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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...
Dynamic modeling and performance evaluation of a vibrating beam microgyroscope under general support motion
, Article Journal of Sound and Vibration ; Volume 301, Issue 1-2 , 2007 , Pages 146-164 ; 0022460X (ISSN) ; Jalili, N ; Durali, M ; Sharif University of Technology
Academic Press
2007
Abstract
A general modeling framework is presented for the development of the frequency equation of a microgyroscope, which is modeled as a suspended cantilever beam with a tip mass under general base excitation. Specifically, the beam is considered to vibrate in all the three directions, while subjected to a base rotational motion around its longitudinal direction. This is a common configuration utilized in many vibrating beam gyroscopes and well drilling systems. The governing equations are derived by using the Extended Hamilton's Principle with a general 6-dof base motion. The natural frequency equation is then extracted in a closed-form for the case where the beam support undergoes longitudinal...
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...
Ring microgyroscope modeling and performance evaluation
, Article 2005 ASME International Mecahnical Engineering Congress and Exposition, IMECE 2005, Orlando, FL, 5 November 2005 through 11 November 2005 ; Volume 7 MEMS , 2005 , Pages 241-247 ; 1096665X (ISSN); 079184224X (ISBN); 9780791842249 (ISBN) ; Durali, M ; Jalili, N ; Sharif University of Technology
2005
Abstract
This paper discusses the effects of substrate motions on the performance of a microgyroscope modeled as a ring structure. Using Extended Hamilton's Principle, the equations of motion are derived. The natural frequency equation and response of gyroscope are then extracted in closed-form for the case where substrate undergoes normal rotation. The Galerkin approximation is used for discretizing the partial differential equations of motion into ordinary differential equations. In these equations, the effects of angular accelerations, centripetal and coriolis accelerations are well apparent. The response of the system to different inputs is studied and the system sensitivity to input parameter...
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....
Analytical study of micro-rotating disks with angular acceleration on the basis of the strain gradient elasticity
, Article Acta Mechanica ; Volume 230, Issue 9 , 2019 , Pages 3259-3278 ; 00015970 (ISSN) ; Asghari, M ; Danesh, V ; Sharif University of Technology
Springer-Verlag Wien
2019
Abstract
The small-scale effects on the mechanical responses of micro-rotating disks with angular acceleration are investigated based on the strain gradient theory, as one of the powerful non-classical continuum theories which have been developed to justify the empirical observations of mechanical behavior in small-scale structures and components. The differential equations governing motion of the micro-disk elements in radial and circumferential direction together with the corresponding boundary conditions are derived. Then, an analytical solution is presented for the components of the displacement field which can be used as a base for determination of the components of the stress field. In a...
Elasticity formulation for motion equations of couple stress based micro-rotating disks with varying speeds
, Article Mechanics Based Design of Structures and Machines ; Volume 49, Issue 1 , 2021 , Pages 1-19 ; 15397734 (ISSN) ; Asghari, M ; Sharif University of Technology
Bellwether Publishing, Ltd
2021
Abstract
The elasticity formulation for equations of motion of micro-rotating disks in the presence of angular acceleration as well as the corresponding boundary conditions are developed based on the non-classical continuum theory of couple stress. The system of the boundary value problem is derived on the basis of the variational method. Analytical elasticity solutions to the system of equations are then provided. Based on the elasticity solution, the mechanical responses, including the displacement and stress fields, for varying-speed micro-rotating disks are studied. In a numerical case study, the effect of the couple stresses on the distribution of stress and displacement components are...
Analysis of Micro Rotating Disk with Angular Acceleration Based on the Non-Classical Continuum Mechanics
, M.Sc. Thesis Sharif University of Technology ; Asghari, Mohsen (Supervisor)
Abstract
Incapability of the classical continuum mechanics theory to justify the experimental observations of the mechanical response of the small-scale structures and parts motivated the researchers to pursue the introduction and utilization of the non-classical continuum theories for analysis and design of such structures and parts. In this paper, utilizing the modified couple stress theory and the strain gradient theory as well-known and powerful non-classical continuum theories, the mechanical response, including the displacement and stress fields, for micro-rotating disks with angular acceleration is investigated. The governing differential equations of motion and the corresponding boundary...
Elasticity formulation for motion equations of couple stress based micro-rotating disks with varying speeds
, Article Mechanics Based Design of Structures and Machines ; 2019 ; 15397734 (ISSN) ; Asghari, M ; Sharif University of Technology
Taylor and Francis Inc
2019
Abstract
The elasticity formulation for equations of motion of micro-rotating disks in the presence of angular acceleration as well as the corresponding boundary conditions are developed based on the non-classical continuum theory of couple stress. The system of the boundary value problem is derived on the basis of the variational method. Analytical elasticity solutions to the system of equations are then provided. Based on the elasticity solution, the mechanical responses, including the displacement and stress fields, for varying-speed micro-rotating disks are studied. In a numerical case study, the effect of the couple stresses on the distribution of stress and displacement components are...
Elasticity formulation for motion equations of couple stress based micro-rotating disks with varying speeds
, Article Mechanics Based Design of Structures and Machines ; 2019 ; 15397734 (ISSN) ; Asghari, M ; Sharif University of Technology
Taylor and Francis Inc
2019
Abstract
The elasticity formulation for equations of motion of micro-rotating disks in the presence of angular acceleration as well as the corresponding boundary conditions are developed based on the non-classical continuum theory of couple stress. The system of the boundary value problem is derived on the basis of the variational method. Analytical elasticity solutions to the system of equations are then provided. Based on the elasticity solution, the mechanical responses, including the displacement and stress fields, for varying-speed micro-rotating disks are studied. In a numerical case study, the effect of the couple stresses on the distribution of stress and displacement components are...