Sharif Digital Repository

We propose a model for friction between two rough surfaces based on extreme value statistics (EVS). Different models for single-asperity contact, including adhesive and elasto-plastic contacts, were combined with EVS. The Hertzian model for contacts and Gumbel distribution for summit heights show the closest conformity with Amonton’s law. The range over which Gumbel distribution mimics Amonton’s law is wider than that of the Greenwood–Williamson (GW) model. In comparison with other EVS distribution, Gumbel distribution seems the proper choice for summit‘ s height. Interestingly, here again, elasto-plastic contact and Gumbel distribution for summits achieve the best conformity with Amontons... 

In this essay we study the concepts of nuclearity in C-algebras, and amenability in Banach algebras. A proof on the "every amenable C-algebra is nuclear" is studied. A Banach algebra A is called amenable if every continous derivation D : A ! E , is inner i.e. there exists anif in this denition E is a dual Banach A-module and norm continuity replace by w-continuity then we have Connes-amenability; Connes-amenability was rst considered for von Neumann algebras in [J-K-R] (and thus should perhaps be called Johnson-Kadison-Ringrose amenability). The reason why this notion of amenability is usually associated with A. Connes are his papers [Conn 1] and [Conn 2] The name "Connes-amenability" seems... 

In this thesis to simulate the behavior of liquid engine Thrust chamber of hot gas from a quasi one dimensional code used when the effects of the heat transfer and friction in those terma. As well as during the regenerative channel is simulated by considering the equation’s of continuity, momentum and energy for one dimensional, effects of increase temperature, pressure drop, change the density of coolant flow resulting from the warming which is visible along the way to increase the accuracy of calculation of the thermal flux output of the engine, use a suitable model for unclear boiling in consideration of heat transfer coefficient used coolant flow it has been. As well as coupling of heat... 

In this thesis the instability regimes of the liquid sheet resulted from interactions of three converging jets is investigated. To this end, the shadowgraphy method is used. All the experiments have been done under the atmospheric pressure by using water as the jet fluid. The injectors are orifice ones.In our study, the effects of changing the jet velocities and changing the three jets’ structure (planar and non-planar) in having different liquid sheet shapes are investigated.Although so many researches have been done on interactions of two converging jets until now, there is almost not any researches about interactions of three converging jets. Considering this, this thesis topic is novel,... 

With the increase in the average age of the world's population, osteoporosis is a worldwide incidence. This disease, along with natural disasters, are important factors in the occurrence of fractures in various bones of the body. One of the methods for solving this problem and replacing with broken body bones is the use of metal implants with hydroxyapatite-based coatings. One of the common problems with using implants in the body is the infection in the adjacent parts of the implant. To overcome this problem, several studies have been carried out on the use of hydroxyapatite coatings with metal ions or antibacterial oxide compounds. In the present study, the influence of factors such as the... 

Liquid atomization have broad range of usage in different industries. Colliding two jets is one method for atomization of different kind of fluids especially high viscose and viscoelastic fluids. Here, we experimentally investigated the effect of skewness and velocity differential of two Newtonian viscose colliding jets on formation of a special oscillating liquid sheet pattern with periodic fragmentation called “fishbone”. For this work, four liquid sheet regimes; triple chain, double chain, close rim, and open rim which fishbone pattern could be observed were produced and Skewness and jets velocity differential were applied to them. A synced CCD camera and stroboscope illumination source... 

In the present work we first introduced ILIDS and review the theory of interferometry and light scattering from droplets. Bases on ILIDS method, droplets are irradiated by monochrome sheet laser, where the superposition of reflected and first-order refracted beams form a parallel fringe pattern at out of focus plane on the imaging sensor in the forward-scatter region. This pattern can be related to the droplet size by using simple geometrical optics. For the present work, an image processing algorithm is utilized to capture weak and noisy images of droplets to reduce the lost data in the sizing procedure. Since ILIDS method is applied for small and dilute spray, it is suitable for... 

The velocity of the hot outflow gas in laminar premixed flame is one of the important properties of combustion, along with other properties such as temperature and flame components. In fact, laminar flame velocity has been employed in a multitude number of concepts ranging from engine design to achieving flame properties under turbulent conditions. In this research, a cylindrical Bunsen burner and appropriate TIO2 particles were used. Particles with diameters between 10-23 microns were used and the exit diameter of burner considered 14 mm. In this study, the equivalence ratio with a value between 0.9-1.2 are fed with LPG fuel to create a laminar premixed flame. As a result of the present... 

In most of the studies conducted on the physics of the outflow from impinging jet injectors, Newtonian fluids have been used for their research and experiments. These studies have investigated the effect of factors such as geometrical parameters of the injector and physical properties of the fluid on different regimes resulting from the impact of the jet stream; Unfortunately, very few studies have been conducted on how to form spray and atomization in gel non-Newtonian fluids containing nanoparticles to investigate the above factors when using impinging jet injectors. Furthermore, although the addition of nanoparticles has advantages for better combustion, there are still problems in... 

Quantitative measurement of pressure on surfaces in wind tunnels and flight tests is essential to understand the aerodynamic performance of flying vehicles. Pressure data are also essential for validation and verification of computational fluid dynamics codes. One of the relatively new methods of measuring pressure distribution on aerodynamic surfaces is the method of pressure sensitive paint (PSP). The PSP method is an optical technique that can measure the pressure distribution on the surface without using common pressure sensors or transducers, with greater spatial resolution and lower cost. This method has a unique ability for non-contact (non-interfering) measurements. In this method,... 

Injecting liquid fuel into the cross flow of air provides high penetration of the liquid, rapid mixing with air, and increased efficiency. This method has widespread applications in the propulsion systems of gas turbines, scramjets, turbine blade cooling, and fuel injection for engine afterburners. One of the design strategies for future aircraft engines is to reduce pollutants using fuel spray into the cross flow instead of direct jet fuel injection and using renewable energy sources. The applications of cross flows include injecting fluid through rotating pressure injectors in exhaust flows, injecting fluid through pressure-rotating injectors in radial injectors, and using slinger... 

In the present work, the local Chemiluminescence method has been implemented on a laminar premixed propane-air flame. The goal of this work is to achieve a system capable of measuring the intensity of Chemiluminescent radiations of CH* and OH* radicals locally and with high spatial and temporal accuracy. For this purpose, a setup has been designed and developed. In order to achieve high spatial accuracy for local measurements, a Cassegrain lens has been designed and built, which has the ability to collect light from a cylindrical control volume with a cross-sectional diameter of 58 μm and a depth of 3.4 mm. An optical system for dividing and filtering light based on wavelength has also been... 

Due to importance of designing geometry and working condition of injector it is necessary that by testing cold flow, we gain better understanding of atomization characteristics and in particular initial atomization close to injector which defines the spray characteristics. Up to today experimental measurements in the high density zone close to injector has been difficult to to optical limitations and also analytical solutions of atomization process is limited due to complexity and highly nonlinear equations. Numerical solutions are also under development and researchers have recently done researches and simulations. In this field the modeling of liquid sheet collapse has challenged numerical... 

Injection of liquid fuel in the cross-flowing air provides a means of higher penetration, rapid mixing of liquid fuel and air, and is encountered in many engineering applications. Air-breathing propulsion systems (e.g. gas turbine combustors, ramjets, and scramjets), liquid rocket engines,cooling sprays for turbine blades, and injection of fuel in the afterburners are examples of such applications. The identification of microscopic characteristics is one of the basic methods of atomizer examination, which has not been taken into account due to inadequate experimental equipment. In the present study, droplet mono-frame velocimetry and size distribution of secondary atomization in a pressure...