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Shear flow induced vibrations of long slender cylinders with a wake oscillator model

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Acta Mechanica Sinica 2011年第3期27卷 330-338页

作者： Fei Ge Wei Lu Lei Wang You-Shi Hong State Key Laboratory of Nonlinear Mechanics Institute of Mechanics CAS 100190 Beijing China

A time domain model is presented to study the vibrations of long slender cylinders placed in shear flow. Long slender cylinders such as risers and tension legs are widely used in the field of ocean engineering. They are subjected to vortex-induced vibrations（VIV） when placed within a transverse incident flow. A three dimensional model coupled with wake oscillators is formulated to describe the response of the slender cylinder in cross-flow and in-line directions. The wake oscillators are distributed along the cylinder and the vortex-shedding frequency is derived from the local current velocity. A non-linear fiuid force model is accounted for the coupled effect between cross-flow and in-line vibrations. The comparisons with the published experimental data show that the dynamic features of VIV of long slender cylinder placed in shear flow can be obtained by the proposed model,such as the spanwise average displacement,vibration frequency,dominant mode and the combination of standing and traveling waves. The simulation in a uniform flow is also conducted and the result is compared with the case of nonuniform flow. It is concluded that the flow shear characteristic has significantly changed the cylinder vibration behavior.

关键词： Vortex-induced vibration Vortex-induced wave Shear flow Wake oscillator Long slender cylinder

Flow-induced vibrations of long circular cylinders modeled by coupled nonlinear oscillators

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Science China(Physics,Mechanics & Astronomy) 2009年第7期52卷 1086-1093页

作者： GE Fei LONG Xu WANG Lei HONG YouShi State Key Laboratory of Nonlinear Mechanics Institute of MechanicsChinese Academy of SciencesBeijing 100190China

The dynamics of long slender cylinders undergoing vortex-induced vibrations (VIV) is studied in this work. Long slender cylinders such as risers or tension legs are widely used in the field of ocean engineering. When the sea current flows past a cylinder, it will be excited due to vortex shedding. A three-dimensional time domain model is formulated to describe the response of the cylinder, in which the in-line (IL) and cross-flow (CF) deflections are coupled. The wake dynamics, including in-line and cross-flow vibrations, is represented using a pair of non-linear oscillators distributed along the cylinder. The wake oscillators are coupled to the dynamics of the long cylinder with the acceleration coupling term. A non-linear fluid force model is accounted for to reflect the relative motion of cylinder to current. The model is validated against the published data from a tank experiment with the free span riser. The comparisons show that some aspects due to VIV of long flexible cylinders can be reproduced by the proposed model, such as vibrating frequency, dominant mode number, occurrence and transition of the standing or traveling waves. In the case study, the simulations show that the IL curvature is not smaller than CF curvature, which indicates that both IL and CF vibrations are important for the structural fatigue damage.

关键词： vortex-induced vibration (VIV) vortex-induced wave (VIW) wake oscillator long cylinder fluid-structure interaction

An implicit relation between temperature and reaction rate in the SLFM

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Theoretical & Applied Mechanics Letters 2011年第1期1卷 47-49页

作者： Jian Zhang,~(a)) Guowei He,~(b)) and Guodong Jin lnm,Institute of Mechanics,Chinese Academy of Sciences,Beijing 100190,China lnm Institute of Mechanics Chinese Academy of Sciences Beijing 100190 China

The Arrhenius law implies that reaction rate is a continuous function of temperature. However,the steady laminar flamelet model(SLFM) does not explicitly give this functional relationship. The present study addresses this relation in the *** is found that reaction rate is not continuous in the mixture-fraction *** a result,the SLFM is unable to predict local extinction and ***,we use the unstable branch of the'S-curve'to fill the gap between steady burning branch and extinction one,and find that this modification leads to a continuous dependent of reaction rate on *** the modified SLFM can describe the local extinction and reignition.

关键词： nonpremixed turbulent combustion local extinction and reignition steady laminar flamelet model unstable branch