Search for: numerical-optimizations
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    Experimental and Theoretical Investigation of Mixture Formation in CNG Direct Injection of Spark Ignition

    , Ph.D. Dissertation Sharif University of Technology Chitsaz, Iman (Author) ; Saidi, Mohammad Hasan (Supervisor) ; Mozafari, Ali Asghar (Supervisor)
    Due to increasing of internal combustion engine applications in metropolitan, reduction of emission is one of the challenging issues for engine companies. Natural gas is a promising fuel for the strict legislation of emission in many countries. Vast variety of natural gas sources in Iran and also lower carbon to hydrogen content of natural gas motivates us to use this fuel for engine application. Using natural gas also helps to increase the variety of fuel basket in Iran. Present research has focused on mixture formation and injection characteristics of natural gas direct injection engine. Injection and mixture formation in direct injection engines is very important for good combustion and... 

    Numerical Optimization and Parametric Study of Cooperative Salvo Attack Using Particle Swarm Optimization Algorithm

    , M.Sc. Thesis Sharif University of Technology Shahadati, Mohammad (Author) ; Saghafi, Fariborz (Supervisor)
    In this research work, several guidance laws have been utilized and validated, considering the contraints on the missslie seeker angle and maximum acceleration, in order to simultaneously intercept the so-called Close-in Weapon System (CIWS) by multiple missiles. First of all, the existing guidance laws for salvo-attack are reveiwed. Then, a simulation program has been developed and validated for the misslie and CIWS as a five and two degrees of freedom systems, respectively. Optimization of the system is then carried out by the method of Particle Swarm Optimization, considering the given constraints. In the next step, for the improvement of the optimized guidance law, paramertic study has... 

    Piece-wise Linear Approximation of Step Response for GSI Interconnects

    , M.Sc. Thesis Sharif University of Technology Benam, Majid (Author) ; Sarvari, Reza (Supervisor)
    Since interconnects are playing a very important role in today’s IC technology, introducing new models and approximations is vital to IC designers. In this dissertation, maxwell equations are introduced as they are the main equations governing transmission lines. Different methods to model interconnects are also presented. Moreover, because of the importance of the step response of a system, available methods for finding the step response of interconnects are briefly discussed. Some approximations are also described, which result in faster but not very accurate responses. Delay and noise in integrated circuit connections have been the subject of several investigations for a long time. Since... 

    Diagrammatic approach for constructing multiresolution of primal subdivisions

    , Article Computer Aided Geometric Design ; Volume 51 , 2017 , Pages 4-29 ; 01678396 (ISSN) Bartels, R ; Mahdavi Amiri, A ; Samavati, F ; Mahdavi Amiri, N ; Sharif University of Technology
    Elsevier B.V  2017
    It is possible to define multiresolution by reversing the process of subdivision. One approach to reverse a subdivision scheme appropriates pure numerical algebraic relations for subdivision using the interaction of diagrams (Bartels and Samavati, 2011; Samavati and Bartels, 2006). However, certain assumptions carried through the available work, two of which we wish to challenge: (1) the construction of multiresolutions for irregular meshes are reconsidered in the presence of any extraordinary vertex rather than being prepared beforehand as simple available relations and (2) the connectivity graph of the coarse mesh would have to be a subgraph of the connectivity graph of the fine mesh. 3... 

    Optimization-based gravity-assisted calibration and axis alignment of 9-degrees of freedom inertial measurement unit without external equipment

    , Article Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering ; Volume 234, Issue 2 , 2020 , Pages 192-207 Razavi, H ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Applicable in numerous fields, low-cost micro-electromechanical system inertial measurement units often require on-sight calibration by the end user due to the existence of systematic errors. A 9-degrees of freedom inertial measurement unit comprises a tri-axis accelerometer, a tri-axis gyroscope, and a tri-axis magnetometer. Various proposed multi-position calibration methods can calibrate tri-axis accelerometers and magnetometers to a degree. Yet the full calibration of a tri-axis gyroscope and axis alignment of all the sensors still often requires equipment such as a rate table to generate a priori known angular velocities and attitudes or relies on the disturbance-prone magnetometer... 

    Blade shape optimization of marine propeller via genetic algorithm for efficiency improvement

    , Article Proceedings of the ASME Turbo Expo ; Volume 5 , 2012 , Pages 235-242 ; 9780791844717 (ISBN) Taheri, R ; Mazaheri, K ; Sharif University of Technology
    In this paper, a numerical optimization method has been carried out to optimize the shape and efficiency of a propeller. For analysis of the hydrodynamic performance parameters, an extended vortex lattice method was used by implementing an open-source code which is called OpenProp. The method of optimization is a non-gradient based algorithm. After a trade-off between a few gradient-based and non-gradient based algorithms, it is found that the problem of being trapped in local optimum solutions can be easily solved by choosing nongradient based ones. Hence, modified Genetic algorithm is used to implement the so-called hydrodynamic performance analyzer code. The objective function is to... 

    Optimal relaying in a slotted aloha wireless network with energy harvesting nodes

    , Article IEEE Journal on Selected Areas in Communications ; Volume 33, Issue 8 , 2015 , Pages 1680-1692 ; 07338716 (ISSN) Moradian, M ; Ashtiani, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2015
    In this paper, we derive optimal policies for cooperation of a wireless node in relaying the packets of a source node, in a random access environment. In our scenario, the source node sends its packets by its harvested energy and the relay node exploits its harvested energy in relaying the source packets not detected successfully at the destination. The relaying policies determine whether the relay node accepts or rejects the unsuccessfully transmitted source packets and how the relay node prioritizes the accepted source packets to its own packets. The optimization goal is to minimize the average transmission delay of source packets with and without a constraint on the average transmission... 

    Design of mid-infrared ultra-wideband metallic absorber based on circuit theory

    , Article Optics Communications ; Volume 381 , 2016 , Pages 309-313 ; 00304018 (ISSN) Arik, K ; Abdollahramezani, S ; Farajollahi, S ; Khavasi, A ; Rejaei, B ; Sharif University of Technology
    Elsevier B.V  2016
    An ultra-broadband absorber of light is proposed by using periodic array of ultra-thin metallic ribbons on top of a lossless quarter-wavelength dielectric spacer placed on a metallic reflector. We propose a fully analytical circuit model for the structure, and then the absorber is duly designed based on the impedance matching concept. As a result, normalized bandwidth of 99.5% is realized by the proposed absorbing structure in mid-infrared regime. Performing a numerical optimization algorithm, we could also reach to normalized bandwidth of 103%  

    Numerical optimization and inverse study of a microfluidic device for blood plasma separation

    , Article European Journal of Mechanics, B/Fluids ; Volume 57 , 2016 , Pages 31-39 ; 09977546 (ISSN) Shamloo, A ; Vatankhah, P ; Bijarchi, M. A ; Sharif University of Technology
    Elsevier Ltd  2016
    In this paper, a passive microfluidic device for continuous real time blood plasma separation has been studied and optimized. A numerical model is used to solve both the fluid flow and the particles confined within it. Red blood cells are considered as particles with diameter of 7μm. A parametric study is performed in order to characterize the effect of different parameters on separation and purity efficiency. In this study, four different variables were introduced to design the microfluidic device for blood plasma separation including: the angle between the daughter channels and the main channel, the widths, the diffuse angle and the number of daughter channels. Results show that the... 

    Outpatient appointment systems in healthcare: A review of optimization studies

    , Article European Journal of Operational Research ; Volume 258, Issue 1 , 2017 , Pages 3-34 ; 03772217 (ISSN) Ahmadi Javid, A ; Jalali, Z ; Klassen, K. J ; Sharif University of Technology
    Elsevier B.V  2017
    Outpatient appointment scheduling problems have recently gained increasing attention. This paper provides a comprehensive review of recent analytical and numerical optimization studies that present decision-support tools for designing and planning outpatient appointment systems (OASs). A structure for organizing the recent literature according to various criteria is provided, including a framework that classifies decisions at the strategic, tactical, and operational levels. The OAS literature is evaluated from four perspectives: problem settings, environmental factors, modeling approaches, and solution methods. In addition, research gaps and areas of opportunity for future research are... 

    Development a planar neuro-musculoskeletal arm model in post-stroke patients

    , Article 26th National and 4th International Iranian Conference on Biomedical Engineering, ICBME 2019, 27 November 2019 through 28 November 2019 ; 2019 , Pages 236-241 ; 9781728156637 (ISBN) Nikzad Goltapeh, A ; Asghari, M ; Behzadipour, S ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2019
    Computational models of the central nervous system after a stroke helps to reveal the physiological mechanisms that may have strong impacts on the neuro-motor rehabilitation approaches. This paper studies the stroke subject's motor control mechanism in reaching movements by extending the previous study by incorporating the kinematics of motion as well as neural disconnection between the muscles and the CNS to further develop a planar patient specific neuro-musculoskeletal model of arm. The developed model was calibrated to eight post-stroke individuals by altering the Muscle Significance Factors (MFS) using numerical optimization to match the simulated motions with those measured... 

    A broad reconsideration of anti-vortex film cooling method using numerical optimization and an improved heat-flux model

    , Article International Journal of Heat and Fluid Flow ; Volume 89 , 2021 ; 0142727X (ISSN) Chaharlang Kiani, K ; Mazaheri, K ; Sharif University of Technology
    Elsevier B.V  2021
    This paper represents the detailed results of an evolutionary optimization framework towards the exploration of vortex mechanisms leading to effective anti-vortex film cooling. In this regards, several arrangements of triple cooling holes were studied on flat and curved geometries using differential-evolution optimization algorithm and a modified Reynolds-stress based flow solver. Depending on the flow and geometric parameters, four distinct types of vortex interaction with different cooling mechanisms were identified. The vortex-trapping mechanism, observed in the optimized upstream arrangement acts through imposing a mild downwash over the main counter-rotating vortex pair and provides the... 

    On the reduction of the number of required motions in the dynamic analysis using a refined spectral matching

    , Article Earthquake and Structures ; Volume 21, Issue 4 , 2021 , Pages 425-444 ; 20927614 (ISSN) Harati, M ; Mashayekhi, M ; Mohammadnezhad, H ; Jaberi, H ; Estekanchi, H. E ; Sharif University of Technology
    Techno-Press  2021
    This study aims to show the efficiency of a proposed spectral matching technique for the reduction of required ground motions in the dynamic time history analysis. In this non-stationary spectral matching approach, unconstrained optimization is employed to adjust the signal to match a target spectrum. Adjustment factors of discrete wavelet transform (DWT) coefficients associated with the signals are then considered as decision variables and the Levenberg-Marquardt algorithm is employed to find the optimum values of DWT coefficients. This matching algorithm turns out to be quite effective in the spectral matching objective, where matching at multiple damping ratios can be readily achieved.... 

    Optimal Control of Spacecraft on the Earth-Moon Lagrange Point Orbits considering Sun and other Planets and Elliptic Orbit Perturbations

    , M.Sc. Thesis Sharif University of Technology Ghorbani, Mehrdad (Author) ; Assadian, Nima (Supervisor)
    In this thesis, optimal station keeping of spacecraft on the closed-orbits near the Earth-Moon Lagrange points has been investigated. Lagrange points L1 and L2 are unstable equilibrium points of the circular restricted three-body problem (CRTBP), and periodic orbits near them are the destination of modern missions. However, perturbations resulting from the gravitational forces of the Sun and the planets and the eccentricity of the orbit of the Moon around the Earth make the Lagrange point unstable, even L4 and L5, which are stable in CRTBP. The most suitable choice for spacecraft mission near the collinear Lagrange points is the Halo and other closed-orbits around them, which need... 

    Multi-point optimization of lean and sweep angles for stator and rotor blades of an axial turbine

    , Article Proceedings of the ASME Turbo Expo ; Vol. 2C, issue , 2014 Asgarshamsi, A ; Hajilouy-Benisi, A ; Assempour, A ; Pourfarzaneh, H
    In this research, numerical optimization of the rear part of a gas turbine, consisting of a single stage axial turbine is carried out. Automated aerodynamic shape optimization is performed by coupling a CFD flow simulation code with the Genetic Algorithm. An effective multi-point optimization method to improve efficiency and/or pressure ratio of the axial turbine is performed. Some variations of optimization parameters such as lean and sweep angels of stator and rotor blades are accomplished. Furthermore, during the optimization process, three-dimensional and turbulent flow field is numerically investigated using a compressible Navier-Stokes solver. The gas turbine experimental... 

    Genetic algorithm-based numerical optimization of powder compaction process with temperature-dependent cap plasticity model

    , Article International Journal of Advanced Manufacturing Technology ; Volume 64, Issue 5-8 , 2013 , Pages 1057-1072 ; 02683768 (ISSN) Keshavarz, S ; Khoei, A. R ; Molaeinia, Z ; Sharif University of Technology
    In this paper, a shape optimization technique is presented for the cold and hot isostatic pressing of metal powders based on the genetic algorithm (GA) approach. The GA technique is used to obtain the desired optimal compacted component by changing the boundaries of component and verifying the prescribed constraints. The coupled thermomechanical analysis of hot isostatic pressing is employed for metal powders during densification process. The numerical modeling of hot powder compaction simulation is performed based on the large deformation formulation, temperature-dependent cap plasticity model, and frictional contact algorithm. The modified cap plasticity takes the temperature effects into... 

    A new nonlinear optimization method for parameter estimation in enzyme kinetics

    , Article Energy Sources, Part A: Recovery, Utilization and Environmental Effects ; Volume 37, Issue 12 , 2015 , Pages 1275-1281 ; 15567036 (ISSN) Heydari, A ; Fattahi, M ; Khorasheh, F ; Sharif University of Technology
    Taylor and Francis Inc  2015
    A new nonlinear optimization method for parameter estimation in Michaelis-Menten equation has been developed. This method is based on a special mathematical form of the Michaelis-Menten equation to finding the best fit of the linear plot of R versus S/(S + Km) where R, S, and Km are the reaction rate, concentration of substrate, and the Michaelis-Menten constant, respectively. By setting the intercept of this line to zero, the proper Km will be obtained and the slope would give the saturation rate, Vmax. As a result, a nonlinear, two-parameter optimization is simplified into finding the roots of a nonlinear equation. Generated data sets were used... 

    Muscle synergies based on a biomechanical biaxial isometric shoulder model minimizing fatigue

    , Article ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, ESDA2010, 12 July 2010 through 14 July 2010 ; Volume 1 , 2010 , Pages 797-804 ; 9780791849156 (ISBN) Nassajian Moghadam, M ; Aminian, K ; Asghari, M ; Parnianpour, M ; Sharif University of Technology
    In this study we utilize the concept of synergy formation as a simplifying control strategy to manage the high number of degrees of freedom presented in the maintenance of the posture of the shoulder joint. We address how to find the muscle synergy recruitment map to the biomechanical demands (biaxial external torque) during an isometric shoulder task. We use a numerical optimization based shoulder model to obtain muscle activation levels when a biaxial external isometric torque is exposed at the shoulder glenohumeral joint. In the numerical simulations, different shoulder torque vectors parallel to the horizontal plane are considered. For each selected direction for the torque, the... 

    Numerical optimization and manufacturing of the impeller of a centrifugal compressor by variation of splitter blades

    , Article ASME Turbo Expo 2016, Turbomachinery Technical Conference and Exposition, 13 June 2016 through 17 June 2016 ; Volume 8 , 2016 ; 9780791849866 (ISBN) Moussavi Torshizi, S. A ; Hajilouy Benisi, A ; Durali, M ; International Gas Turbine Institute ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME) 
    Design and optimization of centrifugal compressors, based on main blades configuration of impeller have been vastly discussed in open literature, but less researches have addressed splitters. In this research, the impeller of a commercial turbocharger compressor is investigated. Here, profiles of main blades are not changed while the effect of changing the configuration of splitters is studied. An optimization study is performed to find the best configuration using genetic algorithm over a complete operating curve of the compressor. CFD codes with experimental support are used to predict the compressor performance. Quantumetric tests beside destructive analysis of two impellers are... 

    Numerical optimization of laboratory combustor geometry for NO suppression

    , Article Applied Thermal Engineering ; Volume 102 , 2016 , Pages 1328-1336 ; 13594311 (ISSN) Mazaheri, K ; Shakeri, A ; Sharif University of Technology
    Elsevier Ltd  2016
    In this article, geometry optimization of a jet stirred reactor (JSR) combustor has been carried out for minimum NO emissions in methane oxidation using a combined numerical algorithm based on computational fluid dynamics (CFD) and differential evolution (DE) optimization. The optimization algorithm is also used to find a fairly accurate reduced mechanism. The combustion kinetics is based on a five-step mechanism with 17 unknowns which is obtained using an optimization DE algorithm for a PSR-PFR reactor based on GRI-3.0 full mechanism. The optimization design variables are the unknowns of the five-step mechanism and the cost function is the concentration difference of pollutants obtained...