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    Optimization of freestream flow effects on thrust shock vector control nozzle

    , Article Journal of Applied Fluid Mechanics ; Volume 11, Issue 2 , 2018 , Pages 361-374 ; 17353572 (ISSN) Forghany, F ; Taeibe Rahni, M ; Asadollahi Ghohieh, A ; Sharif University of Technology
    Isfahan University of Technology  2018
    Abstract
    The present study attempted to utilize a computational investigation to optimize the external freestream flow influence on thrust-vector control. The external flow with different Mach numbers from 0.05 to 1.1 and with optimum injection angles from 60° to 120° were studied at variable flow conditions. Simulation of a converging-diverging nozzle with shock-vector control method was performed, using the unsteady Reynoldsaveraged Navier-Stokes approach with Spalart-Allmaras turbulence model. This research established that freestream flow and fluidic-injection angle are the significant parameters on shock-vector control performance. Computational results indicate that, increasing freestream Mach... 

    Analysis of carrier dynamic effects in transistor lasers

    , Article Optical Engineering ; Volume 51, Issue 2 , December , 2012 ; 00913286 (ISSN) Horri, A ; Mirmoeini, S. Z ; Faez, R ; Sharif University of Technology
    2012
    Abstract
    We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated  

    Comprehensive study on the results of tension leg platform responses in random sea

    , Article Journal of Zhejiang University: Science ; Volume 7, Issue 8 , 2006 , Pages 1305-1317 ; 10093095 (ISSN) Tabeshpour, M. R ; Golafshani, A. A ; Seif, M. S ; Sharif University of Technology
    2006
    Abstract
    Compliant offshore structures are used for oil exploitation in deep water. Tension leg platform (TLP) is a suitable type for very deep water. The nonlinear dynamic response of TLP under random sea wave load is necessary for determining the maximum deformations and stresses. Accurate and reliable responses are needed for optimum design and control of the structure. In this paper nonlinear dynamic analysis of TLP is carried out in both time and frequency domains. The time history of random wave is generated based on Pierson-Moskowitz spectrum and acts on the structure in arbitrary direction. The hydrodynamic forces are calculated using the modified Morison equation according to Airy's linear... 

    Dynamic Response of a Finite Beam Subjected to a Moving Oscillator

    , M.Sc. Thesis Sharif University of Technology Mottahedin, Aida (Author) ; Vafaei, Abolhassan (Supervisor)
    Abstract
    Vibration of a stationary structure excited by another structure moving on the surface of the stationary Structure is very common in engineering, such as vibration of bridges or railway track under travelling vehicles. In the simplest case, the moving structure maybe modeled as a constant load or a mass or an oscillator, in this case the moving mass is attached to the structure either by a spring or by a mass-spring assembly.The model of a moving mass brings some improvements to the model of the moving load where there is no inertia effect. However, the relative displacement between the moving structures and the beam cannot be considered in the moving mass model. A more appropriate model in... 

    Simulation of deep level traps effects in quantum well transistor laser

    , Article Journal of Computational Electronics ; Volume 12, Issue 4 , August , 2013 , Pages 812-815 ; 15698025 (ISSN) Horri, A ; Faez, R ; Sharif University of Technology
    2013
    Abstract
    In this paper, we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analyze is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporate the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

    Analysis of deep level trap effects in transistor lasers

    , Article Lasers in Engineering ; Volume 25, Issue 5-6 , 2013 , Pages 313-322 ; 08981507 (ISSN) Horri, A ; Mirmoeini, S ; Faez, R ; Sharif University of Technology
    2013
    Abstract
    In this paper we present an analytical model to analyze the influence of deep level traps on the static and dynamic responses of transistor laser (TL). Our analysis is based on analytically solving the continuity equation and rate equations including the effect of the deep level trap (DLT), which incorporates the virtual states as a conversion mechanism. The results of simulation show that the main characteristics of laser such as threshold current, quantum efficiency, output power, and modulation bandwidth are affected by total density of traps in the active region  

    Large signal analysis of double quantum well transistor laser

    , Article Optical and Quantum Electronics ; Volume 45, Issue 5 , 2013 , Pages 389-399 ; 03068919 (ISSN) Horri, A ; Faez, R ; Sharif University of Technology
    2013
    Abstract
    In this paper, we present an analytical model for the large-signal analysis of the double quantum well (DQW) transistor laser. Our model is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. By using the presented model, effects of barrier width on DQW transistor laser static and dynamic performances are investigated. Also the static and dynamic responses of DQW transistor lasers are compared with single quantum well ones. Simulation results are in agreement with the numerical and experimental results reported by other researchers  

    Studying higher mode effects on the performance of nonlinear static analysis methods considering near-fault effects

    , Article KSCE Journal of Civil Engineering ; Volume 17, Issue 2 , March , 2013 , Pages 426-437 ; 12267988 (ISSN) Ghahari, S. F ; Moradnejad, H. R ; Rouhanimanesh, M. S ; Sarvghad Moghadam, A ; Sharif University of Technology
    2013
    Abstract
    Daily development in civil engineering arena and the importance of economical aspects in the design of structures have motivated the engineers to shift their approaches from designing upon strength to designing upon performance. This is of more importance regarding the forces induced by earthquakes which have unpredicted and random nature. However, it is not possible to design or assess exactly the structural performance against strong ground motion using analytical methods which are applied for static loads and therefore precise dynamic analysis methods are needed. Despite significant progress in the analytical methods and engineering software, using nonlinear time history analysis is very... 

    Conceptual study on dynamic response of semi-submersible

    , Article Proceedings of the Institution of Civil Engineers: Maritime Engineering ; 2021 ; 17417597 (ISSN) Tabeshpour, M. R ; Hajnoruzi, F ; Sharif University of Technology
    ICE Publishing  2021
    Abstract
    Hydrodynamic analysis of semi-submersible offshore structures has been the topic of many researches performed numerically and experimentally in the past. In this paper, the effect of structure alignment and mooring lines on dynamic behaviour of semi-submersible platforms has been taken into account. The contribution of pitch and roll in heave motion of side points is also investigated. Mooring lines are connected to semi-submersible at sides and therefore total displacement of side points is related to total displacement of mooring lines and total tension as well. A three dimensional boundary element model of Amirkabir platform in Caspian Sea is implemented using boundary element method... 

    Studying Dynamic Response of Landslides Using 1g Shaking Table Tests and Comparing with Analytical Methods

    , M.Sc. Thesis Sharif University of Technology Rajabigol, Morteza (Author) ; Jafarzadeh, Fardin (Supervisor)
    Abstract
    Evaluation of seismic slope stability is very important because it has a decisive role in stimating the earthquake damages. According to the past studies, medium to large earthquakes usually cause thousands landslides and many casulties and financial damages. Since nearly half a century ago, several methods have been developed for predicting the occurrence of landslides and permanent movements, but due to the influnce of many parameters on the seismic stability of the slopes further researches is needed.
    In present study, to investigate the dynamic behavior of the slopes, four physical models of slopes had been made on shaking table in Sharif university of technology. These slopes have 3... 

    Prediction of dynamic response of machine tool by sub-structure analysis

    , Article Eighth International Conference on Vibrations in Rotating Machinery, Swansea, 7 September 2004 through 9 September 2004 ; Volume 2004 2 , 2004 , Pages 141-151 ; 13561448 (ISSN) Movahhedy, M. R ; Gerami, J. M ; Sharif University of Technology
    2004
    Abstract
    Stability analysis of machine tool requires determining of frequency response function (FRF) of spindle. Since this response is changed with a change of tool, Receptance coupling sub-structuring analysis may be used to couple the tool and spindle FRFs. A major difficulty in this regard is the determination of joint model between the two sub-structures. In particular, the identification of rotational DOFs at joints is difficult. In this research, a joint model which accounts for rotational DOFs is proposed and verified which does not require any rotational DOF measurement on machine tool. An optimization method based on genetic algorithm is employed to find parameters of the joint model.... 

    Investigation of Dynamic Response of Shallow Foundations on Sandy Soil to Horizontal Harmonic Loading by Physical Model Tests

    , M.Sc. Thesis Sharif University of Technology Ghassemi, Ramin (Author) ; Jafarzadeh, Fardin (Supervisor)
    Abstract
    The most important step in current dynamic analysis of machine foundations is determining dynamic impedance functions. Impedance functions are defined as ratios of applied force or moment to induced displacement or rotation angle of foundation. In this research, horizontal dynamic response of foundation on homogeneous halfspace was investigated using physical modeling. Soil medium was built in a 1mx1mx0.8m steel box whose interior walls were covered by 0.1m of sawdust (a material with high damping). In order to prevent possible reflection of waves, this cover was extended to the box bottom with 0.2 m thickness. Sand raining method was used to build soil medium. In this method, with... 

    Structural Design Optimization and Dynamics Analysis of Non-Uniform Thickness Laminated Beam Reinforced with Nano-Particles

    , M.Sc. Thesis Sharif University of Technology Momeni, Saman (Author) ; Zabihollah, Abolghassem (Supervisor) ; Selk Ghafari, Ali (Co-Advisor)
    Abstract
    Non-uniform laminated beams are being used in many engineering applications as primary elements. Helicopter blades, wind turbine blades and robot arms are examples of applications of these structures, in which the high stiffness-to-weight ratio and the non-uniform geometry are of high importance. Changing the thickness in laminated structures is a big challenge in fabrication view as different tapering configurations may significantly alter the stiffness of the structure. Thus, increasing the stiffness and dynamics characteristics of tapered beams with simple configuration is of high importance. The present work aims to investigate the effect of adding nano particles in resin during the... 

    Investigation onthe Seismic Behavior of Steel MRF with Shape Memory Alloy Equipped Connections

    , M.Sc. Thesis Sharif University of Technology Farhidzadeh, Ali Reza (Author) ; Rahimzadeh Rofooei, Fayyaz (Supervisor)
    Abstract
    Various types of passive energy dissipating systems have been introduced for controlling the seismic response of structures during the last few decades. A number of these control devices have been practically implemented in different structures all over the world. Shape Memory Alloy (SMA) is among those passive control systems that have attracted a large attention due to its innate features, i.e., recovering the induced residual strains upon unloading (superelastic effect) or by heating (shape memory effect).This study investigates the seismic behavior of a set of steel structural models with different number of stories and eccentricities equipped with a type of fixed SMA connections. In the... 

    Numerical Study of Dynamic Response of Shallow Foundations to Vertical Loads Induced by Machines

    , M.Sc. Thesis Sharif University of Technology Pourdeilami, Abbas (Author) ; Ahmadi, Mohammad Mehdi (Supervisor)
    Abstract
    The main purpose of designing machine foundation is to limit its motion to such an amount that not to prevent the perfect workability of machine, not to let the foundation strains exceed the elastic limit and also not to disturb the persons working around the machine. The key note in successfull design of machine foundation, is to precisely analyse the response of foundation to dynamic loads induced by machine operations.The numerical study of shallow foundations response to vertical harmonic loads induced by machinaries have been discussed in this investigation.To aim this purpose, FLACD3D has been utilized in order to 3 dimensionally analyse a continuum medium comprising soil-foundation or... 

    Nonlinear Vibration Analysis of Non-Uniform Beam in two Lateral Directions by Multiple Scales Method: Application in Wind Turbine

    , M.Sc. Thesis Sharif University of Technology Karimi, Behnam (Author) ; Moradi, Hamed (Supervisor)
    Abstract
    Environmental issues and energy crisis have led the world attention to the renewable energies; especially wind power, since they have low cost and high reliability. One of the most challenging areas of studying for wind power is to increase the capacity of wind turbines. As a result, over the years, wind turbines have got progressively larger. Vibration is one of the problems that reduces the life and efficiency of wind turbines; and the growing size of the blades has worsen this problem due to the importance of nonlinear effects in large scale wind turbines. Researchers have been constantly working on this issue in order to make the wind turbines more efficient. In this research, a... 

    Investigation of Dynamic Response of Soil Exposed to Surface Explosion Pressure Waves

    , M.Sc. Thesis Sharif University of Technology Khakdaman, Alireza (Author) ; Farhanieh, Bijan (Supervisor)
    Abstract
    Explosion in soil medium have been a favourite topic for researchers From many years ago. however Most of researchs studied the impact of surface explosion on Perimeter environment (like mine explosion) and effect of the parameters like soil material and water content on pressure waves progressing inside of soil have been lees paid attention. In present work firstly we derive the data necessary for soil dynamic response computer modelling using different soil models from various resources. Then the impact of surface explosion will be investigated soil internally, using Ansys Autodyn numerical modelling. Results show that with an increase in soil water content, pressure wave peak overpressure... 

    Dynamic Response of Concrete Funicular Shells under Impulse Loads

    , M.Sc. Thesis Sharif University of Technology Sabermahany, Hadi (Author) ; Vafai, Abolhassan (Supervisor) ; Mofid, Massoud (Co-Advisor)
    Abstract
    Reinforced concrete shells are widely used to cover the small to large area with more aesthetics at minimum cost. Shell structures carries load through their shape rather than material strength. Funicular shells are special type of shells that their shape is obtained so that stresses be compressive under a special load (for shell, this load is its dead weight). This study deals with forced vibration of funicular shells on a rectangular ground plan under impulse loads using shallow shells theory. Two boundary conditions, simply supported and clamped, are considered. Displacement components are product of position and time functions. The analysis is based on the expansion of displacement... 

    Evaluating the Usage of Polystyrene Protection Behind the Buried Pipelines on Dynamic Response of Soil Slope with using a 1g Shaking Table

    , M.Sc. Thesis Sharif University of Technology Azargoon, Amirbahador (Author) ; Jafarzadeh, Fardin (Supervisor)
    Abstract
    Studying of slope stability under dynamic loading such as earthquakes is one of the critical issues. This importance is attributed to many of the slopes are located in urban areas, either around them or in the important buildings and infrastructure. Thus, evaluation of slope’s behavior is very essential. On the other hand, preparing fundamental arrangements to improve the current situation, surrounding and buried areas in the slope is necessary.
    In this study, a physical model of Tehran's slopes by 0.1 ratio with pipes that have been retrofitted by plastofoam developed. This model was tested on the shaking table under dynamic loading. The dimensions of the slope were 1 meter width, 3... 

    Extending the inverse receptance coupling method for prediction of tool-holder joint dynamics in milling

    , Article Journal of Manufacturing Processes ; Volume 14, Issue 3 , 2012 , Pages 199-207 ; 15266125 (ISSN) Rezaei, M. M ; Movahhedy, M. R ; Moradi, H ; Ahmadian, M. T ; Sharif University of Technology
    Elsevier  2012
    Abstract
    Recently, receptance coupling substructure analysis (RCSA) is used for stability prediction of machine tools through its dynamic response determination. A major challenge is the proper modelling of the substructures joints and determination of their parameters. In this paper, a new approach for predicting tool tip FRF is presented. First, inverse RCSA formulation is extended so that the holder FRFs can be identified directly through experimental modal tests. The great advantage of this formulation is its implementation in arbitrary point numbers along joint length. Therefore, in comparison with previous inverse RCSA approaches, a more realistic joint model can be considered. In addition, due...