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    Mooring system design and optimization for floating bridge of Urmia lake

    , Article Proceedings of the 21st International Conference on Offshore Mechanics and Arctic Engineering (OMAE), Oslo, 23 June 2002 through 28 June 2002 ; Volume 1 , 2002 , Pages 613-620 Daghigh, M ; Paein Koulaei, R. T ; Seif, M. S ; ASME ; Sharif University of Technology
    2002
    Abstract
    In order to get better understanding on the response of floating bodies, different design aspects of mooring lines has been investigated in this paper. Mooting lines are categerized into two types; the catenary settling on the sea floor (type 1) and the limited one which has no dead-length on sea floor (type 2). It has been observed that the stiffness of both types may be well predicted by Jain's formulation and in the design process of floating bodies the mooring lines may be replaced by uncoupled horizontal and vertical springs. On the other hand, the anchor capacity against sliding and release from the mean still water has been studied in this paper. From the results of a parametric... 

    A micromechanical study of rolling and sliding contacts in assemblies of oval granules

    , Article International Journal for Numerical and Analytical Methods in Geomechanics ; Volume 27, Issue 5 , 2003 , Pages 403-424 ; 03639061 (ISSN) Shodja, H. M ; Nezami, E. G ; Sharif University of Technology
    2003
    Abstract
    The evolution of the microstructure of an assembly of cohesionless granular materials with associated pores, which carry the overall applied stresses through frictional contacts is a complex phenomenon. The macroscopic flow of such materials take place by the virtue of the relative rolling and sliding of the grains on the micro-scale. A new discrete element method for biaxial compression simulations of random assemblies of oval particles with mixed sizes is introduced. During the course of deformation, the new positions of the grains are determined by employing the static equilibrium equations. A key aspect of the method is that, it is formulated for ellipse cross-sectional particles, hence... 

    Development of a saturation-based μ(I)-rheology for wet granular materials using discrete element method

    , Article Scientia Iranica ; Volume 28, Issue 5 B , 2021 , Pages 2719-2732 ; 10263098 (ISSN) Ghorbani, R ; Taghizadeh Manzari, M ; Hajilouy Benisi, A ; Sharif University of Technology
    Sharif University of Technology  2021
    Abstract
    The present study employs Discrete Element Method (DEM) to establish a rheological model that relates the apparent viscosity of a granular material to shear rate, normal stress, and water saturation. In addition, a theoretical model was developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces were embedded in a 3D shear cell as a numerical rheometer, and a wet specimen was sheared between two walls. A power law rheological model was then obtained as a function of inertia number and saturation. It was found that up to a critical saturation, the apparent viscosity increased with saturation that was higher than that of... 

    A new, publicly verifiable, secret sharing scheme

    , Article Scientia Iranica ; Volume 15, Issue 2 , 2008 , Pages 246-251 ; 10263098 (ISSN) Behnad, A ; Eghlidos, T ; Sharif University of Technology
    Sharif University of Technology  2008
    Abstract
    A Publicly Verifiable Secret Sharing (PVSS) scheme, as introduced by Stadler, has a feature where anyone, besides the participants, can verify the validity of the shares distributed by the dealer. Schoenmakers added a new feature, by providing a proof of correctness of the shares released by the players in the reconstruction process. This protocol is claimed to be an improvement on Stadler's and Fujisaki-Okamoto's, both in efficiency and in the type of intractability assumptions. However, Young-Yung improved Schoenmakers' PVSS, using a Discrete-Log instead of a Decision Diffie-Hellman. In this paper, a new PVSS is presented, having an intrinsic difference with its predecessors, that is, the... 

    Study of the Effects of Powder Dispensing Mechanism on Selective Laser Sintering Process

    , M.Sc. Thesis Sharif University of Technology Mahmoodi, Amir Hossein (Author) ; Movahhedy, Mohammad Reza (Supervisor)
    Abstract
    Additive manufacturing (Simply called A.M.) is a group of manufacturing technologies that is developing rapidly and is being used widely in some industries like car manufacturing, Aerospace and producing Biomedical devices, In a way that some researchers believe that A.M. methods will change the future of manufacturing. One of the most important A.M. techniques is the Selective Laser Sintering (SLS) method that is mostly used in industrial applications. A SLS machine has a lot of sub systems and mechanisms that have key role in the Laser Sintering process. One of the mechanisms of SLS machine is the Powder Dispensing mechanism that produce layers of unsintered powder as thin as 100 microns... 

    Dem Simulation of Triaxial Tests on Coarse Aggregates Applicable for Base and Sub-Base of Roads and Railways

    , M.Sc. Thesis Sharif University of Technology Hajian, Sadegh (Author) ; Pak, Ali (Supervisor)
    Abstract
    In this study, numerical modeling of the micromechanical behavior of gravel aggregates applicable for base and sub-base of roads and railways under triaxial compression tests is conducted. The material is a type of well-graded gravelly soil with a maximum particle size of 20 mm, whose application is recommended by the UK Highways Agency. The prominent role of this material in the performance and endurance of the roads shows the importance of studying its behavior to acquire a better understanding of its mechanical properties. A number of triaxial tests using monotonic and cyclic loadings have been performed in the laboratory to investigate the behavior of this type of material. In the... 

    A hardwired discrete simulation algorithm

    , Article Scientia Iranica ; Volume 14, Issue 6 , 2007 , Pages 566-570 ; 10263098 (ISSN) Nojumi, M. H ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    The architecture of a hardwired simulator for implementation of a discrete event-driven simulation of digital systems at the logic level is presented. In the design of this system, attempts have been made to utilize techniques of high performance computing to have a system capable of simulating the digital circuits rapidly. The centralized event-driven simulation algorithm chosen here, has the advantages of being efficient and conceptually straightforward. The high reliability of the simulator has been taken care of through a collection of handshake signals between each two of the three main modules. © Sharif University of Technology, December 2007  

    Direct Discrete Method (DDM) and its application to neutron transport problems

    , Article Scientia Iranica ; Volume 14, Issue 1 , 2007 , Pages 78-85 ; 10263098 (ISSN) Vosoughi, N ; Salehi, A. A ; Shahriari, M ; Heshmatzadeh, M ; Sharif University of Technology
    Sharif University of Technology  2007
    Abstract
    The objective of this paper is to introduce a new direct method for neutronic calculations. This method, called Direct Discrete Method (DDM), is simpler than the Neutron Transport Equation and more compatible with the physical meanings of the problem. The method, based on the physics of the problem, initially-runs through meshing of the desired geometry. Next, the balance equation for each mesh interval is written. Considering the connection between the mesh intervals, the final discrete equation series are directly obtained without the need to first pass through the set-up of the neutron transport differential equation. In this paper, a single and multigroup neutron transport discrete... 

    Coupled lattice boltzmann - Discrete element method for numerical modelling of sand production

    , Article Particle-Based Methods II - Fundamentals and Applications, 26 October 2011 through 28 October 2011 ; 2011 , Pages 371-382 ; 9788489925670 (ISBN) Ghassemi, A ; Pak, A ; Sharif University of Technology
    Abstract
    In this study, a coupled numerical approach based on Lattice Boltzmann Method (LBM) and Discrete Element Method (DEM) is employed for 2D simulation of fluid flow in porous media comprising of movable circular particles. The developed model is used for simulation of sand production which is one of the important problems in petroleum industry. The numerical tool has proved to have the capability of investigating the mechanisms involved in sand production problem. The results show that the rate of sand production is strongly affected by flow rate and confining pressure  

    Dynamic modeling of the turning process of slip-cast fused silica ceramics using the discrete element method

    , Article Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture ; Volume 234, Issue 3 , 2020 , Pages 629-640 Roostai, H ; Movahhedy, M. R ; Sharif University of Technology
    SAGE Publications Ltd  2020
    Abstract
    Simulation of brittle regime machining of materials (such as ceramics) is often difficult because of the complex material removal mechanisms involved. In this study, the discrete element method is used to simulate the dynamic process for machining of slip-cast fused silica ceramics. Flat-joint contact model is exploited to model contacts between particles in synthetic discrete element method models. This contact model is suitable for modeling of brittle materials with high ratios (higher than 10) of unconfined compressive strength to tensile strength. The discrete element method has the ability to simulate initiation, propagation, and coalescence of cracks leading to chip formation in the... 

    Simulation of Two-Fluid Flow Through Particlulate Porous Media Contaning Moving Particles at Pore Scale Using Combined LB-DE Method

    , Ph.D. Dissertation Sharif University of Technology Ghassemi, Ali (Author) ; Pak, Ali (Supervisor)
    Abstract
    A considerable number of engineering applications deal with flow of fluid(s) through particulate porous media. For certain engineering problems, fluid flow may displace and even dislodge the solid particles from the mass where a fluid-particle flow occurs. The complexity of involving processes which should be studied at the scale of moving particles transforms the analyses of these problems towards a difficult engineering task. Characteristics of solid grains such as size and shape and properties of the flowing fluid(s) such as viscosity and surface tension play essential roles in the behavior of fluid-particle systems. Also, when fluid flows through porous media, secondary processes such as... 

    Modeling and Analysis of the Powder Deposition Mechanisms of Selective Laser Sintering Process

    , M.Sc. Thesis Sharif University of Technology Shakiba, Abdorreza (Author) ; Movahedi, Mohamad Reza (Supervisor)
    Abstract
    Selective laser sintering is a technique which uses a laser as the power source to sintering some selected points at a bed of powder in order to create a solid structure. In this research the SLS mechanisms of powder deposition is simulated and surface smoothness and layer density created by each mechanism is computed. For this purpose roller, blade and hopper mechanisms are simulated. For this simulation, polyamide 12 (PA2200) which is a common material is used. In this simulation at first powder specifications are extracted according to the references and for particle shape instead of using the spherical particle shape we use a certain shape that is more close to reality which created by... 

    Experimental Study and Simulation of Ultrasonic Vibration Effect on Powder Spreading in Selective Laser Sintering Process

    , M.Sc. Thesis Sharif University of Technology Ghovvati, Sadegh (Author) ; Movahhedi, Mohamadreza (Supervisor)
    Abstract
    Selective laser sintering is an additive manufacturing technique based on fusion of powder bed, wherein after spreading a powder layer, a focused laser beam directs onto selected points of powder bed to fuse powder particles together. This process is repeated layer by layer until the final part is created. Although utilization of blade as a conventional powder spreading (CPS) mechanism has a good compression ability, the fixed contact line between blade and powder bed surface results in improper powder flowability and increasing shear forces applied on underneath layer. In this study, in order to obtain the basis for conducting practical experiments, discrete element simulation of powder... 

    Numerical Modeling and Experimental Investigation of the Efficiency of the Laser-assisted Machining for Ceramics

    , Ph.D. Dissertation Sharif University of Technology Roostaei, Hossein (Author) ; Movahhedy, Mohammad Reza (Supervisor) ; Shoja Razavi, Reza (Co-Supervisor)
    Abstract
    Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The... 

    Simulation of Rainfall-triggered Landslides with Considering the Rheology Changes in Sandy Soils

    , Ph.D. Dissertation Sharif University of Technology Ghorbani, Ramin (Author) ; Taghizadeh Manzari, Mehrdad (Supervisor) ; Hajilouy-Benisi, Ali (Co-Supervisor)
    Abstract
    This study presents an integrated two-dimensional numerical framework for simulating rainfall-induced landslides from instability initiation to post-failure flow. The discrete element method (DEM) is used to establish a rheological model that relates the apparent viscosity of a granular sand to shear rate, normal stress, and water saturation. A theoretical model is developed to determine water distribution and water-induced forces between particles for different saturations. The resulting forces are embedded in a 3D shear cell as a numerical rheometer and a wet sand is sheared between two walls. A power law rheological model is obtained as a function of inertia number and saturation. It was... 

    Investigation of the Effective Parameters on the Scouring Phenomenon of Seabed Pipelines by a Combination of Computational Fluid Dynamics and Discrete Elements Method

    , M.Sc. Thesis Sharif University of Technology Mirza, Mitra (Author) ; Khorasanchi, Mahdi (Supervisor)
    Abstract
    Occurrence of scouring around the seabed pipelines can lead to pipe failure and pose a serious threat to the marine environment, economic losses and waste of oil and gas. Therefore, to prevent the occurrence of scouring, by simulating this phenomenon and identifying the parameters affecting it, we can help to design a more efficient placement of pipes in the seabed. Various methods such as potential flow theory and turbulent single-phase and two-phase models have been proposed to simulate this phenomenon. The purpose of this article is to simulate and investigate the effective parameters of this phenomenon by combining computational fluid dynamics and separate elements. The innovation of... 

    Optimal constrained non-renewable resource allocation in PERT networks with discrete activity times

    , Article Scientia Iranica ; Volume 19, Issue 3 , 2012 , Pages 841-848 ; 10263098 (ISSN) Hashemin, S. S ; Fatemi Ghomi, S. M. T ; Modarres, M ; Sharif University of Technology
    2012
    Abstract
    In this paper, we develop an approach to optimally allocate a limited nonrenewable resource among the activities of a project, represented by a PERT-Type Network (PTN). The project needs to be completed within some specified due date. The objective is to maximize the probability of project completion on time. The duration of each activity is an arbitrary discrete random variable and also depends on the amount of consumable resource allocated to it. On the basis of the structure of networks, they are categorized as either reducible or irreducible. For each network structure, an analytical algorithm is presented. Through some examples, the algorithms are illustrated  

    Numerical Modelling of Armour Layer Stability in Low-crested Breakwaters Using Smoothed Particle Hydrodynamics (SPH) and Discrete Element Method (DEM)

    , Ph.D. Dissertation Sharif University of Technology Sarfaraz, Mohammad (Author) ; Pak, Ali (Supervisor)
    Abstract
    Rubble mound low-crested breakwaters protect the structures and ships in the port against wave attacks. Due to the overtopping, these structures provide a more attractive landscape and helps preserve the port's environment. Stability of low-crested breakwaters relies on the stability of the armor layer against the wave action, requiring the choice of the appropriate diameter for the armour blocks. For cubic armours that are of interest to the designers, there is currently no design relationship, and they inevitably use formulae specified for high-crested breakwaters that may not be in the safe side. The conventional method for determining the required armour diameter for a breakwater is... 

    Experimental Investigation and Design of an Optimum Fouling Removal Method for a Hull Cleaning Robot

    , M.Sc. Thesis Sharif University of Technology Gharaghani, Pedram (Author) ; Khorasanchi, Mahdi (Supervisor) ; Durali, Mohammad (Co-Supervisor)
    Abstract
    The repair, maintenance and cleaning of marine equipment and ships, as well as the optimization of these operations to reduce their costs have always been of interest to researchers. After a few hours of floating in seawater, an inanimate organic layer forms on the surface of marine structures. After a few months, the thickness of this layer increases. This will increase the drag by 30 to 40 percent. Hull cleaning operation increases efficiency, saves time and money, prolongs equipment life and reduces maintenance and repair costs.In this project, the types of marine fouling according to environmental conditions were identified, next a type of fouling (Barnacle) was selected, which has more... 

    Simulation and Optimization of Relatively New Catalyst Recovery from Old Catalysts Used in the FCC Process by Applying Electrostatic Field

    , M.Sc. Thesis Sharif University of Technology Najafi, Mehrdad (Author) ; Rashtchian, Davood (Supervisor) ; Fotovat, Farzam (Supervisor)
    Abstract
    In this thesis, the separation process for used and relatively new catalysts of residue fluid catalytic cracking unit by applying an electric field was evaluated. The main purpose of this dissertation is to simulate and design a separation system for separating used and relatively new catalysts of the FCC process in the electrostatic fields. In this regard, various separators were studied, and most of them were simulated under different circumstances. Finally, after examining and analyzing the particle behavior in each of the scenarios, the proposed system was introduced as more effective and efficient than the other separators in order to achieve the ideal separation of the used and...