Sharif Digital Repository

Concrete-filled FRP tubes have gained popularity among structures in areas with harsh environmental condition. Despite their unique material properties such as resistance to corrosion, noticeable axial stiffness, and durability, FRP materials have poor resistance to elevated temperatures. This paper presents numerical investigations on the behavior and capacity of concrete-filled pultruded GFRP tubes (CFGFTs) after exposure to elevated temperatures under concentric compression. Variables in this study were the tube’s thickness of 3, 5, and 7mm, the infill concrete’s compressive strengths of 30 and 60MPa, and the exposure temperature of 25, 100, 200, 300, and 400°C. The results in this study... 

In many modern medical procedures, needle insertion is an inevitable part of the diagnosis or treatment protocols. The accuracy of the needle insertion is adversely affected by a number of factors. A needle, frequently assumed to be flexible, is inserted into a soft tissue and induces complex mechanical interactions that may result in considerable uncertainties. Tissue intrinsic characteristics as well as its deformation and rotation may cause dramatic complexities. This work considers the needle movement inside the tissue from the dynamics and control point of view. The proposed approach can be regarded as an initial step towards automation of needle insertion procedures; it can also be... 

This study aims for investigating a novel type of Steel Plate Shear Wall (SPSW) system in which the plate to boundary column connections are eliminated and the plate is reinforced with side, horizontal or cross stiffeners. SPSWs are one of the best lateral load resisting systems specially in high-rise buildings which makes it to be widely used in modern construction projects. SPSW system was first used in Japan and United States and found its way to other countries through the next years. In contrary to United States, stiffened SPSWs are more popular in Japan as it is a high seismic area. Despite the numerous advantages of this system, the main drawback of SPSWs is the large column sections... 

In present research forming process of nanopowders, which is a part of powder metallurgy was investigated by molecular dynamics method. Powder metallurgy is a relatively new method for production of industrial parts by pouring powder into die and compaction to desired density. One can reach parts with higher quality and strength by decreasing size of powder’s particles and entering the nano scale. Particle with smaller size have higher specific surface and due more intensity to react. Classic methods for investigation of this process don’t cover the atomic scale effects, so using newer procedures such as molecular dynamics is highly recommended. In present research, at first compaction of... 

The probability of crack appearance in soil structures and porous media is not avoidable, which could be the reason of structures collapse. According to the important affects, which they play in the vulnerability of the structures, they should be taking into account. The cracks have different effects on various materials. The most properties that cracks have, is their ability of conveying the fluid flow. For the most accurate analysis of discontinues domains, their governing equations should be taken and solved. Finite Element Method is one of the best solutions of differential governing equations. However, the appearance of some problems in the modeling of discontinues domain, was the... 

The aim of this work is numerical analysis of wave propagation in earth by using spectral element method for single and multi phase with application in oil industry. In this method, numerical solution has high accuracy due to using high order polynomials and appropriate integration points. Also, the mass matrix is diagonal by using this method which results in considerable decrease in computational cost with respect to finite element method.
The wave propagation in the mentioned models is studied by many researchers. The main problem in petroleum industry is large dimension of the model which results in high computational costs. Thus, using the proper numerical approach for these... 

In this work, the mechanical behavior of smart hydrogels is studied for temperature sensitive and, pH and temperature sensitive ones. First, an equilibrium model is presented for the temperature sensitive hydrogles which is continuous and numerically stable especially in the vicinity of the phase transition temperature. The model results are validated through comparing them with the experimental data available in the literature. The model results are in good agreement with those of experiments especially for hydrogels with high cross-linking density. Then, the model is implemented in a finite element framework by which some homogeneous and inhomogeneous problems are numerically solved.... 

The leads with heavy current passing through the covering plates, and the winding in a transformer, are sources of eddy current losses. Due to this loss some regions of tank wall are subject to serious local overheating. It affects the safety and reliability of this expensive bject and power delivery.Heavy current in large power transformers and special type transformers give rise to a concentrated passage of eddy currents which in turn cause high local losses and overheating in the metallic parts especially in the steel tank walls of transformer.This local overheating is dangerous for transformer oil and the solid insulations. Therefore the calculation of losses and proper design of... 

In this research, molecular structural mechanics method is employed to calculate the Young’s modules of a two-layered carbon graphene sheet. For this purpose, covalent bonds are modeled using non-linear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered from all other atoms located in its cut-off radius. Young’s modulus, bending modules and Poisson’s ratio of single and two-layered graphene sheets were calculated and the results revealed that Young’s modulus decreases... 

The injection process on cell is a very accurate and sensitive operation. This method is used for several new invented approaches such as tracytoplasmic Cell Injection or drug delivery. Controlling the injection force in micro scale is one of the problems of mentioned operations. Current huge and expensive laboratorial devices are helping the operators to do injection operation with :nore success. In this study a simple and novel microelectromechanical (MEMS) mechanism for doing injection process automatically on the biological cells is proposed. In order to controlling this device properly, we should model and simulate the operation condition from initial position to final condition. This... 

Numerical methods in fracture and crack propagation problems usually involve high computational costs. Adaptive finite element method is one of the techniques which can be used to simulate the crack propagation with an acceptable accuracy. In this thesis, various constitutive models are implemented for simulation of fracture, including the linear elastic fracture mechanics, cohesive zone model and continuum damage mechanics. The fracture mechanical evaluation is performed on a general integral technique for non-planar curved cracks in LEFM. In the second model, a bilinear cohesive zone model is applied to implement the traction-separation law. The Lemaitre damage model is employed and the... 

Rolling contact fatigue (RCF) phenomena is important in reducing the fatigue life and increasing the cost of maintenance. Accurate prediction of crack growth on wheels and the influence of residual stresses by FEM modeling can affect the maintenance planning. Therefore, investigation of rolling contact fatigue and its effect on rolling members life seem necessary. The first step to solve a rolling contact fatigue problem is the residual stress determination. In this research, wheel/rail contact is assumed. A bandage wheel with accurate geometry using finite element method is studied. For this purpose, a 3D elastic-plastic finite element model in ANSYS is conducted using model. The... 

In some cases, because of the need for installations, creating cutouts in the existing RC slabs will be necessary whereas these cutouts can cause weakness in the strength and stiffness of the slabs. Nowadays, expanding the use of FRP materials can provide the possibility of easier strengthening of such slabs. There are various methods for strengthening with FRP including Externally Bonded FRP sheets, Near Surface Mounted FRP rebars, and Mechanically Fastened FRP sheets. To select the most appropriate techniques for strengthening RC slabs with cutouts, it is essential to know different structural performance of these strengthened slabs. This research tends to model one and two-way spanning RC... 

This work presents a quick method in estimation of spring back effect in sheet metal forming. In this method, the so called Inverse Finite Element Method (IFEM) has been adopted for compution of strains and also blank shape. Although the of element used is membrane, the effect of bending/ unbendiing is considered by addition of some extra forces as the bending forces to the nodal forces. The results of strain distribution obtained by IFEM are applied to another algorithm developed for computation of the spring back . this algorithm has been developed for the sections with plane starin assumption. Therefore, spring back of longitudinal parts, can be estimated by this method in a short time.... 

During the past two decades, laminated composite structures have been used for many engineering applications, including aerospace, automotive, sport equipment and pressure vessels.
In spite of the excellent properties of strength to weight ratio, composite structures are vulnerable to failure when subjected to impact and vibration. It is well known that impact damage may severely degrade the strength and stability of laminated composite structures. For this reason the effect of impact on composites has been a subject of extensive research.
There are several ways of decreasing the vibration energy of structures, such as diminishing the source energy, designing structures... 

In this study, a fully coupled thermo-hydro-mechanical model for two-phase fluid flow and heat transport in fractured/fracturing porous media is introduced using the extended finite element method (XFEM) for numerical solution. The subject is important in the environmental and industrial fields such as hydraulic fracturing in petroleum industry, CO2 geo-sequestration, geothermal energy extraction and radioactive waste disposal in unsaturated porous media. In the fractured porous media, there are couplings of traction and heat and mass transfer between the fracture space and the surrounding media. Therefore, consideration of the fracture geometry explicitly in the modeling is important to... 

In this research, a comprehensive numerical model for Thermo-Hydro-Mechanical and Chemical multiphysics problems in fractured porous media was introduced using the eXtended Finite Element Method (XFEM), and its efficiency was demonstrated in two-dimensional problems. For the simplicity of the formulation and according to the common assumptions in the corresponding fields of study, the solid phase was assumed linear elastic and the flow was taken into account via Darcy's law. The system of governing equations comprised the linear momentum balance of the solid phase, mass conservation of pore fluids, thermal energy balance, and mass conservation of chemical species. The coupling of these... 

Bridges play a vital role in road-related transport industries. Significant changes to contemporary bridge design specifications have also been mainly related to strength issues. The transitions from allowable stress design to load factor design, and more recently to load and resistance factor design (LRFD), reflect this line of thinking. It is important to note that in the early 1970s, bridge engineers developed criteria for steel bridge details to protect against fatigue and fracture failure. These were indeed service life design provisions. By industry growth and extensive need for goods transportation, there is a need for the construction of new bridges and renewal of older bridges plus... 

Regarding the advantages of steel shear walls compared with other lateral load-bearing systems, the need for having better knowledge on their performance becomes more obvious. While much study, either theoretically or experimentally, have been conducted on these systems in the past, less attention has been paid to their nonlinear behaviour. This has happened where in many practical situations some parts of such systems experience nonlinearity. Therefore, it is necessary to study the nonlinear behaviour of such walls either individually or as part of a framing system. In this project, using Finite Elements Methods (FEM), the behaviour of a number of samples of an innovative steel shear wall,...