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1.
Experimental Study on Coupled Cross-Flow and in-Line Vortex-Induced Vibration of Flexible Risers 总被引：1，自引：1，他引：0
In this work, we study the coupled cross-flow and in-line vortex-induced vibration （VIV） of a fixedly mounted flexible pipe, which is free to move in cross-flow （ Y- ） and in-line （ X- ） direction in a fluid flow where the mass and natural frequencies are precisely the same in both X- and Y-direction. The fluid speed varies from low to high with the corresponding vortex shedding frequency varying from below the first natural frequency to above the second natural frequency of the flexible pipe. Particular emphasis was placed on the investigation of the relationship between in-line and cross-flow vibration. The experimental results analyzed by using these measurements exhibits several valuable features. 相似文献
2.
Ji-ning Song Lin Lu Bin Teng Han-il Park Guo-qiang Tang Hao Wu 《Ocean Engineering》2011,38(11-12):1308-1322
Laboratory tests have been conducted on vortex-induced vibration (VIV) of a long flexible riser towed horizontally in a wave basin. The riser model has an external diameter of 16 mm and a total length of 28.0 m giving an aspect ratio of about 1750. Reynolds numbers ranged from about 3000 to 10,000. Fiber optic grating strain gages are adopted to measure the dynamic response in both cross-flow and in-line directions. The cross-flow vibrations were observed to vibrate at modes up to 6 and the in-line reached up to 12. The fundamental response frequencies can be predicted by a Strouhal number of about 0.18. Multi-mode responses and the asymmetry of the bare pipe response in uniform flow were observed and analyzed. The experimental results confirmed that the riser pipe vibrated multi-modally despite it being subject to a uniform current profile and all of the excited modes vibrated at the Strouhal frequency. The asymmetrical distribution of displacement mainly resulted from the modal composition. Higher harmonics of the VIV response such as the third, fourth and fifth harmonics frequencies were found to be steady over the entire duration of the test even if they varied along the length of the riser pipe. 相似文献
3.
管内流动会影响输流管的振动响应,目前关于输流弹性管涡激振动方面的研究较少。基于计算流体力学(CFD)方法,开展内外流对细长输流弹性管振动特性影响的研究。首先在不考虑内流的情况下将弹性管涡激振动数值预报结果与模型试验数据进行对比,验证了数值方法的可靠性。再者考虑内外流耦合作用情况下,对不同内流流速下细长输流弹性管振动位移时—空分布、顺流向最大平均偏移、振动轨迹、内部横向涡的形成与分布等进行了对比分析。结果发现,与外流流速相比,内流流速的增加虽然难以改变弹性管的主振模态,但对沿管体的振动强度影响显著。顺流向最大偏移处管体运动轨迹发生明显的变形和跳跃。在剪切外流和均匀内流对弹性管的联合作用下,沿管跨方向模态间能量转换频繁,伴随着间歇性出现或消失的沿弹性管传播的行波组分,这主要归因于复杂的双重流固耦合系统(外流—管体,内流—管体)。在内流以附加质量力、离心力和科氏力形式的激励下,弹性管内二次流现象明显。在振动过程中,内部横向涡沿管壁生成、脱落并逐渐散布于整个横截面。 相似文献
4.
Analytical solution of mean top tension of long flexible riser in modeling vortex-induced vibrations
The vortex-induced vibration (VIV) of flexible long riser with combined in-line and cross-flow motion has been studied using a wake oscillator in this paper. The analytical solution of mean top tension of long flexible riser is evaluated and compared with experimental results, and good agreement is observed to verify its validity. Then the nonlinear coupled dynamics of the in-line and cross-flow VIV of a long tension-dominated riser were analyzed through wake oscillator model with the consideration of variation of the mean top tension. The in-line and cross-flow resonant frequencies, lift and drag coefficients, dominant mode numbers, amplitudes and instantaneous deflections are reported and compared with experimental results, and excellent agreements are observed. The comparison of mode numbers between the calculation with and without consideration of variation of mean top tension shows that the proposed analytical solution of the mean top tension can produce a better prediction of multi-mode VIV. 相似文献
5.
To analyze the stress wave propagation associated with the vortex-induced vibration (VIV) of a marine riser, this paper employed a multi-signal complex exponential method. This method is an extension of the classical Prony''s method which decomposes a complicated signal into a number of complex exponential components. Because the proposed method processes multiple signals simultaneously, it can estimate the "global" dominating frequencies (poles) shared by those signals. The complex amplitude (residues) corresponding to the estimated frequencies for those signals is also obtained in the process. As the signals were collected at different locations along the axial direction of a marine riser, the phenomena of the stress wave propagation could be analyzed through the obtained residues of those signals. The Norwegian Deepwater Program (NDP) high mode test data were utilized in the numerical studies, including data sets in both the in-line (IL) and cross-flow (CF) directions. It was found that the most dominant component in the IL direction has its stress wave propagation along the riser being dominated by a standing wave, while that in the CF direction dominated by a traveling wave. 相似文献
6.
A numerical study based on a wake oscillator model was conducted to determine the response performance of vortex-induced vibration(VIV) on a long flexible cylinder with pinned-pinned boundary conditions subjected to linear and exponential shear flows. The coupling equations of a structural vibration model and wake oscillator model were solved using a standard central finite difference method of the second order. The VIV response characteristics including the structural displacement, structural frequency, structural wavenumber, standing wave behavior,travelling wave behavior, structural velocity, lift force coefficient and transferred energy from the fluid to the structure with different flow profiles were compared. The numerical results show that the VIV displacement is a combination of standing waves and travelling waves. For linear shear flow, standing waves and travelling waves dominate the VIV response within the low-velocity and high-velocity zones, respectively. The negative values of the transferred energy only occur within the low-velocity zone. However, for exponential shear flow, travelling waves dominate the VIV response and the negative energy occurs along the entire length of the cylinder. 相似文献
7.
In order to investigate the effect of internal friction of umbilical cable on its vortex-induced vibration(VIV)responses, the experimental study on VIV of bond umbilical cable(BUC) and un-bond umbilical cable(UBUC) was carried out in an experimental tank. A current generator in the laboratory simulated the uniform current, and the current velocities were observed in real time by using a Doppler Velocimeter. In addition, different sizes of top tension were applied to the umbilical cable model. The VIV responses of the umbilical cable model were measured by using Fiber Bragg grating(FBG) strain sensors. The displacement responses of umbilical cable model were reconstructed based on the experimental strain data processed by modal superposition method. In this paper, the traveling wave characteristics, the spatial-temporal distribution characteristics of frequency and fatigue damage of the BUC and UBUC under VIV are studied. The experimental results show that there are obvious differences between BUC and UBUC in the response characteristics of VIV. The UBUC appears the traveling wave sooner than BUC, but its standing wave characteristics are more obvious than those of BUC at high velocities. Compared with BUC, the spatial-temporal distribution of UBUC frequencies appears wide-band distribution sooner, but has narrower bandwidth in the "lock-in" state. The level of fatigue damage of BUC was approximately the same as that of UBUC. 相似文献
8.
The dynamic characteristics of marine risers/pipes often present serried modes with various frequencies due to high levels of structural flexibility and slenderness, especially when the flow velocity is non-uniformly distributed along the span. Therefore, the vortex-induced vibration (hence VIV) for slender risers/pipes is usually characterized by multi-mode motions. In this paper, by means of a newly developed empirical mode decomposition (EMD) method which contributes to more efficient instantaneous multi-mode identification and analysis, new characteristics of a multi-mode “lock-in” vibration process of a large-scale flexible pipe subject to shear flow were discussed. Because the two-degree vibration along the span can be analyzed simultaneously, the effects of multi-mode VIV were investigated systematically. From the given illustrative examples, it was found that the vibration energy diffusion between the fluid and the structure, and among the participating modes, may be repeatable and reversible, or even irreversible, which causes VIV to be highly intricate. The coexistence of multiple modes, energy transfer, and mode switching/jump is observed when the reduced velocity is relatively high. The multi-dominant mode phenomenon is also found in both cross-flow (CF) and in-line (IL) VIVs. Energy transfers between the CF and IL directions occasionally occur, and CF VIV is apt to dominate the vibration process, because it is superior to IL VIV with the increment of the reduced velocity. 相似文献
9.
Experimental Study on Response Performance of VIV of A Flexible Riser
with Helical Strakes 总被引：1，自引：1，他引：0
Laboratory tests were conducted on a flexible riser with and without helical strakes. The aim of the present work is to further understand the response performance of the vortex induced vibration (VIV) for a riser with helical strakes. The experiment was accomplished in the towing tank and the relative current was simulated by towing a flexible riser in one direction. Based on the modal analysis method, the displacement responses can be obtained by the measured strain. The strakes with different heights are analyzed here, and the response parameters like strain response and displacement response are studied. The experimental results show that the in-line (IL) response is as important as the cross-flow (CF) response, however, many industrial analysis methods usually ignore the IL response due to VIV. The results also indicate that the response characteristics of a bare riser can be quite distinct from that of a riser with helical strakes, and the response performance depends on the geometry on the helical strakes closely. The fatigue damage is further discussed and the results show that the fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. 相似文献
10.
《中国海洋工程》2015,(5)
Laboratory tests were conducted on a flexible riser with and without helical strakes. The aim of the present work is to further understand the response performance of the vortex induced vibration(VIV) for a riser with helical strakes. The experiment was accomplished in the towing tank and the relative current was simulated by towing a flexible riser in one direction. Based on the modal analysis method, the displacement responses can be obtained by the measured strain. The strakes with different heights are analyzed here, and the response parameters like strain response and displacement response are studied. The experimental results show that the in-line(IL) response is as important as the cross-flow(CF) response, however, many industrial analysis methods usually ignore the IL response due to VIV. The results also indicate that the response characteristics of a bare riser can be quite distinct from that of a riser with helical strakes, and the response performance depends on the geometry on the helical strakes closely. The fatigue damage is further discussed and the results show that the fatigue damage in the CF direction is of the same order as that in the IL direction for the bare riser. However, for the riser with helical strakes, the fatigue damage in the CF direction is much smaller than that in the IL direction. 相似文献
11.
The effects of different helical strake coverage on the vortex-induced vibration (VIV) of a model flexible riser were studied experimentally, with the aim of further improving the understanding of VIV responses. Uniform and linearly sheared currents were simulated to study response parameters such as non-dimensional displacement, fatigue damage, suppression efficiency, and the comprehensive evaluation is further studied. Test results of the bare model for a uniform current showed that the behavior of both the standing wave and traveling wave dominated VIV displacement. However, for a linearly sheared current, traveling wave behavior dominated VIV displacement in the high-velocity range. The results of the straked model tests indicated that the response was strongly dependent upon the amount of coverage of helical strakes. The flexible riser with 75% strake coverage gave the best comprehensive evaluation in a uniform current, and 50% strake coverage gave the best comprehensive evaluation in a linearly sheared current. 相似文献
12.
Based on the full water-wave equation, a second-order analytic solution for nonlinear interaction of short edge waves on a constant plane sloping bottom is presented in this paper. For special case of slope angle b=p/2, this solution can be reduced to the same order solution of deep water gravity surface waves traveling along parallel coastline. Interactions between two edge waves including progressive, standing and partially reflected standing waves were also discussed. The unified analytic expressions with transfer functions for kinematic-dynamic elements of edge waves were also discussed. The random model of the unified wave motion processes for linear and nonlinear irregular edge waves is formulated, and the corresponding theoretical autocorrelation and spectral density functions of the first and second orders are derived. The boundary conditions for the determining determination of the parameters of short edge wave are suggested, that may be seen as one special simple edge wave excitation mechanism and an extension to the sea wave refraction theory. Finally some computation results are demonstrated. 相似文献
13.
Based on the full water-wave equation,a second-order analytic solution for nonlinear interaction of short edge waves on a plane sloping bottom is presented in this paper.For special case of slope angle β=π/2,this solution can reduced to the same order solution of deep water gravity surface waves traveling along parallel coastline.Interactions between two edge waves including progressive,standing and partially reflected standing waves are also discussed.The unified analytic expressions with transfer functions for kinematic-dynamic elements of edge waves are also given.The random model of the unified wave motion processes for linear and nonlinear irregular edge waves is formulated,and the corresponding theoretical autocorrelation and spectral density functions of the first and the second orders are derived.The boundary conditions for the determination of the parameters of short edge wave are suggested,that may be seen as one special simple edge wave excitation mechanism and an extension to the sea wave refraction theory.Finally some computation results are demonstrated. 相似文献
14.
Experimental Investigation of Instantaneous Properties of Wave Slamming on the Plate 总被引：1，自引：0，他引：1
The purpose of this paper is to investigate the instantaneous properties of wave slamming on the plate structure of an open structure.The advanced instantaneous measuring technique-Particle Image Velocimetry(PIV) is applied to acquire the instantaneous velocity field of wave slamming.From the cross-correlation analysis results of the images captured by the CCD camera,the flow fields of wave impacting on the structure are displayed visually,and the instantaneous whole-field fluid velocity vectors are obtained.The relation between the instantaneous peak impacting pressures and the instantaneous velocities of water particles is studied by probability analysis. 相似文献
15.
The determination of the characteristics of a standing wave boundary layer, such as water particle velocities and shear stresses, is a vital issue in the prediction of sediment transport rate. Thus, an accurate measure of boundary layer characteristics is a key factor in the study of the wave boundary layer. In this study, a fiber-optic laser Doppler velocimeter (FLDV) is applied to directly measure the velocity profile in the standing wave boundary layer. As the experimental data presented in this paper, the antinode points of standing waves are found to move in the temporal domain. The previous second-order solution for a standing wave boundary layer is insufficient for the prediction of larger Ursell numbers. 相似文献
16.
In this study, a set of generalized analytical solutions are developed for the wave-induced response of a saturated porous seabed under plane strain condition. When considering the water waves originating in deep water and travelling towards the shore, their velocities, lengths and heights vary. Depending on the characteristics of the wave and the properties of the seabed, different formulations (fully dynamic, partly dynamic, quasi-static) for the wave-induced response of the seabed are possible. The solutions for the response with these formulations are established in terms of non-dimensional parameters. The results are presented in terms of pore pressure, shear stress and vertical effective stress distributions within the seabed. For typical values of wave period and seabed permeability, the regions of applicability of the three formulations are identified and plotted in parametric spaces. With given wave and seabed characteristics, these regions provide quick identification of the appropriate formulation for an adequate evaluation of the wave-induced seabed response. 相似文献
17.
A model test with a steel catenary riser (SCR) was conducted in a towing tank. The main purpose of the experiment was to gain further understanding of the global SCR dynamic behavior with vortex-induced vibration (VIV). To this end, a large model scale factor (250) was considered. The mass and stiffness of the riser model are very low, and the Reynolds number in the experiment ranged from 400 to 600. The experimental results demonstrated the influence of traveling waves on the cross-flow response of the riser model, which was verified by several analytical methods. This study provided important indications that the sources of the traveling waves (power-in regions) seem to change position along the riser length over time. Finally, the experimental design, data processing procedure, experimental set-up, and results are described in detail. 相似文献
18.
An experimental and numerical study of the freak wave speed 总被引：2，自引：2，他引：0
The propagation speed is one of the most important characteristics for describing freak waves. The research of freak wave speed is not only helpful for understanding the generation mechanism and evolution process of freak waves, but also applicable to the prediction. A stable and accurate method is proposed for the calculation of the freak wave speed, in which physical model tests are carried out to measure the motion of the largest wave crest along the wave tank. The linear regression relationship between the spatial position of the largest wave crest and instantaneous moment is established to calculate the speed of totally 248 cases of experimental freak waves and 312 supplementary cases of numerical freak waves. Based on the calculate results, a semitheoretical and semiempirical formula is proposed by using a regression analysis method to predict the speed of the freak wave, and the nonlinear characteristic of the freak wave speed is also investigated. 相似文献
19.
应用基于势流理论的时域高阶边界元方法,建立一个完全非线性的三维数值波浪水槽,通过实时模拟推板造波运动的方式产生波浪。通过混合欧拉-拉格朗日方法和四阶Runge-Kutta方法更新自由水面和造波板的瞬时位置。利用所建模型分别模拟了有限水深波和浅水波,与试验结果、相关文献结果和浅水理论结果吻合较好,且波浪能够稳定传播。系统地讨论造波板的运动圆频率、振幅和水深等对波浪传播和波浪特性的影响,并对波浪的非线性特性进行分析,研究发现造波板运动频率、运动振幅以及水深均将对波浪形态和波浪非线性产生显著影响。结果为真实水槽造波机的运动控制以及波浪生成试验提供了依据,便于实验室设置更合理的参数来准确模拟不同条件下的波浪。 相似文献
20.
利用东矶列岛海域一年实测波浪资料,统计分析波要素特征,以台风“利奇马”为例,分析台风浪演变过程。结果表明：研究海域年平均有效波高0.88 m,年平均周期4.3 s,年最大波高8.67 m出现在夏季台风“利奇马”影响时。研究海域以轻浪为主,其次是小浪和中浪;常浪向为ESE,次常浪向为E和SE;强浪向为SSE,次强浪向为SE。波浪平均持续时间和波高之间符合指数衰减关系。台风“利奇马”影响期间,最大谱峰56.20 m2/Hz,台风浪谱型以双峰谱为主,台风浪类型经历了涌浪—混合浪—风浪—混合浪—涌浪这一演变过程。 相似文献