نشریه مهندسی مکانیک مدرس
سال چهاردهم شماره 2 (اردیبهشت 1393)

Parallel piezo-flexural nanopositioning stages are extensively used in advanced nano-scale imaging and manipulation applications such as scanning probe microscopy systems. One of the major deficiencies of these devices is the coupled motion between their different axes. That is, the motion of stage in one direction interferes with motions in the other directions, leading to undesirable disturbances. In this paper, analytical, dynamic, experimental, and finite element analyses are carried out to investigate the major root cause of the cross-coupling effect. Using ABAQUS FEA software, a 3D model of the stage has been developed. Model consists of a central elastic body connected to the fixed frame through four flexural hinges. A cylindrical stack of multiple piezoelectric layers is placed between the moving central body and the fixed frame. Simulations are carried out for two different friction coefficients in the contact surfaces of the piezoelectric layers, and for different frame materials. It is observed that the main cause of the cross-coupling effect is the rotation of piezoelectric stack due to its friction with the stage moving in the tangential direction, concurrent with a change in the geometry of the stage.

Sheet metal components frequently are used in industry. There are several methods to produce them. Progressive die one of the most widely applied devices to sheet metal components manufacturing. The progressive dies reduce the time and cost of producing complex sheet metal components. However, the design and manufacture of these dies are difficult. CAD/CAM systems have been proved to be very useful tools for this task. In this paper, two the important stages of die design process, Nesting and Piloting system are studied. By using fuzzy set theory and three fuzzy rules: scrap percentage, type of pilots, distance between pilots, the optimum state of nesting and piloting is determined. These rules are applied according to expert comments and industrial observations. According to our investigation, piloting accuracy impresses the final nesting design, thus a new fuzzy rule based on distance between pilots is proposed in this paper. The presented method is based on algebra algorithm that it determines suitable and exact place of semi-direct and indirect pilots and decrease calculation time. Three components taken from industry and previous papers are used to show the capability of the proposed method.

Drilling is the most widely used process for producing holes through the manufacturing parts. Drilling, as well as other machining processes, produce undesired raised material on both entrance and exit edges. The raised material caused by plastic flow is defined as burr, which is necessary to be removed for critical and precise part. In this work, magnetic abrasive deburring (MAD) was used to investigate the deburring performance of stainless steel. Firstly preliminary simulations were carried out by Maxwell software to determine appropriate MAD tool. Then, influence of MAD variables such as height of gap, mesh number and rotational speed were studied on burr height variation. Results indicated that mesh number of abrasive particles has the dominate effect in burr removal of stainless steel plate by this process.

This paper studies the effects of soluble cutting fluid-based CuO Nanofluid on machining force and surface roughness in turning of hardened AISI 4340 tool steel. These influences, Moreover, are compared with the outputs of similar tests through dry and soluble cutting fluid. The obtained results showed 1% volume fraction of CuO Nanoparticles added to soluble oil as cutting fluid was considerably reduced machining force and surface roughness in comparison to soluble cutting oil and dry. The investigations indicated that CuO Nanofluid reduced surface roughness and machining force by 49% and 24% respectively. Moreover, the results illustrated that the lowest surface roughness obtained in cutting speed 250 m/min, feed rate 0.1 mm/rev and cutting nanofluid.

Inspired by the muscle arrangement of the octopus and skeleton of the snakes, a wire-driven serpentine robot arm has been simulated and constructed in this article. The robot links which are connected via flexible beam act as the snake backbone. Instead of using motors at each joint, four sets of wire are employed as octopus muscles to drive the robot arm. For the spatial inverse kinematics, after determining the generalized coordinates of the system, governing algebraic equations of the system including constraint equations of the joints and cables and favorable movements have been determined. For displacement analysis, these equations have been solved using the Newton-Raphson method. Using this method robot workspace has also been determined.For the inverse dynamics of the robot, cables tension force has been considered as external forces. Using Embedding technique with specified constraint matrix, mass matrix and acceleration vectors that are determined from inverse kinematics, cables tension force and torque of motors are specified. To validate the snake robot model, a prototype has been built and programmed for some circular and arcuate routs. Travelled pass by end effector have been obtained. Comparing the results with the desired path, accuracy of the designed robot has been investigated.

In this paper, the experimental behavior of grid cylindrical composite structures which are used widely in engineering structures under ballistic impact is investigated. In the present study, the grid cylindrical composites were manufactured by the filament winding process with fiber placement procedure and perforated by projectile using the ballistic gas gun. Input and output velocities of projectile were recorded. The results show that presence of discrete ribs prevents spread damage from one cell to it’s adjacent cells and structure behaves differently against projectile with velocity near ballistic limit velocity and higher velocities. With approach to the ribs location ballistic limit has been increased. However due to reduce fracture area, overall and local deformations after impact in velocity which is higher than ballistic limit velocity, projectile has been came out from grid samples with higher velocity than simple composite shells. In this paper, delamination in outer composite shell and ribs, debonding between shell and ribs, residual velocity of projectile, fracture area of the grid specimens and the effects of curvature in two deferent velocities were reported and commented upon as results.

Syntactic foams are a kind of composite; consist of polymeric matrix and hollow micro-balloons. They have high strength to weight ratio if it compare to the neat matrix material. In this paper epoxy resin as matrix and ceramic micro-balloons are used and 36 kinds of syntactic foam were fabricated to investigate the effect of preparation factors such as: mixing speed, mixing time, mixing sequence and extracting bubbles by a vacuum oven on the mechanical properties. Also, two undesirable events like micro-balloon flotation in matrix and porosity are investigated as they affect the foam`s strength. The results show that the speed and sequence of mixing are not effective seriously. However the time needed for mixing would be changed for different volume percent of micro-balloons. It should be noted that as flotation and porosity increases the compression strength decreases. Using the vacuum pressure before molding may decrease the matrix porosity for above 40% micro-balloon volume fraction syntactic foams. Converse to previous, using the vacuum pressure for below 40% micro-balloon volume fraction syntactic foams would increase the floatation and decreases the compression strength.

In the PEM fuel cells, gas phase (air and vapour) and liquid water could simultaneously flow through the cathode Gas Diffusion Layer (GDL). On the other hand, the performance of fuel cell and the main characteristic parameters of the flow can be influenced by the interaction of these gas and liquid phases. In the present study, the main parameters of two-phase flow in the GDL such as capillary pressure, mole concentrations of gas species, gas velocity and liquid velocity have been evaluated by considering the interactional effects of the aforementioned two phases. Also, the impact of changing the value of cathode channel humidity and fuel cell temperature on the value of the mentioned parameters has been investigated. The results indicated that decreasing of relative humidity in the cathode channel causes an increase in the rate of water vaporization. Thus, this leads to a decrease in the liquid water velocity, capillary pressure gradient and saturation gradient in the GDL. Also, increasing the temperature causes an increase in the rate of water vaporization and a decrease in the gas velocity and gas pressure gradient.

In this paper, dynamic analysis of simply-supported composite sandwich beam under a moving mass including rotary inertia and transverse shear deformation are investigated. Governing equations are gained using Hamilton's principal. Modal superposition method used to deriving ordinary differential equation of motion in matrix form. Fourth order Runge-Kutta method applied to solving the ODE with time varying coefficients. Parametric studies such as effects of stacking, aspect ratio, core thickness and stiffness, mass and speed of moving load on the midpoint deflection, dynamic magnification factor and critical speed have been studied. The obtained results show that core thickness and stiffness have considerable effects on critical speed. Inertia of moving mass has distinct effects on dynamic response of beam depend on load velocity.

As the coefficient of performance and the cooling power of adsorption chillers are low, the irreversibility calculation can identify the sources which limit the increase of performance parameters and effectively be used in association with current performance improvement techniques. Adopting the numerical modeling and calculating the temporal distribution of temperature in adsorber elements, this study measures the exergy destruction in different parts and processes of the adsorbent bed. The results show the maximum exergy destruction rate in isosteric phases, yet the total exergy destruction is low due to the short phase times. The highest total exergy loss is observed in isobaric heating phase due to the high irreversibility of desorption process and also long phase duration. Furthermore the effects of fin height and fin spacing on the exergy destruction of adsorbent bed are investigated. The results show that increasing fin height and fin spacing increase the total exergy destruction; however the dependency of fin spacing on exergy destruction is relatively low.

Due to growth of energy consumption and depletion of fossil fuels sources, power generation of renewable energy sources such as wind energy has become one of the main interests of researchers. Among different types of wind turbines used for extracting electric power from wind flow, vertical axis wind turbines can be implemented in urban areas and in proximity of energy consumers because of their independence of wind direction, low sensitivity to wind turbulence and lower noise production. In this paper a straight-bladed vertical axis wind turbine has been simulated 3 dimensionally by use of a commercial CFD code. The numerical results have been validated against available experimental data. To improve the performance of the turbine, the effects of blade mount point offset and preset pitch have been investigated. The results show that appropriate blade offset and preset pitch for this case study leads to a 60 and 65 percent increase in the maximum performance coefficient respectively.

In this study, the collision of two drops using Lattice Boltzmann numerical method in two-phase flow has been investigated. The simulation for incompressible fluid is based on the model represented by Lee. The prominent feature of this model is to simulate fluids with high density ratios. Thus, the model has easily been compared with experimental results and its validity has been investigated. Using this simulation, the variation of non-dimensional parameters such as Weber number, Reynolds number, Impact parameter, density ratio, kinematic viscosity ratio, diameter ratio and velocity ratio of two drops were studied. Considering the results, it was shown that the Reynolds number, density ratio and relative velocity ratio have no effect on separation or coalescence of drops collision; while the variation of Weber number, Impact Parameter and kinematic viscosity ratio results in separation or coalescence. Moreover, by increase in Weber number, Reynolds number or density ratio or decrease in kinematic viscosity, the number of oscillations and the time needed to reach equilibrium increases. Likewise, the amplitude of oscillation and the deformation of the drops increase when the Weber number, Reynolds number or density ratio rise or the kinematic viscosity lowers.

In this research, the effects of cutting parameters on material removal rate and surface roughness, are investigated. Therefore, after that the comprehensive model of low-immersion milling is developed, the optimum cutting conditions has to be found for optimizing all of them. The stability criterion is considered as the optimization constraint which is calculated by TFEA. On the other hand, instead of using explicit equation for calculating surface roughness, such as previous works, surface roughness is calculated by TFEA for all of the cases that are needed. Finally, the ability of Genetic algorithm, Particle Swarm Optimization and Imperialist Competitive Algorithm for searching optimum cutting parameters are compared and the results are reported. By comparing the results of the three algorithms it is shown that the ICA is more powerful to deal with nonlinearity aspects of the problem and to tackle sticking in local minimums. Also it is demonstrated that the convergence rate of the ICA is faster than the other two methods. Finally, experiments to confirm the changes of the objective function toward optimal point are done and error percentage of objective function at obtained optimal point compared with experimental result is determined.

An optimum humidification of the reactant gases of proton exchange membrane (PEM) fuel cell extremely affects its performance. Here, an analytic model of a membrane humidifier for PEM fuel cell is proposed where the effect of mass flow rates, inlet temperatures and pressures are investigated. The governing equations: water transfer equation and the law of conservation of energy in whole humidifier are written, which form a Non-linear system of equations, solved through FORTRAN software. At each stage, the outlet temperatures, the water transfer rate, relative humidity and the dew point at dry side outlet are calculated and discussed. The closer the dry side outlet dew point to the wet side inlet dew point, leads to the better humidifier performance. The results show that an increase in mass flow rate at dry side inlet leads to the weaker humidifier performance; while, an increase in mass flow rate at wet side inlet leads to the better performance. An increase in the pressure at dry side inlet enhances humidifier performance; while, the pressure at wet side inlet does not affect significantly on humidifier performance. Here, preheating the dry gas is not essential and use the cooler wet gas is recommended

Solar field transfer heat of solar radiation to the heat transfer fluid. Appropriate size of solar field is one of the most important parameters in levelized cost of solar electricity. In this paper optimum solar field size in an integrated solar combined cycle is determined. Furthermore, an algorithm is presented for the simulation of parabolic trough solar collector performance. Four solar fields by different size but same power block are considered. Thermal performance of each field in terms of nominal and partial load conditions is studied. Solar field and combined cycle are simulated by coding in EES software. According to The hourly meteorological data, electricity generated for a year is calculated. Levelized cost of solar electricity for each field size is calculated and optimum size of the field is selected. According to the economic analysis, the optimum solar field size in an integrated solar combined cycle is depended to location of plant, HRSG power demand, and the constraints of the power block and solar field.

Dynamic model identification and state variables estimation from the corrupted measurement data have been attracted much research efforts during the recent years. In this way, Kalman and H-infinity filters have been increasingly used to estimate the parameters individually. In this paper, a mixed kalman-H_∞ filter is designed in an innovative approach using a multi-objective optimization method. It is desired to simultaneously employ the advantages of both filters to minimize both the root-mean squared errors and the upper bounds limit of estimation errors associated with Kalman and H-infinity filters, respectively. Some Pareto optimum design points are presented for two case studies from which trade-off optimum design points can be simply selected.

Forming limit diagram (FLD) shows the formability of metal sheets under different loading conditions before that necking is taken place. In this paper, the application of plastic instability criterion for prediction of necking and also FLD has been investigated. Using Balart’s anisotropic yield function and plastic instability criterion in different strain ratios, limit strains have been calculated, and then the limit strains have been converted to limit stresses. To verify the analytical results, a free bulge setup with the ability of applying the axial feeding has been fabricated. Tubes have been undergone different loading paths and different plane strain conditions have been induced to obtain FLD. FLDs which have been obtained using plastic instability criterion have been compared with experimental results. The results show that swift instability criterion for tubes have the best prediction of FLD in tube hydroforming process.

In this paper, the effect of gas and liquid inlet superficial velocities and distance from upstream on slug frequency is studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for liquid holdup αl= 0.75 and three distances from inlet in a long horizontal channel made of Plexiglas with dimensions of 510 cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.11-0.56 m/s and 1.88-13 m/s, respectively. The obtained results show that slug frequency is dependent to superficial liquid velocity directly. Slug frequency decreases with slip ratio increase. Slug frequency has strong dependency on superficial liquid velocity and increases monotonically with it. However, superficial gas velocity has damping effect on slug frequency. As slug moves towards downstream, slug frequency will be decreased but slug velocity will be increased.

In the present paper a micro-pelton turbine with very small dimension has been studied. This micro turbine was designed for 15 kW output power and was utilized in KhorasanRazavi. To analyze and evaluate the efficiency and effectiveness of physical and geometrical parameters, the turbine flow was simulated using the commercial software Ansys CFX 13 and the simulation results of the performance point were compared and evaluated with experimental results. Because of complexity of simulation and heavy computation, instead of entire turbine, just a part of it containing several buckets was simulated. A 3D transient flow simulation was applied using the SST turbulent model. In order to model two-phase flow, the standard homogeneous free surface model was employed. In the results the effect of rotating speed on the efficiency was investigated. Moreover, the effect of physical parameters: flow rate and head and geometric parameters: the distance from nozzle to the axis of buckets, the number of buckets in constant pitch circle diameter and constant bucket size, the number of buckets in constant pitch circle diameter and variable bucket size and the number of buckets in variable pitch circle diameter and constant bucket size on the performance of a micro-turbine was investigated.

Patients with medial compartment knee osteoarthritis (OA) may exhibit different kinematics during walking according to the disease stage, also most of differences are in the frontal plane. The objective of this study was to compare lower extremity kinematics in frontal plane between medial knee OA patients and control subjects.Three dimensional gait analysis was performed on 25 women (35 to 53 years old): 10 control subjects, 10 mild medial knee OA and 5 moderate medial knee OA patients. Kinematics waveforms were reduced dimensionally by using Principal Component Analysis (PCA). PCA scores were compared between three groups (control, mild OA and moderate OA) with ANOVA and Post-Hoc TukeyHSD statistical analysis. Ankle of mild OA patients had a leaning towards inversion and moderate OA patients had a leaning towards eversion. Patients with mild OA, had smaller range of ankle motion than two other groups (p>0.05). Knee adduction angle increased with progression of OA severity (p>0.05). Range of hip motion in frontal plane decreased with progression of OA severity and this difference was significant between mild and moderate OA groups (p=0.05).

The Incremental Sheet Metal Forming (ISMF) process is a new and flexible method that is well suited for small batch production or prototyping. In this study, after the process simulation with ABAQUS software and verification of results through experimental tests, the effects of three parameters including friction coefficient, tool diameter and vertical step size on three objectives including vertical force, minimum thickness of deformed sheet and amount of spring-back are investigated. A neural-network model is developed based on simulation data and the effects of parameters are studied on each objective. Also multi-objective genetic algorithm is performed to get the Pareto front of optimum points.

The purpose of this paper is to investigate the effect of unsteady trailing edge flapping on lift generation for fixed airfoils at low angles of attack. To do this, a 2D unsteady compressible flow around a fixed airfoil is analyzed at different angles of incidence by means of Coarse Grid CFD (CGCFD) method with spring dynamic network. In this method Euler system of equation is solved with coarse Grid and no slip boundary condition using vorticity confinement technique. At first for code validation, the results of fixed airfoil at different angles of attack and also pitching airfoil are compared with experiments. Further, the CGCFD consequences are compared with the results of RANS with SA turbulent model in the quasi steady case. Then trailing edge flapping (TEF) is added to the fixed airfoil at low angles of attack. The effects of unsteady parameters such as the amplitude and the frequency of TEF are investigated at different low angles of attack. The results show that in a specific low angle of attack, adding TEF results in increasing the lift coefficient comparing with the fixed airfoil without TEF.

Cold spray is a process which is used in coating industry and manufacturing of new parts. Experimental studies of this process are expensive and also very difficult due to high velocity of particles. Therefore, one effective method to study this process is its computer simulation. Previous works show that the Johnson-Cook hardening law has been usually used for simulation of this process. However, it is unanimously believed that this model is not able to reproduce the material behavior at extremely high strain rates commonly occurred in the cold spray process. Therefore, the simulation results are expected to improve if a suitable material model for extremely high strain rates is used. In this study, the PTW1 model was implemented in ABAQUS commercial finite element package. The cold spray process was then simulated for copper using both the PTW and Johnson-Cook hardening models. A comparison between the simulation and experimental results showed that the PTW model did improve the simulation results. The predicted flow stress by Johnson-Cook model was also shown to be not so sensitive to strain rate at extremely high strain rates.

Acoustic Emission technique is a non destructive method which can be used for detection of corrosion mechanism. In this paper the corrosion of sulfuric and hydrochloric acids solution on some kinds of stainless steel like 304, 316 and GTD-450 with and without residual stress was surveyed by acoustic emission technique. Considering tests diagrams, cumulative counts in the samples with residual stress is more than other ones due to high sensitivity of stainless steel samples to stress corrosion cracking. Also frequency in the samples with residual stress is lower than other ones. Cumulative count in the stainless steel 304 is more than stainless steel 316 for all of the samples. A sudden and intensive corrosion in the hydrochloric acid environment was observed specially in the samples with residual stress. For stainless steel 304, this event was very harmful, because, it will the cause of some pitting corrosion, which concentrates stress in these locations and finally creates crack in structure.