Sharif Digital Repository

Evolution of electrical devices and the need for wireless sensor and remote control has led to extensive research in field of energy harvesting. Regarding this approach, most studies devoted to use of piezoelectric effect in converting the dissipative vibration energy into usable electrical energy. Despite extensive progress made in this field of engineering, there were no significant growth in analytical solution and implementation of mathematical equations related to dynamic and electricity of piezoelectric harvester of beams with different geometries. The main focus of this thesis is solving constitutive and coupled electromechanical equations of piezoelectric harvester related to a... 

Vibration based energy harvesting is the process of trapping and collecting vibrational energy from ambient sources which seem unusable at first sight. The smart materials with the capability of coupling two different fields can be used in converting vibrational energy to electrical one. One of this smart material which has been taken into account recently is the Magnetic Shape Memory Alloy (MSMA) and it can couple the magnetic and mechanical fields. In MSMAs the total magnetization vector changes with the application of stress and make it possible to harvest energy from Faraday law’s of induction. An important phenomena that exist in MSMA is the dependency of magnetization-strain behavior... 

The need to supply energy of low voltage electronic circuits such as sensors and wireless systems has attracted many researchers in recent years. As a solution to this problem, the energy needed for electronic devices can be obtained from the surrounding environment. An important part of energy harvesters are the systems that use vibrating energy of mechanical devices known as vibration power generators. Most linear vibration generators are systems that operate in resonance mode. As the frequency of the environment moves away from the natural frequency of the generator, the amount of converted energy decreases significantly. For this reason, some solutions are needed to solve this problem. ... 

Having unique characteristic behaviors of Shape memory alloys (SMAs) known as shape memory effect (SME), and superelasticity (SE), make them an appropriate choice for innovative engineering applications. Optimum design of SMA applications, calls for constitutive models and finite element simulations. It is evident that using structural elements (bar, beam, plate, shell) considerably reduces computational cost (CPU time) when compared to continuum elements. Therefore, structural elements are usually preferred in the early stages of design process. In this thesis, we simulate shape memory based structures using beam elements.Up to now, we have studied phenomenological constitutive models that... 

A new eccentrically braced system is discussed. In this system which Named “eccentrically braced frame with vertical link”, the braces is connected to vertical link, instead of floor beam. The vertical link acts as a ductile energy-dissipating element, allowing the rest of the construction such as floor beams, braces and columns remain in the elastic range. In this paper, a parametric study is performed on sample frames with push-over analysis. In these analysis, the efficacy of the variation of link length, link area and the position of the link beam, is studied. The results showed that, the most important effective parameters in improvement of inelastic behavior of frame is decreasing of... 

The behavior of a beam under moving mass has been always interested in the dynamic of structures. In this study, the dynamic response of beam and plate with general boundary conditions under moving mass were investigated using the Dynamic Green Function. Since the majority of previous studies did not consider the Coriolis acceleration, therefore, this acceleration was used in the present study. Boundary conditions are modeled by the rotational and translational restraint. By moving close to the spring constants of the rotational and translational restraint to extreme values (zero and/or infinity), the boundary conditions can be attained for the desired combinations of end boundary conditions... 

In the first part of this thesis, the linear and nonlinear governing differential equations of motion of an inclined Euler-Bernoulli beam are used by tacking into account the effect of beam’s mid-plane stretching. Then nonlinear coupled governing partial differential equations of vibrations by including rotation of cross section, longitudinal and transverse displacements in the Timoshenko beam theory on Pasternak foundation under the act of moving concentrated force and as wll as moving mass are drived. To do this the energy method (Hamilton’s principle) based on the large deflection theory in conjuncture with the von-Karman relations is used. These equations are solved by applying... 

There are some important technologies for the 5th generation of wireless communication (or 5G) and one of them is transmitting signals by millimeter waves or mmWave. Since mmWave antennas are so small and they have high frequencies, mmWave signals are highly directable. MmWave antennas can generate transmission patterns that have a number of beams directed in different directions with small beam width.In this thesis, we propose a scheduling scheme for the mmWave networks with directional antennas.Since using millimeter waves is one of the most important choices for 5G, designing an efficient transmission scheduling algorithm in these networks have been a quite big challenge. As there are... 

In this study, static and dynamic buckling of laminated composite beams resting on an elastic foundation under thermal and mechanical load is studied. Beam is resting on an elastic foundation with hardening/softening term. Nonlinear governing equations are obtained based on the energy method and are solved via the multi-term Galerkin method and the Newton-Raphson numerical method. Critical dynamic load is estimated by the Hoff Simitses criterion. The results are validated with the results of available articles in this field. In the following, the effects of different parameters of the problem on the results are examined. Results reveal that for a sufficiently stiff softening elastic... 

In this thesis, it is shown that by detuning the array peripheral elements, without using phase shifters, and locking the array to the common frequency there exists a phase difference between two adjacent elements which is constant along the array and is proportional to the amount of free running frequency detuning. By changing free running frequency and therefore resultant phase difference, one can control the array beam direction. Linear, ring, hexagonal and triangular array configurations have been analyzed so far. In this work we endeavor to explore a circular planar array with weak coupling. The aim is to yield an analytical relationship to determine the free running frequency of each... 

Structural defects such as cracks may be produced in structures and machineries under fatigue load operating conditions. The presence of crack can lead to catastrophic failures in certain conditions. The occurrence of cracks affects the dynamic and vibration behavior of the structure considerably. These vibrations can be used for identifying the cracks and appropriate actions can be taken to prevent more damage to the system. Therefore, in this thesis vibration analysis of a Timoshenko beam with a vertical and horizontal crack has been considered. A continuous model for vibration analysis of a beam with an open edge crack including the effects of shear deformation and rotary inertia has been... 

Nowadays binary sensors such as infrared sensors are vastly employed in industrial, commercial and general applications due to their simplicity and low price. Beam sensors are common type of these sensors which can detect objects when they cross its beam. Sequence of sensors which are crossed in a time order is called sensor word. Consider an object, produced sensor word shows the order which it has crossed the beams. If we have more than one object then sensor word is combination of all sensor words produced by all object. We need to separate each sensor word. In this research, sensor word is developed to Fixed-Charge Minimum Cost Maximum Flow Network type.In this case, the consequent... 

Long thin rectangular beams are used in many industrial engineering including railways, aerospace and etc. Beam subjected to moving mass is one of the classic problems in mechanics and vibrations of beams and have been studied by many researchers. In most of done works, the moving mass was assumed to be small compared to beam mass and only acceleration effect of mass was considered. Also in many of researches only bending of beams was studied. Moving mass imposes 2 type of force in the supporting beam, first one is weight and the other is due to motion of mass and contains lateral, coriolis and centrifugal acceleration effects. In addition, due to the particular geometry considered (narrow... 

During the past decade, micromachining technology has become available to fabricate micron-sized mechanical parts. The miniaturization of almost all types of devices and systems is arguably a greater opportunity for commercial profit and beneficial technological advances (e.g., micromechanical, microfluidic, microthermal, micromagnetic, microoptical and microchemical). However, instead of the traditional evolutionary engineering effort to reduce size and power while simultaneously increasing the performance of such a diverse set of systems, the field of microelectromechanical systems (MEMS) represents an effort to radically transform the scale, performance and cost of these systems by... 

This study considers the flutter analysis rotating blade of a turbo machinery made of magneto rheological elastomer core. The Smith theory is used for modeling the compressible subsonic flow. The classical Hamilton’s principle along with the assume mode method is used to set up the equations of motion. The validity of the derived formulation is confirmed through comparison with those obtained from the finite element software and the available results in the literature. Various parametric studies including the effects of applied magnetic field, core layer thicknesses, rotating speed, setting angle are examined for considered configuration of the rotating blade. The results show that the first... 

The issue of solid and fluid interaction in horizontal axis wind turbines with diameter of more than 120 meters is one of the most important researching subjects of this type of turbines. This issues needs quick and exact solutions because of the high computational cost of fluid and structural domains.In this research a quick method with acceptable accuracy has been suggested which is based on computational fluid dynamic to examine the aeroelastic behavior of rotor and wind turbine tower. The actuator disc method in two domains of axisymmetric and three-dimensional has been used to compute aerodynamic forces. For this purpose a code has been written in C++ to set down virtual momentum on... 

In this research, the effect of application of viscoelastic material with fractional derivatives pattern in aeroelastic stability analysis for a sandwich wing, has been examined. In order to study the wing’s aeroelastic behavior and the effect of inner layer on aeroelastic instability boundaries (fluttering), the wing is modeled as a cantilever sandwich beam with a fractional viscoelastic core. The Wagner approximation is used for applying the unstable aeroelastic loads. To obtain the characteristics and behaviors of the structure some assumptions including non-classical effects, are considered. These non-classical effects are the inner layer shear stress, the axial movements, the wing’s... 

Due to the use of rotor dynamics, in the rotating systems such as pumps, turbines and machine tool spindle gained special significance in recent decades and a growing need for rotating machines with high speed, leading to extensive research in this area. Due to instability in the dynamics of these systems, check the stability of the rotor system has been given special emphasis, so that studies and research in terms of models and methods allocated to this topic. The project analyzed the stability of a rotor that includes an elastic shaft is placed on the bearings as it is objective. From point of modeling, the rotor is modeled using Timoshenko beam theory and the rotor mounted on bearing with... 

Recently, there has been a great interest toward site–specific modeling of outdoor radio wave propagation. Wave propagation in very large environments compared to a wavelength builds up an important category of electromagnetic wave propagation problems which occurs in
versatile criteria from optical devices to long wireless microwave links. Well-known methods such as different ray tracing schemes used in these problems suffer from long execution time and great amount of needed memory. A new method has been proposed in this thesis to overcome such difficulties for high frequency wave propagation in large scale problems. The proposed method is based on tracing 3D vectorial Gaussian beam.... 

In this study, irregularities of the mode shapes are utilized to determine the delamination situation in a composite laminated beam. Modal analysis is used to obtain the mode shapes of the beam; afterwards, the mode shapes are filtered to extract their irregularities. Presence of any delamination and its situation (number, size and location along the length and thickness of the beam) affects the extracted irregularities. Here, detection of delamination is based on these irregularities of the mode shapes. One of the most important advantages of this method is that unlike many other similar methods, in many cases, the mode shapes of damaged structure are sufficient and the exact mode shapes...