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مرکز اطلاعات علمی SID1
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
مرکز اطلاعات علمی SID
Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    1
  • End Page: 

    8
Measures: 
  • Citations: 

    0
  • Views: 

    285
  • Downloads: 

    80
Abstract: 

In this paper, the diffusion coefficient in a normal tissue and tumor are to be estimated by the method of inverse problems. At the beginning, distribution of drug (with the assumption of uniform and isentropic diffusion coefficient) in the tissue is considered as the direct problem. In the direct problem, the governing equation is the convection–diffusion, which is the generalized form of Fick’s law. Here, a source and a sink are defined; the source as the rate of solute transport per unit volume from blood vessels into the interstitial space and the sink as the rate of solute transport per unit volume from the interstitial space into lymph vessels are added to this equation. To solve the direct problem, the finite difference method has been considered. Additionally, the diffusion coefficient of a normal tissue and tumor will be approximated by parameter estimation method of Levenberg-Marquardt. This method is based on minimizing the sum of squared errors which, in the present study considered error is the difference of the estimated concentration and the concentration measured by medical images (simulated numerically). Finally, the results obtained by Levenberg-Marquardt method have provided an acceptable estimation of diffusion coefficient in normal tissue and tumor.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    101
  • End Page: 

    110
Measures: 
  • Citations: 

    0
  • Views: 

    142
  • Downloads: 

    89
Abstract: 

In spite of several advantages of parallel robots, they generally have limited workspace. Therefore, it is of paramount importance to obtain the workspace by considering the mechanical interference. In this paper, the mechanical interference in planar parallel mechanisms, including interference between links and, collision between links and obstacles and between end-effector and obstacles, are investigated using geometrical reasoning. For this purpose, a new geometric method is proposed for collision detection in the workspace of planar parallel mechanisms based on the lines segment intersection. In this method, the configurations of the planar parallel robot are obtained in the entire workspace. Then, the interference of links with each other and obstacles, which are respectively modeled by line segment and polygon, are determined. Finally, the collision-free workspace of the parallel robot is obtained for a specified orientation of the moving platform. Moreover, in this paper, an index is presented which can be used for examining the workspace by considering mechanical interference. The foregoing index provides some insight into obtaining a well-conditioned workspace. For the sake of validation, this method is implemented on two planar parallel robots, namely as 3-RRR and 3-PRR, for different working modes. The obtained results reveal that the ratio of the practical workspace to the theoretical workspace is decreased upon increasing the orientation of the end-effector for both clockwise and counterclockwise directions. Furthermore, due to differences in the number of the moving links, the mechanical interference-free workspace of 3-RRR parallel robot is usually more limited than 3-PRR parallel robot.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    111
  • End Page: 

    116
Measures: 
  • Citations: 

    0
  • Views: 

    151
  • Downloads: 

    91
Abstract: 

Reliability Based Topology Optimization (RBTO) is a process of determining optimal design satisfying uncertainties of design variables. Sometimes frequency optimization might produce a design with low stiffness or stiffness optimization might lead to a design with low frequency. In this paper, the multiobjective optimization for both stiffness and frequencies is presented. This article presents RBTO using Bi-directional Evolutionary Structural Optimization (BESO) with an improved filter scheme. A multiobjective topology optimization technique is implemented to simultaneously consider the stiffness and natural frequency. In order to compute reliability index the First Order Reliability Method (FORM) and Standard Response Surface Method (SRSM) for generating limit state function is employed. To increase the efficiency of the solution process the reliability estimates are coupled with the topology optimization process. Topology optimization is formulated as volume minimization problem with probabilistic displacement and frequency constraints. Young’s module, density, and external load are considered as uncertain variables. The topologies obtained by RBTO are compared with that obtained by Deterministic Topology Optimization (DTO). Results show that RBTO using BESO method is capable of the multi-objective optimization problem for stiffness and frequency effectively.

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Writer: 

OMIDPANAH MOHAMMAD | GANDJALIKHAN NASSAB SEYED ABDOLREZA

Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    117
  • End Page: 

    124
Measures: 
  • Citations: 

    0
  • Views: 

    160
  • Downloads: 

    87
Abstract: 

In this paper, an inverse analysis of combined radiation and convection heat transfer in a 2-D rectangular duct is presented. The working fluid is a mixture of air including CO2 and H2O as two radiating gases. The purpose is to verify the effects of gas mole fractions on the solution of inverse design problem in which the conjugate gradient method is used to find the temperature distribution over the heater surface to satisfy the prescribed temperature and heat flux distributions over the design surface. The radiating gas is considered to be a gray participating medium with absorption, emission and isotropic scattering. The Planck mean absorption coefficient is calculated and used in radiative calculations. To obtain the temperature field, the energy equation for participating medium is solved by the finite difference method and the discrete ordinates method is used to solve the radiative transfer equation. An attempt is made to determine the temperature distributions over the heater surface while the enclosure is filled with different mole fractions of CO2 and H2O. The effects of other parameters such as radiation conduction parameter on the solution of inverse problem is examined. It is revealed that increase in mole fraction of gases mixture needs a heater surface with higher power input.

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Writer: 

SHAHAMIRIAN SEYED MOHAMMAD EBRAHIM | LARI KHOSRO | AMIRI HOSSEIN

Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    125
  • End Page: 

    133
Measures: 
  • Citations: 

    0
  • Views: 

    119
  • Downloads: 

    79
Abstract: 

In the present work, the thermal effects of a CW laser on skin tissues with blood perfusion are simulated. For this purpose, a one-dimensional medium is considered that is exposed to the laser beams from one side and the other side is at the constant temperature (37oC) because of being touched by other parts of the body. The laser beams are considered to be collimated and perpendicular to the surface of the tissue. The skin tissue is a strong anisotropic scattering medium and is assumed to be gray with black walls. Also, the blood perfusion is considered in the bioheat transfer equation of the skin tissue.The governing equations of this problem are radiative heat transfer coupled with conductive heat transfer in which the discrete ordinates method, finite volume method and scaling method are used to solve the radiative transfer equation, the energy equation and to model the anisotropic scattering of the tissue, respectively. Validation of the model is performed by comparison with the other related works.Then, the effects of different optical and physical parameters of tissue such as conduction-radiation parameter, scattering albedo, extinction coefficient, blood perfusion and the effects of laser power on the time of temperature increase of the tissue and thermal penetration depth are studied. It should be mentioned that the results of the present study show valuable guidance for understanding the coupled light and bioheat transport in tissues in therapy, surgery and diagnostic tasks.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    134
  • End Page: 

    142
Measures: 
  • Citations: 

    0
  • Views: 

    122
  • Downloads: 

    111
Abstract: 

In this paper stability analysis of a nonlinear micro rotating shaft when the system is near the primary resonances by considering the modified couple stress theory and micro inertia effect is investigated. The geometric nonlinearities due to classical and non-classical theories (the modified couple stress theory) are considered. Using Hamilton principle, the nonlinear equations of motion are obtained. In order to solve the equations of motion the multiple scales method is used and the analytical expressions are presented for forward and backward frequencies which illustrate the effects of modified couple stress theory and micro inertia effect. The frequency response curves, amplitude versus damping coefficient, amplitude versus total eccentricities etc. are reported. It is seen that due to the modified couple stress theory and micro inertia effect the amplitude of the system decreases and the loci of bifurcation points is changed. Symmetrical micro-shaft in the presence of classical theory and without micro inertia effects becomes completely stable in the lowest damping coefficient and asymmetrical micro-shaft in the presence of classical theory and without micro inertia effects becomes completely stable in the highest damping coefficient. Symmetrical micro-shaft in the presence of modified couple stress theory and with micro inertia effects becomes completely stable in the lowest total eccentricity and asymmetrical micro shaft in the presence of classical theory and without micro inertia effects becomes completely stable in the highest total eccentricity. So, considering the small-scale effects due to strain and velocity gradients for analysis of the system is mandatory.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    143
  • End Page: 

    153
Measures: 
  • Citations: 

    0
  • Views: 

    462
  • Downloads: 

    134
Abstract: 

Additive manufacturing methods and/or 3D printing have become increasingly popular with particular emphasis on methods used for metallic materials. Selective Laser Melting (SLM) process is one of the additive manufacturing methods for production of metallic parts. The method was developed specifically to process metal parts that need to be more than 99 percent dense. In this method, according to a predefined pattern, the top surface of the powder layer is scanned by the laser and a local (selective) melt pool is produced in the place of the laser spot which results in a fully dense layer after solidification. In this study, a semi-coupled thermo-mechanical simulation of SLM process is carried out in ABAQUS finite element software. In order to simulate the moving heat flux and update material properties from the powder to the dense solid, the ability of the software for employing user -defined subroutines is used. Investigation of the residual stress distribution and distortion of a part built using SLM process are the main objectives of this simulation. Results presented for two different mechanical boundary conditions show that when the bottom face of the layer is clamped, the top face of the built layer deforms in a concave shape, while the lateral faces of the layer have simply-supported boundary conditions and the bottom face of the layer is free, the part is warped.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    154
  • End Page: 

    160
Measures: 
  • Citations: 

    0
  • Views: 

    114
  • Downloads: 

    95
Abstract: 

With the development of micro-mechanical systems, researchers have become interested in concentrating on the small-scale impact on the flow and heat transfer in micro-channels. A microchannel is required for a gas sensor to guide the gas flow. Reducing the size of channel has led scientists to concentrate on micro-sensor. Metal oxide gas micro- sensors are used to detect gases such as O3, SO2, CO2, NO, NH3, CH4, etc. Metal oxide gas micro-sensors are small in size, cheaper to fabricate and consume little power. The purpose of the current study is to numerically investigate the micro-channel wall thickness and diameter on gas inlet temperature under the influence of thermal creeping. The governing nonlinear differential equations, mass, momentum, energy, and species, are coupled and solved by a commercial code. The channel is assumed to be two dimensional. Since the Knudsen number is between 0.01 and 0.1, the slip boundary condition, Maxwell equation, is utilized. The result shows that as wall thickness increases the gas inlet temperature increases and temperature difference between gas inlet and outlet decreases. On the other hand, as channel diameter decreases the gas inlet temperature increases.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    161
  • End Page: 

    167
Measures: 
  • Citations: 

    0
  • Views: 

    113
  • Downloads: 

    81
Abstract: 

In this research, in order to study effects of fabrication method the square-shaped bistable composites laminates with asymmetric layers were prepared and investigated. Different kinds of bistable composite laminates were fabricated by thermoplastic PVC and glass fibers and the effects of composites laminate dimensions and mold temperature were investigated. The maximum height of the bistable composite laminate is selected as the output of experiments. The results derived from ANOVA analysis showed that the dimensions of the laminates have the highest effects on bistability height and the effects of mold temperature are very low. It was also determined that with the larger dimensions of composite laminates and lower mold's temperature, the heights of bistability were higher. Also, these bistable composite laminates were simulated in ABAQUS and the simulation results were compared with the experimental results. The results indicated that simulation method anticipated the higher bistability height rather than the experimental results and the difference between these results is less than 10% in all specimens.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    168
  • End Page: 

    176
Measures: 
  • Citations: 

    0
  • Views: 

    128
  • Downloads: 

    79
Abstract: 

Accurate investigation of physical phenomena is one of the important challenges in engineering fields.The present study investigates a wet tank in which entrance of water is investigated in three cases.When the water wave moves into a tank, complex flow regimes are created. This complexity is mainly associated with different flow mechanisms during the entrance of water and propagation of waves at the bottom bed that should be modelled by means of Navier-Stokes equations with free-surface capability and in 3D phase. Due to complexity and time consumption of Navier-Stokes equations modelling, shallow water equations are used with the assumption of hydrostatic pressure. First case is about efflux over a wet bed. Second, water influx from the middle top is investigated and then influx from top edges is modelled. A dimensionless number is introduced for each case based on water velocity, gap length and drop height which shows acceptable domain for appropriate compatibility between results. Finally, results of numerical modelling are compared with Navier-Stokes solutions which are obtained from STAR-CD software. Results show admissible compatibility with each other based on observations and inspections.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    17
  • End Page: 

    28
Measures: 
  • Citations: 

    0
  • Views: 

    354
  • Downloads: 

    257
Abstract: 

Windows, as elements connecting built and natural environment, play an important role in providing internal comfort. During winter, solar heat gain through windows reduces heating demand, heating load and energy consumption of the building. On the other hand, it increases cooling load in summer. Hence, using blinds is common in office buildings to control solar radiation. Although using blinds prevents part of the solar radiation from entering the space, simultaneously, it improves comfort conditions for the employees. It should be mentioned that an appropriate control of blinds, regarding changes in external and internal environmental conditions, will lead to a decrease of energy consumption and discomfort caused by direct solar radiation.. In this paper, the use of blinds on windows is simulated for cardinal orientations and different blind angles and positions. Finally, the total thermal load of the space and the amount of glare is studied. According to the results, blinds have a significant impact on spaces total load, as well as reduction of interior glare compared to the reference case with no blinds.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    177
  • End Page: 

    187
Measures: 
  • Citations: 

    0
  • Views: 

    111
  • Downloads: 

    87
Abstract: 

Analysis of air bubbles entrainment in liquid slug body is one of the most important and complicated phenomena during slug flow regime. In the present attempt, a method is proposed for slug modeling to consider the air bubble entrainment into slug liquid body. The effect of consequences and their impact on slug behaviour to predict more accurate correlations for slug parameters is estimated and calculated.A two-fluid single pressure model is considered that is combined with population balance model for equal bubble diameter series and is solved using volume of fluid. In this regard, based on slug and hydraulic jump similarity, a correlation for air bubble entrainment rate and its mechanism is selected.This correlation is developed in the form of a user defined function code and is coupled with other models in FLUENT solver to calculate slug flow. Finally, the result of this numerical modeling is validated with the result of other numerical and experimental results in the related literature. The result is consist with the slug flow profile, entrained air bubble profile and their diameter distribution, slug mixture velocity, etc.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    188
  • End Page: 

    198
Measures: 
  • Citations: 

    0
  • Views: 

    123
  • Downloads: 

    87
Abstract: 

Unbalance in rotating machines causes malfunction of the system operation and may lead to its failure.Therefore, the sources for imbalance should be investigated, identified, and measured to solve the mentioned challenges. Rotating unbalance appears when the geometric and the inertia axes of the rotor do not coincide, and as a result this causes self- excited vibrations. One of the methods to control and reduce the unbalances is utilizing automatic ball balancer (ABB). In previous studies, the stability and the dynamic behavior of ABB have been mostly investigated using numerical methods, and the perturbation methods are applied only for stability analysis. Because of the advantages of the analytical methods in studying the dynamics of the systems, in the present study, for the first time the dynamic behavior as well as the stability of a rotor equipped with an ABB is analyzed by the multiple scales method. To this end, nonlinear equations of the systems are derived using the Lagrange’s equations and, firstly, the multiple scales method is applied to investigate the stability of system and then the response of the system is achieved considering one and two terms of approximation. The results demonstrate that the stability analysis using the multiple scales method and the first method of Lyapunov lead to the same results. Moreover, the responses obtained by the multiple scales method and the mostly used numerical method, Runge-Kutta technique, are in a good agreement.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    199
  • End Page: 

    208
Measures: 
  • Citations: 

    0
  • Views: 

    217
  • Downloads: 

    105
Abstract: 

Planar inlet concepts play an important role in the design of supersonic propulsion systems. The inlet reduces the speed of supersonic flow by the oblique shock wave or an array of oblique shock waves and a final normal shock provides the subsonic flow after the throat of the diffuser. In this paper, a design method of Mach 3.0 supersonic multi-ramp inlet is explained; the geometry is designed and simulated by the numerical solver. Designing the inlets for the high supersonic Mach range between 3 and 5 is very challenging because of the viscosity interactions and the related effects on the propulsive efficiency. The considered inlet in this study is a mixed system which provides the required compression by a combination of the three external ramps and a subsonic diffuser. A computational code calculated the optimum dimensions numerically and a second order CFD solver has simulated the inlet operations with an accuracy of 10E-05. In addition to aerodynamic performance, advantages and challenges of such a combination, development of boundary layer and its interactions with the normal shock and performance of bleeding mechanism are simulated and studied. Finally, this paper presents compact details of design, simulation and viscosity effect of mixed compression surface.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    209
  • End Page: 

    216
Measures: 
  • Citations: 

    0
  • Views: 

    153
  • Downloads: 

    117
Abstract: 

In this paper conceptual design and optimization of gliding parachute configuration are discussed. To this end, a design cycle is planned for conceptual design procedure and an optimization-based design approach is established to provide an integrated design algorithm for gliding parachute platforms. The optimization problem is formulated with a cost minimization approach which is constrained by static stability and safe landing velocity as design criteria. The parachute configuration is defined with minimum required parameters and aerodynamics, stability and performance characteristics are provided based on a semi-theoretical approach. Hence, a computational software is incorporated with theoretical approximations to provide the required disciplinary dataflow in the design cycle. The significant design parameters are verified by available wind tunnel test data. Optimization problem is solved using genetic algorithm method whereas constraints are handled by penalty function approach. Trim points are obtained like an all-at-once approach through a simultaneous analysis and design algorithm. Finally, as a case study, optimized configuration is achieved for a real gliding parachute. Results show a fair estimation of parachute characteristics along with the reduction in manufacturing cost for new configuration up to 25%.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    217
  • End Page: 

    224
Measures: 
  • Citations: 

    0
  • Views: 

    205
  • Downloads: 

    115
Abstract: 

Friction stir welding (FSW) is a solid-state joining process that leads to several advantages over fusion welding methods as problems associated with cooling from the liquid phase are avoided. In the current research, a new method is presented to improve the microstructure and mechanical properties of joint obtained using FSW. In this method, the joining work pieces are vibrated during FSW. The joining work pieces are fixed on fixture in a butt position and the fixture is vibrated mechanically normal to weld line through camshaft mechanism. The new method is described as friction stir vibration welding (FSVW) process. Microstructure and mechanical properties of welded specimens using FSW and FSVW processes are compared. The results show that weld region grain size of FSV welded specimen is lower than that in specimen welded by FSW by about 30% and the ultimate tensile strength of joint obtained using the former process is higher than that relating to the latter one by about 12%. This is attributed to more generation of dislocations and correspondingly enhanced dynamic recrystallization as vibration is applied. The results also indicate that the weld region grain size of FSV welded specimen increases and mechanical properties of joint decrease as tool rotation speed increases and traverse speed decreases. This is related to temperature increase during FSVW. It is concluded that FSVW is a proper candidate for FSW and its application is recommended for industries.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    225
  • End Page: 

    236
Measures: 
  • Citations: 

    0
  • Views: 

    115
  • Downloads: 

    81
Abstract: 

In this study, the integration of multi-effect desalination (MED) system with cogeneration of heat and power system has been considered. Low-pressure steam in two case studies has been utilized as the motive steam of MED system. R-curve is a powerful tool that can be used to identify fuel utilization amount in different operation points of the cogeneration system. R-curve explains utility system operation improvement procedure without capital cost. By deploying and development of the R-curve concept, the freshwater demand of the total site and total annual cost of the site have been evaluated.These curves can be used as a tool to improve the operation and economic parameters in every operating point of cogeneration system and present comprehensive view about the improvement of utility system operation condition at each operating point. For the first time, R-curve has been used to identify the impact of cogeneration system integration with a thermal desalination system on the cogeneration system operating point. The performance of the cogeneration system can either be enhanced or impaired by integration of desalination system. As demonstrated in a case study, integration of 2.2 MW MED system can either provide 52.765 MW energy saving or deprive 30.257 MW fuel energy based on the operating state of the cogeneration system before and after integration.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    237
  • End Page: 

    246
Measures: 
  • Citations: 

    0
  • Views: 

    94
  • Downloads: 

    93
Abstract: 

The problem of power loss in rotating machinery subjected to the angular misalignment and unbalancing faults are of great importance in relevant industries. Therefore, in this study, evaluation of the power loss and bearing forces of a typical coupling-disk-shaft system with angular misalignment and unbalancing faults is conducted using a novel approach based on the multibody dynamics. In this concern, the flexible coupling is modeled by linear and torsional spring-damper elements. After introducing the model, the kinematic constraints as well as the general form of Euler -Lagrange equations of motion are expressed. Then, the generalized forces are derived in detail. The equations of motion are then solved numerically by the 5th order Runge-Kutta method to evaluate the system power loss. In addition, the effect of angular misalignment and unbalancing faults on the disk displacements as well as the bearing forces are discussed. In the next part of this study, the theoretical results of the power loss are verified experimentally on a faulty simulator system. For measuring the power consumption, a digital power analyzer is used. The results of this research clearly highlight how the power loss is affected by increasing the amount of the system rotational velocity, the angle of misalignment, and the unbalance mass.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    247
  • End Page: 

    254
Measures: 
  • Citations: 

    0
  • Views: 

    146
  • Downloads: 

    103
Abstract: 

In this paper, the behavior of a new type of auxetic composite (composite with negative Poisson’s ratio) consisting of polyester fibers and ABS tubes as reinforcement as well as polyurethane foam as matrix was investigated by finite element method. Furthermore, the effect of negative Poisson’s ratio and mechanical properties of auxetic composite under quasi-static pressure were analyzed and the results were compared with the published experimental works. Good agreements were found between the results. Considering stress-strain diagram, it is concluded that this type of composite can operate as a damping material due to the specific properties such as high shear strength, indentation strength toughness. So, the foresaid properties make them a great choice with high potential application in various industries.Also, the ways to get the effective parameters to achieve more negative Poisson’s ratio were investigated. The parameters include the foam density as well as material, diameter and distances between ABS tubes. The results show that with decreasing foam density and decreasing distances between ABS tubes, the negative Poisson’s ratio first increases to reach the critical value and then decreases.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    255
  • End Page: 

    266
Measures: 
  • Citations: 

    0
  • Views: 

    127
  • Downloads: 

    95
Abstract: 

“Tensegrity” refers to a class of discrete structures with two-force members (bars and cables) wherein cables only take tensile loads and bars only take compressive loads. The pre-stressed members are interconnected so as to form a self-equilibrium structure. Compared to a truss, supporting the same external loading, a tensegrity structure has fewer members and could weigh less. Determining the stable topology (member connectivities), shape (node coordinates) and size (cross-sectional areas of members) of a tensegrity structure for weight minimization is a challenging task, as the governing equations are nonlinear and the conventional matrix analysis methods cannot be used. This article addresses the weight minimization of a class one tensegrity structure with a given number of bars and cables, anchored at certain nodes and supporting given load (s) at certain node (s). In this paper, a novel procedure is proposed to optimize topology, shape and size of tensegrity structures simultaneously based on evolutionary methods. Member connectivities and their cross-sectional areas and force densities are taken as design variables, whereas the members’ strength and buckling requirements and maximum nodal displacements constitute the constraints, along with the coordinates of the floating nodes to make the structure symmetric. Constraints are evaluated through the nonlinear shape design of the self-equilibrium structure and the linear analysis of the loaded structure, assuming small displacements. Using a novel approach, optimization is simultaneously performed in multiple promising areas of the solution space, resulting in multiple, optimum solutions. The diversity of the solutions is demonstrated by applying the proposed approach to a number of structural design problems.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    267
  • End Page: 

    276
Measures: 
  • Citations: 

    0
  • Views: 

    182
  • Downloads: 

    90
Abstract: 

With the rapid progress of nanotechnology, application of nano-scale materials has been extensively increased. Due to increase of surface effects at small sizes, the classical theories are not capable of modeling nano-scale systems. On the other hand, more accurate methods at small sizes are based on the quantum and atomistic models which are too time consuming, and hence using these methods is limited to very small sizes for a short period of time. In this research coarse-graining models for accelerating molecular dynamics simulations for the analysis of silicon structures are proposed. In this technique, after assigning a proper map between beads of the coarse-grained model and atoms of the main structure, the system parameters are modified in a scheme in which the original model and the coarse-grained models have the same physical properties. By using various static and dynamic simulations and evaluating the size effect, the accuracy and speed of the proposed model is examined. The error of this CG model for investigating the Young modulus, longitudinal and transversal vibration is less than 5 percent, while it is about 8 times faster than AA model.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    277
  • End Page: 

    284
Measures: 
  • Citations: 

    0
  • Views: 

    183
  • Downloads: 

    101
Abstract: 

In this study, a numerical investigation of using Rapeseed Oil in National Diesel Engine (EFD) has been developed and validated against the experimental data. By using validated model, the effect of injection timing, exhaust gas recirculation and initial pressure on performance and emissions of this engine with three different range of using diesel and biodiesel fuels have been investigated. The results from simulation showed that the increase in biofuel percentage increase thermal efficiency and decrease monoxide carbon emission. Biofuel has a lower heating value compared to diesel fuel, resulting in a lower combustion heat release and lower power. On the other hand lower heat release reduces the temperature of cylinder contents which tends to reduce nitrogen oxide. In some cases that there is an Oxygen shortage in the cylinder, the existence of Oxygen in the structure of the fuel will complete the combustion process and it may improve the combustion efficiency compared to diesel fuel. The increase in heat release due to higher combustion efficiency of biofuel may compensate for its low heating value and result in increasing the engine power and nitrogen oxide emission.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    285
  • End Page: 

    289
Measures: 
  • Citations: 

    0
  • Views: 

    322
  • Downloads: 

    172
Abstract: 

The main concern in the design of multi-cavity molds is flow balance between cavities. Any departure in flow balancing of the cavities can result in difficulties in processing and quality of injected parts. In this paper, flow balance in a two-cavity plastic injection mold with different sizes (or family-cavity mold) was investigated. Mold flow software was implemented to predict the filling phase through the cavities. Diameters of runners related to each cavity were adjusted to attain a balanced flow. Evaluation of the flow balance was conducted by injection molding as short-shot and measuring the weight of each cavity. A high density polyethylene (HDPE) was applied as plastic material in this research. Good agreement was observed between experimental and simulation results. Moreover, in this paper one of the runners could be resized while injection molding via an insert located in the mold. The effect of flow balance on the tensile properties of the injection molded specimens was investigated. The results indicated that the parts obtained from the balanced mold exhibit a higher tensile strength and elongation at break up to 14% and 18%, respectively. The dimensions of injected parts were measured. It was found that there are not any differences between the shrinkage of specimens obtained by balanced and unbalanced mold.

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Writer: 

SHAHRIARI ALIREZA

Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    29
  • End Page: 

    40
Measures: 
  • Citations: 

    0
  • Views: 

    167
  • Downloads: 

    95
Abstract: 

In the present paper, natural convection heat transfer of CuO-water Nano fluid subjected to a uniform magnetic field within an enclosed cavity considering Brownian motion is studied by adopting the lattice Boltzmann model. The left wavy wall is heated sinusoidally, while the right flat wall is maintained at the constant temperature of Tc. The top and the bottom horizontal walls are smooth and insulated against heat and mass. The variation of density is slight; thus, hydrodynamics and thermal fields equations are coupled using the Boussinesq approximation. The density and energy distribution are both solved by D2Q9 model. In this paper, the influence of pertinent parameters such as solid volume fraction of nanoparticles, Rayleigh number, Hartmann number and wavy-wall geometry parameters on flow and heat transfer fields are investigated. Results show that the heat transfer increases with the increment of Rayleigh number and nanoparticles volume fraction, but it decreases with the increment of the Hartmann number. The enhancement of magnetic field increases or decreases the effect produced by the presence of nanoparticles at different Rayleigh numbers. In addition, it is shown that for a fixed Rayleigh number and Hartmann number, the heat transfer performance depends on tuning the wavy surface geometry parameters. The greatest effect of nanoparticles is observed by considering the role of Brownian motion. This study can provide useful insight for enhancing the convection heat transfer performance within enclosed cavities with wavy-wall surfaces and sinusoidal temperature distribution under influence of magnetic field.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    290
  • End Page: 

    298
Measures: 
  • Citations: 

    0
  • Views: 

    138
  • Downloads: 

    88
Abstract: 

The anti-lock braking system is one of the main factors to provide safety in designing vehicles. The brake pressure control and desired slip tracking through severe braking ensure safety in vehicles.Because of uncertainty in parameters and sever nonlinear factors, robust controller designing is suitable for this system. In this paper, various types of sliding mode controller have been used to achieve a vehicle desired slip and its stop. Sliding surface and terminal attractions will be analyzed in all of the designed controllers. Also, a new structure with high terminal attraction has been used for the fast terminal sliding mode controller (FTSMC). The proposed method has reduced tracking error as well. In this paper, the performance of this controller is compared with normal terminal sliding mode controller and fast terminal sliding mode. Moreover, all design parameters are determined to decrease error ratio using particle swarm optimization (PSO) algorithm. This method is suitable for solving complex optimized solution based on certain cost function. Simulation results using MATLAB software, present better performance of the suggested controller in comparison with normal and fast terminal sliding mode controller.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    299
  • End Page: 

    306
Measures: 
  • Citations: 

    0
  • Views: 

    150
  • Downloads: 

    86
Abstract: 

Electrohydraulic forming (EHF) is a high velocity sheet metal forming process in which two or more electrodes are positioned in a water filled chamber and a high-voltage discharge between the electrodes generates a high-pressure to form the sheet. In this study extensive experimental tests were carried out to investigate the effect of different parameters (such as discharge energy, standoff distance and electrodes gap) on the maximum drawing depth and implicit on shock wave maximal pressure in electrohydraulic free forming. EHF is a complex phenomenon and experimental work alone is not sufficient to properly understand this process. To explain different aspects of the problem, Arbitrary Lagrangian Eulerian (ALE) formulations coupled with fluid–structure interaction (FSI) algorithms that are available in the advanced finite element code LS-DYNA were used for the numerical simulation. In order to model the effect of the electrical discharge, two different approaches were implemented; explosive equivalent mass and energy leak. In the first approach, according to the similarity between explosion and electrical discharge in the water, electrical discharge energy was converted to equivalent TNT mass. In the second approach electrodes gap is replaced by a plasma channel and electrical discharge energy was leaked to it in a short amount of time which makes the channel expand and generate shock waves propagating toward the work piece. Finally, a good correlation was observed between the experimental and simulation results.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    307
  • End Page: 

    314
Measures: 
  • Citations: 

    0
  • Views: 

    143
  • Downloads: 

    134
Abstract: 

Controlling the path of drugs movement is one of the processes that can effectively aid in treating a variety of diseases. For example, in chemotherapy, a small fraction of a drug is delivered to cancer cells and other amounts can cause destruction of healthy tissues of body, as a result, before destruction of tumors, the body might be destroyed. Hence tumors cannot be removed from the body completely. If it is possible to control the path of drugs, tumors could be removed with the least injury. One of the ways through which movement of the drugs could be controlled is Magnetic Drug Targeting (MDT). In this project, movement of magnetic particles and their interactions would be inspected in the blood with consideration of a constant magnetic field gradient. After introduction of governing equations and presenting a good model for the forces between particles, these processes are be simulated in the Fluent software. The model that is used is a vein with 8 mm diameter. The simulation was done from the time of injection over an 8 cm length of the vein. The base fluid is blood which is considered as a non-Newtonian fluid. Distribution of magnetic particles in the base fluid has been governed by multiphase approach. Simulation results show that residence time of the drug in the presence of magnetic field increases, which in turn increases the possibility of drug absorption.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    315
  • End Page: 

    321
Measures: 
  • Citations: 

    0
  • Views: 

    153
  • Downloads: 

    79
Abstract: 

The early success in the 1960s of the Kalman filter in aerospace applications led to attempts to apply it to more common industrial applications in the 1970s. However, these attempts quickly made it clear that a serious mismatch existed between the underlying assumptions of Kalman filters and industrial state estimation problems. Accurate system models and statistical nature of the noise processes are not as readily available for industrial problems. In this paper, a novel method of combining both nonlinear unscented Kalman filter and H¥ unscented Kalman filter is presented so that the results are a compromise between the addition of more reliability compared to that of two other filters. One characteristic of this filter is there is no need to linearize the nonlinear problems and more suitable results are obtained than the other two filters with non-Gaussian noise. Investigations show, when in a part of estimating the UKF is best and in the other part the UH¥F, the hybrid filter can give better results. The variance analysis indicated that the filter is robust to statistical noises and a proper response can be found by changing its variable. Validation of results is performed by simulation of two nonlinear problems, free falling and inverted pendulum in mechanical engineering.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    322
  • End Page: 

    330
Measures: 
  • Citations: 

    0
  • Views: 

    344
  • Downloads: 

    85
Abstract: 

Nowadays the use of fiber-metal laminate due to advantages such as high strength to low weight ratio, easy fabrication of structural components despite complex geometries to various industries such as aviation industry, widely increased. The fiber-metal laminates are a kind of hybrid composites which connect the layers of metal and fibers which together are mediated by material and in the wake of this combination, positive characteristics of metals and fibers composites simultaneously in structural integration offer significant capabilities. Addition of shape memory alloy to fiber metal laminate composite, due to the super elasticity properties of alloy, causes the alloy to form during the impact hysteresis loop, and will attract considerable energy and the impact properties of the fiber metal laminate composites will increase. In this study, effects of different strains of nickel-titanium shaped memory alloy wire at high temperature, was investigated experimentally in this type of composites against low speed impact using the impact falling. In the metal part of fiber metal laminate composites, 2024-T3 aluminum alloy sheet and in composite part of glass fibers and epoxy resin is used.6 wires with the pre strains 1, 2 and 3% were used in order to wrap the fibers in metal laminate composites.Increase in the impact resistance of such composites which include reducing the force shock of impact, increasing the contact time, reducing the amount of displacement, reducing absorbed energy and reducing the damaged area by increasing pre strain as well as the energy absorbed by the shape memory alloy when impact, were the results of this research.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    331
  • End Page: 

    340
Measures: 
  • Citations: 

    0
  • Views: 

    132
  • Downloads: 

    95
Abstract: 

In this article, mixing in the combined electroosmotic/pressure driven flows of non-Newtonian fluid in a micro channel with rectangular obstacles and non-homogeneous ζ-potential has been studied numerically. The non-Newtonian behavior of the fluid is considered for the flow field using power law rule. Also, the nonlinear Poisson-Boltzmann equation is used to model the distribution of ions across the channel and the electric potential. Numerical solutions of coupled equations of momentum, electric field and concentration field are performed by means of finite element method. In this study, the effects of various parameters such as pressure gradient, rheological behavior of the fluid and the geometrical and physical parameters of obstacles on the mixing quality are investigated. The results indicate that applying adverse pressure gradient to the flow, the dilatant behavior of the fluid, as well as the height of barriers, is highly effective in the enhancement of the mixing quality within the microchannel. It is found that for microchannels with heterogeneous V-potential, increasing the length of obstacles significantly increases the mixing efficiency while for the microchannels with homogeneousV-potential, barrier length has a slight effect on mixing efficiency.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    341
  • End Page: 

    348
Measures: 
  • Citations: 

    0
  • Views: 

    254
  • Downloads: 

    86
Abstract: 

In present study, the entropy analysis for laminar MHD flow over a stretching sheet with variable heat flux in presence of heat source and constant suction is done. The flow is influenced by uniform transverse magnetic field. The PDE governing differential equations including continuity, momentum, and energy are reduced to ODE ones by similarity solution. Then, the ODEs are solved by applying the 4th-order Runge-Kutta method. To validate, the result of this study and the published result are compared and the agreement is achieved. Bejan number is used as a design criterion parameter for a qualitative study about the cooling. The effects of suction parameter, heat source parameter, magnetic parameter, Prandtl number and heat flux parameter on dimensionless velocity and temperature, dimensionless entropy generation and Bejan number are shown in several plots. The results show that with increasing Prandtl number, suction, heat source parameter, magnetic parameters and parameters related to heat flux, the Bejan number is decreased, decreased, increased, decreased and decreased, respectively. The results of this research can be used for the increasing the cooling in the surface in the coating.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    349
  • End Page: 

    358
Measures: 
  • Citations: 

    0
  • Views: 

    163
  • Downloads: 

    108
Abstract: 

Slug flow is one the most complicated flow regimes in industrial processes that is seen for a wide range of fluid flow. However, there are always a lot of differences between experimental and numerical studies on slug flow. Following the previous attempt on the selection of the best turbulent model for numerical simulation, the slug flow is solved two-dimensionaly with implicit VOF method and k-e RNG turbulent model using FLUENT solver to extract the slug flow parameters behavior accurately.The differences of numerical simulation of slug flow with and without turbulent model are also presented. To overcome this procedure, a new user defined function code is developed. This UDF computes and predicts slug parameters from FLUENT solver result without increasing the computational cost. The important slug parametrs are presented which are: liquid slug body velocity, liquid film velocity, slug front and tail velocity, slug center position and length, slug front and tail positions, pressure difference across slug, wall shear stress, slug mixture velocity, slug initiation time and position from the duct inlet. These parameters are discussed in detail, then validated.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    359
  • End Page: 

    368
Measures: 
  • Citations: 

    0
  • Views: 

    153
  • Downloads: 

    89
Abstract: 

Dynamic stall behavior of a NACA0012 airfoil undergoing pitching motion has been studied by a numerical approach. The turbulence intensity, oscillation frequency and amplitude and the Reynolds number were found to be the major contributors in dynamic stall. The flow field structure and the associated vortices for this airfoil as well as the impact of the oscillation frequency on aerodynamic efficiency were also studied. The simulations were two dimensional and the k-w SST turbulence model was utilized for the present analysis. The results show that increasing the oscillation frequency and amplitude and the turbulence intensity, postpones the dynamic stall to higher angles of attack.Furthermore, as the Reynolds number is increased, both the lift coefficient and the width of the associated hysteresis loop decrease. The airfoil aerodynamic efficiency variation with oscillation frequency has been shown to have a maximum point for all angles of attack considered. The flow field structure revealed that the main cause of the dynamic stall is a series of low pressure vortices formed at the leading edge which shed into downstream and separate from the surface. A secondary vortex will then appear and increase the lift coefficient dramatically. The present simulation results are in a good agreement with those found in the literature.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    369
  • End Page: 

    380
Measures: 
  • Citations: 

    0
  • Views: 

    393
  • Downloads: 

    146
Abstract: 

Courtyard has been recognized as one of the main elements in the Iranian culture, architecture and building design. According to its micro-climate effect in improving thermal performance of building, courtyard has been considered as a considerable subject for many researches. This paper investigates the courtyard’s design parameters and geometric configurations in pre-design states for improving thermal performance and comfort. For achieving this point, in this research the influence of courtyard orientation, horizontal dimensions and other parameters related to geometry have been evaluated. Due to micro-climate effect of courtyard on parameters related to thermal comfort, three main geometric layouts such as closed, semi-closed and open geometry have been investigated and compared by CFD simulations in ENVI-met software. The thermal comfort parameters are also investigated through comparing mean PMVin all simulations cases, using Fanger’s extended model. The results showed that thermal performance of closed shaped courtyard is better than other layouts. Also the comparison of results related to different aspect ratios (length to width ratios), provide evidence that thermal performance improves as the aspect ratio gets close to 1. That means as the courtyard shape encloses to the form of a square, the thermal performance improves and the mean air temperature in the investigated microclimates declines. To determine the best configuration for Tehran’s climate, the results showed north-south orientation of building and increase of the height of the courtyard, are the two most appropriate considerations that will directly improve the thermal performance and comfort, specifically in closed and semi-closed layout.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    381
  • End Page: 

    392
Measures: 
  • Citations: 

    0
  • Views: 

    106
  • Downloads: 

    93
Abstract: 

Vehicle vibration and noise characteristics play a major role in ride comfort. Noise of tire in contact with the road is one of the main sources of noise in passenger cars, caused by the rolling of tire on uneven surfaces. Excitation is done through tread structure to fluid cavity and noise and vibrations transmission to the rims are of particular importance. In this paper, vibration analysis of coupled acoustic model of tire, rim and fluid acoustic cavity is performed. For this purpose, a coupled numerical finite element model is used. First, tire modeling has been addressed, taking into account the tread and two side walls and steel wheel rim. Then modal analysis has been performed to identify the structural and acoustic resonance frequencies and mode shapes. Then, using the harmonic environment coupled with static and modal analyses, acoustically coupled models of tire, rim and cavity are used to calculate the acoustic pressure of the fluid cavity and sound pressure level, and the harmonic frequency response of the wheel hub system including the forces of wheel hub is discussed. According to the presented model, the parameters affecting tire noise levels are discussed.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    393
  • End Page: 

    398
Measures: 
  • Citations: 

    0
  • Views: 

    97
  • Downloads: 

    87
Abstract: 

In this paper, static analysis of transversely anisotropic laminate is investigated using improved zig-zag theory. Variation of in-plane displacement is assumed to be sinusoidal while transverse displacement is assumed to remain constant through the thickness. This piece-wise continuous sinusoidal function satisfies transverse shear stresses continuity in interfaces. The Hamilton principle is utilized to derive governing equations and related boundary conditions. The Navier-type solution is presented for simply supported boundary conditions. The theory has the same unknown variable field as Euler Bernoulli beam although it predicts stresses with high accuracy. The validity of solutions is confirmed by comparing present model results with that reported in the literature. Numerical results are given to study the influences the transverse anisotropy on displacement, strain and stress fields through the thickness.The piece-wise continuous sinusoidal function offers more accurate transverse stress distribution in comparison with the piece-wise polynomial function. The present theory provides a slightly more accurate stress field through the thickness compared to high order shear deformation theory, which in turn is more accurate than Euler-Bernouli theory. The result shows the continuity of normal strain through thickness predicted by Euler-Bernouli theory has no physical basis. Furthermore, the improved zig-zag theory is capable of capturing precise stress field through the thickness in transversely anisotropic laminate.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    399
  • End Page: 

    409
Measures: 
  • Citations: 

    0
  • Views: 

    144
  • Downloads: 

    148
Abstract: 

The aim of this research is to dynamically investigate the effect of high-heel shoes on the amount of internal forces and torques produced in the lower body joints (hip, knee, and ankle joints) during walking. To do so, the gait analysis of the subject, in two states of walking barefoot and with high-heel shoes, has been conducted in a Musculoskeletal Research Center and then the required kinematic data including rotation matrices, angular velocity and angular acceleration of lower legs using kinematic analysis of legs have been derived. Also, the ground reaction forces have been measured using a force plate installed in the lab and by presenting a 3D dynamic model of lower legs and solving the inverse dynamic problem of model, forces and moments of the joints for the two above modes during stance phase of a gait cycle have been calculated. Based on obtained results from investigation of dynamic effect of high-heel shoes during walking, variations of internal joint forces have not been salient.However, internal joint moments in state of gait with high-heel shoes with respect to barefoot walking increased considerably. According to the results, long-term use of high-heel shoes can lead to damage of lower body joints, especially the knee joint, as well as driving muscles of these joints.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    41
  • End Page: 

    51
Measures: 
  • Citations: 

    0
  • Views: 

    103
  • Downloads: 

    77
Abstract: 

In during take-off and landing phases, flow structures and aerodynamics forces differ from the unbounded flow field. Computational fluid dynamics were used to study the flow field of a cranked kite wing with the focus on studying vortices treatment. Different Angles of attack and heights were investigated at the freestream 70m/s. Q-criteria shows that in ground effect, vortices treatment is at angles of attack 2o, similar to 0o and angle of attack 8o similar to angles 4o and 6o.According to the topology of pressure gradient vectors at the angle of attack 2o, the center of all vortices in ground effect is fixed approximately. Axial residual vorticity, axial velocity and induced suction of all vortices increase and is surfaces of Q-criteria become thicker. At the angle of attack 8o with decreasing height, axial residual vorticity of the primary vortex and the wing kink location vortex increase and decrease respectively. Also, the kink location vortex approaches the primary vortex and it takes away from the wing surface. At the angle of attack 8o, the coherent structure of vortex between leading edge and the kink location vortex breaks down in ground effect and recirculation bubble form on the wing surface.With decreasing height, the most drag and the lift coefficients increment occur on the lower surface of the wing.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    410
  • End Page: 

    418
Measures: 
  • Citations: 

    0
  • Views: 

    309
  • Downloads: 

    88
Abstract: 

Cladding on metallic products is relatively applicable in industries, e.g. aerospace, automotive and oil.One layer cladding on metallic specimens could improve mechanical, thermal and corrosion resistance properties considerably. Nowadays carbon steels have the highest share of metallic materials among different industries. One layer cladding on this type of steel with the aim of enhancing the corrosion resistance could decrease the price of them when they are put into use in different conditions. In this study, for the first time, cladding of the carbon steel by 6061-T6 Al alloy via Friction Stir was carried out successfully. In order to control cladding, the effect of different rotational speeds and traverse speeds on mechanical properties and structure of cladded layer was inspected. Results of shear test showed that by increasing the traverse speed the shear strength of the cladded layer increases due to the addition of material into the joint area uniformly. By decreasing the rotational speed and increasing the traverse speed, the generated heat from friction decreases and prevents over-stirring in joint area and as a result the shear strength of the joint will increase.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    419
  • End Page: 

    430
Measures: 
  • Citations: 

    0
  • Views: 

    145
  • Downloads: 

    143
Abstract: 

In this paper, a new immersed boundary-lattice Boltzmann method (IB-LBM) is developed to simulate heat transfer problems with constant heat flux boundary condition. In this method, the no-slip boundary condition is enforced via implicit velocity correction method and the constant heat flux boundary condition is implied considering the difference between the desired heat flux and the estimated one. The velocity correction represented as a forcing term is added to Boltzmann equation and for temperature correction, a heat source/sink term is introduced to energy equation. Elimination of sophisticated grid generation process, simplicity and effectiveness while keeping the accuracy, are the main advantages of the proposed method. Using the developed method, natural convection around a hot circular cylinder with constant heat flux in an enclosure with cold walls has been simulated at Rayleigh numbers of 103-106. Moreover, effects of diagonal position of cylinder on the flow and heat transfer patterns and local Nusselt number distribution on the surface of cylinder and walls of enclosure have been investigated.The obtained results show that the location of maximum local Nusset number is extremely dependent on the diagonal position of the cylinder. According to the results of this simulation, it can be said that the present method is able to imply accurately the constant heat flux boundary condition.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    431
  • End Page: 

    442
Measures: 
  • Citations: 

    0
  • Views: 

    160
  • Downloads: 

    81
Abstract: 

Lateral jet control systems are being considered as attractive alternatives to conventional control systems in recent years. In present study which is divided in two parts, the effects of lateral jet interaction with supersonic cross flow on aerodynamic behavior of a standard projectile at zero angle of attack has been studied numerically. In the first part, results of the effects of parameters such as jet location, Mach number and nozzle type on pressure coefficient drag coefficient drag force and pressure distribution on the fins are presented and analyzed. In the second part, longitudinal static and dynamic stability coefficients of the projectile in presence of lateral jet haves been achieved and evaluated according to the mentioned parameters. According to the results, jet location is the most effective parameter. In the first part, the pressure distribution on the fins is considerably dependent on jet location. Effect of Mach number on pressure coefficient, drag force and drag coefficient is also significant. Besides variation of the pressure distribution on the fins becomes more obvious at the final locations by variation of Mach number. In the second part, lateral jet effect leads to decreasing longitudinal static stability. Increasing the Mach number also results in decreasing longitudinal dynamic stability and jet displacement make nonlinear behavior over pitch damping moment coefficient, therefore choosing proper jet location is dependent on desired parameters of designer. According to the results, effect of nozzle type has been insignificant for all cases.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    443
  • End Page: 

    452
Measures: 
  • Citations: 

    0
  • Views: 

    175
  • Downloads: 

    114
Abstract: 

Design of fault detection and diagnosis systems (FDDS), although extending the control strategies, are challenged by controller interferences in fault diagnosis. In this study, in order to improve performance and accuracy of FDDS in the fault detection process, influential parameters and the level of corresponding interferences are investigated. For this purpose, a powerful method in fault pattern recognition of industrial plants based on dynamic behavior and dynamic model using soft computing is designed and tested on simulated suspension system of a vehicle. The suspension system is one of the parts that most affects reliability and safety of the vehicle. For investigating the level of interference caused by the control unit, the simulations of both passive and active (equipped with hydraulic actuator) suspension systems are utilized in association with the control unit. The results of tests under variable circumstances (using random values) demonstrate that the presence of control unit restricts the FDDS process and reduces the robustness of the system against disturbances and noise. Considering the way in which the control unit affects the process, application of suggested solutions in this research have a considerable impact on limiting the adverse effects. Fault detection program which is provided by Matlab software is a useful tool to investigate and define the effect of control units and can be considered as a useful device to facilitate the research and precipitate conduction of tests in different stages.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    52
  • End Page: 

    60
Measures: 
  • Citations: 

    0
  • Views: 

    113
  • Downloads: 

    88
Abstract: 

Today, many researchers focus on proposing severe plastic deformation (SPD) methods due to the superior mechanical and physical properties of achieved ultra-fine grain material. In all SPD methods a large strain is implied without any substantial dimensional change of work piece to generate UFG and even nanograin (NG) materials. Equal Channel Angular Pressing (ECAP) is one of the most successful techniques for industrial applications. Using a long and thin rod is limited in ECAP process. In the present study, a combined process composed of ECAP and Extrusion processes is used on Titanium grade 2. Titanium is extensively used in aviation and other industries because of its high strength to weight value. Using the combined process leads to production of long length and thin nanostructured rod. The main goal of this process is evaluation of the temperature in Extrusion process on nanostructures Titanium rods. At first, Titanium rods were processed for 4 passes by ECAP process at 400oC and then they were processed by Extrusion process at 5 different temperatures including 300, 350, 400, 450 and 500oC. The result showed that the best mechanical properties achieved for the specimen were extruded at 300oC. Strength and hardness were severely improved. Also, the microstructure was very homogenous and refined. The mechanical properties of titanium grade 2 after combined process were equivalent to titanium grade 5 which is used in medical applications and is expensive.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    61
  • End Page: 

    66
Measures: 
  • Citations: 

    0
  • Views: 

    198
  • Downloads: 

    105
Abstract: 

Measurement of fracture toughness is one of the quality control parameters in rail manufacturing process. Fracture toughness value is needed for designing the rail lines, analysis of defects and other common prevalent works in mechanical engineering. The goal of this research is to introduce a relation for measuring fracture toughness of rail materials with grade R260 by Charpy V-notch number. At first the fracture toughness of rail material has been determined by 3-point bending technique according to ASTM E399 in ambient temperature. The fracture energies have been measured by Charpy impact test and it has been illustrated that fracture energies have no significant change in the tests temperature limit. Relations between the chemical analysis and mechanical properties have been studied and compared with results of the other researchers. Uniaxial tension test, analysis of chemical composite, metallography and hardness test have been carried out for better study of the process. Finally, a relation to connect the Charpy V-notch number and fracture toughness has been introduced and the fracture toughness of the rails material over the impact test temperature limit has been calculated. Good agreement between calculated results and the result of 3-pint bending test indicate appropriate accuracy of the introduced equation.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    67
  • End Page: 

    77
Measures: 
  • Citations: 

    0
  • Views: 

    273
  • Downloads: 

    129
Abstract: 

In this paper, dynamic modeling, optimal path planning and control scheme on a redundant parallel cable robotis presented. Path planning in parallel robots necessitates the consideration of robot’s kinematics to discern the singularities in the workspace. Also, dynamics analysis is required to consider actuation constraints. To this end, kinematics and dynamics of cable driven redundant parallel robot is derived. In this modeling, cables are assumed to be rigid with negligible mass and hence, tension and sagging along the cable are neglected. Next, a sampling-based algorithm upon rapidly-exploring random tree is developed to increase the convergence rate. In this scheme, distance, epochs and safety are considered as optimization constraints. To evaluate the performance of the proposed algorithm in collision avoidance, a number of obstacles have been considered too. Tracking of the planned path has been handled using a feed-forward controller in the presence of obstacles. Regarding the redundancy feature of robot, a redundancy resolution scheme is considered for optimal force distribution. Path planning and control algorithms are implemented on the RoboCab (ARAS Lab.) and experimental results reveal the efficiency of the proposed schemes.

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  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    78
  • End Page: 

    84
Measures: 
  • Citations: 

    0
  • Views: 

    140
  • Downloads: 

    102
Abstract: 

Friction stir extrusion (FSE) is a process based on the heat generated by friction between die and materials in which a sample is produced through consolidation and extrusion of precursor materials such as metal chips. In this paper, the wire samples produced by friction extrusion of aluminum alloy AA7022 chips are investigated. The samples were extruded at different rotational speeds and extrusion forces, and impacts of these two parameters were studied. At first, structural properties of samples were studied using optical microscopy and scanning electron microscopy (SEM). The result showed that the samples produced at higher rotational speeds and lower forces had a far better surface quality and lower surface crack were seen on them. On the other hand, the temperature of process and grain size was increased with rise of rotational speed. The SEM micrographs showed that by changing rotational speed and extrusion force, the amount of adhesion and sintering between aluminum particles change and by optimizing these parameters can decrease wire’s internal defects and pits. In the following, to study mechanical properties, micro hardness and compression tests were used. The values of hardness and yield stress of samples were decreased with increasing rotational speed and increasing the extrusion force to a certain extent caused increase in yield stress of material.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    85
  • End Page: 

    91
Measures: 
  • Citations: 

    0
  • Views: 

    140
  • Downloads: 

    106
Abstract: 

The usages of Stirling engine in many industries such as aerospace, submarines and combined heat and power systems, requires more and detailed analysis in such engines. This type of engine is an external combustion which may use almost any type of fuel. In this article the Nusselt number and friction coefficient of a Stirling engine heat exchanger is investigated numerically. The geometry of this heat exchanger is an arc shape pipe with reciprocating flow. Various parameters such as angular frequencies, type of fluids, working gas pressures, flow regime and heater geometry impact on the Nusselt number and friction coefficient of the heater were investigated. By increasing the angular frequency and the working gas pressure the Nusselt number increases but the friction coefficient decreases. The influences of different working fluids indicated that carbon dioxide has the highest Nusselt number. The results also show that the friction coefficient is highly dependent on the flow regime. Comparison between the two different geometry type heaters shows that the arc-type geometry led to higher Nusselt number. The friction coefficients of both geometries are almost similar to each other at high frequencies.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    9
  • End Page: 

    16
Measures: 
  • Citations: 

    0
  • Views: 

    117
  • Downloads: 

    80
Abstract: 

This article aims to study the effect of membrane initial configuration and the membrane spontaneous curvature (local asymmetry of layers) on the shape transformation of lipid bilayer vesicles. Since the evolutionary models are considered as a generalization to the equilibrium methods, the used model is developed based on the dynamic equilibrium between the membrane bending potential and the environmental fluid friction in each domain of two-phase vesicle. The effect of membrane inertia on the dynamics of the system is ignored. Key parameters are the size of each phase and different combinations of protein distribution as the local spontaneous curvature. Assumed initial conditions are simple shapes such as dumbbell, biconcave and oblate; free vesicles are usually visible in these shapes.Previously published experimental observations are used to evaluate the numerical results. Some situations of homogeneous and multi-phase vesicles and red blood cells under the influence of the spontaneous curvature induction mechanisms (for example, the composition of the membranes, membrane proteins such as albumin, environmental solution concentration changes) are simulated and the results presented in detail. The possibility of the membrane deformation and the relation of membrane phenomena with the primary form and various curvature distributions are discussed.

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Issue Info: 
  • Year: 

    2017
  • Volume: 

    17
  • Issue: 

    4
  • Start Page: 

    92
  • End Page: 

    100
Measures: 
  • Citations: 

    0
  • Views: 

    122
  • Downloads: 

    95
Abstract: 

In this paper, the results obtained from experimental measurements of average and turbulence quantities of a turbulent rectangular impinging jet hitting a fixed wall are reported using the laser doppler anemometry (LDA) method. The nozzle to plate distance is 10 times the nozzle width, and the tests are repeated for three different Reynolds numbers, namely Re=3000, 6000 and 9000. The aim of the current research was to investigate and compare flow in different Re and also to determine the two effective experimental errors on average velocities, namely data sampling and residence time in measurement volume. The results reveal that the previous stated correlation for prediction of the number of data required for ensuring independence of the average flow variables on the number of the sampled data is not sufficient by itself, and depending on the turbulence intensity of the flow, this correlation could become ineffective. Further, in the present study, the residence time is used for calculation of average velocities, and the results are compared with those obtained by particle image velocimetry (PIV) method. The comparison shows good agreement between the results from LDA and PIV when considering effect of residence time within the averaging equations in the former method. The results show that the behavior and quantity of the dimensionless average velocities for various Reynolds numbers are identical at most cross sections of the flow domain while the dimensionless turbulent stresses have different quantities at different values of the Reynolds number.

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