Search for: dynamic-response
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    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)
    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... 

    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)
    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... 

    Performance Evaluation of Tuned Liquid Column Damper (TLCD)on Dynamic Response Mitigation of Tension Leg Platform

    , M.Sc. Thesis Sharif University of Technology Nikmehr, Latif (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    In recent decades due to declining reserves of fossil fuels on land and in shallow water areas, exploration and exploitation of oil and gas from deeper seas and oceans are rapidly making progress and since there are huge volumes of oil and gas reserves in deep waters of the Caspian Sea bed, in order to fulfill the purpose of oil exploration and exploitation in all sectors of the Caspian Sea, it seems mandatory to study in the field of platforms required for use in this area. One of these platforms is Tension Leg Platform with mooring lines called tendons that directly connected to the seabed. High axial stiffness makes this type of mooring lines constrained the vertical degrees of freedom... 

    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)
    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... 

    Stability and Dynamic Response of Tension Leg Platform in Damaged Condition (Tendon Removed)

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Mohammad Reza (Author) ; Tabeshpour, Mohammad Reza (Supervisor)
    The tension leg platform is one of the compliant structures which are generally utilized for deep water oil explorations. With respect to the horizontal degrees of freedom, it behaves like a floating structure moored by vertical tethers which are pretension due to the excess buoyancy of the platform, whereas with respect to vertical degrees of freedom it is stiff and resembles a fixed structure and is not allowed to float freely. A sudden disconnection of a tendon causes a change of stiffness and unbalance of forces and moments of the total system. The objective of this study is experimental and numerical investigation on behavior of ISSC TLP. Experiments were performed in the National... 

    Dynamic Response of a Finite Beam Subjected to a Moving Oscillator

    , M.Sc. Thesis Sharif University of Technology Mottahedin, Aida (Author) ; Vafaei, Abolhassan (Supervisor)
    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... 

    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)
    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... 

    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)
    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... 

    Vibration Based Health Monitoring for Damage Detection of Composite Laminates

    , M.Sc. Thesis Sharif University of Technology Ghaffari, Hamid Reza (Author) ; Zabihollah, Abolghasem (Supervisor)
    Development of composite materials is one of the boldest technological advances of the last half of the twentieth century. This is due to their specific characteristics mostly considerably high strength-to-weight ratio, compared to metals and their highly customizing properties for different applications which make them a suitable material to be used in variety of domain from aerospace and automobiles to medical and sport equipments. Multi-stable asymmetrical laminates and non-uniform thickness laminated composite beams are being used as structural elements in a wide range of advanced engineering applications. Multi-stable asymmetrical laminates can be snapped between two or more geometries... 

    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)
    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... 

    Thermo-mechanical Modeling of Angular Contact Ball-Bearings in High Speed Machine Tool Spindles

    , M.Sc. Thesis Sharif University of Technology Zahedi, Ali (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Machining in its general concept forms the major part of manufacturing processes regarding time and cost. Therefore any progress in machining techniques would be well beneficial. High speed machining is one of the recent concepts in machining technology which has attracted much attention and effort. But high speed spindles as the main part of high speed machines, have been notorious for their lack of reliability and sudden failure which originates mostly from thermal problems. In order to ensure reliable operation of spindles it is necessary to predict thermo-mechanical behavior of machine-tool spindles. The major sources of heat in a spindle are angular contact ball bearings (the most... 

    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)
    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... 

    Low-velocity Impact Response of FML Beams with Considering Plasticity of Metal

    , M.Sc. Thesis Sharif University of Technology Rashedi, Hossein (Author) ; Koochakzadeh, Mohammad Ali (Supervisor)
    In this thesis an analytical model is applied to the dynamic response of fiber-metal laminate beams subjected to low-velocity impact. By using quasi-static consider-tions, a static model is developed using first order shear deformation beam theory and minimum total potential energy. In the next step, this static model is applied to the one degree of freedom non-linear spring-mass system for developing a model to predict dynamic response of low-velocity impact with the inclusion of material plasticity. By new explicit and simple expression, load-deflection curve, velocity-deflection curve, force-time history and deflection-time history can be derived. By using this analytical approach... 

    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)
    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... 

    Development of Inverse Vibration Technique for Damage Detection of Offshore Jacket-type Platforms

    , Ph.D. Dissertation Sharif University of Technology Haeri, Mohammad Hassan (Author) ; Golafshani, Ali akbar (Supervisor) ; Mohtasham Dolatshahi, Kiarash (Supervisor)
    In this dissertation a new approach is introduced for damage detection in offshore jacket platforms. The procedure uses the measured ambient vibration responses and the corresponding readable natural frequencies and mode shapes of the structural systems. Since offshore platforms are composed of heavy topsides supported by jacket structures, participation of the first mode is dominant in each direction in the response of the structure under field excitations. Moreover, ambient vibrations such as wave loads and boat impacts only excite the first modes of the structure. Therefore, it is difficult to find higher modes and the pertinent frequencies by use of accelerometers data. The introduced... 

    Dynamic Analysis of Floating Offshore Wind Turbines

    , M.Sc. Thesis Sharif University of Technology Imani, Hassan (Author) ; Abbaspour Tehrani Fard, Madjid (Supervisor)
    Use of wind energy is always one of the aims of man during the times. He used this energy for wheat grinding and sometimes for marine transportations. During recent decades, technology development forced human to harness this energy and use that for electricity production by employing onshore wind turbines. However, the modern engineering employed different arms of engineering such as marine engineering, civil engineering, mechanical engineering and electrical engineering for designing and installation of offshore wind turbines. But, huge water depths in offshore regions make the fixed leg turbines to be unacceptable solution. So, the floating wind turbines with mooring lines which attach... 

    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)
    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... 

    A semi-active SMA-MRF structural stability element for seismic control in marine structures

    , Article Applied Ocean Research ; Volume 100 , 2020 Zareie, S ; Zabihollah, A ; Sharif University of Technology
    Elsevier Ltd  2020
    The stability and integrity of structures under indeterminant external loadings, particularly earthquakes, is a vital issue for the design and safe operation of marine and offshore structures. Over the past decades, many structural control systems, such as viscous-based systems, have been developed and embedded in marine and offshore structures, particularly oil platforms to maintain the stability and mitigate the seismic hazards. Rapid improvement in intelligent materials, including shape memory alloys (SMAs) and Magnetorheological fluid (MRF), have led to the design and development of efficient structural control elements. The present work aims to establish a framework for the structural... 

    A new power management control strategy for a MV microgrid with both synchronous generator and inverter-interfaced distributed energy resources

    , Article IEEE International Symposium on Industrial Electronics ; 1- 4 June , 2014 , pp. 2529-2534 ; ISBN: 978-147992399-1 Zangeneh, M ; Hamzeh, M ; Mokhtari, H ; Karimi, H ; Sharif University of Technology
    Control strategies of a microgrid which includes both synchronous generators and converter-based distribution generation (DG) units must be designed such that effective operation of the microgrid is achieved. The main objective of this paper is to develop a high performance control strategy for an islanded medium voltage (MV) microgrid consisting of inverter and non-inverter interfaced DG units. A new control method for the synchronous generator in an islanded microgrid is proposed based on a virtual droop scheme. The proposed strategy can effectively manage the real and reactive powers of the microgrid among the inverter and non-inverter based DG units. The steady state and dynamic... 

    Thermo-mechanical modeling of high speed spindles

    , Article Scientia Iranica ; Volume 19, Issue 2 , 2012 , Pages 282-293 ; 10263098 (ISSN) Zahedi, A ; Movahhedy, M. R ; Sharif University of Technology
    Prediction of the thermo-mechanical behavior of machine-tool spindles is essential in the reliable operation of high speed machine tools. In particular, the performance of these high speed spindles is dependent on their thermal behavior. The main source of heat generation in the spindle is the friction torque in angular contact ball bearings. This paper presents an effort to develop a comprehensive model of high speed spindles that includes viable models for the mechanical and thermal behavior of its major components, i.e., bearings, shaft and housing. Spindle housing and shaft are treated as six-degree-of-freedom Timoshenko beam elements. Bearings are modeled as two-node elements with five...