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WAVELET ANALYSIS OF COHERENT STRUCTURES IN A THREE-DIMENSIONAL MIXING LAYER

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Acta Mechanica Sinica 2002年第1期18卷 42-52页

作者：林建忠邵雪明倪利民 department of mechanics State Key Laboratory of Fluid Power Transmission and ControlZhejiang University Hangzhou China 310027

Wavelet analysis is applied to the results obtained by the direct numerical simulation of a three-dimensional (3D) mixing layer in order to investigate coherent structures in dimension of scale. First, 3D orthonormal wavelet bases are constructed, and the corresponding decomposition algorithm is developed. Then the Navier-Stokes equations are transformed into the wavelet space and the architecture for multi-scale analysis is established. From this architecture, the coarse field images in different scales are obtained and some local statistical quantities are calculated. The results show that, with the development of a mixing layer, the energy spectrum densities for different wavenumbers increase and the energy is transferred from the average flow to vortex structures in different scales. Due to the non-linear interactions between different scales, cascade processes of energy are very complex. Because vortices always roll and pair at special areas, for a definite scale, the energy is obtained from other scales at some areas while it is transferred to other scales at other areas. In addition, energy dissipation and transfer always occur where an intense interaction between vortices exists.

关键词： wavelet transforms numerical simulation mixing layer coherent structure

Dynamics of self-organizing single-line particle trains in the channel flow of a power-law fluid

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Chinese Journal of Chemical Engineering 2021年第6期34卷 12-21页

作者： Xiao Hu Jianzhong Lin Dongmei Chen Xiaoke Ku department of mechanics State Key Laboratory of Fluid Power and Mechatronic SystemsZhejiang UniversityHangzhou 310027China

The formation of self-organizing single-line particle train in a channel flow of a power-law fluid is studied using the lattice Boltzmann method with power-law index 0.6≤n≤1.2,particle volume concentration 0.8%≤Φ≤6.4%,Reynolds number 10≤Re≤100,and blockage ratio 0.2≤k≤*** numerical method is validated by comparing the present results with the previous *** effect n,Φ,Re and k on the interparticle spacing and parallelism of particle train is *** results showed that the randomly distributed particles would migrate towards the vicinity of the equilibrium position and form the ordered particle train in the power-law *** equilibrium position of particles is closer to the channel centerline in the shear-thickening fluid than that in the Newtonian fluid and shear-thinning *** particles are not perfectly parallel in the equilibrium position,hence IH is used to describe the inclination of the line linking the equilibrium position of each *** self-organizing single-line particle train is formed,the particle train has a better parallelism and hence benefit for particle focusing in the shearthickening fluid at highΦ,low Re and small ***,the interparticle spacing is the largest and hence benefit for particle separation in the shear-thinning fluid at lowΦ,low Re and small k.

关键词： Particle non-Newtonian fluids Inertial migration Channel flow Numerical simulation

Experimental and theoretical analyses of package-on-package structure under three-point bending loading

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Chinese Physics B 2012年第12期21卷 346-354页

作者：贾苏王习术任淮辉 department of Engineering mechanics AMLTsinghua University China Longyuan power Group Corporation Limited China Goudian

High density packaging is developing toward miniaturization and integration, which causes many difficulties in designing, manufacturing, and reliability testing. Package-on-Package （POP） is a promising three-dimensional high- density packaging method that integrates a chip scale package （CSP） in the top package and a fine-pitch ball grid array （FBGA） in the bottom package. In this paper, in-situ scanning electron microscopy （SEM） observation is carried out to detect the deformation and damage of the PoP structure under three-point bending loading. The results indicate that the cracks occur in the die of the top package, then cause the crack deflection and bridging in the die attaching layer. Furthermore, the mechanical principles are used to analyse the cracking process of the PoP structure based on the multi-layer laminating hypothesis and the theoretical analysis results are found to be in good agreement with the experimental results.

关键词： high density package in-situ SEM observation three-point bending multi-layer lami- nating hypothesis

Non-Fourier heat conduction in a thin gold film heated by an ultra-fast-laser

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Science China(Technological Sciences) 2015年第4期58卷 638-649页

作者： MAO Yu Dong XU Ming Tian department of Engineering mechanics School of Civil Engineering Shandong University School of Energy and power Engineering Shandong University

Based on the dual-phase-lagging(DPL)heat conduction model,the Cattaneo-Vernotte(CV)model and the improved CV model we investigate the one-dimensional heat conduction in gold films with nano-scale thickness exposed to an ultra-fast laser *** influence of system parameters on the temperature field is *** find that for all the non-Fourier heat conduction models considered in this work,a larger Knudsen number normally leads to a higher *** the DPL model,the large ratio of the phase lag of temperature gradient to the phase lag of heat flux reduces the maximum temperature and shortens the time for the system to reach its steady *** CV model and the improved CV model lead to the similar thermal wave behavior of the temperature field,but the thermal wave speeds for these two models are different,especially for large Knudsen *** the phase lag of temperature gradient is smaller,the difference between the DPL model and the improved CV model is not significant,but for the large phase lag of temperature gradient the difference becomes quite significant,especially for the large Knudsen *** addition,the effect of the surface accommodation coefficient,which is a parameter in the slip boundary condition,on the temperature field of the gold film heated by ultra-fast laser pulses is investigated based on the DPL model.

关键词： Nano-scale heat conduction ultrafast laser heating thin film Knudsen number

Non-axisymmetric instability in the Taylor-Couette flow of fiber suspension

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2005年第B8期6卷 1-7页

作者：万占鸿林建忠游振江 department of mechanics the State Key Laboratory of Fluid Power Transmission and Control Zhejiang University department of mechanics the State Key Laboratory of Fluid Power Transmission and ControlZhejiang University School of Informatics and Engineering Flinders University of South Australia

An analysis of the instability in the Taylor-Couette flow of fiber suspensions with respect to the non-axisymmetric disturbances was performed. The constitutive model proposed by Ericksen was used to represent the role of fiber additives on the stress tensor. The generalized eigenvalue equation governing the hydrodynamic stability of the system was solved using a direct numerical procedure. The results showed that the fiber additives can suppress the instability of the flow. At the same time, the non-axisymmetric disturbance is the preferred mode that makes the fiber suspensions unstable when the ratio of the angular ve- locity of the outer cylinder to that of the inner cylinder is a large negative number.

关键词： Fiber suspensions Taylor-Couette flow Hydrodynamic instability

Wettability and Surface Free Energy Analyses of Monolayer Graphene

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Journal of Thermal Science 2018年第4期27卷 359-363页

作者： SU Ruixia ZHANG Xing Key Laboratory for Thermal Science and power Engineering of Ministry of Education Department of Engineering Mechanics Tsinghua University

Recently Rafiee et al. experimentally demonstrated the wetting transparency of graphene, but there is still no comprehensive theoretical explanation of this physical phenomenon. Since surface free energy is one of the most important parameters characterizing material surfaces and is closely related to the wetting behavior, the surface free energy of suspended monolayer graphene is analyzed based on its microscopic formation mechanism. The surface free energy of suspended monolayer graphene is shown to be zero, which suggests its super-hydrophobicity. Neumann's equation of state is applied to further illustrate the contact angle, θ, of any liquid droplet on a suspended monolayer graphene is 180 o. This indicates that the van der Waals(vd W) interactions between the monolayer graphene and any liquid droplet are negligible; thus the monolayer graphene coatings exhibit wetting transparency to the underlying substrate. Moreover, molecular dynamics(MD) simulations are employed to further confirm the wetting transparency of graphene in comparison with experimental results of Rafiee et al. These findings provide a fundamental picture of wetting on ideal single atomic layer materials, including monolayer graphene. Thus, these results provide a useful guide for the design and manufacture of biomaterials, medical instruments, and renewable energy devices with monolayer graphene layers.

关键词： monolayer graphene wettability surface free energy Neumann's equation of state contact angle molecular dynamics simulations

An experimental study on the velocity fluctuations generated by the flow past fixed spheres

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Journal of Hydrodynamics 2022年第2期34卷 214-225页

作者： Ling-xin Zhang Xin-sheng Cheng Ze-cai Zhou Qi Gao Xue-ming Shao State Key Laboratory of Fluid power and Mechatronic Systems Department of MechanicsZhejiang UniversityHangzhou310027China

We perform a series of experiments to study the velocity fluctuations generated by the flow past fixed *** particle image velocimetry(PIV)is carried out to characterize the properties of the liquid *** fluctuation induced by the spheres can be decomposed into the temporal fluctuation and the spatial fluctuation,which represent the contribution of flow instability and spatial inhomogeneity,*** particularly,we focus on the contributions of temporal fluctuations and spatial fluctuations between low and high Reynolds *** low Reynolds number(20200,but not for Re<*** ending scale is aroundλ=0.5d and decreases slightly as Re increases.

关键词： Multiphase flow turbulence modulation particle image velocimetry(PIV)

ON INSTABILITY OF DILUTE FIBER SUSPENSIONS IN AN AXISYMMETRIC TAYLOR-COUETTE FLOW

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Journal of Hydrodynamics 2005年第4期17卷 398-403页

作者： WAN Zhan-hong LIN Jian-zhong LI Bing-ru department of mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang University Hangzhou 310027 China

A stability analysis of flow between two coaxial rotating cylinders in the presence of fibers was performed. Based on the axisymmetric normal mode for the disturbances, a modified stability equation was derived. Then the numerical solution of the eigenvalue problem about the equation was obrained using the fourth order finite difference scheme. The marginal curves that determine the instability property were drawn. The results show that the flow instability of the dilute fiber suspensions is governed by the aspect ratio of fiber H, the inerement of H causes an increase of critical inner Reynohts number. The fiber additives effectively attenuate the instability of the flow. which is in agreement with those of related experiments.

关键词： linear stability fiber suspensions Taylor-Couette flow numerical simulation

NUMERICAL STUDY ON PROPULSIVE PERFORMANCE OF FISH-LIKE SWIMMING FOILS

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Journal of Hydrodynamics 2006年第6期18卷 681-687页

作者： DENG Jian SHAO Xue-ming REN An-lu department of mechanics State Key Laboratory of Fluid Power Transmission and Control Zhejiang UniversityHangzhou 310027 China

Two-dimensional numerical simulations are performed to study the propulsive performance of fish-like swimming foils using the immersed-boundary method. A single fish as well as two fishes in tandem arrangement are studied. First, the effect of the phase speed on the propulsive performance of a single fish is analyzed. The wake structures and pressure distribution near the wavy fish are also examined. The results show good correlation with those by previous researchers. Second, two tandem fishes with the same phase speed and amplitude are studied. The results show that the fish situated directly behind another one endure a higher thrust than that of a single one.

关键词： biomechanics fish-like swimming traveling wavy foil immersed-boundary method