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electromagnetic-forces
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Design and Fabrication of a Novel Mercury Micropump Actuated Electeromagneticaly
, M.Sc. Thesis Sharif University of Technology ; Shafii, Mohammad Behshad (Supervisor)
Abstract
Considering the advantages and disadvantages of reported micropumps, we aimed to introduce a novel idea to diminish the disadvantages and promote the advantages of PiezoElectric micropumps. This novel idea operates based on a mercury slug actuation in a microchannel. This cyclic motion of the mercury slug which is similar to a piston, push the fluid in the microchannel and pump the flow. However, to bring this idea into the practice, a control system must be designed. This system contains: LABVIEW code, DAQ board & a switching Board. The pattern of actuating mercury is drawn in LABVIEW. DAQ Board produces electrical signals according to LABVIEW code. Switching board will transform the...
Trapping, Levitation, and Optomechanics of Nanoparticles
, Ph.D. Dissertation Sharif University of Technology ; Mehrany, Khashayar (Supervisor)
Abstract
The electromagnetic (EM) force is the pivot on which this thesis revolves. We inspect different formulations of the distribution of the EM force (and momentum) inside matter, and show that the Einstein-Laub force density is incompatible with special relativity. We study the exerted EM force on small particles in depth, and explain when the conventional dipole approximation fails to yield accurate results. We propose an all-dielectric structure which is able to trap very small dielectric particles (of diameters as small as 10 nm). One of the achievements of this thesis is an explanation for an adverse phenomenon observed in many experiments on the optomechanical systems employing...
Critical study and discrimination of different formulations of electromagnetic force density and consequent stress tensors inside matter
, Article Physical Review A - Atomic, Molecular, and Optical Physics ; Vol. 89, issue. 4 , April , 2014 ; ISSN: 10502947 ; Mehrany, K ; Sharif University of Technology
Abstract
By examination of the exerted electromagnetic (EM) force on boundary of an object in a few examples, we look into the compatibility of the stress tensors corresponding to different formulas of the EM force density with special relativity. Ampere-Lorentz's formula of the EM force density is physically justifiable in that the electric field and the magnetic flux density act on the densities of the total charges and the total currents, unlike Minkowski's formula which completely excludes the densities of the bounded charges and the bounded currents inside homogeneous media. Abraham's formula is fanciful and devoid of physical meaning. Einstein-Laub's formula seems to include the densities of...
Time-Variant evaluation of electromagnetic forces on transformer windings during inrush current and short-circuit by FEM
, Article Arabian Journal for Science and Engineering ; Volume 38, Issue 4 , 2013 , Pages 883-893 ; 13198025 (ISSN) ; Vakilian, M ; Sharif University of Technology
2013
Abstract
Time-variant axial and radial electromagnetic for ces under inrush current and short-circuit current are calculated (by finite element method; FEM) and compared. A simplified analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this method are compared with the measured values. A compact three-phase, core-type 132/20 KV, 30 MVA, power transformer is modeled, employing two-dimensional (2D) FEM, the different forces under short-circuit and inrush current conditions are evaluated as a function of time. The simulation results for this sample transformer show that the inrush current axial force is larger than clamping force (which is...
On the effects of aero boundary layer control on pressure drag reduction in supercavitating bodies
, Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 2 , 2005 , Pages 665-675 ; Yazdani, M ; Sharif University of Technology
2005
Abstract
Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we'll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present...
Evaluation of Electromagnetic Forces on three-phase Core-Type Power Transformer Windings during Inrush Current by FEM
, M.Sc. Thesis Sharif University of Technology ; Vakilian, Mehdi (Supervisor)
Abstract
Inrush Current is a form of over-current that occurs during energization of a transformer. For power transformers, the magnitude of the first peak of inrush current is initially several times the rated load current but slowly decreases until it finally reaches the normal exciting current value. This process typically takes several minutes. Time-variant axial and radial electromagnetic forces under inrush current and short-circuit current are calculated (by finite element method; FEM), and compared. An analytic method is presented for computation of inrush current in transformer. The simulation results obtained by this proposed method are compared with the measured values. A compact...
Green’s Function Formulation for Studying Optomechanics of Subwavelength Nanoparticles
, M.Sc. Thesis Sharif University of Technology ; Mehrany, Khashayar (Supervisor)
Abstract
In this thesis, we study optomechanics of subwavelength nanoparticles based on the Green's function formulation. First, we investigate the optical force exerted upon Rayleigh particles in the free space using the dipole approximation method. Then, we present a new method based on the Taylor expansion of the polarization field to calculate the optical forces beyond the Rayleigh regime. Subsequently, we study the optical force exerted upon Rayleigh particles in non-free spaces, and model the backaction effect using the scattering Green's function. We show that the backaction effect can modify the polarizability of the particle and thereby can affect the gradient force, radiation pressure, and...
Critical ambient pressure and critical cooling rate in optomechanics of electromagnetically levitated nanoparticles
, Article Journal of the Optical Society of America B: Optical Physics ; Volume 38, Issue 12 , 2021 , Pages 3652-3662 ; 07403224 (ISSN) ; Sharif University of Technology
The Optical Society
2021
Abstract
The concept of critical ambient pressure is introduced in this paper. The particle escapes from its trap when the ambient pressure becomes comparable with or smaller than a critical value, even if the particle motion is cooled by one of the feedback cooling (or cavity cooling) schemes realized so far. The critical ambient pressure may be so small that it is not a limiting factor in ground-state cooling, but critical feedback cooling rates, which are also introduced in this paper, are limiting factors. The particle escapes from its trap if any of the feedback cooling rates (corresponding to the components of the particle motion) becomes comparable with or larger than its critical value. The...
Self-induced backaction in optical waveguides
, Article Optics Express ; Volume 30, Issue 24 , 2022 , Pages 42967-42981 ; 10944087 (ISSN) ; Mehrany, K ; Sharif University of Technology
Optica Publishing Group (formerly OSA)
2022
Abstract
In this paper, we study the backaction effect on the force exerted upon Rayleigh particles in guided structures. We show that the backaction becomes stronger as the group velocity of the guided modes is decreased, which is not unexpected since the fall of group velocity increases the interaction time between the particle and the electromagnetic field. Interestingly, the sign of the group velocity affects the pushing and pulling nature of the exerted electromagnetic force. We specifically investigate the case of a single mode optical waveguide both in the propagating and evanescent regimes, and show that the backaction enables us to enhance the ratio of the potential depth to the trapping...
Investigation of weld pool in aluminum alloys: geometry and solidification microstructure
, Article International Journal of Thermal Sciences ; Volume 49, Issue 5 , 2010 , Pages 809-819 ; 12900729 (ISSN) ; Serajzadeh, S ; Kokabi, A. H ; Sharif University of Technology
Abstract
In the present research, weld pool geometry, thermal cycle, temperature and velocity fields during gas tungsten arc welding of aluminum alloys were predicted by solving three-dimensional equations of conservation of mass, energy and momentum under steady-state conditions. Welding experiments were then conducted on several samples with different thicknesses and chemical compositions. The geometries of the weld pools as well as the thermal cycles were measured. It is found that the calculated geometry of the weld fusion zone and the weld thermal cycles are in good agreement with the corresponding experimental results. In addition, the magnitude of the maximum velocities under different...
Relativistic high harmonics generation in underdense plasma produced by a super intense femtosecond laser pulse
, Article Progress in Electromagnetics Research Symposium 2009, PIERS 2009 Beijing, Beijing, 23 March 2009 through 27 March 2009 ; Volume 2 , 2009 , Pages 1025-1029 ; 15599450 (ISSN); 9781618390554 (ISBN) ; Salimi, K ; Beijing Jiaotong University; MIT Cent. Electromagn. Theory Appl./Res. Lab. Electron.; National Natural Science Foundation of China; The Electromagnetics Academy; The Electromagnetics Academy at Zhejiang University; Zhejiang University ; Sharif University of Technology
Electromagnetics Academy
2009
Abstract
A high intensity laser incident on a vacuum-plasma interface, insert an Intensive electromagnetic force on electrons and charged particles. Relativistic charged particle movements lead to the high order harmonics generation of the incident wave. Efficiency of high harmonics increases with the intensity laser incident, So that the non-relativistic velocities of the particles vary to the relativistic velocities. Efficiency of high harmonics increases with the intensity laser incident. In previous works that has done in this field the researcher have reported-odd harmonics generated in direction of propagation of laser incident and even harmonics generated in normal direction of propagation of...
A new multi-winding traction transformer equivalent circuit for short-circuit performance analysis
, Article International Transactions on Electrical Energy Systems ; Vol. 24, issue. 2 , 2014 , pp. 186-202 ; ISSN: 20507038 ; Vakilian, M ; Faiz, J ; Sharif University of Technology
Abstract
Current and force calculations in different short-circuit conditions are required for short-circuit performance analysis of a multi-winding traction transformer which is one of the most important requirements in its design process. This paper extends the available low-frequency three-winding star equivalent circuits to develop a novel equivalent circuit for the four-winding traction transformers. The leakage inductances of the traction transformer are determined and employed to calculate the parameters of this developed star model. It is shown that the star equivalent circuit is a valid and appropriate model to simulate the steady-state and dynamic performance of the traction transformer...
Nonlinear identification of electro-magnetic force model
, Article Journal of Zhejiang University: Science A ; Volume 11, Issue 3 , 2010 , Pages 165-174 ; 1673565X (ISSN) ; Tariverdilo, S ; Salarieh, H ; Sharif University of Technology
2010
Abstract
Conventional attractive magnetic force models (proportional to the coil current squared and inversely proportional to the gap squared) cannot simulate the nonlinear responses of magnetic bearings in the presence of electromagnetic losses, flux leakage or saturation of iron. In this paper, based on results from an experimental set-up designed to study magnetic force, a novel parametric model is presented in the form of a nonlinear polynomial with unknown coefficients. The parameters of the proposed model are identified using the weighted residual method. Validations of the model identified were performed by comparing the results in time and frequency domains. The results show a good...
Sliding mode control of electromagnetic tethered satellite formation
, Article Advances in Space Research ; Volume 58, Issue 4 , 2016 , Pages 619-634 ; 02731177 (ISSN) ; Assadian, N ; Sharif University of Technology
Elsevier Ltd
Abstract
This paper investigates the control of tethered satellite formation actuated by electromagnetic dipoles and reaction wheels using the robust sliding mode control technique. Generating electromagnetic forces and moments by electric current coils provides an attractive control actuation alternative for tethered satellite system due to the advantages of no propellant consumption and no obligatory rotational motion. Based on a dumbbell model of tethered satellite in which the flexibility and mass of the tether is neglected, the equations of motion in Cartesian coordinate are derived. In this model, the J2 perturbation is taken into account. The far-field and mid-field models of electromagnetic...