This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of v...This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.展开更多
As a fundamental fluid-structure interaction(FSI)phenomenon,vortex-induced vibrations(VIVs)of circular cylinders have been the center of the FSI research in the past several decades.Apart from its scientific significa...As a fundamental fluid-structure interaction(FSI)phenomenon,vortex-induced vibrations(VIVs)of circular cylinders have been the center of the FSI research in the past several decades.Apart from its scientific significance in rich physics,VIVs are paid great attentions by offshore engineers,as they are encountered in many ocean engineering applications.Recently,with the development of research and application,wake-induced vibration(WIV)for multiple cylinders and galloping for VIV suppression attachments are attracting a growing research interest.All these phenomena are connected with the flow-induced vibration(FIV).In this paper,we review and give some discussions on the FIV of offshore circular cylinders,including the research progress on the basic VIV mechanism of an isolated rigid or flexible cylinder,interference of multiple cylinders concerning WIV of multiple cylinders,practical VIV suppression and unwanted galloping for cylinder of attachments.Finally,we draw concluding remarks,give some comments and propose future research prospects,especially on the major challenges as well as potentials in the offline/online modelling and prediction of real-scale offshore structures with high-fidelity CFD methods,new experimental facilities and applications of artificial intelligence tools.展开更多
The flow past a finite circular cylinder with a height-to-diameter ratio of 1.5 and an infinite circular cylinder of the same diameter at a Reynolds number Re= 3 900 is investigated using the large eddy simulation（LE...The flow past a finite circular cylinder with a height-to-diameter ratio of 1.5 and an infinite circular cylinder of the same diameter at a Reynolds number Re= 3 900 is investigated using the large eddy simulation（LES）. The objective of the present study is to explore the differences of the flow mechanisms between the finite and infinite circular cylinders. It is shown that the free end of the finite circular cylinders affects the wake region significantly. The mean drag coefficient and the fluctuating lift coefficient of the finite circular cylinder are smaller than those of the infinite circular cylinder. The three-dimensional separation and the separated shear layer instability of the finite circular cylinder can obviously be observed. The existence of an arch vortex in the average flow downstream of the free end is demonstrated.展开更多
The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞ from 0.85 to 0.98 and the Reynolds number 2×105 based on the diameter of the cy...The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞ from 0.85 to 0.98 and the Reynolds number 2×105 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞<Mcr, and the other is a quasi-steady flow state with nearly sta-tionary shock waves formed in the near wake for M∞>Mcr, suppressing vortex shedding from the cylin-der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu-tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc<1 in the unsteady flow regime and Mc>1 in the quasi-steady flow regime, resulting in different evolutions of the shear layers.展开更多
基金supported by the National High Technology Research and Development Program of China(863 Program,Grant No.2006AA09Z350)the National Natural Science Foundation of China(Grant No.10702073)the Knowledge Innovation Program of Chinese Academy of Sciences(Grant No.KJCX2-YW-L02)
文摘This article proposes a new wake oscillator model for vortex induced vibrations of an elastically supported rigid circular cylinder in a uniform current. The near wake dynamics related with the fluctuating nature of vortex shedding is modeled based on the classical van der Pol equation, combined with the equation for the oscillatory motion of the body. An appropriate approach is developed to estimate the empirical parameters in the wake oscillator model. The present predicted results are compared to the experimental data and previous wake oscillator model results. Good agreement with experimental results is found.
基金Project supported by the National Natural Science Foundation of China(Grant No.11872250)the National Basic Research and Development Program of China(973 Program,Grant No.2015CB251203)the National Major Science and Technology Specific Project of China(Grant No.2016ZX05028-001).
文摘As a fundamental fluid-structure interaction(FSI)phenomenon,vortex-induced vibrations(VIVs)of circular cylinders have been the center of the FSI research in the past several decades.Apart from its scientific significance in rich physics,VIVs are paid great attentions by offshore engineers,as they are encountered in many ocean engineering applications.Recently,with the development of research and application,wake-induced vibration(WIV)for multiple cylinders and galloping for VIV suppression attachments are attracting a growing research interest.All these phenomena are connected with the flow-induced vibration(FIV).In this paper,we review and give some discussions on the FIV of offshore circular cylinders,including the research progress on the basic VIV mechanism of an isolated rigid or flexible cylinder,interference of multiple cylinders concerning WIV of multiple cylinders,practical VIV suppression and unwanted galloping for cylinder of attachments.Finally,we draw concluding remarks,give some comments and propose future research prospects,especially on the major challenges as well as potentials in the offline/online modelling and prediction of real-scale offshore structures with high-fidelity CFD methods,new experimental facilities and applications of artificial intelligence tools.
基金Project supported by the National Natural Science Foundation of China(Grant No.40906049)
文摘The flow past a finite circular cylinder with a height-to-diameter ratio of 1.5 and an infinite circular cylinder of the same diameter at a Reynolds number Re= 3 900 is investigated using the large eddy simulation（LES）. The objective of the present study is to explore the differences of the flow mechanisms between the finite and infinite circular cylinders. It is shown that the free end of the finite circular cylinders affects the wake region significantly. The mean drag coefficient and the fluctuating lift coefficient of the finite circular cylinder are smaller than those of the infinite circular cylinder. The three-dimensional separation and the separated shear layer instability of the finite circular cylinder can obviously be observed. The existence of an arch vortex in the average flow downstream of the free end is demonstrated.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 90405007, 90605005)Science and Technology Innovative Foundation of Chi-nese Academy of Sciences (Grant No. CXJJ-237)
文摘The effect of Mach number on transonic flow past a circular cylinder is investigated numerically for the free-stream Mach number M∞ from 0.85 to 0.98 and the Reynolds number 2×105 based on the diameter of the cylinder. The work provides an insight into several salient features, including unsteady and quasi-steady flow state, formation of local supersonic zone, and evolution of turbulent shear layer. Results show that there exist two flow states dependent of a critical Mach number Mcr around 0.9. One is an unsteady flow state characterized by moving shock waves interacting with the turbulent flow in the near region of the cylinder for M∞<Mcr, and the other is a quasi-steady flow state with nearly sta-tionary shock waves formed in the near wake for M∞>Mcr, suppressing vortex shedding from the cylin-der. Some flow behaviors in the unsteady and quasi-steady flow states are revealed. From time evolu-tion of flow structures, local supersonic zones are identified in the wake and generated by two typical processes, i.e. reverse flow behind the cylinder and shed vortices in the near wake. The convective Mach number Mc of turbulent shear layers shed from the cylinder is identified nearly as Mc<1 in the unsteady flow regime and Mc>1 in the quasi-steady flow regime, resulting in different evolutions of the shear layers.
