Sharif Digital Repository

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... 

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... 

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... 

The effect of complexity level of a lumped kinetic model for heavy residue hydroconversion on estimated values of kinetic parameters was investigated in this work by imposing constraints for the parameter estimation algorithm of a complex six-lump kinetic model and deriving a simpler modified model from the complex model. Kinetic analysis was performed using available experimental data reported in the literature from a study on hydrocracking of Chinese Gudao vacuum residue in a bench-scale reactor using ammonium phosphomolybdate (APM) as a dispersed catalyst. The kinetic models also included coke formation reactions that had previously been ignored by most investigators due to the rather... 

T Wave Alternans (TWA) is considered as an indicator of Sudden Cardiac Death (SCD). In this paper for TWA detection, a method based on a nonlinear dynamic model is presented. For estimating the model parameters, we use an Extended Kalman Filter (EKF). We propose EKF6 and dualrate EKF6 approaches. Dualrate EKF is suitable for modeling the states which are not updated in all time instances. Quantitative and qualitative evaluations of the proposed method have been done on TWA challenge database. We compare our method with that proposed by Sieed et al. in TWA challenge 2008. We also compare our method with our previous proposed approach (EKF25-4obs). Results show that the proposed method can... 

A number of challenges including instability, nonconvergence, nonuniqueness, nonoptimality, and lack of a general guideline for inverse modelling have limited the application of automatic calibration by generic inversion codes in solving the saltwater intrusion problem in real-world cases. A systematic parameter selection procedure for the selection of a small number of independent parameters is applied to a real case of saltwater intrusion in a small island aquifer system in the semiarid region of the Persian Gulf. The methodology aims at reducing parameter nonuniqueness and uncertainty and the time spent on inverse modelling computations. Subsequent to the automatic calibration of the... 

Most of the reported robust and non-robust optimization works are formulated based on a single-objective optimization, commonly in terms of net present value. However, variation of economical parameters such as oil price and costs forces such high computational optimization works to regenerate their optimum water injection policies. Furthermore, dynamic optimization strategies of water-flooding often lack robustness to geological uncertainties. This paper presents a multi-objective while robust optimization methodology by incorporating three dedicated objective functions. The goal is to determine optimized and robust water injection policies for all injection wells. It focuses on reducing... 

Estimating the energy consumption of applications is a key aspect in optimizing embedded systems energy consumption. This paper proposes a simple yet accurate instruction-level energy estimation model for embedded systems. As a case study, the model parameters were determined for a commonly used ARM7TDMI-based microcontroller. The total energy includes the energy consumption of the processor core, Flash memory, memory controller, and SRAM. The model parameters are instructions opcode, number of shift operations, register bank bit flips, instructions weight and their Hamming distance, and different types of memory accesses. Also, the effect of pipeline stalls have been considered. In order to... 

Hyperelastic behavior of isotropic incompressible rubbers is studied to develop a strain energy function which satisfies all the necessary characteristic properties of an efficient hyperelastic model. The proposed strain energy function includes only three material parameters which are somehow related to the physical quantities of the material molecular network. Moreover, the model benefits from mathematical simplicity, well suitting in all ranges of stretch and possessing the property of deformation-mode-independency. This reduces the required number of experimental tests for parameter calibration of the model. Results of the proposed model are compared with results of some available models... 

A new nonlinear model reference adaptive impedance controller is presented for the control of robot manipulators with uncertainties in model parameters such as friction coefficients. This method provides asymptotic tracking of a reference impedance model for the robot end-effector in operational space which is more sensible for the patient compared to the joint space impedance used in previous works. The model uncertainties such as friction coefficients are compensated using an adaptation law. The asymptotic tracking of the reference impedance model is shown using a Lyapunov function. The tracking performance and friction compensation are also demonstrated through simulation on a... 

A search is performed in pp collisions at √s=7TeV for exotic particles decaying via WZ to final states with electrons and muons. The data sample corresponds to an integrated luminosity of approximately 5fb -1. No significant excess is observed in the data above the expected standard model background. Upper bounds at 95% confidence level are set on the production cross section of the W ′ boson described by the sequential standard model and on the W ′ WZ coupling. W ′ bosons with masses below 1143 GeV are excluded. Limits are also set in the context of low-scale technicolor models, under a range of assumptions concerning the model parameters  

Local circuits in the cortex and hippocampus are endowed with resonant, oscillatory firing properties which underlie oscillations in various frequency ranges (e.g. gamma range) frequently observed in the local field potentials, and in electroencephalography. Synchronized oscillations are thought to play important roles in information binding in the brain. This paper addresses the collective behavior of interacting locally synchronized oscillations in realistic neural networks. A network of five neurons is proposed in order to produce locally synchronized oscillations. The neuron models are Hindmarsh-Rose type with electrical and/or chemical couplings. We construct large-scale models using... 

In this paper, a model-based dynamics equation for the needle movement through the soft tissue is developed. A model-based control scheme which uses the force estimation calculated through the simulated tissue deformation data and the dynamic finite element as the tissue model is proposed. To compare the performance of the proposed controller, a PD controller is also used for the proposed needle dynamics equation. It is shown that even with uncertainty in model parameters; the mode-based controller outperforms the PD controller. Furthermore, although increasing the controller gain improves the performance of PD, but the model-based controller's performance is still superior  

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.... 

Forming limit diagrams (FLDs) are extensively used in industries, particularly the auto industry. The establishment of these diagrams using a predictive approach can lead to reduction in both cost and time. In the present work, Gurson-Tvergaard-Needleman (GTN), a porosity-based model, was used to predict the FLD of an interstitial-free steel via finite element simulation. Optimum values of the GTN model were obtained by applying a response surface methodology (RSM) based on central composite design. Results show that RSM is a good method for an appropriate determination of the GTN model parameters, such as initial void volume fraction, effective void volume fraction, critical void volume... 

Equations of state based on the statistical associating fluid theory for potentials of variable range (SAFT-VR) and the perturbed chain statistical associating fluid theory (PC-SAFT) have been used to model the PVT behavior of ionic liquids and the solubility of H2S in six imidazolium-based ionic liquids. The studied systems included [bmim][PF6], [hmim][PF6], [bmim][BF4], [hmim][BF4], [bmim][NTF2] and [hmim][NTF2] at various temperatures and pressures.For pure components, parameters of the models have been obtained by fitting the models to experimental data on liquid densities; the average relative deviation between the calculated and experimental densities for ionic liquids is less than... 

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... 

In this work, a new model of transformer winding is developed. The components in the model are determined by the geometric and electric data of the winding. Under different degrees of axial displacement and radial deformation in the winding, circuit parameters in the model will be changed and thus the character of the circuit will be influenced. After acquiring the model parameters in the intact and faulted cases, transfer function coefficients derived in model from nodal analysis. Then using introduce the new index based on coefficients we can specify the type and extent of penetration of the fault in the winding. Results presented demonstrate the potential of this method  

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...