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    Performance of phase-modulated microwave photonics in the presence of group delay and reflection amplitude ripples of the dispersive device

    , Article Conference Proceedings - 11th International Conference on Laser and Fiber-Optical Networks Modeling, LFNM 2011, 4 September 2011 through 8 September 2011, Kharkov ; 2011 ; 9781612848136 (ISBN) Mokhtari, A ; Akbari, M ; Sharif University of Technology
    We develop an analytic approach to investigate the effect of reflection amplitude and group delay ripples of the dispersive device on the performance of phase-modulated microwave-photonic filters. Experimental results conform to our proposed analytical approach  

    Drilled shafts in sand: failure pattern and tip resistance using numerical and analytical approaches

    , Article International Journal of Geotechnical Engineering ; 2021 ; 19386362 (ISSN) Jazebi, M ; Ahmadi, M. M ; Sharif University of Technology
    Taylor and Francis Ltd  2021
    Drilled shafts are one of the most important types of pile foundations. Several researchers have suggested different soil failure patterns for driven piles; however, for drilled shafts, this issue is inadequately addressed in the literature. In this paper, a numerical approach was pursued to obtain the location and dimensions of plastic zones around the tip of drilled shafts. The dependence of the suggested failure pattern size on the soil properties and drilled shaft dimensions was investigated. Based on several analyses, a soil jug-shaped failure pattern around the tip of drilled shafts was proposed, and its dimensions were determined using the regression-based and trial and error... 

    The group delay ripple effects on the performance of phase-modulator based microwave-photonic filter

    , Article 2011 18th International Conference on Telecommunications, ICT 2011, 8 May 2011 through 11 May 2011, Ayia Napa ; 2011 , Pages 162-166 ; 9781457700248 (ISBN) Mokhtari, A ; Akbari, M ; Sharif University of Technology
    We have developed an analytic approach to investigate the effect of group delay ripple on the performance of phase-modulated microwave photonic filter. Two cases with and without ripple are analyzed to clarify the ripple's effects on the performance of microwave-photonic filter. Comparison of our proposed analytical approach with simulated OptiSystem® results shows a good agreement  

    Generalized analytical approach to assess reliability of renewable-based energy hubs

    , Article IEEE Transactions on Power Systems ; Volume 32, Issue 1 , 2017 , Pages 368-377 ; 08858950 (ISSN) Moeini Aghtaie, M ; Farzin, H ; Fotuhi Firuzabad, M ; Amrollahi, R ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    This paper proposes a generalized analytical approach to evaluate the reliability of active distribution networks. The studies are implemented in the context of renewable-based energy hubs. The reliability of energy demands is determined as a function of reliability characteristics of energy hub input resources and converters as well as hub operating strategies. The framework proposed in this paper involves the main attributes of different distributed generation technologies as well as vehicle-to-grid (V2G)-capable vehicles in the reliability studies. Dealing with the uncertainty in energy services provided by the wind turbine output generation and V2G programs, efficient probabilistic... 

    Estimation of modulus of elasticity for closed-cell aluminum foam

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 3, Issue PARTS A, B, AND C , 2012 , Pages 1285-1289 ; 9780791845196 (ISBN) Ahmadian, M. T ; Gobal, A ; Alkhani, R ; Sharif University of Technology
    Monodisperse closed cell aluminum foam was analyzed numerically to determine the relationship between its elastic modulus, porosity and pore diameter. It was found a nonlinear relationship exists between porosity, pore diameter and modulus of elasticity. In this regard, an empirical equation is developed and implemented for the prediction of modulus of elasticity versus porosity and pore diameter. Comparing experimental and analytical approaches by other researchers with those obtained in this research shows agreement exists within 1 to 3 percent  

    A study on the extent of the contact and stick zones in multiple contacts

    , Article Archive of Applied Mechanics ; Volume 89, Issue 9 , 2019 , Pages 1825-1836 ; 09391533 (ISSN) Ghanati, P ; Adibnazari, S ; Sharif University of Technology
    Springer Verlag  2019
    In this paper, we analyze a general quasi-static two-dimensional multiple contact problem between two elastically similar half-planes under the constant normal (including applied moments) and oscillatory tangential loading utilizing the classical singular integral equations approach. Boundary conditions at nonsingular edges of discrete contact zones are applied and new side conditions are extracted and named “the consistency conditions” for multiple contacts. These conditions are mandatory for determination of the positions of the nonsingular edges of the contact and stick zones, when the number of them exceeds the number of the discrete contact and stick zones, respectively. Consequently, a... 

    Numerical and Analytical Investigation of Unequal Size Droplets Generation Process in Micro and Nano Channels

    , Ph.D. Dissertation Sharif University of Technology Bedram, Ahmad (Author) ; Moosavi, Ali (Supervisor) ; Kazemzadeh Hannani, Siamak (Co-Advisor)
    In this paper, we introduced two methods for producing unequal sized droplet from an initial one that don’t have the disadvantages of the available methods. We developed a comprehensive analytical theory for the T-junction with valve method. Also the geometry was simulated using a VOF algorithm and a comparison was performed between numerical and analytical results and very good agreement was observed. The accuracy of numerical results was confirmed by doing the grid independency and time step independency and comparing the results with two analytical benchmarks. We derived accurate analytical relations for calculating the droplet volume ratio, droplet length (L1, L2 and Lwhole) and pressure... 

    Theoretical investigation of the capture effect in intensity-modulation direct-detection microwave photonic links

    , Article Applied Optics ; Volume 52, Issue 28 , 2013 , Pages 7011-7021 ; 1559128X (ISSN) Hosseini, S. E ; Banai, A ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    We introduce the capture effect concept in microwave photonic links (MWPLs) for the first time to our knowledge. The capture effect or the small-signal suppression is the change in the amplitude ratio of the two signals between input and output of the intensity-modulation direct-detection (IMDD) MWPLs. An analytical explanation of the performance of external IMDD MWPLs due to the effects of nonlinearity combined with sum of several input sinusoidal signals is given.We have investigated the suppression of a weaker signal in these links. General analytic expression for the small-signal suppression is derived using a nonlinear analytical approach. We show that the small-signal suppression is... 

    Oscillations in fractional order LTI systems: Harmonic analysis and further results

    , Article Signal Processing ; Volume 93, Issue 5 , 2013 , Pages 1243-1250 ; 01651684 (ISSN) Siami, M ; Tavazoei, M. S ; Sharif University of Technology
    This paper studies undamped oscillations generated by marginally stable fractional order linear time invariant (LTI) systems. In this study, an analytical approach is proposed to be used for harmonic analysis of such oscillations in marginally stable commensurate order LTI systems. Also, it is shown that the Q-semi norm of the limit sets for a trajectory of these systems can be analytically determined based on the Q-semi norm of the initial condition, where Q is a specific matrix. Moreover, this result is extended to the wider class of rational order systems. Finally, some numerical examples are presented to demonstrate the use of the paper results  

    An analytical approach to obtain optimum load impedance using X-parameters®

    , Article 2012 Workshop on Integrated Nonlinear Microwave and Millimetre-Wave Circuits, INMMIC 2012 ; 2012 ; 9781467329491 (ISBN) Zargar, H ; Banai, A ; Cai, J ; Brazil, T ; Sharif University of Technology
    This paper introduces an analytical approach to obtain fundamental and harmonic load-pull contours using X-parameters. This method is proposed to obtain the optimum load impedance at different harmonics. This approach has been applied on a two port X-parameter model and its results are independently verified by ADS simulation  

    Droplet breakup in an asymmetric microfluidic T junction

    , Article European Physical Journal E ; Volume 34, Issue 8 , 2011 ; 12928941 (ISSN) Bedram, A ; Moosavi, A ; Sharif University of Technology
    Breakup of non-uniform droplets in an asymmetric T junction consisting of an inlet channel and two different-size outlet channels has been investigated numerically. Also, an analytical approach in the limit of the lubrication approximation has been extended to provide some analytical relations to study the system and verify the numerical results. Parameters that are important in the performance of the system have been determined and discussed. Our results indicate that smaller droplets can be produced by increasing the capillary number. As the geometry becomes symmetric the pressure drop decreases. Our results also reveal that the breakup time and the pressure drop for this system are... 

    Impact of correlation on reserve requirements of high wind-penetrated power systems

    , Article International Journal of Electrical Power and Energy Systems ; Volume 73 , 2015 , Pages 576-583 ; 01420615 (ISSN) Riahinia, S ; Abbaspour, A ; Fotuhi Firuzabad, M ; Moeini Aghtaie, M ; Sharif University of Technology
    Elsevier Ltd  2015
    This paper investigates the effects of two important factors, i.e., correlation of wind farms output with load and wind speed coincidence in determining the required static reserve in a high wind-penetrated power system. To this end, it suggests an analytical approach to involve the effects of these two factors in probabilistic analytical multi-state models of wind farms output generation. Based on an optimization framework with the objective of reaching the desirable level of correlation, the key idea is to calculate some joint probabilities for equivalent models of wind farms. As a result, these models become compatible with the ones for conventional generation units in adequacy studies of... 

    Method for designing PIλDμ stabilisers for minimum-phase fractional-order systems

    , Article IET Control Theory and Applications ; Volume 4, Issue 1 , January , 2010 , Pages 61-70 ; 17518644 (ISSN) Merrikh Bayat, F ; Karimi Ghartemani, M ; Sharif University of Technology
    This paper deals with the problem of designing the PI λDμ-type controllers for minimum-phase fractional systems of rational order. In such systems, the powers of the Laplace variable, s, are limited to rational numbers. Unlike many existing methods that use numerical optimisation algorithms, the proposed method is based on an analytic approach and avoids complicated numerical calculations. The method presented in this paper is based on the asymptotic behaviour of fractional algebraic equations and applies a delicate property of the root loci of the systems under consideration. In many cases, the resulted controller is conveniently in the form of P, Iλ, PDμ or PIλDμ. Four design examples are... 

    Analytical approach for calculating the sheet output curvature in asymmetrical rolling: In the case of roll axis displacement as a new asymmetry factor

    , Article International Journal of Mechanical Sciences ; Volume 105 , 2016 , Pages 11-22 ; 00207403 (ISSN) Aboutorabi, A ; Assempour, A ; Afrasiab, H ; Sharif University of Technology
    Elsevier Ltd  2016
    In this paper, a less studied factor in the asymmetrical rolling process of sheets, namely the rolls horizontal displacement, is investigated using an analytical approach based on the slab method analysis. The presented method is capable of computing the force and torque of the process under different asymmetrical factors such as the rolls horizontal displacement, the interface friction inequality, and the rolls speed mismatch. A formula is presented to predict the outgoing sheet curvature induced by the rolls horizontal displacement. The results can be potentially used in producing curved sheets of various shapes by the asymmetrical rolling process. The analytical model is compared with a... 

    Derating of distribution transformers under non-linear loads using a combined analytical-finite elements approach

    , Article IET Electric Power Applications ; Volume 10, Issue 8 , 2016 , Pages 779-787 ; 17518660 (ISSN) Ghazizadeh, M ; Faiz, J ; Oraee, H ; Sharif University of Technology
    Institution of Engineering and Technology 
    Supplying non-linear loads causes increased losses in transformers which eventually leads to their reduced life spans. Therefore, transformers are derated in order to protect them against premature loss of life. To do this, load losses including ohmic loss and winding eddy current (WEC) loss need to be estimated. This study suggests an improved analytical approach using finite element method (FEM) which includes all material characteristics and geometrical structures in order to calculate WEC loss under non-sinusoidal load current in each winding individually. By adopting this procedure, harmonic loss factor as a dominant parameter in transformers derating is estimated. By emphasising the... 

    Post-buckling analysis of piezo-magnetic nanobeams with geometrical imperfection and different piezoelectric contents

    , Article Microsystem Technologies ; Volume 25, Issue 9 , 2019 , Pages 3477-3488 ; 09467076 (ISSN) Mirjavadi, S. S ; Forsat, M ; Barati, M. R ; Abdella, G. M ; Hamouda, A. M. S ; Mohasel Afshari, B ; Rabby, S ; Sharif University of Technology
    Springer Verlag  2019
    Thermal post-buckling behavior of a geometrically imperfect/perfect piezo-magnetic nano-scale beams made of two-phase composites is analyzed in the present paper based on nonlocal elasticity theory. For the first time, the material properties of the nanobeam are considered as functions of piezoelectric phase percentage. All previous investigations on piezo-magnetic nanobeams neglect the effect of geometrical imperfection which is very important since the nanobeams are not always ideal or perfect. The post-buckling problem of such nanobeams is solved by introducing an analytical approach to derive buckling temperatures. The present solution is simple and easily understandable. For both... 

    Two building blocks of microwave photonics filters in the presence of group delay ripple: A comparative survey

    , Article Optical and Quantum Electronics ; Volume 44, Issue 8-9 , 2012 , Pages 403-414 ; 03068919 (ISSN) Mokhtari, A ; Akbari, M ; Sharif University of Technology
    Springer  2012
    We have developed an analytic approach to investigate the effect of group delay ripple of the dispersive devices on the performance of two major building blocks of microwave- photonic filters. Firstly, performance of PM-based block in the presence of an arbitrary group delay ripple (GDR) is analyzed and compared with the ripple-free case to reveal the destructive effects of added group delay ripple. In the next step, we repeat the proposed approach for the AM-based one; again, the performance is compared with the ripple-free case. Two distortion metrics are also introduced to quantify this distortion. Comparison of the performance of two building blocks in the presence of group delay ripple... 

    Effect of a phasor group delay ripple on the performance of phase-modulator based microwavephotonic filter

    , Article 2010 5th International Symposium on Telecommunications, IST 2010, 4 December 2010 through 6 December 2010 ; 2010 , Pages 143-146 ; 9781424481835 (ISBN) Mokhtari, A ; Akbari, M ; Sharif University of Technology
    We have developed an analytic approach to investigate the effect of a sinusoid group delay ripple on the performance of phase-modulated microwave photonic filter. Frequency of fabricated sinusoid ripple determines the pole's frequency of the resulted transfer function. Comparison of our proposed analytical approach with simulated OptiSystem results shows a good agreement  

    A Parametric Study on Application and Analysis of Beam to Column "Reversed Channel" Connection in Tubular Systems

    , M.Sc. Thesis Sharif University of Technology Kokabi, Sina (Author) ; Mofid, Massoud (Supervisor)
    Today steel tubular systems are used more than before, especially in recent years. A difficulty with this type of systems is making beam to column connections using bolts due to no access to holes of bolts from the inside of tube or hollow circular column. Reverse channel connection is devised and introduced to prevail this problem. Access to holes in this connection is from the inside of channel. In this connection, the web of the channel is connected to steel beam using bolts and the two legs of channel is welded to face of tube column.
    This type of connection does include some innovations; not too many researchers work on different versions of this connection. This thesis provides an... 

    Short-Term and Mid-Term Reliability Evaluation of High-wind Penetrated Power Systems in Peresence of Energy Storage Systems

    , M.Sc. Thesis Sharif University of Technology Parvini, Zohreh (Author) ; Abbaspour Tehrani Fard, Ali (Supervisor) ; Fotuhi Firuzabad, Mahmud (Co-Advisor)
    Depletion of the fossil fuel resources along with the environmental concerns have led to a significant growth in utilization of Renewable Energy Resources (RERs). Among different kinds of RERs, wind energy due to maturity of its associated conversion technologies and also its widespread presence in different regions has experienced a more rapid usage in generation sector of power systems. Despite numerous benefits of this environmentally-friendly energy, uncontrollability and uncertainty in output power of wind turbines has resulted in many technical issues for operators of power systems. However, it has been shown that the presence of various storage system technologies can alleviate these...