Sharif Digital Repository

Rotor contact with a stationary element of a rotating machine and the subsequent rubbing at the contact area is a serious malfunction that may lead to the machine’s catastrophic failure. In the past decades, many studies have been done on the rubbing phenomena, its different regimes and its various consequences on the machine performance and safety. However, most of them have used a simple model to investigate the rubbing interaction between the rotor and the stator. This simple model consists of the Jeffcott rotor, as a model for the real rotors, and a rigid annular block surrounding the rotor, as a model for the real stators. The objective of this thesis is to build an algorithm to... 

All rotating machines (such as internal combustion engines, reciprocating compressors, propulsion systems, etc.) experience torsional vibration during Start up, continuous working conditions and blackout. Torsional vibrationis due to pressure rhythms, engine dynamic torques, etc. All components of a rotating system must convey dynamic torque in addition to the static torque.Excessive Torsional vibrations cause wear and damage such as gears, gear teeth damage and failure to the main shaft.Online monitoring of torsional vibrations of the machine can be displayed machine condition at any moment and consider the risk in early diagnosis. Shaft torsional vibration monitoring can detect cracks in... 

In order to increase the service life and prevent the breakdown of apparatuses, instalations and equipments, we are in a position to maintain them. In this regard, there are three methods for maintenance of machineries, which are called reaction maintenance, preventive maintenance and predictive maintenance. By carrying out a predictive method or monitoring the situation, it is possible to know the health of the machine and take the necessary measures before the damages occurs. Vibration analysis, temperature analysis, oil analysis and flow analysis can be used for monitoring the situation. Reciprocating compressors are one of the most costly repair equipment that needs to be monitored... 

The use of multiple sensors that produce different physical parameters of the measured system for its health monitoring raises the reliability of the diagnosis. At the moment, the fault detection capacities of ball bearings by means of proximity probe are detected by exploiting the advantages and reducing its defects by appropriate signal processing of the raw data in the time domain. Also, the application of numerical derivation and integration to achieve to the desired frequency spectrum in defect detection is investigated. A set of experiments with different sizes of internal ring, outer ring and ball defects, four levels of speed and two load levels have been performed. Data acquisition... 

Screw compressors are one of the most applicable compressors in marine engineering. Producing of compressed air for ignition of ship’s disel engine, air conditioning, cooling of food and producing of Nitrogen are applications of this compressor in marine industry. So, improving reliability of these compressors is so important.First of all, componenets of screw compressors, failure modes and different ways for improving reliability of this compressor are studied. The best way to improve reliability of rotating machinery is condition monitoring and so this way was chosen to be studied. In this approach, by using CM data and failure history data of a high pressure water descaling pump are used... 

Failure of mechanical parts in the industry lead to a larger system downtime and even imposing economic losses to the factory. For this Purpose, for many years, researchers have been trying to find ways to predict early failure and to prevent losses from occurring. Creation of new sciences like artificial intelligence, helped researchers in this field.In the current study, using experimental data of a set of bearings that have been tested and recorded in the Intelligent Systems Research Center, A new approach with sufficient accuracy is presented for the prediction algorithm. Among the features extracted, three features of entropy, root mean square and maximum are the most appropriate... 

Anti-lock brakes car as one of the most fundamental and vehicle stability control system is considered. Solenoid valves, one-way valves, Accumulator, damper orifices and other components is a crucial role in the anti-lock system performance, so that the performance of the system and thus affect the dynamic performance of the vehicle. This is the most important part of the anti-lock brake System and These components are all new brake system.In this study a complete modeling of hydraulic control unit and obtain sufficient data to model the dynamic behavior of the hydraulic control unit to be seen. operators working in higher frequencies are weak and virtually reached saturation and efficient... 

Surface plasmons are the result of a resonant interaction between the waves and the mobile electrons at the interface between negative and positive permittivity materials stimulated by incident light. Due to their specific quantum mechanical nature and zero electrical resistance, superconductors are capable of supporting low-loss plasma waves with extremely large propagation length. In this study, palsmon confinement in some superconducting waveguide structures has been measured by computing the effective index parameter. Superconductors are classified in to high-Tc an low-Tc categories. It is not possible for plasma waves to propagate in low-Tc superconductors, because the plasma energy... 

In recent years, the challenges of using fossil energy causes governments and researchers to focus on renewable energies. In this regard, one of the strategies for generating power is using wave energy converters. The aim of present study is modeling frequency and time domain analysis of the wave energy converter. the study focuses on the effect of Power-Take-Off system on the output power and efficiency under the Macoran sea waves. First, the concept of wave converters is explained and the commercialized ones are introduced. Then the related previous works are reviewed and the wave theories are briefly presented. In the following, a specified one-degree-of-freedom converter is modeled in... 

Experimental investigation of drillstring dynamics is essential to complete the theoretical studies and to alleviate complexity of such dynamic models. Vibration is one of the most effective parameter affecting drilling operation. Most of the experimental setups are looking for drilling mud tests, operational characteristics of bit under several bad condition and bit mud stone interaction in drilling operation and there are few setups to study vibration of the drilling setups. In this project a test rig has been introduce which is a scale of a real industrial drilling rig by the factor of 10300. Then based on the field studies of drilling failures in Iranian oil drilling rig , a crack has... 

Suspension system is one of the most influential components of vehicle in the area of stability and comfort. The suspension system is designed based on the use of the vehicle and stable characteristics. Obviously, being distant from the designed spots and applying various gates, its optimized performance is lost. Semi-active suspensions by changing their features get floating designed spots to be created and suspension system is always in optimum conditions through a suitable control. This research covers the efficacy of using damper Magneto Rheological which is called damper (MR) on the performance of seat suspension system in reducing vibrations. This damper is considered as a device in... 

Membrane bioreactors (MBRs) which are commonly understood as the combination of membrane filtration and biological treatment using activated sludge have several advantages, but membrane fouling reduces the membrane efficiency, permeability and lifetime. An alternative is replacing a moving bed biofilm reactor (MBBR) with the activated sludge system which may reduce the effect of membrane fouling. The sludge produced in MBBRs has poor settling characteristics, therefore, their efficiency is limited by the sedimentation tank performance and they require a larger settling surface. The combination of moving bed biofilm reactors and membrane bioreactors can compensate for the drawbacks of both of... 

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... 

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... 

Condition monitoring and fault detection is an important way to provide economy in both time and costs. Many methods are developed for this purpose. Vibration analysis is one of the most important ways in this field. In this thesis, fault detection of mechanical rotary systems with nonlinear and non-stationary nature has been developed by use of empirical mode decomposition (EMD) and Hilbert transform. Firstly the measured signal is transformed into some intrinsic mode functions (IMF’s) by EMD, and then the Hilbert transform is implemented on each IMF. With Hilbert transform, the instantaneous frequency of system and then the mean frequency are obtained. Mean frequency is a key definition... 

Internet video networks have already attracted millions of Internet users, and Internet video is one of the fast growing Internet services. The peer-to-peer (P2P) network is an efficient solution to supporting large scale video streaming on the Internet. P2P networks can deliver live multimedia content to millions of users with low cost at any time, and at anywhere they want. In this thesis, we investigate solutions to enhancing the performance of the unstructured mesh-based. Locality awareness or network proximity is one of the essential characteristics of P2P networks. In live P2P video streaming we face to some challenges like bandwidth heterogeneity of peers, and peer churn. In the P2P... 

So far, investigations have shown that open dielectric resonator antennas (DRAs) offer several advantages at microwave and millimeter wave frequencies. These advantages include small size, large impedance bandwidth, high radiation efficiency, ease of manufacturing and simple feed-coupling mechanisms (such as probe coupling, aperture coupling or proximity coupling to micro-strip lines). Most microwave ferrites have dielectric constants in the desirable range and they can be used in place of dielectric materials. Such ferrite resonator antennas (FRAs) offer a potential advantage in that their permeability tensor can be controlled by applying an external magnetic field. Up to now and by the... 

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... 

The effect of Vibration on the human body is considered as one of the limitations in design and use of HSCs at high speeds. One way to reduce the effect of vibration on the human body is to isolate deck vibrations from the crew by means of seat suspension system. This thesis has studied the effect of using an MR damper on the performance of seat suspension in vibration reduction. In fact, employing MR dampers in seat suspension systems enables us to change their damping. Using an MR damper makes it possible to control seat suspension by semi active control strategies. In this work, a number of proposed mathematical models of an MR damper were studied for numerical analysis and the most... 

Today as various electronic and telecommunication devices like cell phones and PDAs are being popularized, MMIC technology is gaining a significant importance. One of the priorities of this technology is trying to miniaturize these popular devices. But reducing size of passive microwave components used in these devices requires microwave wavelength to decrease.Components fabricated by conventional deposition techniques aren’t thick enough to reduce the wavelength, so permittivities much higher than those of conventional dielectrics could be a possible solution. Artificial dielectric layers (ADL) can provide such high permittivities.So utilizing these layers can possibly reduce the size of...