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State functions: the milestone of fracture
, Article Archive of Applied Mechanics ; Volume 86, Issue 7 , 2016 , Pages 1311-1324 ; 09391533 (ISSN) ; Ranjbaran, M ; Sharif University of Technology
Springer Verlag
2016
Abstract
The fracture phenomenon is defined via the change of state of structure (entity) between the intact and the fractured end states as the function of the state variable. The twin state functions are defined for the transition of unit of the entity between its two end states. The state ratio is defined as the ratio of the two state functions. The property of the cracked structure is defined as the product of the structure property and the state ratio. The work is then used to derive the main parameters of the fracture mechanics. The work is verified via five examples. © 2016, Springer-Verlag Berlin Heidelberg
State-based buckling analysis of beam-like structures
, Article Archive of Applied Mechanics ; Volume 87, Issue 9 , 2017 , Pages 1555-1565 ; 09391533 (ISSN) ; Ranjbaran, M ; Sharif University of Technology
2017
Abstract
Beam, column, plate, and any other structure, under full or partial compressive loading, are prone to failure by the buckling phenomenon. At the instant of failure, the structure may be in unpredictable elastic, elastic–plastic, full plastic, cracked, or other forms of deterioration state. Therefore, in spite of so much study, there is no definite solution to the problem. In this paper a unified, simple, and exact theory is proposed where buckling is considered as the change of state of structure between intact and collapsed states, and then the buckling capacity is innovatively expressed via states and phenomena functions, which are explicitly defined as functions of state variable. The...
Innovative theory for the compliance computation in rotors
, Article Scientia Iranica ; Volume 24, Issue 4 , 2017 , Pages 1779-1788 ; 10263098 (ISSN) ; Ranjbaran, M ; Sharif University of Technology
2017
Abstract
The conventional energy release rate approach to the computation of the crack compliance in rotors is critically reviewed and its shortcoming is highlighted. The state functions and the generic compliance are introduced, defined, and verified. The proposed functions are defined based on the end states' conditions and are exact. The crack compliance of the shaft in torsion is explicitly defined as the function of the crack depth ratio and recommended as a good alternative to the classical procedure of the energy release rate method. The accuracy and efficiency of the work are verified by concise mathematical formulation and comparison of the results of the work with the others in four...
A Model for Supplier Selection by Considering Buyer and Supplier Benefits
, M.Sc. Thesis Sharif University of Technology ; Kianfar, Farhad (Supervisor)
Abstract
Supply chain problems consist of a large number of issues. One of the key problem in this area is supplier selection in supply chain. Several criteria must be considered in the supplier selection. So, multi criteria decision making approach, neural network, mathematical programming and etc. are used for solving this problems. In most of these problems, supplier selection is done according to the buyer’s objectives.
So far, several methods are provided for supplier selection problem. In majority of them, supplier selection problem is surveyed from buyer’s viewpoint and in those have only been considered the buyer’s benefit maximization that will not necessarily lead to optimal condition...
So far, several methods are provided for supplier selection problem. In majority of them, supplier selection problem is surveyed from buyer’s viewpoint and in those have only been considered the buyer’s benefit maximization that will not necessarily lead to optimal condition...
An interface tool for finite element–based optimal design
, Article International Journal on Interactive Design and Manufacturing ; Volume 18, Issue 1 , 2024 , Pages 375-383 ; 19552513 (ISSN) ; Khodaygan, S ; Sharif University of Technology
2024
Abstract
Optimal design of engineering systems with complex geometry under multiple loadings is always a challenging procedure. This paper introduces a computational interface tool between ABAQUS® and MATLAB® that can be used for carrying out the parametric optimal design of complex mechanical components. The software is developed entirely in MATLAB® environment which can handle constrained optimization problems without the need for the user to explicitly define the constraints using mathematical equations or functions. In this software, the design variables are proposed for selection through a user-friendly environment and the objective function can be iteratively evaluated by the finite-element...
Investigating the Influence of a Silty Layer on the Liquefaction of Saturated Sandy Soils through Numerical Methods
, M.Sc. Thesis Sharif University of Technology ; Pak, Ali (Supervisor)
Abstract
One of the main geotechnical phenomena that causes severe damage during earthquake is liquefaction. This incident occurs due to the undrained behavior of loose sandy soils. In this occurrence, the interaction between the solid and liquid phases in a cyclic motion leads to an increase in pore water pressure and a decrease in interactive forces (effective forces) between grains in the solid grains. Therefore, shear strength decreases. Different aspects of the aforementioned phenomenon is investigated, namely, field, laboratory, and numerical; nevertheless, the study is largely focused on the numerical modelling. Most studies in this field are carried out on a one-layer saturated sand. However,...
Prediction of Hydraulic Fracturing Technology in Naturally Fractured Rocks, by Considering Immiscible Two-phase Flow
, Ph.D. Dissertation Sharif University of Technology ; Taghikhani, Vahid (Supervisor) ; Ayatollahi, Shahab (Supervisor) ; Shad, Saeed (Supervisor) ; Ranjbaran, Abdolrasul ($item.subfieldsMap.e)
Abstract
To have a deeper understanding of Hydraulic fracturing operation, in this study four important parts in this field was developed and simulated. In the first part, continuity and momentum equations for a single phase flow in a propagating penny-shaped fracture inside an impermeable matrix was revisited based on a fixed coordinate system. Its correctness was validated against experimental data and its features were compared with the well-known lubrication theory in analytical form. The new derived continuity equation caused the fracture tip to have a positive and finite pressure while, the conventional model predicted negative infinity for that. In the second part, Finite Volume method was...
A heuristic insight on end-point calculation and a new phase interference parameter in two-phase relative permeability curves for horizontal fracture flow
, Article Transport in Porous Media ; Volume 119, Issue 3 , 2017 , Pages 499-519 ; 01693913 (ISSN) ; Shad, S ; Taghikhani, V ; Ayatollahi, S ; Sharif University of Technology
2017
Abstract
Relative permeability curves of two-phase flow in a fracture have been a subject of study in recent years. The importance of these curves have been widely observed in multidisciplines, such as water subsurface resources, geothermal energy and underground hydrocarbon resources, especially fractured oil and gas reservoirs. Extensive experimental studies have been cited alongside the numerical studies in this area. However, simple analytical and practical solutions are still attractive. In the current study, wettability effects and phase interference explicitly were tried to be implemented in a simple analytical formula. The wettability effects are represented by residual saturations which...
Dispersion and gain investigation of free electron laser based on legendre polynomial expansion
, Article Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, Toronto, ON, 12 September 2005 through 14 September 2005 ; Volume 5971 , 2005 ; 0277786X (ISSN) ; Chamanzar, M ; Mehrany, K ; Rashidian, B ; Ranjbaran, M ; Morandotti R. A ; Ruda H. E ; Yao J ; Sharif University of Technology
2005
Abstract
Free electron lasers have been the subject of intensive interest during the recent decades. In this paper, free electron laser having sheet electron beam with arbitrary inhomogeneous profile of transverse distribution of the beam current density is studied in the linear regime, whereas a novel approach based on the Legendre polynomial expansion of eigenfunctions, already used in analyzing optical structures including stratified structures and diffraction gratings, is adapted to find the eigenfunctions and eigenvalues of the structure. As for this method is unconditionally stable, it works pretty well even in those cases in which the conventional transfer matrix method suffers from numerical...
Three-dimensional diffraction analysis of phase and amplitude gratings based on legendre expansion of electromagnetic fields
, Article Photonic Applications in Nonlinear Optics, Nanophotonics, and Microwave Photonics, Toronto, ON, 12 September 2005 through 14 September 2005 ; Volume 5971 , 2005 ; 0277786X (ISSN) ; Mehrany, K ; Rashidian, B ; Ranjbaran, M ; Morandotti R. A ; Ruda H. E ; Yao J ; Sharif University of Technology
2005
Abstract
Three-dimensional vectorial diffraction analysis of phase and amplitude gratings in conical mounting is presented based on Legendre expansion of electromagnetic fields. In the so-called conical mounting, different fields components are coupled and the solution is not separable in terms of independent TE and TM cases. In contrast to conventional RCWA in which the solution is obtained using state variables representation of the coupled wave amplitudes by expanding space harmonic amplitudes of the fields in terms of the eigenfunctions and eigenvectors of the coefficient matrix defined by rigorous coupled wave equations, here the solution of first order coupled Maxwell's equations is expanded in...
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
Ambiguity function based receiver placement in multi-site radar
, Article 2016 CIE International Conference on Radar, RADAR 2016, 10 October 2016 through 13 October 2016 ; 2017 ; 9781509048281 (ISBN) ; Chitgarha, M. M ; Nazari Majd, M ; Nayebi, M. M ; Sharif University of Technology
2017
Abstract
It has been shown that using multiple antennas in a radar system improves the performance considerably, since multiple target echoes are received from different aspect angles of the target. In this way, the target detection is improved. However, when using multiple antennas, some problems, such as designing the transmit signals, synchronization, etc. emerge that should be solved. One of such problems is the receiver placement. Receiver placement deals with choosing a proper position for the receive antenna in order to optimize the whole system's performance. In this paper, a receiver placement procedure based on improving the radar ambiguity function is proposed for the case of a multisite...