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    Entropy minimization in turbine cascade using continuous adjoint formulation

    , Article Engineering Optimization ; Volume 48, Issue 2 , 2016 , Pages 213-230 ; 0305215X (ISSN) Zeinalpour, M ; Mazaheri, K ; Sharif University of Technology
    Taylor and Francis Ltd  2016
    Abstract
    A complete continuous adjoint formulation is presented here for the optimization of the turbulent flow entropy generation rate through a turbine cascade. The adjoint method allows one to have many design variables, but still afford to compute the objective function gradient. The new adjoint system can be applied to different structured and unstructured grids as well as mixed subsonic and supersonic flows. For turbulent flow simulation, the k-ω shear-stress transport turbulence model and Roe's flux function are used. To ensure all possible shape models, a mesh-point method is used for design parameters, and an implicit smoothing function is implemented to avoid the generation of non-smoothed... 

    Three-dimensional Aerothermal Shape Optimization of Turbine Blade, Using Gradient Adjoint-based Methods

    , Ph.D. Dissertation Sharif University of Technology Zeinalpour, Mehdi (Author) ; Mazaheri, Karim (Supervisor)
    Abstract
    The most important challenge and the most time consuming part of the gradient based optimization algorithms in the aerodynamic shape optimization problems is the evaluation of the sensitivity of the objective function with respect to the design variables. The adjoint method which has been the subject of many research in the recent three decades, is capable of computing the complete gradient information needed for optimization by solving the governing flow equations and their corresponding adjoint equations only once, regardless of the number of design parameters. In this study, the continues adjoint equations for compressible inviscid and viscous flows are derived and the formulation of... 

    Turbine blade aerodynamic optimization on unstructured grids using a continuous adjoint method

    , Article ASME 2012 International Mechanical Engineering Congress and Exposition, IMECE 2012, Houston, TX, 9 November 2012 through 15 November 2012 ; Volume 1 , 2012 , Pages 425-431 ; 9780791845172 (ISBN) Zeinalpour, M ; Mazaheri, K ; Irannejad, A ; Sharif University of Technology
    2012
    Abstract
    A gradient based optimization using the continuous adjoint method for inverse design of a turbine blade cascade is presented. The advantage of the adjoint method is that the objective function gradients can be evaluated by solving the adjoint equations with coefficients depending on the flow variables. This method is particularly suitable for aerodynamic design optimization for which the number of design variables is large. Bezier polynomials are used to parameterize suction side of the turbine blade. The numerical convective fluxes of both flow and adjoint equations are computed by using a Roe-type approximate Riemann solver. An approximate linearization is applied to simplify the... 

    Sensitivity analysis of gas turbine fuel consumption with respect to turbine stage efficiency

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 1 , 2012 , Pages 419-423 ; 9780791845172 (ISBN) Zeinalpour, M ; Mazaheri, K ; Irannejad, A ; Sharif University of Technology
    2012
    Abstract
    In this paper, the effect of turbine stage efficiency on fuel consumption of both gas turbines and aerial engines is assessed quantitatively. At the beginning of the gas generator optimization to decrease the fuel consumption, it is necessary to analyze the sensitivity of fuel consumption to its main components efficiencies. This will guide us which component is more important to be optimized. Here a zero-dimensional analysis has been done to determine the effect of turbine stage efficiency on the fuel consumption. Results of this analysis are evaluated in the context of thermodynamic cycle of a gas turbine generator and an aerial engine. As an example, it is shown that if the efficiency of... 

    Performance analysis and comparisons of different ultra-wideband multiple access modulation schemes

    , Article IEE Proceedings: Communications ; Volume 153, Issue 5 , 2006 , Pages 705-718 ; 13502425 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Sharif University of Technology
    2006
    Abstract
    The multiuser performance of two kinds of ultra-wideband (UWB) systems, namely, multi-carrier frequency-hopping-UWB and time-hopping-UWB, is evaluated. We derive the bit error rate of these systems in both AWGN and fading channels. Our numerical results show that the TH-UWB system always outperforms the MC-FH-UWB system with non-coherent detection. However, the MC-FH-UWB system with coherent detection presents a better performance than TH-UWB in a very few cases. Then, we use a practical low-rate convolutional error correcting code, which does not require any extra bandwidth further than that needed by the uncoded scheme, to improve the system performance. The results show that the coded... 

    Multiuser performance comparisons of fast frequency hopping and multicarrier slow frequency hopping systems:Uncoded and coded schemes

    , Article 2004 IEEE 60th Vehicular Technology Conference, VTC2004-Fall: Wireless Technologies for Global Security, Los Angeles, CA, 26 September 2004 through 29 September 2004 ; Volume 60, Issue 3 , 2004 , Pages 1894-1898 ; 15502252 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Sharif University of Technology
    2004
    Abstract
    In this paper, we evaluate and compare the multiuser performance of the Fast Frequency-Hopping (FFH) and the MultiCarrier slow Frequency-Hopping (MC-FH) systems employing non-coherent detection for both uncoded and coded schemes in AWGN and slowly frequency-selective Rayleigh fading channels, based on Gaussian distribution assumption for the decision variable. Our numerical resulte indicate that with non-coherent detection, both systems show the same performance. However, the MC-FH system can be easily implemented using FFT algorithm. Furthermore with a slow hopping rate and high number of carriers, a coherent detection for the MC-FH system is feasible. Our results will indicate that the... 

    A coupled adjoint formulation for non-cooled and internally cooled turbine blade optimization

    , Article Applied Thermal Engineering ; Volume 105 , 2016 , Pages 327-335 ; 13594311 (ISSN) Zeinalpour, M ; Mazaheri, K ; Chaharlang Kiani, K ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    Most researches on the application of the adjoint method in turbine blade design are concentrated on the aerodynamic shape optimization without considering the heat transfer to/from the blade material. In this study, the adjoint method is extended to the conjugate heat transfer problems in which the viscous flow field is coupled to heat transfer in the solid region. Introducing a new adjoint variable in the solid domain, a heat adjoint equation is derived which is coupled with the energy adjoint equation in the fluid zone at the fluid/solid interface. The detailed mathematical description associated with the derivation of the heat adjoint equation with corresponding boundary conditions are... 

    Performance of UWB linked relay network with time-reversed transmission in the presence of channel estimation error

    , Article IEEE Transactions on Wireless Communications ; Volume 11, Issue 8 , 2012 , Pages 2958-2969 ; 15361276 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Aazhang, B ; Sharif University of Technology
    2012
    Abstract
    In this paper, we present the bit error probability (BEP) of a relay network employing UWB links between its nodes. Since UWB systems can resolve many paths and are thus rich in multipath diversity, the use of the Rake diversity combining is very effective. However, because of the complexity, it is impractical in the scenarios with portable terminals or in the networks with multiple relays. Time-reversal technique, in which the transmitting nodes can do the pre-diversity filtering of UWB signal before transmission, is known as an approach to achieve the performance equivalent to the Rake combining without increasing the receiver complexity. The performance of such a network with simple... 

    Bit error probability analysis of UWB communications with a relay node

    , Article IEEE Transactions on Wireless Communications ; Volume 9, Issue 2 , 2010 , Pages 802-813 ; 15361276 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Aazhang, B ; Sharif University of Technology
    2010
    Abstract
    In this paper, the extension of cooperative communication to the context of TH-UWB is investigated. In particular, the average bit error probability (BEP) is provided for cooperative TH-UWB systems with decode-and-forward relaying protocol. In the considered relay network, UWB links among the nodes are modeled according to IEEE 802.15.4a standards. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. We use Gaussian quadrature numerical method to approximate the CF of interference component appeared in decision variable term. This technique permits to predict the system performance in different IEEE 802.15.4a defined... 

    BER derivation for UWB communication with a relay node in the presence of inter-channel interference

    , Article 2009 IEEE 3rd International Symposium on Advanced Networks and Telecommunication Systems, ANTS 2009, 14 December 2009 through 16 December 2009, New Delhi ; 2009 ; 9781424459896 (ISBN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Aazhang, B ; Sharif University of Technology
    2009
    Abstract
    In this paper, we present the average bit error probability (BEP) of a decode-and-forward relay network employing UWB links, developed by IEEE 802.15.4a standards, between its nodes. Our methodology is based on computing the Characteristic Function (CF) of the decision variable at the destination terminal. Numerical results show that significant improvement in the BEP of impulse radio UWB system is obtained by adding a relay node. The analytical expressions are also validated by computer simulations which confirm the accuracy of the approximations used in obtaining the BEP  

    Space-frequency coded cooperation in OFDM multiple-access wireless networks

    , Article IET Communications ; Volume 1, Issue 6 , December , 2007 , Pages 1152-1160 ; 17518628 (ISSN) Jamshidi, A ; Nasiri Kenari, M ; Zeinalpour, Z ; Taherpour, A ; Sharif University of Technology
    2007
    Abstract
    A cooperative space-frequency (SF) coded orthogonal frequency division multiplexing system is considered and its performance over quasi-static frequency-selective Rayleigh fading channels is evaluated. An expression for exact outage error probability is derived and its tight closed-form lower bound is presented. The tightness of the lower bound is demonstrated through Monte Carlo simulation. Asymptotic analysis indicates that the proposed protocol achieves full spatial and frequency diversities available in the cooperative communication system. The theoretical analysis of the proposed SF coded cooperation protocol is further confirmed by computer simulation using a previously introduced SF... 

    Numerical Modeling of Vacuum Assisted Resin Transfer Moulding

    , M.Sc. Thesis Sharif University of Technology Zeinalpour, Mehdi (Author) ; Mazaheri, Karim (Supervisor) ; Taheri, Bahram (Co-Advisor)
    Abstract
    Here, we have simulated isothermal vacuum assisted resin transfer moulding (VARTM) using a control volume/finite element scheme. Two dimensional and dimensional (shell geometries) spatial discretization is used. Resin motion through fibers is enforced by vacuum negative pressure in downstream. The governing equations are mass conservation and well known Darcy equation. Using an unstructured triangular grid, complex geometries could be modelled. Application of a quasi-steady algorithm results in a system of linear equation for pressure distribution. This system must be solved in each time step. The point successive over-relaxation (PSOR) scheme is used to solve the system of linear... 

    Upper bounds on the ergodic and outage capacities of relay networks using UWB links

    , Article 40th Asilomar Conference on Signals, Systems, and Computers, ACSSC '06, Pacific Grove, CA, 29 October 2006 through 1 November 2006 ; 2006 , Pages 646-650 ; 10586393 (ISSN); 1424407850 (ISBN); 9781424407859 (ISBN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Wehinger, J ; Mecklenbräuker, C. F ; Sharif University of Technology
    2006
    Abstract
    We derive, evaluate, and discuss upper bounds on ergodic and outage capacities for a three-node relay network. The considered relay network has ultra-wideband (UWB) radio channels between the source, destination, and relay nodes. The derived bounds indicate that ergodic and outage capacities of the considered UWB-linked network increase up to 300% when a relay between the source and the destination is used. Furthermore, the bounds indicate that there is an optimum position for the relay node between the source and the destination, where ergodic capacity is maximized. Our numerical results shows that for the non-line-of-sight (NLOS) scenario, with the same signal to noise ratio on all links,... 

    Asymptotically optimum detection of primary user in cognitive radio networks

    , Article IET Communications ; Volume 1, Issue 6 , December , 2007 , Pages 1138-1145 ; 17518628 (ISSN) Taherpour, A ; Norouzi, Y ; Nasiri Kenari, M ; Jamshidi, A ; Zeinalpour Yazdi, Z ; Sharif University of Technology
    2007
    Abstract
    Traditionally, the frequency spectrum is licensed to users by government agencies in a fixed manner where the licensee has exclusive right to access the allocated band. However, with increasing demand for the spectrum and scarcity of vacant bands, a spectrum policy reform seems inevitable. Meanwhile, recent measurements suggest the possibility of sharing spectrum among different parties subject to interference-protection constraints. In order to enable access to an unused licensed spectrum, a secondary user has to monitor licensed bands and opportunistically transmit whenever no primary signal is detected. Spectrum-sharing between a primary licensee and a group of secondary users has been... 

    Bounds on the delay-constrained capacity of UWB communication with a relay node

    , Article IEEE Transactions on Wireless Communications ; Volume 8, Issue 5 , 2009 , Pages 2265-2273 ; 15361276 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Aazhang, B ; Wehinger, J ; Mecklenbrauker, C. F ; Sharif University of Technology
    2009
    Abstract
    We derive bounds on the expected capacity and outage capacity of a three-node relay network for UWB communications. We also provide a simple tight approximation for the derived upper bound on the capacity and then using this bound we obtain the outage probability of the network. Numerical results show that a significant improvement in the system capacity and outage probability is obtained by adding a relay node. Moreover, our theoretical results reveal that the diversity gain of a relay channel substantially increases by using UWB links instead of NB links. We also derive these bounds when we have a constraint on the total transmitted power of the source and the relay nodes. © 2009 IEEE  

    Performance Analysis of Ultra-Wide Band (UWB) Communication with a Relay Node

    , Ph.D. Dissertation Sharif University of Technology Zeinalpour Yazdi, Zolfa (Author) ; Nasiri Kenari, Masoumeh (Supervisor) ; Azhang, Behnaam (Supervisor)
    Abstract
    In recent years, there has been an increased interest on employing low-cost, high-speed, low-latency wireless links for short range communications (< 10m). Ultra-wideband (UWB) radio is a promising technology to meet this interest. However, due to the limitation on its transmitted power level, UWB system faces major challenges to achieve an adequate system performance. Therefore, it is greatly necessary to find some efficient methods to enhance the system performance. Recently, cooperative diversity has emerged as an effective scheme to overcome multipath fading and thus to improve the quality of service in the physical layer of wireless networks without increasing the transmission power of... 

    Design and Fabrication of Inductive High Temperature Superconducting Fault Current Limiter

    , Ph.D. Dissertation Sharif University of Technology Hekmati, Arsalan (Author) ; Vakilian, Mehdi (Supervisor) ; Fardmanesh, Mehdi (Supervisor)
    Abstract
    The continuous rise in electricity demand and the ever growing power generation in different power networks over the world have caused the short circuit level in the power systems to exceed the operational rating of the installed power devices (including cables, circuit breakers and buses). Replacing these devices with new higher rating devices is an expensive solution. From this point of view, utilizing fault current limiters is an economical solution. Superconducting fault current limiters form an efficient category of current limiters. This type is expected to be studied and used widely in future due to their advantages. In this thesis, the first chapter reviews the superconductivity... 

    , M.Sc. Thesis Sharif University of Technology Mardiha, Milad (Author) ; Vakilian, Mehdi (Supervisor) ; Fardmanesh, Mehdi (Supervisor)

    Enhancement of THz Radiation from Josephson Junctions in Superconductors Using Electromagnetic Resonators

    , M.Sc. Thesis Sharif University of Technology Iranmehr, Masoud (Author) ; Ahmadi Boroujeni, Mehdi (Supervisor) ; Fardmanesh, Mehdi (Supervisor)
    Abstract
    Terahertz waves which includes frequencies between 100 GHz to 10 THz of electromagnetic spectrum have found many applications in science, medical treatments and industry. One of the recent methods to produce these waves is using nonlinear properties of superconductors based on Josephson junctions which inherently appear in some superconductors called BSCCO. Stack of intrinsic junctions of these superconducting materials can radiate terahertz waves by only applying a DC voltage across them. This Thesis investigates some of these structures based on Josephson junctions to produce coherent radiation of terahertz waves. For the optimization of the radiation power, this study also investigates... 

    On the Spectrum of Modified Theories of Gravity

    , M.Sc. Thesis Sharif University of Technology Seraj, Ali (Author) ; Golshani, Mehdi (Supervisor) ; Sheikh Jabbari, Mohammad Mehdi (Supervisor)
    Abstract
    There are different approaches in modifications of General Relativity as the theory of gravity. The modified theories of gravity are important cases in this context, which mostly start by modifying the Einstein-Hilbert action, while keeping the general covariance. Within the modified theories of gravity, we consider two cases. The first is the f(R) theories of gravity, and the second is curvature squared theories of gravity with an action like S = ∫d4x pg( 116GR + (R)2 + R2 +(R)2). Curvature squared theories of gravity have interesting feautures, most important of which is renormalizability, in contrast with General Relativity. But this advantage, as noted by K.S. Stelle in 1977 comes at...