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The Effect of the Step Height on Energy Dissipation in Stepped Spillways Using Numerical Simulation
, Article Arabian Journal for Science and Engineering ; Vol. 39, issue. 4 , 2014 , p. 2587-2594 ; Hosseini, K ; Abdi, H ; Hosseini, M ; Sharif University of Technology
2014
Abstract
From 1970s, studies have been conducted on the hydraulic design of stepped spillways and many empirical formulas were developed. Despite the simple geometry of these spillways, their hydraulic behavior is complicated. As a result, for many cases, the physical models are studied to verify the design. Numerical simulation is considered as a tool to reduce the laboratory tests, in order to save time and money. Furthermore, the parameters which are not investigated or measured in physical models could be evaluated. In this paper, the results of numerical simulations are compared with the results of physical models and empirical formulas for the spillway of Renwick dam studied in a 1/8 scale...
A failure analysis study on the fractured connecting bolts of a filter press
, Article Case Studies in Engineering Failure Analysis ; Volume 4 , 2015 , Pages 26-38 ; 22132902 (ISSN) ; Alizadeh, R ; Attarian, M ; Jaferian, Y ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
The purpose of this study was to investigate the main causes of the co-fracture of sixteen connecting bolts of a filter press cylinder-piston system. Stress state of the bolts during the service conditions has been analyzed and the failure reasons were determined from the fractography analysis and gathered information. According to the obtained results, it was concluded that the bolts had failed by the fatigue mechanism. It seems that insufficient torque was used during assembly
Failure analysis of superheater tube
, Article Engineering Failure Analysis ; Volume 48 , February , 2015 , Pages 94-104 ; 13506307 (ISSN) ; Plasseyed, S. S ; Attarian, M ; Sharif University of Technology
Elsevier Ltd
2015
Abstract
The failure analysis of a ruptured superheater tube after 20. years service in the oil-fueled boiler, as the typical problems in power plants, was investigated. A thin-lipped rupture at failed region was observed in superheater tube. By measuring the tube's wall thicknesses far from failed region, non-uniformity was seen. The suggested main root cause of failure was fireside corrosion of the tube during the service. Because of low grade of used fuel, sodium, sulfur, and vanadium elements were observed at the outer surface, which caused continuously scale formation and reduction of wall thickness, by metal consumption. In addition, it seems that it has been worsened by occurrence of long-term...
Oxidation behavior of AISI 321, AISI 316, and AISI 409 stainless steels: Kinetic, thermodynamic, and diffusion studies
, Article Journal of Materials Research ; 2016 , Pages 1-9 ; 08842914 ; Pelaseyed, S.S ; Attarian, M ; Shokrallahzadeh, R ; Sharif University of Technology
Cambridge University Press
2016
Abstract
The oxidation behavior of three types of stainless steels, namely AISI 321, AISI 316, and AISI 409, was compared. In all stainless steels, oxide layers were formed and their masses and thicknesses increased with oxidation time. Among them, AISI 409 ferritic stainless steel demonstrated higher oxidation rate. According to the kinetical oxidation behavior of them at elevated temperatures, the oxidation mechanism was determined. Among them, the AISI 409 ferritic stainless steel showed the lowest and AISI 321 austenitic stainless steel demonstrated the highest oxidation resistance. Based on the experimental results, it was suggested that the kinetic of oxide growth in stainless steels was...
Microstructural evolution in creep aged of directionally solidified heat resistant HP-Nb steel alloyed with tungsten and nitrogen
, Article Materials Science and Engineering A ; Volume 659 , 2016 , Pages 104-118 ; 09215093 (ISSN) ; Karimi Taheri, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
The effect of tungsten and nitrogen on the as cast and the creep aged microstructures of heat resistant HP-Nb steel was studied. The steel was directionally solidified under two cooling rates of 31.2 and 7.6 K sec-1. Creep rupture tests were performed at temperatures of 1150-1255 K on the specimens prepared from the cast ingots in transverse and longitudinal directions. It is shown that the addition of nitrogen significantly increases the eutectic temperature and thus refines the dendrites and alters the morphology of M7C3 eutectic carbide. Also, it is found that due to short time aging, nitrogen addition decreases the M7C3 carbide fragmentation, increases the secondary M23C6 precipitation...
Metallurgical evaluation and failure analysis of turbo expander Tie-bolt
, Article Engineering Failure Analysis ; Volume 151 , 2023 ; 13506307 (ISSN) ; Pelaseyed, S ; Hayatian, R ; Sharif University of Technology
Elsevier Ltd
2023
Abstract
Failure in a turbo-expander Tie-Bolt (stud) made of superalloy A-286 was investigated. The evaluation of the chemical composition and tensile properties confirmed compliance with the relevant standard. However, the coarsening of γ′ due to over aging condition, the non-uniform grain size and banded coarse MC carbide particles, the segregation of phosphorus to grain boundaries and the growth of carbide particles at the grain boundaries led to a decrease in fatigue strength of the alloy. Fractography studies showed that fracture occurred due to primary axial and secondary bending loads. Multiple ratchets and tire tracks on the fracture surface were consistent with low-cycle fatigue (LCF)...
Effect of ethylene-vinyl acetate copolymer on the rheological behaviour of alumino-silicate/polyethylene wax suspensions
, Article Ceramics International ; Volume 28, Issue 5 , 2002 , Pages 507-514 ; 02728842 (ISSN) ; Taheri Nassaj, E ; Davami, P ; Sharif University of Technology
2002
Abstract
Ceramic suspensions were prepared from an alumino-silicate powder, polyethylene wax (PE-wax) as binder with additions of stearic acid (SA). The ceramic powder consisted of mullite, corundum and tridymite phases. The organic binders contained 3 to 8 wt.% ethylene-vinyl acetate (EVA) and were filled with various volume fractions of ceramic powder. The yield stresses of suspensions were estimated using shear stress-shear rate data measured at 90-120 °C. The addition level of EVA was shown to have a considerable effect on the yield stress of suspensions. The effect of EVA on the flow parameters was also investigated over the temperature range of 90 to 120 °C. It was shown that the addition of 5...
Microstructural evaluation and fracture mechanisms of failed IN-738LC gas turbine blades
, Article Case Studies in Engineering Failure Analysis ; Volume 1, Issue 2 , April , 2013 , Pages 85-94 ; 22132902 (ISSN) ; Khoshmanesh, R ; Nategh, S ; Davami, P ; Sharif University of Technology
2013
Microstructural and failure analysis of welded primary reformer furnace tube made of HP-Nb micro alloyed heat resistant steel
, Article Engineering Failure Analysis ; Volume 68 , 2016 , Pages 32-51 ; 13506307 (ISSN) ; Karimi Taheri, A ; Jalilvand, S ; Habibi, A ; Sharif University of Technology
Elsevier Ltd
2016
Abstract
In this paper, the failure of the reformer furnace tube, made of HP-Nb micro alloyed heat resistant steel is investigated. The failure was due to a longitudinal crack developing in the circumferential weld joint close to the outlet end of the tube, where the mean wall temperature had reached the highest value during service. According to the temperature records during the period of 7 years of being in service, the tube had experienced temperatures higher than the tubes designed temperature. This situation besides the occurrence of several sudden shutdowns caused the mechanical properties degradation.Macroscopic and microscopic examinations revealed that the failure had occurred due to the...
Microstructure and segregation behaviour of directionally solidified tungsten bearing 25Cr-35Ni-Nb heat-resistant stainless steels
, Article International Journal of Cast Metals Research ; Volume 30, Issue 2 , 2017 , Pages 112-122 ; 13640461 (ISSN) ; Karimi Taheri, A ; Varahram, N ; Davami, P ; Sharif University of Technology
Taylor and Francis Ltd
2017
Abstract
Two series of heat-resistant 25Cr-35Ni-Nb stainless steels with tungsten addition and Nb/C ratio of ≈2.6 and 3.9 were directionally solidified under two cooling rates of 23–6 °C s−1, respectively. EDS analysis, electron backscatter diffraction (EBSD), differential thermal analysis (DTA) and field emission scanning electron microscopy (FESEM) tests were carried out to show that tungsten as a carbide phase nucleant promoted weak coupled eutectic growth of γ/ M7C3 and decreased the lamellar eutectic colonies. Substantial negative segregation of Ni and Fe and positive segregation of Nb and Cr in tungsten-bearing alloys stimulated the γ/M23C6 reaction and the M23C6 possessed a dendritic...
The Evaluation of Microstructure and Mechanical Properties of a HSHR Stainless Steel Strengthen by Nano-Precipitates
, Ph.D. Dissertation Sharif University of Technology ; Karimi Taheri, Ali (Supervisor) ; Davami, Parviz (Co-Advisor)
Abstract
In this research, a computational method based on thermodynamic and physical metallurgy coupled by the d-electron approach was used to design the composition of a high strength and heat resistant (HSHR) stainless steel. Then, three series of the heat resistant 25Cr-35Ni-Nb (HP-Nb) stainless steels with tungsten, nitrogen, and micro alloying elements additions were cast. In these alloys a Nb/(C+ 6/7 N) ratio of ≈ 2.4 to 3.7 was chosen and they were directionally solidified under two cooling rates of 23 Ks-1 and 6 Ks-1. The effects of the alloy chemical composition and solidification cooling rate on the macrostructure, microstructure, microsegregation, and inclusions in the alloys were...
Probability of missed detection as a criterion for receiver placement in MIMO PCL
, Article IEEE National Radar Conference - Proceedings, 7 May 2012 through 11 May 2012, Atlanta, GA ; 2012 , Pages 0924-0927 ; 10975659 (ISSN) ; 9781467306584 (ISBN) ; Chitgarha, M. M ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
IEEE
2012
Abstract
Using multiple antennas at the transmit and receive sides of a passive radar brings both the benefits of MIMO radar and passive radar. However one of the obstacles arisen in such configuration is the receive antennas placement in proper positions so that the radar performance is improved. Here we just consider the case of positioning one receiver among multiple illuminators of opportunity. Indeed it is a start for the solution of optimizing the geometry of the multiple receivers in a passive radar
An efficient method for the ring opening of epoxides with aromatic amines by Sb(III) chloride under microwave irradiation
, Article Journal of Chemical Research ; Issue 4 , 2008 , Pages 220-221 ; 03082342 (ISSN) ; Hashemi, M. M ; Mottaghi, M. M ; Foroughi, M. M ; Sharif University of Technology
2008
Abstract
SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity
Resource allocation for uav-enabled integrated sensing and communication (isac) via multi-objective optimization
, Article ICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings ; Volume 2023-June , 2023 ; 15206149 (ISSN); 978-172816327-7 (ISBN) ; Naghsh, M. M ; Karbasi, M ; Nayebi, M. M ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2023
Abstract
In this paper, we consider an integrated sensing and communication (ISAC) system with wireless power transfer (WPT) where an unmanned aerial vehicle (UAV)-based radar serves a group of energy-limited communication users in addition to its sensing functionality. In this architecture, the radar senses the environment in phase 1 (namely sensing phase) and mean-while, the communications users (nodes) harvest and store the energy from the radar transmit signal. The stored energy is then used for information transmission from the nodes to UAV in phase 2, i.e., uplink phase. Performance of the radar system depends on the transmit signal as well as the receive filter; the energy of the transmit...
MIMO radar signal design to improve the MIMO ambiguity function via maximizing its peak
, Article Signal Processing ; Volume 118 , 2016 , Pages 139-152 ; 01651684 (ISSN) ; Radmard, M ; Nazari Majd, M ; Karbasi, S. M ; Nayebi, M. M ; Sharif University of Technology
Elsevier
2016
Abstract
One of the important obstacles in MIMO (Multiple Input Multiple Output) radars is the issue of designing proper transmit signals. Indeed, the capability of signal design is a significant advantage in MIMO radars, through which, the system can achieve much better performance. Many different aspects of this performance improvement have been considered yet, and the transmit signals have been designed to attain such goal, e.g., getting higher SNR or better detector's performance at the receiver. However, an important tool for evaluating the radar's performance is its ambiguity function. In this paper, we consider the problem of transmit signal design, in order to optimize the ambiguity function...
Detection-localization tradeoff in MIMO radars
, Article Radioengineering ; Volume 26, Issue 2 , 2017 , Pages 581-587 ; 12102512 (ISSN) ; Radmard, M ; Chitgarha, M. M ; Bastani, M. H ; Nayebi, M. M ; Sharif University of Technology
2017
Abstract
Two gains play key roles in recently developed MIMO wireless communication systems: "spatial diversity" gain and "spatial multiplexing" gain. The diversity gain refers to the capability to decrease the error rate of the MIMO channel, while the multiplexing gain implicitly refers to the amount of increase in the capacity of the MIMO channel. It has been shown that there is a fundamental tradeoff between these two types of gains, meaning interplay between increasing reliability (via an increase in the diversity gain) and increasing data rate (via an increase in the multiplexing gain). On the other hand, recently, MIMO radars have attracted much attention for their superior ability to enhance...
Antenna placement and power allocation optimization in MIMO detection
, Article IEEE Transactions on Aerospace and Electronic Systems ; Vol. 50, Issue 2 , April , 2014 , pp. 1468-1478 ; Chitgarha, M. M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
It is a well known fact that using multiple antennas at transmit and receive sides improves the detection performance. However, in such multiple-input multiple-output (MIMO) configuration, proper positioning of transmitters and receivers is a big challenge that can have significant influence on the performance of the overall system. In addition, determining the power of each transmitter under a total power constraint is a problem that should be solved in order to enhance the performance and coverage of such a system. In this paper, we design the Neyman-Pearson detector under the Rayleigh scatter model and use it to introduce a criterion for the antenna placement at both transmit and receive...
Ambiguity function of MIMO radar with widely separated antennas
, Article Proceedings International Radar Symposium ; 16 -18 June , 2014 ; ISSN: 21555753 ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
2014
Abstract
There has been much interest, recently, towards exploiting the Multiple-Input Multiple-Output (MIMO) technique in radar. It is shown that using multiple antennas at transmit and receive sides can improve the performance of the system. However, in order to analyze the system's performance, its ambiguity function, i.e. the ambiguity function of a MIMO radar, is needed to be defined. In this paper, beginning from the information theoretic definitions, we derive such function, specifically for a MIMO radar with widely separated antennas
Choosing the position of the receiver in a MISO passive radar system
, Article European Microwave Week 2012: "Space for Microwaves", EuMW 2012, Conference Proceedings - 9th European Radar Conference, EuRAD 2012 ; 2012 , Pages 318-321 ; 9782874870293 (ISBN) ; Majd, M. N ; Radmard, M ; Nayebi, M. M ; Sharif University of Technology
2012
Abstract
By combining the two ideas of MIMO (Multiple Input Multiple Output) and PCL (Passive Coherent Location) in radar, one can achieve the advantages of both recently developed techniques simultaneously. While using multiple antennas at the receive side provides a spatial diversity of the object to be detected, using multiple illuminators of opportunity, most importantly, makes the radar covert to the interceptors. One obstacle in such MIMO configuration is choosing the positions of the receive antennas. In this paper, after analyzing the Neyman-Pearson detector for the DVB-T based PCL, we introduce the probability of missed detection as a criterion to place the receive antenna. Here, we only...
Adaptive filtering techniques in passive radar
, Article Proceedings International Radar Symposium, Dresden ; Volume 2 , June , 2013 , Pages 1067-1078 ; 21555753 (ISSN) ; 9783954042234 (ISBN) ; Radmard, M ; Majd, M. N ; Nayebi, M. M ; Sharif University of Technology
2013
Abstract
One of the most important obstacles in passive radar applications is removing the direct signal from the target channel. Otherwise, week echoes from the targets in the target channel would be ignored due to the limited dynamic range of the system. One of the most effective techniques in this field is using adaptive filters. In this paper various adaptive filters are introduced and their performances are shown and compared