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A heuristic complexity-based method for cost estimation of aerospace systems
, Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 227, Issue 11 , 2013 , Pages 1685-1700 ; 09544100 (ISSN) ; Jafari, M. H ; Sharif University of Technology
2013
Abstract
Cost estimation plays an essential role in the development of aerospace systems that are perhaps the most complex, time- and labor-consuming ones. Regarding this matter, it is unavoidable to take a systematic approach to build a realistic model through a deliberative, heuristical and easy-to-do process in the early stages of design. In the current study, complexity index theory is utilized to develop a heuristic complexity-based method to estimate various costs of aerospace systems. This method promises to be logically and practically more reliable and accurate than classical parametric methods. Logically, manipulating a group of parameters, instead of only one or two, reduces the...
Model Predictive Controller Design for Regenerative Electronic AC Load
, M.Sc. Thesis Sharif University of Technology ; Zolghadri, MohammadReza (Supervisor)
Abstract
Generally, virtual loads is used to test all AC power and energy meters and are usually passive. To prevent possible damage of this heat and to control the temperature, cooling blowers are used which increases the volume and weight. So, recycling the power delivered from the grid causes a small amount of power to be converted to heat in proportion to the load efficiency. The purpose of this study is design, predictive controller model for programmable electronic regenerative AC load. The structure used is a back-to-back converter consisting of an AC-DC converter and a DC-AC converter, which according to existence of capacitance between these two structures, two converters can be controlled...
A Bio-Inspired Modeling of the Retina
, M.Sc. Thesis Sharif University of Technology ; Vosoughi Vahdat, Bijan (Supervisor)
Abstract
The retina is a light-sensitive layer of tissue at the back of the eyeball wall and is the initial stage of the brain's visual processing stages. This tissue contains more than 60 types of neurons placed in different neuronal layers. All the visual information received from the surrounding environment passes the retina and is encoded into neural signals. Therefore, studying the retina's functionality and bio-inspired modeling of its neurons and their connections are essential in recognizing visual dysfunctions caused by problems in the retina. Also, this modeling can help researchers in proposing solutions for building retinal prosthetics and, in general, performing simulations in the...
Resonant frequency and sensitivity of an AFM microcantilever modeled by the non-local theory
, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011 ; Volume 11 , November , 2011 , Pages 239-245 ; 9780791854976 (ISBN) ; Kahrobaiyan, M. H ; Ahmadian, M. T ; Sharif University of Technology
Abstract
In this paper, utilizing the non-local theory, the resonant frequency and sensitivity of an AFM microcantilever are investigated. To that end, the governing equation of motion and corresponding boundary conditions are obtained using the variational approach. Afterwards, the resonant frequency and sensitivity of the AFM microcantilever are derived analytically and depicted in some figures versus the contact stiffness of the sampling surface. The results of the current model are compared to those of the classical theory. The comparison shows that the difference between the results of the non-local theory and those of the classical theory is significant when the non-local parameter is high but...
A size-dependent beam element based on the modified couple stress theory
, Article ASME 2011 International Mechanical Engineering Congress and Exposition, IMECE 2011, 11 November 2011 through 17 November 2011, Denver, CO ; Volume 8 , 2011 , Pages 591-597 ; 9780791854945 (ISBN) ; Khajehpour, M ; Ahmadian, M. T ; ASME ; Sharif University of Technology
Abstract
In this paper, the modified couple stress theory is employed to develop a size-dependent beam element able to predict the size-dependency observed in microbeams. The stiffness matrix is obtained for the aforementioned beam element. As an example, the deflection of a microcantilever is evaluated using the proposed beam elements and the results of the finite element method are compared to the analytical results obtained by the classical beam theory. The maximum deflection of the beam is depicted versus the ratio of the beam thickness to the material length scale parameter, the parameter appearing in non-classical continuum theories. The results show that when the characteristic size of the...
Torsion of strain gradient bars
, Article International Journal of Engineering Science ; Volume 49, Issue 9 , September , 2011 , Pages 856-866 ; 00207225 (ISSN) ; Tajalli, S. A ; Movahhedy, M. R ; Akbari, J ; Ahmadian, M. T ; Sharif University of Technology
2011
Abstract
The governing differential equation and both classical and non-classical boundary conditions of strain gradient bars are derived using variational approach. A closed-form analytical solution is obtained for static torsion and the characteristic equation, which gives the natural frequencies, is derived and analytically solved for the free torsional vibrations of the strain gradient microbars. A fixed-fixed microbar is considered as a specific case to investigate the torsional size-dependent static and free-vibration behavior of strain gradient microbars. The results of the current model are compared to those of the modified couple stress and classical theories
Optimization of geometrical dimensions of single-slope basin-type solar stills
, Article Desalination ; Volume 424 , 2017 , Pages 159-168 ; 00119164 (ISSN) ; Soltanieh, M ; Karimi Estahbanati, M. R ; Jafarpur, K ; Ashrafmansouri, S. S ; Sharif University of Technology
Abstract
In the present work, effects of height, length, and width of a single-slope basin-type solar still on its distillate production was investigated. For this purpose, a radiation model was developed which accounts for the influences of all walls on quantities of received solar radiation by the base and saline water of the still. Moreover, in this radiation model, the side walls of the still were considered as the trapezoid and the diffuse as well as beam components of solar irradiance were separately taken into account for the first time. Abilities of the present model were compared with earlier ones. Furthermore, the predictions of the current model were compared with the present experimental...
Rigid-body molecular dynamics of DNA inside a nucleosome
, Article European Physical Journal E ; Volume 36, Issue 3 , March , 2013 ; 12928941 (ISSN) ; Berdy Besya, A ; Ejtehadi, M. R ; Schiessel, H ; Sharif University of Technology
2013
Abstract
The majority of eukaryotic DNA, about three quarter, is wrapped around histone proteins forming so-called nucleosomes. To study nucleosomal DNA we introduce a coarse-grained molecular dynamics model based on sequence-dependent harmonic rigid base pair step parameters of DNA and nucleosomal binding sites. Mixed parametrization based on all-atom molecular dynamics and crystallographic data of protein-DNA structures is used for the base pair step parameters. The binding site parameters are adjusted by experimental B-factor values of the nucleosome crystal structure. The model is then used to determine the energy cost for placing a twist defect into the nucleosomal DNA which allows us to use...
Modeling of CO2-brine interfacial tension: Application to enhanced oil recovery
, Article Petroleum Science and Technology ; Volume 35, Issue 23 , 2017 , Pages 2179-2186 ; 10916466 (ISSN) ; Abbasi, P ; Baghban, A ; Zargar, G ; Abbasi, P ; Sharif University of Technology
Abstract
Development of reliable and accurate models to estimate carbon dioxide–brine interfacial tension (IFT) is necessary, since its experimental measurement is time-consuming and requires expensive experimental apparatus as well as complicated interpretation procedure. In the current study, feed forward artificial neural network is used for estimation of CO2–brine IFT based on data from published literature which consists of a number of carbon dioxide–brine interfacial tension data covering broad ranges of temperature, total salinity, mole fractions of impure components and pressure. Trial-and-error method is utilized to optimize the artificial neural network topology in order to enhance its...
Learning improvement by using matlab simulator in advanced electrical machine laboratory
, Article RPC 2010 - 1st Russia and Pacific Conference on Computer Technology and Applications, 6 September 2010 through 9 September 2010 ; 2010 , Pages 107-116 ; Fazly, M ; Sharif University of Technology
Abstract
This paper presents how can teach complicated problems in electrical engineering subjects (electrical machines) by using simulators such as MATLAB/SIMULINK. Simulation of direct vector control of induction machine (IM) drive on the rotor flux direction with composite model flux observer can improve electrical machine teaching-learning procedure for graduated and under graduated levels. In the indirect vector control of IM, current reference values are used for estimation angle of the rotor flux space vector (ARFSV), however using current reference values instead of current real values can decrease accuracy of ARFSV. In the direct vector control, current real values (current feedback)...
A combined model flux observer for vector control of traction asynchronous motors
, Article 7th International Conference on Power Electronics and Drive Systems, PEDS 2007, Bangkok, 27 November 2007 through 30 November 2007 ; 2007 , Pages 1295-1300 ; 1424406455 (ISBN); 9781424406456 (ISBN) ; Chini Foroosh, S ; Sharif University of Technology
2007
Abstract
Vector control induction motor drives are particularly sensitive to the variation of motor parameters. As a consequence, the field orientation is missed, leading to substantial degradation of performance. The performance of traction motors can be even more degraded by the substantial core loss due to their high supply frequency. In this paper, a flux observer using combined voltage and current model is presented. The influence of the core loss resistance is considered in motor models. This control system is robust against simultaneous variations of the stator resistance, rotor resistances, as well as the mismatch of the equivalent stator core-loss resistance, yielding a globally stable...