Sharif Digital Repository

Cost-effective and reliable damage detection is critical for utilization of composite materials. This research investigates a wavelet-based approach for SHM and detection of through-thickness crack in different lengths and angles in [0/45/-45/90]s CF/EP composite plate utilizing ANSYS finite element method (FEM) software and digital signal processing technique utilizing MATLAB software. To this end, a dual-PZT actuation scheme is applied, aimed at generating the S0 mode at a square composite plate. This study contributes to the damage detection by developing an improved wavelet-based signal processing technique that enhances the visibility and interpretation of the Lamb wave signals related... 

The current study aimed to investigate the differential effects of multimedia input with no subtitle, subtitle, or caption (L2 subtitle) on vocabulary retention while controlling for the possible effects of students' vocabulary size and language aptitude as covariates. A total of 81 undergraduate university students were assigned to the study from three intact groups at Sharif University of Technology. All of the participants were Persian speakers and were in the age range of 18 and 22 years old; homogeneity of the students regarding their language proficiency was also established. During two different sessions, students' vocabulary size and language aptitude were measured. The groups were... 

In recent years, some listed companies have re-evaluated their assets, an event that has generally received market attention; In fact, the market seems to be reacting very positively to an accounting phenomenon. In this study, we seek to investigate the market reaction to the revaluation of listed companies in Iran. To do this, we first estimate the market reaction to the news of the revaluation of assets. We then examine the possible reasons for the market reaction to the revaluation. Asset revaluation can improve the firm's access to finance by improving some financial ratios; On the other hand, the increase in capital from the revaluation of firms is accompanied by the issuance of bonus... 

Increasing competition in global market and different requirements of customers persuade manufacturers to improve the efficiency of their manufacturing activities. For this end cellular manufacturing systems can be introduced as an innovative and compromising practice for companies. Among the necessary decisions for a successful cellular manufacturing design and implementation, production routing selection (PRS), cell formation (CF), group layout (GL) and group scheduling (GS) are the four most important ones. This research investigates these decisions and proposes a new approach to integrate them. We use important production factors such as production volume, operation sequence, operational... 

Springs parts are widely used in many industries including the automative industries where the disability of the springs can cause damage. Spring forming processes induce residual stresses on the surface of spring. Residual stress is affected by various processes, such as heat treatment or shot peening. When a coiled spring is heat treated, depending on the temperature and time of heat treatment residual stresses are partially relieved, but they generally do not disappear.An important characteristic of spring steel is its resistance against stress relaxation at different temperatures and times. Stress relaxation in valve springs working at high temperatures causes some problems for... 

This thesis aims to develop a numerically efficient nonlinear layer-wise shell element formulation for delamination analysis of laminated composite shell structures. The element, in a mesoscale scheme, is formulated based on a zig-zag theory and features three translational degrees of freedom for each node on the mid-surface of the shell in addition with two rotational degrees of freedom for each layer. In this way, the displacement field is formulated via adapting the Mindlin-Reissner theory in each layer and an ordered second-order algorithm for finite rotations. To verify the proposed formulation, many popular benchmark problems for geometric nonlinear analysis of shell problems are... 

Index funds are one of the most vital financial institutions providing a wide range of values for different investors. Despite the importance of these funds, not only are index funds recently developed, but they also do not replicate their indices effectively. In this paper, we analyze the portfolio performance of the Karafarin Index Fund as an open-end fund for case study in various frameworks. First of all, the asset allocation and security selection attributions are assessed for capturing the capabilities to choose the suitable security at the right time. In addition, this assessment is done for the industry allocation and security selection attribution in the stock portfolio of the... 

The behavior of boundary layer under the effect of the sweep angle is considered. The measurements were performed by a pitot tube rake. Three models with various sweep angels at angles of attack -2, 0 and 2 degree were tested. Both tip and root of all wings were closed by flat plates in order to prevent the flow to roll-up. However the flow field on the wing was still three-dimensional because of the sweep angle. The velocity on the wing has two components; longitudinal and lateral. The cross flow emerges due to the non-equilibrium of pressure and centrifugal forces. The velocity profiles showed that the magnitude of cross flow was stronger near the leading edge of the wing. The cross flow... 

Alumina as an engineering ceramic has special characteristics such as hardness, high abrasive, fatigue and corrosion resistance but suffers from low toughness. One effective method in improving toughness is adding second phases such as tetragonal zirconia and carbon nanotubes.
In this research, alumina- zirconia nanopowders has been prepared by solution combustion method and carbon nanotubes was added to it by two different ways: 1) in situ synthesis of CNTs by CVD 2) dispersion of CNTs by heterocoagulation method. In the case of in situ synthesis of CNTs in AZ matrix, the synthesis temperature and flow ratio of N2/C2H2 gases was investigated and optimum conditions were 800̊C and 300/30,... 

A Flying Electric Generator (FEG) can be a wind turbine which operates at high altitudes, where there is a continuous fast flow of air and converts wind energy to electrical power.The related field is an interdisciplinary area and is mostly related to the Aerospace Engineering and Energy Conversion. We focused on Iran, as one of the few lands in the northern hemisphere that has a high overall amount of high altitude wind energy for at least half of the year over it, according to the information of atlas of airborne wind energy in this work.So to install the FEGs in Iran, we had to find, places with a safe aerial space overhead which grant us reliable spots over country. These places found by... 

In this study some experiments were performed to investigate the effect of sweep angle on the transition location of laminar flow to turbulent flow. Three half wing models were used, each having a different sweep angle but with the same aspect ratio in various angles of attack. Two flat plates were used at the ends of the swept wing models to prevent the flow from rolling up over the wing. By simulating flow over infinity swept wing by eliminating tip vertices, the effect of sweep angle on flow transition phenomenon was investigated.
The experiments included the study of transition flow via hot-film sensors, which were glued on the wing surface. We found that the small leading-edge... 

Walking is one of the most important physical activities in daily life and it plays an important role on body health. Despite the importance of this issue, today many people suffering from walking abnormalities. This thesis aims at designing an exoskeleton for the rehabilitation in order to help patient’s lower limb movement. The hip joint is crucial for walking and is problematic for a large number of aged people or the patients who suffered from paralysis. A number of hip and knee model checked, one model for knee and one for hip selected to combine in order to achieve a unique model for walking exoskeleton. A mechanism consisting of six link and seven joints with four degrees of freedom... 

Nowadays, microgyroscopes are among the most important products of MEMS. The production of small, precise and inexpensive gyroscopes has become possible as the result of recent developments in fabrication technology. In this thesis it is intended to introduce a new method for manufacturing more precise microgyroscopes regarding manufacture facilities. Using this new method, sensitivity and resistance of microgyroscopes are increased against noises which are primarily caused by vibration and rotation about undesirable axes. The rotational movement imposed on the gyro is detected through fluid flow within its torus channel. This transformation facilitates the measurement of the initial motion.... 

With altering natural state and increasing impervious surfaces, traditional urbanization leads to deteriorating the environment and water catchments. During the years most efforts in order to control the urban runoff outflow, have been focused on quantity; and awareness about improving water quality has been raised just in the last few years and, which emphasizes on pollution source control. Standard water quality sampling methods are time consuming, expensive and because of sampling in broad geographic areas, difficult; however modeling is a more efficient way in assessing water quality and as worries about non-point source pollution grows, different kinds of models have been used to... 

In this project Deployment of multi-agent systems was studied. Maximum coverage over a point or curve or area is desired in deployment of multi-agent systems. A facility location optimization function was derived from geometrical concepts such as voronoi, n- geometric median and fermat-weber problem by optimization of which the deployment of multi-agent systems is performed. First, it is assumed that dynamic of agents is first order and second order .Next, it is assumed that agents are in a fluid. In all situations a suitable control algorithm was derived to optimize the facility location function to perform deployment. Next, another facility location function was derived by optimization... 

Concrete structures require reinforcement and retrofitting because of possible mistakes in design or calculation, inconformity between plan and implementation, change in occupancy or applied loads, and decay. Development in technology, production of materials, and new methods play important roles in development of structure construction and reinforcement methods. Emerge of new materials creates great demand in studying, surveying, and determining design characteristic and criteria for these materials. One of these materials is FRP composite which is used in concrete structure reinforcement in different ways. In this laboratory research, the effect of external wrapping by GFRP composite... 

In recent two decades, different anonymous communication systems has been proposed. These systems are interested by journalists, bank employees, military forces, and human rights advocates. Tor is one of the most popular anonymous communication systems. Tor uses onion routing for privacy preserving. Re-cently, many attacks has been introduced against the anonymity of Tor users.In these attacks entry and exit nodes are compromised. One of these malicious nodes, makes the attack on the intented flow and the other one recognizes the flow. All these attacks admit their vulnerability against dummy messages. They state that, because of dynamics of onion’s keys, any dummy injection will dis-turb... 

Recently many organizations outsource their data to an external server due to easier data maintenance. One of the security issues in data outsourcing scenario is the enforcement of data owner’s access control policies. This includes some challenges; namely, the number of keys needed to access authorized resources, efficient policy updating, write access control enforcement, user and data owner overhead, and preserving confidentiality of data and policies . Most of the existing proposed solutions address only some of these challenges, while they impose high overhead on both the data owner and users. Moreover, most of them address enfrocement of policies in form of access control matrix and... 

Because of the working conditions of semiconductors at ambient temperature and pressure, degradation of organic pollutants through semiconductors photocatalysis has attracted the interest of many researchers. Because of its large exciton binding energy,high chemical and physical stability,high electron and hole mobility, and low cost; zinc oxide, an n-type semiconductor with 3.2 eV direct band gap, is widely used in applications such as photocatalysts, solar cells, and light-emitting diodes. Among various morphologies of ZnO, 1D nanostructures such as nanowires and nanorods have recieved much attention due to their high surface to volume ratio. However, the application of ZnO as a...