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Numerical simulation of incipient particle motion

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International Journal of sediment Research 2020年第1期35卷 1-14页

作者： ali Nasrollahi ali akbar salehi neyshabouri Goodarz Ahmadi Masoud Montazeri Namin Civil Engineering Department Tarbiat Modares University Department of Mechanical and Aeronautical Engineering Clarkson University Civil Engineering Department University of Tehran

A two-dimensional(2 D) computational model for simulation of incipient sediment motion for noncohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method(DEM).The model was calibrated and verified using various experimental data reported in the literature and compared with different theories of incipient particle *** analysis was done and the effects of relevant parameters were *** addition to hydrodynamic forces such as drag,shear lift and Magnus force,the particle-particle interaction effects were included in the *** asymptotic critical mobility number was evaluated for various critical particle Reynolds numbers(R*) in the range of very small and very large R*.The obtained curve is classified into four *** was found that in the linear region,the drag force has the principal role on the initiation of ***,the critical mobility number is independent of particle diameter.A procedure for estimating the critical shear velocity directly from the information on particle diameter and roughness height was ***,the mechanism of incipient motion for the different regions was studied and the effect of different forces on the incipient particle motion was *** was found that the maximum effects of lift and Magnus forces were,respectively,less than ten and twenty percent of the total *** drag force,however,was typically the dominant force accounting for majority of the net hydrodynamic force acting on sediment particles at the onset of incipient motion.

关键词： Incipient motion shields curve Numerical simulation Drag force Lift force Magnus force Discrete Element Method

Issues in Eulerian-Lagrangian modeling of sediment transport under saltation regime

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International Journal of sediment Research 2018年第4期33卷 441-461页

作者： Reza Barati seyed ali akbar salehi neyshabouri Goodarz Ahmadi Faculty of Civil and Environmental Engineering Tarbiat Modares University Water Engineering Research Center Department of Civil Engineering Tarbiat Modares University Department of Mechanical and Aeronautical Engineering Clarkson University

The saltation regime is very important for understanding the sediment transport mechanism. However,there is no consensus on a model for the saltation regime. This study answers several questions raised with respect to the Eulerian-Lagrangian modeling of sediment transport. The first question is why the previous saltation models that use different combinations of hydrodynamic forces yielded acceptable results? The second question is which shear lift model(i.e. a shear lift expression and its coefficient) is more appropriate? Another important question is which hydrodynamic forces have greater contributions to the saltation characteristics of a sediment particle? The last question is what are the contributions of the turbulence fluctuations as well as effects of using two-and three-dimensional(2 D and 3 D) models on the simulation results? In order to fairly answer these questions, a systematic study was done by considering different scenarios. The current study is the first attempt to clearly discuss these issues. A comprehensive 3 D saltation model for non-cohesive sediment was developed that includes all the hydrodynamic forces acting on the particle. The random nature of sediment transport was included using turbulent flow and bed-particle collision models. The eddy interaction model was applied to generate a3 D turbulent flow field. Bed-particle collisions were considered using the concept of a contact zone and a corresponding contact point. The validation of the model was done using the available experimental data for a wide range of sediment size(0.03 to 4.8 cm). For the first question, the results indicated that some of the hydrodynamic effects show opposing trends and some have negligible effects. With these opposing effects it is possible to adjust the coefficients of different models to achieve acceptable agreement with the same experimental data while omitting some aspects of the physics of the process. A suitable model for the shear lift force was develop

关键词： Two-phase model Turbulent flow sediment transport saltation Hydrodynamic forces

scour and flow field around a spur dike in a 90° bend

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International Journal of sediment Research 2008年第1期23卷 56-68页

作者： Majid FAZLI Masoud GHODsIAN seyed ali akbar salehi neyshabouri Department of Civil Engineering Tarbiat Modares University Water Engineering Research Center Department of Civil Engineering Tarbiat Modares University Water Engineering Research Center Department of civil Engineering Tarbiat Modares University

spur dike is an important element in river training that creates rapid variations in flow field, sediment transport and bed topography. The mechanism of flow and sediment transport in a channel bend is very complex, especially when a spur dike is constructed in a bend. Most of previous investigations on flow behavior and scour around spur dike were carried out in straight channels. In this paper results of experiments on flow field and scour around a spur dike in a 90 degree channel bend are presented. sand with uniform grain size was used as the bed material. Experiments were conducted for different locations and different lengths of spur dikes at the bend with different values of discharge. The three dimensional flow fields around a spur dike were investigated. The maximum depth of scour was correlated to the Froude numbers, lengths and the locations of spur dike in the bend.

关键词： spur dike scouring 90° channel bend Bed topography Movable bed Flow pattern

Analytical determination of non-local parameter value to investigate the axial buckling of nanoshells affected by the passing nanofluids and their velocities considering various modified cylindrical shell theories

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Chinese Physics B 2023年第4期32卷 511-528页

作者： soheil Oveissi Aazam Ghassemi Mehdi salehi s.ali Eftekhari saeed Ziaei-Rad Department of Mechanical Engineering Najafabad BranchIslamic Azad UniversityNajafabadIran Department of Mechanical Engineering Khomeinishahr BranchIslamic Azad UniversityKhomeinishahrIran Department of Mechanical Engineering Isfahan University of TechnologyIsfahan 84156-83111Iran

We analytically determine the nonlocal parameter value to achieve a more accurate axial-buckling response of carbon nanoshells conveying nanofluids. To this end, the four plates/shells' classical theories of Love, Fl ¨ugge, Donnell, and sanders are generalized using Eringen's nonlocal elasticity theory. By combining these theories in cylindrical coordinates,a modified motion equation is presented to investigate the buckling behavior of the nanofluid-nanostructure-interaction problem. Herein, in addition to the small-scale effect of the structure and the passing fluid on the critical buckling strain,we discuss the effects of nanoflow velocity, fluid density(nano-liquid/nano-gas), half-wave numbers, aspect ratio, and nanoshell flexural rigidity. The analytical approach is used to discretize and solve the obtained relations to study the mentioned cases.

关键词： buckling nonlocal cylindrical shell model anofluid-nanostructure interaction carbon nanotubes

An extended iterative direct-forcing immersed boundary method in thermo-fluid problems with Dirichlet or Neumann boundary conditions

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Journal of Central south University 2017年第1期24卷 137-154页

作者： ali akbar Hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K.N.Toosi University of TechnologyP.O.B.19395-1999 TehranIran

An iterative direct-forcing immersed boundary method is extended and used to solve convection heat transfer *** pressure,momentum source,and heat source at immersed boundary points are calculated simultaneously to achieve the best *** of convection heat transfer problems with both Dirichlet and Neumann boundary conditions are *** approaches for the implementation of Neumann boundary condition,*** and indirect methods,are introduced and compared in terms of accuracy and computational *** test cases include forced convection on a heated cylinder in an unbounded flow field and mixed convection around a circular body in a lid-driven ***,the proposed method is applied to study the mixed convection around a heated rotating cylinder in a square enclosure with both iso-heat flux and iso-thermal boundary *** results show that the order of accuracy of the indirect method is less than the direct ***,the indirect method takes less computational time both in terms of the implementation of the boundary condition and the post processing time required to compute the heat transfer variables such as the Nusselt *** is concluded that the iterative direct-forcing immersed boundary method is a powerful technique for the solution of convection heat transfer problems with stationary/moving boundaries and various boundary conditions.

关键词： immersed boundary method direct forcing thermo-fluid problems neumann boundary condition

Flow Confinement Effects on the Wake structure behind a Pitching Airfoil： A Numerical study Using an Immersed Boundary Method

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Journal of Bionic Engineering 2017年第1期14卷 88-98页

作者： ali akbar Hosseinjani ali Ashrafizadeh Faculty of Mechanical Engineering K. N. Toosi University of Technology Tehran P.O.B. 19395-1999 Iran

The flow patterns and wake structures behind a pitching airfoil in an un-bounded domain have been studied extensively. In contrast, the flow phenomena associated with a pitching airfoil near a solid boundary have not been adequately studied or reported. This paper aims at filling this research gap by considering the flow confinement effects on the flow pattern around a pitching airfoil. To achieve this goal, the flow fields around a flapping airfoil in un-bounded, bounded and semi-bounded domains are studied and compared. Numerical simulations are carried out at a fixed Reynolds number, Re = 255, and at a fixed oscillation frequency corresponding to st = 0.22. An accurate immersed boundary method is employed to calculate the unsteady flow fields around the airfoil at various flapping amplitudes. It is argued that two flow mechanisms, here called ＂the interaction effect＂ and ＂the induced reverse flow effect＂ are responsible for the variations of the flow field due to the presence of a nearby solid boundary.

关键词： immersed boundary method pitching airfoil vortex street induced momentum aligned vortex

seed Mediated Growth of Gold Nanoparticles Based on Liquid Arc Discharge

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Plasma science and Technology 2013年第4期15卷 376-381页

作者： ali akbar AsHKARRAN Department of Physics Faculty of Basic Sciences University of MazandaranBabolsar Iran

We report studies on the growth of gold nanoparticles by a seed-mediated approach in solution. The synthetic method is adapted from one we published earlier （Ashkarran et al. Appl. Phys. A 2009, 96, 423）. The synthesized gold nanoparticles were characterized by X-ray diffraction （XRD）, dynamic light scattering （DLs）, UV-Vis spectroscopy, optical imaging and atomic force microscopy （AFM）. Optical absorption spectroscopy of the prepared samples at 15 A arc current in HAuCI4 solution shows a surface plasmon resonance around 520 nm. It is found that sodium citrate acts as a stabilizer and surface capping agent of the colloidal nanoparticles. The intensity of the plasmonic peak of the prepared gold nanoparticles for 1 minute arc duration gradually increases due to seed mediation for up to 6 hours. The formation time of gold nanoparticles at higher seed concentrations is less than that at lower seed concentrations.

关键词： gold nanoparticles liquid arc discharge seed mediation optical properties

EFFECT OF POLYANILINE As A sURFACE MODIFIER OF TiO_2 NANO-PARTICLEs ON THE PROPERTIEs OF POLYVINYL CHLORIDE/TiO_2 NANOCOMPOsITEs

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Chinese Journal of Polymer science 2013年第3期31卷 481-494页

作者： ali Olad sepideh Behboudi ali akbar Entezami Polymer Composite Research Laboratory Department of Applied ChemistryFaculty of ChemistryUniversity of Tabriz Polymer Research Laboratory Department of Organic ChemistryFaculty of ChemistryUniversity of Tabriz

surface of TiO2 nanoparticles was modified with the in situ chemical oxidative polymerization of aniline. Polyaniline modified TiO2 nanoparticles （PANI-TiO2） were characterized with the FT-IR, XRD, sEM and TEM techniques. Results confirmed that PANI was grafted successfully on the surface of TiO2 nanoparticles, therefore agglomeration of nanoparticles decreased dramatically. Polyvinyl chloride nanocomposites filled with 1 wt%-5 wt% of PANI-TiO2 and TiO2 nanoparticles were prepared via the solution blending method. PVC nanocomposites were analyzed with FT-IR, XRD, sEM, TG/DTA, DsC and tensile test techniques. Effect of PANI as surface modifier of nanoparticles was discussed according to the final properties of PVC nanocomposites. Results demonstrated that deposition of PANI on the surface of TiO2 nanoparticles improved the interfacial adhesion between the constituents of nanocomposites, which resulted in better dispersion of nanoparticles in the PVC matrix. Also PVC/PANI-TiO2 nanocomposites showed higher thennal resistance, tensile strength and Young＇s modulus compared to those of unfilled PVC and PVC/TiO2 nanocomposites.

关键词： Polymer nanocomposite Polyvinyl chloride Polyaniline TiO2 nano-additive surface modification.

Relativistic symmetries in the Hulthn scalar-vector-tensor interactions

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Chinese Physics B 2013年第8期22卷 257-263页

作者： Majid Hamzavi ali akbar Rajabi Department of science and Engineering Abhar Branch Islamic Azad UniversityAbhar Iran Physics Department Shahrood University of TechnologyShahrood Iran

In the presence of spin and pseudospin （p-spin） symmetries, the approximate analytical bound states of the Dirac equation for scalar-vector-tensor Hulth6n potentials are obtained with any arbitrary spin-orbit coupling number using the Pekeris approximation. The Hulth6n tensor interaction is studied instead of the commonly used Coulomb or linear terms. The generalized parametric Nikiforov-Uvarov （NU） method is used to obtain energy eigenvalues and corresponding wave functions in their closed forms. It is shown that tensor interaction removes degeneracy between spin and p-spin doublets. some numerical results are also given.

关键词： Dirac equation Hulth6n scalar-vector-tensor potential spin and p-spin symmetry NU method