Sharif Digital Repository

Setar is a traditional Persian musical instrument. Nowadays, Setar is one of the most common musical instruments in Persian music. A systematic method for Setar production modification has not been introduced yet. This work is the first scientific work about analysis of this instrument. The aim of this study is to undertake early steps for Setar quality improvement. In this thesis, after analysis of the wood using in Setar construction, numerical and experimental methods have been utilized to analyze this instrument. After that, some works has been performed to extract an objective function which can judge about Setar quality. The results show good agreement between experimental and... 

Rolling bearings are important parts in rotating machinery. Unsuitable practice of this bearing causes unsuitable output in this collection. In some machines like helicopters, sudden faults of this rolling bearing cause body dangers. According to this point, diagnose of bearing fault is an important case in condition monitoring domain. There are many ways for diagnose of fault in bearing which most of them are important subject in signal processing. In this project first of all, the most important and applicable signal processing methods, which are useful in diagnose of fault in bearings are introduced then three of these methods are chosen and applied on time signals of experimental... 

In this thesis a comprehensive software code has been developed for analyzing dynamic behavior of rotary systems. Dynamic analysis of rotors consists of calculating critical speeds, mode shapes and vibrational response. The code is also capable to model unbalance, bend and misalignment faults. Due to the complexity of current misalignment models, a simplified model was developed. Rotor, disks and bearings were modeled and joined together to build the complete model. A novel procedure was suggested for modeling of multisectional rotors (such as, Tie-rod and Tie-bolts). Vibrational response has been calculated for each of the faults and effect of shaft and bearing parameters has been observed.... 

This thesis addresses the main stages of ship vibration analysis and introduces applied strategies for vibration reduction of an existing ship. First, the basic theory of ship vibration is considered and the main sources of ship vibration are enumerated. Then, the manner and the steps of vibration measurement on ship structure are presented and a summary of vibration measurement guidelines is mentioned. Afterward, the procedure how to analyze the measured data of ship vibration is outlined and a comparison between the measured data and standard limits for vibration level considering structural vibration, machinery vibration and human comfort is done. Next, human response to vibration and the... 

Reciprocating Machinery are one of the key components of chemical and petrochemical plants and their down time cause loss of production. Therefore condition monitoring in these machinery is of special interest and high value. In this thesis first, different methods of condition monitoring for reciprocating compressors are introduced then the main cause of high vibrations of three compressors in a refinery is investigated. Finally by using the foundation model prepared, it would be shown that insufficient strength of foundation block has lead cracks initiation and development in these foundations. Therefore high vibration is consequence of weak design  

Despite of many advantages, electro submersible pumps (ESP) have very high costs in maintenance. Since ESP usually operates in deep wells, it should be transported to the surface in order to malfunction. In addition, the state of ESP equipment cannot be determined because of unavailability of vibration measurement on the site. Thus, this equipment fails suddenly. This process costs a lot on country’s oil and water & wastewater industry. so in this thesis, at first, the potential failure modes (PFM) of ESPs are investigated, then proper methods are presented for condition monitoring. Finally, the presented methods are verified by experimental tests and wavelet analysis. The results show that... 

Snaking Vibration and buckling of drill string in the horizontal well was investigated in this research. Sinusoidal and helical critical buckling load are obtained for a specific drill string.
Drill string is modeled both analytically and numerically (finite element method). Drill pipes are considered as a clamped-clamped beam with constant cross section and the well is considered as a hollow cylinder. The thickness of cylinder was large enough to model the surrounding soil of the well. Buckling is a complex deformation and is somehow a random phenomenon. In addition, the length and the continuous contact between drill pipes and the well make the finite element model very huge and the... 

Torsional vibrations of internal combustion engines and reciprocating compressors, is one of the challenges in the design process. It can reduce power of productivity, equipment operating lifetime and increase noise of the system. Torsional viscous damper is a method to reduce torsional vibrations in rotating equipment. In this study, three-dimensional simulations of torsional viscous damper is performed as a matter of FSI, with consider harmonic excitation on the external walls and calculation of damping response inertia ring in CFX software. The viscoelastic non-Newtonian model properties of damping fluid is calculated in MATLAB software with respect to viscoelastic parameters. For... 

The main aim of this thesis is to develop a mathematical model for vibration analysis of cracked rotors. This model should be a simple and precise model for prediction of the cracked rotor vibration behavior and suitable for vibration control. In order to create such model, the pure bending of a cracked beam is analyzed at first. This analysis is performed for two different orientations of the crack with respect to the beam and the bending vector. In this section a continuous bending model with continuous model for crack is developed which can predict the full deformation of the cracked beam in bending and can estimate the stress distribution in the beam with good approximation. Comparison... 

Non-uniform composite structures are widely being utilized in many modern industries including aerospace and automobile and wind turbine machines. Excessive vibration in these structures leads to dynamic instability and structural failure. In the present work, the vibration control of non-uniform composite structure particularly trapezoidal plates has been investigated using magnetorheological materials. The application of various smart materials including magnetorheological (MR) elastomer and magnetorheological fluids has been reviewed for vibration control. A trapezoidal composite plate with holes filled by MR elastomer has been considered for numerical simulations. The effect of location... 

Managing industries into the 21st century is a challenging task, because of increasing global competition, fast technological change, consumer’s perceptions towards total quality, reliability, health and safety, environmental considerations and changes in management structure.To overcome these difficulties, maintenance planning is a must such as condition monitoring (CM) technologies.Khouzestan Steel Company as the second largest Steel manufacturer in Iran, using some CM techniques & tools - like VCM, OCM, TCM and … - to maintain its continuous improvement.To assess what KSC has done, we focus on cost-benefit (CB) and availability; BY defining three phases: 1) Data Gathering, 2) Calculation... 

A major concern in directional well drilling is the transport mechanism of cuttings by drilling fluid. This thesis describes the effect of angular velocity and postbuckled vibrations of drillstring on cuttings transport in a directional well drilling. The analysis proceeds in two stages. First, a finite element model is used to predict the dynamic behavior of postbuckled drillstring inside a directional well. Second, a coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM) approach to simulate the cuttings transport considering the dynamic collision process. In the combined computational fluid dynamics and discrete element method (CFD-DEM), the fluid phase is treated... 

Magnetorheological (MR) materials show variations in their rheological properties when subjected to varying magnetic fields. They have quick time response, in the order of milliseconds, and thus are potentially applicable to structures and devices when a tunable system response is required. When integrated with a structural system, they can produce higher variations in the dynamic response of the structure. In this thesis, vibration behavior of laminated-composite beam with MR Fluid is investigated.In most studies, shear strain across the thickness of MR layer has been considered as a constant value which does not precisely describe the actual shear strain field. Shear modulus of MR layer in... 

High speed and high accuracy are two of the major trends for many systems in the 21st century, such as machine tools and semiconductor equipment. For the purpose of high speed, it is well known that active magnetic bearing (AMB) is an inevitable substitute for conventional bearings. The noncontact nature of AMB brings up many advantages over the conventional bearing, including energy efficiency, low wearing, long life span, and absence of lubrication. Hence, AMBs are especially essential for high-speed rotating devices nowadays.
While the 3-pole AMB has been proposed for many years, it received little attention due to the magnetic coupling between poles that makes the 3-pole AMB system... 

Rotary equipment are being used in many industries over a wide range of applications, such as gas turbine. Due to the nature of the operating conditions, gas turbines are subjected to variety of damages especially crack propagation of a blade. The Cracks propagation may lead to catastrophic failure during operation. Therefore, detection of the crack presence and its propagation is very important and may reduce possible significant cost of the whole system failure. The thesis aims to investigate the cracks presence and their propagation effects on vibration of a turbine blade which is located at the National Iranian South Oilfields. First, theoretical study is calculated to validate an... 

Torsional vibration is undeniable in rotary systems, and it is more important in gearbox because it is the main cause of failure and noise. In this research The stiffness and damping between teeth are considered and mean stiffness between teeths are calculated by using material, contact ratio,and geometrical parameters. Transfer matrix method is used for obtaining natural frequencies and mode shapes.
In this thesis, effects of geometrical parameters of gears, backlash value, harmonic and constant torque on rattle noise show that increase in backlash, amplitude and frequency of excitation, magnify the power of impacts, also the time of rattle phenomenon and number of impacts decrease by... 

The ability to predict the remaining life of bearings is one of main aspects for improvement of reliability of bearings. However, techniques to predict the lifetime of a bearing under the practical operating conditions have not been well developed. In this thesis, prognostic model for bearing systems based on vibration response analysis is considered as a single-degree-of-freedom vibratory system. As the bearing system is considered as a single-degree-of-freedom vibratory system, its acceleration amplitude at the natural frequency can be related to the system stiffness. Moreover, the relationship between failure lifetime, running time and stiffness variation can be established from the... 

Electrical connectors that used in high speed systems interrupt the connection at the effect of Inertia. Also connectors should be able to work in high vibration conditions without any problems. Vibration of the connector pins can reduce the contact area or even remove it at very short time intervals, which lead to increase connector resistance or disconnection of instantaneous current. These current fluctuations will result in unpredictable performance disturbanceof the electrical system in very sensitive systems and therefore it should be avoided. In this Project, impacts of shock and vibration loads on the connectors is modeled by using FEM and with consideration of this model, connection... 

Aiming to improve the extraction performance of wind energy has led to the noticeable increase of the structural dimensions in the modern wind turbines. The larger blade with more flexibility experiences large structural deformation even under nominal operational loading, so the nonlinear modeling and analysis of these structures have become as important subject of the recent wind turbine researches. In this dissertation, the geometrical exact model of the rotating wind turbine blade under the effects of the tower tip's motion, and also the operational loading comprising the aerodynamic and gravitational loadings is presented. In this way, the geometrical exact beam formulation is developed... 

The failure in rolling element bearings as an important part of rotary machine can lead to machine breakdown.Consequently, bearings can reduce reliability of these components and therefore a maintenance strategy is essential to keep reliability in a desired level. The first and primitive strategy is called breakdown or unplanned maintenance. The next is preventive or planned maintenance. In this scheme, maintenance is done after a specified time period irrespective of machine health status. Out of place maintenance is the disadvantage of preventive maintenance. The most effective generation of maintenance strategy is condition based maintenance (CBM) which suggests maintenance decision based...