Sharif Digital Repository

It is aimed in this study to numerically investigate the effect of contact angle on the heat transfer coefficient in oil-water two-phase flow. For this purpose, the finite element method (FEM) is used to solve the unsteady Navier-Stokes and energy equations. The level set method is also used to capture the interface between the phases. In the first part of the study, two-phase flow of the water and calibration oil is considered in a T-junction geometry at contact angles of 5°, 40°, and 75°. It is observed that the flow patterns formed in the microchannel depend on the initial flow condition which results in the hysteresis phenomenon. Investigating the effect of wall contact angle on the... 

Contact happens when two bodies collide. Depending on our assumption, it can be considered as a frictional or frictionless contact. Here we have assumed that friction accompanies the contact phenomenon, hence it is called a frictional contact. For modeling contact problems, different procedures can be used such as node-to-node or node-to-surface patterns. Here we want to use the node-to-surface procedure to model the contact problem. The node-to-surface pattern has the capability to model interface behavior between different materials. By using the finite element method through numerical computations and also by applying constraint conditions which are related to contact conditions, we can... 

The present research illustrate the finite element modeling of contact between solid bodies, with a special emphasis on the imposing the contact constraints and modification of contact properties on surface in the case of frictional slip. A new approach for both two-dimensional and three-dimensional formulation of contact constraint that allows for a simple and unified treatment of all potential contact scenarios in the presence of large deformations in static case, is presented. The most important outstanding issue in this approach is symmetrical contact stiffness matrix which reduces computational efforts. Based on the observation of numerical results and comparison by experimental models,... 

Researching in the field of optimization of network immunizing and epidemic spreading is an active and important area. According to literature review, influential nodes are detected based on global graph metrics such as centrality measures. On the other hand, when a network infrastructure is not available and a direct or straight path between source and destination may not be accessible, one can use opportunistic networks routing protocols in Delay Tolerant Networks to recognize influential users is an appropriate approach. In this work, we use a real world three layer dataset which consists of digital data (social relations and Bluetooth contact traces) of individuals. We convert the real... 

Fretting fatigue is one of the main factors leading to failure in structures that have components temporarily connected to each other. The occurrence of fretting at the connection region of a structure under cyclic loading is inevitable, and only various methods can delay its occurrence or minimize the damage resulting from it. Fretting is dependent on various factors, and this has made previous studies unable to lead to a unified approach for predicting the fretting fatigue crack initiation life. In this thesis, after reviewing previous studies, a proving ring is designed for fretting fatigue testing. In the next step, fretting fatigue tests using the bridge-type method are performed on... 

In contacts, the presence of both variable loading and low-amplitude movements causes a kind of fatigue in these components called FRETTING FATIGUE. fretting fatigue has reduced the life of parts. Due to the high cost of replacing some parts in case of failure, it is necessary to take effective measures to delay this exhaustion. One of the effective solutions that can be applied is the use of coating and surface treatments in the contact areas. In this research, first, the fretting fatigue maps of Ti-6Al-4V alloy have been calculated and drawn according to the recommendations of the ASTM standard by using finite element methods. In the next step, by using experimental experiments, the damage... 

In many industrial devices and machines, variable loading is applied to the parts, which will lead to fatigue in these parts. Most of these components are in contact with other components, and when the device is operating, low-amplitude movements occur at the contact point. Variable loading conditions and low-amplitude movements at the point of contact can cause failure on parts called FRETTING FATIGUE. This type of failure occurs in many aerospace components, such as where the compressor blade roots connect to the disc. In recent years, many failures due to fretting fatigue has been reported, which has made the need to take solution to prevent this type of failure more and more obvious. One... 

In recent years, there have been a tremendous research performed in the field of sestems containing small scales. However, besides all advantages of such systems, microfluidic systems have extraordinary difficulties and pumping liquid drops as part of some of these systems has been very important issue. An approach related to flow control is use of surface acoustic waves (SAW), which is known as acoustofluidic device. So far, most researches have only qualitatively investigated acoustic flux phenomenon. On the other hand, computational research is ongoing more emphasizing on accuracy, optimization, and obtaining more detailed physical understanding of SAW applications. Investigation of the... 

In this Thesis ,the two-dimensional thermoelastic tractive rolling contact problem for an FGM coated half-plane under the plane strain deformation is investigated. A rigid cylinder rolls on the surface of an FGM coated half-plane with constant translational velocity, generating frictional heat in the slip zones of the contact area. Thermo-mechanical properties of the FGM vary exponentially along the thickness. It is assumed that the contact area consists of a central stick zone and two slip zones of the same sign. The transfer matrix method and Fourier integral transform technique are used to achieve a system of two Cauchy singular integral equations. The associated governing equations are... 

Turbine blades are exposed to mechanical and thermal stresses due to their operation in critical conditions and get into various damages such as fatigue and wear. These factors reduce the life of the blades and lead to expensive maintenances. As a result, recognizing the type of possible damage helps to increase the life of the blade and to delay the occurrence of failures by taking the necessary actions.The subject of this thesis is to investigate the effect of geometric parameters on the slip amplitude in the root of a turbine blade. In this work, the effect of three parameters of contact area length, contact angle, and coefficient of friction on relative slip amplitude and contact... 

Surface roughness has an enormous influence on many important physical phenomena such as contact mechanics, sealing, adhesion and friction. Contact mechanics was studied as an important topic for long years in order to realize the friction phenomena, contact fatigue and fluid leaking between rough surfaces. Therefore, the contact of rough surfaces has been widely invistageted by engineers for different purposes like rejouvination, prevention of environmental pollution and stress analysis. Failure modes have been studied in this research for a specific type of injector by experimental methods. After that, injector's rough surfaces were modeled. Firstly the proper point cloud was modeled by... 

The problem of fretting fatigue due to the inherent complexity and high probability of its occurrence in many engineering systems, is very important for engineering design. Fretting Fatigue is a significant failure mode in many contacting mechanical components, in which two contact surfaces experience low amplitude oscillatory movement due to cyclic loading. There are many significant contact fatigue problems in structural design which fretting fatigue at lap joints in aging aircraft and fretting fatigue of dovetail joints in gas turbine engine are the most important of them. Numerical simulations provide an appropriate and powerful tool for parametric study of fretting fatigue behavior of... 

Nowadays, the use of finite element Software applications in enigineering departments has become Inevitable and commonplace. Acceptance of the necessity of using such software applications for reducing the cost of research and development does not require any evidences of financial instruments to be presented. Reducing design and manufacture time together with pseudo-empirical approach has cuased the finite element science to become a conventional designing tools.
Since contact is the main method to apply a load on a ductile object,and stress concentration caused thereby is often a major cause of failure in mechanical parts, the issue of contact is a fundamental topic in mechanics of... 

Modeling of contact is a important problem in word science, so a lot of method presented by researchers .
In practical industry, if members of contact have complex shape or large deformation, analytical method can not solve the problem and use numerical method.
This method by using ansys , first analyze one-area contact and compare between numerical result and analitical result, then analyze two-area contact between two body with vertical force, and compare result with considering effect of slip and target surface.
Finaly to analyze a practical multiple contact problem, use modeling of tyre and road surface partial slip, and compare between ansys result with experimental result ,... 

In the present study, an analytical procedure has been presented to analyze a generic two-dimensional frictional multiple contact problem between two isotropic, homogeneous and elastically similar half planes, under the constant normal (including applied moments) and oscillatory tangential loading, with partial slip behavior. This procedure is based on the classical singular integral equations approach. By applying boundary conditions at nonsingular end points, new side conditions have been derived and titled “the consistency conditions” for multiple contacts. These conditions are necessary for determining the position of nonsingular end points, when the number of them exceeds the number of... 

This study focuses on the mathematical modeling of the rolling contact problem of an FGM coating-substrate system. The first part presents the uncoupled rolling contact problem of an FGM coated half-plane under the assumption of a central stick zone with two slip zones of the same sign. Considering all possible stick/slip scenarios, the fully coupled rolling contact problem of a graded coating is given in the second part. Finally, the rolling contact problem of two elastically similar cylinders with graded coatings will be discussed. Generally, all mentioned problems can be solved in three consecutive steps. First, the governing equations of the relevant rolling contact problem are... 

In many mechanical components, contact loading has a major role in stress field analysis. In this thesis, a combination of crack growth simulation and unilateral contact problem was carried out numerically. The Finite Element Method provides a powerful numerical tool to analyze contact problems. In the traditional FEM discontinuities should not cross through elements, so crack will grow through boundaries of elements, therefore, the model should remesh in each step of crack growth in order to align the mesh along the boundaries of discontinuities. This limitation causes major errors and computational costs. To overcome this limitation, the extended Finite Element Method (XFEM) will be used... 

Most of the current application and potential FGM included in the areas related to contact mechanic .These issues essentially are related to the transfer of force between two objects, that in general is with friction, so in this study the contact under the loading of horizontal and vertical with its different aspect such as the effect of contact region, the effect of round and also the effect of getting harden and soften of FGM.
The used method is a numerical method ¬(finite element method) that will resulted in contact equation discretisce by use of Penalty method. In this thesis is also presented the needed algorithms for solving the problem and the finite element code for solving the... 

In this research, the surface contact and lateral stress distribution due to the contact between a rigid flat punch and a FG coating is investigated through macro and micro mechanical modeling due to FEM. The effects of important parameters in modeling of contact mechanics, both macro mechanically and micromechanically investigated. Study of such parameters is important, especially in fracture mechanics point of view, since stress distribution of mechanical contacts can cause the crack nucleation and evolution and finally catastrophic failure. Investigating the effective parameters in FEM models and analyzing the result admittedly help to improve manufacturing methods in order to smooth the... 

In this research, the surface stress distribution function due to the contact between a rigid rounded apex wedge and a FG coating is investigated. This study is important, especially in the fracture mechanics point of view, because stresses due to the contact can be considered as a fine crack source which grows gradually and finally leads to the failure of the structure. The structure includes two components. The first is the FG coating and then, the homogeneous substrate which is connected to the FG coating. Usually, it is considered that the homogeneous substrate is a metal, and properties at the connection are metallic, then properties change gradually through the thickness of the FG...