Sharif Digital Repository

A fuzzy controller has been suggested for attitude control of magnetic actuated satellites in order to calculate the desired mechanical torque based on the attitude error including error in the angles and their rates. The problem of selecting proper magnetic dipole based on the known desired mechanical torque has been investigated, two different methods for the purpose has been suggested and the performance of the attained fuzzy magnetic attitude controllers has been shown under two different simulated conditions. © 2009 IEEE  

The problem of time optimal magnetic attitude control is treated and an open loop solution is first obtained using a variational approach. In order to close the control loop, a neural network with time varying weights is proposed as a feedback optimal controller applicable to the time varying nonlinear system. The good robustness and low real-time computational burden of the proposed neuro-controller makes the controller more useful compared to the other control methods. © 2008 IEEE  

Surface modification of ultrafiltration membranes has shown a significant potential to reduce fouling and increase flux and lifetime, which are the most important factors in membrane filtration. In this study, the surface-modified membranes were prepared by grafting hyperbranched polyethyleneimine (HBPEI) onto polyvinylidene fluoride (PVDF)-sulfonated polyethersulphone (SPES) blending membranes. Electrostatic interactions between HBPEI and SPES result in a well-attached positive-charged HBPEI grafting layer on the PVDF membrane surface. Surface-modified membranes were examined for the removal of cationic E-coat paint and their performance was measured in terms of total permeation flux, paint... 

This paper presents an algorithm for synchronizing two different chaotic systems by using a combination of Unscented Kalman-Bucy Filter (UKBF) and sliding mode controller. It is assumed that the drive chaotic system is perturbed by white noise and shows stochastic chaotic behavior. In addition the output of the system does not contain the whole state variables of the system, and it is also affected by some independent white noise. By combining the UKBF and the sliding mode control, a synchronizing control law is proposed. Simulation results show the ability of the proposed method in synchronizing chaotic systems in presence of noise  

In the present study, oblique low-velocity impact (OLVI) on GLARE fiber-metal laminates (FMLs) has been modeled using finite element analysis (FEA) for the first time. Two types of boundary conditions (BCs) can be considered for impactor in the low-velocity impact: constrained (if the impact angle between the impactor and target remains constant during and after the contact) and free (if rotation of the impactor and change in angle with respect to the target is likely) BCs. The more details of these BCs are described in the paper. The OLVI is numerically modeled for four different impact angles. Effect of BC types and impact angle on energy absorption, as well as maximum contact force, is... 

In the present study, oblique low-velocity impact (OLVI) on GLARE fiber-metal laminates (FMLs) has been modeled using finite element analysis (FEA) for the first time. Two types of boundary conditions (BCs) can be considered for impactor in the low-velocity impact: constrained (if the impact angle between the impactor and target remains constant during and after the contact) and free (if rotation of the impactor and change in angle with respect to the target is likely) BCs. The more details of these BCs are described in the paper. The OLVI is numerically modeled for four different impact angles. Effect of BC types and impact angle on energy absorption, as well as maximum contact force, is... 

In this study, a thermal method was used to synthesize spinel NiCo2O4 and carbon nanotubes (CNTs)@NiCo2O4 with an average size 50 nm and 20 nm, respectively. Addition of CNTs into NiCo2O4 noticeably increases the active surface area compared to pure spinel NiCo2O4. SEM analyses showed that the morphologies are spherical in both pure and composite samples. Uniform CNTs@NiCo2O4 nanoparticles exhibit high specific capacitance of 210 F g−1 at 2 A g−1 and a good retention capacity of 92.70% after 2500 cycles, which shows a considerable improvement compared to NiCo2O4. Additionally, an exceptional rate capability of about 73.2% was obtained at 50 A g−1. Such remarkable electrochemical performance... 

A new approach, based on Adaptive-Network-based Fuzzy Inference System (ANFIS), is presented for the classification of arthrometric data of normal/ACL-ruptured knees, considering the insufficiency of existing criteria. An ANFIS classifier was developed and tested on a total of 4800 arthrometric data points collected from 40 normal and 40 injured subjects. The system consisted of 5 layers and 8 rules, based on the results of subtractive data clustering, and trained using the hybrid algorithm method. The performance of the system was evaluated in four runs, in the framework of a 4-fold cross validation algorithm. The results indicated a definite correct diagnosis for typical injured and normal... 

It is not common to build a geomechanical model for depleted reservoirs as logging and coring are costly and time consuming in such reservoirs. On the other hand, in regular analysis of wellbore stability, the effect of time is completely ignored. As a result, with time there will be some errors in the evaluation of wellbore stability in depleted reservoirs. In order to determine the optimum wellbore trajectory during the reservoir life, it is necessary to have a model which can estimate the rock properties based on the first full logging suite and also consider the depletion effect. In this study, a novel model is proposed which combines a mechanical earth model, borehole circumferential... 

Ceramic-matrix composites containing TiC-TiN have been used in a variety of application because of their superior properties such as high hardness, good wear resistance and high chemical stability. In this research, effect of coke and coke/calcium beds in synthesis of Al2O3-Ti(C, N) composites using alumino-carbothermic reduction ofTiO2 has been investigated. Al, TiO2 and active carbon with additives of extra carbon and NaCl and without additives, in separate procedures, have been mixed. Afterwards, mixtures were pressed and synthesized in 1200°C for 4hrs, in coke and coke/calcium beds, separately. Al2O3-Ti(C,N) composite was synthesized in ternary system of Al-TiO2-C with excess carbon and... 

The objective of this paper is to provide optimization of falling film Li/Br solution on a horizontal single tube based on minimization of entropy generation. Flow regime is considered to be laminar, the effect of boiling has been ignored and wall temperature is constant. Velocity, temperature and concentration distributions are numerically determined and dimensionless correlations are obtained for predicting the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to non-isothermal heat transfer; fluid flow friction and mass transfer irreversibility. Scale analysis shows that... 

In this paper, heat and mass transfer phenomena occurring simultaneously in falling film generator of absorption chillers have been studied. The analysis is based on the laminar flow of an Li/Br solution over a horizontal single tube and tube bundle having a constant tube wall temperature. The effect of boiling has been ignored. An extensive numerical code is provided to calculate the heat transfer coefficient and the rate of evaporation. A parametric study is performed on the coefficient of heat transfer and the evaporation flux of the refrigerant. Dimensionless correlations are obtained to calculate the heat transfer coefficient on the horizontal tube and tube bundle. The comparison... 

The purpose of this research is to explain the surface modification of fabricated polyamide reverse osmosis (RO) membranes using UV-initiated graft polymerization at different irradiation times (15, 30, 60, and 90 s) and various acrylamide concentrations (10, 20, and 30 g L−1). Also, coating of membranes surface with various concentrations of TiO2 nanoparticles (10, 20, 30, and 50 ppm) followed by the same UV irradiation times was investigated. After that, the membranes modification was done by grafting of acrylamide blended with TiO2 nanoparticles via UV irradiation. The characterization of membranes surface properties and their performance were systematically carried out. The results... 

The objective of this study was to propose a new analytical model for studying response of head impacts. Head is modeled by fluidfilled ellipsoidal shell of inconstant thickness impacted by a solid elastic sphere. Modeling the head as an ellipsoid is more realistic than modeling it as a sphere, the previous model existing in the literature [3]-[8]. In this model, the effect of Hertzian contact stiffness and local shell stiffness are combined to derive explicit equations for impact duration, the peak force transmitted to head, and the head injury criterion. One of the advantages of the model presented is sensitivity to the site of impact. A comparison between the present analytical results... 

Ultrasound hyperthermia is used to treat tumors in human tissue by heat. It is characterized by the application of high intensity focused ultrasound (HIFU), high local temperatures and short treating time of a few seconds. HIFU is a non-invasive treatment modality for a variety of cancers, including breast, prostate, kidney, liver, bone, uterus, and pancreatic cancers. Computer models have been used to determine tissue temperatures during ultrasound hyperthermia. In this work, we consider a liver tissue with a tumor at its center. We calculated temperature distribution in the presence a large blood vessel. We studied the effect of varying the exposure time (heating duration) and the diameter...