Sharif Digital Repository

The investigation of interface residual stress and interface elastic moduli tensors plays a crucial role in enhancing the conventional theory of elasticity. These considerations allow us to account for size effects and eliminate nonphysical singularities near defects. The primary objective of this study is to comprehensively calculate interface energy, residual stress components, and interface elastic moduli tensors for various interfaces between non-magnetic fcc metals using density functional theory (DFT). We achieve this by performing ab initio DFT calculations to determine the interface energies for different coherent interfaces among these metals. Subsequently, these energies are... 

Control of powered lower limb prostheses has a locomotion mode- ependent structure which demands a pattern recognizer that can classify the current locomotion mode and also detect transitions between them in an appropriate time. In the way to achieve this goal, this project presents a locomotion mode recognition system to classify daily locomotion modes consist of level- walking, stair climbing, slope walking, standing and sitting using low-cost mechanical sensors. Since these signals have a quasi-periodic nature, using sequential pattern recognition tools, such as Hidden Markov Model(HMM) improves the recognition performance,because they use sequences of information to make a decision. On... 

Exoskeleton is a wearable active device used to augment human power in upper or lower extremities. The integration of robotic devices and conventional physiotherapy is becoming more and more acceptable worldwide. The main scope of this thesis is to design and develop a prototype of a light, low-cost and wearable robotic exoskeleton to rehabilitate the upper extremity in stroke patients at home. For this purpose mechanism of a wearable exoskeleton will be proposed compatible with upper extremity degrees of freedoms with minimum number of actuators which is constructed inexpensively to eliminate the demand of expensive and professional therapists. The conceptual design of such a system should... 

Elastic optical networks, due to their key features including flexible spectrum allocation, ability to convey high bitrates, and distance adaptive modulation assignment are considered as a promising solution for providing higher capacity, more efficiency, and scalability in core optical networks.Furthermore, Multi-Core Fibers (MCFs) and Space Division Multiplexing (SDM) technique can be utilized to overcome the capacity limitation of the conventional Single Mode Fibers (SMFs). However, the inter-core crosstalk issue in MCFs should be addressed in the design of these networks.With the use of these technologies and, as a result, increasing the transmission rate in optical networks, the issue... 

Recently, elastic optical networks have attracted high interest to provide more efficiency and scalability in optical core networks. Due to the high transmission rates and the importance of the transmitted data in these networks, a failure may cause vast data losses. Thus, addressing the problem of survivability in these networks is of great importance. According to different time domain behaviors and reliability requirements of incoming traffic, supporting different quality of services is another important concern. On the other hand, using multi-core fibers is a way to scale the network capacity to provide high-speed transmission services but there is a concern that the inter-core crosstalk... 

Hydraulic steering technology has been used in vehicles for decades. Recently, a trend has been seen towards the use of electronic steer-by-wire systems that provide greater design flexibility by customizing the connection between the steering wheel and the steering mechanism. Steer-by-Wire systems (SbW) offer the potential to enhance steering functionality by enabling features such as automatic lane keeping, park assist, variable steer ratio, and advanced vehicle dynamics control. The lack of a steering intermediate shaft significantly enhances vehicle architectural flexibility. The task of a SbW system is two-fold: turning the steered wheels by tracking the hand wheel (HW) rotation and... 

Nowadays, many structural engineers use fillet welds in their designs because of their high strength and affordability. In these welds, eccentric loadings either out-of-plane or in-plane create complex condition in welds from stress point of view. To determine the capacity of such fillet welds different methods have been proposed over time. For instance, the method approved by AISC is the Elastic method. This method when combined with load factors, as required by the LRFD design method, yields very conservative designs for fillet welds. Therefore, in this project, we try to propose the plastic method for welds under eccentric loadings. This method is more economical than the elastic method... 

Fillet welds are widely used in steel construction due to their high strength and economy. In the joints used in construction, eccentricity loads in complex weld stress. The current research involves 72 bending specimens and 16 torsion specimens being modeled to study different design code relationships regarding the plastic properties of welds. In line with an even comprehensive study, the previous experimental programs in this field have been added to the modeling results.Reliability analysis has been applied to examine code relationships more precisely. The analysis involved examination of various uncertainties which showed that applying elastic methods proves more conservative than other... 

With regard to daily developments in micro and nanotechnology , the use of micro robots, In a different of applications increased extensively. The aim of this research was to introduce a mobile micro robot and analysis its behavior. this micro robot has several microlegs which are formed from microbeam mechanism and piezoelectric actuators. The degrees of freedom by taking any micro beam, any of these microlegs are able to move in a three-dimensional space. The mechanism used in this research for each of the microrobot legs, as was the consecutive series and its increase, in manor motor .In this research, unlike the previous tasks, piezoelectric actuators are considered as end effectors and... 

In many problems, the traditional elasticity cannot predict phenomenon such as nano-scale defects, surface effects, and stress concentration correctly. For example, analysis near the crack tip, dislocation and inhomogeneity shows inconsistent results because in this case values of stress go to infinity. Therefore for solving these kinds of problems, higher order continuum theories were introduced. The appearance of additional constants in the equations of motion can represent the atomic nature of materials. Furthermore, they can be utilized for determining properties of materials vibration with high frequency, granular materials, and polymers.First strain gradient theory introduced by... 

The first project ,paid to review and analysis types of crack and agents Also, was referred methods to control them in rail industry .
The wheel of Alestom train and UIC60 rail were simulated and stress analysis by software FEM (ANSYS and ABAQUS) , and effect of various parameters such as applied forces , train wheel diameter , contact position and rail inclination on stress values was studied . For comparision of results has been used analytic Hertz theory .
By using experimental data on the subsurface crack , those cracks were created in the wheel . For load on the modeling wheel and rail, ,assuming contact on the wheel rolling point , were used vertical load of wagon weight ( with... 

Motor imagery causes Event related Synchronization/Desynchronization (ERS/ERD) in Electroencephalogram (EEG) signal. These potentials can be used as an input for a Brain Computer Interface (BCI) system. To do so, it is necessary for these inputs to be correctly classified. The quality of classification is severely affected by the features extracted. Common Spatial Patterns (CSP) algorithm is often used for this task. Some of this method disadvantages are neglecting non-stationary properties of EEG signal and its proneness to overfitting. Additionally, its success is highly dependent on the frequency band that the algorithm is performed in. The most suitable sub band is interchangeable... 

To explain the dependence of sliding friction on or between the layers of wet sand, one first needs to have a rather good understanding of the elastic properties of wet granular material. Experimental work that has been done on the subject so far, has shown that these elastic properties have a peculiar dependence on the water volume fraction of the sand system. But till nowno theoretical model has been presented that could illustrate the physical causes of such findings. More specifically, these handful of theoretical models have not been able to explain the complex relationship between the shear modulus of sand and the water volume percentage. In this thesis at first the nature and... 

At first, we introduce composite optimization problems some review the proposed methods to solve these problems. To solve the composite optimization problems with strongly convex objective function, recently Chamboll and Pock proposed a general fast iterative shrinkage and thresholding algorithm (GFISTA). After that, Calatroni and Chambolle proposed a backtracking strategy for this algorithm. Unlike classical Armijo-type line searching, proposed backtracking rule allows for local increasing or decreasing of the descent step size along the iterations. In this thesis, we describe this algorithm with backtracking and prove its accelerated convergence rate. We also discuss some heuristic... 

Nowadays, robots are become more common in many important applications, such as academic and industrial issues. One of the most important robots are Multi-Arm manipulators which are used in many application such as moving objects, coloring, automatic welding and etc. Working with this kind of robots needs some vital attentions like planning their moving path. It is Because of the large number of obstacles that they face with in the path. Therefore, not only robots are not allowed to collision with themselves, but also they must not touch the obstacles. In the other words, they need Path planning. Generally, the equations of these robots are nonlinear. Therefore, computers and numerical... 

The electro-elastic fields of nano-sized piezoelectric structures are considered based on the non-classical continuum theory. Nowadays because of increasing the application of piezoelectric materials in nano technology and exclusive properties of this kind of materials, they can use as the ingredients of electromechanical systems. Therefore, the determination of induced electro-mechanical fields is important. In this study the constitutive equations based on non-classical continuum theory and general anisotropy for the elastic, piezoelectric and dielectric tensors are considered, and the electromechanical fields are determined using the micromechanical method. Furthermore, the size effects... 

DNA cyclization mechanism, has an important role in many biological processes such as gene regulation, DNA replication and recombination. In addition there are DNA-loops in Bacteria an around the Histones in Chromosomes in scale of 5-100 nm. We need to a appropriate model to study about bending and loop formationin in this important molecule which is able to describe elasticity properties of DNA.One of the most successful models, to describe the physical behaviour of a long DNA molecule, is the elastic rod model. In this model, DNA is considered as a  ixable rod that its bending energy is isotropic. Asymmetric elastic rod model is another model to describe elasticity properties of DNA.... 

Porous titanium and titanium alloys products are proper to use as implants which because of good properties such as high corrosion resistance, good biocompatibility, high strength to weight ratio and low elastic modulus. Porosity induces a decrease in elastic modulus and an increase of bioactivity. In present work, porous specimens of pure titanium and Ti-26Nb-1Si alloy were produced via conventional powder metallurgy route by applying low pressure. The influence of TiH2 Powder addition on some physical and mechanical properties of samples was investigated. The amount of TiH2 powder was used in the range of 0-40 weight percent. The powders were firstly mixed for 3 hours and then compacted... 

The utility of nano-beams in MEMs and NEMs has progressed a lot in recent years. Such systems have found wide spread use in sensors and actuators due to small size, low weight, high accuracy and low energy consumption. By a decrease in size of nano-beams, surface effect increases which makes the classical theories unable to modeling such beams. Therefore new models are required for evaluating the dynamic behavior of nano-beams. In this thesis we have attempted to develop a suitable Coarse-Grain model for analysis of such beams. At first a suitable Coarse-Grain mapping with determined Sutton-Chen potential parameters is introduced for FCC metals. In the next step, EAM is considered as... 

Many regulations around the world use the Newmark method, directly or indirectly, in the design spectrum. Research on the Newmark design spectrum shows that this spectrum sometimes significantly differs from the earthquakes response spectra that have occurred; therefore, it is necessary to develop and introduce new design spectra by modifying the Newmark method to be more compatible with reality. The developed design spectra in seismic regulations around the world are directly affected by the records involved in their development. Thus, the appropriate design spectrum should be prepared based on the seismic characteristics of the faults of each country. Evaluation of the Iranian Seismic...