AUT Journal of Mechanical EngineeringAUT Journal of Mechanical Engineering
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Tue, 17 Jul 2018 05:25:10 +0100FeedCreatorAUT Journal of Mechanical Engineering
http://ajme.aut.ac.ir/
Feed provided by AUT Journal of Mechanical Engineering. Click to visit.Thermal Analysis Circular Couette Flow of Non-Newtonian Fluid with Viscous Dissipation
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Volume 2, Issue 1, Winter and Spring 2018, Page 3-12<br><br>The forced convection heat transfer in the circular couette flow of Non-Newtonian fluid is investigated when the inner cylinder is rotated at angular speed and the outer cylinder is fixed. The fluid viscosity is considered concurrently to be dependent on the temperature and shear rate. The temperature dependency of viscosity is modeled exponentially according to the Nahme law and dependence of viscosity on shear is modeled with the Carreau equation. The Viscous dissipation term is adding intricacy to the already highly interdependent set of governing motion and energy equations. The highly nonlinear governing equations are derived for the steady state base flow in the narrow gap limit. The perturbation method has been applied to obtain an approximate solution for these equations. The effect of governing parameter such as Brinkman numbers and Deborah number on the thermal stability is examined. In addition, the analysis illustrated that the Nusselt number of the outer cylinder increases as the Deborah number increases. It, although, decreases by increasing Brinkman number. The pseudoplastic fluid between concentric cylinders is heated as Brinkman number and increases due to frictional loss and it is cooled as Deborah number increases due to the fluid elasticity behavior.Thu, 31 May 2018 19:30:00 +0100The Buckling Analysis of Conical Sandwich Shells with Temperature Dependent Properties and an ...
http://ajme.aut.ac.ir/article_2738_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this study, an improved higher-order theory is used for buckling analysis of sandwich conical shells with thin functionally graded face sheets and homogenous soft core and with temperature-dependent properties. In-plane and transverse displacements of the core are assumed by cubic functions, and displacements of the FG face sheets are assumed by first-order shear deformation theory. The linear variation of temperature is assumed in the face sheets and the core. The material properties of the FG face sheets are assumed to be temperature-dependent by a third-order function of temperature and vary continuously through the thickness according to a power-law or an exponential distribution in terms of the volume fractions of the constituents. The nonlinear Von-Karman relations are used. Analytical solution for static analysis of simply supported sandwich conical shells under axial in-plane compressive loads and thermal conditions is performed by using Galerkin’s solution. The results show that the values of the critical dimensionless static axial load are affected by the configurations of the constituent materials, compositional profile variations, semi-vertex angle, thermal condition and the variation of the sandwich geometry. The comparisons show that the present results are in a good agreement with those in the literature.Sun, 17 Dec 2017 20:30:00 +0100Simulation of Natural Convection in Eccentric Annulus: A Combined Lattice Boltzmann and ...
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Volume 2, Issue 1, Winter and Spring 2018, Page 13-26<br><br> In the present study, a hybrid method of thermal lattice Boltzmann and smoothed profile methods have been applied to simulate free convection in an eccentric annulus with a constant temperature wall. Smoothed profile method employs an Eulerian approach to consider the fluid-solid interaction without using an extra mesh for capturing solid boundary. As a result of this property, the combination of this method and Lattive Boltzmann method can be considered as an efficient method to simulate free convection in complex geometries like annulus. In order to investigate the effect of inner cylinder position on the natural convection, the inner cylinder was placed in different horizontal, vertical and diagonal positions. Influences of the Rayleigh number (103 ≤ Ra ≤ 105), eccentricity (-0.75 ≤ e ≤ 0.75)) and the radial ratio (Ro /Ri=2, 2.6 and 3.2) on the streamlines, isotherms and Nusselt number were studied. It was found that the Nusselt number has a positive relationship with Rayleigh number and radial ratio. Also, it can be confirmed that Nusselt number in the case with the negative eccentricity (e=−0.75) was larger than the others. It was found that a very good agreement exists between the present results and those from the open literature.Thu, 31 May 2018 19:30:00 +0100Influence of Burner Head Design on Its Thermal and Environmental Characteristics
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Volume 2, Issue 1, Winter and Spring 2018, Page 27-38<br><br>In this paper, for the first time, four thermal and environmental objective functions are simultaneously taken into account in the process of the optimal design of a natural gas diffusion burner. The burner thermal efficiency and the emissions of carbon monoxide, nitrogen oxide, and unburned methane constitute the objective functions of the present study. In the first step, the burner is numerically simulated, and the simulation results are verified through being compared with the available experimental data. Next, the simulation is carried out for the different set values of design variables (the dimensions of the air and fuel inlets, and the overall equivalence ratio) and the optimum design is chosen by using “Pareto front concept”. The paper will show that as a result of the mentioned procedure, the burner thermal efficiency is increased by 29.4%, and the emissions of carbon monoxide, nitrogen oxide, and unburned methane are decreased by 81.2%, 98.6%, and 83.9%, respectively. The manuscript explains the reasoning for the superiority of the modified design over the reference one in detail.Thu, 31 May 2018 19:30:00 +0100Energy and Exergy Analysis and Optimization of a Heat Sink Collector Equipped with Rotational ...
http://ajme.aut.ac.ir/article_2744_257.html
Volume 2, Issue 1, Winter and Spring 2018, Page 39-50<br><br>In this paper, the forced convection flow in a heat sink collector equipped with stationary and rotational obstacles is studied numerically. Three-dimensional governing equations are solved by control volume approach based on the SIMPLE algorithm and k.. turbulence model. Reynolds numbers are considered in the laminar-turbulent range of 50 < Re < 12,000. The optimization was carried out by variation of related parameters. It is concluded that using heat sink, instead of a customary instrument, increases the outlet temperature from the collector and exergy efficiency due to longer installing of the fluid inside the collector. Also, it is realized that using the stationary and rotational obstacles enhance the outlet fluid temperature (about 2.5°C), energy efficiency and exergy efficiency. Nevertheless, using the rotational obstacles is more effective than the stationary obstacles. While the trend of exergy efficiency variation with effective parameters is increasing, applying the obstacles precipitates the efficiency increment (from 4% to 5.3%). In addition, for the case that the trend of exergy efficiency variation by changing these parameters is decreasing, the decreasing trend gets slow. There is a unique mass flow rate (0.005 kg/s) that the exergy efficiency gets a maximum value and for the higher mass flow rates, the efficiency decreases slightly and then remains unchanged.Thu, 31 May 2018 19:30:00 +0100A Fluid-Structure Interaction Study on Vulnerability of Different Coronary Plaques to Blood ...
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Volume 2, Issue 1, Winter and Spring 2018, Page 51-60<br><br>Pathological studies have shown that coronary atherosclerotic plaques are more prone to rupture under physical exercise. In this paper, using a fully coupled fluid-structure interaction (FSI) analysis based on arbitrary Lagrangian-Eulerian (ALE) finite element method, the effect of the coronary blood flow rate increase during physical exercise on the plaque rupture risk is investigated for different plaque types. It is proved that the increase in coronary blood flow rate during physical exercise considerably increases the maximum stress in the plaque fibrous cap which can potentially lead to the plaque rupture. The issue is investigated for different plaque shapes and their vulnerability to exercise condition is compared. It is observed that the diffused plaque type which experiences the maximum stress of 187.9 kPa at rest and 544 kPa at exercise is the most critical plaque type. Because it is subjected to the highest stress in both of these conditions. However, the descending plaque type exhibits the highest susceptibility to physical activity, since its maximum stress increases from 68.9 kPa at rest to 280.5 kPa at exercise which means an increase of about 308%.Thu, 31 May 2018 19:30:00 +0100Numerical Investigation of Water/〖Al〗_2 O_3 Nanofluid Dryout Phenomenon in a Vertical Channel
http://ajme.aut.ac.ir/article_2742_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>Critical heat flux (CHF) phenomenon has been recognized as the upper limit for the safe operation of many cooling systems which may lead to the occurrence of dryout causing a large temperature gradient in the heated wall. One way to increase the level of the CHF is to add certain nanoparticles such as Al_2 O_3 to the base fluid. The present paper concerns the effect of nanoparticles on dryout phenomenon within computational fluid dynamics (CFD). Wall boiling phenomena are modeled using the mechanistic nucleate boiling model developed in Rensselaer Polytechnic Institute (RPI) which is extended to simulate the critical heat flux phenomena by partitioning wall heat flux to liquid and vapor phases. It was shown that the dryout phenomenon can be delayed by increasing the nanoparticles concentration, and in certain concentration of nanoparticles (5 percent), film boiling phenomenon would not occur and for the formation of dryout phenomenon in such concentrations, exerted wall heat flux should be increased to about 13 percent of the base heat flux magnitude.Sun, 17 Dec 2017 20:30:00 +0100Robustness of Controlled Lagrangian Method to the Structured Uncertainties
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Volume 2, Issue 1, Winter and Spring 2018, Page 61-72<br><br>Controlled Lagrangian method uses the inherent geometric structure of the energy of the mechanical systems to provide a stabilizing algorithm for underactuated mechanical systems. The presented method belongs to a larger family of nonlinear control algorithms, namely energy shaping methods in which the controller is designed by providing necessary modifications in the mechanical energy of the system. This paper presents a sensitivity analysis of Controlled Lagrangian method. It is shown that the method presents a suitable performance under the effect of structured (or parametric) uncertainties such as masses values, their positions and their influence on the inertia tensor. Then, the sequel investigates the robustness level of the designed controller in the presence of structured uncertainties. A detailed robustness proof of the scheme is established in this paper. Simulations are provided for a linear inverted pendulum cart system to validate analytical results of robustness to parametric uncertainties. Simulation results confirm that the designed controller for the inverted pendulum, which is unstable and underactuated, is well robust against parametric uncertainties as the analytical studies predicted. The method was also compared with the sliding mode approach, which showed a superior robustness against parametric uncertainties and a more practical control input value. Thu, 31 May 2018 19:30:00 +0100Exact Closed-Form Solution for Vibration Analysis of Beams Carrying Lumped Masses with Rotary ...
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Volume 2, Issue 1, Winter and Spring 2018, Page 73-90<br><br>In this paper, an exact closed-form solution is presented for free vibration analysis of Bernoulli–Euler beams carrying attached masses with rotary inertias. The proposed technique explicitly provides frequency equation and corresponding mode as functions with two integration constants which should be determined by external boundary conditions implementation and leads to the solution to a two by two eigenvalue problem. The concentrated masses and their rotary inertia are modeled using Dirac’s delta generalized functions without implementation of continuity conditions. The non-dimensional inhomogeneous differential equation of motion is solved by applying integration procedure. Using the fundamental solutions which are made of the appropriate linear composition of trigonometric and hyperbolic functions leads to making the implementation of boundary conditions much easier. The proposed technique is employed to study the effects of quantity, position and translational and rotational inertia of the concentrated masses on the dynamic behavior of the beam for all standard boundary conditions. Unlike many of the previous exact approaches, the presented solution has no limitation in a number of concentrated masses.Thu, 31 May 2018 19:30:00 +0100Effect of Concentrated Axial Harmonic Force on Lateral Vibration of a Mono- Disk Rotating Shaft
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Volume 2, Issue 1, Winter and Spring 2018, Page 91-96<br><br> Rotors are widely used in industry and studying their vibrations is important. Lateral vibration of the rotors during operation is more important than its other vibration modes such as axial and torsional. The aim of this paper is to determine the effects of loads axially exerted on the assembled disk on a rotor as an introduction to modeling common phenomena such as surge and chock in rotors. Therefore, in this paper, the effect of a concentrated axial force acted on disk on the lateral vibration of a jeffcott rotor is investigated. Also, the effect of unbalance force on vibration behavior of the rotor is studied. The equation of motion was derived from Timoshenko beam model. The set of governing equations for vibration analysis of the rotor consist of four coupled partial differential equations. Since the derived equations are complex and coupled, and they have time-varying coefficients, they are solved by a combination of Galerkin and Newmark methods. Numerical examples are analyzed. The accuracy of derived equations is verified for a simple beam. Results show that the axial load is considerably effective on the amplitude of the lateral vibration of the rotor.Thu, 31 May 2018 19:30:00 +0100Residual Stresses Measurement in UIC 60 Rail by Ring-Core Method and Sectioning Technique
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Volume 2, Issue 1, Winter and Spring 2018, Page 97-104<br><br>The measurement of residual stress in rail foot, according to manufacturing standards is mandatory. In this study, the ring-core method and the sectioning technique are used to measure the residual stresses. A calibration technique for the ring-core method has been explained and simulated by the finite element analysis. The calibration coefficient has been determined for certain parameters and various depths of the annular groove. The ring-core method has been simulated for the uniaxial residual stress field and it is observed that the maximum error in the maximum principal residual stress was about 13% which is about 5% of material yield stress. The residual stresses have been measured at the UIC 60 rail foot by the ring-core method and the sectioning technique, and the results are in a good agreement with earlier investigations in this field. Also, it has been indicated that maximum residual stresses on the rail foot are not in the longitudinal direction and in the subsurface of the rail foot, the maximum principal direction coincides with the longitudinal direction. Both methods indicated tensile residual stresses on the rail foot, but the ring-core method predicted 27% higher longitudinal residual stress on the rail foot in comparing with the sectioning technique.Thu, 31 May 2018 19:30:00 +0100The Effect of Impact Energy Parameters on the Closed-Cell Aluminum Foam Crushing Behavior Using ...
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Volume 2, Issue 1, Winter and Spring 2018, Page 105-114<br><br> The present study is devoted to the numerical and experimental investigation of the influence of dominant impact parameters, including inertia and impact velocity, on the closed-cell aluminum foam behavior. In order to access 3D modeling of the internal microstructure of the foam samples, a new technique based on computerized tomography (CT) of 2D images is utilized. The influence of the abovementioned influential parameters is studied for three different foam densities. In order to validate finite element results, low-velocity impact tests were conducted. The results demonstrate that for a constant level of impactor energy, two primary impact quantities of interest, i.e. maximum stress and energy absorption, are highly dependent on the values of impactor momentum. In contrast, increasing the value of impactor inertia results in negligible variations of energy absorption for different foam densities. Similarly, increasing inertia at a constant foam density shows no significant variation in peak stress and a slight change in energy absorption. On the other hand, the velocity of impactor at a constant level of impactor energy plays a crucial role such that for all three different foam sample densities, the case of higher impactor velocity causes greater values of peak stress as well as energy absorption.Thu, 31 May 2018 19:30:00 +0100Multi-objective Optimization of Surface Roughness and Material Removal Rate Using an Improved ...
http://ajme.aut.ac.ir/article_2769_257.html
Volume 2, Issue 1, Winter and Spring 2018, Page 115-122<br><br>Surface roughness is one of the main characteristics of a work piece in the quality control process. Several parameters such as cutting tool material and geometry, cutting parameters, work piece material properties, machine tool and coolant type affect the surface quality. An important task of process planners is the proper selection of three main cutting parameters: cutting speed, feed rate, and depth of cut in order to have not only low surface roughness, but also to perform the process within a reasonable amount of time. In this paper, using full factorial experiment design, the multiple regression equation for the surface roughness in the climb milling process of DIN 1.4021 martensitic stainless steel has been obtained and then used as one of the objective functions in the Multi-objective Improved Self- Adaptive Particle Swarm Optimization (MISAPSO) algorithm. This algorithm has been used to obtain cutting parameters to achieve low surface roughness simultaneously with a high material removal rate. The relatively new algorithm MISAPSO developed with some changes in the common particle swarm optimization (PSO) technique, has been used in multi-objective optimization of machining processes and was shown to be able to help the process planners in selecting cutting parameters.Thu, 31 May 2018 19:30:00 +0100Nonlinear Free Transverse Vibration Analysis of Beams Using Variational Iteration Method
http://ajme.aut.ac.ir/article_2761_0.html
Articles in Press, Accepted Manuscript , Available Online from 18 December 2017<br><br>In this study, Variational Iteration Method (VIM) is employed so as to investigate the linear and non-linear transverse vibration of Euler-Bernoulli beams. This method is a very powerful approach with high convergence speed which gives analytical and semi-analytical solution to the linear equations and is able to be extended to present semi-analytical solution to the non-linear ones. In this method, firstly, Lagrange`s multiplier and Initial Function should be chosen. Suitable choice of these two elements would effectively affect the convergence speed. In this attempt, in addition to presenting a discussion on how to choose these two functions appropriately, the calculated frequencies in non-linear state are compared with those obtained from DQM and FEM approaches, and the accuracy and convergence speed are studied as well. The proper choice of Lagrange`s multiplier and Initial Function will play a key role in this method. Semi analytical results presented in linear state show that the obtained values will converge to the accurate values quickly in a way that the first and second frequencies will reach the accuracy of four point decimal after four and six iterations respectively.Sun, 17 Dec 2017 20:30:00 +0100Nonlinear Aerothermoelastic Analysis of Functionally Graded Rectangular Plates Subjected to ...
http://ajme.aut.ac.ir/article_2786_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>In this study, the aerothermoelastic behavior of Functionally Graded (FG) plates under hypersonic airflow is investigated. The classical plate theory based on both mid-surface and the neutral surface position is used to model the structural treatment. Also, Von Karman strain-displacement relations are utilized to involve the structural nonlinearity. To consider the applied hypersonic aerodynamic loads, nonlinear (third–order) piston theory is employed to model unsteady aerodynamic pressure in hypersonic flow regime. Material properties of the FG panel is assumed to be temperature dependent and altered in the thickness direction according to a simple power law distribution. The Generalized Differential Quadrature Method (GDQM) is used to transfer the governing partial differential equation into ODE one. The onset of flutter instability, the stability boundaries and the time response analysis of a FG plate are determined by applying the fourth order Runge-Kutta method. Moreover, the effect of some important parameters such as Mach number, in-plane thermal load, plate thickness ratio and volume fraction index on the plate aerothermoelastic behavior is examined. Comparison of the obtained results with the available results in literature confirms the accuracy and reliability of the proposed approach to analyzing aerothermoelastic of FG plates in hypersonic flow.Tue, 30 Jan 2018 20:30:00 +0100ارتعاش آزاد غیرخطی نانو تیرهای مدرج تابعی کمانش ...
http://ajme.aut.ac.ir/article_2787_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>در مطالعه حاضر ارتعاش غیرخطی نانو-تیر مدرج تابعی که تحت بار حرارتی، کمانش کرده است بررسی می شود. از تئوری غیرخطی تیر غیرمحلی اولر-برنولی توام با مدهای ارتعاش خطی نانو-تیری که حول پیکربندی مد اول کمانش خود ارتعاش می کند، برای استخراج دسته معادلات دیفرانسیل معمولی حاکم بر مساله با استفاده از روش گالرکین استفاده شده است. حل نیمه تحلیلی حاکم بر فرکانسهای غیرخطی ارتعاش جانبی نانو-تیر کمانش کرده با استفاده از روش اختلال هموتوپی و روش تغییر تکرار بدست آمده است. نتایج نشان می دهد که اختلاف میان فرکانس خطی و غیرخطی با افزایش بیشترین خیز اولیه جانبی، مقدار مقیاس کوچک و شاخص قانون توانی افزایش می یابد. بررسی اثر نسبت طول به ضخامت بر اختلاف بین فرکانسهای خطی و غیرخطی نشان می دهد که نسبت منظری تاثیر چندانی بر نسبت فرکانس غیرخطی به خطی کلاسیک ندارد اما نسبت فرکانس غیرخطی به خطی غیرمحلی با افزایش نسبت منظری، کاهش می یابد. برخلاف نسبت اولین فرکانس غیرخطی به خطی که با افزایش بار محوری-فشاری کاهش می یابد، مقدار بار محوری فشاری که فراتر از بار بحرانی نانو-تیر می باشد تاثیری بر نسبت دومین فرکانس غیزخطی به خطی ندارد.Tue, 30 Jan 2018 20:30:00 +0100Surface stress size dependency in nonlinear instability of imperfect piezoelectric nanoshells ...
http://ajme.aut.ac.ir/article_2788_0.html
Articles in Press, Accepted Manuscript , Available Online from 31 January 2018<br><br>In this paper, the nonlinear instability of piezoelectric cylindrical nanoshells under the combined radial compression and electrical load including the effects of surface free energy is studied. To consider the surface effects, the Gurtin-Murdoch elasticity theory is utilized along with the classical shell theory to develop an efficient size-dependent shell model. To satisfy the balance conditions on the surfaces of nanoshells, a linear variation of normal stress is assumed through the thickness of the bulk. Electrical field is also exerted along the transverse direction. Based on the virtual work's principle, the size-dependent nonlinear governing differential equations are derived in which transverse displacement and Airy stress function are considered as independent variables. Finally, a two-stepped singular perturbation technique is employed to obtain the size-dependent critical buckling pressure and the associated postbuckling equilibrium path for alternative electrical loadings. It is revealed that the electrical load increases or decreases the critical buckling pressure and critical end-shortening of nanoshell which depends on the sign of applied voltage. Moreover, it is found that by taking surface free energy effects into account, the influence of electrical load on the postbuckling behavior of nanoshell increases.Tue, 30 Jan 2018 20:30:00 +0100Pertinence of Sheep Knee Joint for Calibration of Ligaments’ Constitutive Equations; ...
http://ajme.aut.ac.ir/article_2888_0.html
Articles in Press, Accepted Manuscript , Available Online from 29 April 2018<br><br>The knee joint is one of the most complex joints in human body because of its complex geometry and articulations. On the other hand, due to many practical constraints for studying the anatomy and biomechanics of the human knee, in vivo and in vitro animal models have been widely used. Based on this fact, an objective comparison of the sheep samples especially from mechanical behavior point of view is needed. Therefore, a purpose of the present study is to evaluate priority of usage of sheep specimens via comparing the biomechanical differences of normal ligaments between sheep and human. To this end, some experimental tensile tests have been done on the different knee ligaments of sheep including hyperelastic behavior of the anterior cruciate ligament (ACL), medial collateral ligament (MCL), posterior cruciate ligament (PCL), and lateral collateral ligament (LCL). So, an objective comparison of the sheep and human samples has been done. Furthermore, the magnitude of material constants of different hyperelastic constitutive equations including 3rd order Ogden, Yeoh and Fung–Demiray models, as well as the maximum experienced stress by the knee ligaments have been considered.Sat, 28 Apr 2018 19:30:00 +0100Thermodynamic analysis and feasibility study of internal combustion engine waste heat recovery ...
http://ajme.aut.ac.ir/article_2889_0.html
Articles in Press, Accepted Manuscript , Available Online from 29 April 2018<br><br>Automobiles refrigeration systems are mainly vapor compression refrigeration systems, and they use high power which is taken directly from the engine. The use of these systems will increase fuel consumption, and this fuel consumption will increase up to 15%. By considering the importance of fuel saving, optimum use of fuel will be necessary. One of the effective ways, is the engine exhaust gas waste heat recovery. The purpose of this study is to propose thermodynamic analysis of a new cogeneration system which is based on internal combustion engines. In fact, the system will generate power with exhaust gases waste heat recovery, and then the power will be used to run the refrigeration system. The system is used in the actual operating modes of gasoline and diesel engines. Different refrigerants are used in the system. Results show that the system can generate required refrigeration capacities of both automobiles and buses. Furthermore, additional refrigeration capacities will also be available. R245fa and R600 refrigerants have better performances in the system. Maximum refrigeration capacity generated by the system is 20 kW when using gasoline engine exhaust gases waste heat recovery, and 130 kW when using diesel engine exhaust gases waste heat recovery.Sat, 28 Apr 2018 19:30:00 +0100Fault analysis of complex systems via Dynamic Bayesian Network
http://ajme.aut.ac.ir/article_2890_0.html
Articles in Press, Accepted Manuscript , Available Online from 29 April 2018<br><br>Nowadays, several components and systems are designed and produced based on reliability. Since the reliability criterion has an important role in purchasing and implementation of these systems. In the design of a reliable system, fault and failure analysis must be carried out in order to reduce fault probability of the system. When dependency and the relation between components of a complex system are important and should be mentioned, determination of system reliability is very difficult. In this paper, Dynamic fault tree (DFT) is used to evaluate the systems reliability that their behavior is varied with time. DFT is constructed and then it converted to Dynamic Bayesian network (DBN). In this paper, the principle of DFT gates and their mapping into DB are explained and some new relations between events and gates for this mapping are proposed. GeNIe package is used to determine DBN based on stochastic sampling algorithms. Four systems (Cardiac assist system, Hypothetical Cascaded PAND System, INS/GPS integrated and Emergency detection system) are investigated; reliability and fault probability of these systems are calculated. Comparison of the results with other researches shows the proposed method effectiveness for systems reliability modeling and assessment via DBN.Sat, 28 Apr 2018 19:30:00 +0100Effect of multi-hole configuration on film cooling effectiveness
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Articles in Press, Accepted Manuscript , Available Online from 19 June 2018<br><br>A numerical study is performed to investigate the effects of shaped multi-hole on film cooling effectiveness over a flat plate. Hence a single cylindrical film cooling hole with 11.1 mm diameter is replaced with the shaped multi-hole (14 holes with 2.97 mm diameter) while maintaining constant blowing ratio. Numerical simulations are performed at fixed density ratio of 1.6, length-to-diameter of 4 and inclined angle of 35o. Two configurations of hook and fan shapes are considered for multi-hole. The control-volume method with a SIMPLEC algorithm has been used to solve the steady-state RANS equations. The k-ε model is applied for modeling the turbulent behavior of the flow and heat transfer. It is found that replacing a single hole with the shaped multi-hole leads to a considerable increase in film cooling effectiveness in both axial and lateral directions. Results of the present study show that at lowing ratio 0.6, the hook shape and fan shape configurations of multi-hole, provide a higher area-averaged film cooling effectiveness by 48% and 58.2% more than the single hole respectively.Mon, 18 Jun 2018 19:30:00 +0100A simplified description of the uniaxial tensile test used for calibrating constitutive models ...
http://ajme.aut.ac.ir/article_2947_0.html
Articles in Press, Accepted Manuscript , Available Online from 19 June 2018<br><br>In the present work, a simplified model of the uniaxial tensile test is developed for orthotropic metallic sheets. This model is mainly established for tensile test analysis and calibration of material parameters. The constitutive equations included in the model are based on an anisotropic Gurson-Tvergaard-Needleman (GTN) model combined with the Hill 1948 quadratic yield criterion. At first, a detailed description of the constitutive equations along with their computer implementation is presented. Then, by comparing the force and void evolution diagrams predicted by the model with numerical and experimental results the efficiency and accuracy of the model are assessed. Finally, the effect of different parameters on the traction force and evolution of voids during uniaxial tensile tests are studied. The material parameters used in the calibration procedure are as follows: initial void volume fraction, two adjusting parameters, nucleation of void volume fraction, standard deviation, mean value of void nucleation strain, and sample orientation with respect to the rolling direction. The tests performed by the authors prove the capability of the simplified model to describe accurately the mechanical response of orthotropic sheet metals., , , , , , , , , , , , , , , , , , , ,Mon, 18 Jun 2018 19:30:00 +0100Determining a suitable location for wind turbines using inverse solution and mast data in a ...
http://ajme.aut.ac.ir/article_2954_0.html
Articles in Press, Accepted Manuscript , Available Online from 24 June 2018<br><br>The aim of this study is to determine the optimum location to install a wind turbine in a mountainous terrain using computational fluid dynamics (CFD). This aim is achieved with the use of inverse methods, with the objective of maximizing the efficiency of the turbines while minimizing loss expenses caused by placing them in a less optimum area. One of the conventional methods for determining the location of turbines is accomplished by employing the meteorological mast data installed in the region. However this method has proven very challenging in mountainous terrains.Numerical methods used to solve this type of problems must be approached differently from conventional ones, since the answers to a part of the solution, meteorological mast, are known. Such problems are commonly considered as inverse problems.Unknown boundary conditions are determined by SD optimization method. 2-D mountain geometry with the mast installed on the flat area is the reference of evaluating the performance of the proposed method in this paper. Simulation results show a considerable difference between the power outputs of the turbines installed at different points of the domain. Turbine performance in the initial installation point and in the point derived from the algorithm is then compared.Sat, 23 Jun 2018 19:30:00 +0100Softening effect in stretching stiffness of a rippled graphene: molecular dynamics simulation
http://ajme.aut.ac.ir/article_2955_0.html
Articles in Press, Accepted Manuscript , Available Online from 24 June 2018<br><br>In this paper, the stretching stiffness of a rippled graphene is studied using the molecular dynamics simulation. The uneven surface of the rippled graphene is modeled by a random function with different amplitudes and frequencies. Two models of the rippled graphene are simulated. In the first model, it is supposed that the graphene has random wrinkles with different amplitudes and frequencies. It can be regarded as an opened crumpled graphene. In the second model, the uneven surface of the rippled graphene is modeled by the trigonometric sine shapes. The AIREBO potential function is utilized to model the covalence bonding of the carbon atoms and the Nose-Hoover thermostat is used to control temperature of the system. It is implemented in the software package large scale atomic/molecular massively parallel simulator (LAMMPS) in order to simulate covalent bond formation between carbon atoms in the structure of graphene layer. Results are presented for both zigzag and armchair rippled graphene sheets with different initial surfaces. It is concluded that the failure strain of a rippled graphene under uniaxial tensile loading is less than that of a flat one. It is also demonstrated that the rippled graphene has softening stretching behavior due to its uneven surface.Sat, 23 Jun 2018 19:30:00 +0100Experimental Investigations of Static and Fatigue Crack Growth in Sandwich Structures with Foam ...
http://ajme.aut.ac.ir/article_2956_0.html
Articles in Press, Accepted Manuscript , Available Online from 24 June 2018<br><br>Debonding of face-core interface is the most important damage mechanisms which make loss of structural integrity in sandwich structures. In this paper, mode-I and mode-II fracture of face-core interface in sandwich structures have been investigated under both static and fatigue loadings. The considered sandwich structures contain of different face sheet fiber-metal laminates (FMLs) and the core material is PVC foam. Several specimens are fabricated and the experiments are carried out to find the effects of initial debonding location and various FML face sheets on the fracture toughness under static and fatigue loadings. Double Cantilever Beam (DCB) specimens are used for mode-I and End Notch Flexure (ENF) specimens for mode-II loading conditions. The resistance strength curves are plotted for mode-I and mode-II under static loading to find the instability point which is the border of stable and unstable crack growth and determine the critical crack length too. The strain energy release rates of mode-I and mode-II are also obtained for fatigue loading to investigate the resistance against damage evolution. Also, the global damage parameter is defined for both static and fatigue loading which is the combination of all damage mechanisms occurred in sandwich structures. Finally, the more efficient layup configurations under static and fatigue loadings among the investigated layups are introduced in mode-I and mode-II fracture conditions separately.Sat, 23 Jun 2018 19:30:00 +0100Experimental and Numerical Study on the Accuracy Residual Stress Measurement by Incremental ...
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Articles in Press, Accepted Manuscript , Available Online from 24 June 2018<br><br>In this study, the calibration factors of incremental step method have been determined by FE analysis to calculate the residual stresses by the ring-core method. The calibration coefficients have been determined by simulation the uniaxial and biaxial loading. It is indicated that the loading approach has not effect on the calibration constants and they are unique. The uniaxial condition has been used to determine the calibration coefficients in the experimental method. To verify the determined constants, the calibration factors have been used to calculate the residual stresses in the case of uniform and non-uniform residual stresses. The axial and biaxial conditions have been studied and the results are in good accordance with applied stresses in simulations. In the uniaxial loading the measured residual stresses in FE model completely accommodated by the applied stresses and presented formula and calibration constants determined the direction of the maximum principal stress by clearance less than 0.7%. Clearance of the measures stresses and applied stresses in the non-uniform case was about 1 %. An experimental test has been used to show the effectiveness of the obtained calibration coefficient by FE analysis. Also, it is indicated that the results of the experimental test are satisfactory.Sat, 23 Jun 2018 19:30:00 +0100Viscoelastic effects on nonlinear dynamics of microplates with fluid interaction based on ...
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Articles in Press, Accepted Manuscript , Available Online from 24 June 2018<br><br>In this paper, a size-dependent theory is developed for viscoelastic materials in the framework of the consistent couple stress theory. The previously presented modified couple stress theory was based on some consideration making its use doubtful, to some extent. This paper uses the recent finding for the problems of the modified couple stress theory and developed the original couple stress theory to analyze the nonlinear dynamics of a microplate with nonlinear viscoelasticity and fluid interaction. The viscoelastic material supposed to follow the Leaderman integral nonlinear constitutive relation. Moreover, the fluid damping force is taken into account. In order to capture the geometrical nonlinearity, the von–Karman strain displacement relation is used. The viscous parts of the size-independent and size-dependent stress tensors are calculated in the framework of the Leaderman integral and the resultant virtual work terms are obtained. The governing equations of motion are derived using the Hamilton’s principle in the form of the nonlinear second order integro-partial differential equations with coupled terms. These coupled size-dependent viscoelastic equations are simplified by expansion theory and Galerkin procedure, then analytically solved using harmonic balance method. The results show that the viscoelastic model predicts more reliable dynamical behavior than elastic model with linear damping.Sat, 23 Jun 2018 19:30:00 +0100