Amirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Robust Performance Analysis for a Cascade Nonlinear H∞ Control Algorithm in Quadrotor Position Tracking151168341610.22060/ajme.2019.15561.5779ENFatemeRekabiSchool of Mechanical Engineering, University of TehranFarzadA. ShiraziSchool of Mechanical Engineering, University of TehranMohammad JafarSadighSchool of Mechanical Engineering, University of TehranJournal Article20181231This paper presents a new hierarchical robust algorithm to solve the position tracking problem, in presence of exogenous disturbances and modeling uncertainties, of a quadrotor helicopter. The suggested controller includes a nonlinear <em>H</em>∞ algorithm to track the reference trajectory in the outer loop and a nonlinear <em>H</em>∞ controller to stabilize the rotational movements in the inner loop. The resultant controller consists of three important parts to regulate tracking errors for translational and rotational motions, maintain robust performance confronting random disturbances and modeling uncertainties and reject the sustained disturbances from the system to vanish the steady-state errors. Analytical study on the stability of the cascade system is mentioned to verify the compatibility of two controllers considering coupling terms. Numerical performance analysis is accomplished using Monte-Carlo simulation. Statistical results obtained from 1000 simulations considering environmental disturbances and modeling uncertainties depict less than 5 cm for position tracking error and less than 2 degrees for attitude tracking error in steady state performance. The closed-loop performance of the controller is also compared with two previous algorithms by determining two numerical indexes for state tracking performance and control efforts, respectively. Simulation results of the suggested control algorithm depict a significant reduction in both indexes for a similar mission.https://ajme.aut.ac.ir/article_3416_61e6ae46f7a047bab603077bade102eb.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601A Comparison between Virtual Constraint-Based and Model Predictive-Based Limit Cycle Walking Control in Successful Trip Recovery169182356710.22060/ajme.2019.15574.5781ENBehnamMiripour FardFaculty of Mechanical Engineering, University of Guilan, Rasht, Iran.0000-0002-2791-6591Journal Article20190103Falling is one of the main causes of the injuries among healthy adults. The foremost causes of the falls are: slipping and tripping. Understanding the phenomenon of human balance recovery against these disturbances is a very important issue in the field of biomechanics as well as in the robotics. Previous studies have shown that human movements can be reproduced using engineering techniques and computational facilities. The prediction of movements can be related to an optimization problem. In the present study, control and prediction of human movements in successful trip recovery are addressed.To formulate the optimization problem, a hybrid dynamic model of the human body with seven degrees of freedom is considered. The tripping perturbation is modeled as an instantaneous contact of the swing leg with an obstacle and the dynamics of impact are derived. Two optimization based methods are used to control and predict the gait: (i) virtual constraint-based limit cycle optimization (ii) model predictive based limit cycle optimization. The simulated results are compared with the human-observed experimental data from the literature. The results show that the second method provides more humanlike predictions than the first method in the kinematic level. The second method can predict proper actions to keep away violating constraints in the future. The theoretical results are in agreement with the aresults of experimental studies on movement adjustments during trip recovery.https://ajme.aut.ac.ir/article_3567_6f472c2e6eecf139e93c07898b8476ea.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Intelligent Control of Biped Robots: Optimal Fuzzy Tracking Control via Multi- Objective Particle Swarm Optimization and Genetic Algorithms183192361710.22060/ajme.2019.16171.5808ENMohammad JavadMahmoodabadiDepartment of Mechanical Engineering, Sirjan University of Technology, Sirjan, Iran.0000-0002-4249-8623MiladTaherkhorsandiDepartment of Mechanical Engineering, University of Texas at San Antonio, San Antonio, TX 78249, USA.0000-0003-0158-2199Journal Article20190424This paper is concerned with fuzzy tracking control optimized via multi-objective particle swarm optimization for stable walking of biped robots. To present an optimal control approach, multi-objective particle swarm optimization is used to design the parameters of the control method in comparison to three effectual multi-objective optimization algorithms in the literature. In particle swarm optimization, a dynamic elimination technique is utilized as a novel approach to prune the archive effectively. Moreover, a turbulence operator is used to skip the local optima and the personal best position of each particle is determined by making use of the Sigma method. Normalized summation of angles errors and normalized summation of control efforts are two conflicting objective functions addressed by dint of multi-objective optimization algorithms in the present investigation. By contrasting the Pareto front of multi-objective particle swarm optimization with the Pareto fronts of other methods, it is illustrated that multi-objective particle swarm optimization performs with high accuracy, convergence and diversity of solutions in the design of fuzzy tracking control for nonlinear dynamics of biped robots. Finally, the proper performance of the proposed controller is demonstrated by the results presenting an appropriate tracking system and optimal control inputs. Indeed, the appropriate tracking system and optimal control inputs prove the efficiency of optimal fuzzy tracking control in dealing with the nonlinear dynamics of biped robots.https://ajme.aut.ac.ir/article_3617_a493ad39d0d94e19c4b69c9a6617378c.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Investigation on Effect of Train Speed in Displacement of Railway Ballasted Track with Unsupported Sleepers193200347310.22060/ajme.2019.15656.5787ENMojtabaAziziSchool of Railway Engineering, Iran University of Science and Technology, Tehran, Iran0000-0002-2216-8897MajidShahraviSchool of Railway Engineering, Iran University of Science and Technology, Tehran, Iran0000-0002-6903-1417Jabbar AliZakeriSchool of Railway Engineering, Iran University of Science and Technology, Tehran, Iran0000-0002-4946-7192Journal Article20190117One of the main problems of the damages of rail tracks which is caused by track settlement is unsupported sleeper. Due to this defect the underlying area of sleeper is not supported on the ballast and causes the sleeper displacement to increase. The increase creates vibration in the track and vehicle components and causes problems on their performance. Hence, in this study the investigation of rail displacement in tracks with unsupported sleeper has been dealt with. Three dimensional modeling of the vehicle and ballasted track has been carried out using ANSYS and SIMPACK programs. To use this software, the modeling of a flexible track in the vehicle multibody model is possible. Ballasted track which is formed from components as rail, sleeper and ballast, has been considered to be flexible. In simulating the vehicle all of its main components have been considered and damping and stiffness values of bogie suspension systems have been considered to be nonlinear. The results obtained from numerical simulation have good agreement with field test results. The results show that the speed of the vehicle on the track displacement with less than four unsupported sleepers has no effect, but by increasing the number of unsupported sleepers, the effect of increasing velocity would be considerable.https://ajme.aut.ac.ir/article_3473_abef32fb0cff299ef84136004eb7a312.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Dynamic Stability Analysis of Euler-Bernoulli and Timoshenko Beams Composed of Bi-Directional Functionally Graded Materials201214361110.22060/ajme.2019.15913.5792ENAliGhorbanpour AraniFaculty of Mechanical Engineering, Department of Solid Mechanics, University of Kashan, Kashan, IranShariarNiknejadFaculty of Mechanical Engineering, Department of Solid Mechanics, University of Kashan, Kashan, IranJournal Article20190302In this paper, dynamic stability analysis of beams composed of bi-directional functionally graded materials rested on visco-Pasternak foundation under periodic axial force is investigated. Material properties of beam vary continuously in both the thickness and longitudinal directions based on the two types of analytical functions including exponential and power law distributions. Hamilton’s principle is employed to derive the equations of motion according to the Euler-Bernoulli and Timoshenko beam theories. Then, the generalized differential quadrature method in conjunction with the Bolotin method is used to solve the differential equations of motion under different boundary conditions. Various parametric investigations are performed for the effects of the gradient index, static load factor, length-to-thickness ratio and viscoelastic foundation coefficients on the dynamic stability regions of bi-directional functionally graded beam. The results show that the influence of gradient index of material properties along the thickness direction is greater than gradient index along the longitudinal direction on the dynamic stability of beam for both exponential and power law distributions. Also, the system become more stable and stiffer when beam is resting on visco-Pasternak foundation. Moreover, by increasing static load factor, the dynamic instability region moves to the smaller parametric resonance. The results of presented paper can be used to the optimal design and assessment of the structural failure and thermal rehabilitation of turbo-motor and turbo-compressor blades.https://ajme.aut.ac.ir/article_3611_02b44bd908bcbbffd59916b337df8ee4.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Small Scale Effect on Vibration of Thermally Postbuckled Monolayer Graphene Nanoribbon Based on Nonlocal Elasticity Theory215228347810.22060/ajme.2019.16038.5799ENGholam AliVarzandianDepartment of Mechanical Engineering, Yasouj University, Yasouj, IranSimaZiaeeDepartment of Mechanical Engineering, Yasouj University, Yasouj, IranMehrdadFaridSchool of Mechanical Engineering, Shiraz University, Shiraz, IranAbbasNiknejadDepartment of Mechanical Engineering, Yasouj University, Yasouj, IranJournal Article20190320In the present research, vibration behavior is presented for a thermally postbuckled two side clamped monolayer graphene nanoribbon. The monolayer graphene nanoribbon is modeled as a nonlocal orthotropic plate strip which contains small scale effects. The formulations are based on the Kirchhoff’s plate theory, and von Karman-type nonlinearity is considered in strain-displacement relations. The thermal effects are also included and the material properties are assumed to be temperature-dependent. The initial deflection caused by thermal postbuckling and internal loads are taken into account. A coupled system of equations is derived and a new semi analytical solution is obtained. The effects of variation of small scale parameter <em>e</em>0 <em>a </em>to the natural frequencies, deflections and mode shapes of graphene nanoribbon are analyzed and the numerical results are obtained from the nonlocal plate model; also, molecular dynamics simulations are used to investigate different properties of graphene nanoribbon including both buckling and vibrational behaviors. The small scale coefficient is calibrated using molecular dynamics simulations. Numerical results are compared with those of similar researches. Effects of various parameters on the postbuckled vibration of graphene nanoribbon in thermal environments such as scale parameter, length and thermal load are presented. Stability and occurrence probability of internal resonance between vibration modes around a buckled configuration is investigated.https://ajme.aut.ac.ir/article_3478_e69595752b16557e8104ca8948abfed3.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Analysis of Workpiece Locating Error Using Geometric Fixture Model: A Theoretical and Experimental Study229240352210.22060/ajme.2019.16034.5798ENHadiParvazFaculty of Mechanical and Mechatronics Engineering, Shahrood University of Technology, Shahrood, Iran0000-0003-4806-7311MehdiBodaghy AlenyTarbiat Modares University, Mechanical Engineering Department, Tehran, IranJournal Article20190318Investigation of the robustness of the locating layout is an important analysis which is usually conducted in the verification stage of the fixture design procedure. In such an analysis, workpiece locating error is modeled by considering its sources in the workpiece and locating elements. The main focus of the present study is to investigate the robustness of the locating layout which is designed for the workpiece in the machining fixture, both theoretically and experimentally. Geometric model of the fixture is employed for theoretical analysis of errors in locating a workpiece using the well-known 3-2-1 locating principle. For validation, computer-aided assembly model is designed for calculating the workpiece locating error and comparing the results to the theoretical predictions. Experiments are also designed and conducted for validation of the theoretical predictions. Two types of the machining workpiece are incorporated as case studies for the validation process. Maximum error values equal to 3.6% and 6.1% are obtained between the theoretical predictions for the workpiece locating error and results of the computer-aided design model and experiments, respectively. Results of the present study confirmed that the locating layout with the maximum distance between its locators provided the minimum locating error value for the workpiece. Agreement between the theoretical predictions and results of the computer-aided model and experiments confirmed the applicability of the geometric fixture model and credibility of its results.https://ajme.aut.ac.ir/article_3522_cbb84cfc188a8761bfc3e77228de5a4d.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601A Changing-Connectivity Moving Grid Method for Large Displacement241256358510.22060/ajme.2019.15690.5790ENMohammad MahdiRazzaghi NaeiniDepartment of Mechanical Engineering, Najafabad Branch, Islamic Azad University, Najafabad, IranJournal Article20190123A moving grid method is introduced in this paper and different motions of the body are simulated using this method. This study indicates that by regular and systematic change of grid connections in some elements with regard to the size of the body’s motion, a moving-grid can be obtained which is capable of being adapted to the large motions of the body without reducing the quality of elements. In order to model the rotational or translational motions of the body, cylindrical or elliptical shells from the elements around the body are taken into consideration to change the grid connections. To indicate the correct performance of introduced moving-grid method, several test cases including rotational and translational motions are solved. The Euler equations in the three dimensional unsteady form is solved using a dual time implicit approach. Numerical dissipative term using Jameson method is added to the equations. To accelerate convergence, local pseudo-time stepping, enthalpy damping and residual averaging are used. The results are validated with experimental or numerical data and excellent agreements among the results are observed.https://ajme.aut.ac.ir/article_3585_737c0a14d985b5fc3910cc4ecc148a45.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Impact of a Control Rod on the Heat Transfer Enhancement of a Wall Jet257266347610.22060/ajme.2019.15665.5788ENSeyed EsmailRazaviFaculty of Mechanical Engineering, University of Tabriz, Tabriz, IranBehnamVojoudiFaculty of Mechanical Engineering, University of Tabriz, Tabriz, IranJournal Article20190119Influence of a control rod on the heat transfer characteristics of an incompressible wall jet with an isothermal plate boundary condition is investigated numerically in the turbulent regime. The main issue is to find an efficient way to increase the rate of convective heat transfer in the wall jet. The rod is placed in various horizontal and vertical locations. In addition, different diameters for the rod are examined. The performance of realizable K-ϵ, standard K-ω, and shear stress transport turbulence models are compared with the experimental data to find the suitable one for the simulations. It was found that the shear stress transport model generates more accurate results than the others. The control rod with a particular diameter and location causes a noticeable enhancement in the heat transfer rate with a negligible increase in the skin friction coefficient. The results showed that the effect of the rod on the heat transfer enhancement increases with the Reynolds number. Two correlations were found as the variation of average Nusselt number and Stanton number against the Reynolds number, which could be used in designs and practices.https://ajme.aut.ac.ir/article_3476_b38f17f933e16ce0e388b8f822a8fdcb.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601IInverse Problem of Coupled Radiative and Conductive Heat Transfer in a Cavity Filled with CO2 and H2O at Different Mole Fractions267276352710.22060/ajme.2019.15613.5783ENMohammadOmidpanahDepartment of Mechanical Engineering, Faculty of Shahid Sadooghi, Yazd Branch, Technical and Vocational University (TVU), Yazd, IranS.Abdol RezaGandjalikhan NassabDepartment of Mechanical Engineering, School of Engineering, Shahid Bahonar University of Kerman, Kerman, IranJournal Article20190109This paper deals to an inverse analysis of combined conduction and radiation and heat transfer in a square cavity filled with radiating gases by numerical technique. The radiating medium is considered an air mixture with CO2 and H2O at different mole fractions, which is treated as homogeneous, absorbing, emitting and scattering gray gas. The main purpose is to verify the effects of gas mole fractions (carbon dioxide and water vapor) on the solution of inverse design problem. In the analysis, the conjugate gradient method is used to investigate the temperature distribution upon the heater surface to satisfy the prescribed temperature and heat flux distributions on the design surface. The temperature distributions over the heater surface while the enclosure is filled with different mole fractions of CO2 and H2O in an air mixture are calculated in this paper. It is found that the heater surface needs more power to maintain the design surface under uniform temperature and heat flux when the air mixture contains high mole fractions of CO2 and H2O. Numerical results reveal that by increasing the mole fractions of carbon dioxide and water vapor two times in the air mixture, the average heat flux over the heater surface increases about 16%. The present numerical results for the direct problems are compared with theoretical findings by other investigators and good consistencies are seen.https://ajme.aut.ac.ir/article_3527_8b7a0083ec06ba51700a5c707df02f62.pdfAmirkabir University of TechnologyAUT Journal of Mechanical Engineering2588-29374220200601Fault Detection in Compression Refrigeration System with a Fixed Orifice and Rotary Compressor277286356910.22060/ajme.2019.16081.5802ENSeyed AliShamandiYoung Researchers and Elite Club, Khomeinishahr Branch, Islamic Azad University, KhomeiniShahr, Isfahan, IranSaeidRasouliIslamic Azad University Khomeinishahr Branch, isfahan, iranJournal Article20190406In compression refrigeration systems such as air conditioning, chiller, split unit, which the refrigerant gas compression is used for cooling, the operation of the device is always dependent on parameters such as pressure, the temperature of different points, and consumed ampere. A tangible change in each of these items represents the existence of a potential fault in the cycle. The basic problem often arises from the fact that there is a time gap between the occurrence of fault and detection of it by the operator, causing damage to the device irreparably and the coefficient of performance is affected. Simulation has been performed by changing the refrigerant gas charge from 40% to 150%, causing condenser and evaporator clogging up to 30% and 60%, and also creating leakage in the compressor and fault detection and diagnosis is done with these parameters. In this paper, it is shown that a slight change in any of these parameters causes a change in the operation of the refrigeration cycle. In this study, Fault detection it was shown that the superheat value in refrigerant overcharge fault increasing to 16.5°C and in dirty condenser fault decreasing to 2.1°C and reduced evaporator air flow fault decreasing to 1.7°C. Also sub-cooling value in refrigerant undercharge, dirty condenser, reduced evaporator air flow, compressor failure fault decreasing to 4.2°C, 12.6°C, 12.8°C, 10°C.https://ajme.aut.ac.ir/article_3569_23b0205d46bae87b9f49cc88f05ac847.pdf