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Offline Optimization of a Four Dimensional TF/TA Problem Considering Engine Dynamics
, M.Sc. Thesis Sharif University of Technology ; Nobahari, Hadi (Supervisor) ; Banazadeh, Afshin (Supervisor)
Abstract
In this thesis, the problem of offline trajectory optimization of a flying vehicle has been solved. Terrain following/ terrain avoidance has been considered as a guiadanec strategy of vehicle. The point-mass model in three dimensional space for flight simulation and the transfer functions for modeling of vehicle dynamics has been used. One of the constraints of this problem is related to engine’s dynamic behavior, which is not considered in the privious works. So in this thesis at first, a turbofan engine has been modeled and it’s static and dynamic model has been obtained. Then, the effect of engine’s dynamic model in the trajectory optimization has been investigated. The results show that...
Effects of boundary-layer bleed parameters on supersonic intake performance
, Article Journal of Propulsion and Power ; Volume 31, Issue 3 , March , 2015 , Pages 826-836 ; 07484658 (ISSN) ; Younsi, J. S ; Farahani, M ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2015
Abstract
The performance and the buzz onset of a supersonic mixed-compression axisymmetric intake are experimentally investigated. Effectsof the slot bleed position, angle, and width onthe intake performance and onthe buzz initiation at three different Mach numbers of 1.8, 2.0, and 2.2 and at a zero degree angle of attack are studied. The intake performance is assessed using the total pressure recovery, mass flow ratio, flow distortion, and bleed mass flow ratio. The results show that applying the bleed at a position near the intake entrance and reducing the bleed entrance slant angle and width all improve the intake performance considerably. Moreover, these parameters postpone the buzz onset. In...
Vibrational analysis of single-walled carbon nanotubes using beam element
, Article Thin-Walled Structures ; Volume 47, Issue 6-7 , 2009 , Pages 646-652 ; 02638231 (ISSN) ; Ahmadian, M. T ; Vafai, A ; Sharif University of Technology
2009
Abstract
Vibrational analysis of single-walled carbon nanotubes (SWCNTs) is performed using a finite element method (FEM). To this end, the vibrational behavior of bridge and cantilever SWCNTs with different side lengths and diameters is modeled by three-dimensional elastic beams and point masses. The beam element elastic properties are calculated by considering mechanical characteristics of the covalent bonds between the carbon atoms in the hexagonal lattice. The mass of each beam element is assumed as point masses at nodes coinciding with the carbon atoms. Implementing the atomistic simulation approach, the natural frequencies of zigzag and armchair SWCNTs are computed. It is observed that the...
Imprints of gravitational millilensing on the light curve of gamma-ray bursts
, Article Astrophysical Journal ; Volume 922, Issue 1 , November , 2021 ; 0004637X (ISSN) ; Ibrahim, A ; Reza Rahimi Tabar, M ; Rahvar, S ; Sharif University of Technology
IOP Publishing Ltd
2021
Abstract
In this work, we search for signatures of gravitational millilensing in gamma-ray bursts (GRBs) in which the source-lens-observer geometry produces two images that manifest in the GRB light curve as superimposed peaks with identical temporal variability (or echoes), separated by the time delay between the two images. According to the sensitivity of our detection method, we consider millilensing events due to point-mass lenses in the range of 105 - 107 M o˙ at lens redshift about half that of the GRB, with a time delay on the order of 10 s. Current GRB observatories are capable of resolving and constraining this lensing scenario if the above conditions are met. We investigated the Fermi/GBM...