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A New Extrapolation Treatment for Boundary Conditions in Lattice Boltzmann Method

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Chinese Physics Letters 2013年第9期30卷 89-93页

作者： WANG Zheng-Dao YANG Jian-Fei WEI Yi-Kun QIAN Yue-Hong Shanghai Institute of Applied Mathematics and Mechanics Shanghai UniversityShanghai 200072 Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai 200072 Shanghai Program for Innovative Research Team in Universities Shanghai 200072 Faculty of mechanical Engineering and Automatic Zhejiang Sci-Tech UniversityHangzhou 310018 department of mechanical and aerospace enigineering UC IrvineCA 92617USA

The lattice Boltzmann method is widely used in solving hydrodynamics for various *** accuracy of the extrapolation method for boundary conditions and Mei’s method for curved boundary is not high *** propose a modified extrapolation method for boundary *** simulations conform the higher accuracy and stability compared with the other methods.

关键词： conditions methods boundary

An automated approach to calculating the maximum diameters of multiple cutters and their paths for sectional milling of centrifugal impellers on a 4_(1/2)-axis CNC machine

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Chinese Journal of Aeronautics 2019年第4期32卷 1030-1039页

作者： Baohai WU Zezhong C.CHEN Ming LUO Dinghua ZHANG Feiyan HAN School of mechanical Engineering Northwestern Polytechnical University department of mechanical Industrial and Aerospace EngineeringConcordia University College of mechanical Engineering Xi'an University of Science and Technology

Power generators and chemical engineering compressors include heavy and large centrifugal impellers. To produce these impellers in high-speed machining, a 4?-axis milling machine(or a 4-axis machine plus an indexing table) is often used in the industry, which is more rigid than a5-axis milling machine. Since impeller blades are designed with complex B-spline surfaces and impeller channels spaces vary significantly, it is more efficient to use multiple cutters as large as possible to cut a channel in sections and a blade surface in patches, instead of only using a small cutter to machine a whole blade and a channel. Unfortunately, no approach has been established to automatically calculate the largest diameters of cutters and their paths, which include the indexing table angles. To address this problem, an automated and optimization approach is proposed. Based on the structure of a 4?-axis machine, a geometric model for a cutter gouging/interfering the impeller is formulated, and an optimization model of the cutter diameter in terms of the indexing table angle is established at a cutter contact(CC) point on a blade surface. Then, the diameters of the tools,their orientations, and the indexing table angles are optimized, and each tool's paths are generated for machining its corresponding impeller section. As a test, an impeller is efficiently machined with these tools section by section; thus, this approach is valid. It can be directly used in the industry to improve efficiency of machining centrifugal impellers.

关键词： Automated path generation 4_(1/2)-Axis CNC machining Centrifugal impeller machining Cutter diameter optimization Sectional machining

mechanical and Microstructural Properties of Ultra-fine Grained AZ91Magnesium Alloy Tubes Processed via Multi Pass Tubular Channel Angular Pressing(TCAP)

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Journal of Materials Science & Technology 2014年第2期30卷 134-138页

作者： G.Faraji P.Yavari S.Aghdamifar M.Mosavi Mashhadi department of mechanical Engineering University College of EngineeringUniversity of Tehran department of mechanical and aerospace Engineering Science and Research BranchIslamic Azad University

Ultra-fine grained （UFG） cylindrical tubes were produced via recently developed tubular channel angular pressing （TCAP） process through different passes from as-cast AZ91 magnesium alloy. The microstructure and mechanical properties of processed tube through one to four passes of TCAP process at 200℃ were investigated. Microhardness of the processed tube was increased to 98.5 HV after one pass from an initial value of 67 Hr. An increase in the number of passes from one to higher number of passes has no more effect on the microhardness. Yield and ultimate strengths were increased by 4.3 and 1.4 times compared to those in as-cast condition. Notable increase in the strength was achieved after one pass of TCAP while higher number of passes has no more effect. Microstructural investigation shows notable decrease in the grain size to around 500 nm from the primary value of - 150 μm. Dissolution and distribution of hard MglTAI12 phase in the grain boundaries of dynamically recrystallized UFG AZ91 with a mean grain size of - 500 nm was an interesting issue of TCAP processing at 200 ℃ compared to other severe plastic deformation processes.

关键词： Severe plastic deformation Tubular channel angular pressing AZ91 Grain refinement mechanical behaviour

Parametric Study of Low Frequency Broadband Rectilinear-to-Rotary Vibrational Energy Harvesting

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Transactions of Nanjing University of Aeronautics and Astronautics 2018年第1期35卷 1-9页

作者： Chen Jingfan Deng Wei Wang Ya Inman Dan department of mechanical Engineering Stony Brook University department of mechanical Engineering Texas A&M University department of aerospace Engineering University of Michigan

A parametric study of a high-power-density dual resonator for achieving low frequency broadband electromagnetic energy harvesting is *** dual resonator consists of a rectilinear oscillator(R_LO)performing magnetic levitation and a rotary oscillator(R_TO)performing electromagnetic coupling through a stator and a *** oscillators,coupled by magnetic forces generated by a set of arc permanent magnets,radially magnetized and centro-symmetrically fixed onto the R_LO and the rotor of the R_TO achieve the reciprocating-to-rotary motion conversion and frequency ***,the dual resonator is able to convert stochastic reciprocating motion into controllable rotation,provide intrinsic frequency up-conversion,use non-contact magnetic coupling to provide near loss-free energy transfer and be configured into specific applications to obtain and maintain high-energy orbits of multi-stable energy *** solely focusing on developing a dual resonator provides substantial benefits,its dynamic behavior is unclear,thus electromagnetic-dynamic governing equations are derived,and a curve fitting model of restoring torque of R_TO under different repulsive magnets configurations are developed to predict key characteristics and to improve performance of the electromechanical *** analysis is carried out for providing aquantitative guidance of customizing the harvester to achieve an optimal power density.

关键词： curve fitting model non-contact rectilinear-to-rotary motion transformation frequency up-conversion systematic modeling parametric study

Effect of ultrasonic vibration-assisted laser surface melting and texturing of Ti-6Al-4V ELI alloy on surface properties

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Journal of Materials Science & Technology 2019年第2期35卷 295-302页

作者： Sourabh Biswas S.Habib Alavi Bhishma Sedai Frank D.Blum Sandip P.Harimkar School of mechanical and aerospace Engineering Oklahoma State University department of Chemistry Oklahoma State University

Ultrasonic vibration-assisted laser surface processing that involves application of vertical ultrasonic vibrations to the Ti-6 Al-4 V alloy substrates while being irradiated with a CO_2 laser was performed for the development of laser melted and textured surfaces with potential applications in biomedical *** laser processing resulted in very consistent repeating undulating grooved surfaces, and the undulations were significantly more pronounced in the samples processed with higher ultrasonic power *** phase evolution, studied by x-ray diffraction, confirmed that the laser processing triggered transformation of globular α→ acicular α and martensitic α' as well as increased amounts of retained α phases,which were also reflected in the microscopic analysis. The surface texture developed by laser processing resulted in increased surface wettability with increasing ultrasonic power output. The textured surfaces exhibited marked decrease in coefficients of friction during sliding wear testing performed under simulated body fluid due to lubricant entrainment within the textured grooves. The texturing also resulted in significant reduction in surface contact area during the wear process, which considerably reduced the overall wear rates due to abrasive wear.

关键词： Laser texturing Laser melting Ultrasonic vibrations Wear

A novel energy storage system incorporating electrically rechargeable liquid fuels as the storage medium

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Science Bulletin 2019年第4期64卷 270-280页

作者： Haoran Jiang Lei Wei Xinzhuang Fan Jianbo Xu Wei Shyy Tianshou Zhao department of mechanical and aerospace Engineering The Hong Kong University of Science and Technology Clear Water Bay

We propose a novel concept of energy storage that incorporates electrically rechargeable liquid fuels made of electroactive species, known as e-fuels, as the storage medium. This e-fuel energy storage system comprises an e-fuel charger and an e-fuel cell. The e-fuel charger electrically charges e-fuels, while the efuel cell subsequently generates electricity using charged e-fuels whenever and wherever on *** e-fuel energy storage system possesses all the advantages of conventional hydrogen storage systems,but unlike hydrogen, liquid e-fuels are as easy and safe to store and transport as gasoline. The potential efuel candidates have been identified to include inorganic electroactive materials, organic electroactive materials, and suspension of solid electroactive materials. In this work, we demonstrate an example efuel energy storage system for large-scale energy storage using inorganic e-fuels composed of V^(2+)/V^(3+) and VO_2^+/VO_2^+ redox couples, and compare the performance of the e-fuel energy storage system with that of existing technologies. Results show that our e-fuel charger achieves a charge efficiency of as high as～94%, while the e-fuel cell is capable of delivering a peak power density of 3.4 W cm^(-2), which is 1.7 times higher than that of hydrogen fuel cells. More excitingly, the e-fuel energy storage system exhibits a round-trip efficiency of 80.0% and an electrolyte utilization of 83.0% at an ultra-high discharge current density of 1,000 mA cm^(-2), which are 19.9% and 67.3% higher than those of conventional vanadium redox flow batteries. This unprecedented performance allows a 27.0% reduction in the capital cost of the e-fuel energy storage system compared with that of vanadium redox flow batteries.

关键词： Renewable energy Energy storage Batteries E-fuel energy storage system

3D Janus plasmonic helical nanoapertures for polarization-encrypted data storage

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Light(Science & Applications) 2019年第1期8卷 788-796页

作者： Yang Chen Xiaodong Yang Jie Gao department of mechanical and aerospace Engineering Missouri University of Science and TechnologyRollaMO 65409USA

Helical structures have attracted considerable attention due to their inherent optical ***,we report a unique type of 3D Janus plasmonic helical nanoaperture with direction-controlled polarization sensitivity,which is simply fabricated via the one-step grayscale focused ion beam milling *** dichroism in transmission of as large as 0.72 is experimentally realized in the forward direction due to the spin-dependent mode coupling process inside the helical ***,in the backward direction,the nanoaperture acquires giant linear dichroism in transmission of up to *** encoding the Janus metasurface with the two nanoaperture enantiomers having specified rotation angles,direction-controlled polarization-encrypted data storage is demonstrated for the first time,where a binary quick-response code image is displayed in the forward direction under the circularly polarized incidence of a specified handedness,while a distinct grayscale image is revealed in the backward direction under linearly polarized illumination with a specified azimuthal *** envision that the proposed Janus helical nanoapertures will provide an appealing platform for a variety of applications,which will range from multifunctional polarization control,enantiomer sensing,data encryption and decryption to optical information processing.

关键词： helical specified backward

Stability of steel thixoforming process

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中国有色金属学会会刊：英文版 2010年第S3期20卷 937-942页

作者： J.C.PIERRET A.RASSILI G.VANEETVELD J.LECOMTE-BECKERS ThixoUnit ULg Material Sciences UnitDepartment of Aerospace and Mechanical EngineeringUniversity of Liège

To improve the industrialization of the process,the study of a thixoforming line stability was *** thixoforming line is fully automated to optimize the repeatability of the *** of the heating cycle,the slug temperature,the tool temperature and the forming speed were *** each of them,a range of the expected variations in a steady-state process as well as the effects of these variations on the process itself(forming load and parts quality) were *** variations are shown to be *** different tools were used in the *** mathematical simulations were realized on the finite elements code Forge2008with a semi-solid constitutive *** capacity of the model to represent the process stability was *** simulation results are in agreement with the experiment results.

关键词： thixoforming steel high melting point stability robustness process

Improved nonlinear fluid model in rotating flow

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Applied Mathematics and Mechanics(English Edition) 2012年第11期33卷 1419-1430页

作者： N. ASHRAFI H. KARIMI-HAGHIGHI department of mechanical and aerospace Engineering Science and Research Branch Islamic Azad University

The pseudoplastic circular Couette flow （CCF） in annuli is investigated. The viscosity is dependent on the shear rate that directly affects the conservation equations solved by the spectral method in the present study. The pseudoplastic model adopted here is shown to be the suitable representative of nonlinear fluids. Unlike the previous studies, where only the square of the shear ered to ease the numerical manipulations, quadratic power is also taken into account. rate term in the viscosity expression is consid- in the present study, the term containing the The curved streamlines of the CCF can cause the centrifugal instability leading to toroidal vortices, known as the Taylor vortices. It is further found that the critical Taylor number becomes lower as the pseudoplastic effect increases. The comparison with the existing measurements on the pseudoplastic CCF results in good agreement.

关键词： pseudoplastic circular Couette flow (CCF) toroidal vortex spectralmethod