Sharif Digital Repository

In this study a new method is introduced to suppress libration of a tethered satellite system (TSS). It benefits from coupling between satellites and tether libration dynamics. The control concept uses the main satellite attitude maneuvers to suppress librational motion of the tether, and the main satellites actuators for attitude control are used as the only actuation in the system. The study considers planar motion of a two body TSS system in a circular orbit and it is assumed that the tethers motion will not change it. Governing dynamic equations of motion are derived using the extended Lagrange method. Controllability of the system around the equilibrium state is studied and a linear LQG... 

In this study a new nonlinear control approach is introduced to suppress libration of a tethered satellite system (TSS). It benefits from coupling between satellites and tether libration dynamics. The control concept uses the main satellite attitude maneuvers to suppress librational motion of the tether. To achieve this goal, the main satellite attitude control actuators are used as the only actuation in the system. The study considers planar motion of a two body TSS system in a circular orbit. Governing dynamic equations of motion are derived using extended Lagrange method. Controllability of the system about equilibrium state is studied and a nonlinear controller is designed using feedback... 

Hydrodynamically fully developed flow of power-law fluids under combined action of electroosmotic and pressure gradient forces in rectangular microreactors is analyzed considering heterogeneous catalytic reactions. The Poisson-Boltzmann, Cauchy momentum, and concentration equations are considered in two dimensions and after being dimensionless are numerically solved applying a finite difference algorithm. Variation of axial concentration gradient, and axial and horizontal mass diffusions are taken into account as well. To accomplish a more general analysis, the velocity distribution is obtained by solving continuity and Cauchy momentum equations and is not considered as an average axial... 

In the present work, mesoporous nitrogen-doped carbon nanotubes (N-CNTs) were synthesized by using a low-cost and unique set of precursors (camphor and urea). The CVD method at 1000 °C was used with different camphor/urea ratios, and Co-Mo/MgO nanocatalyst was utilized as growth catalyst. Application of mesoporous N-CNTs in selective oxidation of H2S was studied experimentally and N-CNTs interactions with H2S was also investigated using DFT calculations. The as-synthesized N-CNTs were characterized using FTIR, FE-SEM, elemental analysis, X-ray diffraction (XRD), XPS and nitrogen adsorption/desorption. The N-CNT2 sample with urea to camphor ratio (U/C) of 1 showed the highest sulfur yield at... 

Modern sensors consist of arrays of detectors specially arranged to enhance precision, capabilities, and field of view (FOV). Sensor arrays can have multiple functionalities, such as the simultaneous detection of position and motion. We use a linear sensor model and develop an optimization method to design an array of photodiodes. Our objective function minimizes bias and variance estimations. We introduce a maximum likelihood technique to approximate and determine the bias caused by measurement errors, and verify our theory by statistically complete simulations. We apply our theory to design an optimal sun sensor. The sensor has a predefined conical FOV, and its accuracy is controlled by a... 

We report the design, fabrication and error analysis of a sun sensor array composed of six photodiodes. The sensor estimates the direction of the sun using a linear least squares method. The performance of the sensor is deteriorated by three major sources: fabrication errors, scattered environmental light, and inexact modeling of photodiodes. Using a calibration procedure and modeling the uniform component of the environmental light, we mitigate the first two errors and significantly reduce root mean squared error from 2.63° to 0.83°. For a Field of View (FOV) of 110°, the maximum estimation error also drops from 3.8° to 1.6°. Through exact mathematical modeling of photodiodes, we...