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Total 34 records

#### An analytical investigation of elastic-plastic deformation of FGM hollow rotors under a high centrifugal effect

, Article International Journal of Mechanical and Materials Engineering ; Volume 14, Issue 1 , 2019 ; 18230334 (ISSN) ; Aghajani, S ; Hemati, M ; Sharif University of Technology
Springer
2019

Abstract

Functionally graded material shafts are the main part of many modern rotary machines such as turbines and electric motors. The purpose of this study is to present an analytical solution of the elastic-plastic deformation of functionally graded material hollow rotor under a high centrifugal effect and finally determine the maximum allowed angular velocity of a hollow functionally graded material rotating shaft. Introducing non-dimensional parameters, the equilibrium equation has been analytically solved. The results for variable material properties are compared with the homogeneous rotor and the case in which Young’s modulus is the only variable while density and yield stress are considered...

#### Vibration Analysis of Drill String under Inclined Drilling Including Stick-Slip Phenomenon

, M.Sc. Thesis Sharif University of Technology ; Ahmadiyan, Mohammad Taghi (Supervisor)
Abstract

Vibration is one of the most important factors in design, operation and lifetime of drill string. Evaluation of vibration in the drill string like other rotating machines is very important and according to the length of drill string, whirling is one of the issues discussed. The aim of this thesis is non-linear analysis of the oblique long drill string. By considering the effects of passing drill mud around drill as well as properties of the drilling mud and stick - slip effect in creating whirling. Therefore, the equations related to kinetic and potential energy of a rotating drill string by taking longitudinal and transverse vibrations are written and by using the Lagrange method, equations...

#### Optimal stability of a redundant mobile manipulator via genetic algorithm

, Article Robotica ; Volume 24, Issue 6 , 2006 , Pages 739-743 ; 02635747 (ISSN) ; Naderi, D ; Eslami, S ; Sharif University of Technology
2006

Abstract

Once the path of the vehicle and the desired task of the end-effector are predefined, in order to apply the optimal stability criterion, the manipulator should be redundant. In this paper, the goal is to find the position, angular velocity, and angular acceleration of the redundant link of the manipulator such that the entire system becomes optimally stable. By considering the full dynamic interaction between the manipulator and its vehicle, the stability issue becomes more complex. There are some measures of stability and one of them is the tire's upward force. This measure tries to equalize the upward forces of the tires that lead to optimal stability and better steer-ability. Optimizing...

#### Coupled Vibration Analysis of Directional Drilling String Considering Effect of Drilling Mud

, M.Sc. Thesis Sharif University of Technology ; Ahmadian, Mohammad Taghi (Supervisor) ; Farrahi, Gholamhossein (Co-Advisor)
Abstract

Vibration is one of the most important factors in design, operation and lifetime of drill strings. There for, investigation of vibrations in drill string, like every other rotary machine, is very important. The main goal of this research is developing a nonlinear model for a drill string system dynamics in an inclined well. Effects of drilling mud flow rate, weight on bit, angular velocity along with viscous damping, on the stability and vibration of a drill string are studied. Dynamic equation of the model is developed considering axial displacement and lateral bending geometric nonlinear coupling. The effect of drilling mud flow is modeled using Paidoussis formulations. Equation of motion...

#### Investigation of the Influence of Geometry and External Field on Fluid Flow Through Carbon Nanotubes by Molecular Dynamics Simulation

, M.Sc. Thesis Sharif University of Technology ; Moosavi, Ali (Supervisor)
Abstract

Water transportation through carbon nanotubes is key for designing nanodevices. The directed transport of water molecules through a rotating charged carbon nanotube (CNT) is investigated by molecular dynamics simulations. It is found that the net flux of continuous unidirectional water flow depended sensitively on the charge distribution, charge density and rotation of the CNT. we find that for a constant charge density, the water flux increases with the increase of the charge difference. Besides, we find that the water flux shows a nonlinear dependence on the angular velocity of the rotation. The rotation of the CNT with low angular velocities, can not generate a continuous water flux. The...

#### Modeling active micromixers with multiple microstirrers using smoothed particle hydrodynamics

, Article Scientia Iranica ; Vol. 21, issue. 4 , 2014 , pp. 1390-1402 ; ISSN: 10263098 ; Pishevar, A ; Saidi, M. S ; Sharif University of Technology
Abstract

The smoothed particle hydrodynamics method is used to explore the effects of design parameters on the mixing efficiency of two types of active micromixer. First, the complex flow field and the mixing process of two separated fluids in a square mixing chamber with nine symmetric microstirrers are simulated. The influence of design parameters, such as the microstirrer rotation arrangement and the angular velocity of the microstirrer, on the mixing performance, is investigated. The mixing index parameter on ten control points is calculated and the average mixing index is compared for different cases. Simulations illustrate that the rotation arrangement of microstirrers is a key parameter in the...

#### Slipping and rolling on an inclined plane

, Article European Journal of Physics ; Volume 32, Issue 4 , 2011 , Pages 1049-1057 ; 01430807 (ISSN) ; Aghamohammadi, A ; Sharif University of Technology
2011

Abstract

In the first part of the paper, using a direct calculation two-dimensional motion of a particle sliding on an inclined plane is investigated for general values of friction coefficient (μ). A parametric equation for the trajectory of the particle is also obtained. In the second part of the paper, the motion of a sphere on the inclined plane is studied. It is shown that the evolution equation for the contact point of a sliding sphere is similar to that of a point particle sliding on an inclined plane whose friction coefficient is 7/2 μ. If μ > 2/7 tanθ, for any arbitrary initial velocity and angular velocity, the sphere will roll on the inclined plane after some finite time. In other cases, it...

#### Analyzing mixing quality in a curved centrifugal micromixer through numerical simulation

, Article Chemical Engineering and Processing: Process Intensification ; 2017 ; 02552701 (ISSN) ; Vatankhah, P ; Akbari, A ; Sharif University of Technology
Elsevier B.V

Abstract

The Lab On a CD (LOCD), also known as Centrifugal Microfluidics, has evolved into a sophisticated platform for performing biomedical assays due to its marvelous miniaturization and accurate simulation of biological reactions. Among the numerous applications of the LOCD is fluid mixing. In this paper a centrifugal, serpentine micromixer is simulated and reformed toward better mixing performance. The micromixer was chosen to be curved as a curved design was found to be thrice as functional and compact as a rectilinear design, mixing-wise. The two angular velocity and opening radius parameters were originally hypothesized to affect mixing performance. Effect of angular velocity was studied over...

#### Transformation of sliding motion to rolling during spheres collision

, Article Granular Matter ; Volume 19, Issue 4 , 2017 ; 14345021 (ISSN) ; Kaviani Rad, H ; Jafari Shad, H ; Sharif University of Technology
Abstract

In this research, we have investigated the three-dimensional elastic collision of two balls, based on friction in the tangential plane. Our aim is to offer analytical closed form relations for post collision parameters such as linear and angular velocities, collision time and tangential and normal impulse in three dimensions. To simplify the problem, stick regime is not considered. In other words, balls have a low tangential coefficient of restitution. Sliding, sliding then rolling, and rolling at the beginning of contact are three cases that can occur during impact which have been considered in our research. The normal interaction force is described by the Hertz contact force and...

#### Analyzing mixing quality in a curved centrifugal micromixer through numerical simulation

, Article Chemical Engineering and Processing: Process Intensification ; Volume 116 , 2017 , Pages 9-16 ; 02552701 (ISSN) ; Vatankhah, P ; Akbari, A ; Sharif University of Technology
Elsevier B.V
2017

Abstract

The Lab On a CD (LOCD), also known as Centrifugal Microfluidics, has evolved into a sophisticated platform for performing biomedical assays due to its marvelous miniaturization and accurate simulation of biological reactions. Among the numerous applications of the LOCD is fluid mixing. In this paper a centrifugal, serpentine micromixer is simulated and reformed toward better mixing performance. The micromixer was chosen to be curved as a curved design was found to be thrice as functional and compact as a rectilinear design, mixing-wise. The two angular velocity and opening radius parameters were originally hypothesized to affect mixing performance. Effect of angular velocity was studied over...

#### Swirl effects on spinning solid propellant rocket motor performance

, Article AIAA/ASME/SAE/ASEE 42nd Joint Propulsion Conference, Sacramento, CA, 9 July 2006 through 12 July 2006 ; Volume 6 , 2006 , Pages 4586-4590 ; 1563478188 (ISBN); 9781563478185 (ISBN) ; Mazaheri, K ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2006

Abstract

Spining is used in some of solid rocket motors to increase the flight trajectory precision or for stability requirements. The angular acceleration due to the spin increases the burning rate of solid propellant and changes the motor performance by increasing the operating pressure and decreasing the burning time. On the other hand, due to the rocket and its grain rotation, the gases injected from propellant surface to the flow field have an initial angular velocity. The angular velocity of each particle increases as it approaches to the center due to the conservation of angular momentum and a reduction in its radial location, although it vanishes close to the central axis due to viscous...

#### Reducing the effects of inaccurate fault estimation in spacecraft stabilization

, Article Journal of Aerospace Technology and Management ; Volume 9, Issue 4 , 2017 , Pages 453-460 ; 19849648 (ISSN) ; Alikhani, A ; Fathi Jegarkandi, M ; Sharif University of Technology
Abstract

Reference Governor is an important component of Active Fault Tolerant Control. One of the main reasons for using Reference Governor is to adjust/modify the reference trajectories to maintain the stability of the post-fault system, especially when a series of actuator faults occur and the faulty system can not retain the pre-fault performance. Fault estimation error and delay are important properties of Fault Detection and Diagnosis and have destructive effects on the performance of the Active Fault Tolerant Control. It is shown that, if the fault estimation provided by the Fault Detection and Diagnosis (initial “fault estimation”) is assumed to be precise (an ideal assumption), the...

#### Sifs for radial cracks in annular discs under internal and external shrinkage pressure and constant angular velocity

, Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 7 , 2007 , Pages 653-659 ; 0791843017 (ISBN) ; Gowhari Anaraki, A. R ; Hardy, S. J ; ASME ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2007

Abstract

Finite element method has been implemented to predict stress intensity factors (SIFs) for radial cracks in annular discs under constant angular velocity. Effects of internal and external uniform pressure on the SIFs have also been considered. Linear elastic fracture mechanics finite element analyses have been performed and results are presented in the form of crack configuration factors for a wide range of components and crack geometry parameters. These parameters are chosen to be representative of typical practical situations. The extensive range of crack configuration factors obtained from the analyses is then used to develop equivalent prediction equations via a statistical multiple...

#### Numerical Simulation of Turbulent Flow in Annulus with Rotation of an Inner Cylinder in High Angular Speed

, M.Sc. Thesis Sharif University of Technology ; Farhanieh, Bijan (Supervisor)
Abstract

In this thesis velocity and temperature fields of concentric cylinders with rotation of inner wall have been investigated numerically. Air enters the gap between cylinders and attains fully developed in both velocity and temperature fields after certain lengths. Adiabatic and constant heat flux boundary conditions have been applied and Nusselt number was calculated. In order to analyze the variations of velocity and temperature fields, different angular velocities at constant axial Reynolds number and different axial velocities at constant angular velocity have been investigated. The turbulent stresses were approximated with k ?? ...

#### Modelling and Analysis of the Effect of Angular Velocity and Acceleration on Brain Strain Field in Traumatic Brain Injury

, M.Sc. Thesis Sharif University of Technology ; Ahmadiyan, Mohammad Tagh (Supervisor) ; Zohoor, Hassan (Supervisor)
Abstract

Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the modeling facilities for soft tissue modeling have improved, the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of which is still being studied. This study aims to present an optimized model of human head after a comprehensive study of the previous models; which includes the brain, skull, and...

#### Modelling and analysis of the effect of angular velocity and acceleration on brain strain field in traumatic brain injury

, Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 3 A , 2013 ; 9780791856215 (ISBN) ; Ahmadian, M. T ; Barari, A ; Beidokhti, H. N ; Sharif University of Technology
Abstract

Traumatic brain injury (TBI) has long been known as one of the most anonymous reasons for death around the world. A presentation of a model of what happens in the process has been under study for many years; and yet it remains a question due to physiological, geometrical and computational complications. Although the facilities for soft tissue modeling have improved and the precise CT-imaging of human head has revealed novel details of brain, skull and the interface (the meninges), a comprehensive FEM model of TBI is still being studied. This study aims to present an optimized model of human head including the brain, skull, and the meninges after a comprehensive study of the previous models....

#### ECG denoising using angular velocity as a state and an observation in an Extended Kalman Filter framework

, Article Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society, EMBS ; 2012 , Pages 2897-2900 ; 1557170X (ISSN) ; 9781424441198 (ISBN) ; Shamsollahi, M. B ; Jutten, C ; Coppa, B ; Sharif University of Technology
2012

Abstract

In this paper an efficient filtering procedure based on Extended Kalman Filter (EKF) has been proposed. The method is based on a modified nonlinear dynamic model, previously introduced for the generation of synthetic ECG signals. The proposed method considers the angular velocity of ECG signal, as one of the states of an EKF. We have considered two cases for observation equations, in one case we have assumed a corresponding observation to angular velocity state and in the other case, we have not assumed any observations for it. Quantitative evaluation of the proposed algorithm on the MIT-BIH Normal Sinus Rhythm Database (NSRDB) shows that an average SNR improvement of 8 dB is achieved for an...

#### Rotation rate estimation in parametrically excited micro gyroscopes

, Article Mechatronics ; Volume 31 , October , 2015 , Pages 264-275 ; 09574158 (ISSN) ; Salarieh, H ; Alasty, A ; Sharif University of Technology
Elsevier Ltd
2015

Abstract

This paper reports the estimation of angular velocity in micro gyroscopes with parametric excitation. The identification procedure is done into two consecutive steps: In the first step, the physical parameters of the gyroscope (stiffness, damping, and actuator parameters) are estimated via continuous time Extended and Unscented Kalman filter. In the second step, a separate Kalman filter is dedicated to estimate the time varying rotation rate, using the output of the first step. Using numerical simulations, it is found that by introducing an artificial noise in the observer equations and tuning its variance, arbitrary temporal variation of angular velocity can be well tracked by the proposed...

#### Rotation induced by uniform and non-uniform magnetic fields in a conducting fluid carrying an electric current

, Article RSC Advances ; Volume 6, Issue 113 , 2016 , Pages 112641-112645 ; 20462069 (ISSN) ; Nasiri, M ; Amjadi, A ; Nejati, A ; Sobhani, S.O ; Habibi, M ; Sharif University of Technology
Royal Society of Chemistry
2016

Abstract

We study the dynamics of a conducting fluid carrying (i) a uniform current in the presence of a non-uniform magnetic field or (ii) carrying a non-uniform current in the presence of a uniform magnetic field, using particle image velocimetry (PIV). Our results show that the average angular velocity of the induced rotation has a power-law dependence on the electric current passing through the fluid with an exponent ≈2/3, in excellent agreement with our simulation results, for the same system. To explain the experimental observations we explore all possibilities for inducing rotation in a fluid carrying an electric current. Our theoretical discussion indicates two scenarios wherein applying...

#### Investigating the effects of quadrature error in parametrically and harmonically excited MEMS rate gyroscopes

, Article Measurement: Journal of the International Measurement Confederation ; Volume 87 , 2016 , Pages 152-175 ; 02632241 (ISSN) ; Salarieh, H ; Sharif University of Technology
Elsevier B.V
2016

Abstract

Some factors like environmental conditions and manufacturing errors affect performance of a MEMS rate gyroscope. Because they may result to parameter mismatch between the designed gyroscope and the fabricated one. The Parametrically excited gyros are more robust to these changes than the harmonically excited gyros. However, these types of gyros also experience reduction in their accuracy in angular velocity determination due to these changes. One of parameters that affect the accuracy of the gyroscope is quadrature error that here, its effect in the accuracy of angular velocity determination is investigated in two typically designed harmonically and parametrically excited MEMS gyroscopes....