Sharif Digital Repository

Damage to structures with the concept of inelastic behavior and consequently hysteresis energy is very close. Therefore, it can be said that hysteresis energy at these levels can be a significant criterion for designing or controlling the structure. In this research, the first three steel frames of 4, 8, and 12 floors with the medium bending frame system have been designed with the statically equivalent method according to valid international regulations; then, all frames have been subjected to nonlinear dynamic analysis by seven accelerometers. The purpose of this study is to investigate the distribution of damage, energy, relative displacement, roof displacement, and base shear in the... 

Partial discharge (PD) measurement is one of the best methods for condition monitoring of transformers. In this paper, we use 5 different types of defects as follows: scratch on winding insulation, bubble in oil, moisture in insulation paper, a very small free metal particle in the transformer tank, and a fixed sharp metal point on the transformer tank, for our PD-related studies. Each type of defect is implemented into 1 of the 5 identical transformer models, which had been developed in the authors' recent work. The continuous wavelet transform is applied to each related measured time-domain PD signals. This process results in an image, for each PD pulse in the time-frequency domain. Using... 

Partial discharge (PD) is a common phenomenon which occurs in insulation of high voltage equipments, such as; transformers and has a damaging effect on the insulation. If data mining techniques be used to find specifications and features of different types of partial discharges in power transformers, one can monitor the insulation condition of such equipment online and continuously. Those results can be employed to develop preventive measures more exactly and consequently the maintenance would require less time and cost for electric utility and improve the life time expectancy of the transformers. In this paper experiments are set up to create models for some types of PD that occurs in Power... 

Despite the great use of concrete, tensile strength and low flexibility and brittleness are its weaknesses. Many solutions have been provided to eliminate the mentioned defects. In order to increase the flexibility of concrete in previous studies, crushed rubber tire particles have been added to concrete. Recycling car tires helps the environment and makes concrete much more flexible than regular concrete. In this research, silicone rubber has been replaced by 0%, 2%, 4%, 8%, 12.5%, 25%, and 50% of mineral aggregates. This rubber was initially in liquid form, which, after mixing with ordinary concrete, dispersed into the concrete texture and formed a uniform mixture, and this liquid rubber... 

An approach composed of the thermodynamics-based dislocation model and the Taylor theory is used to investigate the evolution of microstructure and flow stress during high-pressure torsion (HPT). The incremental temperature rise is considered through the modelling of HPT. The temperature can affect the annihilation of dislocations and thus the dislocation density. The model predicts the dislocation density, sub-grain size and flow stress during HPT. The modelling results are compared with the experimental data and the modelling results without considering the incremental temperature rise. A remarkable agreement is observed between the modelling results with considering the temperature rise... 

Two-internal variable thermodynamics model is presented to investigate the evolution of microstructure and flow stress during severe plastic deformation. Previous studies have shown that due to heterogeneous distribution of dislocations during severe plastic deformation, the use of multivariable models is needed. In this regard, a two-internal variable model is presented. In the present paper, the dislocation densities in the subgrain boundaries and interiors are considered as internal variables. The model uses general laws of thermodynamics and describes the evolution of the dislocation densities on the basis of parameters such as the self-diffusion activation energy and the stacking fault... 

Recent investigations have shown that the steady state grain size of severely deformed materials is dependent on the stacking fault energy. In this paper, a model is presented to investigate such a dependency which uses thermodynamics based calculations. The present model shows that the relationship between the steady state grain size and the stacking fault energy of material is in power law form, directly. Furthermore, the model shows that the steady state grain size has an exponential relationship with the self-diffusion activation energy and a decrease in the self-diffusion activation energy increases the steady state grain size. The model predictions are in good agreement with the... 

The main goal of high-pressure torsion (HPT) process is to reduce the grain size. Experiments have shown that this aim is achievable, but there is a limit in reducing the grain size. The present paper investigates this limit through a thermodynamics-based model. However, this was investigated by other researches through dislocation density-based model. At first, the validity of the model in description of the limiting grain size obtainable by HPT of different materials is examined. Then, the influence of inherent material parameters is investigated. Finally, the present results are compared with those obtained by equal channel angular pressing. © 2019, © 2019 Institute of Materials, Minerals... 

The strength evolution during the processing/cycling of the metal matrix composite through accumulative roll bonding (ARB) as a severe plastic deformation method is studied by performing a twofold model. It is shown that the strength evolution during cycling consists of two parts: monolithic-like behavior and composite-like behavior. The contribution of each behavior is obtained. The particle effectiveness is at the lowest value at the beginning of the cycling and reaches its highest during the final cycles. It is shown that there is a critical strain at which monolithic-like behavior initiates to decline. The process also shows a minimum strain at which composite-like behavior dominates. ©... 

Although Al–Mg alloys have various desirable properties, to broaden the applications, it is needed to increase the strength of these alloys. Severe plastic deformation (SPD) is a candidate method for this purpose. In this paper, a model is presented for the strength and microstructure evolution during severe plastic deformation. The model is applied to 5 Al–Mg alloys with different solute contents of 1, 2, 3, 4, and 5 wt% Mg. The model is also employed for pure Al for the sake of comparison. The model evaluates the effectiveness of Mg addition, quantitatively. It is shown that the combining of solute addition and severe plastic deformation can provide a considerable increase in the strength... 

Reviewing the various Partial Discharges (PD data mining researches which have been reported so far, this study compares the performance of different feature spaces and different classifiers employed for PD classification in insulation condition monitoring of power transformers. In this process, first a knowledge basis is developed through construction of 4 different types of PD models in the high voltage laboratory. Background noise is considered as one class in this knowledge basis. The high frequency time domain current signals of high voltage equipment are captured over one power frequency cycle. The single PD activities within this captured signal are extracted by application of a... 

Suggestion and application of a set of new features for on-line Partial Discharge (PD) monitoring, where there is no information about the type of PD is a challenging task for condition assessment of power equipments, such as a power transformer. This is looked for in this paper. So far, in past various techniques have been employed to develop a comprehensive PD monitoring system, however limited success has been achieved. One of the challenging issues in this field is the discovering of proper features capable of differentiating the involvement of possible types of PD sources. In order to examine the efficiency of the method established in this paper, which is based on application of a set... 

The small-signal gain coefficient and the saturation intensity of a copper vapor laser have been measured for both 510.6- and 578.2-nm transitions through the implementation of a discharge driven oscillatoramplifier configuration. Pressure dependence of the gain and saturation property of the laser has been investigated. © 2003 Optical Society of America