Robust distributed control of spacecraft formation flying with adaptive network topology

, Article Acta Astronautica ; Volume 136 , 2017 , Pages 281-296 ; 00945765 (ISSN) Shasti, B ; Alasty, A ; Assadian, N ; Sharif University of Technology

Elsevier Ltd 2017

Abstract

In this study, the distributed six degree-of-freedom (6-DOF) coordinated control of spacecraft formation flying in low earth orbit (LEO) has been investigated. For this purpose, an accurate coupled translational and attitude relative dynamics model of the spacecraft with respect to the reference orbit (virtual leader) is presented by considering the most effective perturbation acceleration forces on LEO satellites, i.e. the second zonal harmonic and the atmospheric drag. Subsequently, the 6-DOF coordinated control of spacecraft in formation is studied. During the mission, the spacecraft communicate with each other through a switching network topology in which the weights of its graph...

A reconfigurable fault-tolerant routing algorithm to optimize the network-on-chip performance and latency in presence of intermittent and permanent faults

, Article Proceedings - IEEE International Conference on Computer Design: VLSI in Computers and Processors ; 2011 , Pages 433-434 ; 10636404 (ISSN) ; 9781457719523 (ISBN) Jabbarvand Behrouz, R ; Modarressi, M ; Sarbazi Azad, H ; Sharif University of Technology

2011

Abstract

As the semiconductor industry advances to the deep sub-micron and nano technology points, the on-chip components are more prone to the defects during manufacturing and faults during system operation. Consequently, fault tolerant techniques are essential to improve the yield of modern complex chips. We propose a fault-tolerant routing algorithm that keeps the negative effect of faulty components on the NoC power and performance as low as possible. Targeting intermittent faults, we achieve fault tolerance by employing a simple and fast mechanism composed of two processes: NoC monitoring and route adaption. Experimental results show the effectiveness of the proposed technique, in that it offers...

Modeling and Decentralized Control of Spacecraft Formation Flying

, Ph.D. Dissertation Sharif University of Technology Shasti, Behrouz (Author) ; Alasty, Aria (Supervisor) ; Assadian, Nima ($item.subfieldsMap.e) ; Salarieh, Hassan ($item.subfieldsMap.e)

Abstract

In this study, the distributed six degree-of-freedom (6-DOF) coordinated control of spacecraft formation flying in low earth orbit (LEO) has been investigated. For this purpose, an accurate coupled translational and attitude relative dynamics model of the spacecraft with respect to the reference orbit (virtual leader) is presented by considering the most effective perturbation acceleration forces on LEO satellites, i.e. the second zonal harmonic and the atmospheric drag. Subsequently, the 6-DOF coordinated control of spacecraft in formation is studied. During the mission, the spacecraft communicate with each other through a switching network topology in which the weights of its graph...

Dynamic Modeling and Congestion Control in Computer Networks

, M.Sc. Thesis Sharif University of Technology Kahe, Ghasem (Author) ; Jahangir, Amir Hossein (Supervisor) ; Ebrahim, Behrouz (Co-Advisor)

Abstract

Active queue management (AQM) is a key factor in congestion control and should provide appropriate feedback for flow control in traffic sources to overcome the congestion problem. Beside providing congestion control, achieving predictable queuing delay, maximizing link utilization, simplicity and robustness are also the main objectives of an AQM controller. We propose in this thesis an improved queue dynamic model while incorporating the packet drop probability as well. The proposed model is evaluated using ns2 platform. By applying the improved model, a new compensated proportionalintegral- derivative (PID) AQM controller is developed for TCP network. The time-varying nature of the network...

Recovery of Uranium(VI) from UCF Waste by Selective Transportacross Aliquid Membrane

, M.Sc. Thesis Sharif University of Technology Soltani Behrouz, Masoud (Author) ; Samadfam, Mohammad (Supervisor) ; Fasihi, Javad (Supervisor)

Abstract

Due to environmental and economical impacts, recovery of the uranium from nuclear wastes is of continuing interest.This work reports the separation of uranyl ionusing transport technique through chloroform liquid membrane containing a mixture of DBDA15C4 and oleic acidas cooperative carrier.The pH of the feed phase (10-4 M of UO22+) was adjusted with nitric acid and acetic acid/NaOH for pHrange of 2-6.The receiving phase was hydrochloric acid 1M.The organic phase was chloroform which includesthe carrier DBDA15C4 (0.0001 M) and also the oleic acid (0.015M).The results showed that the transport increased with increasing pH and reached to maximumat pH of 5.Maximum cooperative effect of oleic...

Determination of Optimum Material and Thickness of Filter Based on Radiation Energy in Digital Industrial Radiography (CR) Using MCNP Monte Carlo Simulation Code

, M.Sc. Thesis Sharif University of Technology Haghizadeh, Cyrus (Author) ; Vosoughi, Naser (Supervisor) ; Rokrok, Behrouz (Supervisor) ; Movafeghi, Amir (Co-Supervisor)

Abstract

In this study, the effect of external filter on the various parameters of image quality in digital industrial radiography by CR method for steel and aluminum piece has been investigated. The filter reduces the noise of scattered beams by absorbing the low-energy beams in the X-ray spectrum that are most likely to be scattered, but high filter thicknesses can attenuate the more energetic beams and have a negatively effect on the image quality. On the other hand, the absorption of those low-energy beams increases the average spectrum energy and thus reduce the contrast, so it is necessary to use the appropriate material and thickness of the filter. For this purpose, to examine the filter...