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Development of Chebyshev Collocation Spectral Lattice Boltzmann Method for Solution of LowSpeed Flows
, M.Sc. Thesis Sharif University of Technology ; Hejranfar, Kazem (Supervisor)
Abstract
In this study, a Chebyshev collocation spectral lattice Boltzmann method (CCSLBM) is developed and assessed for the computation of low speed flows. Both steady and unsteady flows are considered here. The discrete Boltzmann equation (DBE) with the Bhatnagar-Gross-Krook (BGK) approximation based on the pressure distribution function is considered and the space discretization is performed by the Chebyshev collocation spectral method to achieve a highly accurate flow solver. To provide accurate unsteady solutions, the time integration of the temporal term in the LB equation is made by the fourth-order Runge-Kuta scheme. To achieve numerical stability and accuracy, the physical boundary...
Experimental Investigation of Geometric Parameters Effect on Energy Harvesting from FIV in Bluff Bodies
, M.Sc. Thesis Sharif University of Technology ; Ebrahimi, Abbas (Supervisor)
Abstract
The purpose of this research is to design and construct a test stand for the study of the kinematic and flow pattern of bluff bodies oscillating motion due to the induction of wake vortices. An experimental investigation was conducted to explore the effect of bluff bodies cross section to optimize the amount of electrical energy withdraw by electromagnetic harvester. The tests are carried out on cylinders with square section and rectangular sections with a length to width ratio of 1/2 and 2/1 and height of 50 cm, at speeds of 5 to 35 m/s in eiffel type wind tunnel. The effect of cylinder cross-section on the amount of energy harvested showed that the amplitude of oscillation in square-shaped...
Review of worldwide activities in liquid-fed pulsed plasma thruster
, Article Journal of Propulsion and Power ; Volume 30, Issue 2 , March-April , 2014 , Pages 253-264 ; ISSN: 07484658 ; Schonherr, T ; Sharif University of Technology
Abstract
A review of worldwide activities in liquid-fed pulsed plasma thruster (LPPT) is discussed. Pulsed plasma thruster are extensively recognized as one of the most promising electric space propulsion systems to perform propulsive tasks on micro- and nanosatellites, including cubesats, because they offer many advantages compared with other electric space propulsion systems. The low plasma exhaust velocity measured by a Langmuir probe showed that thrust is mainly produced by 0.3 μg mass ionized by the first trigger and a much greater quantity of propellant introduced by the main discharge remained neutral at low speed. Various propellant feeding and discharge initiation methods have been applied...
A fast method for prior probability selection based on maximum entropy principle and Gibbs sampler
, Article 2007 9th International Symposium on Signal Processing and its Applications, ISSPA 2007, Sharjah, 12 February 2007 through 15 February 2007 ; 2007 ; 1424407796 (ISBN); 9781424407798 (ISBN) ; Kasaei, S ; Khabbazian, M ; Sharif University of Technology
2007
Abstract
One of the problems in Bayesian inference is the prior selection. We can categorize different methods for selecting prior into two main groups: informative and non-informative. Here, we have considered an informative method called filters random filed and minimax entropy (FRAME). Despite of its theoretical interest, that method introduces a huge amount of computational burden, which makes it very unsuitable for real-time applications. The main critical point of the method is its parameter estimation part, which plays a major role in its very low speed. In this paper, we have introduced a fast method for parameter estimation to fasten the FRAME approach. Although the kernel of our approach is...
Effect of surface roughness on an airfoil in pitching motion
, Article 36th AIAA Fluid Dynamics Confernce, San Francisco, CA, 5 June 2006 through 8 June 2006 ; Volume 4 , 2006 , Pages 2785-2792 ; 1563478102 (ISBN); 9781563478109 (ISBN) ; Soltani, M. R ; Sharif University of Technology
2006
Abstract
Extensive experimental tests have been conducted to examine the roughness effects on the aerodynamic performance of a model in an oscillatory motion. All tests were carried out in a 0.8×0.8 m 2 low-speed wind tunnel. The model had 0.25m chord and was pitched about its quarter-chord. Data were acquired at various Reynolds number and reduced frequencies. Surface roughness was applied at two different locations of the model upper surface, leading edge and the point of maximum thickness. Furthermore, tunnel turbulent was varied and all tests were repeated. The results indicate that the width of the hysteresis loop, position of the figure eight shape, slope of the normal force coefficient curve,...
Chebyshev collocation spectral lattice boltzmann method in generalized curvilinear coordinates
, Article Computers and Fluids ; Volume 146 , 2017 , Pages 154-173 ; 00457930 (ISSN) ; Hajihassanpour, M ; Sharif University of Technology
Abstract
In this work, the Chebyshev collocation spectral lattice Boltzmann method is implemented in the generalized curvilinear coordinates to provide an accurate and efficient low-speed LB-based flow solver to be capable of handling curved geometries with non-uniform grids. The low-speed form of the D2Q9 and D3Q19 lattice Boltzmann equations is transformed into the generalized curvilinear coordinates and then the spatial derivatives in the resulting equations are discretized by using the Chebyshev collocation spectral method and the temporal term is discretized with the fourth-order Runge–Kutta scheme to provide an accurate and efficient low-speed flow solver. All boundary conditions are...
The unsteady behavior of subsonic wind tunnel wall pressure during pitching motion of the model
, Article Scientia Iranica ; Vol.21, issue.1 , 2014 , p. 192-202 ; 10263098 ; Soltani, M. R ; Ghaeminasab, M ; Sharif University of Technology
Abstract
Extensive low speed wind tunnel experiments have been undertaken to measure the test section, oor wall pressure distribution, in the presence of a 2D wing inside the test section. The experiments were performed for both the static and dynamic pitching motion of the model under difierent conditions. In these measurements, the efiects of the existence and oscillations of a 2D wing on the oor wall pressure at various locations were studied. According to the results, as the oscillation parameters, such as mean angle of attack and frequency, change, wall pressures at the points located in the front part of the test section, in the upstream region, exhibit difierent behavior from those in the...
Minimum time trajectory optimization of a tail-sitter aerial vehicle using nonlinear programming
, Article 2012 International Conference onAdvanced Mechatronic Systems, ICAMechS 2012 ; 2012 , Pages 275-280 ; 9780955529382 (ISBN) ; Assadian, N ; Saghafi, F ; Sharif University of Technology
2012
Abstract
Aerial tail-sitters have drawn many attentions in recent years. The main challenge of employing these vehicles is to ensure safe and efficient takeoff and landing. The aim of the current study is to develop a gradient-base optimization algorithm for a jet aerial tail-sitter in order to obtain minimum time trajectories in transition flight phases. The vehicle is supposed to utilize thrust vectoring system instead of conventional control surfaces that will pose minimal drawbacks in terms of low speed efficiency and complexity. The time-optimal trajectories are computed using the nonlinear dynamic equations of motion of the vehicle in order to make sure that the vehicle can follow the optimum...
Optimized fuzzy control strategy for a spa hybrid truck
, Article International Journal of Automotive Technology ; Volume 13, Issue 5 , August , 2012 , Pages 817-824 ; 12299138 (ISSN) ; Foumani, M. S ; Sharif University of Technology
2012
Abstract
In this paper, an optimized control strategy is proposed for a split parallel hydraulic hybrid truck. The model of the vehicle was simulated in Simulink. According to a global optimization technique, a fuzzy control strategy is developed for the vehicle. This strategy shows flexibility for different drive cycles and a desirable fuel consumption reduction, especially for a low speed drive cycle, which is extracted according to an urban utility vehicle mission
Comparison of efficiency for different switching tables in six-phase induction motor DTC drive
, Article Journal of Power Electronics ; Volume 12, Issue 1 , 2012 , Pages 128-135 ; 15982092 (ISSN) ; Rahmati, A ; Kaboli, S ; Sharif University of Technology
2012
Abstract
In this paper, different switching tables proposed for the Direct Torque Controlled (DTC) of a six-phase induction machine are simulated and implemented. A six-phase induction motor has 64 space voltage vectors which result in increased complexity in the selecting of inverters switching. The unsuitable selection of a switching table leads to large harmonics especially at low speed and it also reduces drive efficiency. A six-phase induction machine has large zero sequence harmonic currents of the order 6k ±1. These harmonic currents are varied in various techniques. Decreasing this loss is essential in a six-phase induction machine. The main purpose of this paper is to improve the ST-DTC of...
Experimental investigation on turbulence intensity reduction in subsonic wind tunnels
, Article Aerospace Science and Technology ; Volume 15, Issue 2 , 2011 , Pages 137-147 ; 12709638 (ISSN) ; Soltani, M. R ; Manshadi, M. D ; Sharif University of Technology
Abstract
Experiments are performed to evaluate the impact of trip wires on the turbulence intensity in a few low speed wind tunnels. Trip wires of different sizes are installed at different positions in the contraction section of four different wind tunnels and measurements are made at various free stream velocities. The results indicate that the pressure distributions are altered compared to the clean condition. Trip wires move the adverse pressure gradient toward the inlet of the contraction section. Consequently, the turbulence intensity in the test section of the wind tunnels is reduced and the flow uniformity is improved considerably. Frequency and statistical analysis are performed and the...
Canard flow improvement in a split canard configuration
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 229, Issue 6 , 2015 , Pages 1076-1087 ; 09544100 (ISSN) ; Askari, F ; Soltani, M. R ; Sharif University of Technology
Abstract
Extensive low-speed wind-tunnel tests are performed to study the flow field structure over a dual-surface canard, known as split canard, in comparison to the conventional configurations. Surface pressure for both steady deflections and unsteady oscillations of the canard are measured and compared for both canard-alone and split-canard cases. The split canard shows a superior advantage at high angles of attack, where a delay in the vortex breakdown phenomena on the canard surface is observed. For the split-canard configuration, the downwash of the front canard reduces the effective angle of attack at the inboard section of the rear element which postpones formation of the leading-edge vortex....
Power spectrum and FFT-based signal analysis in turbulence measurements
, Article World Academy of Science, Engineering and Technology ; Volume 40 , 2009 , Pages 275-278 ; 2010376X (ISSN) ; Tamadonfar, P ; Soltani, M. R ; Ghorbanian, K ; Masdari, M ; Sharif University of Technology
2009
Abstract
In this research, the employment of an innovative but simple and cost effective method for turbulent reduction in a low speed wind tunnel is investigated and the effect of this turbulence reduction on the Power Spectrum and FFT-Based signals that obtained from Hot-wire Anemometry is studied. These terms represents the amount of power contained in the signals. Several situations are studied in this paper. One of these situations is when there are four screens in the settling chamber of the wind tunnel and after that by adding the trip strip in the contraction region of the wind tunnel the tests were repeated. In the next stage, three screens were removed from the settling chamber of the wind...
Surface contamination effects on the 2-D and unsteady wind turbine blade section performance
, Article 25th AIAA Applied Aerodynamics Conference, 2007, Miami, FL, 25 June 2007 through 28 June 2007 ; Volume 2 , 2007 , Pages 795-801 ; 10485953 (ISSN) ; 1563478986 (ISBN); 9781563478987 (ISBN) ; Birjandi, A. H ; Goreishi, S. M ; Sharif University of Technology
2007
Abstract
A series of unsteady low speed wind tunnel tests on a section of a 660 Kw wind turbine blade under construction were conducted to examine the effects of distributed surface contamination on its performance characteristics. Our data shows that the airfoil is very sensitive to the applied surface roughness. Results show that contamination decreases static maximum lift coefficient more than 40 percent. In the dynamic test this effect is the same and is about 38 percent. Contamination decreases the width of the dynamic diagrams loop such and leads to the smooth stall on the airfoil
Low-speed wind energy harvesting from a vibrating cylinder and an obstacle cylinder by flow-induced vibration effect
, Article International Journal of Environmental Science and Technology ; 2021 ; 17351472 (ISSN) ; Shariatzadeh, M. J ; Bijarchi, M. A ; Pournasiri Masouleh, E ; Shafii, M. B ; Sharif University of Technology
Springer Science and Business Media Deutschland GmbH
2021
Abstract
An experimental setup has been developed to analyse the impact of cylinder transverse vibration caused by flow-induced vibration, and to improve wind energy harvesting from these vibrations. The setup consists of a cylinder mounted on four springs and is subjected to a uniform and steady flow of wind. In the first part, the effect of mounting a fixed cylinder as an obstacle with different diameters and distances from the downstream vibrating cylinder is investigated. It has been observed that the vibration amplitude on the wake of an unequal-sized obstacle is greatly amplified compared to the case of a single cylinder or an equal-sized cylinder. Numerical simulations has been conducted to...
Comparison of the transitional boundary layer during pitching and heaving motions
, Article Journal of Aircraft ; Volume 58, Issue 1 , 2021 , Pages 203-209 ; 00218669 (ISSN) ; Soltani, M. R ; Sharif University of Technology
AIAA International
2021
Abstract
In an experimental study, investigation is performed based on the surface-mounted hot-film sensors and surface pressure and rake pressure measurements. The boundary-layer (BL) events such as laminar separation (LS), transition onsets, and variations of the wall shear stress are discussed and compared for both pitching and plunging oscillations for various cases of before, within, and beyond the static stall angle of attack (AOA) conditions. All experiments are conducted in a low-speed wind tunnel. The surface pressures are measured using differential pressure sensors with a range from 0.075 to 1.0 psi and with a maximum error of 0.15% of their full span. In addition, the wake profile behind...
Comparison of the transitional boundary layer during pitching and heaving motions
, Article Journal of Aircraft ; Volume 58, Issue 1 , 2021 , Pages 203-209 ; 00218669 (ISSN) ; Soltani, M. R ; Sharif University of Technology
AIAA International
2021
Abstract
In an experimental study, investigation is performed based on the surface-mounted hot-film sensors and surface pressure and rake pressure measurements. The boundary-layer (BL) events such as laminar separation (LS), transition onsets, and variations of the wall shear stress are discussed and compared for both pitching and plunging oscillations for various cases of before, within, and beyond the static stall angle of attack (AOA) conditions. All experiments are conducted in a low-speed wind tunnel. The surface pressures are measured using differential pressure sensors with a range from 0.075 to 1.0 psi and with a maximum error of 0.15% of their full span. In addition, the wake profile behind...
Microfluidic-assisted fiber production: Potentials, limitations, and prospects
, Article Biomicrofluidics ; Volume 16, Issue 6 , 2022 ; 19321058 (ISSN) ; Nilghaz, A ; Saadatmand, M ; Naeimirad, M ; Demello, A. J ; Sharif University of Technology
American Institute of Physics Inc
2022
Abstract
Besides the conventional fiber production methods, microfluidics has emerged as a promising approach for the engineered spinning of fibrous materials and offers excellent potential for fiber manufacturing in a controlled and straightforward manner. This method facilitates low-speed prototype synthesis of fibers for diverse applications while providing superior control over reaction conditions, efficient use of precursor solutions, reagent mixing, and process parameters. This article reviews recent advances in microfluidic technology for the fabrication of fibrous materials with different morphologies and a variety of properties aimed at various applications. First, the basic principles, as...
Design and Implementation of Low-Speed Controller Area Network (CAN) Transceiver in High Voltage BCD 0.18μm Process
, M.Sc. Thesis Sharif University of Technology ; Medi, Ali (Supervisor)
Abstract
In this thesis, a Fault-Tolerant Low-Speed Controller Area Network (CAN) transceiver chip has been designed and implemented in High Voltage BCD 0.18um technology. The designed transceiver is compliant to ISO 11898 functional standard, TJA1055 datasheet as a reference chip, as well as the standards related to Electro-Magnetic Compatibility (EMC). Its failure management capability is completely based on the measurement results of the reference chip. All the characteristics of the designed transceiver, after two constructions, were measured using three types of test boards, in addition to room temperature in chambers with temperatures of -40 °C and 125 °C.This transceiver has a normal mode and...
Effect of reduced frequency on the aerodynamic behavior of an airfoil oscillating in a plunging motion
, Article Scientia Iranica ; Volume 16, Issue 1 , 2009 , Pages 40-52 ; 10263098 (ISSN) ; Rasi Marzabadi, F ; Sharif University of Technology
2009
Abstract
A series of low speed wind tunnel tests were conducted to study the unsteady aerodynamic behavior of an airfoil sinusoidally oscillating in plunge. The experiments included measuring the surface pressure distribution over a range of reduced frequencies, k = 0.03 - 0.06. In addition, steady state data were acquired and were used to furnish a baseline for further analysis and comparison. The model was oscillated with amplitude of ±15 cm and at three different mean angles of attack of 0, 10° and 18°. The unsteady aerodynamic loads were calculated from the surface pressure measurements, 64 ports, along the chord for both upper and lower surfaces. The plunging displacements were transformed into...