Sharif Digital Repository

With the advent of various advanced materials, the idea of flying like birds has attracted considerable attention in recent years. In addition, aeroacoustics has become an important issue and is being widely studied. In this work, based on the shape of Owls’ wings, an attempt was made to improve the aeroacoustic and aerodynamic performances of conventional aircraft wings. For this purpose, wings with different elements, namely, square, triangular, and semicircular, on their top surface were examined. In addition, three different spatial distributions of the elements according to the Owl’s wings shape were considered. For incompressible airflow, aerodynamic and aeroacoustic parameters of wing... 

In this study, high harmonic generation from a multi-atomic nitrous oxide molecule was investigated. A comprehensive three-dimensional calculation of the molecular dynamics and electron trajectories through an accurate time-dependent density functional theory was conducted to efficiently explore a broad harmonic plateau. The effects of multi-electron and inner orbitals on the harmonic spectrum and generated coherent attosecond pulses were analyzed. The role of the valence electrons in controlling the process and extending the harmonic plateau was investigated. The main issue of producing a super-continuum harmonic spectrum via a frequency shift was considered. The time-frequency... 

Over the recent decades, many different ducted turbines have been designed to augment efficiency of wind turbines. The design and number of blades are the most important parameters to optimize efficiency of wind turbines. In this paper, effects of design, number and attack angles of blades on rotational speed are experimentally studied in a duct which increases wind velocity up to 2.46 times numerically and 2.32 times experimentally as great as far-field flow. In order to realize this, 3 different types of aerodynamic blades were designed and then, 2-bladed, 3-bladed and 4-bladed impellers were created by these blades; finally, 9 impellers were built on aggregate. The rotational speed of... 

Analyzing contact stress in rails and wheels are very important in mechanical and railway engineering. In this paper, new formulations of the contact stress are presented for two rolling bodies by exponential and power law forms semi-analytically. Innovative elastic wheel-rail contact models and FE Modeling are proposed. The present model assumes the collection of rail and wheel as elastic deformable bodies and needs numerical and novel analytical solutions. Results of this work are close to the Hertz Stress, previous published work and FEM results, in which good agreements are found among the results. So, we can rely on this method and their results. With this approach, suitable results... 

In this article we study the effects of emotion on brain activity through nonlinear processing of EEG. EEG was recorded from 19 sites (10-20systems) in different states of brain activity; induced by emotionally valance music stimulus and also during no-task resting states. Then, we compared the EEG complexity of the rest condition with each emotional states. After that we determined the locations in which correlation dimension was changed in different states through one-way ANOVA test. In this study four excerpts of music from both Iranian traditional music and Western classical music, two negative valance and two positive valance pieces, were selected according to the results of... 

The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution... 

The formation of crystals from solutions plays a key role in various industrial applications. In this study, a new approach is presented into the optimal control of batch cooling crystallizers through a genetic algorithm. The Population balance is formularized for a typical batch crystallizer. The objective functions considered here are related to quality of products at the end of the batch. These functions are objective function of maximum mean weight size, closeness to the specified value and minimum coefficient of variation. By using an optimization algorithm (genetic algorithm), the minimum and maximum values of the objective function the input temperature parameter are obtained. The... 

In this study, effects of geometric factors and material properties are investigated on stress behavior of circular rotating disk with constant rotation in various industrial mechanisms using equilibrium equations, geometric relations and stress functions. In this way, research on a thin uniform and homogeneous circular disk under constant rotation is considered. The rotating motion produces centrifugal acceleration on each element of the rotating disk, and this rotating motion becomes the source of external loading for the mentioned problem. Additional exterior loadings are not assumed in this problem. It is comfortable to handle the centrifugal force loading by relating it to a body force... 

In this paper, a generalized intelligent water drops algorithm (IWD) for solving robot path planning problem is proposed. The authors want to reduce the time of reaching the optimal solution as much as possible. To do this, some new heuristic operators and a multi section graph model of environment is introduced. The authors divide graph to equal sections and compare behaviour of the solutions (paths) in each section with behaviour of them in other sections. This comparison uses a fuzzy inference system. Base on this comparison, a fuzzy number is assigned to each part of solutions. This fuzzy number determines the worth of a solution in a section. Less worth solutions need more improvement.... 

The challenge of finding an optimized and reliable path dates back to emersion of mobile robots. Several approaches have been developed that have partially answered this need. Satisfying results in previous implementations has led to an increased utilization of sampling-based motion planning algorithms in recent years, especially in high degrees of freedom (DOF), fast evolving environments. Another advantage of these algorithms is their probabilistic completeness that guarantees delivery of a path in sufficient time, if one exists. On the other hand, sampling based motion planners leave no comment on safety of the planned path. This paper suggests biasing the Rapidly-exploring Random Trees... 

A new mathematical insight based on logarithmic, polynomial mapping functions (MF), and dimensionless parameter (DP) models is presented for determination of some unknowns in the steady state creep stage of short fiber composites subjected to axial loading. These unknowns are displacement rate in outer surface of the unit cell, shear and equivalent stresses at interface and outer surface of the unit cell, and average axial stress in fiber. Dimensionless parameter technique is presented for determination of displacement rate and equivalent stress in outer surface of the unit cell. However, the polynomial mapping function is presented for determination of average axial stress in fiber. Most... 

FEM study is carried out for predicting the behavior of the short fiber composites in the steady state creep with application in optoelectronic and photonic devices. The study on the creep behavior is necessary in order for failure, fracture, fatigue, and creep resistance of the short fiber composites. In this article, the creep behavior of the short fiber composite is predicted under tensile axial loading by the numerical method. One of the significant applications of the work is in the short fiber composite designing and optimizing. Also, the available experimental results [10] are used for the FEM simulation  

Finite element analysis of creeping short fiber composites is carried out in the second stage creep with application in microelectronic and optoelectronic/photonic devices. Prediction of the creep behavior is very significant for designing the optoelectronic and photonic composites with optical fibers. Study on the creep behavior is necessary for failure, fracture, fatigue, and creep resistance of the optoelectronic/photonic composites. The creep behavior of the short fiber composites is estimated by FEM. Study on the creep behavior is necessary for defect analysis and creep resistance of the short fiber composites. In this research work, prediction of the creep behavior of the short fiber... 

Application of nanoparticles for wettability alteration offers a practical approach to resolve some surface-related problems encountered in the nowadays technological process. Examples are underground/subsurface engineering implications, including the enhanced oil recovery from the oil-wet carbonate reservoirs. However, the common wettability evaluating techniques such as contact angle and flotation cannot be representative of the dynamic phenomena occurring at the pore scale and hence are unable to give accurate information about the process. Therefore, in the present work, the electrokinetic evaluations are utilized to explore the wettability alteration of initially oil-wet carbonate rock... 

The objective of this paper is to present some novel insights for solving a second stage creep problem in metal matrix composites. First, a new analytical approach is developed for obtaining some unknowns in second stage creep of short fiber composites under an applied axial load. The unknowns are the radial, circumferential, axial, shear and equivalent stresses, which are determined by approximation of creep constitutive equations and using proper assumed displacement rates. A nonlinear differential equation is solved employing suitable and correct approximate assumptions. Then, the difference of the stress components utilizing creep constitutive equations and assumed displacement rates is... 

A new analytical formulation is presented to study the steady-state creep in short fiber composites using complex variable method. In this new approach, both the fiber and matrix creep at low stresses and temperatures. To analyze the crept fiber, a plane stress model was used. Important novelties of the present analytical method are determination of displacement rates with proper boundary conditions in the crept fibers and also using the complex variable method in creep analyzing. It is noteworthy that the method can be useful to study the creep behavior in polymeric matrix composites due to their high capability of creep. Moreover, another significant application of the present method is to...