Sharif Digital Repository

In this paper, an optimal control framework is formed to control rotor-Active Magnetic Bearing (AMB) systems. The multi-input-multi-output non-affine model of AMBs is well established in the literature and represents a challenging problem for control design, where the design requirement is to keep the rotor at the bearing centre in the presence of external disturbances. To satisfy the constraints on the states and the control inputs of the AMB nonlinear dynamics, a nonlinear optimal controller is formed to minimize tracking error between the current and desired position of the rotor. To solve the resulted nonlinear constrained optimal control problem, the Gauss Pseudospectral Collocation... 

The inhibition effects of 3.5 bis (2-pyridil) 4-amino 1,2,4 triazole (NBTA) and 1-10 phenantrolin (PHEN), on corrosion of mild steel in acid solutions, (sulphuric acid and hydrochloric acid) were studied. The Tafel polarisation and ac impedance techniques were employed. Results obtained reveal that both compounds are relatively good inhibitors. The inhibition efficiencies of NBTA are higher in hydrochloric acid than in sulphuric acid. This has been attributed to the synergistic effect of chloride ions present in hydrochloric acid. The mechanism of inhibition of PHEN is believed to be owing to the formation of insoluble chelates between the organic molecules and atom/ion on the metal surface.... 

In this paper, the problem of optimal tracking control for a container ship is addressed. The multi-input-multi-output nonlinear model of the S175 container ship is well established in the literature and represents a challenging problem for control design, where the design requirement is to follow a commanded maneuver at a desired speed. To satisfy the constraints on the states and the control inputs of the vessel nonlinear dynamics and minimize the heading error, a nonlinear optimal controller is formed. To solve the resulted nonlinear constrained optimal control problem, the Gauss Pseudospectral Method (GPM) is used to transcribe the optimal control problem into a Nonlinear Programming... 

In This paper detailed frequency-domain system identification method is applied to identify steering dynamics of a naval coastal patrol vessel using a data analysis software tool, called CIFER. Advanced features such as Chirp-Z transform and composite windowing techniques are used to extract high quality frequency responses. An accurate, linear and robust transfer function models are derived for yaw and roll dynamics of the vessel. In addition, to evaluate the accuracy of the identified model, time-domain responses from a 45-45 zig-zag test are compared with the responses predicted by the identified model. The model shows excellent predictive capability that is well suited for simulation... 

The Zagreb indices have been introduced by Gutman and Trinajstić as M1(G) = ∑ v∈V (G) (dG(v))2 and M2(G) = ∑ uv∈E(G) dG(u)dG(v), where dG(u) denotes the degree of vertex u. We now define a new version of Zagreb indices as M1 *(G) = ∑ uv∈E(G) [εG(u) + εG(v)] and M2 * (G) = ∑ uv∈E(G) εG(u)εG(v), where εG(u) is the largest distance between u and any other vertex v of G. The goal of this paper is to further the study of these new topological index  

Omega polynomial was introduced by Diudea. Following Omega polynomial, the Sadhana polynomial was defined by Ashrafi et al. In this paper we compute Omega and Sadhana polynomials of three classes of dendrimers  

The ABC index is a topological index was defined as where dG(u) denotes degree of vertex u. Now we define a new version of ABC index as where The goal of this paper is further the study of the ABC4 index  

This paper investigates the harmonic distortion and losses in power distribution systems due to the dramatic increase of nonlinear loads. This paper tries to determine the amount of the harmonics generated by nonlinear loads in residential, commercial and office loads in distribution feeders and estimates the energy losses due to these harmonics. Norton equivalent modeling technique has been used to model the nonlinear loads. The presented harmonic Norton equivalent models of the end user appliances are accurately obtained based on the experimental data taken from the laboratory measurements. A 20 kV/400V distribution feeder is simulated to analyze the impact of nonlinear loads on feeder... 

Let ∑ be the class of finite graphs. A topological index is a function Top from ∑ into real numbers with this property that Top(G) = Top(H), if G and H are isomorphic. is defined as half sum of the distances between all the pairs of vertices in a molecular graph. The goal of this paper is to further the study of Wiener index of special case of a chain of fullerenes  

The Zagreb indices have been introduced more than thirty years ago by Gutman and Trinajstić. In this paper we introduce a new version of Zagreb indices and then we compute them for an infinite family of nanostar dendrimers  

To achieve higher accuracy in the prediction of cutting forces in finish milling process of sculptured parts, the curvatures of in-process workpiece surface are necessary to be taken into consideration in the calculation of cutter-workpiece engagement boundaries. These curvatures, however, are not readily available in tool path data, as the main existing source of geometrical information of the process. In this paper, first, a new straightforward algorithm is proposed to extract the principal curvatures and principal directions of the in-process workpiece surface from ball-end finish milling tool path data. These quantities, then, are employed to calculate the boundaries of engagement... 

This paper presents a new analytical model for calculating the cutter-workpiece engagement (CWE) boundaries in the ball-end finish milling process of curved surfaces. To this end, first, a quadratic mathematical representation considering the principal curvatures of the surface is employed to locally describe the workpiece surface around the instantaneous cutting region. This description, then, is utilized to find the intersection curves of the tool rotary and workpiece surfaces in three ball-end milling modes including slotting, first cutting, and following cutting. Through comparison studies, the model predictions are verified by the corresponding results obtained via solid modeling in... 

In this study, titanium dioxide nano powders were electrophoretically deposited on the stainless steel in Isopropanol and Triethanolamine as a solvent and dispersant, respectively. The effects of deposition parameters including deposition voltage (5 to 20 V) and deposition time (5 to 60 s) on the microstructure and surface topography were examined by scanning electron microscope (SEM) and scanning probe microscope (SPM), respectively. In addition, the effects of these deposition parameters on packing density were investigated. This research revealed that substrate surface is fully covered with increasing deposition voltage and deposition time. Therefore packing density of deposited films is... 

This paper presents a high performance direct torque control (DTC) theme for the induction motor (IM). To solve those problems associated with conventional DTC, such as flux and torque ripple, variable switching frequency, inaccuracy in motor model and other parts of system. The Active Learning Method (ALM) is implemented on the DTC. In the Active Learning Method for information modeling, a method known as Ink Drop Spread (IDS) is used. The simulation results of DTC system based on ALM and the comparison of motor performance under the proposed control system with respect to those obtained under conventional DTC confirms its effectiveness and accuracy  

We synthesize TiO2@SnO2 core-shell nanoparticles (NPs) by a facile two-step aqueous sol-gel method and their photocatalytic activity is compared with the pure TiO2 and SnO2 NPs for degradation of methylene blue under UV irradiation. The chemical property, crystal structure and morphology of the synthesized samples are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FE-SEM) and transmission electron microscope (TEM) techniques. The mechanisms of electron–hole recombination and separation of charge carriers are studied by photoluminescence (PL) and diffuse reflectance spectroscopy (DRS). Furthermore, the kinetics... 

In this paper, a virtualized ball-end milling model is presented in Unity game engine environment, in which the machining process is simulated by proposing a new geometric approach. The model calculates and illustrates cutter-workpiece engagement area and cutting forces in a real-time manner. To calculate cutter-workpiece engagement, the workpiece surface is considered a set of nodes. Then, using a new geometric method, the engagement area is calculated at any node on the engaging surface. Utilizing the calculated engagement area and adopting mechanistic force model, the cutting forces applied from each node on the workpiece surface to the tool’s cutting edge are calculated. Adopting the... 

Two edges e and f of a plane graph G are in relation opposite, e op f, if they are opposite edges of an inner face of G. Relation op enables the partition the edge set of G into opposite edge strips ops. On this ground, Diudea defined Omega and Theta polynomial while Ashrafi et al. defined the Sadhana polynomial. In this paper a weighted version of these polynomials was introduced and several relations between them are demonstrated. Some molecular weights are suggested in view of using the derived topological indices in correlational studies  

A new counting polynomial, called Omega, was recently proposed by Diudea. It is defined on the ground of opposite edge strips "ops". The Sadhana polynomial has been defined to evaluate the Sadhana index of a molecular graph. A third one, called Theta polynomial is also derived from ops. In this paper we compute Omega, Sadhana and Theta polynomials of the Cartesian product graphs  

A new counting polynomial, called Omega Ω(G,x), was recently proposed by Diudea. It is defined on the ground of "opposite edge strips" ops. Two related polynomials: Sadhana Sd(G,x) and Theta Θ(G,x) polynomials can also be calculated by ops counting. Close formulas for calculating these three polynomials in infinite nano-structures resulted by embedding the titanium dioxide pattern in plane, cylinder and torus are derived. For the design of titanium dioxide pattern, a procedure based on a sequence of map operations is proposed  

The electrodeposition of cobalt, nickel and Ni-Co alloys was studied by electrochemical techniques. Cyclic voltammetry and current transient measurements were used to characterize the Co-Ni system in other to obtain the nucleation and growth mechanism. The cyclic voltammetry results clearly showed that electrodeposition of cobalt, nickel and Co-Ni alloy is diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Co and Ni are shifted to more cathodic potentials in the Co-Ni alloy system. In addition, the current transients revealed that nucleation mechanism is instantaneous with a typical three-dimensional (3D) nucleation and growth process. The number of...