Sharif Digital Repository

Structural vibrations can be reduced using an opposite force generated from an active controller. Nowadays implementation of smart materials for active controlling of vibration is growing increasingly specially in aircrafts, spacecrafts and other state of art manmade machines. In aerospace structures as the weight is extremely a limiting factor, the lightweight structural control strategies are more demanded. Considering these motivations, in recent decades, engineers have done many researches to implement active structural damping methods in industrials applications. Among all active vibration approaches, using piezoelectric materials is one of the most attractive ways because of their... 

The main function of respiratory system is to exchange gasses between air and blood. However selection of the suitable geometry and solution of the fluid flow precede all other phenomena in the lung, including particle deposition and gas exchange. The most complicated phenomena take place at the terminal generations of the lung which is known as acinar region. Due to small dimensions and inability to use experimental measurements, numerical simulations are adequate methods in this region. In the first part of this thesis a method is proposed to reduce the computational space and make it possible to model all acinar region, simultaneously. Results show that the characteristic of streamlines... 

The PCP theorem is the result of a line of work on interactive proofs and probabilistically checkable proofs. The first theorem relating standard proofs and probabilistically checkable proofs is NEXP?PCP[poly(n),poly(n)] . Subsequently, the method used in the proof of this statement were extended to yield a proof of the PCP theorem. However, this proof is relatively long and complicated. The PCP theorem is equivalent to hardness of approximation of some optimization problems. In 2006, Irit Dinur discovered a different proof of the PCP theorem. Dinur’s proof is a rather shorter and simpler than original proof. The main purpose of this survey is to present the main concepts and tools used in... 

Effects of temperature on the behavior of soils and rocks have been studied widely in recent years. Following the need for understanding the effects of temperature on the behavior of clayey soils, several experimental and numerical studies on thermo-mechanical behavior of clayey soils have been carried out and a number of thermo-mechanical constitutive models have been developed for saturated and unsaturated clayey soils. In this research, a two-yield surface thermo-plastic constitutive model developed by Abuel-Naga et al. (2007, 2009), has been chosen for THM analysis of the behavior of saturated clayey soils. This constitutive model is based on Modified Cam-Clay (MCC) model. The MCC model... 

Through the recent years application of FRP material in structural engineering has been developed significantly. According to possible changes of a building function during its lifetime or alteration of the building codes, building structures usually need to be strengthened. Referring to merits of FRP material, its application seems to be a convenient idea toward the cited requirement. Curved beam and slab are known as highly used elements in building structures. Bridges composed of horizontal or vertical arches could be noted as common examples which need to be reinforced by FRP. However curved concrete surfaces, reinforced by FRP plates, seem to be studied than it is really required; For,... 

Studying the performance of irregular structures in past earthquakes reveals that due to their severe vulnerability, we need to accurately assess the behavioral characteristics of such structures. On the other hand, all existing seismic codes recommend the use of response modification factor to determine the base shear, design forces of the members, and the design drift ratios, which seem to have limited comprehensiveness. Moreover, the response modification factor for a structural system is discussed in a general manner and the effect of factors such as number of bays, number of stories, span length, story height and irregularities are not considered. In this research, the effects of... 

One drawback of polypropylene (PP) as a widely-used semicrystalline thermoplastic is its low toughness at sub-zero temperatures. Along with adding elastomers to PP as impact modifiers, modification of PP’s crystalline structure by means of beta-phase nucleating agents —beta being the toughest polymorph of PP —is a standard method of improving PP’s toughness. Nucleation efficiency is highly dependent on the optimum dispersion of the nucleating agent. Therefore, improving the dispersion of the nucleating agents assumes an essential role. The objective of this study is to determine the influence of the incorporation method of calcium pimelate (CaPi), a highly-selective beta nucleating agent, on... 

Nowadays, methods based on deep learning networks are the most effective artificial in­ telligence methods. Although they have achieved success in various fields (such as machine vision and object recognition), practical and experimental cases show the fragility of deep learning networks against perturbations and unwanted changes of the input pattern. All these perturbations must be in a way that the main class of the perturbed input pattern can be rec­ ognized by human, but the network makes a mistake in recognizing its correct class. This thesis seeks a more accurate evaluation by designing adversarial attacks such that the main class of the adversarial pattern is detectable by human...