9 results on '"Tang, Youhong"'
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2. Natural Frequency Ratio Effect on 2 DOF Flow Induced Vibration of Cylindrical Structures
- Author
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Han, Xiangxi, Zhao, Chengbi, Tang, Youhong, Chen, Xiaoming, Lin, Wei, Sammut, Karl, Li, Kenli, editor, Xiao, Zheng, editor, Wang, Yan, editor, Du, Jiayi, editor, and Li, Keqin, editor
- Published
- 2014
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3. Numerical study of the vortex-induced vibration of a riser taking into account the variation of the tension.
- Author
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Han, Xiangxi, Ruan, Weidong, Gu, Jian, Tang, Youhong, Meng, Zhanbin, Ren, Di, and Wu, Jiaming
- Subjects
RISER pipe ,VORTEX shedding ,FREQUENCIES of oscillating systems ,FLUID-structure interaction - Abstract
Previous studies of the marine riser VIV have primarily considered the constant values of the tension, but limited work has been done to consider the variations of the tension with riser vibrations. In addition, previous studies have mainly focused on the effect of the inflow velocity profile on a riser VIV, while a study of a riser VIV at a wide range of velocities is still lacking. This study presents a model that can take into account the variation of the tension with riser vibrations. The VIV characteristics of the riser were investigated based on the fluid-structure coupling methods. It is shown that the model that takes into account the variation of the tension is able to accurately capture the bimodal character of the amplitude-ratio curve and the vortex shedding pattern, and to calculate the vibration frequencies accurately. [ABSTRACT FROM AUTHOR]
- Published
- 2023
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4. Two degree of freedom flow-induced vibration of cylindrical structures in marine environments: frequency ratio effects
- Author
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Han, Xiangxi, Lin, Wei, Zhang, Xiaojun, Tang, Youhong, and Zhao, Chengbi
- Published
- 2016
- Full Text
- View/download PDF
5. Surface roughness effects on a tensioned riser vortex-induced vibration in the uniform current.
- Author
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Han, Xiangxi, Tang, Youhong, Meng, Zhanbin, Ruan, Weidong, Qiu, Ang, Gu, Jian, and Wu, Jiaming
- Subjects
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RISER pipe , *SURFACE roughness , *VORTEX shedding , *COMPUTATIONAL fluid dynamics , *TENSILE architecture , *REYNOLDS number , *NUMERICAL calculations - Abstract
• The modified model of rough wall velocity gradient is introduced to construct the numerical calculation program of a rough riser VIV. • The program is used to study effects of various key parameters (surface roughness, inflow velocities) on the dynamic characteristics, vibration response, wake vortex shedding patterns and vibration trajectories of a rough riser. • Larger surface roughness will enhance the multi-frequency and broadband vibration characteristics of the riser in the streamwise direction. With the increase of surface roughness, the multi-frequency vibration characteristics decrease gradually, but the broadband vibration characteristics increase gradually in the transverse direction. • The surface roughness can suppress 2T and 2P wake vortex shedding pattern and enhance 2C wake vortex shedding pattern. Due to the long-term operation of marine riser, marine organisms will adsorb on its surface, thus affect its surface roughness. The surface roughness of the riser will affect the wake flow field of the riser, and then affect the dynamic characteristics of the vortex-induced vibration (VIV). The study of the influence of surface roughness on the characteristics of a rough riser VIV is helpful to improve our understanding of the mechanism of a rough riser VIV and ensure the safety of the riser during its service life. Based on the methods of computational fluid dynamics (CFD) and computational structure dynamics (CSD), this study presents the model considering tension variation with the structure vibration and the modified model of rough wall velocity gradient to construct the numerical calculation program of a rough riser VIV to study effects of various key parameters (surface roughness, inflow velocities) on the dynamic characteristics, vibration response, wake vortex shedding patterns and vibration trajectories of a rough riser. The results show that in the range of Reynolds number Re = 2.515 × 104∼1.258×105 and reduced velocity U * = 1.35–6.74, compared with a smooth riser, the streamwise vibration amplitude of a rough riser decreases, and with the increase of inflow velocity and surface roughness, the streamwise vibration amplitude of a rough riser decreases more and more obviously. In the range of reduced velocity U * = 2.70–5.39, the transverse vibration amplitude of a rough riser increases slightly. At a higher reduced velocity (U * = 6.74), the transverse vibration amplitude of the rough riser decreases. Larger surface roughness will enhance the multi-frequency and broadband vibration characteristics of the riser in the streamwise direction. With the increase of surface roughness, the multi-frequency vibration characteristics decrease gradually, but the broadband vibration characteristics increase gradually in the transverse direction. Surface roughness can suppress 2T and 2P wake vortex shedding pattern and enhance 2C wake vortex shedding pattern. This study will provide a profound understanding to guide the practical marine riser VIV research with the consideration of surface roughness. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
6. Surface roughness effect on cylinder vortex-induced vibration at moderate Re regimes.
- Author
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Han, Xiangxi, Tang, Youhong, Meng, Zhanbin, Fu, Fei, Qiu, Ang, Gu, Jian, and Wu, Jiaming
- Subjects
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RISER pipe , *SURFACE roughness , *COMPUTATIONAL fluid dynamics , *VORTEX shedding , *NUMERICAL calculations - Abstract
The marine riser is the key equipment connecting the floating platform with the seabed wellhead, and the vortex-induced vibration (VIV) is the main cause of its fatigue damage, which contains complex and substantial dynamics content. Marine risers are operated for a long time. As time goes by, marine organisms will attach on the marine riser surfaces, thus significantly affect their surface roughness of the riser. The increased surface roughness makes the dynamic characteristics of the riser VIV more abundant and complex, including jumping, multi-frequency vibration, broadband vibration, resonance and other dynamic contents. In this study, based on the bidirectional fluid-structure coupling method of computational fluid dynamics (CFD) and computational structure dynamics (CSD), the modified model of rough wall velocity gradient is introduced, and the calculation program of a rough cylinder wall velocity gradient is compiled and embedded into the numerical calculation program of a smooth cylinder VIV to construct the numerical calculation program of a rough cylinder VIV. The program is used to study effects of various key parameters, including surface roughness, and inflow velocities, on the vibration response characteristics, dynamic characteristics, wake vortex shedding patterns and vibration trajectories of a rough cylinder. The differences of VIV characteristics are systematically studied to reveal the nonlinear dynamic behavior of a rough cylinder VIV, such as jumping, multi-frequency vibration, resonance, etc. The influence mechanism of surface roughness on a cylinder VIV is explored to provide a scientific theoretical basis and a practical engineering method for vibration control of a rough marine riser. • The law of the wall modified for roughness is introduced to construct the numerical program of a rough cylinder VIV. • The program is used to study effects of various key parameters on the rough cylinder VIV characteristics. • The differences of VIV characteristics between smooth cylinder and rough cylinder are systematically. • The surface roughness of the cylinder will inhibit the formation of 2T wake vortex shedding pattern. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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7. Effects of natural frequency ratio on vortex-induced vibration of a cylindrical structure.
- Author
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Han, Xiangxi, Lin, Wei, Tang, Youhong, Zhao, Chengbi, and Sammut, Karl
- Subjects
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VORTEX methods , *REYNOLDS number , *FLUID-structure interaction , *UNSTEADY flow , *FLUID dynamics , *FOURIER transforms , *NUMERICAL analysis - Abstract
In this study, vortex-induced vibration (VIV) of a circular cylinder at the low Reynolds number of 200 is simulated by a transient coupled fluid–structure interaction numerical model. The transient coupling between the fluid and the structure is updated by on-line transmission between fluid dynamic loads and structure response data. The structural vibration of the cylinder influences the flow around it, and the change of fluid flow in turn influences the response of the cylinder. The boundary layer near the cylinder is updated by dynamic mesh technology with grid updating at each time step. This method successfully simulates the vortex generation and the real-time flow field of the cylinder. Considering VIV with low reduced damping parameters, the trend of the lift coefficient, the drag coefficient and the displacement of cylinder are analyzed under different oscillating frequencies of the cylinder. The frequency ratio α is a very important parameter, when α is small ( α = 0.5), the amplitude of lift coefficient of an elastic cylinder is large and the response of cylinder is weak. With an increase in α , the lateral displacement of the cylinder increases, but the amplitude of lift coefficient decreases. The amplitude of the lift coefficient reaches its minimum value when α is between 0.9 and 1.2. After that, the amplitude of the lift coefficient begins to increase. The typical nonlinear phenomena of locked-in, beat and phase-switch can be captured successfully. The evolution of vortex shedding from the cylinder with varied α is discussed. The trajectory of the two degrees of freedom (2 DOF) case at different α is also discussed; all appear to have a “ Fig. 8 ” shape. A fast Fourier transformation technique is used to obtain the frequency characteristics of the cylindrical structure vibration. Using the 2 DOF cylinder model in place of the one degree of freedom (1 DOF) cylinder model presents several advantages in simulating the nonlinear characteristics of cylindrical structures including the capacity to model the crosswise vibration generated by in-line vibration. [ABSTRACT FROM AUTHOR]
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- 2015
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8. A sharp interface immersed boundary/VOF model coupled with wave generating and absorbing options for wave-structure interaction.
- Author
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Zhang, Cheng, Lin, Nansheng, Tang, Youhong, and Zhao, Chengbi
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INTERFACES (Physical sciences) , *ABSORPTION , *FLUID-structure interaction , *FREE surfaces , *MATHEMATICAL models , *BOUNDARY value problems - Abstract
Highlights: [•] A model is developed to investigate wave-structure interaction problems. [•] The model can capture free-surface waves with a second-order PLIC-VOF method. [•] A second-order sharp interface IBM is used for the no-slip boundary condition. [•] The model validated by several various cases for different purposes. [Copyright &y& Elsevier]
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- 2014
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9. Numerical simulation of super upper branch of a cylindrical structure with a low mass ratio.
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Han, Xiangxi, Lin, Wei, Wang, Dongjiao, Qiu, Ang, Feng, Zhiqiang, Tang, Youhong, and Wu, Jiaming
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COMPUTER simulation , *SHEARING force , *STRAINS & stresses (Mechanics) , *DRAG (Aerodynamics) , *OCEAN engineering - Abstract
Abstract SST (shear stress transport) k-ω and Newmark-β methods are used to comprehensively understand vortex-induced vibration (VIV) characteristics of a cylindrical structure with a mass ratio of 2.6 in a range of reduced velocity from 2.0 to 14.0. The details of drag and lift forces, cross-flow and streamwise displacements, vortex pattern, trajectory, and frequency of VIV are presented and compared systematically with the experimental work of Jauvtis and Williamson that first captured the super upper branch in VIV with the maximum value of 1.5 D (diameter). In this study, the numerical simulation results successfully captured the initial branch, the lower branch, and the super upper branch. Very few research studies have successfully simulated the super upper branch by numerical methods. The vibration amplitude corresponding to the super upper branch is stable and the maximum value of the super upper branch is 1.46 D, which is fairly consistent with the results of the Jauvtis and Williamson experiment. This research also successfully captured the law of trajectory under different reduced velocities. With the reduced velocity increasing, the trajectories switch from an irregular shape to a regular "Figure 8″ shape and then enter into an irregular movement, finally again into a regular movement of a Figure 8 shape or crescent. In the range of the super upper branch, the vibration trajectories gradually change from a Figure 8 shape to a crescent shape with the increase of the transverse vibration amplitude. This work has successfully captured the different vortex patterns corresponding to each branch under different reduced velocities, and found the transitional forms of 2S to 2T, 2T to 2P, and 2P to 2S, respectively. Highlights • The numerical simulation results successfully captured the super upper branch. • The details of VIV are presented and compared systematically with the experimental work of Jauvtis and Williamson. • With the reduced velocity increasing, the trajectory switches from regular shape to regular shape three times. • This work has successfully captured the different vortex patterns corresponding to each branch. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
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