Sharif Digital Repository

In seismic regions, the construction of structures with appropriate seismic performance and re-centering capability that can reduce residual displacement and damage, are necessary. As an alternative, prestressed columns were developed in recent years which can limit the permanent deformation and structural damage effectively. After severe damage and residual displacement of bridge piers and building’s columns, extensive research was carried out on prestressed columns. Most researches have been conducted on the prestressing of bridge piers and precast columns in self-centering system but prestressed columns in common moment resisting frame and comparing their advantages and disadvantages with... 

Water transportation through carbon nanotubes is key for designing nanodevices. The directed transport of water molecules through a rotating charged carbon nanotube (CNT) is investigated by molecular dynamics simulations. It is found that the net flux of continuous unidirectional water flow depended sensitively on the charge distribution, charge density and rotation of the CNT. we find that for a constant charge density, the water flux increases with the increase of the charge difference. Besides, we find that the water flux shows a nonlinear dependence on the angular velocity of the rotation. The rotation of the CNT with low angular velocities, can not generate a continuous water flux. The... 

One important aspect of privacy, is confidentiality. A common solution to preserve the confidentiality in network communications is ”Virtual Pri- vate Network”. VPNs todays are expected to be more secure and support higher throughput for their new applications, such as Inter-Cloud VPN and Virtual Private Cloud. block cipher is an important security com- ponent employed in most VPNs.On the other hand, most block ciphers have mathematical weaknesses in their structures, so the ttacker can use these weaknesses to break them faster than brute-force attacks. This thesis proposes a new method named ”Chaos-based Selective Key (CSK) Cryptosystem”, for increasing the security of block ciphers in a much... 

Streamline Curvature method is one of the most commonly used methods by industry for prediction of axial flow compressors. This method analyze axial compressor by solving radial equations in the meridional plane to locate streamlines and also by using empirical models to predict total pressure loss. Despite growth of CFD models, Streamline Curvature method has been considered as most practical method for compressor preliminary design and performance assessment because of it’s high speed and good precision. In the current work a C++ code (SLC) has been developed using streamline curvature for axial flow compressor performance analysis. This code receives compressor geometry, properties of... 

Soil-structure interaction may have a considerable effect on the response of the superstructure. One of the main steps in analyzing the soil-structure system is determining the soil impedances which vary with frequency. Although it is possible to analyze a dynamic system with complex frequency-dependent property matrices, this cannot be taken into account in most standard general-purpose softwares. In addition, the nonlinear behaviour of the structure can only be studied in time domain. Therefore, in the past two decades efforts have been made to replace the soil media with discrete models having a small number of degrees of freedom (DOFs) and a few springs, dashpots and masses with... 

Multi-directional forging is used as a severe plastic deformation process for producing ultrafine grained materials in which a sample undergoes consecutive compressive strains and as a result, coarse grains break to smaller grains. The strength of multi-directionally forged material increases because of grain refinement, although the high strain energy reserved in a sample after large plastic deformation lessens its ductility. Metals experience non-isothermal heating cycle during annealing till they reach the target temperature. Non-isothermal heating cycle can affect microstructure and mechanical properties of severely deformed material due to its high strain energy. Thus, investigation of... 

The use of sandwich panels has become very common in recent engineering designs when the weight of the part or structure is important and we are looking to lose weight while maintaining strength. The mechanical properties of this type of structures, including yield stress, fatigue behavior and estimation of their life, failure modes, natural frequencies and resonance phenomena, etc. are affected by various factors, including geometric and environmental factors. Fatigue is one of the most common failures in these structures. Composite materials have complex structures. In these materials, due to the viscoelastic properties, the fatigue behavior changes with changing stress, stress frequency,...