Sharif Digital Repository

Concrete arch dams, because of their special shape as a 3-D huge shell which is fixed from three sides, are very sensitive to temperature and its variation. Therefore, it is required to include the temperature variations and their related thermal stresses and strains in the safety analysis of dams. In this research, the effect of applying the thermal gradients caused by the most critical thermal conditions, on dynamic behavior of concrete arch dams was studied. For this purpose, first a roughly exact 3-D finite element model of Karoon ІV arch dam was prepared by ANSYS program. Then, the temperature distribution through the dam thickness was determined by Stucky-Derron method and in a more... 

Ultrasonic flowmeters are one of the common and profitable measurement tools and applied in many industrial fields.Ultrasonic flowmeters work based on transit-time technique. The transit-time utilizes the propagation time of the ultrasonic signal in the fluid. Since ultrasonic signals can also penetrate solid materials, a pair of transducers is installed on the surface of tube. Each transducer works alternatively as both transmitter and receiver of ultrasonic signals.In this study, effect of temperature gradient on flowmeter measurements by applying constant temperature and uniform heat flux on the boundary is investigated numerically for methane gas in laminar flow regime and the results... 

Transient liquid phase (TLP) bonding of Al2024-T6 alloy, using gallium interlayer, has been investigated. Bonding experiments were carried out using two basic methods; Conventional and Temperature gradient TLP bonding. Optimum values of isothermal solidification temperature and time, pressure, surface roughness, heating rate and homogenizing conditions were determined in conventional TLP bonding experiments. Aluminum oxide layer was not removed before TLP bonding to prevent gallium attack.this layer is crashed during bonding. Al2O3 particles are not soluble in the liquid and are pushed into liquid by solidification front progression. These particles are accumulated in grain boundaries and in... 

Design of thick-walled spherical and cylindrical vessels as fluids containers of high gradient thermal loading is a challenging issue. Using these tanks in high pressure and temperature gradient, particularly in chemical industries, needs to use new methods in design. Elasto-Plastic solution for thick-walled hollow spherical and cylindrical tanks made of FG materials subjected to internal pressure and temperature loading is presented. The power law modeling is used for through-the-thickness variation of mechanical properties. This method is using the new advanced materials with high pressure and thermal strength in fabricating these vessels. One of these materials is functionally graded (FG)... 

Centrifuge is a method in which great gravitational-like forces are used. Gravitational forces which cause molecules to move and are relevant to molecular weight; can cause isotope separation. The separation of light isotope from heavy one is done with a centrifugal field which produces a pressure gradient for the gas mixture. Pressure gradient is different for each of the isotopes due to the dependence of pressure gradient to the mass of the materials. But the separation in this way is very limited. The capacity of separation can be brought up by producing an additional axial flow in the rotor. This rotational flow can be produced with internal or external incitement. Rotational flow with... 

As a result of fission reaction in a nuclear reactor, the produced high neutron flux would affect the material of Reactor Pressure Vessel (RPV). This neutron radiation has a detrimental impact on the mechanical properties of the RPV material such as hardening (or embrittlement) while neutrons are absorbed by the material. A major concern in embrittled RPVs is propagation of critical flaw causing through-wall cracks. Some transients leading to overcooling of RPV intensify the propagation of theses cracks and result in thermal load on RPV, known as Pressurized Thermal Shock (PTS). Such situation could be created in case of Emergency Core Cooling System (ECCS) actuation which leads to injection... 

Nowadays functionally graded materials have many applications in various industries. One of these applications can be the manufacturing of thick-walled vessels. Thick-walled vessels under internal pressure and high temperatures gradient require materials with higher strength, like Functionally Graded Materials (FGM) and can be reinforced by some mechanical processes like autofrettage. In this process under certain loading some part of vessels enters into plastic zone and upon unloading some residual stresses will be generated. Moreover it is very important to find out the depth of this plastic zone, In addition, minimizing the stress distribution vs. depth of plastic zone under applied...