Sharif Digital Repository

Having information about the amount of water storage is essential to estimate the amount of water available for use in agriculture, industrial, etc. The purpose of this study is to propose a method for estimating the water budget in large-scale basins using remote sensing data. Using ground-based measurements to obtain water budget components is a challenging issue. This may be due to the limited access to in-site data in temporal and spatial resolution, especially in large scale basins. In recent years, with the increasing growth of satellite data, the application of remotely sensed data to estimate changes in water storage is increasing. In this study, due to the limitation of access to... 

In recent decades, the technology of utilizing millimeter wave frequency bands has made remarkable progress. This frequency band is widely employed in important areas such as security applications, medical imaging, quality control testing, and future telecommunications. The main characteristics of waves in this band are their low risk due to low-energy photons compared to X-rays, and higher image resolution in imaging due to their shorter wavelength compared to microwaves. This thesis aims to investigate the effect of irregular reflection of electromagnetic waves from the edges of a metallic body located adjacent to an dielectric background by analyzing the electromagnetic scattering. Then,... 

Intelligent fault diagnosis (IFD) involves the application of machine learning (ML) theories to machine fault diagnosis. Vibration analysis is a common technique used for diagnostics and prognostics. A hybrid method that integrates both physics-based and data-driven approaches could offer an effective strategy for monitoring health. In this research, the artificial neural network (ANN) and convolutional neural network (CNN) algorithms, which are common models, have been used. Then, based on the results obtained, developing a physics-informed neural networks (PINN) model, more specifically physics-informed convolutional neural network (PICNN), is proposed. The algorithm used for PICNN... 

Valve leak detection is very important due to bad direct effects on parts life and engine power. Acoustic emission (AE) has a good known ability on leak detection between fault detection methods. The aim of this thesis is presenting the ability of AE method for valve leak detection in internal combustion engines. The research method in a general framework based on the idea that firstly some evaluations were done in static tests for leakage due to three faults including clearance, quasi-crack and notch. Then, the evaluations were continued with dynamic analysis of rotational speeds and different loads on the engine. Finally, the neural network approach was used to automatically detect all... 

In recent years, due to urban expansion and population growth, number of floors and excavations depth has increased. Stabilization of excavations is one of the most important issues in geotechnical engineering. Today, one of the most widely used methods that is used in deep excavations is brace soil by steels and pretension them. In this thesis tries to evaluate static behavior of flexible supporting structures with pretension anchors by using PLAXIS2D, FLAC3D and GEOSTUDIO softwares. The objective of this modeling is better understanding the static behavior of walls, comparing the two and three dimensional modeling and the effect of corners of excavation on deformation. The results shows... 

Resonance acoustic spectroscopy (RAS) is one of the techniques used for monitoring the production quality and evaluation of mechanical properties of cylindrical components, due to their non-destructivity, high precision and quickness.
In this technique, the resonance effects are caused by the excitation of eigenvibrations of structure by an incident acoustic wave located in far-field. The resonance spectroscopy (isolation and identification of the resonance features) is performed on the far-field scattered pressure field which contains valuable information about the characteristics of the target. Appropriate exploitation of these resonance informations from the theoretical model and... 

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... 

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... 

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 wireless communication systems increasing the gain of antennas is seminal to increase in coverage and data transmission rate, and reducing the possible errors. One of the main factors for improving the antenna gain is matching the polarizations of the transmitter and the receiver antennas. Towards this end, both the transmitter and the receiver antennas should have the same axial ratio, specific direction and polarizations. As far as the flexibility of the direction angle between the transmitter and the receiver is concerned, the so-called circular polarization is preferred do the linear polarization. The antennas with circular polarizations are prominently utilized in satellites,... 

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... 

Operational modal analysis (OMA) techniques are proper methods to identify the modal parameters of the structures such as natural frequencies, damping ratios and mode shapes based on the system responses. First research in this area are stared from civil engineering. Difference between civil structure and industrial machines are in the type of excitation.in most industries such as aerospace or mechanical, colored or harmonic forces due to rotary machines, excited the system. Under this condition, traditional methods in OMA are not capable any more. Many works has been done to modify traditional methods. Most of these work limited to situations that forces are harmonic and harmonic... 

In the recent years, cloud data center issues have been the center of attention. Also for them topologies with multi paths between end hosts are offered. For use of multi path traffic engineering is essential. Researches show congestion occurred in the cloud data center networks, because the mean of link utilization is down. This means, some of links are congested while there are some other with much available bandwidth. Currently, the most common method is Equal Cost Multipath (ECMP) algorithm for routing flows in the data center network. ECMP decides on routing without any attention to network congestion condition. There, may be two big flows placed in the one path and it causes creation... 

The main objective of this research is to predict the life of a bearing that works in variable speed working condition. In this project, two series of experiments were conducted to investigate the vibration of the bearings. In the first series of experiments, multiple imperfections have been created on parts of the bearing that are susceptible including the inner ring, the outer ring and the balls. The results of this test have been used to study the importance of speed compared to other parameters in increasing the vibration levels of the bearing. In addition, the results of this experiment have been used as inputs to a neural network. This neural network is trained to classify bearing... 

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... 

Predicting the probability distribution of asset remaining useful life is an essential procedure in the intelligent maintenance. It also plays an important role in improving system reliability and optimizing further decisions. The main concern of this project is to estimate the probability distribution of rolling element bearing remaining useful life. For this purpose, the bearing degradation process is modeled through the statistical models, considering the major variabilities in the degradation process. The models parameters are updated, once a new measurement of the equipment is available. Then, the constructed model is utilized in order to predict the probabitity distribution of... 

Rolling element bearings (REBs) are one of the most critical components in rotating ma-chines. Failure of these components may lead to fatal and costly breakdowns in rotating machinery. Therefore, it is significant to detect faults at early stage accurately. The pur-pose of this study is to compare vibration analysis and shock pulse method (SPM) in early detection of fault and remaining useful life prediction of REBs. To the aim, a set of ac-celerated life tests on REBs was planned. Vibration and shock pulse values accelerated life tests of the REBs were simultaneously measured from the moment of start to the end of the failure by two vibration and shock pulse sensors and their changes were...