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Modern midcourse guidance laws in the endoatmosphere
, Article AIAA Guidance, Navigation, and Control Conference 2005, San Francisco, CA, 15 August 2005 through 18 August 2005 ; Volume 6 , 2005 , Pages 4560-4576 ; 1563477378 (ISBN); 9781563477379 (ISBN) ; Pourtakdoust, S. H ; Sharif University of Technology
American Institute of Aeronautics and Astronautics Inc
2005
Abstract
In this paper, midcourse guidance strategies are derived considering approximate models for drag and thrust in the presence of gravity and autopilot dynamics. The guidance/control system is assumed as a linear time-varying and of arbitrary-order. The zero-effort miss differential equation is obtained in a way that three classes of guidance laws, namely optimal fuel, optimal energy, and closed-loop explicit strategy, can be derived by available methods for minimum and nonminimum phase autopilots. The resulting guidance laws have the structure of a guidance gain multiplied by the zero-effort miss. Several thrust/drag models arc also considered and discussed to obtain the effective navigation...
Numerical investigation of the inlet baffle, header geometry, and triangular fins effects on plate-fin heat exchangers performance
, Article Heat Transfer Engineering ; Volume 36, Issue 16 , 2015 , Pages 1397-1408 ; 01457632 (ISSN) ; Afshin, H ; Farhanieh, B ; Sharif University of Technology
Taylor and Francis Ltd
2015
Abstract
In this study, the optimal location of baffle in the header of air-to-air plate heat exchangers and the geometry of the header and the effects of triangular fins arrays on the effectiveness were numerically investigated for different flow rates and Reynolds numbers on different models. The main purpose of inlet baffle and geometry changes is to improve the pattern of flow distribution and assist flow uniformity. The investigations show that the optimal location of the inlet baffle with high Reynolds numbers has an insignificant effect on effectiveness, while with Reynolds numbers 250-3000, the effectiveness is affected significantly by baffle location. On the other hand, the reduction in...
Flight Performance and Maneuverability Enhancement of a Twin Engine Fighter Aircraft Using Integrated Thrust-Vector and Aerodynamic controls
, M.Sc. Thesis Sharif University of Technology ; Saghafi, Fariborz (Supervisor)
Abstract
In this thesis, maneuverability enhancement of a given twin engine fighter aircraft with integrated thrust-vector and conventional aerodynamic control surfaces havebeen studied. For this purpose a nonlinear 6DOF simulation program base on a near exact mathematical model has been prepared for the aircraft, and then a thrust vectoring system for producing moments about three body axes, like that used in F/A-18, has been added to the simulation. The control method that is employed to control the aircraft in simulation environment is based on Nonlinear Dynamic Inversion (NDI). Finally the Velocity Vector Roll (VVR) maneuver has been considered as an example tostudymaneuverability enhacement. It...
Optimal apogee burn time for low thrust spinning satellite in low altitude
, Article European Journal of Operational Research ; Volume 222, Issue 2 , 2012 , Pages 386-391 ; 03772217 (ISSN) ; Assadian, N ; Sharif University of Technology
2012
Abstract
In this study, the optimal burn time for low-thrust impulsive propulsion systems is investigated to raise the perigee altitude of a low-Earth orbit. The maneuver is done using spin-stabilized attitude control and impulsive thrusting system for a time interval centered about apogee point. On the one hand, the low value of the thrust level causes more burn time needed to accomplish the transfer. This, in turn, will cause more thrust loss due to the deviation between the thrust axis (spin axis) and the velocity vector of the satellite. On the other hand, for small thrust duration, the transfer needs more revolutions around the Earth and more travel in lower altitudes with dense atmosphere and...
Numerical investigation of thermo-fluid dynamics of two triangular jets
, Article Mechanika ; Volume 17, Issue 2 , 2011 , Pages 149-155 ; 13921207 (ISSN) ; Farhanieh, B ; Sharif University of Technology
2011
Abstract
This paper addresses the numerical simulation of thermo-fluid characteristics of triangular jets. The results of spatially developing, three dimensional jets from isosce-les and equilateral nozzles at different Reynolds numbers and distances between jets are presented. The system of governing equations, subject to the proper boundary condi-tions is solved with the finite volume method with collo-cated grid arrangement. SIMPLEC algorithm was used for the pressure-velocity coupling to discrete the governing equations of flow and energy. The turbulent stresses are approximated using k-ε model. The velocity and tempera-ture fields are presented and rates of their decay at jet cen-terline are...
Numerical investigation of turbulent free jet flows issuing from rectangular nozzles: The influence of small aspect ratio
, Article Archive of Applied Mechanics ; Volume 80, Issue 7 , 2010 , Pages 727-745 ; 09391533 (ISSN) ; Maddahian, R ; Faghani, P ; Farhanieh, B ; Sharif University of Technology
2010
Abstract
In this research, the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results of three-dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent stresses are approximated using k-ε model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay at the jet centerline are noted. The velocity vectors of the main flow and the secondary flow are illustrated. Also, effect of aspect ratio on mixing in...
Application of fuzzy decision making in mobile robot navigation in dynamic environments
, Article IEEE International Conference on Fuzzy Systems, 20 August 2009 through 24 August 2009 ; 2009 , Pages 877-881 ; 10987584 (ISSN) ; 9781424435975 (ISBN) ; Seifipour, N ; Sharif University of Technology
Abstract
This paper presents a modified sensor-based online method for mobile robot navigation generating paths in dynamic environments. The intelligent part of the algorithm is a Fuzzy Decision Maker (FDM) which enables the robot to do both the guidance-based tracking algorithm and the obstacle avoidance simultaneously. The output of FDM is a weighted combination of velocity vectors generated by velocity obstacle algorithm and guidance based tracking algorithm. The results prove that the robot can track a moving target while maneuvering safely in dynamic environment and avoids stationary and moving obstacles
Modeling of reactive acid transport in fractured porous media with the Extended–FEM based on Darcy-Brinkman-Forchheimer framework
, Article Computers and Geotechnics ; Volume 128 , December , 2020 ; Salehi Sichani, A ; Hosseini, N ; Sharif University of Technology
Elsevier Ltd
2020
Abstract
In this paper, a fully coupled numerical model is developed based on the X-FEM technique to simulate the reactive acid transport in fractured porous media. The porous medium consists of the solid and fluid phases, in which the fluid phase includes water and acid components, and chemical reactions can be occurred between acid component and solid phase at the solid–fluid interfaces. The governing equations include the mass and momentum conservation laws for fluid phase, and the advective–diffusive transport of acid component that must be solved to obtain the primary unknowns, including the pore fluid pressure, acid concentration, and fluid velocity vector. Applying the...
Numerical investigation of effect of aspect ratio of rectangular nozzles
, Article 2008 2nd International Conference on Thermal Issues in Emerging Technologies, ThETA 2008, Cairo, 17 December 2008 through 20 December 2008 ; July , 2008 , Pages 391-398 ; 9781424435777 (ISBN) ; Farhanieh, B ; Maddahian, R ; Faghani, P ; Sharif University of Technology
2008
Abstract
In this research the fluid and thermal characteristics of a rectangular turbulent jet flow is studied numerically. The results of three dimensional jet issued from a rectangular nozzle are presented. A numerical method employing control volume approach with collocated grid arrangement was employed. Velocity and pressure fields are coupled with SIMPLEC algorithm. The turbulent stresses are approximated using k-e model with two different inlet conditions. The velocity and temperature fields are presented and the rates of their decay at jet centerline are noted. The velocity vectors of a main flow and secondary flow are illustrated. Also effect of aspect ratio on mixing in rectangular cross...
Flow field around side-by-side piers with and without a scour hole
, Article European Journal of Mechanics, B/Fluids ; Volume 36 , 2012 , Pages 152-166 ; 09977546 (ISSN) ; Aslani Kordkandi, A ; Sharif University of Technology
2012
Abstract
The present study provides the experimental results of the flow pattern around two-circular piers positioned in side-by-side arrangement. The experiments were performed for two bed configurations (with and without a scour hole). Velocities were measured by an Acoustic Doppler Velocimeter (ADV). Flat bed and scour hole were frozen by synthetic glue to facilitate the performance of the experiments. The contours and distributions of the time-averaged velocity components, turbulence intensities, turbulence kinetic energy, and Reynolds stresses at different horizontal and vertical planes are presented. Streamlines and velocity vectors obtained from time-averaged velocity fields are used to show...
Experimental study of three-dimensional flow field around a complex bridge pier
, Article Journal of Engineering Mechanics ; Volume 136, Issue 2 , 2010 , Pages 143-154 ; 07339399 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
2010
Abstract
In this paper, three-dimensional turbulent flow field around a complex bridge pier placed on a rough fixed bed is experimentally investigated. The complex pier foundation consists of a column, a pile cap, and a 2×4 pile group. All of the elements are exposed to the approaching flow. An acoustic-Doppler velocimeter was used to measure instantaneously the three components of the velocities at different horizontal and vertical planes. Profiles and contours of time-averaged velocity components, turbulent intensity components, turbulent kinetic energy, and Reynolds stresses, as well as velocity vectors are presented and discussed at different vertical and horizontal planes. The approaching...