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Effects of fundamental structure parameters on dynamic responses of submerged floating tunnel under hydrodynamic loads

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Acta Mechanica Sinica 2009年第3期25卷 335-344页

作者： Xu Long Fei Ge Lei Wang Youshi Hong state key laboratory of {3. {3., Institute of {3., chinese academy of sciences, beijing 100190, china state key laboratory of {3. {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

This paper investigates the effects of structure parameters on dynamic responses of submerged floating tunnel （SFT） under hydrodynamic loads. The structure parameters includes buoyancy-weight ratio （BWR）, stiffness coefficients of the cable systems, tunnel net buoyancy and tunnel length. First, the importance of structural damp in relation to the dynamic responses of SPT is demonstrated and the mechanism of structural damp effect is discussed. Thereafter, the fundamental structure parameters are investigated through the analysis of SFT dynamic responses under hydrodynamic loads. The results indicate that the BWR of SFT is a key structure parameter. When BWR is 1.2, there is a remarkable trend change in the vertical dynamic response of SFT under hydrodynamic loads. The results also indicate that the ratio of the tunnel net buoyancy to the cable stiffness coefficient is not a characteristic factor affecting the dynamic responses of SFT under hydrodynamic loads.

关键词： Submerged floating tunnel Structural dampBuoyancy-weight ratio Cable stiffness coefficient ,Tunnel net buoyancy - Hydrodynamic load

Direct numerical simulation of shock/turbulent boundary layer interaction in a supersonic compression ramp

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Science china(Physics,mechanics & Astronomy) 2010年第9期53卷 1651-1658页

作者： LI XinLiang1,FU DeXun2,MA YanWen2 & LIANG Xian1 1 key laboratory of High Temperature Gas Dynamics,Institute of mechanics,{3.,{3.,china 2 the state key laboratory of nonlinear mechanics,Institute of mechanics,{3.,{3.,china 1. key laboratory of High Temperature Gas Dynamics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China2. The State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

A direct numerical simulation of the shock/turbulent boundary layer interaction flow in a supersonic 24-degree compression ramp is conducted with the free stream Mach number *** blow-and-suction disturbance in the upstream wall boundary is used to trigger the *** the mean wall pressure and the velocity profiles agree with those of the experimental data,which validates the *** turbulent kinetic energy budget in the separation region is *** show that the turbulent production term increases fast in the separation region,while the turbulent dissipation term reaches its peak in the near-wall *** turbulent transport term contributes to the balance of the turbulent conduction and turbulent *** on the analysis of instantaneous pressure in the downstream region of the mean shock and that in the separation bubble,the authors suggest that the low frequency oscillation of the shock is not caused by the upstream turbulent disturbance,but rather the instability of separation bubble.

关键词： compression ramp shock/turbulent boundary layer interaction direct numerical simulation shock oscillation

Large-eddy simulation of flows past a flapping airfoil using immersed boundary method

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Science china(Physics,mechanics & Astronomy) 2010年第6期53卷 1101-1108页

作者： YANG XiaoLei,HE GuoWei & ZHANG Xing The state key laboratory of {3. {3.,Institute of {3.,chinese academy of sciences,beijing 100190,china 1. The state key laboratory of {3. {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

The numerical simulation of flows past flapping foils at moderate Reynolds numbers presents two challenges to computational fluid dynamics: turbulent flows and moving boundaries. The direct forcing immersed boundary(IB) method has been developed to simulate laminar flows. However,its performance in simulating turbulent flows and transitional flows with moving boundaries has not been fully evaluated. In the present work,we use the IB method to simulate fully developed turbulent channel flows and transitional flows past a stationary/plunging SD7003.airfoil. To suppress the non-physical force oscillations in the plunging case,we use the smoothed discrete delta function for interpolation in the IB method. The results of the present work demonstrate that the IB method can be used to simulate turbulent flows and transitional flows with moving boundaries.

关键词： transitional flows moving boundary immersed boundary method smoothed discrete delta function

Numerical simulation of Richtmyer-Meshkov instability

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Science china Mathematics 2004年第z1期47卷 234-244页

作者： FU Dexun, MA Yanwen, ZHANG Linbo & TIAN Baolinstate key laboratory of {3. {3., Institute of {3., chinese academy of sciences, beijing 100080, china state key laboratory of Scientific and Engineering Computing, Institute of Computational Mathematics, chinese academy of sciences, beijing 100080, china 1. state key laboratory of {3. {3. Institute of Mechanics Chinese Academy of Sciences 100080 Beijing China2. State Key Laboratory of Scientific and Engineering Computing Institute of Computational Mathematics Chinese Academy of Sciences 100080 Beijing China

The compressible Navier-Stokes equations discretized with a fourth order accurate compact finite difference scheme with group velocity control are used to simulate the Richtmyer-Meshkov (R-M) instability problem produced by cylindrical shock-cylindrical material interface with shock Mach number Ms=1.2 and density ratio 1:20 (interior density/outer density). Effect of shock refraction, reflection, interaction of the reflected shock with the material interface, and effect of initial perturbation modes on R-M instability are investigated numerically. It is noted that the shock refraction is a main physical mechanism of the initial phase changing of the material surface. The multiple interactions of the reflected shock from the origin with the interface and the R-M instability near the material interface are the reason for formation of the spike-bubble structures. Different viscosities lead to different spike-bubble structure characteristics. The vortex pairing phenomenon is found in the initial double mode simulation. The mode interaction is the main factor of small structures production near the interface.

关键词： R-M instability, direct numerical simulation, shock-interface interaction.

A Dugdale model based geometrical amplifier enables the measurement of separation-to-failure for a cohesive interface

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Theoretical & Applied mechanics Letters 2011年第1期1卷 25-29页

作者： Yu-Jie Wei~(a)) state key laboratory of {3. {3.,Institute of {3.,chinese academy of sciences, beijing 100190,china state key laboratory of {3. {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

Regardless of all kinds of different formulae used for the traction-separation relationship in cohesive zone modeling,the peak tractionσ_m and the separation-to-failureδ_0(or equivalently the work-to-separationΓ) are the primary parameters which control the interfacial fracture behaviors. Experimentally,it is hard to determine those quantities,especially forδ_0,which occurs in a very localized region with possibly complicated geometries by material *** on the Dugdale model,we show that the separation-to-failure of an interface could be amplified by a factor of L/r_p in a typical peeling test,where L is the beam length and r_p is the cohesive zone *** an amplifier makesδ_0 feasible to be probed quantitatively from a simple peeling test. The method proposed here may be of importance to understanding interfacial fractures of layered structures,or in some nanoscale mechanical phenomena such as delamination of thin films and coatings.

关键词： cohesive zone dugdale model separation-to-failure thin film peeling test

Dynamics of morphological changes for mitochondrial fission and fusion

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Science china(Physics,mechanics & Astronomy) 2010年第4期53卷 680-689页

作者： WANG ShiQi 1,2,4 , FU ChangLiang 1,2 , ZHANG Yan 1,2 , CHEN Quan 3.& LONG Mian 1,2 1 key laboratory of Microgravity (National Microgravity laboratory), {3., {3. 2 Center for Biomechanics and Bioengineering, Institute of mechanics, chinese academy of sciences, {3., {3. 3.state key laboratory of Biomembrane and Membrane Biotechnology, Institute of Zoology, chinese academy of sciences, beijing 100101, {3. 4 Institute of Vertebrate Paleontology and Paleoanthropology, chinese academy of sciences, beijing 100044, {3. 1. key laboratory of Microgravity (National Microgravity laboratory) Beijing 100190 China2. Center for Biomechanics and Bioengineering Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China4. Institute of Vertebrate Paleontology and Paleoanthropology Chinese Academy of Sciences Beijing 100044 China3. State Key Laboratory of Biomembrane and Membrane Biotechnology Institute of Zoology Chinese Academy of Sciences Beijing 100101 China

Mitochondria experience continuous fusion and fission in a living cell, but their dynamics remains poorly quantified. Here a theoretical model was developed, upon a simplified population balance equation (PBE), to predict the morphological changes induced by mitochondrial fission and fusion. Assuming that both fission and fusion events are statistically independent, the survival probability of mitochondria staying in the fission or fusion state was formulated as an exponentially-decayed function with time, which depended on the time-dependent distribution of the mitochondrial volume and the fission and fusion rates. Parametric analysis was done for two typical volume distributions. One was Gamma distribution and the other was Gaussian distribution, derived from the measurements of volume distribution for individual mitochondria in a living cell and purified mitochondria in vitro. The predictions indicated that the survival probability strongly depended on morphological changes of individual mitochondria and was inversely correlated to the fission and fusion rates. This work provided a new insight into quantifying the mitochondrial dynamics via monitoring the evolution of the mitochondrial volume.

关键词： mitochondria morphology fission fusion dynamics modeling

Research on the mechanics of underwater supersonic gas jets

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中国科学：物理学、力学、天文学英文版 2010年第3期53卷 527-535页

作者： SHI HongHui1, WANG BoYi2 & DAI ZhenQing2 1 College of Mechanical Engineering and Automation, Zhejiang Sci-Tech University, Hangzhou 3.0018, china 2 state key {3. of {3. mechanics, Institute of mechanics, chinese academy of sciences, beijing 100190, china 1. College of Mechanical Engineering and Automation Zhejiang Sci-Tech University Hangzhou 310018 China2. State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.

关键词： underwater supersonic gas jet pressure oscillation flow visualization shock wave feedback

nonlinear FLUID DAMPING IN STRUCTURE-WAKE OSCILLATORS IN MODELING VORTEX-INDUCED VIBRATIONS

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Journal of Hydrodynamics 2009年第1期21卷 1-11页

作者： LIN Li-ming LING Guo-can WU Ying-xiang ZENG Xiao-hui Division of Engineering sciences Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China The state key laboratory of {3. {3. Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

A nonlinear Fluid Damping （NFD） in the form of the square-velocity is applied in the response analysis of Vortex-Induced Vibrations （VIV）. Its nonlinear hydrodynamic effects on the coupled wake and structure oscillators are investigated. A comparison between the coupled systems with the linear and nonlinear fluid dampings and experiments shows that the NFD model can well describe response characteristics, such as the amplification of body displacement at lock-in and frequency lock-in, both at high and low mass ratios. Particularly, the predicted peak amplitude of the body in the Griffin plot is in good agreement with experimental data and empirical equation, indicating the significant effect of the NFD on the structure motion.

关键词： Vortex-Induced Vibration (VIV) nonlinear Fluid Damping (NFD) wake oscillator

Influence of processing temperature on microstructure and microhardness of copper subjected to high-pressure torsion

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Science china(Technological sciences) 2010年第6期53卷 1534-1539页

作者： XIE ZiLing1,2,XIE JiJia2,HONG YouShi2 & WU XiaoLei2 1 College of Architecture and Civil Engineering,University of Wenzhou,Wenzhou 3.503.,china 2 state key {3. of {3. mechanics,Institute of mechanics,chinese academy of sciences,beijing 100190,china 1. College of Architecture and Civil Engineering University of Wenzhou Wenzhou 325035 China2. State Key Laboratory of Nonlinear Mechanics Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

Cu samples were subjected to high-pressure torsion (HPT) with up to 6 turns at room temperature (RT) and liquid nitrogen temperature (LNT),*** effects of temperature on grain refinement and microhardness variation were *** the samples after HPT processing at RT,the grain size reduced from 43.μm to 265 nm,and the Vickers microhardness increased from HV52 to ***,for the samples after HPT processing at LNT,the value of microhardness reached its maximum of HV150 near the center of the sample and it decreased to HV80 at the periphery *** observations revealed that HPT straining at LNT induced lamellar structures with thickness less than 100 nm appearing near the central region of the sample,but further deformation induced an inhomogeneous distribution of grain sizes,with submicrometer-sized grains embedded inside micrometer-sized *** submicrometer-sized grains with high dislocation density indicated their nonequilibrium *** the contrary,the micrometer-sized grains were nearly free of dislocation,without obvious deformation trace remaining in *** images demonstrated that the appearance of micrometer-sized grains is the result of abnormal grain growth of the deformed fine grains.

关键词： copper high pressure torsion (HPT) microstructure grain size microhardness cryogenic temperature