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Response of Two Unequal-Diameter Flexible Cylinders in A side-by-side Arrangement:Characteristics of FIV

China Ocean Engineering 2020年第4期34卷 475-487页

作者： XU Wan-hai ZHANG Qian-nan MA Wen-chen WANG En-hao State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China Department of Civil and Environmental Engineering and Construction University of NevadaNV 89154USA

Till now,little information is available on the flow-induced vibration(FIV)of multiple flexible cylinders with unequal *** FIV characteristics of unequal-diameter cylinders can be predicted based on the knowledge of equal-diameter cylinders,while there are still other features remaining *** this paper,the FIV characteristics of two flexible cylinders with unequal diameters arranged side-by-side are experimentally *** diameter ratio of the small cylinder(Small Cyl.)to the large cylinder(Large Cyl.)is nearly *** aspect ratios and mass ratios of the two flexible cylinders are 350/181 and 1.90/1.47,*** centre-tocentre spacing ratio in the cross-flow(CF)direction is kept constant as 6.0 and the two cylinders can oscillate freely in both the CF and in-line(IL)*** towing velocity varies from 0.05 m/s to 1.00 m/*** dominant modes and frequencies,CF and IL displacement amplitudes and response trajectories are *** with the case of two identical cylinders in our previous study,the FIV responses demonstrate some similarities and *** similarities are as *** cylinders exhibit multi-mode vibration features and they interact with each ***,the IL FIV shows a more complex behaviour than that in the CF *** difference is that as the diameter of one cylinder is increased,the effect on the smaller cylinder becomes more *** Large Cyl.,the FIV response is similar to its isolated counterpart,which indicates that Small *** a negligible effect on the FIV of the larger *** Large *** the FIV of Small *** the vibration *** spacing would change when both cylinders are *** interference between the two cylinders and wake shielding effect of the Large *** *** dominant frequencies of Small *** reduced and the wake-induced flutter of Small *** observed from the response trajectories at different mea

关键词： flow-induced vibration(FIV) flexible cylinder side-by-side unequal diameter wake-induced flutter

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Measurements of Wind Loads on side-by-side Semi-Submersibles in A Wind Tunnel

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China Ocean Engineering 2021年第4期35卷 531-543页

作者： DONG Qing GUO Xiao-xian YANG Jian-min LU Hai-ning HUANG Longwei State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University(SJTU)Shanghai 200240China SJTU Yazhou Bay Institute of Deepsea Technology Sanya 572000China

The multi-body system has been a popular form for offshore operations in terms of high *** wind effects are crucial which directly affect the relative positions of floating bodies and operating *** this study,the aerodynamic characteristics for two coupled semi-submersibles were analyzed in a wind tunnel to fill the gaps in literature related to the wind sheltering on offshore *** influences of separation distance were also *** to the results,substantial shielding effects were observed and wind forces on the shielded vessel decreased dramatically:a reduction in the transverse force could be up to 74%.Moreover,the longitudinal wind load was amplified by the platform abreast in a side-by-side *** expected,the interference level became more pronounced with a decreasing separation *** cases in which wind interaction decayed rapidly with distance,logarithmic functions were preferable for describing the relationship between *** linear fitting was reasonable for the transverse wind force when there was still evident sheltering at a quite large *** length of shielding area was another important factor that there was approximately a linear relationship between it and the shielding level for two platforms in close proximity at various wind attack *** on the two parameters,a preliminary wind loads estimation method considering shielding effects was *** approach can aid the industry to have a qualitative assessment of wind sheltering especially at early stages.

关键词： wind loads side-by-side shielding effect wind tunnel test

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Numerical Simulation on Flow Past Two side-by-side Inclined Circular Cylinders at Low Reynolds Number

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China Ocean Engineering 2019年第3期33卷 344-355页

作者： LIU Cai GAO Yang-yang QU Xin-chen WANG Bin ZHANG Bao-feng Ocean College Zhejiang University Zhoushan 316021 China Powerchina Huadong Engineering Corporation Limited Hangzhou 311122 China

A series of three-dimensional numerical simulations is carried out to investigate the effect of inclined angle on flow behavior behind two side-by-side inclined cylinders at low Reynolds number Re=100 and small spacing ratio T/D=1.5 (T is the center-to-center distance between two side-by-side cylinders, D is the diameter of cylinder). The instantaneous and time-averaged flow fields, force coefficients and Strouhal numbers are analyzed. Special attention is focused on the axial flow characteristics with variation of the inclined angle. The results show that the inclined angle has a significant effect on the gap flow behaviors behind two inclined cylinders. The vortex shedding behind two cylinders is suppressed with the increase of the inclined angle as well as the flip-flop gap flow. Moreover, the mean drag coefficient, root-mean-square lift coefficient and Strouhal numbers decrease monotonously with the increase of the inclined angle, which follows the independent principle at small inclined angles.

关键词： two side-by-side inclined cylinders inclined angle wake flow pattern low Reynolds number axial flow

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Use of Helical Strakes for FIV Suppression of Two Inclined Flexible Cylinders in A side-by-side Arrangement

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China Ocean Engineering 2018年第3期32卷 331-340页

作者： XU Wan-hai ZHANG Shu-hai ZHOU Li-dan GAO Xi-feng State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China Collaborative Innovation Centre for Advanced Ship and Deep-Sea Exploration Shanghai 200240China

The experimental studies on flow-induced vibrations(FIV) reduction of two side-by-side flexible cylinders inclined at 45° by using the helical strakes were carried out in a towing tank. The main aim of the experiment is to check whether the helical strakes with a pitch of 17.5 D and a height of 0.25 D, which is considered as the most effective vibration suppression device for the isolated cylinder undergoing vortex-shedding, still perform very well to reduce FIV of two inclined flexible cylinders in a side-by-side arrangement. The vibration of two identical inclined cylinders with a mass ratio of 1.90 and an aspect ratio of 350 was tested in the experiment. The center-to-center distance between the two cylinders was 3.0 D. The uniform flow was simulated by towing the cylinder models along the *** towing velocity varied from 0.05 to 1.0 m/s with an interval of 0.05 m/s. The maximum Reynolds number can be up to 1.6×104. Three cases were experimentally studied in this paper, including two side-by-side inclined smooth cylinders, only one smooth cylinder fitted with helical strakes in the two side-by-side inclined cylinders system and both two cylinders attached with helical strakes. The variations of displacement amplitude, dominant frequency, FIV suppression efficiency and dominant mode for the two side-by-side inclined cylinders with reduced velocity were shown and discussed.

关键词： helical strakes FIV suppression inclined cylinder side-by-side towing tank experiment

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Application of Helical Strakes for Suppressing the Flow-Induced Vibration of Two side-by-side Long Flexible Cylinders

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China Ocean Engineering 2020年第2期34卷 172-184页

作者： XU Wan-hai YANG Meng AI Hua-nan HE Ming LI Mu-han State Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin UniversityTianjin 300072China School of Hydro Science&Engineering Taiyuan University of TechnologyTaiyuan 030024China

Helical strakes have been widely applied for suppressing the vibration of flexible cylinders undergoing vortexshedding in offshore ***,most research works have concerned on the application of helical strakes for the isolated flexible cylinder subjected to vortex-induced vibration(VIV).The effectiveness of helical strakes attached to side-by-side flexible cylinders in vibration reduction is still *** this paper,the response characteristics of two side-by-side flexible cylinders with and without helical strakes were experimentally investigated in a towing *** configuration of the helical strakes used in the experiment had a pitch of 17.5D and a height of 0.25D(where D is the cylinder diameter),which is usually considered the most effective for VIV suppression of isolated marine risers and *** center-to-center distance of the two cylinders was *** uniform flow with a velocity ranging from 0.05 m/s to 1.0 m/s was generated by towing the cylinder models along the *** results,including the displacement amplitude,the dominant frequency,the dominant mode,and the mean drag force coefficient,were summarized and *** the case where only one cylinder in the two-cylinder system had helical strakes,the experimental results indicated that helical strakes can remarkably reduce the flow-induced vibration(FIV)of the staked *** the case of two straked cylinders in a side-by-side arrangement,it was found that the performance of helical strakes in suppressing the FIV is as good as that for the isolated cylinder.

关键词： side-by-side FIV reduction helical strakes flexible cylinder center-to-center distance

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Numerical study on the cavity dynamics for vertical water entries of twin spheres

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Defence Technology（防务技术） 2024年第2期32卷 459-472页

作者： Xu Wang Xujian Lyu Ruisheng Sun Dongdong Tang School of Energy and Power Engineering Nanjing University of Science and TechnologyNanjing210094China Shanghai Institute of Spacecraft Equipment Shanghai200240China

In this study, a three dimensional(3D) numerical model of six-degrees-of-freedom(6DOF) is applied to simulate the water entries of twin spheres side-by-side at different lateral distances and time *** turbulence structure is described using the shear-stress transport k-ω(SST k-ω) model, and the volume of fluid(VOF) method is used to track the complex air-liquid interface. The motion of spheres during water entry is simulated using an independent overset grid. The numerical model is verified by comparing the cavity evolution results from simulations and experiments. Numerical results reveal that the time interval between the twin water entries evidently affects cavity expansion and contraction behaviors in the radial direction. However, this influence is significantly weakened by increasing the lateral distance between the two spheres. In synchronous water entries, pressure is reduced on the midline of two cavities during surface closure, which is directly related to the cavity volume. The evolution of vortexes inside the two cavities is analyzed using a velocity vector field, which is affected by the lateral distance and time interval of water entries.

关键词： Twin water entries side-by-side Cavity Numerical simulation

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A Review on Vibration Control of Multiple Cylinders Subjected to FlowInduced Vibrations

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China Ocean Engineering 2024年第2期38卷 183-197页

作者： XU Wan-hai MA Ye-xuan State Key Laboratory of Hydraulic Engineering Intelligent Construction and Operation Tianjin UniversityTianjin 300350China Institute of Mechanics Chinese Academy of SciencesBeijing 100190China

The fatigue damage caused by flow-induced vibration(FIV)is one of the major concerns for multiple cylindrical structures in many engineering *** FIV suppression is of great importance for the security of many cylindrical *** active and passive control methods have been employed for the vibration suppression of an isolated cylinder undergoing vortex-induced vibrations(VIV).The FIV suppression methods are mainly extended to the multiple cylinders from the vibration control of the isolated *** to the mutual interference between the multiple cylinders,the FIV mechanism is more complex than the VIV mechanism,which makes a great challenge for the FIV *** efforts have been devoted to vibration suppression of multiple cylinder systems undergoing FIV over the past two *** control methods,such as helical strakes,splitter plates,control rods and flexible sheets,are not always effective,depending on many influence factors,such as the spacing ratio,the arrangement geometrical shape,the flow velocity and the parameters of the vibration control *** FIV response,hydrodynamic features and wake patterns of the multiple cylinders equipped with vibration control devices are reviewed and *** FIV suppression efficiency of the vibration control methods are analyzed and compared considering different influence *** research on the FIV suppression of multiple cylinders is suggested to provide insight for the development of FIV control methods and promote engineering applications of FIV control methods.

关键词： flow-induced vibration vibration control multiple cylinders tandem side-by-side staggered

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Hydrodynamic Interactions of Three Barges in Close Proximity in A Floatover Installation

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China Ocean Engineering 2016年第3期30卷 343-358页

作者：许鑫李欣杨建民肖龙飞 State Key Laboratory of Ocean Engineering Shanghai Jiao Tong University

The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coefficients in the frequency domain were calculated for both the system of multiple bodies and the isolated body using both low-order and higher-order boundary-element methods with different element numbers. In these calculations, the damping-lid method was used to modify the free-surface boundary conditions in the gap and to make the hydrodynamic results more reasonable. Then far-field, mid-field and near-field methods were used to calculate wave-drift forces for both the multi-body system and the isolated body. The results show that the higher-order method has faster convergence speed than the low-order method for the multi-body case. Comparison of different methods of computing drift force showed that mid-field and far-field methods have better convergence than the near-field method. In addition, corresponding model tests were performed in the Deepwater Offshore Basin at Shanghai Jiao Tong University. Comparison between numerical and experimental results showed good agreement.

关键词： multi-body side-by-side hydrodynamic interaction floatover

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Analysis of Mission Task Loading Based on the External Disturbance

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Journal of Computer and Communications 2015年第11期3卷 92-98页

作者： Eunghyun Lee Suhwan Kim Yongjin Kwon Departmant of Industrial Engineering Ajou University Suwon South Korea 1st Division 3rd Department Agency for Defense Development Daejeon South Korea

This research investigates the impact of changing weather conditions on the crew members who sit in a side-by-side cockpit, which is unusual for attack helicopters. Extensive review conducted by the authors fails to locate similar studies;hence a helicopter simulator is developed in order to conduct the experiments. The simulator represents the realistic flight characteristics as well as the digital cockpit instruments that contain the advanced mission equipment. During the experiments, a camcorder is used to record the pilots to accurately analyze the task completion time and the physical motions of both pilots. NASA-TLX is also used to collect the workload data to assess the impact of task assignments among the pilots. The analytical findings from this study will be instrumental in improving the cockpit design for enhanced mission effectiveness.

关键词： Attack Helicopter Task Assignment Weather-Related Pilot Workload TLX side-by-side Cockpit

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基于多参考帧的平行立体视频视间编码的实现

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电视技术 2012年第5期36卷 12-14页

作者：王凌杰周军上海交通大学图像通信与信息处理研究所上海200240

side-by-side(SbS)是立体视频常用的格式。传统的视频编码方法利用帧内预测或帧间预测对视频进行压缩编码。基于H.264视频压缩编码标准,针对SbS格式的立体视频提出了一种基于多参考帧方式的视间预测编码方法,并在JM测试代码基础上将其... 详细信息

side-by-side(SbS)是立体视频常用的格式。传统的视频编码方法利用帧内预测或帧间预测对视频进行压缩编码。基于H.264视频压缩编码标准,针对SbS格式的立体视频提出了一种基于多参考帧方式的视间预测编码方法,并在JM测试代码基础上将其实现。实验结果表明,加入视间预测编码后,以很小的PSNR损失为代价,使得SbS视频的压缩效率提高了大约10%～20%。

关键词： side-by-side 立体视频 H.264 视间预测

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