Modares Mechanical Engineering
Year:2015 | Volume:15 | Issue:2|Papers Count:37

Nowadays, computer simulations are becoming more and more important in performance investigation of thermal systems. In this article, radiator from a cooling system of a diesel engine of ER24PC locomotive is simulated. The radiator is composed of parallel and series arrangement of compact heat exchangers with offset strip fins. It also has two high and low temperature sections. Due to the complexity and compactness of heat transfer plates implemented in the radiator, the simulation is carried out in two steps. First, a relation for coolant-side and air -side heat transfer coefficient is correlated using computational fluid dynamics. Due to vortex shedding phenomenon in the staggered fin arrays, governing equations are solved transiently in twodimensional space. Appropriate timestep for the transient solution is chosen according to time period of vortex shedding from the surface. In the second step, using the developed computational code, the overall thermal performance of the radiator is simulated as a heat exchanger. Consequently, temperature distribution inside the radiator and its thermal performance are studied. Amount of heat released from the radiator in different flow rates and temperatures of fluid flowing out of the radiator are among the outputs of the developed code. Finally, thermal performance curve of radiator is obtained.

In this paper, 3-D simulation of heat transfer in a power electronic device and its cooling system is performed. The device is a high voltage three-phase inverter manufactured by Semikron Company; its main application is in electric and hybrid vehicles. Cooling system is a forced-air plate-fin heat sink. A limitation factor of designing heat transfer is maximum temperature of the inverter’s chips, heat sources, called IGBT. Maximum temperature of IGBTs should be below 125oC in order to avoid both the thermal and the mechanical failures. One of the primary objectives is the reduction of the maximum temperature by designing the layout of chips. Also, the heatsink geometry design is accomplished by taking intoconsideration the maximum temperature and tradeoff between both the usage material volume and the heatsink efficiency. Geometries are the number of fins, the fin height, fin thickness and the base thickness of the heatsink. The power dissipation is estimated using datasheet information and output waveforms obtained from simulation in MATLAB. A thermal model of the inverter and its cooling system are simulated by using finite-element method (FEM). The accuracy of the thermal model and power dissipation estimation are verified by Semisel software. The maximum temperature is significantly reduced about 20ᵒC by designing the layout precisely. Also, the heatsink efficiency is increased 10.35%, 16.67% and 27.51% with the increase of the material volume about 22.52%, 13.51% and 0% for the heat transfer coefficient, 50, 75 and 100 (W/m2.K) by good design of the heatsink geometry, respectively.

In this paper, elastic-plastic symmetrical buckling of a thin solid circular plate of variable thickness under uniform edge pressure is investigated, based on both Incremental Theory (IT) and Deformation Theory (DT). Two kinds of simply supported and clamped boundary conditions have been considered. A power-law function was assumed for thickness variation. To minimize the integral uniqueness criterion, based on Rayleigh-Ritz method, transversal displacement was approximated by a test function which includes some unknown coefficients and satisfies geometric boundary conditions. Substituting the test function in the stability criterion and minimizing with respect to the unknown coefficients results in a homogeneous algebraic set of equations in terms of unknown coefficients. For non-trivial solution, the determinant of coefficient matrix should be equated to zero. Using this equation, critical buckling load is determined. The results of the present study were compared with existing analytical solutions for circular plate of constant thickness and a good agreement was observed. This clearly shows the validity of the presented analysis. Then the effect of thickness variation and boundary conditions type on the critical buckling load was investigated for commercial aluminum and steel 1403 materials. The results show that when the thickness of circular plate center is 10% greater than its edge thickness the buckling load may increase up to 40% compared with the circular plate for which the center thickness is 10% less than its edge thickness.

Employing complex surfaces in different industries such as aerospace and die and mold is increasing. For milling of such surfaces, taking factors such as strategies and machining parameters which affect the machinability into consideration is necessary. The objective of this study is to investigate the effect of different strategies and machining parameters on microhardness of a typical curved surface (convex) of stainless steel 1.4903. The cutting tool used in this study was ball nose end mill coated TiN and the strategies employed were Raster, 3Doffset, Spiral and radial. Design of experiments was done using Taguchi method. The input parameters were cutting speed, feed rate and step over. After conducting experiments, surface layers hardness of milled samples were measured. The results showed that various tool paths have different influence on microhardness of milled surfaces. Regardless of cutting condition, surface hardness after machining in all strategies was more than the primary hardness of the workpiece material. Spiral strategy provided the maximum hardness and radial strategy the minimum hardness. In addition, increasing the feed rate, cutting speed and step over, increased surface hardness and step over had the least influence on hardness. The maximum hardness magnitude was reported in cutting speed of 180 m/min, feed rate of 0.18 mm/tooth and step over of 0.7 mm which shows 56% increase.

This study attempts to numerically investigate the hydro-thermal characteristics of a ferrofluid (water and 4 vol % Fe3O4) in a counter-current horizontal double pipe heat exchanger, which is exposed to a non-uniform transverse magnetic field with different intensities. The magnetic field is generated by an electric current going through a wire located parallel to the inner tube and between two pipes. The single phase model and the control volume technique have been used to study the flow. The effects of magnetic field have been added to momentum equation by applying C++ codes in Ansys Fluent 14. The results show that applying this kind of magnetic field causes kelvin force to be produced perpendicular to the ferrofluid flow, changing axial velocity profile and creating a pair of vortices which leads to an increase in Nusselt number, friction factor and pressure drop. Comparing the enhancement percentage of Nusselt number, friction factor and pressure drop demonstrates that the optimum value of magnetic number for Reff=50 is between Mn=1.33×106 and Mn=2.37×106. So applying non-uniform transverse magnetic field can control the flow of ferrofluid and improve heat transfer process of double pipe heat exchanger.

In this study, the water entry problem of a spherical-nose projectile is investigated numerically and experimentally. For the numerical simulations, a three dimensional model of the projectile with six-degree-of-freedom rigid body motion is considered. A Coupled Eulerian-Lagrangian (CEL) method is employed for modeling fluid-structure interactions. Through Eulerian- Lagrangian contact, Eulerian material can interact with Lagrangian elements. Also, an equation of state model describes the hydrodynamic behavior of the material. The numerical results are well compared with the available experimental results of a falling sphere in the literature and also the experiments of the current study. The experiments are performed for a spherical-nose projectile in a water tank equipped with a launching system and a high speed camera. The simulation results such as air cavity shape and the projectile trajectory are compared with the presented experiment data. The good agreement observed between the numerical results and those of the experiments, revealed the accuracy and capability of the proposed numerical algorithm. Also, it has been shown that the pinch-off time is a weak function of impact velocity, however, increasing velocity leads to a linear increase in depth of pinch-off.

In this study, microstructure, microhardness and residual stress in the butt jointed friction stir welded aluminum alloy 2024-T351 plates with different tool’s rotational and traverse speed is studied. According to the 2024-T351 aluminum is a heat treatable alloy, Hardness test results showed that increasing rotational speed or decreasing traverse speed of the tool reduced hardness in the weld zone. Then, using standard X-ray diffraction, which is a non-destructive method, residual stress in the welded samples is determined. A thermal model of friction stir welding process is simulated by using finite element method in the ABAQUS software. Comparison of residual stress results that obtained from the numerical solution with experimental measurements show that, the numerical model can predict the residual stress fields in friction stir welding joints reasonably.The results show that, increasing rotational speed, cause to higher residual stress in the weld zone, due to generation the higher thermal gradient and also, The higher tool traverse speed will induce a greater high-stress zone with a higher stress value in the weld, because of, a lower heat input and result in the relatively harder metal in the weld zone, causes a greater resistance to the plastic extrusion.

In this paper, a laminated composite plate that was subjected to bending fatigue load was modeled based on the strength degradation theory of the composites. Also, effects of the fiber directions in the layers and layer stacking on the fatigue life of the plate were studied. First, the governing equation of the laminate plate in bending was obtained by the Navier theory. Then, by solving the governing equation, the deflection and stresses in the plies of each layer were obtained. Finally, using the Brotman-Sahu strength degradation theory, reduction of strength and stiffness in each layer of the plate in each loading step was determined. The data obtained in each step were used to specify the data and material properties of the next solution step. This process was repeated until a fatigue failure in the fiber or matrix began in one or more layers. Using the sudden death theory and iteration of the solution process, the final fatigue life of symmetric laminates with various stacking and fiber direction was investigated. In the numerical results, the carbon/epoxy composite laminate with different layer stacking was studied.

In this paper, a single solid oxide fuel cell with internal reforming and parallel flow is modeled and optimized. The single fuel cell is a part of a stack of fuel cell system used for cogeneration of heat and work. The governing equations including the conservation equations of mass, momentum, energy and electrochemistry relations are solved by gPROMS software and validated using the data available in literature. The effect of quantities such as the rate of fuel consumption, amount of excess air and the percentage of pre reforming of fuel on the power and the efficiency of the fuel cell were evaluated. The results show that the percentage of the fuel pre reforming on the performance of fuel cell is more effective than other parameters and the power output and energy efficiency increase with it as well. Optimal working point of fuel cell with three objective functions (output power, the product of output voltage in voltage efficiency and output power in energy efficiency) has been obtained. The optimal current density is less than the current density of maximum power output. The optimal power output and energy efficiency taking minimum energy dissipation into account are 1.11W/cm2 and 42% respectively and by considering minimum exergy are 1.46 W/cm2 and 24%, respectively.

Industrial kilns and power plants with high consumption of fossil fuels play a significant role in the production of air pollutants. Nitrogen oxide is one of these pollutants. In the present work, effect of different geometries on NO reduction in stack of industrial kilns and power plants is investigated numerically based on a selective non catalytic reduction (SNCR) method. In SNCR method, the NO reacts with ammonia which is injected into the kiln stack at temperature range of about 1150-1350 K and nitrogen is formed. In this study, a cylindrical stack with 500 cm length and 5 cm diameter is chosen, similar to Ostberg’s experimental work. Four geometries for ammonia injection with one, two, and four nozzles and by a ring around the stack have been studied. Numerical simulation of NO reduction by SNCR method shows that injection with one nozzle has lower efficiency than other injection geometries. Also, effect of gas stack length on NO reduction has been investigated. The results show that increasing stack length has a significant effect on ammonia slip reduction phenomenon. To investigate the effect of ammonia injection nozzle angle on SNCR efficiency, nozzle angles between -75 to 75 degrees were analyzed. Results show that the efficiency of this phenomenon decreases by increasing absolute value of injection nozzle angle. Finally, effect of baffle presence in mainstream has been studied. It is observed that the required time and length for reaction decrease due to better mixing.

In recent decades, modeling the instability of nanostructures has attracted a great deal of attention in nanomechanics. Nanomechanical switches are fundamental building blocks for the design of NEMS applications, such as nanotweezers and nanoscale actuators. One common type of NEMS including nano-bridge in micro mirrors, is used. At nano-scales, the decreasing gap between the two electrodes produces surface traction due to molecular interaction such as van der Waals that must be taken into account in the analysis of NEMS. In this study, strain gradient theory has been used to investigate the size dependent pull-in instability of beam-type (NEMS) where an inherent instability is found in them. The von-Karman nonlinear strain has been applied to derive the constitutive equation of the system. Effect of intermolecular force has been included in the nonlinear governing equations of the system. Homotopy perturbation method (HPM) has been employed to solve the nonlinear equations. Effect of intermolecular attraction and the size dependency and the importance of coupling between them on the instability performance i.e., critical deflection and instability voltage have been discussed. According the findings of this research, it can be concluded that intermolecular forces decrease pull-in voltage, and size effect parameter in nano scale leads to an increase of pull-in parameters. Also, HPM method can be applied as an efficient method to analyze beam type nano structures.

Grains in polycrystalline texture have anisotropic deformation nature. This cause material to show completely different behavior at meso and micro scale than they do at macro scale. To be specific, deformation at these scales is heterogeneous and cannot be modeled using constitutive equation in continuum plasticity. In this paper, in order to investigate deformation behavior of 316L stainless steel at micro scale a crystal plasticity finite element (CPFE) modeling system has been developed. The crystal plasticity equations were implemented in the ABAQUS/Implicit FE code through a user-defined material subroutine, UMAT. Verification was done through comparing the CPFE result against those obtained through implementing crystal plasticity formulation in MATLAB software. Comparison show good agreement between the analytical and CFFE result. Afterward, three dimensional simulation of tensile test on Stainless Steel type 316L is carried out using CPFE method and continuum macro mechanic FE. Deformation characteristic and localization behavior of single grain specimen during tensile test has been captured and predicted using CPFE method; on the other hand, macro mechanic finite element is unable of predicting localization and evolution of lattice at micro and meso scale. At the last part, a set of CPFE analysis are conducted on representative volume elements with 10 Grain and a set of different grain orientations. Results show a scattering in plastic part of stress-strain response of material with switching from one set of grain orientation to another set. It has been found that the material behavior at these scales is highly direction dependent.

In articulated vehicle, the importance of adjustment or confinement of the side slip angle has not yet been investigated. However, its proper dynamic behavior is of great significance. In this research, based on a planar model of articulated vehicle and adopting a proper method, the significance of this quantity is examined. In this article, after a review of the literature, the articulated vehicle model is clarified. The selected model is a validated model of articulated vehicle with 14 degrees of freedom that simulates the vehicle’s directional dynamics. In the stability analysis, phase plane method based on the nonlinear model of articulated vehicle with three degrees of freedom is used, which includes the major degrees of freedom in planar motion. In this section, the traction phase plane is drawn via two variables, the side slip angle and the rotational velocity of the articulated vehicle by terms of constant longitudinal velocity of the vehicle as the critical condition and then stable and unstable zones are separated. Fuzzy estimator systems have been based on the Takagi-Sugeno fuzzy model and offer a stable range for the articulated vehicle’s motion according to the results from the phase plane. Finally, the application of phase plane in studying the stability ismagnified by designing two control systems based on the stable range, in order to control the articulation angle and the side slip angle. Eventually, the results are analyzed, and the method is tested based on the vehicle’s full model.

In the present study, in order to evaluate the elastic displacement field and subsequently the fracture parameters within the isotropic homogeneous elastic solids with the edge or interior cracks, the extended finite element method with level set technique was used to avoid the disadvantages associated with the standard finite element method. An over deterministic least squares method was utilized to determine the crack stress intensity factors as well as the coefficients of the higher order terms in the Williams' asymptotic series solution for structures containing crack in various modes of failure by fitting the series solution of displacement fields around the crack tip to a large number of nodal displacements obtained from the extended finite element method. For validating the results, several cracked specimens subjected to pure mode I, pure mode II, and mixed modes I/II loading were performed. Comparisons with results available from the literature obtained by the other formulations reveal the efficiency and the simplicity of the proposed method and demonstrate the capability of it to capture accurately the crack stress intensity factors and the coefficients of higher order terms.

The present study aims to implement an approach for trajectory control of a 3-RPR parallel manipulator over a path with obstacles in the workspace. For this purpose, using the spline curves approach and based on the cuckoo optimization algorithm, a smooth reference trajectory with minimum length is generated in the workspace to avoid robot collision with obstacles. The performance and accuracy of the cuckoo optimization algorithm in converging to the optimal solution is then compared with the Genetic algorithm. In the next step, the robust sliding mode control technique is adopted for trajectory control of the robot in the presence of some uncertainties. These uncertainties usually include the lengths and mass of the robot’s links. The obtained results confirm the demanded level of performance and accuracy of the cuckoo optimization algorithm. It is also observed that the optimal trajectory with minimum length is generated using the spline curves approach. In addition, it is concluded that based on the sliding mode control technique, the robot can follow the desired trajectory very precisely in spite of the presence of the uncertainties in length and mass of the robot's links.

Aluminum alloys have high strength to weight ratio and suitable corrosion resistance. Poor formability at room temperature is the main drawback of using these alloys. In order to overcome this limitation, the work material is formed at higher temperature. One of the forming processes is hydrodynamic deep drawing assisted by radial pressure on which no relevant research has been reported in warm condition. In the present paper, after examining the formability of 5052 aluminum alloy in warm hydrodynamic deep drawing, the effect of media pressure, temperature and forming speed on thickness distribution and punch force in forming of flat-bottom cylindrical cups was investigated. In order to perform a complete investigation, the simulation of the process was established using ABAQUS software. It was shown that the results were in accordance with the experimental findings. It was also demonstrated that increasing the maximum oil pressure to a specified level could improve the thickness distribution and lead to increasing the punch force. The required punch force was decreased with increase in temperature but remained unchanged by punch speed variation. Additionally, the maximum thickness reduction was decreased with increasing and decreasing of temperature and punch speed, respectively. Moreover, the forming of the sheet at room temperature, isothermal and non-isothermal warm forming processes was compared. It was concluded that the maximum thickness reduction in the formed part was less in the cases of cold forming and non-isothermal warm forming than the isothermal warm forming. But the required forming force is decreased in isothermal warm forming when compared with the other two conditions.

One of the most important devices for absorbing energy of the impact is circular tubes which absorb energy in different modes of plastic deformation. But one of the most important modes of deformation is dynamic progressive buckling caused by the axial collapse. This mode has the most energy absorption. In this study, the behavior of thin walled tubes (with caps) which have a fossa near the end edges of the tube has been investigated in a numerical and experimental way. This is contrary to the previous researches on energy absorption which used the quasi-static form. To carry out experimental tests, a drop hammer machine has been used. In the numerical part, capabilities of Abaqus have been employed. The results show that caps improve energy absorption, thus more energy is absorbed in less length crushing, and the up and down fossa of the tube causes the maximum collapse force to occur with a delay. Also, these absorbers have a linear behavior in absorbing energy with respect to the crushing length and the average collapse force has not been changed by increasing the hammer weight. An experiment was conducted to assess the collisions with the same kinetic energy to study strain rates in four collisions. It was seen that a reduction of 16.9 percent in strain rate increases 2.6 percent of the crushing length.

This paper deals with the design and fabrication of an adjustable, two finger flexible miniature gripper based on porous magnetorheological nanocomposites having the adjustability of preopening of the jaw’s tips and its operational study according to performance. The fabricated gripper holds the small size and lightweight objects, maintains them and releases them as required upon reducing the electrical current. The magnetic analysis has been done and magnetic simulation was conducted using Vizimag software. Lead, condensed paper, foam and silicon wafer sheets were used as under experiment materials and it was observed that the device is working properly to grip the things which have rough surfaces. For greater objects, it can be adjusted through its tips as well. In this scheme, the magnetic actuation has been used because the magnetorheological nanocomposite is the most sensitive material against the magnetic field. This type of gripper includes the simple montage, lower fabrication prices and its own lower volume as well as weight, and there is no need to apply the classic mechanical linkage inside. These types of grippers are recommended for applications in the fields of the micro electromechanical systems, especially in the holding and transporting of sensitive work pieces against scratches, fingerprints and pressure.

A differential thermal model for simulation of Stirling engines was presented. In the new model polytropic expansion/compression processes were substituted for traditional isothermal or adiabatic models of previous studies. In addition, the developed polytropic model was corrected for various loss mechanisms of real engines. In this regard, the effect of non-ideal operation as well as heat recovery in the regenerator was considered. In addition, non-ideal heat transfer of heater and cooler were implemented into the model. In pressure analysis and evaluation of work produced or consumed in cylinders, the effect of finite speed motion of piston was considered based on the concept of finite speed thermodynamics. Moreover, the effects of heat leakage in regenerator, leakage effect and shuttle effect were evaluated. Finally, new differential polytropic models were employed on a benchmark Stirling engine, so-called GPU-3, and accuracy of models was validated through comparison with experimental results as well as previous models. As thermal performance of Stirling engines is significantly affected by thermohydraulic performance of regeneratorand there are various thermohydraulic models for regenerator, three famous thermohydraulic models of regenerator were integrated into models and through comparison with experimental performance of GPU-3 engine, a more accurate thermohydraulic model was introduced.

When the cantilever beam thickness is scaled down to micron, the dimension of material and the intrinsic length scale affect the mechanical behavior of the beam. The purpose of this paper is to analyze the bending of cantilever micro-beam and present a relation for the beam deflection using Chen-Wang gradient plasticity theory. To this end, the Euler-Bernoulli beam model is utilized and three cases including elastic, rigid-plastic and elasto-plastic beams are considered. Clear relations for elastic and plastic strains are given. For all mentioned cases, the beam deflection is determined for different intrinsic lengths and the obtained results are compared with each other and experimental data and some explanations are presented. The results obtained from classical theory are also shown in the results section to prove that classical theories do not have the ability to predict behavior of micron-size structures precisely. Numerical results clarify the dependence of responses to the range of dimensions and intrinsic lengths. The comparison between the present results and those observed from experimental tests authenticate the reliability of utilized gradient theory.

Usage in low temperatures causes embrittlement of many structures; consequently, selection of welding parameters for maintaining the toughness of welded structures is crucial. In this paper, effects of arc heat input and welding speed on the cryogenic impact strength of type 304L austenitic stainless steel weld metal are investigated. For this purpose, 304L austenitic stainless steel sheet with 5 mm thickness was welded with gas tungsten arc welding process and by changing the parameters of arc heat input and welding speed, the effect of these parameters on the microstructure, weld metal ferrite content and low temperature, charpy impact energy of samples was determined. The arc heat input range applied was between 1.04 and 3.23 kW, and the welding speed varied between 30 and 240 mm/min. It was found that increasing arc heat input can reduce weld metal ferrite content, which improves low temperature impact strength, but on the other hand, slow cooling due to increasing heat input results in coarser dendritic structures in the weld metal, and can adversely affect impact strength. Changes of welding speed can also affect the amount of ferrite and microstructure and thus have an influence on the impact strength. Finally, having carried out the numerous tests, optimum impact properties at low temperature were obtained at 1.67 kW arc heat input and 120 mm/min welding speed.

In the present study, volume of fluid method in Open FOAM open source CFD package will be extended to consider phase change phenomena due to condensation process. Both phases (liquid-vapor) are incompressible and immiscible. Vapor phase is assumed in saturated temperature. Interface between two phases is tracked with color function volume of fluid (CF-VOF) method. Surface Tension is taken into consideration by Continuous Surface Force (CSF) model and mass transfer occurring along interface is considered by Lee mass transfer model. Pressure-Velocity coupling will be solved with PISO algorithm in the collocated grid. This solver is validated with Stefan problem. In one dimensional Stefan problem, the desistance of interface motion from cold wall is compared with the analytical solution. Then condensate laminar liquid film flow over vertical plate is simulated in the presence of gravity. Numerical result shows calculated film thickness from numerical simulation is thinner than analytical solution. Also, it shows Nusselt number is a function of vapor specific heat which is neglected in existing correlations, therefore analytical solution and experimental correlation should be modified to consider this effect on the Nusselt Number.

In this study, the non-linear bending analysis of isotropic and orthotropic rectangular plates is performed by Dynamic Relaxation (DR) method. In order to model the plate, the four-variable refined plate theory, which is a new and simple higher-order shear deformation theory and has a good capability in analysis of thick plates, is adopted. Despite the first-order shear deformation plate theory, this theory does not need the shear correction factor, predicts shear strains and stress parabolically across the plate thickness and satisfies the zero stress conditions on free surfaces. The governing equations are obtained using virtual work principle and the Von-Karman nonlinear terms are considered in strain-displacement equations. The non-linear coupled governing equations are solved by DR method combined with finite difference technique, and for this purpose a computer code is provided in MATLAB software. In order to demonstrate the accuracy of the present method, the numerical results are compared with the existing ones and very good agreement is observed. Also, the effects of side-to-thickness ratio and boundary conditions on the results are examined. Finally, the variations of shear effects by changing the plate thickness and also changing the orthotropy ratio in orthotropic plates are investigated.

In this paper, the effect of ductile damage on the behavior of a dented pipe subjected to internal pressure is investigated by experimental and numerical methods. In the numerical investigation, the plastic behavior of pipes under indentation is studied using continuum damage mechanics theory and the elastic-plastic finite element analysis. Finite element calculations are carried out using the damage plasticity model proposed by Xue and Wierzbicki (X-W).The proposed damage plasticity model incorporates effects of four parameters that play an important role in predicting the fracture initiation, namely the damage rule, the softening effect, the hydrostatic pressure and the Lode angle. The target dent depth is considered an indication of the load bearing capacity of the pipe under indentation process by a rigid spherical indenter. To validate numerical calculations, a series of experimental tests are conducted on the API XB steel pipe with atmospheric pressure. After verification, numerical calculations for different ranges of internal pressures, wall thickness and indenter diameter with and without damage effect are carried out for aluminum 2024-T351 pipe and results are compared. It is shown that damage plays an important role on the load bearing capacity of an indented pipe. Results of the present study confirm the credibility of the proposed model in predicting the ductile fracture under multi-axial state of stress loadings.

One of obstacles in simulation of two phase flow is parasite currents. These currents cause unphysical distortion at interface which impairs interface capturing and numerical results. In present study, two methods (using Filter and s-CLSVOF) are implemented in Open FOAM two phase flow solver called inter Foam to reduce parasite current. 3 filters are added to color function volume of fluid (CF-VOF) method. These filters reduce parasite current in different ways, one smoothes color function, one smoothes curvature and the other one compresses the interface. The original and the modified solvers are tested with a quiescent bubble bench mark to investigate the effect of each filter on parasite currents. Then optimum arrangement of filters is compared with s-CLSVOF method and inter Foam. Present study shows parasite current magnitude can be reduced at least up to 50% in the modified solvers. Also, the comparison of pressure jump from numerical results and analytical result with Young-Laplace equation shows modified solvers can predict pressure jump better than original solver. The pressure jump error is reduced up to 400% in the modified solvers. Also present study shows filters have better performance than s-CLVOF method and it can be considered as a suitable substitution of coupled methods.

In this paper, the behavior of copper and steel rectangular plates with clamped boundary conditions subjected to underwater explosion loading is investigated. Cavitation is a phenomenon that occurs in this process. During the cavitation, the total pressure of the explosion becomes zero, so that the governing equations of motion time will be different before and after the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a rectangular plate at underwater explosive loading. To calculate the cavitation time, the equations of motion of a rectangular plate underwater explosive loading are derived first, based on Hamilton principle and variation method. Then, in order to obtain the forced response of the rectangular plate, the exact free vibration solution of the rectangular plate is derived for exact mode shapes. Then, the speed and generated stress of plate during cavitation time are calculated and compared with the yield stress of copper and steel rectangular plates. Using this method, one can distinguish the cavitation with in the elastic or plastic regimes. Results show that the cavitation time is on the order of microsecond.

Detection of tool wear and breakage during machining operations is one of the major problems in control and optimization of the automatic machining process. In this study, the relationship between tool wear with vibration in the two directions, one in the machining direction and the other perpendicular to machining direction was investigated during face milling. For this purpose, a series of experiment were conducted in a vertical milling machine. An indexable sandvik insert and ck45 work piece were used in the experiments. Tool wear was measured by a microscope. It was observed that there was an increase in vibration amplitude with increasing tool wear. In this study adaptive neuro - fuzzy inference systems (ANFIS) and multi-layer perceptron neural network (MLPNN) were implemented for classification of tool wear. In this study for the first time, five different states of tool wear was used for accurate tool wear classification. Also to accuracy and speed of the network Principle Component Analysis (PCA) was implemented. Using PCA, the input matrix size was reduced to an acceptable order causing more efficient networks. ANFIS and MLP were trained using feature vectors extracted from the spectrum frequency and time signals. The results showed that for 86 final measurements, the ANFIS and MLP networks were successful in classifying different tool wear state correctly for 91 and 82 percent, respectively. ANFIS due to its high efficiency in diagnosing tool wear and breakage can be proposed as proper technique for intelligent fault classification.

In this study, the forced convective heat transfer of pure water and alumina-water nanofluid with volume concentration of 0.5% and 1%, as a cooling fluid through a microchannel heat exchanger was experimentally investigated. This microchannel consists of 17 parallel channels with a rectangular cross section with 400 µm width, 560 µm height and 50 mm length. The experiments were performed in the range 600 to 1800 of Reynolds and constant heat flux conditions (19 W/cm2). Stability studies showed that alumina-water nanofluid at pH=3 for 3 hours in a bath of the ultrasonic vibrating demonstrate the maximum stability. The variations of microchannel surface temperature, fluid temperature at the entrance region of the microchannel, average heat transfer coefficient of nanofluid and pure water, and their friction factor measured experimentally. Also comparison between average Nusselt number with existing heat transfer relationships was performed. The results show that heat transfer using nanofluid shows considerably increase in comparison to water. So that the maximum amount of average heat transfer coefficient for alumina-water nanofluid with 0.5% concentrations is about 32.8% and for alumina-water nanofluid with 1% concentrations about 49.7% in comparison to pure water. It was also found that the heat transfer coefficient increases with increasing Reynolds number and nanoparticle volume fraction.

In this paper, the dynamic plastic buckling of axisymmetric circular cylindrical shells subjected to axial impact is investigated. The von Mises yield criterion is used for the elastic-plastic cylindrical shell made of linear strain hardening material in order to derive the constitutive relations between stress and strain increments. Nonlinear dynamic circular cylindrical shell equations are solved with the finite difference method for three types of boundary conditions and two types loading. Two types of loading are stationary cylindrical shells impacted axially and traveling cylindrical shells impacted on a rigid wall. The growth and improvement of axial and lateral strains and buckling shapes of cylindrical shells are investigated for different boundary and loading conditions, from the viewpoint of stress wave propagation. It is found that the total length of cylindrical shell is affected by the plastic deformation when the plastic wave reaches unimpacted end. Also it is found that shortening and energy absorption are independent of loading and boundary conditions. The buckling shapes are affected by loading and boundary conditions; also peak loads at impacted and unimpacted ends are affected by loading conditions and are independent of boundary conditions. The presented theoretical results are compared with some experimental results and good agreement is obtained.

Fault detection of ball bearings by the complex and non-stationary vibration signals with noise is very difficult, especially at the early stages. Also, many failure mechanisms and various adverse operating conditions in ball bearings involve significant nonlinear dynamical properties. The quality of chaotic vibration of ball bearings is studied by the reconstructed phase space. The phase space demonstrates different chaotic vibration of ball bearing for different healthy/faulty conditions. But, to easily use of this procedure in the ball bearing fault detection, the chaotic behavior of vibration signal is quantified by a set of new features. The new set of features based on chaotic behavior, including the largest Lyapunov exponent, approximate entropy and correlation dimension are extracted to acquire more fault characteristic information. The effectiveness of the new features based on chaotic vibrations in the ball bearing fault detection is demonstrated by the experimental data sets. The proposed approach can reliably recognize different fault types and have more accurate results. Also, the performance of the new procedure is robust to the variation of load values and shows good generalization capability for various load values.

a numerical study has been carried out in order to understand the heating effect of magnetic nanoparticles used in hyperthermia with the goal of producing a desired increase in temperature at A specific point of tumor location inside the muscle. In fact, a numerical scheme is proposed to solve the bio-heat transfer problem in a two-zone tissue in the context of a spherical geometry with blood perfusion and metabolism. The analytical solution reveals the numerical scheme accuracy and their correctness. Moreover, to predict the temperature increase in terms of characteristics of the magnetic nanoparticles, applied magnetic field and the tissue, Pennes bioheat equation is solved. Results show that the strength of applied alternative current (AC) magnetic field has a negligible effect; on the other hand, the volume fraction as well as the frequency of applied AC magnetic field has moderate effect and the diameter of the nanoparticles has the major effect on the rise in temperature. Among materials investigated in this study, FePt has the most significant effect on hyperthermia.

In this paper, plastic deformation of the clamped mild steel and aluminum circular plates subjected to different hydrodynamic impact loading conditions are investigated. Extensive experimental tests were carried out by using a drop hammer. The experimental results presented in terms of central deflection of the plates, deflection profiles, and strain distributions. The effect of different parameters such as material properties, plate thickness, stand off distance of hammer or the transfer energy were also investigated on behavior of deformation of plate. Analytical modeling was carried out using energy approach and introducing the deflection profile function based on observes result of experimental. In this model effect of strain rate, hoop strain, radius strain and also effects of bending strain energy and membrane strain energy have been inserted. Calculations of the cases indicate that the proposed analytical models are based on reasonable assumptions. So, this method can be used for study of plastic deformation of plates under dynamic loading. The agreement between analytical and experimental results indicates that new analytical approach presented in this work maybe successfully employed for prediction of central deflection in different hydrodynamic impact loading conditions.

In this paper, a non - isothermal and two-phase flow in the cathode gas diffusion layer (GDL) of PEM fuel cell is modeled. To achieve more accurate boundary conditions, other components of fuel cell (membrane and anode GDL) are modeled. Governing equations including energy, mass and momentum conservation and auxiliary equations are solved by numerical method and the effect of gas mixture pressure in channels, relative humidity and effect of contact and mass exchange between two phases are investigated. Results show, it is necessary that both the contact and mass exchange between the gas and liquid phase to be considered. The performance curve and temperature distribution for single and two phase flow are compared for different amount of cathode channel humidity. The relative value of performance and temperature for single and two phase flow depends on the humidity of cathode channel. With increasing the cathode pressure from 0.5 to 5atm the value of water content in membrane and gas diffusion interface will increase about 20%. With increasing the water content in the membrane therefore the ohmic loss is reduced. With the reduction in the ohmic loss the temperature distribution along the fuel cell decreases but if the anode pressure increases the temperature distribution along the fuel cell increases.