Plates and Shells
Abdolhossein Fereidoon; Kamal Kolasangiani; Amin Akbarpour; Mahmoud Shariati
Abstract
In this paper, simulation and analysis of thin steel cylindrical shells with elliptical cutouts under oblique loading were studied using finite element method. First, the numerical results were validated by the results of experimental test performed by an INSTRON 8802 servo hydraulic machine. Also, the ...
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In this paper, simulation and analysis of thin steel cylindrical shells with elliptical cutouts under oblique loading were studied using finite element method. First, the numerical results were validated by the results of experimental test performed by an INSTRON 8802 servo hydraulic machine. Also, the effect of cutout angle (θ), cutout size, cutout position (L0/L) and cutout aspect ratios (b/a) were investigated, where parameter (a) shows size of the cutout along longitudinal axis of the cylinder, parameter (b) is size of the cutout in circumferential direction of the cylinder on the buckling and post-buckling behavior of cylindrical shells with finite element method. It can be concluded that increasing width of the cutout extremely decreased the buckling load while the cutout height was constant. Moreover, changing position of the cutout from the mid-height of the shell toward the edges increased the buckling load.
Fluid Mechanics
H. Chamani; H. Karimaei; M. Bahrami; S. M. Agha Mirsalim
Abstract
Nowadays, due to the increasing power of diesel engines, especially heavy duty diesel engines, and increasing gas pressure inside the combustion chamber, the forces acting on the engine bearings have dramatically raised. On the other hand, becaus eof the competition in the market, it is necessary to ...
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Nowadays, due to the increasing power of diesel engines, especially heavy duty diesel engines, and increasing gas pressure inside the combustion chamber, the forces acting on the engine bearings have dramatically raised. On the other hand, becaus eof the competition in the market, it is necessary to increase the engine bearing life and reduce its failure as much as possible. The engine bearings analysis is a vital issue in engine design process as well as other related engineering tasks such as engine power upgrading, reverse designing, and bearing failure analysis. So, many attempts have been made to simulate accurate engine bearings. In this paper, results of a thermo-elasto-hydrodynamic (TEHD) analysis of a connecting rod big end (BE) bearing of a heavy duty diesel engine are presented. Here, the oil film viscosity is considered a function of oil's local temperature and pressure. Effects of flexibility of bearing shell and connecting rod structure are also considered. Therefore, the computed oil film pressure and temperature distributions are relatively precise. In the proposed analytical procedure, at first, elasto-hydrodynamic (EHD) analysis is carried out and the averaged fluid velocity in the bearing is obtained. Then, the averaged heat transfer coefficient between oil film and crank pin is calculated, which is used as an input in TEHD analysis. Results of EHD and TEHD analyses are compared with each other and the main characteristic parameters in bearing design are reported and interpreted.
Composite Materials
Meisam Shakouri; Hessam Sarvahed; H.M. Navazi
Abstract
Pressure vessels are used in a variety of applications in many engineering applications. The thin walled cylinders with torispherical heads have been widely used as pressure vessels in engineering applications. In this paper, the free vibration behavior of carbon fiber reinforced composite cylinders ...
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Pressure vessels are used in a variety of applications in many engineering applications. The thin walled cylinders with torispherical heads have been widely used as pressure vessels in engineering applications. In this paper, the free vibration behavior of carbon fiber reinforced composite cylinders ended with torispherical heads with various boundary conditions is investigated. The shape of a torispherical head is consists of a sphere of large radius and a much smaller minor radius at the knuckle. The numerical calculation with finite element method is obtained and the results were compared with the experimental data to confirm the accuracy of the numerical solution. The acceptable accordance between experimental and numerical results leads to use of numerical model instead of expensive experimental tests. In addition, the effects of the thickness of torispherical head and cylindrical section and the lengths of cylinder and torispherical head on vibrational behavior of the structure are studied.
Computational Fluid Dynamics (CFD)
Tamil Chandran A; Suthakar T; Balasubramanian KR; Rammohan S; Jacob Chandapillai
Abstract
Abstract Numerical analysis of drag coefficient of three-dimensional bluff bodies such as flat plates, cylinder, triangular prism, semicircular profiles located in the flow path of the pipe was performed. Bluff bodies of various lengths are analysed using a turbulence model. The effect of bluff body ...
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Abstract Numerical analysis of drag coefficient of three-dimensional bluff bodies such as flat plates, cylinder, triangular prism, semicircular profiles located in the flow path of the pipe was performed. Bluff bodies of various lengths are analysed using a turbulence model. The effect of bluff body thickness on drag coefficient was analysed. A significant observation of the study is the reduction in drag coefficient with an increase in thickness. Effect of pressure coefficient on drag coefficient was evaluated. The study confirms that frictional coefficient has negligible effect on drag coefficient in the studied Reynolds number range. Change in drag coefficient over a wide range of Reynolds number was studied and is reported. Irrespective of geometry and length, the study indicates that there is a significant difference in drag coefficient between two dimensional and three dimensional simulation studies. It is also concluded that the length of a bluff body in a confined domain has a significant effect on its drag coefficient.
Vibration
Mohammad Ebrahim Torki Harchegani; Mohammad Taghi Kazemi
Abstract
Axial vibration effect of shell particles on dynamic stability of a cantilevered cylindrical shell under an axial follower force was addressed. In spite of free-ended shells, the reduced axial force under this effect cannot be derived analytically. Instead, an approximate method was proposed based on ...
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Axial vibration effect of shell particles on dynamic stability of a cantilevered cylindrical shell under an axial follower force was addressed. In spite of free-ended shells, the reduced axial force under this effect cannot be derived analytically. Instead, an approximate method was proposed based on the fact that the static (and harmonic) axial deformation under an axial load in a free-ended beam are (almost) zero in a particular point near the middle of the beam, which was adopted as the equivalent fixed end of a cantilever. The work done by the nonconservative follower force was derived for a cantilevered beam and was extended to the case of a cantilevered cylindrical shell. The flutter load for a long free-ended shell was calculated using the equivalent cantilevered half-shell and compared with the previous results. Then, flutter load was calculated with and without the axial vibration effect for cantilevered shells with different lengths and thicknesses and the effect of each parameter was assessed on the flutter load and the critical circumferential mode number in each case.
Vibration
Ali Nouri; Sajad Hajirezaee
Abstract
In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. While the other ...
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In this research, the modal parameters of a beam in free-free condition are extracted by performing different experiments in laboratory. For this purpose, two different techniques are employed. The first methodology is considered as a time domain method in Operational Modal Analysis. While the other one is frequency domain impact hammer test which is categorized as an Experimental Modal Analysis method and can be regarded as the most common method in modal analysis. Checking the results obtained by the two methods, one can notice a distinct inconsistency in modal damping ratios extracted by each method. However, based on recent publications on the subject, it can be inferred that the time domain methods have better accuracy in identifying damping ratios of structures. In order to confirm the findings, the effect of excitation is examined for each method by altering the excitation tool. For the operational method, it is concluded that changing the excitation tool will not have a noticeable influence on the identified damping ratios, whilst for the Experimental Modal Analysis method changing the hammer tip leads to inconsistent results for damping ratios. This study exemplifies the deficiency of Experimental Modal Analysis methods in their dependency on excitation techniques.
Pressure Vessels
A. R. Shahani*; H. Esmaili; A. Aryaei; S. Mohammadi; M. Najar
Abstract
In this paper, the dynamic simulation for a high pressure regulator is performed to obtain the regulator behavior. To analyze the regulator performance, the equation of motion for inner parts, the continuity equation for diverse chambers and the equation for mass flow rate were derived. Because of nonlinearity ...
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In this paper, the dynamic simulation for a high pressure regulator is performed to obtain the regulator behavior. To analyze the regulator performance, the equation of motion for inner parts, the continuity equation for diverse chambers and the equation for mass flow rate were derived. Because of nonlinearity and coupling, these equations are solved using numerical methods and the results are presented. Additionally, the dynamic analysis results consist of the output pressure change versus time, the displacement of the moving parts versus time, the regulator mass flow rate versus time and the output pressure versus mass flow rate in different controlling spring pre-loads. Furthermore, the sensitivity analysis is carried out and the main parameters affecting the regulator performance are identified. Finally, the results of the dynamic simulation are validated by comparing them with the experimental results.
Heat and Mass Transfer
J. Prakash; K. S. Balamurugan; S. Vijaya Kumar Varma
Abstract
An analytical study was performed to study effects of thermo-diffusion and chemical reactions on a three-dimensional MHD mixed convective flow of dissipative fluid along an infinite vertical porous plate with transverse sinusoidal suction velocity. The parabolic partial differential equations governing ...
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An analytical study was performed to study effects of thermo-diffusion and chemical reactions on a three-dimensional MHD mixed convective flow of dissipative fluid along an infinite vertical porous plate with transverse sinusoidal suction velocity. The parabolic partial differential equations governing the fluid flow, heat transfer, and mass transfer were solved using perturbation technique and the expressions for velocity, temperature, and concentration distributions were obtained. Expressions for skin friction at the plate in the direction of the main flow, rate of heat transfer, and mass transfer from the plate to the fluid were derived in a non-dimensional form. Velocity, temperature, concentration, amplitudes of the perturbed parts of skin friction, rate of heat transfer, rate of mass transfer, and skin friction at the plate are presented in graphs and effects of various physical parameters like Hartmann number M, Prandtl number Pr, Reynolds number Re, Schmidt number Sc, Soret number So, Grashof number for heat transfer Gr, Grashof number for mass transfer Gm, and chemical reaction parameter Kr on the above flow quantities were analyzed and then the obtained results were physically interpreted.
Manufacturing Processes
Ebrahim Haghani; Ahmad Gheysarian; Mohammad Honarpisheh
Abstract
One of the methods for making prototypes is incremental forming process. In this method, the forming tool, performs a pre-programmed movement by the CNC machine and runs the desired path. This modernization process is used in the automotive, aerospace, military, medical and other industries. One of the ...
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One of the methods for making prototypes is incremental forming process. In this method, the forming tool, performs a pre-programmed movement by the CNC machine and runs the desired path. This modernization process is used in the automotive, aerospace, military, medical and other industries. One of the most influential parameters in this process is forming tool. This parameter is effective in forming forces, surface roughness, sheet formability and thickness distribution. In this study, the forming tool was investigated and rotating geometry tool was compared with a rigid tool. Also, the effects of step down, feed rate and spindle speed were investigated on the forming force, surface roughness and thickness distribution by comparing mentioned forming tools. The results indicate that the forming forces, sheet surface quality and thickness changes increase with increasing step down and feed rate. Using the rotary tools improves the forming forces, surface roughness and thickness distribution rather than the non-rotating tool.
Finite Elements Method (FEM)
Farshid Ahmadi; Rohollah Mohammadi
Abstract
Abstract The first step of implanting teeth is to drill a hole in the jaw bone. Excessive temperature produced during drilling is one of the destructive factors for bony tissue. If the temperature generation during surgical drilling exceeds the critical temperature, it could lead to osteonecrosis. This ...
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Abstract The first step of implanting teeth is to drill a hole in the jaw bone. Excessive temperature produced during drilling is one of the destructive factors for bony tissue. If the temperature generation during surgical drilling exceeds the critical temperature, it could lead to osteonecrosis. This research intends to study drilling parameters such as drilling speed, feed rate, cooling condition and tool geometry by FEM method in order to achieve the most appropriate drilling conditions. Three dimensional modeling of lower jaw bone from the CT scan images was made by Mimics 10.01 software. In order to place the drill bit on the mandibular model, two teeth were removed from the final part of model by CATIA V5R20 software. DEFORM-3D (Version 10.2) was used for mandibular cortical bone drilling simulation. For this purpose, drill bits with different geometrical parameter including point angles of 90, 70, and 118 degrees and helix angles of 20, 23, and 30 degrees were designed in the software. The simulations were carried out using different feed rates (60, 90, 120 and 200 mm/min) and rotational speeds (200, 400, 800, and 1200 rev/min). The simulation results showed that the most appropriate conditions for the lowest temperature was as follows: 70 degrees for drill bit point angle, 23 degrees for helix angle, 200 mm/min for feed rate, and 200 rev/min for rotational speed. Also, by using coolant the maximum temperature reduced by approximately 12 degrees. The results also suggest that the rotational speed of 200 rev/min and feed rate of 200 mm/min have the largest thrust force in drilling area. The finite element results were validated by available experimental data.
Optimization
N. Balaji; N. Jawahar
Abstract
This paper deals with a multi-period fixed charge production-distribution problem associated with backorder and inventories. The objective is to determine the size of the shipments from each supplier and backorder and inventories at each period, so that the total cost incurred during the entire period ...
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This paper deals with a multi-period fixed charge production-distribution problem associated with backorder and inventories. The objective is to determine the size of the shipments from each supplier and backorder and inventories at each period, so that the total cost incurred during the entire period towards production, transportation, backorder and inventories is minimised. A 0-1 mixed integer programming problem is formulated. Genetic algorithm based population search heuristic, Simulated annealing based neighbourhood search heuristic and Equivalent variable cost based simple heuristic are proposed to solve the formulation. The proposed methodologies are evaluated by comparing their solutions with the lower bound solutions. The comparisons reveal that Genetic algorithm and Simulated annealing algorithm generate better solutions than the Equivalent variable cost solutions and are capable of providing solutions close to the lower bound value of the problems.
Fluid Mechanics
P. R. Mashaei Mashaei; S. M. Hosseinalipour; K. Esmailpour
Abstract
In recent years, impinging streams have received increasing interest for their high efficiency in heat and mass transfer. This numerical study was conducted to investigate flow and heat transfer characteristics of one-way opposing jets of non-Newtonian fluids. Effects of Reynolds number impinging angle, ...
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In recent years, impinging streams have received increasing interest for their high efficiency in heat and mass transfer. This numerical study was conducted to investigate flow and heat transfer characteristics of one-way opposing jets of non-Newtonian fluids. Effects of Reynolds number impinging angle, momentum ratio and flow behavior index on mixing index were evaluated. The results showed improvement of thermal mixing due to an increase in Reynolds number, flow behavior index and momentum ratio in impinging zone. This study also demonstrated that thermal mixing along the channel increased as the Reynolds number and momentum ratio decreased. Nevertheless, augmentation of the flow behavior index resulted in higher thermal mixing along the channel. The impinging angle had no significant effect on thermal mixing along the channel; but, with increasing impinging angle, thermal mixing improved in the impinging zone.
Heat and Mass Transfer
Amir H. Roohi; H. Moslemi Naeini; M. Hoseinpour Gollo; J. Shahbazi Karami; Sh. Imani Shahabad
Abstract
Laser forming is a thermal forming process which uses laser beam irradiation to produce the desired final forms. In this article, the effect of temperature gradient across Al 6061-T6 aluminum sheets on bending angle is studied. Input parameters including laser power, scan velocity, beam diameter, ...
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Laser forming is a thermal forming process which uses laser beam irradiation to produce the desired final forms. In this article, the effect of temperature gradient across Al 6061-T6 aluminum sheets on bending angle is studied. Input parameters including laser power, scan velocity, beam diameter, and sheet thickness are the effective process parameters which influence the temperature gradient. Thus, a set of 81 numerical simulations based on a full factorial design with varying parameters is carried out and temperature gradient across the sheet thickness is measured. Effects of each input parameter on temperature gradient are determined using analysis of variance. Also, an equation is derived which predicts the temperature gradient for any arbitrary input parameter. The validity of the equation is done by comparing actual and predicted results. Numerical simulation is validated by experimental tests, which show a very close agreement. Finally, the effects of temperature gradient for three different sheet thicknesses on a final bending angle are derived. Results demonstrate that increase in temperature gradient across sheet thickness leads to increase in bending angle.
Fracture Mechanics
Kamal Kolasangiani; Mahmoud Shariati; Khalil Farhangdoost
Abstract
Forming limit curves are used as a parameter in finite element analysis to control the material's level of formability. In this research, forming limit diagram (FLD) of SS304L sheet was obtained by ABAQUSfinite element software. In practice, the experimental determination of a forming limit curve is ...
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Forming limit curves are used as a parameter in finite element analysis to control the material's level of formability. In this research, forming limit diagram (FLD) of SS304L sheet was obtained by ABAQUSfinite element software. In practice, the experimental determination of a forming limit curve is a very time-consuming procedure which requires special and expensive equipment. Forming limit diagram (FLD) is derived by the simulation of Erichsen test (out-of-plane stretching test) using hemispherical punch. There are few studies on the prediction of necking time, which is obtained by the application of Pepelnjak algorithm and ductile fracture criterion. In order for the validation, the numerical result of forming limit diagram (FLD) was compared with the experimental and analytical results and a good correlation was observed. Forming limit stress diagram (FLSD) and MSFLD were determined by plotting the principal in-plane stress and FLD corresponding to the onset of necking localization, respectively. Effect of the thickness of the sheet on forming limit curves was investigated and the results showed that increased thickness of the sheet led to raised level of the FLD and MSFLD; but, FLSD did not change considerably.
Robotics
Mohammad Falsafi; Khalil Alipour; Bahram Tarvirdizadeh
Abstract
Due to various advantages of Wheeled Mobile Robots (WMRs), many researchers have focused to solve their challenges. The automatic motion control of such robots is an attractive problem and is one of the issues which should carefully be examined. In the current paper, the trajectory tracking problem of ...
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Due to various advantages of Wheeled Mobile Robots (WMRs), many researchers have focused to solve their challenges. The automatic motion control of such robots is an attractive problem and is one of the issues which should carefully be examined. In the current paper, the trajectory tracking problem of WMRs which are actuated by two independent electrical motors is deliberated. To this end, and also, computer simulation of the system, first the system model is derived at the level of kinematics. The system model is nonholonomic. Then a simple non-mode-based controller based on fuzzy logic will be proposed. The control input resulted from fuzzy logic will then be corrected to fulfill the actuation saturation limits and non-slipping condition. To prove the efficiency of the suggested controller, its response, in terms of the required computational time burden and tracking error, will be compared with a previously suggested method. The obtained simulation results support the superiority of fuzzy based method over a previous study in terms of the considered measures.
Energy Systems
Armin Emamifar
Abstract
In this research, the thermodynamic analysis of a two-stage absorption compression refrigeration system employing a flash tank with indirect subcooler is presented. The absorption cycle uses LiBr-water solution as the working fluid and prepares the high temperature medium for the bottoming cycle, which ...
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In this research, the thermodynamic analysis of a two-stage absorption compression refrigeration system employing a flash tank with indirect subcooler is presented. The absorption cycle uses LiBr-water solution as the working fluid and prepares the high temperature medium for the bottoming cycle, which is a two-stage compression refrigeration system with R744 refrigerant. The thermodynamic analysis indicates that the proposed system decreases the required electrical work and the total exergy destruction rate results in the improvement of the overall COP and total exergy efficiency. The results are compared with the same system without the subcooler and a simple cascade absorption compression refrigeration system. It was found that the overall COP and the total exergy efficiency of the proposed system are 7.86% and 11.21% higher than the system without the subcooler. These enhancements are 11.42% and 16.48% in comparison with the simple cascade absorption compression refrigeration system. Moreover, the effect of the generator temperature, condenser temperature, cascade condenser temperature, evaporator temperature, and the intermediate pressure of the compression section on the system electrical work, overall COP, total exergy destruction rate, and the total exergy efficiency of the proposed system are discussed.
Computational Fluid Dynamics (CFD)
Siamak Gharahjeh; Ammar Ashraf; Ghorban Mahtabi
Abstract
In this study, a numerical solution of 2D steady incompressible lid-driven cavity flow is presented. Three different numerical schemes were employed to make a comparison on the practicality of the methods. An alternating direction implicit scheme for the vorticity-stream function formulation, explicit ...
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In this study, a numerical solution of 2D steady incompressible lid-driven cavity flow is presented. Three different numerical schemes were employed to make a comparison on the practicality of the methods. An alternating direction implicit scheme for the vorticity-stream function formulation, explicit and implicit schemes for the primitive variable formulation of governing Navier-Stokes equations were attempted. A fairly fine uniform grid was adopted for all the cases after a technical procedure was applied to come up with the proper mesh size that would make the solution roughly independent of mesh quality. The solutions obtained for different Reynolds numbers are presented and compared. Superiority of numerical approaches was investigated and compared to benchmark solutions available in the literature. Based on the results of the present research, it can be claimed that explicit scheme used for primitive variable formulation can be only half the way (as in Re=2500 for explicit to Re=5000 for ADI and implicit schemes) as successful as the other two numerical methods due to its relative simplicity.
Composite Materials
Aidin Ghaznavi; Mohammad Shariyat
Abstract
In the present article, the dynamic behavior of sandwich plates with embedded shape memory alloy (SMA) wires is evaluated for two cases wherein (i) the stress-strain curve of the superelastic behavior of the SMA wires is symmetric and (ii) the mentioned curve is non-symmetric. A modified version of Brinson’s ...
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In the present article, the dynamic behavior of sandwich plates with embedded shape memory alloy (SMA) wires is evaluated for two cases wherein (i) the stress-strain curve of the superelastic behavior of the SMA wires is symmetric and (ii) the mentioned curve is non-symmetric. A modified version of Brinson’s constitutive model is proposed and used. The high non-linearity in the behavior stems from the SMA wires embedded in the sandwich plate. In this regard, in addition to the proposed advanced algorithm for the determination of the martensite volume fraction, a Picard iterative solution algorithm is used in conjunction with Newmark’s numerical time integration method for solving the resulting finite element equations. To improve the accuracy of the results, the variation of martensite volume fraction and material properties of individual points of the structure are updated continuously. Therefore, the kinetic equations of the phase transformation of the SMA are coupled with the motion equations, to accurately model the nonlinear behavior of the sandwich plate. For analysis of the thick sandwich plate, a higher-order global-local theory with novel 3D-equilibrium-based corrections is utilized. One of the features of this theory is the estimation capability of the nonlinear in-plane displacement components, and precise assessment of the transverse shear stresses through satisfying the continuity conditions of the shear stresses at the interfaces between layers. Another advantage of the proposed theory in comparison with the conventional approaches is the ability to simulate changes in the core thickness. This is especially important in cases where the core is relatively thick or soft.
P. Kumar; M. Gupta; V. Kumar
Abstract
With the increased diversity of the customer demand and complexity of the product, Inconel 825 is widely used to meet the actual needs, especially in the aerospace industry. It is difficult-to-cut material because of its high toughness and hardness. The present research attempts to optimize the process ...
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With the increased diversity of the customer demand and complexity of the product, Inconel 825 is widely used to meet the actual needs, especially in the aerospace industry. It is difficult-to-cut material because of its high toughness and hardness. The present research attempts to optimize the process parameters of wire electric discharge machining during the cutting operation of Inconel 825. The wire electric discharge machining characteristics such as pulse-on time, pulse-off time, spark gap voltage, peak current, wire tension, wire feed are taken into consideration. The performance was measured in terms of material removal rate, surface roughness, and wire wear ratio. The central composite design of response surface methodology at an α value of ± 2 was employed to establish the mathematical model between process parameters and performance measures. A multi-objective particle swarm optimization algorithm has been used to find the optimal solutions called Pareto optimal solutions. It uses the concept of dominance to find the non dominated set in the entire population and the crowding distance approach to finding the best Pareto optimal solutions with a good diversity of objectives. The confirmation experiments of the multi-objective particle swarm optimization algorithm show a significant improvement in material removal rate (27.934 to 31.687 mm2/min), surface roughness (2.689 to 2.448μm), and wire wear ratio (0.027 to 0.030). SEM micrograph studies showed the number of cracks, pockmarks, craters, and pulled out material on the workpiece and wire electrode surface. Energy Dispersive X-ray analysis is performed to investigate the presence of elements on the work surface other than the base material.
Composite Materials
Aidin Ghaznavi; Mohammad Shariyat
Abstract
Studying the behavior of sandwich panels is very important due to their widespread use in different industries. Therefore, over the past decades, various theories have been proposed to study the behavior of these panels. In this paper a higher order global-local theory with 3D equilibrium-based corrections ...
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Studying the behavior of sandwich panels is very important due to their widespread use in different industries. Therefore, over the past decades, various theories have been proposed to study the behavior of these panels. In this paper a higher order global-local theory with 3D equilibrium-based corrections is presented to study behavior of thick and thin sandwich plate with flexible and auxetic core. In addition to correcting the results with 3D elasticity equations, another important advantage of the presented theory is the ability to consider the transverse core deformation of the sandwich panels. It should be mentioned that to study the behavior of thick sandwich panels, especially with soft core, the existence of this feature is very necessary and has a great effect on the accuracy of the obtained results. Comparison of the obtained results with those existing in valid references showed that the formulation of the provided finite element had a very good accuracy even for thick and thin sandwich plates. Finally, the effect of different material and geometrical parameters on the behavior of sandwich plates are carefully investigated using the presented theory.
Biomechanics
Puria Talebi Barmi; Bahman Vahidi
Abstract
Arterial embolism is one of the major causes of brain infarction. Investigating the hemodynamic factors of this phenomenon can help us to get a better understanding of this complication. The carotid artery is one of the primary tracts that emboli can go toward the brain through it. In this study, we ...
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Arterial embolism is one of the major causes of brain infarction. Investigating the hemodynamic factors of this phenomenon can help us to get a better understanding of this complication. The carotid artery is one of the primary tracts that emboli can go toward the brain through it. In this study, we used a 3D model of the carotid bifurcation, and two geometries, elliptical and spherical, were considered for the clots. Hyperelastic and visco-hyperelastic models were used for the mechanical properties of clots. The governing equations of the fluid are Navier-Stokes and continuity equations and have been solved in an Arbitrary Lagrangian-Eulerian (ALE) formulation through the fluid-structure interaction method. The hemodynamic parameters of fluid and shear stress on the wall of the carotid artery were calculated. Besides, by using ADINA software, the effective stress (Von Mises stress) of the clots and shear stress created on them were evaluated as well. Results revealed that the elliptical clot has more effects on the hemodynamic parameters of the fluid and the mechanical property of clots has significant effects on the amount of stress created on the clots. Furthermore, clot fracture will not occur due to this point that the maximum effective stress in this study was 1819 Pa but the creation of crack in clots is more probable, and this probability is more for the elliptical clot.
Fluid Mechanics
M. Alemi; R. Maia
Abstract
The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions ...
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The present study aimed to investigate two numerical solutions of the Navier-Stokes equations. For this purpose, the mentioned flow equations were written in two different formulations, namely (i) velocity-pressure and (ii) vorticity-stream function formulations. Solution algorithms and boundary conditions were presented for both formulations and the efficiency of each formulation was investigated by considering a two-dimensional low laminar flow around a square pile in a rectangular computational domain. Simulations under the same conditions were conducted to assess the difference between results generated by both formulations. Furthermore, the accuracy of the results was analyzed through a comparison of the results with the available reference data. In addition, computational efficiency of both formulations was investigated in term of computation time. The corresponding results indicated that both formulations are adequate to the case used in the present study. Moreover, performed simulations showed that solving the vorticity-stream function form of the flow equations is faster than solving the velocity-pressure form of those equations for simulating a two-dimensional laminar flow around a square pile.
Robotics
M. H. Ghasemi; A. H. Korayem; S. R. Nekoo; M. H. Korayem
Abstract
Recording the variation of joint angles as a feedback to the control unit is frequent in articulated arms. In this paper, magnetic sensor AS5045, which is a contactless encoder, is employed to measure joint angles of 6R robot and the performance of that is examined. The sensor has a low volume, two digital ...
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Recording the variation of joint angles as a feedback to the control unit is frequent in articulated arms. In this paper, magnetic sensor AS5045, which is a contactless encoder, is employed to measure joint angles of 6R robot and the performance of that is examined. The sensor has a low volume, two digital outputs and provides a high resolution measurement for users; furthermore its zero position is adjustable. Installation and use of this measurement system on 6R robot has been expressed by using output signals of sensor AS5045 in the digital control board of 6R and equipped with ARM processor LPC1768. First, a sample of digital board is used for controlling a DC motor in both speed and position, in order to investigate specifications of AS5045’s digital and analogue outputs. Simulation of 6R robot in point-to-point motion has been performed with MATLAB software using a proportional derivative (PD) controller. Then, experiment with the same condition and gains via a PD controller has been designed and implemented on the digital control board. The feedback system has been also checked in a circular path to show its advantages in trajectory tracking. The comparison of simulation results with experiments shows improvement: less error and better performance of 6R robot. This new setup omitted the noise of previous analogue feedback system since its digital outputs provides a precise measurement.
Composite Materials
Y. Bayat; M. Alizadeh; A. Bayat
Abstract
In this paper, a general solution for torsion of hollow cylinders made of functionally graded materials (FGM) was investigated. The problem was formulated in terms of Prandtl’s stress and, in general, the shear stress and angle of twist were derived. Variations in the material properties such as ...
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In this paper, a general solution for torsion of hollow cylinders made of functionally graded materials (FGM) was investigated. The problem was formulated in terms of Prandtl’s stress and, in general, the shear stress and angle of twist were derived. Variations in the material properties such as Young’s modulus and Poisson’s ratio might be arbitrary functions of the radial coordinate. Various material models from the literature were also used and the corresponding shear stress and angle of twist were individually computed. Moreover, by employing ABAQUS simulations, finite element results were compared with the analytical ones.
Control
Mohammad Hossein Bayati Chaleshtari; Elahe Norouzi; Habib Ahmadi
Abstract
Functional electrical stimulation (FES) is the most commonly used system for restoring function after spinal cord injury (SCI). In this study, we used a model consists of a joint, two links with one degree of freedom, and two muscles as flexor and extensor of the joint, which simulated in MATLAB using ...
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Functional electrical stimulation (FES) is the most commonly used system for restoring function after spinal cord injury (SCI). In this study, we used a model consists of a joint, two links with one degree of freedom, and two muscles as flexor and extensor of the joint, which simulated in MATLAB using SimMechanics and Simulink Toolboxes. The muscle model is based on Zajac musculotendon actuator and composed of a nonlinear recruitment curve, a nonlinear activation-frequency relationship, calcium dynamics, fatigue/recovery model, an additional constant time delay, force-length and force-velocity factors. In this study, we used a classic controller for regulating the elbow joint angle; a Proportional- Integral- Derivative controller. First, we tuned the PID coefficients with trial and error, and then a particle swarm optimization algorithm was used to optimize them. The important features of this algorithm include flexibility, simplicity, short solution time, and the ability to avoid local optimums. This PSO -PID controller uses particle swarm optimization algorithm to get the required pulse width for stimulating the biceps to reach the elbow joint to the desired angle. The fitness function was defined as sum square of error. The results for PSO -PID controller show faster response for reaching the range of the set point than the PID controller tuned by trial and error. However the PSO -PID is much better in terms of the rise time and the settling time, the PID tuned by trial and error has no overshoot. The time to reach the zero steady state error is half in PSO -PID in comparison to PID tuned by trial and error.
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