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Microstructural ordering of nanofibers in flow-directed assembly

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Science China(Technological Sciences) 2019年第9期62卷 1545-1554页

作者： GAO EnLai WANG ShiJun DUAN ChuanHua XU ZhiPing applied mechanics Laboratory Department of Engineering Mechanicsand Center for Nano and Micro MechanicsTsinghua UniversityBeijing 100084China Department of mechanical engineering Boston UniversityBoston MA 02215USA applied mechanics and Structure Safety Key Laboratory of Sichuan Province School of Mechanics and EngineeringSouthwest Jiaotong UniversityChengdu 611756China

Fabrication of highly ordered and dense nanofibers assemblies is of key importance for high-performance and multi-functional material and device applications. In this work, we design an experimental approach in silico, where shear flow and solvent evaporation are applied to tune the alignment, overlap of nanofibers, and density of the assemblies. Microscopic dynamics of the process are probed by dissipative particle dynamics simulations, where hydrodynamic and thermal fluctuation effects are fully modeled. We find that microstructural ordering of the assembled nanofibers can be established within a specific range of the Peclet numbers and evaporation rates, while the properties of nanofibers and their interaction are crucial for the local stacking order. The underlying mechanisms are elucidated by considering the competition between hydrodynamic coupling and thermal fluctuation. Based on these understandings, a practical design of flow channels for nanofiber assembly with promising mechanical performance is outlined.

关键词： nanofiber nanostructured assemblies shear flow solvent evaporation alignment stacking order densification dissipative particle dynamics

Vibration of an Axially Moving String Supported by a Viscoelastic Foundation

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Acta Mechanica Solida Sinica 2016年第3期29卷 221-231页

作者： Haijuan Zhang Liqun Chen Shanghai Institute of applied Mathematics and mechanics Shanghai University School of mechanical engineering Anhui University of Technology Department of mechanics Shanghai University Shanghai Key Laboratory of mechanics in Energy engineering Shanghai University

The transverse vibration of an axially moving string supported by a viscoelastic foundation is analysed using the complex modal method. The equation of motion is developed using the generalized Hamilton principle. The exact closed-form solution of eigenvalues and eigen- functions are obtained. The governing equation is represented in a canonical state space form defined by two matrix differential operators, and the eigenfunctions and adjoint eigenfunctions are proved to be orthogonal with respect to each operator. This orthogonality is applied so that the response to arbitrary external excitations and initial conditions can be expressed in modal expansion. Numerical examples are presented to validate the proposed approach.

关键词： axially moving string viscoelastic foundation complex modal analysis

Optimizing submerged arc welding using response surface methodology, regression analysis, and genetic algorithm

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Defence Technology（防务技术） 2018年第3期14卷 204-212页

作者： Ajitanshu Vedrtnam Gyanendra Singh Ankit Kumar Department of mechanical engineering Invertis University Department of applied mechanics Motilal Nehru National Institute of Technology Allahabad

The weld quality is significantly affected by the weld parameters(arc voltage, welding current, nozzle to plate distance and welding speed) in the submerged arc welding(SAW). Bead-on-plate welds were performed on stainless steel plates by automated SAW machine. The experimental data were collected in accordance with the response surface methodology(RSM). In addition to RSM, the regression analysis was performed to set up inputeoutput relationships in the SAW process. It was found that weld parameters define the geometry of weld bead and determine the mechanical properties of the joint. The influence of the input variables on weld bead geometry is represented as graphs. It was found that an increment in voltage increases the bead width but decreases the bead height, whereas the current increment result-in an increment in bead height and no change in bead width. The bead width and height decrease with the increment in the welding speed. With an increment in the nozzle-to-plate distance, bead width decrease, but bead height increases. The value of bead hardness increases with the increment in current but the increment in voltage and travel speed does not have a significant influence on the bead hardness. The predictions from the mathematical model developed and the corresponding experimental results are having a fair agreement. Further, the genetic algorithm(GA) is also used for predicting the weld bead geometry.

关键词：回归分析基因算法方法论表面反应弧焊沉没焊接参数

Optimal transient growth in turbulent pipe flow

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applied Mathematics and mechanics(English Edition) 2015年第8期36卷 1057-1072页

作者： Yang SONG Chunxiao XU Weixi HUANG Guixiang CUI Key Laboratory of applied mechanics Department of Engineering MechanicsTsinghua University

The optimal transient growth process of perturbations driven by the pressure gradient is studied in a turbulent pipe flow. A new computational method is proposed, based on the projection operators which project the governing equations onto the sub- space spanned by the radial vorticity and radial velocity. The method is validated by comparing with the previous studies. Two peaks of the maximum transient growth am- plification curve are found at different Reynolds numbers ranging from 20 000 to 250 000. The optimal flow structures are obtained and compared with the experiments and DNS results. The location of the outer peak is at the azimuthal wave number n = 1, while the location of the inner peak is varying with the Reynolds number. It is observed that the velocity streaks in the buffer layer with a spacing of 100δv are the most amplified flow structures. Finally, we consider the optimal transient growth time and its dependence on the azimuthal wave length. It shows a self-similar behavior for perturbations of different scales in the optimal transient growth process.

关键词： turbulent pipe flow optimal transient growth coherent structure

Using the traditional model to evaluate the active force of the human lateral rectus muscle

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Science China(Physics,mechanics & Astronomy) 2014年第5期57卷 983-987页

作者： GAO ZhiPeng CHEN WeiYi JING Lin FENG PengFei WU XiaoGang GUO HongMei Institute of applied mechanics and Biomedical engineering Taiyuan University of Technology Impact mechanics Laboratory Department of Mechanical EngineeringNational University of Singapore

The information on the force of extraocular muscles(EOMs)is beneficial for strabismus diagnosis and surgical planning,and a direct and simple method is important for surgeons to obtain these *** on the traditional model,a numerical simulation method was proposed to achieve this aim,and then the active force of the lateral rectus(LR)muscle was successfully simulated when the eye rotated every angle from 0°to 30°in the horizontal plane from the nasal to the temporal *** order to verify these simulations,the results were compared with the previous experimental *** comparison shows that the simulation results diverged much more than the experimental data in the range of 0°–10°.The errors were corrected to make the simulation results closer to the experimental ***,a general empirical equation was proposed to evaluate the active force of the LR muscle by fitting these data,which represent the relationship between the simulation forces and the contractive amounts of the LR muscle.

关键词： force extraocular muscles lateral rectus muscle eye movement model

Effect of compressive stress on the dispersion relation of the flexural–gravity waves in a two-layer fluid with a uniform current

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Journal of Hydrodynamics 2014年第2期26卷 339-341页

作者：卢东强 Shanghai Institute of applied Mathematics and mechanics Shanghai University Shanghai Key Laboratory of mechanics in Energy engineering Shanghai University Computational Marine mechanics Laboratory Department of Mechanical Engineering University of California

The explicitly analytical solution is derived for the dispersion relation of the flexural-gravity waves in a two-layer fluid with a uniform current. The upper＇ fluid is covered by a thin plate with the presence of the elastic, compressive and inertial forces. The density of each of the two immiscible layers is constant. The fluids of finite depth are assumed to be inviscid and incompressible and the motion be irrotational. A linear system is established within the framework of potential theory. A new representation for the dispersion relation of flexural-gravity waves in a two-layer fluid is derived. The critical value for the compressive force is analytically determined. The dispersion relation for the capillary-gravity with an inertial surface in a two-layer fluid can he obtained in parallel. Some known dispersion relations can be recovered from the present solution.

关键词： Hydroelasticity compressive force current two-layer fluid

Numerical Simulation of the mechanical Properties of Sintered and Bonded Perforated Hollow Sphere Structures (PHSS)

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Journal of Materials Science & Technology 2010年第8期26卷 730-736页

作者： Andreas chsner Seyed Mohammad Hossein Hosseini Markus Merkel Department of applied mechanics Technical University of Malaysia Centre for Mass and mechanical Transport in engineering Materials The University of Newcastle CallaghanNewSouth Wales 2308Australia Department of mechanical engineering University of Applied Sciences Aalen

This paper investigated the uniaxial mechanical properties of a new type of hollow sphere structures. For this new type, the sphere shell was perforated by several holes in order to open the inner sphere volume and surface. The mechanical properties, i.e. elastic properties and initial yield stress of perforated hollow sphere structures （PHSS） in a primitive cubic arrangement were numerically evaluated for different hole diameters and different joining techniques of the hollow spheres. The results are compared to classical configurations without perforation.

关键词： mechanical properties Cellular material Porous structure Finite element method

Combustion Irreversibilities: Numerical Simulation and Analysis

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Journal of Thermal Science 2012年第4期21卷 377-383页

作者： Valter Silva Abel Rouboa CITAB/engineering Department School of Science and Technology of University of U TAD mechanical engineering and applied mechanics Department University of PennsylvaniaPhiladelphia

An exergy analysis was performed considering the combustion of methane and agro-industrial residues produced in Portugal (forest residues and vines pruning). Regarding that the irreversibilities of a thermodynamic process are path dependent, the combustion process was considering as resulting from different hypothetical paths each one characterized by four main sub-processes: reactant mixing, fuel oxidation, internal thermal energy exchange (heat transfer), and product mixing. The exergetic efficiency was computed using a zero dimensional model developed by using a Visual Basic home code. It was concluded that the exergy losses were mainly due to the internal thermal energy exchange sub-process. The exergy losses from this sub-process are higher when the reactants are preheated up to the ignition temperature without previous fuel oxidation. On the other hand, the global exergy destruction can be minored increasing the pressure, the reactants temperature and the oxygen content on the oxidant stream. This methodology allows the identification of the phenomena and processes that have larger exergy losses, the understanding of why these losses occur and how the exergy changes with the parameters associated to each system which is crucial to implement the syngas combustion from biomass products as a competitive technology.

关键词： Exergy Combustion paths Combustion sub-processes Exergetic efficiency Visual Basic Syngas

Fractional nonlinear energy sinks

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applied Mathematics and mechanics(English Edition) 2023年第5期44卷 711-726页

作者： Shengtao ZHANG Jiaxi ZHOU Hu DING Kai WANG Daolin XU College of mechanical and Vehicle engineering Hunan UniversityChangsha 410082China Shanghai Institute of applied Mathematics and mechanics Shanghai Key Laboratory of Mechanics in Energy EngineeringSchool of Mechanics and Engineering ScienceShanghai UniversityShanghai 200072China

The cubic or third-power(TP)nonlinear energy sink(NES)has been proven to be an effective method for vibration suppression,owing to the occurrence of targeted energy transfer(TET).However,TET is unable to be triggered by the low initial energy input,and thus the TP NES would get failed under low-amplitude *** resolve this issue,a new type of NES with fractional nonlinearity,e.g.,one-third-power(OTP)nonlinearity,is *** dynamic behaviors of a linear oscillator(LO)with an OTP NES are investigated numerically,and then both the TET feature and the vibration attenuation performance are ***,an analogy circuit is established,and the circuit simulations are carried out to verify the design concept of the OTP *** is found that the threshold for TET of the OTP NES is two orders of magnitude smaller than that of the TP *** parametric analysis shows that a heavier mass or a lower stiffness coefficient of the NES is beneficial to the occurrence of TET in the OTP NES ***,significant energy transfer is usually accompanied with efficient energy ***,the OTP NES can realize TET under low initial input energy,which should be a promising approach for micro-vibration suppression.

关键词： fractional nonlinearity nonlinear energy sink(NES) targeted energy transfer(TET) micro-vibration control