Sharif Digital Repository

In the present work, the dynamic charactristics of an oil lubricated journal bearing are identified by experimental modal test. First other similar articles were studied. Then according to requrements and specifications of the bearing, a test bed is designed and constracted by existing technologies to perform tests and to collect required data. The test bed consists of several parts, including rotary shaft, stator, oil supply pack, dynamic force shaker and various sensors, which are constructed and assembled with very precise tolerances. In order to identify the dynamic coefficients of the bearing, the test process was performed using dynamic and static forces and collecting required data.... 

Chatter vibration is a major obstacle in high quality machining. This undesirable vibration decreases the production rate, surface quality, tool life and machine tool life. In the last few decades, a lot of models have been presented to predict chatter. Most of the models, whether linear or nonlinear, have focused on modeling of machine tool dynamics and either disregard the effective parameters of chip formation process or apply some of these parameters through simplified equations. In this research, a finite element simulation of chip formation is combined with the dynamics of machine tool to investigate chatter and its effective factors. The proposed approach, unlike common mathematical... 

Chatter in machining systems is a limiting factor of workpiece surface, tool and machine life and material removal rate. Because of this, studying and modeling of vibrations is very important in the machining. This study is much importer in the boring operation because boring bar's length to diameter ratio is very high and so it is very sensitive to vibrations. As we know, vibration characteristics of a machine change between its operating condition and its resting mode. Because of this it's better to study machine's vibrations when it's working. This study requires some methods that can find operating parameters of machine. The aim of this work is to find these parameters. For finding these... 

This thesis aims to provide a method for obtaining the dynamic properties, including stiffness and damping, of rolling bearings in radial and axial directions using an experimental approach. Experimental and laboratory methods such as modal testing, vibration testing, and static tests are recognized as practical approaches to obtain these properties. In this research, all three of these methods were employed to determine these properties. After studying the theoretical relationships governing bearing stiffness coefficients, a test setup was designed and constructed for conducting experiments. Subsequently, various tests were conducted, and data was collected, including shaft displacement... 

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... 

For measuring damping capacity of shape memory alloy, samples containing Fe- 27Mn-6Si-4Cr-4Ni were prepared. In order to produce the alloy 99% pure elemental powders were mixed and pressed in a matrix rod. The packed powders put in 15cc alumina crucibles were held in a 200 °C oven for 10 hours before they were melted inside two–layered alumina and graphite grucible an induction furnace. Resulting samples went under hot and cold rolling, thermomechanical treatment and were shaped into strips by wirecut. Chemical composition ascertainment, Tensile, bending, differential scanning calorimetry (DSC), micro hardness and modal tests were operated. Microstructural investigation was done using... 

This thesis examines the modal characteristics of the payload after connecting to the carrier via the adapter. Basically, the modal characteristics of a payload change after connection to the carrier due to the different stiffness of the coupling mechanism. In this report, it is attempted to split and model the assembly structural system into two substructures interconnected by the V band clamp mechanism. Then, each of the substructures analyze individually and the modal characteristics of the integrated system are extracted using the infrastructure coupling methods. The coupling method is the "Component Mode synthesis" (CMS) method and input data, dynamic and modal characteristics required... 

Cylindrical shells play an important role in a wide range of engineering applications such as mechanics, aerospace, marine engineering, and nuclear applications due to their high load-carrying capacity, light structure, and economic advantages. Because these structures are often made of high lengths and thin sheets, they are very prone to vibration, especially under the conditions that they play a role in the rotating state, which can cause failure. For the reasons mentioned, the vibration analysis of rotating cylindrical shells will be essential in engineering designs. In the present study, after introducing general concepts regarding the analysis of structural vibrations, previous research... 

In this thesis, we investigate the theoretical and experimental vibrations of a cylindrical shell with an electrorheological core. Magnetorheological and electrorheological fluids are the most suitable materials used in smart structures and have various applications in the automotive, aerospace, civil engineering, medical engineering and robotics industries. We use starch particles and silicone oil to make electrorheological fluid. Then we make a sandwich beam with an ER core and extract the modal parameters of the structure using the modal test. Using the ASTM standard, we estimate the shear modulus of the fabricated ER fluid. In the following, based on the equations developed for the...