Sharif Digital Repository

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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... 

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...