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caissons
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Numerical Modeling of the Bearing Capacity of Suction Caisson by Finite Element Method
, M.Sc. Thesis Sharif University of Technology ; Ahmadi, Mohammad Mahdi (Supervisor)
Abstract
Suction caisson is a relatively new technology which was introduced about 30 years ago for the first time and after several investigations, was found its position in the oil industry and construction of anchorages, during previous decade. So nowadays, it is the most effective and economical choice as the mooring of offshore structures in comparison with the other foundations. Suction caisson is a hollow cylinder with an open bottom and a closed top. After placement on the seafloor, the caisson first penetrates into the soil by its self weight and then inserts into the ground by pumping water out of it. Although many researchers have attempted to understand the behavior of suction caissons...
Microstructural Study Of Inconel 718 Alloy Produced by VAR and Comparing it with Other Rapid Solidification Methods
, M.Sc. Thesis Sharif University of Technology ; Ashuri, Hossein (Supervisor)
Abstract
The purpose of this investigation was to study the microstructure of the Inconel718 alloy wich was produced by VAR and suction casting method, and study the effect of cooling rate on the solidification structure of Inconel718 alloy. In the first a labratoary scale VAR furnace was made. After producing some sample's with this furnace, a suction casting sample was produced using a 3mm diameter copper mold. Metallography, SEM, EDS, and microhardness analysis was carried away. Cooling rate evaluation was done by using a equation between secondary dendrite arm spacing and solidification time. Results showed that by increasing cooling rate from 63 c/s to around 2000 c/s, columnar and equiaxed...
Residual stress analysis of autofrettaged thick-walled spherical pressure vessel
, Article International Journal of Pressure Vessels and Piping ; Volume 87, Issue 7 , July , 2010 , Pages 396-401 ; 03080161 (ISSN) ; Farrahi, G. H ; Haghpanah Jahromi, B ; Hosseinian, E ; Sharif University of Technology
2010
Abstract
In this study, residual stress distributions in autofrettaged homogenous spherical pressure vessels subjected to different autofrettage pressures are evaluated. Results are obtained by developing an extension of variable material properties (VMP) method. The modification makes VMP method applicable for analyses of spherical vessels based on actual material behavior both in loading and unloading and considering variable Bauschinger effect. The residual stresses determined by employing finite element method are compared with VMP results and it is demonstrated that the using of simplified material models can cause significant error in estimation of hoop residual stress, especially near the...
Residual stresses in autofrettaged vessel made of functionally graded material
, Article Engineering Structures ; Volume 31, Issue 12 , 2009 , Pages 2930-2935 ; 01410296 (ISSN) ; Farrahi, G. H ; Maleki, M ; Nayeb Hashemi, H ; Vaziri, A ; Sharif University of Technology
Abstract
We used an extension of the Variable Material Property method for materials with varying elastic and plastic properties to evaluate the residual stresses in an autofrettaged thick vessel made of functionally graded metal-ceramic composite. It is shown that the reinforcement of the metal vessel by ceramic particles, with an increasing ceramic volume fraction from inner to outer radius, increases the magnitude of compressive residual stresses at the inner section of an autofrettaged vessel and thus, could lead to better fatigue life and load-carrying capacity of the vessel. A parametric study is carried out to highlight the role of ceramic particle strength and spatial distribution, as well as...
On the material modeling of the autofrettaged pressure vessel steels
, Article Journal of Pressure Vessel Technology, Transactions of the ASME ; Volume 131, Issue 5 , 2009 ; 00949930 (ISSN) ; Hosseinian, E ; Assempour, A ; Sharif University of Technology
2009
Abstract
Material modeling of high strength steels plays an important role in the accurate analysis of autofrettaged tubes. Although, the loading behavior of such materials is nearly elasticperfectly plastic, their unloading behavior due to Bauschinger effect is very complicated. DIN1.6959 steel is frequently used for construction of autofrettaged tubes in some countries such as Germany and Switzerland. In spite of similarity between chemical compositions of this steel with that of A723 steel, due to different material processing, these two steels have an unlikely behavior. In this paper the material behavior of DIN1.6959 was accurately modeled by uniaxial tension-compression test results. Both 6 mm...