Sharif Digital Repository

Changes in thermodynamic properties such as pressure, temperature, and composition may result in asphaltene precipitation and deposition in porous media. In addition, asphaltene deposition can cause wettability alteration, permeability reduction, and ultimately a decrease in the productivity of a reservoir. Natural depletion is one of the most common processes of asphaltene deposition in which pressure changes destabilize the dissolved asphaltene in the oil and settle them onto the rock surface. In this work, natural depletion experiments in consolidated core samples were performed under simulated reservoir conditions to obtain reliable data and analyze the asphaltene deposition mechanisms.... 

Asphaltene deposition causes serious problems in the oil industry. Variation of oil composition and reservoir pressure is reported to be the most important factors that influence asphaltene deposition from reservoir oil. In this study, a mathematical model was developed to simulate asphaltene deposition during primary depletion and CO2 injection. The main purpose of this study is to investigate and to compare asphaltene deposition mechanisms due to primary depletion and CO2 injection. The solid model as thermodynamic model was applied to investigate asphaltene precipitation. A numerical model was established to the governing equations both in space and time and model parameters were... 

Intravitreal injection (IVI) is the most common treatment for eye posterior segment diseases such as endopthalmitis, retinitis, age-related macular degeneration, diabetic retinopathy, uveitis, and retinal detachment. Most of the drugs used to treat vitreoretinal diseases, have a narrow concentration range in which they are effective, and may be toxic at higher concentrations. Therefore, it is critical to know the drug distribution within the eye following intravitreal injection. Having knowledge of drug distribution, ophthalmologists can decide on drug injection frequency while minimizing damage to tissues. The goal of this study was to develop a computer model to predict intraocular... 

There are different thermodynamic models that have been applied for modelling of asphaltene precipitation caused by various reasons, such as solvent/CO2 injection and pressure depletion. In this work, two computer codes based on two different asphaltene precipitation thermodynamic models-the first being the thermodynamic micellization model with a different characterization approach and the second being the solid model-have been developed and used for predicting asphaltene precipitation data reported in the literature as well as in the obtained data for Sarvak reservoir crude, which is one of the most potentially problematic Iranian heavy oil reserves under gas injection conditions. For the... 

Different models have been proposed for deposition of asphaltene on reservoir rocks that due to complexity of asphaltene nature, most of them have not been productive. Here, a reliable model is proposed which despite of previous models, considers the change in asphaltene saturation in the core. The obtained experimental data in the laboratory was used for model validation. In this work, a series of core flooding tests was carried out in presence of connate water at different solvent-oil volume ratios. Pressure drop was measured at three different terminals along the core. The obtained experimental data as well as mass balance equations, momentum equation, asphaltene deposition and... 

Stable control of water level of drum is of great importance for economic operation of power plant steam generator systems. In this paper, a linear model of the boiler unit with time varying parameters is used for simulation. Two transfer functions between drum water level (output variable) and feed-water and steam mass rates (input variables) are considered. Variation of model parameters may be arisen from disturbances affecting water level of drum, model uncertainties and parameter mismatch due to the variant operating conditions. To achieve a perfect tracking of the desired drum water level, two sliding mode controllers are designed separately. Results show that the designed controllers... 

In this paper, some models have been introduced for dynamic thermal modeling of cast-resin transformers which are based on genetic algorithm. A typical 400kVA cast-resin transformer has been selected and the model parameters are estimated and validated with the help of experimental data extracted from different load cycles. The estimated models are used to generate a reliability model for cast-resin dry-type transformers and the effects of variation in load, ambient temperature and atmosphere conditions on the reliability of castresin transformer are illustrated. As it will be shown in this paper, the effects of working conditions on the life-time of insulation in dry-type transformers is... 

In this paper, the order distribution concept in the frequency domain identification has been extended to include fractional order systems having poles and zeros simultaneously. The existing nonlinear optimization problem appeared when both poles and zeros, is are changed to a quadratic problem that can be solved using least squares algorithms. To collect the required data, system is excited by a multi sine input signal with appropriately selected frequencies. Then a nonparametric identification in frequency domain is accomplished to calculate the empirical transfer function estimate (ETFE). This estimate is then used to implement the frequency domain identification on all defined members of... 

In this work, a thermodynamic approach is used for modeling the phase behavior of asphaltene precipitation. The precipitated asphaltene phase is represented by an improved solid model, and the oil and gas phases are modeled with an equation of state. The Peng-Robinson equation of state (PR-EOS) was used to perform flash calculations. Then, the onset point and the amount of precipitated asphaltene were predicted. A computer code based on the solid model was developed and used for predicting asphaltene precipitation data reported in the literature as well as the experimental data obtained from high-pressure, high-temperature asphaltene precipitation experiments performed on Sarvak reservoir... 

An attempt was made to examine thermal effects as well as fade and wear characteristics of rubber-based friction materials (RBFMs). A series of RBFMs with and without fiber reinforcements were prepared. The fiber reinforcements used were carbon fiber, cellulose fiber and aramid pulp. A semi-empirical model describing the correlation of coefficient of friction (COF) and temperature was presented. The effectiveness of the model was evaluated using the experimental data. The results revealed that the model parameters for a given composite show a significant change above a critical sliding velocity, i.e. 300 rpm. This behavior was speculated to be due to the transition of rubbery state of the... 

In this paper, issues related to the identifiability of a fractional order system having its input and output frequency contents are discussed. The effects of the commensurate order α in the identifiability of the model structure and model parameters are analytically studied. It is shown that both identifiabilities (model structure and model parameters) are reduced remarkably for smaller values of α. This phenomenon is observed even though the input signals are rich enough and system belongs to the model set. Our understanding is that the problem arises since differences among different members of the model set fall beyond the practically recognizable precision range. The issue is more... 

In this communication, a hybrid model based on Least Square Support Vector Machine (LSSVM) was constructed to predict CO2 corrosion rate. The input parameters of the model are temperature, CO2 partial pressure, flow velocity and pH. The data used for training and testing of the developed model are 612 and 109 data, respectively. In order to benefit LSSVM from Kernel learning, we compared three kernel functions to select the most efficient one. Furthermore, Coupled Simulated Annealing (CSA) optimization technique was adapted to choose the best optimal values of the model parameters. The results elucidate that Gaussian Kernel functions is the desired function which can afford high accuracy for... 

Train scheduling has been one of the significant issues in the railway industry in recent years since it has an important role in efficacy of railway infrastructure. In this paper, the timetabling problem of a multiple-tracked railway network is discussed. More specifically, a general model is presented here in which a set of operational and safety requirements is considered. The model handles the trains overtaking in stations and considers the stations' capacity. The objective function is to minimize the total travel time. Unfortunately, the problem is NP-hard, and real-sized problems cannot be solved in an acceptable amount of time. In order to reduce the processing time, we presented some... 

The aim of this study is to develop a new fuzzy optimization model to find the optimal factor weights of modified DRASTIC index for groundwater vulnerability mapping an urban aquifer to nitrate contamination. Eight factors including water table depth, recharge, aquifer media, soil media, topography, impact of vadose zone, hydraulic conductivity, and land use are considered and rated. A fuzzy linear regression is formulated between the values of eight factors and corresponding nitrate concentration in groundwater. An optimization model based on real code genetic algorithm with objective of minimizing the sum of the fuzzy spread of the regression coefficients is implemented. Aquifer of Mashhad... 

A new composite adaptive control strategy is developed for both of the reduction of cancer tumor volume and the online identification of tumor parameters during the drug delivery process in chemotherapy. This control strategy is developed for three different nonlinear mathematical cell-kill models of the cancer tumor including the log-kill hypothesis, Norton-Simon hypothesis and Emax hypothesis. All of these models are considered to have fully parametric uncertainties. The stability, tracking convergence and parameters identification convergence during the chemotherapy process are proved using the Lyapunov method. For the first time, the parameters identification of the uncertain... 

Due to flexibility of thin plates, high-amplitude vibrations are observed when they are subjected to severe dynamic loads. Because of the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, Adaptable Vibration Suppressors (AVSs) as a semi-active control approach were utilized to suppress the vibrations in a free circular plate under the concentrative harmonic excitation. Using mode summation method, the mathematical model of the hybrid system including the plate and an arbitrary number of vibration suppressors was analyzed. By developing a complex multiple-loop algorithm, optimum values for the parameters of... 

Due to flexibility of thin plates, high-amplitude vibrations are observed when they are subjected to severe dynamic loads. Because of the extensive application of circular plates in industry, attenuating the undesired vibrations is of foremost importance. In this paper, Adaptable Vibration Suppressors (AVSs) as a semi-active control approach were utilized to suppress the vibrations in a free circular plate under the concentrative harmonic excitation. Using mode summation method, the mathematical model of the hybrid system including the plate and an arbitrary number of vibration suppressors was analyzed. By developing a complex multiple-loop algorithm, optimum values for the parameters of... 

This paper evaluates the reliability impact of UPFC application in power system. The paper proposes a new reliability model for the UPFC which is capable of considering different operating states of UPFC. The model is then applied to a test system to study the reliability impacts of UPFC. The impacts of operating points of different states of the model on the system reliability are analyzed. The role of model parameters in reliability impacts of UPFC is analyzed through the sensitivity analysis. A comparative study is finally conducted to illustrate the applicability of the proposed model compare to that of existing UPFC reliability models. The abilities and deficiencies of the proposed... 

An extension to the classical mass-spring model for more realistic simulation of soft tissues for surgery simulation was proposed. The conventional equations of mass-spring model were generalized for non-linear springs, and model parameters were tuned using experimental data. Results show that the proposed model is fast and interactive, and also demonstrate the typical nonlinear and visco-elastic behaviors of soft tissues well. © 2008 The authors. All rights reserved  

Distributed generation is expected to play an increasing role in emerging power systems. They use different type of resources and technologies to serve energy to power system. DG has positive and negative effects for both the utilities and customers. System and load point reliability indices are normally improved if DG is installed in a distribution network. On the other hand, DG has some specific characteristics which distinguish it from conventional generating units. Therefore, they should not be treated as conventional generating units to perform reliability evaluation. An appropriate model is required to be developed in order to assess impacts of DG on reliability indices. Impacts of DG...