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Design and Dynamics Control of Six Degree of Freedom Microrobot
, M.Sc. Thesis Sharif University of Technology ; Sayyaadi, Hassan (Supervisor)
Abstract
The field of microrobotics has seen tremendous advances in recent years. Potential high impact applications of untethered microrobots such as minimally invasive diagnosis and treatment inside the human body, biological studies or bioengineering, microfluidics, desktop micromanufacturing, and mobile sensor networks for environmental and health monitoring are reported. However, There are significant challenges in microrobotic technology, including energy resources, control systems, reliability and safety, design and manufacturing of micromotors and localization. In this work, overall size scale being micron scale is emphasized where mobile robots able to fit in spaces smaller than a millimeter...
Energy Extraction from Two Oscillating Airfoils in Tandem Configuration at Low-Reynolds-number Turbulent Flow
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
In this study, the physic of an unsteady flow surrounding two oscillating airfoils in tandem configuration at low Reynolds-numbers has been simulated in a 2D manner by utilizing the Sliding-mesh approach and K-ω-SST turbulent model in Ansys-Fluent application. The first step in this study is selecting the decent numerical grid and flow solution scheme. After choosing the proper solution for this problem, next is to verify the methodology with respect to the references. In the next step, The tandem configuration and pitching motion of the airfoils is being implemented with existing tools and the flow structure, leading-edge and trailing-edge vortex shedding and blade-vortex interactions is...
Frequency Analysis of the Wake of an Oscillating Airfoil
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
Understanding the physics of unsteady flow is very important due to various applications. Axial compressors, turbines, helicopter blades, and energy harvesters are the essential applications of this problem. An airfoil under pitching oscillation is one of the common cases in unsteady aerodynamics, and several characteristics of the flow around it have been investigated up to now. The frequency analysis of the wake flow for pitching airfoils has received less attention. In this research, experimental tests have been carried out for symmetric airfoil NACA 0012 under pitching oscillation in low Reynolds flow (6×104) and before the airfoil stall condition. The experiments were carried out in the...
Performance calculations within the conceptual design process of hand-launched aircraft
, Article Applied Mechanics and Materials ; Vol. 629, issue , October , 2014 , p. 145-151 ; Banazadeh, A ; Sharif University of Technology
Abstract
Matching diagram is a key part of the conceptual design process to determine the wing area and the required power. However, it requires drag polar estimation and the assumption of maximum lift coefficient. In case of conventional manned aircraft, early estimation techniques are based on statistical data that are not suitable for hand-launched aircraft. In this study, it has been attempted to present the performance calculations and a proper conceptual design model by acquiring sound values for the aerodynamic coefficients in low Reynolds number, using statistical wetted area as well as a raw design of fuselage, wing and tails. The process is applied to a sample scenario and the results are...
An experimental investigation of transition point over a quasi-2D swept wing by using hot film
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 2 , February , 2015 , Pages 243-255 ; 09544100 (ISSN) ; Soltani, M. R ; Masdari, M ; Davari, A ; Sharif University of Technology
SAGE Publications Ltd
2015
Abstract
In this study, we performed experiments to investigate the effect of sweep angle on the transition location of laminar flow to turbulent flow. Three half wing models were used, each having a different sweep angle but with the same aspect ratio in various angles of attack. Two flat plates were used at the ends of the swept wing models to prevent the flow from rolling up over the wing. By simulating flow over infinity swept wing by eliminating tip vertices, the effect of sweep angle on flow transition phenomenon was investigated. The experiments included the study of transition flow via hot-film sensors, which were glued on the wing surface. We found that the small leading-edge radius and low...
Numerical study of external flow over ducts with various cross-sections
, Article Defect and Diffusion Forum ; Volume 366 , 2016 , Pages 10-16 ; 10120386 (ISSN) ; Sadrhosseini, H ; Sharif University of Technology
Trans Tech Publications Ltd
Abstract
In this article a comprehensive numerical study is performed to compare the effect of fluid flow across a duct with various cross sectional shapes and with different velocities of the flow. Circular, elliptical and rectangular cross sections have been chosen for the ducts and air flows across them with four values of low Reynolds numbers in the range of Re = 1 to Re = 1000. Continuity and momentum equations with proper boundary conditions are solved in two dimensions. Streamlines, pressure distribution and Velocity profiles are obtained and creation of vortices, boundary layers, separation region, wake region, reattachment point and stagnation points are studied in detail and the results are...
The effects of different jet velocities and axial misalignment on the liquid sheet of two colliding jets
, Article Chemical Engineering Science ; Volume 206 , 2019 , Pages 235-248 ; 00092509 (ISSN) ; Kebriaee, A ; Sharif University of Technology
Elsevier Ltd
2019
Abstract
This experimental study investigated the patterns and characteristics of the liquid sheet formed by two axial misaligned colliding jets and two colliding jets with different velocities. The tests were limited to the low Reynolds number region, 100
Shooting at the nanoscale: Collection and acceleration of nanowires with an external electric field
, Article Applied Physics Letters ; Volume 114, Issue 1 , 2019 ; 00036951 (ISSN) ; Esfandiar, A ; Moshfegh, A. Z ; Sharif University of Technology
American Institute of Physics Inc
2019
Abstract
We report an approach for collecting, charging, and exceedingly fast motion of silver nanowires (Ag NWs) using an external static electric field. With a proper choice of suspension medium, dispersed Ag NWs can be efficiently driven to align and accumulate vertically on the edges of two parallel gold microelectrodes on a glass substrate surface by dielectrophoresis. Then, at sufficiently high electric fields (> 2.0 × 10 5 V/m), these NWs break at the electrode contact point while carrying some net charge. Afterwards, they immediately accelerate in the field direction and, despite an extremely low Reynolds number for the motion of NWs in viscous liquids, move with high speeds (> 25 mm/s)...
Experimental study of continuous h2/air rotating detonations
, Article Combustion Science and Technology ; 2020 ; Fahim, M ; Farshchi, M ; Sharif University of Technology
Taylor and Francis Inc
2020
Abstract
An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in...
Effect of active feather length on aerodynamic performance of airfoils at low reynolds number flow
, Article AIAA AVIATION 2020 FORUM, 15 June 2020 through 19 June 2020 ; Volume 1 PartF , 2020 ; Darbandi, M ; Schneider, G. E ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc, AIAA
2020
Abstract
To increase the flight endurance of a Micro air vehicle (MAVs), which operates at low Reynolds number flow, one way is to harvest energy during its flight. By inspiring from the nature when all the birds use their feathers to control and distribute their power along the flying time, a solution might be design of a piezoelectric plate as feathers, which scavenges energy directly from the fluid flow. Cantilevered beam with piezo-ceramic layer undergoing vortex-induced vibrations can convert the mechanical energy available from the ambient environment to a usable electrical power. Since a flow-driven piezoelectric composite beam takes a form of natural three-way coupling of the turbulent fluid...
Independent control of multiple magnetic microrobots: design, dynamic modelling, and control
, Article Journal of Micro-Bio Robotics ; Volume 16, Issue 2 , 27 June , 2020 , Pages 215-224 ; Nejat Pishkenari, H ; Vossoughi, G ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2020
Abstract
Swimming microrobots have a variety of applications including drug delivery, sensing, and artificial fertilization. Their small size makes onboard actuation very hard, and therefore an external source such as the magnetic field is a practical way to steer and move the robot. In this paper, we have designed a novel microrobot steered by magnetic paddles. We have also discussed design parameters where, based on the conducted simulation, the robot speed reaches 520 um/s. It is shown that the microrobot speed depends on the robot paddle dimensions. According to the microrobots motion characteristics and their different reactions to the same input, we have designed a steering strategy for...
3-D simulation of sedimentation in turbidity currents
, Article ASME 2007 International Mechanical Engineering Congress and Exposition, IMECE 2007, 11 November 2007 through 15 November 2007 ; Volume 8 , 2007 , Pages 503-517 ; 0791843025 (ISBN) ; Firoozabadi, B ; Ghasvari Jahromi, H ; Sharif University of Technology
American Society of Mechanical Engineers (ASME)
2007
Abstract
The gravity currents on the inclined boundaries are formed when the inflow fluid has a density difference with the ambient fluid and a tangential component of gravity becomes the driving force. If the density difference arises from the suspended particles, the currents are known as particle-laden density currents, or turbidity currents in which the local density depends on the concentration of particles. A low Reynolds k- Turbulent model is used to simulate three dimensional turbidity currents. Also some laboratory tests were conducted to study the 3D flow resulting from the release of particle laden density currents on a sloping surface in a channel of freshwater via a sluice gate. Kaolin...
Controlled swarm motion of self-propelled microswimmers for energy saving
, Article Journal of Micro-Bio Robotics ; 2021 ; 21946418 (ISSN) ; Nejat Pishkenari, H ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that...
Investigation of time-frequency analysis and transitional boundary layer over a pitching airfoil
, Article Scientia Iranica ; Volume 28, Issue 2 B , 2021 , Pages 860-876 ; 10263098 (ISSN) ; Soltani, M. R ; Maghrebi, M. J ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the...
Controlled swarm motion of self-propelled microswimmers for energy saving
, Article Journal of Micro-Bio Robotics ; 2021 ; 21946418 (ISSN) ; Nejat Pishkenari, H ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
Swarm motion is an amazing collective behavior in nature for energy saving. Inspiring this natural phenomenon in microorganisms’ swimming, we have proposed a motion strategy for a swarm of microrobots to reduce their energy consumption during path tracking. The investigated microrobot is an artificial Self-Propelled Microswimmer (SPM) with high maneuverability at low Reynolds number flow (Re ≪ 1). In this study, we have demonstrated that forming a swarm behavior with minimum energy consumption requires the microswimmers to be close enough to each other, since at small distances the hydrodynamic interactions of microswimmers reduce their energy consumption. Moreover, we also showed that...
Investigation of time-frequency analysis and transitional boundary layer over a pitching airfoil
, Article Scientia Iranica ; Volume 28, Issue 2 B , 2021 , Pages 860-876 ; 10263098 (ISSN) ; Soltani, M. R ; Maghrebi, M. J ; Sharif University of Technology
Sharif University of Technology
2021
Abstract
Transitional boundary layer over a pitching airfoil at low Reynolds number (Re = 2:7 × 105) is experimentally investigated using space-frequency and time-frequency analyses of hot- film signals. Boundary layer events are visualized based on the space-frequency and time-frequency plots. The precursor phenomenon for turbulent and fully separated flows is presented based on the time-frequency analysis. A new technique based on time-frequency analysis of hot- film signals is introduced to measure the transition onset and relaminarization locations. This technique functions based on the analysis of high-frequency disturbances of the measured data. Significant attention has been drawn to the...
Experimental study of continuous H2/Air rotating detonations
, Article Combustion Science and Technology ; Volume 194, Issue 3 , 2022 , Pages 449-463 ; 00102202 (ISSN) ; Fahim, M ; Farshchi, M ; Sharif University of Technology
Taylor and Francis Ltd
2022
Abstract
An experimental study of a lab scale rotating detonation combustor (RDC) has been conducted to identify and classify its modes of operation under different feeding conditions. The chamber uses air as oxidizer and hydrogen as fuel. The stability diagram of the RDC has been determined based on the detonation chamber Reynolds number and reactants mixture equivalence ratio values. The Reynolds number is based on the air volume flow rate, chamber annulus size, and the reactants mixture feeding slot area. Hence the effects of geometrical parameters and operational parameters on the detonation wave stability can be presented in a single stability map. This diagram identifies different zones in...
Numerical study on boundary layer control using CH4[sbnd]H2[sbnd]air Micro-reacting jet
, Article International Journal of Hydrogen Energy ; Volume 41, Issue 47 , 2016 , Pages 22433-22452 ; 03603199 (ISSN) ; Yahyavi Koochaksarai, M ; Javadi, K ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The focus of present numerical study is on assessment of control of laminar separation bubble phenomenon using Micro-scale combustion actuators in an airfoil with low Reynolds number under surface effect and free flows. In this way, the characteristics of laminar separation bubble such as its formation, geometry, and transition from laminar to turbulent around airfoil SD8020 in attack angles of 5 and 8° are investigated. Following that, the new combustion actuators in Micro-scale, cold, and hot air-jet injection are introduced to control boundary layer flow in terms of eliminating the separation bubble. Some mechanisms are identified for improvement of methane-air premixed flame...
Design of a Setup for Simultaneous Control of Multiple Magnetic Microrobots
, Ph.D. Dissertation Sharif University of Technology ; Nejat Pishkenari, Hossein (Supervisor) ; Vossughi, Gholamreza (Co-Supervisor)
Abstract
Microrobots (MRs) have attracted a lot of attention during recent years due to their promising biomedical applications. Due to their small size, these robots have limited capability to carry energy sources, sensors, or actuators, so researchers try to transfer energy from outside as much as possible. For this purpose, various actuation methods such as optical, acoustic, electric, and magnetic have been proposed. Magnetic field is the most used energy source. The current study deals with the design and implementation of a system for simultaneous independent control of multiple swimming magnetic MRs. The ability to control multiple MRs simultaneously and independently could lead to higher...
Long-lived and unstable modes of Brownian suspensions in microchannels
, Article Journal of Fluid Mechanics ; Volume 701 , 2012 , Pages 407-418 ; 00221120 (ISSN) ; Jalali, M. A ; Sharif University of Technology
2012
Abstract
We investigate the stability of the pressure-driven, low-Reynolds-number flow of Brownian suspensions with spherical particles in microchannels. We find two general families of stable/unstable modes: (i) degenerate modes with symmetric and antisymmetric patterns; (ii) single modes that are either symmetric or antisymmetric. The concentration profiles of degenerate modes have strong peaks near the channel walls, while single modes diminish there. Once excited, both families would be detectable through high-speed imaging. We find that unstable modes occur in concentrated suspensions whose velocity profiles are sufficiently flattened near the channel centreline. The patterns of growing unstable...