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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

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

Effects of different friction stir welding conditions on the microstructure and mechanical properties of copper plates

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International Journal of Minerals,Metallurgy and Materials 2016年第7期23卷 799-809页

作者： ali Alavi Nia ali Shirazi Department of Mechanical Engineering Bu-Ali Sina University

Friction stir welding is a new and innovative welding method used to fuse materials. In this welding method, the heat generated by friction and plastic flow causes significant changes in the microstructure of the material, which leads to local changes in the mechanical properties of the weld. In this study, the effects of various welding parameters such as the rotational and traverse speeds of the tool on the microstructural and mechanical properties of copper plates were investigated; additionally, Charpy tests were performed on copper plates for the first time. Also, the effect of the number of welding passes on the aforementioned properties has not been investigated in previous studies. The results indicated that better welds with superior properties are produced when less heat is transferred to the workpiece during the welding process. It was also found that although the properties of the stir zone improved with an increasing number of weld passes, the properties of its weakest zone, the heat-affected zone, deteriorated.

关键词： copper friction stir welding mechanical properties microstructure

Effects of Fe_2O_3 Nanoparticles on Water Permeability and Strength Assessments of High Strength Self-Compacting Concrete

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Journal of Materials Science & Technology 2012年第1期28卷 73-82页

作者： ali Khoshakhlagh ali Nazari Gholamreza Khalaj Department of Materials Engineering Science and Research BranchIslamic Azad University Department of Materials Engineering Saveh BranchIslamic Azad University

In this work, compressive, flexural and split tensile strength together with coefficient of water absorption of high performance self-compacting concrete containing different amount of Fe2Os nanoparticles have been investigated. The strength and the water permeability of the specimens have been improved by adding Fe2Os nanoparticles in the cement paste up to 4.0 wt%. Fe203 nanoparticle as a foreign nucleation site could accelerate C-S-H gel formation as a result of increased crystalline Ca（OH）2 amount especially at the early age of hydration and hence increase the strength of the specimens. In addition, Fe203 nanoparticles are able to act as nanofillers and recover the pore structure of the specimens by decreasing harmful pores to improve the water permeability. Several empirical relations have been presented to predict the flexural and the split tensile strength of the specimens by means of the corresponding compressive strength at a certain age of curing. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results indicate that Fe203 nanoparticles up to 4 wt% could improve the mechanical and the physical properties of the specimens.

关键词： Water permeability Fe203 nanoparticles Compressive strength Split tensilestrength Flexural strength

A VERSATILE AND REGIOSELECTIVE SYNTHESIS OF VICINAL AZIDOALCOHOLS USING CROSS-LINKED POLY(4-VINYLPYRIDINE) SUPPORTED AZIDE ION UNDER SOLVENT-FREE CONDITIONS

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Chinese Journal of Polymer Science 2013年第12期31卷 1660-1669页

作者： Mohammad ali Karimi Zarchi ali Tarabsaz Department of Chemistry College of ScienceYazd University

A new polymeric reagent, cross-linked poly（4-vinylpyridine） supported azide ion, [P4-VP]N3, was introduced as polymeric reagents for efficient and regioselective conversion of epoxides to azidohydrins in the presence of cross-linked poly（4-vinylpyridine） supported sulfuric acid, [P4-VP]H2SO4, as a solid proton source and as catalyst under solvent-free conditions. The advantages of this polymeric reagent over some of those reported in the literature are easy work-up procedure and regeneration of the reagent.

关键词： Ring opening of epoxide fl-Azidoalcohols Poly(4-vinytpyridine) Solvent-free conditions Regioselectivity.

Decrease of back recombination rate in CdS quantum dots sensitized solar cells using reduced graphene oxide

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Chinese Physics B 2015年第4期24卷 372-377页

作者： ali Badawi Department of Physics Faculty of Science Taif University

The photovoltaic performance of CdS quantum dots sensitized solar cells （QDSSCs） using the 0.2 wt% of reduced graphene oxide and TiO2 nanoparticles （RGO＋TiO2 nanocomposite） photoanode is investigated. CdS QDs are adsorbed onto RGO＋TiO2 nanocomposite films by the successive ionic layer adsorption and reaction （SILAR） technique for several cycles. The current density-voltage （J-V） characteristic curves of the assembled QDSSCs are measured at AM1.5 simulated sunlight. The optimal photovoltaic performance for CdS QDSSC was achieved for six SILAR cycles. Solar cells based on the RGO＋TiO2 nanocomposite photoanode achieve a 33% increase in conversion efficiency （η） compared with those based on plain TiO2 nanoparticle （NP） photoanodes. The electron back recombination rates decrease significantly for CdS QDSSCs based on RGO＋TiO2 nanocomposite photoanodes. The lifetime constant （τ） for CdS QDSSC based on the RGO＋TiO2 nanocomposite photoanode is at least one order of magnitude larger than that based on the bare TiO2NPs photoanode.

关键词： reduced graphene oxide nanocomposite photoanode back recombination rate quantum dots sensitized solar cell

Design and Optimization of 3D Radial Slot Grain Configuration

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Chinese Journal of Aeronautics 2010年第4期23卷 409-414页

作者： ali Kamran School of Astronautics Beijing University of Aeronautics and Astronautics

Upper stage solid rocket motors （SRMS） for launch vehicles require a highly efficient propulsion system. Grain design proves to be vital in terms of minimizing inert mass by adopting a high volumetric efficiency with minimum possible sliver. In this arti- cle, a methodology has been presented for designing three-dimensional （3D） grain configuration of radial slot for upper stage solid rocket motors. The design process involves parametric modeling of the geometry in computer aided design （CAD） software through dynamic variables that define the complex configuration. Grain bum back is achieved by making new surfaces at each web increment and calculating geometrical properties at each step. Geometrical calculations are based on volume and change-in-volume calculations. Equilibrium pressure method is used to calculate the internal ballistics. Genetic algorithm （GA） has been used as the optimizer because of its robustness and efficient capacity to explore the design space for global optimum solution and eliminate the requirement of an initial guess. Average thrust maximization under design constraints is the objective function.

关键词： solid rocket motors 3D grains radial slot configuration internal ballistics computer aided design heuristic optimization genetic algorithm

Effect of mineral additives and permeability reducing admixtures having different action mechanisms on mechanical and durability performance of cementitious systems

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Frontiers of Structural and Civil Engineering 2021年第5期15卷 1277-1291页

作者： ali NEMATZADEH Burcu AYTEKIN ali MARDANL-AGHABAGLOU Department of Civil Engineering Bursa Uludag UniversityNilufer-Bursa 16059Turkey

In this paper,the effect of usage of the permeability reducing admixture(PRA)having different action mechanisms on hardened state properties of cementitious systems containing mineral additives is *** this aim,three commercial PRAs were used during *** effective parameters in the first and third PRAs were air-entraining and high-rate air-entraining,*** second one contained the insoluble calcium carbonate residue and had a small amount of the air-entraining *** mixes with binary and ternary cementitious systems were prepared by partially replacing cement with fly ash and *** hardened state properties of mortar mixtures such as compressive strength,ultrasonic pulse velocity,water absorption,drying shrinkage and freeze-thaw resistance were *** ternary cement-based mixture having both fly ash and metakaolin was selected as the most successful mineral-additive bearing mix in regard to hardened state *** this sense,PRA-B,with both insoluble residues and a small amount of air-entraining properties,showed the best performance among the mixtures containing *** combined use of mineral additive and PRA had a more positive effect on the properties of the mixes.

关键词： cementitious system mineral additive permeability reducing admixture mechanical properties durability performance

A Review on Plug-in Electric Vehicles:Introduction, Current Status, and Load Modeling Techniques

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Journal of Modern Power Systems and Clean Energy 2020年第3期8卷 412-425页

作者： ali Ahmadian Behnam Mohammadi-Ivatloo ali Elkamel Department of Electrical Engineering University of BonabBonabIran Institute of Research and Development Duy Tan UniversityDa Nang 550000Vietnam College of Engineering Khalifa University of Science and Technologythe Petroleum InstituteAbu DhabiUnited Arab Emirates

Plug-in electric vehicle(PEV) load modeling is very important in the operation and planning studies of modern power system nowadays. Several parameters and considerations should be taken into account in PEV load modeling, making it a complex problem that should be solved using appropriate techniques. Different techniques have been introduced for PEV load modeling and each of them has individual specifications and features. In this paper, the most popular techniques for PEV load modeling are reviewed and their capabilities are evaluated. Both deterministic and probabilistic methods are investigated and some practical and theoretical hints are presented. Moreover, the characteristics of all techniques are compared with each other and suitable methods for unique applications are proposed. Finally, some potential research areas are presented for future works.

关键词： Plug-in electric vehicles load modeling deterministic and probabilistic techniques distribution networks