromechanical model based on unit-cell approach is used to study the effect of interphase on the non-linear viscoelastic response of multiphase polymer composites. The representative volume element of composite consists of three phases including unidirectional fibers, polymer matrix and fiber/matrix interphase. Perfect bonding conditions are applied between the constituents of composites. The Schapery viscoelastic constitutive equation is used to model the nonlinear viscoelastic matrix. Prediction of the presented micromechanical model for the creep response of polymer material and two-phase composites shows good agreement with available experimental data. Furthermore, the predicted overall elastic behavior of three-phase composites demonstrates close agreement with other available numerical results. The effects of material and thickness of interphase on the creep-recovery strain curves of three-phase composites are studied in detail. Results show that the interphase thickness and material properties have significant effect on the creep-recovery strain responses of the three-phase composites under transverse loading. According to micromechanical modeling results, it is found that the interphase negligibly affects the nano-linear viscoelastic behavior of three-phase composites under axial loading. Effects of the different stress levels and the variation of fiber volume fraction on the creep-recovery strain curves of three-phase composites are also investigated.

In this article, an experimental and theoretical study on the prediction of forming limit diagram (FLD) for aluminum alloy (2024-O) is developed. To identify and calibrate coefficients of YLD2004-18P, YLD2011-18P, YLD2011-27P and BBC2008-16P advanced yield criteria, tensile tests were performed in seven directions with respect to the rolling direction. Directional yield stresses and anisotropy coefficients were determined. Then, an appropriate error-function was defined and optimized by using Levenberg-Marquardt algorithm. By considering 8, 10, 12 and 14 anisotropy parameters, the effect of number of parameters on the accuracy of yield functions was investigated. The best condition with minimum error can be achieved when 14 anisotropy parameters are used. To compare the calculated yield stresses and r-values with experimental data, a method presented by Leacock was used. The results have shown that all four criteria give predictions of yield stresses which are close to experimental values. The prediction of yield stresses and anisotropy coefficients by means of YLD2011-27P and YLD2004-18P criteria have more correlation and good agreement with the experimental data, respectively. For obtaining experimental FLD Nakazima test was performed. In order to simulate the necking phenomenon and calculate the limit strains, the modified Marciniak- Kuczynski (MK) model, Swift hardening law and some new yield criteria including YLD2004-18P, YLD2011-18P, YLD2011-27P and BBC2008-16P were utilized. At the right hand side of FLD, YLD2004-18P and YLD2011-27P criteria and also at the left hand side YLD2011-27P criterion have shown better conformity with experimental results.

In this paper, the longitudinal vibration of nanorod based on Eringen’s nonlocal elasticity theory was studied using Rayleigh-Ritz method. non-uniform nano-rod with variable cross-sectional area, density and Young’s modulus were considered. In the present work, boundary polynomials with orthogonal polynomials were used as shape functions in the Rayleigh-Ritz method which causes the vibrational analysis to be computationally efficient and imposition of boundary conditions to be easier. Using the mentioned polynomials the convergence rate of the obtained results was increased. All of the equations used in this study are nondimensionalized to reduce the number of effective parameters in the solution. The influence of the nonlocal and inhomogeneity parameters on the vibrational behavior of nanorod was investigated. The results were compared to available results in the literature and good agreement was achieved. The results showed that nanorod frequencies were dependent on the small scale effect, nonuniformity, and boundary conditions. For instance, an increase in frequency ratio causes the scale coefficient in all vibration modes to be increased, especially in higher modes. In addition, the frequencies were increased by increasing in the length of the nanorod.

The chaotic behavior of a flexible rotor supported by active magnetic bearings is numerically investigated in this work. A statically unbalanced disk is mounted on the shaft. The rotor is modeled by three lumped mass and 8 D.O.F. The rotor-AMB systems include many non-linear factors, such as nonlinear function of the coil current and the air gap between the rotor and the stator, nonlinearity due to geometric coupling of magnetic actuator, eddy current effect and hysteresis losses of the magnetic core material. In this work, the influence of weight parameter on nonlinear response of the system is investigated. Numerical results showed considering weight parameter has an important effect on the response of the rotor and exhibits a rich variety of nonlinear dynamical behavior including synchronous, sub-synchronous, quasi-periodic and chaotic vibrations. Bifurcation diagrams, phase planes, power spectra, Poincare map and maximum Lyapanov exponents are used to analyze the response of the system under different operational conditions. Chaotic vibrations should be avoided as they induce fluctuating stresses that may lead to premature failure of the machinery’s main component. It will be beneficial to the design of AMB system.

One of the interesting and practical problems in thermo-fluid sciences refers to finding the shape of a boundary on which a specific distribution of pressure, temperature or heat flux is known. Because solving such problems using experimental, semi-experimental and analytical methods is timeconsuming or even impossible in some practical situations, myriad numerical methods have been introduced to solve surface shape design (SSD) problems. In all the numerical algorithms, an initial guess is modified through a numerical process until the desirable distribution of the target variable is achieved. All the numerical algorithms use three computational tools, i.e. grid generator, flow solver and shape updater to solve an SSD problem. In most numerical algorithms not only do the three mentioned tools work separately, but the shape updater is also not derived from the governing equations. In this article, to solve SSD problems containing convection heat transfer, a new shape design algorithm called direct design method is presented in which grid generator, flow solver and shape updater work simultaneously and also the shape updater is directly derived from the governing equations. Some SSD problems containing convection heat transfer in which instead of the boundary shape the distribution of the heat flux is known are solved using the proposed algorithm. The obtained results show the capability of the method in solving SSD problems containing internal convection heat transfer.

Values of tensile strength and hardness of different welding joint area has great importance. In this study combination of welding processes including Friction Stir Welding (FSW) and ultrasonic welding has been used in butt joint for ABS type plastic sheets. Ultrasonic vibrations are put on FSW rotary tool, then some parameter effects such as tool rotary speed, travel speed and tool shoulder diameter on tensile strength and hardness of welded samples have been studied. Taking parameter numbers and related levels for each into consideration, Taguchi method L18 array has been selected for performing experiments. Parameter effects has been studied separately. Results showed that ultrasonic vibration improves tensile strength and hardness of welded joint. After ultrasonic vibration, tool rotary speed, tool shoulder diameter and travel speed were the most effective parameters on tensile strength and hardness of joint respectively. Results from optimization with analysis method showed that ultrasonic vibration resulted in rotary speed of 1200 RPM, travel speed of 60 mm/min and tool shoulder diameter of 22 mm causes the highest hardness and tensile strength of joint simultaneously.

The equations of Lamb wave propagation in an infinite isotropic micro plate on the basis of consistent coupled stress theory is presented in this study. By employing the characteristic length scale parameter, the effect of micro-plate size is considered, and thereby the effects of different plate dimensions on the dispersion of Lamb waves is illustrated. Lamb wave propagation velocity in aluminum nitride microplates has received much interest due to its applications in surface acoustic resonators. In the current work, at first, the dimensionless relations are developed through the definition of dimensionless parameters where the extracted curves can be applied to all thicknesses, propagation wavelengths and characteristic length scale parameters of a micro-plate. In addition, using the quasi-static approximation, the Lamb wave dispersion curves in both symmetric and asymmetric modes for an aluminum nitride micro plate are plotted and compared with the results from the classical theory. The integrity of the present formulation is verified by comparing the obtained results with the experimental data in the literature. Finally, by employing the dispersion curves and the reported experimental data, a novel method has been proposed to determine the size of characteristic length parameter in the consistent coupled stress theory.

Interlaminar thermal stresses and boundary layer effect in thin laminated composite cylinders which are subjected to temperature change are studied. To this aim a laminated cross-ply composite cylinder with finite length which is subjected to thermal loading is modeled. The displacement based layer-wise theory (LWT) is used for modeling the response of the composite cylinder in the thermal loading conditions. Using an appropriate displacement field and employing the LWT, the governing equations of the cylinder and the appropriate boundary conditions in the edges of the cylinder are derived with the principle of minimum total potential energy. An analytical solution is introduced for the governing equations and the solution is obtained for various boundary conditions. The numerical results are validated by comparison of the results of LWT with the predictions of the finite element method (FEM) and good agreements are seen. It is shown that the presented LWT solution is an efficient and accurate method for analysis of the edge effect and interlaminar stresses in composite cylinders. The interlaminar thermal stresses and in-plane stresses in the Glass/Epoxy composite cylinder which are subjected to thermal loading are investigated for various boundary (edge) conditions. Cylinders with symmetric and asymmetric layer staking and free, simple and clamped boundary conditions are studied in the numerical results.

In this paper, an intelligent robust controller is proposed for a class of nonlinear systems in presence of uncertainties and bounded external disturbances. The proposed method is based on a combination of terminal sliding mode control and adaptive neuro-fuzzy inference system with bee’s algorithm training. For this purpose, a sliding surface is firstly designed based on terminal sliding control method. This sliding surface is considered as input for the intelligent controller which is an adaptive neuro-fuzzy inference system and using it, terminal sliding mode control law without the switching part is approximated. In the proposed method, an intelligent bee’s algorithm is also used for updating the weights of the adaptive neuro-fuzzy inference system. Compared with fast terminal sliding mode control, the proposed controller provides advantages such as robustness against uncertainty and disturbance, simplicity of controller structure, higher convergence speed compared with similar conventional methods and chattering-free control effort. The method is applied to an atomic force microscope for nano manipulation. The simulation results show the robustness and effectiveness of the proposed method.

In the present paper, to determine the pressure-dependent yield surface of polypropylene/nanoclay nanocomposites, the extended Drucker-Prager yield criterion is used and its parameters are derived by a combined experimental/numerical/optimization approach. In this method, the difference between the experimental and numerical results obtained from three-point bending test is minimized. In order to alleviate the burdensome numerical simulation, a surrogate model based on Kriging method is used to estimate the cost function. The optimum of this function is obtained by maximizing expected improvement method. Afterwards, the results are verified by tension and compression tests. The results show that this method can substitute the complicated experimental tests which are normally employed to identify the extended Drucker-Prager parameters. Also, this method can be used to determine the mechanical properties of thermoplastic material such as tensile and compressive yield stresses and elastic modulus using only a three-point bending test. In addition, it is found that the volumetric change of thermoplastic during plastic deformation is significant and the non-associative, compared with the associative, plastic flow assumption is more proper for this material for the extended Drucker-Prager criterion.

Simulation of the flow around propeller is a complex fluid flow problem, especially when the propeller is close to free surface. In this study, the effect of immersion depth, advance velocity and the ventilation phenomenon on the performance of a B-Wageningen series propeller close to surface of water have been numerically investigated. For this purpose the ANSYS-FLUENT commercial software has been used to solve the viscous, incompressible and two phase flow field. The rotation of the propeller has been implemented using the rotating reference frame model for steady flow and the sliding mesh for unsteady flow. For turbulent flow modeling and free surface simulation, the k- SST model and the volume of fluid method have been used, respectively. For validation of numerical results due to lack of access to experimental results of propeller close to surface, numerical solution in open water condition has been performed and performance coefficients have been calculated. Comparing the numerical results with the experiment ones shows good agreement and confirms the results of numerical simulation. Results of the numerical solution show that the submergence ratio and ventilation phenomenon affect the performance of propeller so that by reducing submergence ratio from 2.2 to 1.4 in advance ratio J=0.4, ratio of thrust and torsional moment coefficients to open water performance coefficients reduced to 7.7% and 6%, respectively.

Ionic polymer metal composite (IPMC) actuator is a group of electro-active polymers (EAPs) which bend in response to a relatively low electrical voltage because of the motion of cations in the polymer network. IPMC has a wide range of applications in robotics, biomedical devices and artificial muscles. The modeling of the IPMC actuator is a multi-physics task as it involves the electricity, chemistry, dynamics and control fields. Due to its complexity and nonlinearity, IPMC modeling is difficult in terms of mathematics and its behavior is still not fully agreed upon by researchers. This paper presents a novel discrete-time model with state-dependent parameters (SDP) for identification of the nonlinear response of an IPMC actuator. A single-input single-output nonlinear identification algorithm is formulated and demonstrated for an IPMC actuator that exhibits both soft and hard nonlinearities. The nonlinear characteristics of the identified system are represented with coefficients which are a function of the input and output states. Following the SDP algorithm, the model is identified from input–output data to represent the model parameters as functions of past inputs and outputs. The proposed modeling approach is validated using an existing model and shows exact representation of the non-linear behavior of the IPMC actuator.

In the present study, the bainitic form (ferrite-bainite-austenite) of Functionally Graded (FG) steel has been produced using the Electro Slag Remelting (ESR) process. The position of each layer has been determined utilizing the Metallography and Vickers Hardness tests. In order to investigate the fracture behaviour of the notched FGS specimens, the three point bending test configuration has been utilized. The fracture of the notched specimens has been examined in the form of the notch arrester and notch divider. For the mode loading case, the effect of the notch depth on the critical fracture load and Jcr value have been studied. In order to present the differences between the FG and homogeneous steels, the J values of them under constant load have been investigated. Moreover, the effect of the notch depth on the J values for the mentioned case have been studied. Results show that for the notch arrester type the maximum value of the critical facture load has been obtained when the notch tip is located at the beginning of Bainite phase. Results also show that the Jcr values are severely dependent on the material properties of the layers which are located at the front of the notch tip. Results show that for the notch divider type the response of the FG steel specimens is similar to the homogeneous ones. Also, in this case the variation of the Jcr with respect to the notch depth is negligible. The J value of each of the studied configurations was then computed using finite element approach based on Rice theory and good agreement was observed between numerical results with the experimental ones.

In the present work, constructal design of annular finned tube has been studied. Geometrical parameters include fin diameter, fin thickness, fin pitch, tube outer diameter, tube length, while physical parameters involve pressure drop number, Stanton number, fin-to-air conductivity ratio, and in-tube fluid-to- air conductivity ratio. The aim of this study is to enhance heat transfer by allowing the geometrical degrees of freedom to morph. It was observed that at certain flow conditions, there exist optimal geometry and fin number for the finned tube construct in which its thermal resistance is minimum. Fin efficiency and tube-side convective heat transfer coefficient are higher at low pressure drops and Stanton numbers. In these conditions, analytical relationships were proposed to predict optimal heat transfer, optimal fin number and optimal geometry. It was seen that the optimal fin thickness-to-fin pitch ratio is merely dependent on the fin volume fraction; and it rises with the increase in fin volume fraction. Moreover, the optimum fin number is directly proportional to fin spacing – to- fin pitch ratio and inversely proportional to Stanton number. Furthermore, it was seen that in the range of parameters considered in this study, the tube with 3400 fins and aspect ratio of 0.63 has the highest heat transfer rate.

In this study, a numerical method is used to investigate the effects of convergence primary nozzle on the air ejector performance used in Polymer Electrolyte Membrane Fuel Cell (PEMFC). Simulations have been performed by solving the compressible form of two-dimensional Navier–Stokes equations. The turbulence model has been employed to estimate the turbulent region. A comparison of the computed results with the published experimental data exhibits agreement in terms of entrainment ratio at defined operating conditions. The ejector with convergence nozzle is widely used in the aerospace science, jet engine and Polymer Electrolyte Membrane Fuel Cell, because it has many advantages such as jet noise reduction, preventing condensation of water vapor inside the ejector and improvement of conventional converging-diverging nozzle. According to several applications and advantages of convergence nozzle, effects of primary converging nozzle on the flow characterization and the ejector performance have been studied at any part of its. Based on particular application of the ejector with convergence primary nozzle in PEMFC, performance improvement is the purpose of this study. The results have been compared with air ejector with convergence-divergence primary nozzle. The results show that the air ejector performance has been enhanced under changing primary nozzle structure. This means that the ejector can consume available energy in its operation processes optimally besides increasing drawn secondary flow.

Wheeled mobile robots able to inspect pipe interior are typically used in industry. One of the major evaluations of these robots performance is mobility in limited spaces and special environments. Unanticipated area and obstacles along the robot path is one of the major challenges of robot success in missions. In this paper a novel module for increasing the robot traction when encountering small obstacles, paddle or large deposit is introduced. In addition, the mechanism increases the robot traction when moving in high inclination pipes. The mechanism consists of two links mounted beside the four wheel drive robot. When the robot is faced with an obstacle or a paddle and cannot move further, although the robot wheels rotate, contacting the module’s links to pipe surface changes the balance of normal forces applied between the pipe and wheels. Further, when the links are extended to contact the upper part of pipe, the wheels normal forces are increased, providing a higher traction force consequently. Length of links may change in addition to its rotation. So, a two DOFs mechanism is provided in which one motor is used as actuator. For switching active DOF, a locking mechanism is utilized using shape memory alloys actuators. The analysis and simulations show the capability of mechanism in increasing the robot traction. The mechanism performance is validated through ADAMS dynamic modeling software.

In this paper, efficiency of defected graphene nano ribbon incorporated with additional nanoparticles on mass detection operations is studied via the Reverse Non Equilibrium Molecular Dynamics (RNEMD) method. Thermal conductivity management of this structure is challenging because of imposed losses in electrical conductivity and any procedure that could manage the thermal conductivity of grapheme will be useful. In this paper it is observed that on the mass detection operation, due to the porosity generation in the nano ribbon surface or even creation of external nanoparticles, thermal properties of graphene change considerably. This should be noted in calibration of graphene based mass sensors. In summary, Results show that the graphene’s thermal conductivity would reduce by increasing the concentration of nanoparticles and thermal conductivity of graphene is higher when porosities and impurities are at the edges. This indicates that the location of vacancies and nanoparticles influences the thermal conductivity. For a better thermal management with the help of nanoparticles, with respect to the porosities, addition of nanoparticles decreases the thermal conductivity more and more. By increasing the cavity’s diameter from 0.5nm to 4.4nm in a specific single layer graphene, thermal conductivity was reduced from 67 W/mK to 1.43 W/mK.

Conjugate heat transfer is one of the most important aspects of energy conversion and plays an important role in the thermal efficiency and fuel consumption of chambers. In the present work, a twodimensional model for reacting flow is presented to calculate transport equations of mass, momentum, energy and species. A new solver is developed for the open-source OpenFOAM software. This new solver is able to predict the conjugate heat transfer effects of reactions and transport processes in fluid and heat conduction in solid as well as radiation in surrounding surface. The coupled method is used and the continuity of temperature and heat flux on the fluid and solid interface is applied in order to analyze conjugate heat transfer through boundary conditions. Experimental data of honeycomb burner is used to validate the new solver. Numerical results are in good agreement with the experimental data. The results show that change of fluid inlet condition and geometry dimensions affect the interaction of conjugate heat transfer and location of released heat of combustion. The location of flame is moved toward outlet as the inlet velocity is increased and toward inlet as the equilibrium ratio is increased. Increasing the length and thickness of solid reduces the preheated area as well.

In this article, energy consumption properties of 13 random residential complexes with different construction characteristics have been examined and compared. These properties are consist of façade type, cooling and heating system, window type and the gas meters being united or separated for each unit. While introducing selected complexes, their envelope specifications, heating and cooling systems and energy agent used for them are considered and then the energy analysis is done for each of them. At first the energy consumption ratio factor is introduced then the energy consumption ratios are calculated and compared for selected complexes. The comparison of energy consumption ratios show that the use of new construction materials such as metal board facades (decorative sandwich panels) instead of conventional bricks, two- layer windows instead of one-layer one's and using the semi-central heating and cooling systems instead of mechanical rooms, water heaters or heaters can reduce the energy consumption of a building significantly. Also using separated gas meters instead of united type can affect resident's consumption pattern and cause financial motives for them to save energy and therefore the natural gas consumption and energy consumption ratio can be reduced.

In this study, the accuracy of steady and unsteady methods in predicting the required length of air-earth heat exchangers has been compared for cooling application. Also, the impact of different conditions for inlet air temperature (constant, periodic and actual temperature) on unsteady methods has been studied. Results indicated that, steady model cannot provide correct estimation for the required length of channel. In addition, using unsteady method with constant inlet air temperature overestimates the required length of the channel, which can lead to economic and implementation challenges for project. However, using unsteady method with periodic inlet air temperature, allows the required length of the channel can be estimated with acceptable accuracy compared with real situation (unsteady model with actual inlet air temperature).