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Particuology 2022年第4期20卷 112-124页

作者： siamak akhshik Majid Rajabi Department of Mechanical Engineering Sharif University of TechnologyIran Sustainable Manufacturing Research Laboratory School of Mechanical EngineeringIran University of Science and TechnologyIran

Proppants transport is an advanced technique to improve the hydraulic fracture phenomenon,in order to promote the versatility of gas/oil reservoirs.A numerical simulation of proppants transport at both hydraulic fracture(HF)and natural fracture(NF)intersection is performed to provide a better understand-ing of key factors which cause,or contribute to proppants transport in HF-NF *** fluid dynamics(CFD)in association with discrete element method(DEM)is used to model the complex interactions between proppant particles,host fluid medium and fractured *** effect of non-spherical geometry of particles is considered in this model,using the multi-sphere *** interaction forces between fluid flow and particles are considered in the computational ***,the inter-actions of particle-particle and particle-wall are taken into account via Hertz-Mindlin *** results of the CFD-DEM simulations are compared to the experimental *** is found that the CFD-DEM sim-ulation is capable of predicting proppant transport and deposition quality at intersections which are in agreement with experimental *** results indicate that the HF-NF intersection type,fluid velocity and NF aperture affect the quality of blockage occurrence,presenting a new index,called the blockage coefficient which indicates the severity of the blockage.

关键词： Hydraulic fracture process Proppants transport CFD-DEM method HF-NF intersection Blockage coffcient

CFD-DEM simulation of the hole cleaning process in a deviated well drilling： The effects of particle shape

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Particuology 2016年第2期14卷 72-82页

作者： siamak akhshik Mehdi Behzad Majid Rajabi Department of Mechanical Engineering Sharif University of Technology Azadi Avenue Tehran Iran School of Mechanical Engineering lran University of Science and Technology Narmak Tehran Iran

We investigate the effect of particle shape on the transportation mechanism in well-drilling using a three-dimensional model that couples computational fluid dynamics （CFD） with the discrete element method （DEM）. This numerical method allows us to incorporate the fluid-particle interactions （drag force, contact force, Saffman lift force, Magnus lift force, buoyancy force） using momentum exchange and the non-Newtonian behavior of the fluid. The interactions of particle-particle, particle-wall, and particle-drill pipe are taken into account with the Hertz-Mindlin model. We compare the transport of spheres with non-spherical particles （non-smooth sphere, disc, and cubic） constructed via the multi- sphere method for a range of fluid inlet velocities and drill pipe inclination angles. The simulations are carried out for laboratory-scale drilling configurations. Our results demonstrate good agreement with published experimental data. We evaluate the fluid-particle flow patterns, the particle velocities, and the particle concentration profiles. The results reveal that particle sphericity plays a major role in the fluid-solid interaction. The traditional assumption of an ideal spherical particle may cause inaccurate results.

关键词： CFD-DEM method Deviated well drilling Particles transport Two-way coupling scheme Particle-fluid Interaction

Shear wall layout optimization of tall buildings using Quantum Charged System Search

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Frontiers of Structural and Civil Engineering 2020年第5期14卷 1131-1151页

作者： siamak TALATAHARI Mahdi RABIEI Department of Civil Engineering University of TabrizTabriz ***Iran Engineering Faculty Near East UniversityNicosia 99138Turkey

This paper presents a developed meta-heuristic algorithm to optimize the shear walls of tall reinforced concrete *** types of walls are considered as lateral resistant *** this paper,Quantum Charged System Search(QCSS)algorithm is presented as a new optimization method and used to improve the convergence capability of the original Charged System *** cost of tall building is taken as the objective *** the design of the lateral system plays a major role in the performance of the tall buildings,this paper proposes a unique computational technique that,unlike available works,focuses on structural efficiency or architectural *** technique considers both structural and architectural requirements such as minimum structural costs,torsional effects,flexural and shear resistance,lateral deflection,openings and *** robustness of the new algorithm is demonstrated by comparing the outcomes of the QCSS with those of its standard algorithm.

关键词： Quantum Charged System Search shear wall layout optimization tall buildings

Is There a Minimum Electrophilicity Principle in Chemical Reactions？

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Chinese Journal of Chemistry 2007年第10期25卷 1439-1444页

作者： NOORIZADEH, siamak Department of Chemistry College of Sciences Shahid Chamran University Ahwaz 61357-4-3169 Iran

For 25 simple reactions, the changes of the hardness （△η）, polarizability （△α） and electrophilicity index （△ω） and their cube-roots （△η^1/3, △α^1/3, △ω^1/3） were calculated. It is shown that although the Maximum Hardness and Minimum Polarizability Principles are not valid for all reactions, but in most cases △ω^1/3〈0, whereas we always find △ω〈0. Our observation implies to this fact that for those chemical reactions in which the number of moles decreases or at least remains constant, the most stable species （reactants or products） have the lowest sum of electrophilicities. In other words ＂the natural direction of a chemical reaction is toward a state of minimum electrophilicity＂. This fact may be called Minimum Electrophilicity Principle （MEP）.

关键词： maximum hardness principle minimum polarizability principle minimum electrophilicity principle,density functional theory

Assessment of thermal stratification, stability and characteristics of deep water zone of the southern Caspian Sea

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Journal of Ocean Engineering and Science 2017年第3期2卷 203-216页

作者： siamak Jamshidi Iranian National Institute for Oceanography and Atmospheric Science(INIOAS) No.3Etemadzadeh St.Fatemi Ave.Tehran ***Iran

Variations of seawater properties and stratification of water column in the southern deep water zone(470 m depth)of the Caspian Sea were evaluated based on field measured *** of physical characteristics(temperature,salinity,density and sound speed)of seawater mainly were limited to the upper 100 m *** this layer,seasonal changes of seawater parameters were *** structure of temperature in the southern Caspian Sea waters was characterized by a significant seasonal thermocline approximately between 20 and 50 m depths in summer with a vertical gradient of around 16℃.Destruction of the thermocline occurred with the general cooling of the sea surface water and deepening of the mixed layer during late of autumn and *** of stability in water column often across the upper layers(surface mixed and thermocline)was more than deeper *** of salinity were around 12.4 PSU in the time of *** of thermocline and pycnocline were characterized by a significant homogeneity especially in offshore stations during the *** to high agreement between density and temperature in the Caspian Seawater,a strong seasonal pycnocline was observed in the position of the ***,structure of sound speed variations followed vertical variations of seawater *** of chemical characteristics(dissolved oxygen and pH)of seawater mainly were continued from sea surface to near the sea bed in deep water zone.

关键词： Caspian Sea Seawater properties Thermal stratification Water masses,Stability

Reliability assessment of networks-on-chip based on analytical models

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第12期10卷 1801-1814页

作者： Mojtaba VALINATAJ siamak MOHAMMADI Saeed SAFARI School of Electrical and Computer Engineering College of Engineering University of Tehran

As technology scales down, the reliability issues are becoming more crucial, especially for networks-on-chip (NoCs) that provide the communication requirements of multi-processor systems-on-chip. Reliability evaluation based on analytical models is a precise method for dependability analysis before and after designing the fault-tolerant systems. In this paper, we accurately formulate the inherent reliability and vulnerability of some popular NoC architectures against permanent faults, also depending on the employed routing algorithm and traffic model. Based on this analysis, effects of failures in the links, switches and network interfaces on the packet delivery of NoCs are determined. Besides, some extensions to evaluate a fault-tolerant method and some routing algorithms are described. The analyses are validated through appropriate simulations. The results thus obtained are exactly the same as or very close to the analytical ones.

关键词： Networks-on-chip (NoCs) Traffic model Routing algorithm Reliability assessment Permanent fault

Cosmological perturbations in a noncommutative braneworld inflation

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Research in Astronomy and Astrophysics 2012年第6期12卷 625-635页

作者： Kourosh Nozari siamak Akhshabi Department of Physics Faculty of Basic SciencesUniversity of MazandaranP.O.Box 47416-95447BabolsarIran

We use the smeared, coherent state picture of noncommutativity to study evolution of perturbations in a noncommutative braneworld scenario. Within the stan- dard procedure of studying braneworld cosmological perturbations, we study the evo- lution of the Bardeen metric potential and curvature perturbations in this model. We show that in this setup, the early stage of the universe＇s evolution has a transient phan- tom evolution with imaginary effective sound speed.

关键词： early universe cosmology -- cosmology theory

Closed-form dynamics of a hexarot parallel manipulator by means of the principle of virtual work

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Acta Mechanica Sinica 2018年第5期34卷 883-895页

作者： siamak Pedrammehr Saeid Nahavandi Hamid Abdi Institute for Intelligent Systems Research and Innovation Deakin UniversityWaurn Ponds CampusGeelongVIC 3217Australia

In this research,a systematic approach to solving the inverse dynamics of hexarot manipulators is addressed using the methodology of virtual *** the first time,a closed form of the mathematical formulation of the standard dynamic model is presented for this class of *** efficient algorithm for solving this closed-form dynamic model of the mechanism is developed and it is used to simulate the dynamics of the system for different *** of the proposed model is performed using SimMechanics and it is shown that the results of the proposed mathematical model match with the results obtained by the SimMechanics model.

关键词： Parallel mechanism Hexarot Simulator Dynamics Virtual work principle

Cohen-Macaulay Lexsegment Complexes in Arbitrary Codimension

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Algebra Colloquium 2017年第3期24卷 401-406页

作者： siamak Yassemi Rahim Zaare-Nahandi School of Mathematics Statistics & Computer Science University of Tehran Tehran Iran

We characterize pure lexsegment complexes which are Cohen-Macaulay in arbitrary codimension. More precisely, we prove that any lexsegment complex is Cohen- Macaulay if and only if it is pure and its 1-dimensional links are connected, and that a lexsegment flag complex is Cohen-Macaulay if and only if it is pure and connected. We show that any non-Cohen-Macaulay lexsegment complex is a Buchsbaum complex if and only if it is a pure disconnected flag complex. For t≥2, a lexsegment complex is strictly Cohen-Macaulay in codimension t if and only if it is the join of a lexsegment pure discon- nected flag complex with a （t - 2）-dimensional simplex. When the Stanley-Reisner ideal of a pure lexsegment complex is not quadratic, the complex is Cohen-Macaulay if and only if it is Cohen-Macaulay in some codimension. Our results are based on a characterization of Cohen-Macaulay and Buchsbaum lexsegment complexes by Bonanzinga, Sorrenti and Terai.

关键词： squarefree lexsegment ideal Cohen-Macaulay complex Buchsbaum complex,flag complex CMt complex

Studying thin film damping in a micro-beam resonator based on non-classical theories

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Acta Mechanica Sinica 2016年第3期32卷 369-379页

作者： Mina Ghanbari siamak Hossainpour Ghader Rezazadeh Mechanical Engineering Department Sahand University of Technology Mechanical Engineering Department Faculty of Engineering Urmia University

In this paper, a mathematical model is presented for studying thin film damping of the surrounding fluid in an in-plane oscillating micro-beam resonator. The proposed model for this study is made up of a clamped-clamped micro-beam bound between two fixed layers. The microgap between the micro-beam and fixed layers is filled with air. As classical theories are not properly capable of predicting the size dependence behaviors of the micro-beam,and also behavior of micro-scale fluid media, hence in the presented model, equation of motion governing longitudinal displacement of the micro-beam has been extracted based on non-local elasticity theory. Furthermore, the fluid field has been modeled based on micro-polar theory. These coupled equations have been simplified using Newton-Laplace and continuity equations. After transforming to non-dimensional form and linearizing, the equations have been discretized and solved simultaneously using a Galerkin-based reduced order model. Considering slip boundary conditions and applying a complex frequency approach, the equivalent damping ratio and quality factor of the micro-beam resonator have been obtained. The obtained values for the quality factor have been compared to those based on classical theories. We have shown that applying non-classical theories underestimate the values of the quality factor obtained based on classical theo-ries. The effects of geometrical parameters of the micro-beam and micro-scale fluid field on the quality factor of the resonator have also been investigated.

关键词： Thin film damping micro-electromechanical systems(MEMS) Micro-polar theory