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Numerical study of solid fuel evaporation and auto-ignition in a dump combustor
, Article Acta Astronautica ; Volume 67, Issue 7-8 , 2010 , Pages 774-783 ; 00945765 (ISSN) ; Farshchi, M ; Sharif University of Technology
2010
Abstract
Evaporation of polymeric solid fuels in backward facing step geometry subject to an inlet oxidizer flow at elevated temperatures is considered and convective heating of the fuel surface by the hot oxidizing inlet flow and subsequent mixing of the evaporated fuel with the oxidizer flow and its combustion is numerically studied. The objective of this work is to gain insight into the auto-ignition of the fuel and its controlling parameters in this configuration. The system of governing equations is solved with a finite volume approach using a structured grid in which the AUSM scheme is used to calculate the gas phase convective fluxes. The flowfield is turbulent and the SpalartAllmaras...
Dynamic ageing and the mechanical response of Al-Mg-Si alloy through equal channel angular pressing
, Article Materials and Design ; Volume 31, Issue 9 , October , 2010 , Pages 4076-4082 ; 02641275 (ISSN) ; Karimi Taheri, A ; Ig Hong, S ; Seop Kim, H ; Sharif University of Technology
2010
Abstract
In this paper, dynamic ageing characteristics associated with the application of equal channel angular pressing (ECAP) to Al6061 alloy at elevated temperatures was investigated. Followed by ECAP, Vickers microhardness measurement on the cross-sectional planes and microstructural observations were undertaken using transmission electron microscopy. The combination of the ECAP process with dynamic ageing at both 100°C and 150°C resulted in a significant increase in hardness. The grain size was measured as ∼160. nm after four passes. A comparison with the published data on the same alloy processed by ECAP at room temperature and statically aged, suggests several advantages in incorporating...
Investigation of friction and wear behaviors of 2024 Al and 2024 Al/SiCp composite at elevated temperatures
, Article Journal of Alloys and Compounds ; Volume 501, Issue 2 , Jan , 2010 , Pages 326-332 ; 09258388 (ISSN) ; Seyed Reihani, S. M ; Sharif University of Technology
2010
Abstract
Friction and wear behaviors of artificially aged 2024 Al and 2024 Al/20 vol.% SiC composite prepared by powder metallurgy method were investigated in the temperature range 20250 °C. Dry sliding wear tests were conducted at a constant sliding velocity of 0.5 m/s, an applied load of 20 N, and a sliding distance of 2500m using a pin-on-disc apparatus. Worn surfaces and wear debris were also examined by using SEM and EDS techniques. All specimens showed a transition from mild-to-severe wear above a critical temperature. In the mild wear regime, the wear rate and the friction coefficient of the composite specimen were higher than those of the unreinforced alloy. The SiC particles led to an...
The effect of different rare earth elements content on microstructure, mechanical and wear behavior of Mg-Al-Zn alloy
, Article Materials Science and Engineering A ; Volume 527, Issue 7-8 , 2010 , Pages 2027-2035 ; 09215093 (ISSN) ; Masoudi, A ; Khomamizadeh, F ; Sharif University of Technology
2010
Abstract
The effect of Rare earths addition to AZ91 magnesium alloy and its influence on the microstructure and mechanical properties was investigated in this study. Addition of cerium rich misch metal to AZ91 alloy resulted in formation of needle shape particles, which had a very high thermal stability, providing superior mechanical properties compared to AZ91 magnesium alloy. As a result, the grain boundaries were less susceptible for grain boundary sliding at high temperatures. The steady state creep rates were specified and for the AZ91 alloy and the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE added...
Evaluation of energy-based modal pushover analysis in reinforced concrete frames with elevation irregularity
, Article Scientia Iranica ; Volume 17, Issue 2 A , 2010 , Pages 96-106 ; 10263098 (ISSN) ; Mofid, M ; Sharif University of Technology
2010
Abstract
In nonlinear static (pushover) methods of analysis as an alternative to time history analysis, the capacity curve of the structure is established with respect to the roof displacement. Disproportionate increases in the roof displacement and even outright reversals of the higher modes can distort the capacity curve of the equivalent single degree of freedom system in these kinds of method, including MPA. To overcome this problem, recently, "Energy-Based" the Modal Pushover Analysis (Energy-Based MPA) method has been introduced. In this method, the absorbed energy and/or the external work in the pushover analysis is considered. Accordingly, the assessment of the Energy-Based MPA method is...
Effect of rapid solidification on the microstructure and mechanical properties of hot-pressed Al-20Si-5Fe alloys
, Article Materials Characterization ; Volume 60, Issue 11 , 2009 , Pages 1370-1381 ; 10445803 (ISSN) ; Vahidi, M ; Simchi, A ; Davami, P ; Sharif University of Technology
2009
Abstract
The aim of this work is to study the effect of cooling rate and subsequent hot consolidation on the microstructural features and mechanical strength of Al-20Si-5Fe-2X (X = Cu, Ni and Cr) alloys. Powder and ribbons were produced by gas atomization and melt spinning processes at two different cooling rates of 1 × 105 K/s and 5 × 107 K/s. The microstructure of the products was examined using optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The particles were consolidated by hot pressing at 400 °C/250 MPa/1 h under a high purity argon atmosphere and the microstructure, hardness and compressive strength of the compacts were evaluated....
The effect of different content of Al, RE and Si element on the microstructure, mechanical and creep properties of Mg-Al alloys
, Article Materials Science and Engineering A ; Volume 523, Issue 1-2 , 2009 , Pages 1-6 ; 09215093 (ISSN) ; Tari, A ; Khomamizadeh, F ; Sharif University of Technology
2009
Abstract
The effect of Al content and Si addition on the microstructural and creep properties of Mg-Al-RE alloys was investigated in this study. The steady state creep rates were specified and it was found that the creep behavior of the alloy, which is dependent on the stability of the near grain boundary microstructure, was improved by the RE and Si addition. For the AZ91 alloy, the results indicate a mixed mode of creep behavior, with some grain boundary effects contributing to the overall behavior. However for the RE and Si added samples, sliding of grain boundaries was greatly suppressed and the dislocation climb controlled creep was the dominant deformation mechanism. Analysis of creep rates...
Effect of rare earth elements addition and T6 heat treatment on creep properties of Mg-Al-Zn alloy
, Article Magnesium Technology 2009, San Francisco, CA, 15 February 2009 through 19 February 2009 ; 2009 , Pages 483-488 ; 15454150 (ISSN); 9780873397308 (ISBN) ; Khomamizadeh, F ; Magnesium Committee of the Light Metals Division; Minerals, Metals and Materials Society, TMS ; Sharif University of Technology
2009
Abstract
This paper focuses on creep properties of AZ91-RE and heat treated AZ91 magnesium alloy. Influence of heat treatment and rare earths addition on microstructure and mechanical properties were investigated. Creep behavior is dependent on the stability of the near grain boundary microstructure and is improved by rare earth addition. The results show that sliding of grain boundaries has an important part in the deformation mechanism in AZ91 alloy at elevated temperatures which is greatly suppressed by the rare earths addition
The effects of intermediate and post-annealing phenomena on the mechanical properties and microstructure of constrained groove pressed copper sheet
, Article Materials Science and Engineering A ; Volume 515, Issue 1-2 , 2009 , Pages 162-168 ; 09215093 (ISSN) ; Mani, A ; Kazeminezhad, M ; Sharif University of Technology
2009
Abstract
Commercial purity copper sheets were subjected to a severe plastic deformation technique known as constrained groove pressing (CGP). The effect of pass number, intermediate and post-annealing on the yield strength, hardness and final microstructure of the copper specimens were investigated. The initial pass increases the strength much more than the subsequent passes. Intermediate and post-annealing up to 300 °C cannot change the mechanical properties significantly and even in some cases improve the strength and hardness while reduce the hardness inhomogeneity. Microstructure after post-annealing at elevated temperatures shows abnormal grain growth. © 2009 Elsevier B.V. All rights reserved
Microstructure and mechanical properties of Al-20Si-5Fe-2X (X = Cu, Ni, Cr) alloys produced by melt-spinning
, Article Materials Science and Engineering A ; Volume 492, Issue 1-2 , 2008 , Pages 443-449 ; 09215093 (ISSN) ; Simchi, A ; Davami, P ; Sharif University of Technology
2008
Abstract
Al-20Si-5Fe-2X (X = Cu, Ni and Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400 °C for 60 min. The microstructure of the ribbons and the consolidated alloys was investigated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffractometry (XRD) method, and transmission electron microscopy (TEM). The hardness and compressive strength of the specimens at ambient and elevated temperatures were examined. The microstructure of the ribbons exhibited featureless and dendritic zones. Results of XRD and TEM showed formation of spherically shaped Si particles with an average diameter of 20 nm. Ultrafine Si (110-150 nm) and iron-containing...
Surveillance radar target detection with the fourier-hough transform
, Article 2008 International Radar Symposium, IRS, Wroclaw, 21 May 2008 through 23 May 2008 ; 2008 ; 9788372076212 (ISBN) ; Moqiseh, A ; Nayebi, M. M ; Sharif University of Technology
2008
Abstract
In a typical surveillance radar, decision about the existence of a target in certain range-azimuth-elevation cell is made from the echo received in current scan, while still there is useful information in history of that range cell that is not considered in decision making. Based on the potential of the Hough Transform to use history of both range and Doppler information, a new method to increase the probability of detection in surveillance radars is proposed. The new method uses a 3D data space and a special projection to detect targets and extract range, speed, and acceleration of maneuvering targets simultaneously
Processing of Al-20Si-5Fe-2X(X=Cu, Ni, Cr) alloys by melt-spinning and hot-pressing
, Article European International Powder Metallurgy Congress and Exhibition, Euro PM 2008, Mannheim, 29 September 2008 through 1 October 2008 ; Volume 2 , 2008 , Pages 99-104 ; 9781899072033 (ISBN) ; Simchi, A ; Davami, P ; Sharif University of Technology
European Powder Metallurgy Association (EPMA)
2008
Abstract
Al-20Si-5Fe-2X (X=Cu, Ni, Cr) ribbons were produced by melt-spinning and consolidated by hot pressing at 400°C for 60 min. Optical and transmission electron microscopy (TEM), X-ray diffractometry (XRD), and hardness test were used to evaluate the microstructure and mechanical strength of the ribbons and hot consolidated specimens. The compressive strength of the specimens at ambient and elevated temperatures was also examined. The microstructure of the ribbons exhibited featureless and dendritic zones, and contains spherically-shaped Si particles with an average diameter of 20 nm. After hot-pressing, ultrafine Si (110-150 nm) and iron-containing intermetallic particles were formed. The...
Numerical simulation of free-surface waves and wave induced separation
, Article Scientia Iranica ; Volume 15, Issue 3 , 2008 , Pages 323-331 ; 10263098 (ISSN) ; Mousaviraad, S. M ; Firoozabadi, B ; Ahmadi, G ; Sharif University of Technology
Sharif University of Technology
2008
Abstract
The present study is concerned with the numerical simulation of free-surface waves and wave induced separation in the presence of an intrusion. The results of several simulations are reported. The first study was performed for a NACA0024 surface piercing hydrofoil over a range of several Froude numbers (0.19, 0.37, 0.55), along with wave breaking at Fr = 1.0 The NACA0024 foil was of particular interest, as it almost has no separation at large depths; thus the effect of the free-surface wave and the wave induced separation could be studied. Free- surface waves and wave induced separation results were evaluated and compared with both the available experimental data and the previous numerical...
Near-optimal terrain collision avoidance trajectories using elevation maps
, Article 2006 IEEE Aerospace Conference, Big Sky, MT, 4 March 2006 through 11 March 2006 ; Volume 2006 , 2006 ; 1095323X (ISSN); 0780395468 (ISBN); 9780780395466 (ISBN) ; Abbasi, A ; Sharif University of Technology
2006
Abstract
The main attempt of this paper is to present a new methodology to model a generic low-level flight close to terrain, which guarantees terrain collision avoidance. Benefiting the advantages of high-speed computer technology, this method uses satellite elevation maps to generate so called 'Quad-tree forms'. The latter is then used to find the optimal trajectories for low-level flights. The novelty of this approach, entitled the 'cost map', lies in the integration of aircraft dynamics into the segmented map. This procedure results in some near-optimal trajectories with respect to aircraft dynamics that could easily be used for minimization of flight path together with pilot effort. Different...
A novel structural joint with the potential of fire-tolerance improvement
, Article 24th International Conference on Offshore Mechanics and Arctic Engineering, 2005, Halkidiki, 12 June 2005 through 17 June 2005 ; Volume 1 B , 2005 , Pages 747-754 ; Jamshidi Vismeh, A. R ; England, G. L ; Fattahian, N ; Sharif University of Technology
2005
Abstract
A new innovative 'universal' structural joint with multiple applications was devised. The two major conceived contexts for the use of this joint are 'joining beams to columns, ' and 'joining diagonal braces to horizontal ones. ' The main features of this joint are its high rotational capacity, its high shear deformation capacity, its high energy-dissipation capacity, its ability to contain damage, and its repalceability. Due to its geometry, it can well lend itself to protection measures against fire, normally practiced by the involving industries. This makes it a good candidate for being used in structures related to oil and gas industry, offshore or onshore. Through numerical modelling of...
Vibration Analysis of Kish Island Elevated Water Storage Tank
, M.Sc. Thesis Sharif University of Technology ; Selk Ghafari, Ali (Supervisor)
Abstract
Elevated water tanks are one of the most critical elements in civilized society to provide safe servicing resources of drinking water after natural and human-made disasters. Dynamic analysis plays a vital role in investigating structural behavior of the elevated storage system subjected to the earthquake-induced vibration. The main scope of this paper is to address the structural stability analysis of the Kish Island’s elevated reinforced concrete water tank employing finite element method. A complete solid model of the structure with detailed design was constructed, and finite element analysis was carried out utilizing ABAQUS software. To investigate the dynamic behavior of the structure, a...
Post-fire Behavior Evaluation of Slag-Based Geopolymer Concrete
, M.Sc. Thesis Sharif University of Technology ; Toufigh, Vahab (Supervisor)
Abstract
Concrete, a versatile construction material, combines cement, aggregates, and water to form a composite known for its durability and adaptability in various architectural and engineering applications. Its widespread use stems from its ability to efficiently bear heavy loads while maintaining longevity. However, producing concrete's key ingredient, cement, contributes significantly to environmental harm by emitting substantial carbon dioxide during its manufacturing process. This carbon footprint underscores the urgent need for sustainable alternatives and innovative practices in the construction industry to mitigate the detrimental effects on our planet. On the other hand, understanding the...
Compressive and Bond Behavior of Concrete-Filled Pultruded GFRP and PE Tubes Under Elevated Temperatures
, Ph.D. Dissertation Sharif University of Technology ; Khaloo, Alireza (Supervisor)
Abstract
Concrete-filled GFRP and PE tubes are composite systems using the polymeric tubes as confinement for the marine structures to extend their service life. However, elevated temperatures and thermal cycles in marine environments can affect the behavior of such composite systems. In this investigation, the effect of elevated temperatures and thermal cycles on the performance of concrete-filled pultruded GFRP tubes (CFPGT) and concrete-filled polyethylene tubes (CFPT) is assessed, respectively. For this, different parameters such as concrete core strength (30 and 60 MPa), exposure temperature (25, 100, 200, 300, and 400°C), time exposure (60 and 120 min.), number of thermal cycles (50, 100, and...
Effect of DEM Resolution on Hydraulic Modeling of Flood Inundation Area: Case Study of Gorganrood River, Northeast of Iran
, M.Sc. Thesis Sharif University of Technology ; Ataie Ashtiani, Behzad (Supervisor)
Abstract
Digital Elevation Models (DEM) is a crucial element of hydraulic models, including floods. Due to the lack of high-precision topographic data, including ground-based mapping hydraulic modeling is challenging. In recent years, remote sensing data, extensively used by many researchers in hydraulic modeling due to global coverage and free access. One of the most critical questions in hydraulic modeling is the efficiency of these DEMs in flood simulation. This research focused on using remote-sensing-based DEMs, such as SRTM-30m and 90m, ASTER-30m, and ALOS-12.5m DEMs, on the performance of the HEC-RAS-2D model in the Gorganrood river.The results showed that ALOS and SRTM-30m DEMs' accuracy and...
The Study of the Behaviour and Performance of a New Elevated Tank
, M.Sc. Thesis Sharif University of Technology ; Khansari, Vahid (Supervisor)
Abstract
Various types of tanks are used to store a variety of liquids, drinking water, chemicals, petrochemicals, and liquefied natural gas. Of these, one type is ‘elevated tank’ which is used to provide the required pressure for the water distribution systems rather than satisfying the water demand. Satisfactory performance of tanks during strong ground motions is crucial for modern facilities. Theoritical and experimental investigations of the dynamic behaviour of liquid storage tanks are conducted to seek possible improvments in the design of such tanks to resist earthquakes. The behaviour and performance of a new elevated tank was studied in this work. It was carried out through finite elements...