Vibration
Seyed javid Zakavi; Behzad Shiralivand; Mohammad nourbakhsh
Abstract
In this paper the ratcheting behavior of carbon steel(ASTM A106B) and stainless steel(304L) elbows is studied under steady internal pressure and in-plane external moments at frequencies typical of seismic excitations. The finite element analysis with the nonlinear isotropic/kinematic (combined) hardening ...
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In this paper the ratcheting behavior of carbon steel(ASTM A106B) and stainless steel(304L) elbows is studied under steady internal pressure and in-plane external moments at frequencies typical of seismic excitations. The finite element analysis with the nonlinear isotropic/kinematic (combined) hardening model has been used to evaluate ratcheting behavior of the elbows. Material parameters have been obtained from several stabilized cycles of specimens that are subjected to symmetric strain cycles. The rate of ratcheting depends significantly on the magnitudes of the internal pressure, dynamic bending moment and material constants for combined hardening model. The results show that the maximum ratcheting is occurred in the hoop direction at crown. Also, the results show that initially, the calculated rate of ratcheting is large and then decreases with the increasing of cycles. Also, the results obtained by using the Combined hardening model gives acceptable adaptation in comparison with the other hardening models(AF and Chaboche hardening models); however this model gives over estimated values comparing with the experimental data.
Vibration
Mellel Nacim; Ouali Mohammed; Dougdag Mourad; Mohammedi Brahim
Abstract
This paper presents an extended cross modal strain energy change method to estimate the severity of damage associated with limited modal data in beam-like structures. This method takes in account the correlation between the analytical modal data and the measured incomplete modal data. A procedure ...
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This paper presents an extended cross modal strain energy change method to estimate the severity of damage associated with limited modal data in beam-like structures. This method takes in account the correlation between the analytical modal data and the measured incomplete modal data. A procedure was proposed and the analytical elemental stiffness of the damaged element after it is localized is included in quantification of the measured single damage extent. A three-dimensional numerical beam model with different damage cases is used to simulate the CMSE method application and to getting the bending displacements of the damaged element. An experimental modal analysis (EMA) on a cantilever beam with and without crack was carried out to evaluate the effectiveness of the extended CMSE method. The severity magnitude of the damage was predicted within an acceptable error range through the using validation process. Results reveal that the proposed damage estimation method successfully evaluates single damage severity in beam like structure and can be useful in maintenance technology and structural health monitoring system.
Nonlinear Solution
M. Matinfar; M. Ghasemi
Abstract
Variational Iteration method using He's polynomials can be used to construct solitary solution and compacton-like solution for nonlinear dispersive equatioons. The chosen initial solution can be determined in compacton-like form or in solitary form with some compacton-like or solitary forms with ...
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Variational Iteration method using He's polynomials can be used to construct solitary solution and compacton-like solution for nonlinear dispersive equatioons. The chosen initial solution can be determined in compacton-like form or in solitary form with some compacton-like or solitary forms with some unknown parameters, which can be determined in the solution procedure. The compacton-like solution and solitary solution can be converted into each other.
Thermodynamics and Cumbustion
A. A. Mirmohammadi; F. Ommi
Abstract
The purpose of this paper is to studying nonlinear k-ε turbulence models and its advantages in internal combustion engines, since the standard k-ε model is incapable of representing the anisotropy of turbulence intensities and fails to express the Reynolds stresses adequately in rotating ...
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The purpose of this paper is to studying nonlinear k-ε turbulence models and its advantages in internal combustion engines, since the standard k-ε model is incapable of representing the anisotropy of turbulence intensities and fails to express the Reynolds stresses adequately in rotating flows. Therefore, this model is not only incapable of expressing the anisotropy of turbulence in an engine cylinder, but also is unable to provide good performance when computing the swirling and tumbling flows is important in engine cylinders. Thus, in this paper, the results of nonlinear k-ε model are compared with those of the linear one. Results of diesel engine simulation with linear and nonlinear k-ε models in comparison show that turbulence intensity in the nonlinear model simulation is higher than that of the linear model; also, nonlinear k-ε models predict the second peak value because of the bowl shape in expansion stroke for turbulence intensity. Gas injection results show that nonlinear turbulence models predict spray penetration accurately because of correctly turbulence intensities predicting. Also, the results demonstrate that, for high pressure gas injection, turbulence intensity is high and predicted accurately using nonlinear models. Then, its spray penetration length is predicted accurately in comparison to experimental data’s. Although CPU time spending in the nonlinear model is more than that of the linear one, the non-linear stress model is found to increase computation time by 19%.
Aerodynamics
Sarallah Abbasi; Marhamat zienali
Abstract
Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial ...
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Characteristics of rotor blade tip clearance flow in axial compressors can significantly affect their performance and stable operation. It may also increase blade vibrations and cause detrimental noises. Therefore, this paper is contributed to investigate tip leakage flow in a low speed isolated axial compressor rotor blades row. Simulations are carried out on near-stall condition, which is valuable of being studied in detail. In turbomachines, flows are non-isotropic and highly three-dimensional. The reason arises from the complicated structure of bounded walls, tip leakage flows, secondary flows, swirl effects, streamlines curvatures and pressure gradients along different directions. As a result, accurate studies on tip leakage flow would be accompanied by many challenges such as adopting suitable turbulence models. So, investigations are carried out numerically utilizing two well-known turbulence models of k-ε and k-ω-SST, separately. It is shown that the k-ε model yields poor results in comparison to the k-ω-SST model. To realize reasons for this discrepancy, turbulence parameters such as turbulent kinetic energy, dissipation and eddy viscosity terms at the tip clearance region were surveyed in detail. It is found out that estimation for eddy viscosity term is too high in the k-ε model due to excessive growth of turbulent kinetic energy, time scale, and lack of effective damping coefficient. This leads to dissipation of vortical structure of flow and wrong estimation of flow field at the rotor tip clearance region. Nevertheless, k-ω-SST turbulence model provides results consistent with reality.
Heat and Mass Transfer
M. Nasiri; B. Ghasemi
Abstract
This paper modeled heating air of a room through examining free convection in a 3D chamber. The chamber had cold and hot sources with Tc and Th temperatures, respectively. Its other walls were adiabatic. This study aimed at predicting effect of temperature difference, displacement of hot and cold sources ...
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This paper modeled heating air of a room through examining free convection in a 3D chamber. The chamber had cold and hot sources with Tc and Th temperatures, respectively. Its other walls were adiabatic. This study aimed at predicting effect of temperature difference, displacement of hot and cold sources and their aspect ratio on flow field, temperature and heat transfer rate. To conduct the study, mass conservation, momentum and energy equations were applied in laminar and 3D states while assuming fluid constant properties, except density, in the power of buoyancy (Boussinesq approximation). Final difference method (FDM) was used for numerical solution of the governing equations based on the volume control and SIMPLE algorithm. According to the modeling results, the most favorable temperature distribution in the chamber (room) was obtained when the heat source (radiator) was located on the wall under the cold source (window). Reducing the distance between the two sources would result in increasing heat transfer from the heating sources.
Nhu-Tung Nguyen; Dong Van Pham; Dung Tien Hoang; Cuong Duc Pham
Abstract
Cutting force coefficients (CFCs) are the most important factors in the prediction of CFs (CFs) and other machining characteristics (MCs). This study was conducted to model the CFs and MCs in the milling process based on the calculated values of CFCs. From the relationship of average values of CFs and ...
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Cutting force coefficients (CFCs) are the most important factors in the prediction of CFs (CFs) and other machining characteristics (MCs). This study was conducted to model the CFs and MCs in the milling process based on the calculated values of CFCs. From the relationship of average values of CFs and feed rate, CFCs were determined and used to predict dynamic CFs (DCFs) in the flat milling process. In static models, the average values of CFs were presented as a linear regression of feed rate. The DCFs and other MCs were modeled depending on the cutting parameters, cutter geometry, CFCs, and structure parameters of the machine-tool system. By performing the flat-milling process of gray cast iron GG25 using HSS-Co solid tool, the average CFs were modeled as the linear regression of feed rate with large determination coefficients (R2 > 93%). Besides, all CFCs of a pairs of tool and workpiece for each cutting type were successfully determined based on the measured data of CFs from the experimental process. Moreover, the proposed models of DCFs were successfully verified based on the compared results between the predicted CFs and measured CFs in several cutting tests with different cutting parameters. The proposed models of cutting force in this study were successfully used to predict the DCFs and several MCs in milling processes using a flat milling tool. And can be used to design and develop tools and machine in industrial manufacturing.
Vibration
Mahesh Luintel; Tri Ratna Bajracharya
Abstract
Performance and reliability of any rotating machine can be studied by proper dynamic analysis of the machine. In this regard, this paper presents the method to study the dynamic response of the shaft of a Pelton turbine due to the impact of water jet. Equations of motion for the bending vibration of ...
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Performance and reliability of any rotating machine can be studied by proper dynamic analysis of the machine. In this regard, this paper presents the method to study the dynamic response of the shaft of a Pelton turbine due to the impact of water jet. Equations of motion for the bending vibration of Pelton turbine assembly, in two transverse directions, is developed by using Lagrange equation of motion with the help of assumed modes method. The Pelton wheel is assumed as a rigid disk attached on Euler-Bernoulli shaft. The impact provided by the water jet is represented in the form of Fourier series. Critical speeds of the system are determined by performing free vibration analysis and presented in the form of Campbell diagram. The response plots due to impact of water are generated by performing forced response analysis. Both free and forced analyses are carried out by considering first three modes of vibration.
Computational Fluid Dynamics (CFD)
brahim Rostane; ALIANE KHALED; said Abboudi
Abstract
The aim of our study is to analyze the impact of insertion holes in the middle of obstacles on the flow around a surface-mounted cube, In order to do this; we studied four configurations of obstacles in a channel with a Reynods number based on obstacle height ReH = 40000. The hexahedral structured meshes ...
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The aim of our study is to analyze the impact of insertion holes in the middle of obstacles on the flow around a surface-mounted cube, In order to do this; we studied four configurations of obstacles in a channel with a Reynods number based on obstacle height ReH = 40000. The hexahedral structured meshes were used to solve the fluid dynamics equations .The finite volume method are employed to solve the governing equations using the ANSYS CFX code and the turbulence model k-ω SST. The streamwise velocity profiles, the Time-averaged streamlines, the turbulence kinetic energy and the drag coefficient are presented. The results showed the appearance of a second vortex behind obstacles with hole from diameter D/H=0.2. The turbulence kinetic energy was greater on top of the obstacle, it was more intense for the obstacle without hole, this intensity decreased as the hole diameter increased. The drag coefficient was improved only for the case D/H=0.32
Welding
Saman Khalilpourazary; Reza Abdi Behnagh; Ramezanali Mahdavinejad; Nasib Payam
Abstract
This study focused on the optimization of Al—Mg to CuZn34 friction stir lap welding (FSLW) process for optimal combination of rotational and traverse speeds in order to yield favorable fracture load using Grey relational analysis (GRA). First, the degree of freedom was calculated for the system. ...
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This study focused on the optimization of Al—Mg to CuZn34 friction stir lap welding (FSLW) process for optimal combination of rotational and traverse speeds in order to yield favorable fracture load using Grey relational analysis (GRA). First, the degree of freedom was calculated for the system. Then, the experiments based on the target values and number of considered levels, corresponding orthogonal array, Grey relational coefficient and Grey relational grade were performed. In the next step, Grey relational graph of each level was sketched. The performed graph and analysis of Grey results proved the impact of rotational speed and traverse speed on fracture load of resultant joints. Finally, the optimum amount of each parameter for better strength of the welds was obtained. This study showed feasibility of the application of Grey relational analysis for achieving dissimilar friction stir lap welds with the highest quality.
Dynamic Response
Chandan Kumar; Vikas Rastogi Rastogi
Abstract
This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries ...
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This work deals with effects of asymmetric stiffness on the dynamic behaviour of the rotor system. The analysis is presented through an extended Lagrangian Hamiltonian mechanics on the asymmetric rotor system, where symmetries are broken in terms of the rotor stiffness. The complete dynamics of asymmetries of rotor system is investigated with a case study. In this work, a mathematical model is developed considering symmetry breaking of a finite rotor due to stiffness. The natural frequency and amplitude of the rotor are obtained analytically through extended Lagrangian formulation. The asymmetries in rotor are also modeled through bond graph modeling technique for the computational analysis. The simulation result shows a considerable agreement with the analytical results. The limiting dynamics of rotor is shown and analyzed through simulation.
Manufacturing Processes
S. Khalilpourazary; P. M. Kashtiban; N. Payam
Abstract
Nowadays, in order to reach minimum production cost in machining operations, various optimization methods have been proposed. Since turning operation has different parameters affecting the workpiece quality, it was selected as a complicated manufacturing method in this paper. To reach sufficient quality, ...
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Nowadays, in order to reach minimum production cost in machining operations, various optimization methods have been proposed. Since turning operation has different parameters affecting the workpiece quality, it was selected as a complicated manufacturing method in this paper. To reach sufficient quality, all influencing parameters such as cutting speed, federate, depth of cut and tool rake angle were selected as input parameters. Furthermore, both surface roughness and tool life were considered as the objectives. Also, ST37 steel and M1 high speed steel (HSS) were selected as workpiece material and tool, respectively. Subsequently, grey relational analysis was performed to elicit optimal values for the mentioned input data. To achieve this goal, first, degree of freedom was calculated for the system and the same experiments were performed based on the target values and number of considered levels, leading to calculating grey relational generating, grey relational coefficient and grey relational grade. As the next step, the grey relational graph was sketched for each level. Finally, optimum values of the parameters were obtained for better surface roughness and tool life. It was shown that the presented method in the turning operation of ST37 led to high surface quality and tool life.
Meshless Numerical Methods
M. Y. Hashemi
Abstract
In this paper, the laminar incompressible flow equations are solved by an upwind least-squares meshless method. Due to the difficulties in generating quality meshes, particularly in complex geometries, a meshless method is increasingly used as a new numerical tool. The meshless methods only use clouds ...
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In this paper, the laminar incompressible flow equations are solved by an upwind least-squares meshless method. Due to the difficulties in generating quality meshes, particularly in complex geometries, a meshless method is increasingly used as a new numerical tool. The meshless methods only use clouds of nodes to influence the domain of every node. Thus, they do not require the nodes to be connected to form a mesh and decrease the difficulty of meshing, particularly around complex geometries. In the literature, it has been shown that the generation of points in a domain by the advancing front technique is an order of magnitude faster than the unstructured mesh for a 3D configuration. The Navier–Stokes solver is based on the artificial compressibility approach and the numerical methodology is based on the higher-order characteristic-based (CB) discretization. The main objective of this research is to use the CB scheme in order to prevent instabilities. Using this inherent upwind technique for estimating convection variables at the mid-point, no artificial viscosity is required at high Reynolds number. The Taylor least-squares method was used for the calculation of spatial derivatives with normalized Gaussian weight functions. An explicit four-stage Runge-Kutta scheme with modified coefficients was used for the discretized equations. To accelerate convergence, local time stepping was used in any explicit iteration for steady state test cases and the residual smoothing techniques were used to converge acceleration. The capabilities of the developed 2D incompressible Navier-Stokes code with the proposed meshless method were demonstrated by flow computations in a lid-driven cavity at four Reynolds numbers. The obtained results using the new proposed scheme indicated a good agreement with the standard benchmark solutions in the literature. It was found that using the third order accuracy for the proposed method could be more efficient than its second order accuracy discretization in terms of computational time.
Composite Materials
Y. Bayat; H. Ekhteraei Toussi
Abstract
In many cases, a torsional shaft may be a thick-walled radially inhomogeneous cylindrical object. The hollow shafts made of functionally graded materials (FGMs) are such kind of compositions which were studied in this paper. Cylindrical FG shafts are composed of ceramic and metallic parts with power ...
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In many cases, a torsional shaft may be a thick-walled radially inhomogeneous cylindrical object. The hollow shafts made of functionally graded materials (FGMs) are such kind of compositions which were studied in this paper. Cylindrical FG shafts are composed of ceramic and metallic parts with power function distribution across the radial direction. The ceramic phase is isotropic elastic and the metallic phase was elastic-plastic. In this paper, the volume fraction-based elastic–plastic mixture rule of renowned Tamura–Tomota–Ozawa (TTO) was used to model the behavior of the composite material. The elasto-plastic torsion problem was modeled and solved analytically. The results were compared with the simulations of ABAQUS and the accuracy of the solutions was evaluated. Depending on the thickness and level of inhomogeneity, different modes of yielding were obtained. The results showed that plastic zone could occur at the inner or outer surfaces or simultaneously at both surfaces; even it may start in-between the thickness. Moreover, the influence of material inhomogeneity and thickness of shaft upon the plastic zone development were studied and discussed.
Fluid Mechanics
Rahim Shamsoddini
Abstract
Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, ...
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Liquid sloshing is a common phenomenon in the transporting of liquid tanks. Liquid waves lead to fluctuating forces on the tank wall. If these fluctuations are not predicted or controlled, they can lead to large forces and momentum. Baffles can control liquid sloshing fluctuations. One numerical method, widely used to model the liquid sloshing phenomena is Smoothed Particle Hydrodynamics (SPH). Because of its Lagrangian nature, SPH is suitable for simulating free surface flow. In the present study, a relatively accurate Incompressible SPH (ISPH) method improved by kernel gradient correction tensors, particle shifting algorithms, turbulence viscosity calculations, and free surface particle detectors is applied for the free surface flow modeling. In comparison to the other SPH Simulations and experimental data, these results show that the present algorithm is effective for simulating free surface problems. The present algorithm has been applied to simulate liquid sloshing phenomena, while the aim of this study is the investigation of vertical and horizontal baffle effects on the control and damping of liquid sloshing. Results show that for vertical baffles, baffle size has a major role in sloshing fluctuation damping. For horizontal baffles, also including size, the baffle base position has a significant role in liquid sloshing fluctuation damping. When horizontal baffle is near the free surface, sloshing fluctuation-damping increases.
Biomechanics
Mehdi Jahangiri; Mohsen Saghafian; Mahmood Reza Sadeghi
Abstract
A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with non-Newtonian models using ADINA. Blood flow was considered laminar, and the arterial ...
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A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with A numerical study of hemodynamic parameters of pulsatile blood flow is presented in a stenotic artery with non-Newtonian models using ADINA. Blood flow was considered laminar, and the arterial wall was considered rigid. Studied stenosis severities were 30, 50, and 70% of the cross-sectional area of the artery. Six non-Newtonian models were used to model the non-Newtonian behavior of blood, and their results were compared with the Newtonian model. The results showed that in Power-law and Walburn-Schneck models, unlike other models, shear stress values before and after the stenosis were smaller than Newtonian models. Also, in maximum flow rate, the Carreua, generalized Power-law, Casson, and Carreua-Yasuda models showed a reduction in global importance factor of non-Newtonian behavior, and subsequently, the results approached Newtonian model. In minimum flow rate, the global importance factor of Newtonian behavior increased, which highlighted the importance of Newtonian model. In minimum flow rate, Carreua-Yasuda model was more sensitive to the non-Newtonian behavior of blood compared to Carreua, Casson, and Power-law models. Also, in that time period, Walburn-Schneck was less sensitive to the non-Newtonian behavior of blood. On the other hand, this model did not show sensitivity when the flow rate was at its peak. Power-law model overestimated the global importance factor values. Therefore, Power-law model was not suitable, because it showed extreme sensitivity to dimension. Walburn-Schneck model was not suitable too because it lacked sensitivity.
Micro and Nano Systems
Aylar Khooshehmehri; Abdollah Eslami Majd; Elham Arabsheybani
Abstract
The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell, and improving the performance of resonators requires a proper understanding ...
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The hemispherical resonator gyro (HRG) is a type of precision inertial sensor that has the advantages of direct angle measurement and unlimited dynamic range. The overall accuracy of the HRG is due to the quality of its resonator shell, and improving the performance of resonators requires a proper understanding of the processes of energy damping in each resonance cycle, which has a significant impact on sensor performance. In this paper, in order to investigate the losses in the hemisphere shell resonator, first, the equations governing the shell are studied, and three-dimensional modeling is performed in COMSOL software. By performing mechanical simulations, the resonance modes and the natural frequency of the shell are investigated, and finally, the second and third resonance modes are selected as the optimal operating mode of the gyroscope. Also, by performing thermal simulations, the dominant energy damping processes, such as thermo-elastic damping and anchor loss were analyzed and simulated, and the effect of shell material on damping was investigated. Then the quality factor of the resonator was evaluated based on its geometry and material. In this way, according to the scope of work of the gyroscope, this process can be used to design the specifications of the shell to achieve a resonator with the desired quality factor.
Composite Materials
Hamed Khosravi; Reza Eslami-Farsani
Abstract
This work reports the high-velocity impact response of multiscale anisogrid composite (AGC) panels. The aim of the present study is to evaluate the influence of surface-modified multi-walled carbon nanotubes (S-MWCNTs) at different S-MWCNTs contents (0-0.5 wt.% at an interval of 0.1 wt.%) on the high-velocity ...
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This work reports the high-velocity impact response of multiscale anisogrid composite (AGC) panels. The aim of the present study is to evaluate the influence of surface-modified multi-walled carbon nanotubes (S-MWCNTs) at different S-MWCNTs contents (0-0.5 wt.% at an interval of 0.1 wt.%) on the high-velocity impact responses of E-glass/epoxy AGC. Surface modification of MWCNTs is confirmed by Fourier-transform infrared (FTIR) and thermogravimetric (TGA) analyses. AGC panels were fabricated via a manual filament winding technique. E-glass fiber roving and E-glass woven fabric are employed as reinforcing agents in ribs and skin, respectively. The impact test is done on the composite panels by a cylindrical projectile with a conical nose. The results showe that the highest enhancement in the impact characteristics is attributed to the panel containing 0.4 wt.% S-MWCNTs. Based on the analysis of fracture surfaces, enhanced interfacial fiber/matrix bonding is observed for the S-MWCNTs loaded specimen. Furthermore, the incorporation of MWCNTs leads to the reduced damaged area and enhanced tolerance of damage.
Computational Fluid Dynamics (CFD)
Kandassamy K; Prabu Balakrishnan
Abstract
Heat dissipation in electronic circuits is important to maintain their reliability and functionality. In this work, microchannel based bio-inspired flow field models are proposed and numerically analyzed. The proposed flow fields have single to four inlet-outlet pairs. COMSOL is used to do the numerical ...
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Heat dissipation in electronic circuits is important to maintain their reliability and functionality. In this work, microchannel based bio-inspired flow field models are proposed and numerically analyzed. The proposed flow fields have single to four inlet-outlet pairs. COMSOL is used to do the numerical analysis. Conjugate heat transfer analysis is done on the quarter sectional models, utilizing bi-axial symmetry of the flow fields to reduce computational cost. Constant heat flux is applied to the base of the proposed heat sinks. The results show that the thermal and hydraulic resistances of the proposed models are lower than traditional micro-channel arrayed heat sinks. The four inlet-outlet pairs model shows a thermal resistance of 0.121 to 0.158 C/W at constant Re inlet condition, achieved with a pumping power of 0.102-0.126W. Two and four inlet-outlet pair models with aspect ratio 8.6 have a thermal resistance of 0.069 and 0.067 C/W, for pumping powers 2.078 and 4.365 W respectively. The pressure drop of the proposed models is lower than the conventional microchannel arrays.
Robotics
Mohammad Mohammadi; Reza Dehghani; Ali Reza Ahmadi
Abstract
In this paper, a quadrotor with two manipulators constrained on a straight path is modeled and a robust adaptive controller is proposed for it. Adding two manipulators to quadrotor increases its capabilities and applications in industry. Here, these two manipulators are used to place the robot on a constraint ...
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In this paper, a quadrotor with two manipulators constrained on a straight path is modeled and a robust adaptive controller is proposed for it. Adding two manipulators to quadrotor increases its capabilities and applications in industry. Here, these two manipulators are used to place the robot on a constraint path so that the quadrotor can perform monitoring operations more accurately, since the under-actuated quadrotor becomes over-actuated by these constrained manipulators and one can use this feature to accurately control the position of the robot. Reduced form of motion equations is derived for the constrained quadrotor and based on this a robust adaptive controller is proposed. The nonlinear terms in the dynamic model are approximated by basic functions with constant weights; and adaptive laws are designed by projection operator. Stability analysis is performed based on the Lyapunov theory. Evaluation of the presented controller is done by some numerical simulations. The simulation results showed that the robot tracks the reference path with bounded error in spite of dynamic uncertainties and wind force; and satisfies the considered constraints.
Hydraulic and Pneumatic Systems
Lokesh Kumar; Nimai Pada Mandal
Abstract
This study focused on the flow and pressure fluctuations of a fixed displacement radial piston pump with a valve plate with silencing grooves, and the effect of the number of pistons (5, 6, and 7) has been investigated. Over the manifolds of the pump, valve plate silencing grooves are regarded as Top ...
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This study focused on the flow and pressure fluctuations of a fixed displacement radial piston pump with a valve plate with silencing grooves, and the effect of the number of pistons (5, 6, and 7) has been investigated. Over the manifolds of the pump, valve plate silencing grooves are regarded as Top Dead Center (TDC) and Bottom Dead Center (BDC). The mathematical modelling is run in MATLAB Simulink. Analysing the flow characteristics and volumetric efficiency of the pump with and without silencing groove valve plate configuration of pump. The opening and closing area pattern of the kidney port is also analyzed.The percentage reduction of flow and pressure fluctuation with the silencing groove is 19% and 16.16%, respectively, for Z = 7, as compared to the model without silencing groove valve plate. The volumetric efficiency of the model with silencing groove valve plate is improved from 1% to 2% as compared to the model without silencing groove valve plate. The lower the flow and pressure fluctuation coefficients, higher the flow rate and volumetric efficiency of the pump for the model with silencing groove valve plate.
Fatigue
J. Amirian; H. Safari; M. Shirani; M. Moradi; S. Shabani
Abstract
Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in ...
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Generally, fatigue failure in an element happens at the notch on a surface where the stress level rises because of the stress concentration effect. The present paper investigates the effect of a notch on the fatigue life of the HSLA100 (high strength low alloy) steel which is widely applicable in the marine industry. Tensile test was conducted on specimens and mechanical properties were obtained. Rotating bending and axial fatigue tests were performed at room temperature on smooth and notched specimens and S-N curves were obtained. Using the obtained S-N curve for smooth specimens, the fatigue strength factor for the notched specimens were predicted by Weibull's weakest-link, Peterson, Neuber, stress gradient and critical distance methods and compared with experimental results. It was found that the critical distance and also Weibull’s weakest-link methods have the best agreement with experimental results.
Plates and Shells
Abstract
This paper is concerned with an investigation into the localized instability of a thin elastic orthotropic semi-infinite plate. In this study, a semi-infinite plate, simply supported on two edges and under different boundary conditions of clamped, hinged, sliding contact and free on the other edge, is ...
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This paper is concerned with an investigation into the localized instability of a thin elastic orthotropic semi-infinite plate. In this study, a semi-infinite plate, simply supported on two edges and under different boundary conditions of clamped, hinged, sliding contact and free on the other edge, is studied. A mathematical model is used and a general solution is presented. The conditions under which localized solutions exist are investigated.
Composite Materials
S. Mohammadi*; F. Abdi
Abstract
In the presented work, sulfur concrete and rubber were used for producing functionally graded materials (FGM). The physical and mechanical properties of sulfur concrete and rubber were changed continuously across the thickness. On one side, there was just rubber and, on the other, there was pure sulfur; ...
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In the presented work, sulfur concrete and rubber were used for producing functionally graded materials (FGM). The physical and mechanical properties of sulfur concrete and rubber were changed continuously across the thickness. On one side, there was just rubber and, on the other, there was pure sulfur; the properties of each substance were moved to reach another. This kind of material was constructed by applying mechanical pressure on all layers together and heating in a casting die. Thus, it is essential to consider the quantity of sulfur and rubber at each layer and the rule obeyed by physical and mechanical properties. In the drop test, it was found that the elastic impact coefficient changed from sulfur concrete around 50% to rubber around near zero. It seems that, by changing some parameters like combination percentage or layers' thickness, it is possible to optimize the FGM.
Vibration
Rouhollah Hosseini; Mohsen Hamedi
Abstract
The concept of “energy harvesting” is to design smart systems to capture the ambient energy and to convert it to usable electrical power for supplying small electronics devices and sensors. The goal is to develop autonomous and self-powered devices that do not need any replacement of traditional ...
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The concept of “energy harvesting” is to design smart systems to capture the ambient energy and to convert it to usable electrical power for supplying small electronics devices and sensors. The goal is to develop autonomous and self-powered devices that do not need any replacement of traditional electrochemical batteries. Now piezoelectric cantilever structures are being used to harvest vibration energy for self-powered devices. However, the geometry of a piezoelectric cantilever beam will greatly affect its vibration energy harvesting ability. This paper deduces a remarkably precise analytical formula for calculating the fundamental resonant frequency of bimorph V-shaped cantilevers using Rayleigh method. This analytical formula, which is convenient for mechanical energy harvester design based on Piezoelectric effect, is then validated by ABAQUS simulation. This formula raises a new perspective that, among all the bimorph V-shaped cantilevers and in comparison with rectangular one, the simplest tapered cantilever beam can lead to maximum resonant frequency and highest sensitivity. The derived formula can be commonly used as a relatively precise rule of thumb in such systems.
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