凸起型螺旋导板扰流抑制试验研究

为深入研究安装螺旋导板的深水立管涡激振动规律,设计一种月牙凸起型螺旋导板抑振装置,月牙凸起采用橡胶材料,在凸起两端肋高最低处连接成螺旋状。通过变化螺旋导板的螺旋数、螺距及螺高等形状参数,在风-浪-流联合水槽中进行安装该抑振装置的立管涡激振动试验,研究该抑振装置对涡激振动的抑制效率及其对立管动力响应的影响规律。研究结果表明,凸起型螺旋导板可取得优异的抑制效率,有效地降低由漩涡脱落引起的横向振动幅值;随着螺旋数的增加,螺旋导板抑制效率有所提高,但增幅降低,增加螺距对抑制效率影响不大,而随着螺高的增加,抑制效率有较大增幅;同时该抑振装置能有效地扰乱立管振动的主导频率,各抑振立管模型在示波区间内基本没有出现明显的主导频率。     

月牙肋抑振装置对柔性立管涡激振动抑振作用的试验研究

海洋立管的涡激振动会对立管结构的疲劳寿命产生严重的影响。提出1种月牙肋抑振装置,通过在室内水槽中进行物理模型试验,研究该装置在涡激振动情况下对立管的抑振作用。测得该装置在立管表面不同布置方式时顺流向及横流向振动的应变时程曲线,使用DASP软件对所测数据进行分析处理,得到立管的振动幅值和功率谱。试验结果表明:这种月牙肋抑振装置可明显降低立管模型的振动幅值,且对振动频率有一定的影响,同时也表明不同的布置方式对立管的抑振效果也不相同。     

均匀来流下尾翼型抑振装置效果试验研究

基于控制尾流,阻止立管尾流漩涡脱落转换路径的涡激振动抑制机理,设计三角形尾翼、片状尾翼及交错尾翼等三种抑振装置。三种抑振装置分别安装于立管模型表面,立管模型采用外径为18 mm的透明有机玻璃管。通过在均匀流场中进行安装有该抑振装置的立管模型涡激振动试验,研究三种抑振装置对立管涡激振动的抑制效率,并通过与配重裸管的涡激振动数据对比,分析抑振装置对立管动力响应的影响规律。研究结果表明,三种抑振装置均取得了明显的抑振效果,与配重裸管相比,安装片状尾翼及交错尾翼的立管模型抑制效率可达90%以上,安装三角形尾翼后立管模型振动频率略有减小,而安装片状尾翼及交错尾翼的立管模型没有明显的主导频率。     

抑制涡激振动的螺旋列板设计参数研究

基于水池模型实验结果和工程设计经验,结合国内外试验数据,着重分析用于抑制海洋立管涡激振动的螺旋列板几何参数(鳍高和螺距)及覆盖率对立管涡激振动的影响;并对水动力直径和水动力系数的选取对预报涡激振动的影响进行了分析,进而提出了适合于海洋立管工程应用的螺旋列板几何和设计参数选取的建议,为螺旋列板工程应用、海洋立管强度和疲劳设计提供参考。     

新型海洋立管涡激振动抑振装置的敏感性试验

将月牙扰流器按"八"字布置于立管表面用以抑制立管涡激振动,为研究其抑振效果,分析其抑振敏感性,在大型波、浪、流水槽进行涡激振动抑振试验。试验中采用有机玻璃管模拟立管,立管模型长1.5m,外径18mm,壁厚2mm,两端铰接,外流速分别为0.6、0.7m/s。按照不同螺高、螺距及迎水面形式设计8根具有正八字、倒八字抑振装置的不同类型抑振管,同时设计一根与抑振管相同配重的裸管,在立管表面粘贴应变计以测得动态应变数据,经过数据处理得到立管振动位移值。通过各抑振管间以及抑振管与配重裸管之间横向振动位移幅值的对比,研究抑振装置的抑振敏感性。结果表明:在适当尺寸及布置形式条件下,表面按"八"字布置月牙扰流器能够有效抑制立管横向涡激振动;迎水面月牙布置形式不同,抑振效果略显不同,迎水面布置为倒八字其抑振效果优于正八字,但该种抑振装置仍可实现全向性;抑振装置的螺高、螺距对抑振效果有一定影响,螺高增大、螺距减小有利于提高抑振效果。     

海中输流立管涡激振动试验研究及疲劳寿命分析

为研究海洋立管涡激振动响应并预测其疲劳寿命,在中国海洋大学物理海洋实验室大型风-浪-流水槽进行海洋立管涡激振动模型试验.考虑管内流体的流动,运用相似理论将实际海洋立管缩放为试验模型,施加不同流速的外流,测得立管在涡旋脱落时顺流向及横向振动的应变时程曲线,根据实测结果,采用Miner理论对立管进行疲劳寿命分析.结果表明:立管横向振动比顺流向振动强烈,大约高一个数量级;随骀着外流流速的增加,管道横向及顺流向振动明显增加,立管的疲劳寿命降低;立管中部及端部振动比较强烈,疲劳寿命较其它位置处低,容易发生疲劳破坏.     

新型深水海洋输液立管涡激振动抑振装置试验研究

本文设计一种新型涡轮扰流抑振装置,并在风-浪-流联合水槽中通过试验研究了该抑振装置对海洋立管涡激振动的抑制效果。在试验中,针对该新型抑振装置,提出了4种不同结构设计参数,研究了在不同外流速下各种参数工况的抑制效果及振动规律。试验结果表明:涡轮扰流抑振装置不受来流方向的限制,有较强的适用性;同时,该抑振装置能明显降低立管由漩涡脱落引起的横向振动幅值,且流速越高,抑制效果越明显,最大抑制效果可达80.2%;另外,试验结果还表明该抑振装置对立管振动的主频率影响不大。     

螺旋列板——深水立管涡激振动抑制装置

立管是海洋油气开采中必不可少的组成部分,它承担着流体输送和钻探的重要功能。深水立管在来流作用下容易产生涡激振动,涡激振动是造成立管疲劳破坏的主要原因之一,它会加速立管的疲劳破坏,因此需要采取适当的措施抑制深水立管涡激振动。海洋工程中涡激振动的削弱方法多是在立管外侧添加抑制装置,螺旋列板作为一种广泛应用的深水立管涡激振动抑制装置,在墨西哥湾、北海、西非等深水项目中有多年的应用。文中介绍了螺旋列板的设计、加工制作及安装方法,着重阐述了列板形状尺寸、海洋生物、包覆比例等对其抑制效率的影响,最后对螺旋列板的未来发展方向进行了展望。     

三根附属控制杆对海洋立管涡激振动抑制作用实验研究

海洋立管的涡激振动会严重影响立管结构的使用寿命.通过室内水槽实验研究在立管模型周围等分布置三根附属控制杆来减小立管涡激振动响应的新型抑制措施.实验中观测了0.24 m/s、0.31 m/s、0.37 m/s以及0.44 m/s四种均匀流和两个极限来流方向下的涡激振动抑制效果.实验结果表明:三根附属控制杆抑制措施可明显降低立管模型的横向振动幅值,但对主管的振动频率改变不大;同时,这一抑制措施对来流方向有较强的适应性,避免了以往单根控制杆在流向发生改变时可能加剧立管涡激振动的弊端.     

质量比对柔性立管涡激振动影响实验研究

质量比是影响海洋立管涡激振动的一个重要因素.通过在室内物理实验中使立管模型内部分别充填空气、水和沙来改变立管的质量比,从而研究质量比对柔性细长立管涡激振动的影响.实验结果表明:在相同流速下,质量比大的立管模型所激起的模态更高.在低约化速度区域,空管和水管的涡激振动响应频率与涡脱落频率相同,沙管的响应频率则与自振频率更接近,三种质量比立管的响应位移较接近;在高约化速度区域,三种质量比的立管模型的响应频率处于自振频率和涡脱落频率之间,但空管的响应频率随约化速度的增大而不断增大,同一流速下,质量比大的立管模型响应位移小,其中空管的涡激振动响应一直处于大振幅的锁定状态下.共振区域对应约化速度的范围随着质量比增大而减小.     

Experimental Study on Response Performance of VIV of A Flexible Riser with Helical Strakes

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.     

Experimental Study on Response Performance of VIV of A Flexible Riser with Helical Strakes

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.     

Experimental investigation of the effects of the coverage of helical strakes on the vortex-induced vibration response of a flexible riser

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.     

VIV response of a long flexible riser fitted with strakes in uniform and linearly sheared currents

An experimental investigation was conducted on a flexible riser with and without various strake arrangements. The aim of the present work was to further improve the understanding of the response performance of the vortex-induced vibration (VIV) of a riser with helical strakes. Two current profiles, including uniform and linearly sheared flows, were simulated. The uniform current was simulated by towing the riser model in one direction using the towing carriage, and the linearly sheared current was simulated by fixing one end of the riser and using a driven cantilever to traverse a circular arc. Based on the modal superposition method, the displacement responses were obtained from the measured strain. Strakes with different heights and pitches were analysed, and response parameters such as the displacement response and fatigue damage were studied. The results of the bare model test show that the lock-in phenomenon displays multi-order characteristics, and the VIV displacement decreases with an increased order of the lock-in regime. The results of the straked model test indicate that the response characteristics of a bare riser can be quite distinct from those of a riser with helical strakes, and the response performance depends closely on the geometry of the strake configuration.     

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

Helical strakes have been widely applied for suppressing the vibration of flexible cylinders undergoing vortexshedding in offshore engineering. However, 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 unclear. In this paper, the response characteristics of two side-by-side flexible cylinders with and without helical strakes were experimentally investigated in a towing tank. The 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 tendons. The center-to-center distance of the two cylinders was 3.0D. The 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 tank. Experimental results, including the displacement amplitude, the dominant frequency, the dominant mode,and the mean drag force coefficient, were summarized and discussed. For 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 cylinder. For 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.     

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser (SCR) is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration (VIV), which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow (CF) and in-line (IL). When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.     

Passive VIV Reduction of An Inclined Flexible Cylinder by Means of Helical Strakes with Round-Section

A series of experimental tests of passive VIV suppression of an inclined flexible cylinder with round-sectioned helical strakes were carried out in a towing tank. During the tests, the cylinder models fitted with and without helical strakes were towed along the tank. The towing velocity ranged from 0.05 to 1.0 m/s with an interval of 0.05 m/s.Four different yaw angles(a=0°, 15°, 30° and 45°), defined as the angle between the axis of the cylinder and the plane orthogonal of the oncoming flow, were selected in the experiment. The main purpose of present experimental work is to further investigate the VIV suppression effectiveness of round-sectioned helical strakes on the inclined flexible cylinder. The VIV responses of the smooth cylinder and the cylinder with square-sectioned strakes under the same experimental condition were also presented for comparison. The experimental results indicated that the roundsectioned strake basically had a similar effect on VIV suppression compared with the square-sectioned one, and both can significantly reduce the VIV of the vertical cylinder which corresponded to the case of a=0°. But with the increase of yaw angle, the VIV suppression effectiveness of both round-and square-section strakes deteriorated dramatically, the staked cylinder even had a much stronger vibration than the smooth one did in the in-line(IL)direction.     

大长细比柔性杆件涡激振动实验

涡激振动(vortex-induced vibration,VIV)是导致深海细长柔性立管发生疲劳破坏的重要因素。采用实验观测手段研究了长细比为1 750的柔性立管多模态涡激振动特性。实验中,通过采用拖车拖拉立管模型在水池中匀速行进来模拟均匀流作用下的涡激振动响应。利用光纤光栅传感器测量立管模型在横流向(cross-flow,CF)和顺流向(in-line,IL)的应变,进而通过模态分解的方法,获得立管模型涡激振动的位移。在此基础上,研究了CF以及IL方向的响应频率、位移标准差的平均值和最大值等随流速的变化规律,并分析了立管模型上测点的运动轨迹及其影响因素。     

基于可靠性的海洋立管疲劳安全系数研究

综合考虑了立管疲劳安全系数取值的相关因素——立管的安全等级、设计寿命、检验周期、载荷和损伤计算方法等的不确定性,提出了基于可靠度的疲劳安全系数确定方法,筛选了用于计算波致疲劳和VIV(涡激振动)疲劳的随机变量,给出了立管波致疲劳与VIV疲劳安全系数的计算流程,并以某SCR(钢悬链线立管)为例进行了安全系数计算。结果表明,该方法的计算结果优于传统的安全系数确定方法,尤其适合于特殊工程方案或新颖设计的立管疲劳校核。     

Experimental Investigation on Vortex-Induced Vibration of Steel Catenary Riser

Steel catenary riser(SCR) is the transmission device between the seabed and the floating production facilities. As developments move into deeper water, the fatigue life of the riser can become critical to the whole production system, especially due to the vortex-induced vibration(VIV), which is the key factor to operational longevity. As a result, experimental investigation about VIV of the riser was performed in a large plane pool which is 60 m long, 36 m wide and 6.5 m deep. Experiments were developed to study the influence of current speed and seabed on VIV of SCR. The results show that amplitudes of strain and response frequencies increase with the current speed both in cross-flow(CF) and in-line(IL). When the current speed is high, multi-mode response is observed in the VIV motion. The amplitudes of strain in IL direction are not much smaller than those in CF direction. The seabed has influence on the response frequencies of riser and the positions of damage for riser.