立管扰流装置Helical Strakes的数值模拟分析

泻涡脱落诱发的涡激振动是海洋立管疲劳破坏的主要诱因,利用Helical Strakes(螺旋侧板)抑制涡激振动对立管的损伤。通过CFD数值模拟软件,对光滑立管和覆盖两种不同螺旋侧板的立管,在不同的雷诺数下进行模拟分析。将得到拖曳力和升力结果与现有的数值和实验结果进行对比,得到相关的拖曳力系数和升力,研究Helical Strakes的相关特性。数值模拟结果表明,螺旋侧板可以影响拖曳力和升力的变化,扰乱流场,很好地抑制漩涡的产生。

Research on the Influence of Helical Strakes on Dynamic Response of Floating Wind Turbine Platform

The stability of platform structure is the paramount guarantee of the safe operation of the offshore floating wind turbine. The NREL 5MW floating wind turbine is established based on the OC3-Hywind Spar Buoy platform with the supplement of helical strakes for the purpose to analyze the impact of helical strakes on the dynamic response of the floating wind turbine Spar platform. The dynamic response of floating wind turbine Spar platform under wind, wave and current loading from the impact of number, height and pitch ratio of the helical strakes is analysed by the radiation and diffraction theory, the finite element method and orthogonal design method. The result reveals that the helical strakes can effectively inhibit the dynamic response of the platform but enlarge the wave exciting force; the best parameter combination is two pieces of helical strakes with the height of 15%D （D is the diameter of the platform） and the pitch ratio of 5; the height of the helical strake and its pitch ratio have significant influence on pitch response.

Influences of the Helical Strake Cross-Section Shape on Vortex-Induced Vibrations Suppression for A Long Flexible Cylinder

An experimental study on a bare flexible cylinder as well as cylinders fitted with two types of cross-sectioned helical strakes was carried out in a towing tank. The main purpose of this paper is to investigate the effects of strakes’ cross-section on the vortex-induced vibrations （VIV） suppression of a flexible cylinder. The square-sectioned and round-sectioned helical strakes were selected in the experimental tests. The uniform current was generated by towing the cylinder models along the tank using a towing carriage. The Reynolds number was in the range of 800–16000. The strain responses were measured by the strain gages in cross-flow （CF） and in-line （IL） directions. A modal analysis method was adopted to obtain the displacement responses using the strain signals in different measurement positions. The comparison of the experimental results among the bare cylinder, square-sectioned straked cylinder and round-sectioned straked cylinder was performed. The helical strakes can effectively reduce the strain amplitude, displacement amplitude, response frequencies and dominant modes of a flexible cylinder excited by VIV. And the mean drag coefficients of straked cylinders were approximately consistent with each other. In addition, the square-sectioned and round-sectioned strakes nearly share the similar VIV reduction behaviors. Sometimes, the strakes with round-section represent more excellent effects on the VIV suppression of response frequency than those with square-section.

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

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 tank.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.

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.

二维立管Helical Strakes绕流场的ANSYS-CFD分析

利用ANSYS-CFD软件模拟螺旋侧板(helical strakes)对立管涡激振动的抑制作用。对二维的光滑立管和覆盖两种不同螺旋侧板高程的立管,在不同的雷诺数下进行模拟分析,将得到拖曳力和升力结果与数值和实验结果进行对比表明,螺旋侧板可以影响拖曳力和升力的变化,扰乱流场,很好地抑制漩涡的产生。

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.

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.

Passive Control of Flow-Induced Vibration(FIV)by Helical Strakes for Two Staggered Flexible Cylinders

Helical strake is a widely-used device for passive flow-induced vibration(FIV)control of cylindrical structures.It is omnidirectional and can effectively reduce FIV response amplitude.Studies on the passive FIV control for cylindrical structures are mainly concerned with a single isolated cylinder,while the influence of wake interference between multiple cylinders on FIV suppression devices is less considered up to now.In engineering applications,multiple flexible cylinders with large aspect ratios can be subjected to complex flow forces,and the effects of wake interference are obvious.The FIV suppression effect of helical strake of a common configuration(17.5D pitch and 0.25D height,where D is the cylinder diameter)in two staggered cylinders system is still unknown.This paper systematically studied the FIV response of multiple cylinders system fitted with the helical strakes by model tests.The relative spatial position of the two cylinders is fixed at S=3.0D and T=8.0D,which ensures the cylindrical structures in the flow interference region.The experimental results show that the helical strakes effectively reduce the FIV response on staggered upstream cylinder,and the suppression efficiency is barely affected by the smooth or straked downstream cylinder.The corresponding FIV suppression efficiency on the downstream cylinder is remarkably reduced by the influence of the upstream wake flow.The wake-induced vibration(WIV)phenomenon is not observed on the staggered downstream cylinder,which normally occurs on the downstream straked cylinder in a tandem arrangement.

Experimental investigation of influence of strake wings on self-induced roll motion at high angles of attack

The modern high performance air vehicles are required to have extreme maneuverability,which includes the ability of controlled maneuvers at high angle of attack. However, the nonlinear and unsteady aerodynamic phenomena, such as flow separation, vortices interaction, and vortices breaking down, will occur during the flight at high angle of attack, which could induce the uncommanded motions for the air vehicles. For the high maneuverable and agile air missile, the nonlinear roll motions would occur at the high angle of attack. The present work is focused on the selfinduced nonlinear roll motion for a missile configuration and discusses the influence of the strake wings on the roll motion according to the results from free-to-roll test and PIV measurement using the models assembled with different strake wings at a = 60°. The free-to-roll results show that the model with whole strake wings(baseline), the model assembled with three strake wings(Case A)and the model assembled with two opposite strake wings(Case C) experience the spinning, while the model assembled with two adjacent strake wings(Case B), the model assembled with one strake wing(Case D) and the model with no strake wing(Case E) trim or slightly vibrate at a certain "×"rolling angle, which mean that the rolling stability can be improved by dismantling certain strake wings. The flow field results from PIV measurement show that the leeward asymmetric vortices are induced by the windward strake wings. The vortices would interact the strake wings and induce crossflow on the downstream fins to degrade the rolling stability of the model. This could be the main reason for the self-induced roll motion of the model at a = 60°.

Suppression of vortex-induced vibrations of a flexible riser by adding helical strakes

3-D computational fluid dynamics/ computational structure dynamics (CFD/CSD) numerical two-way coupling simulations are conducted for a flexible rise in order to study the dynamic response performance of the riser with and without helical strakes exposed to the vortex-induced vibration (VIV). The VIV responses of a PVC riser without helical strakes are computed and compared with experimental data, to verify the accuracy of the present two-way coupling method. Subsequently, the dynamic behaviors of a short PVC riser with different kinds of helical strakes are studied. The vibration amplitudes along the riser, the trajectories of the riser's monitor point and the vortex shedding contours are obtained in a series of simulations. The helical strakes5 VIV suppression mechanisms are found involving the breaking of the vortex structures and the reduction of the vortex shedding frequency of the bare riser. Moreover, a good suppression effect can be achieved by attaching the helical strake structure with a reasonable geometrical configuration (such as the appropriate strake height, strake pitch, the number of starts and strake coverages) to the flexible riser. The effect is also diverse at different reduced velocity (Ur). The remarkable effect is found at Ur = l for the short riser, with about 97% reduction in the transverse vibration response.

Simulation on effect of throat contraction ratio and strake stagger angle on flow field and aerodynamic performance of scrampressor

The design methods of typical supersonic aircraft intakes and shock wave compression technology have been applied to ram-rotor,an attractive compression system.A ram-rotor is of a typical structure including the compression ramp,the throat and the subsonic diffuser;a scrampressor is similar to ram-rotor,the only difference is that scrampressor has no subsonic diffuser.The work was the continuation of the preparatory work.In order to further study the effect of throat contraction ratio and strake stagger angle on the flow field and performance of a scrampressor,the flow field of a scrampressor with a three-dimensional flow path was numerically simulated with different throat contraction ratios and strake stagger angles.Simulated results indicated that the optional aerodynamic performance of a scrampressor could be achieved with an adiabatic efficiency of 0.8413atotal pressure recovery coefficient of 0.8446,a total pressure ratio of 7.14 and a static pressure ratio of 5.17for a throat contraction ratio of 0.6 and a strake stagger angle of 12°.It was therefore concluded that an appropriate decrease in throat contraction ratio and an increase in strake stagger angle could help the comprehensive improvement of a scrampressor in performance.

大兴安岭地区森林雷击火发生的时空分布

森林火灾是森林植被区最为重要的扰动因子,而雷击火是森林火灾的重要组成部分。大兴安岭地区频繁的森林火灾己成为当地经济发展的沉重压力和巨大威胁。利用地理信息技术、SPSS统计软件和m atlab等工具,分析了1966-2006年黑龙江省大兴安岭地区森林雷击火发生的时空演变规律。结果表明:上述41年间,该地区共发生森林雷击火560起,6月份是雷击火的高发期,而一天中15,16时又是雷击火的高发时段,且雷击火的发生存在着24 a的显著周期震荡和12 a,2 a的次显著周期震荡。同时,雷击火火场质心呈显著的带状分布,并有向东南偏移的趋势。此项研究可为大兴安岭林区科学有效地开展森林防火工作提供参考。

柔性立管涡激振动抑制装置试验研究

为深入研究带螺旋列板的柔性立管涡激振动响应特性,进行立管螺旋列板抑制装置的拖曳水池试验。由拖车拖动立管产生来流测得应变数据,基于模态叠加法获得立管位移响应等参数。分析螺旋列板抑制装置的螺距变化,系统研究不同螺旋列板状态下立管应变、位移响应等参数。结果表明,流向响应与横向响应同样重要不可忽略;裸管响应特性与带螺旋列板的立管响应特性区别较大,响应特性与螺旋列板几何形状紧密相关。

剪切来流下柔性立管涡激振动抑制装置试验研究

文章针对柔性立管螺旋列板抑制装置在剪切流场中的涡激振动响应特性进行了试验研究,试验过程中通过旋转臂架从而形成相对剪切来流。通过测试得到的应变数据,基于模态叠加法,可得到立管的位移响应等参数。试验中针对螺旋列板的螺距和鳍高的变化进行了分析,系统地研究了不同螺旋列板状态下立管的主导频率、主导模态、无量纲振幅比以及疲劳损伤等参数。研究结果表明:螺旋列板可以很好地抑制立管的涡激振动响应;与螺距相比,鳍高对立管涡激振动响应会带来更大的影响;剪切流场中立管螺距恒定为5.0D(D为立管外径)时,鳍高为0.15D时的立管具有最好的抑制效果。

运输机上翘后体侧鳍减阻技术研究

采用CFD方法研究运输机上翘后体的侧鳍减阻技术。研究了侧鳍安装角、长度及厚度等几何参数对减阻效果的影响,探索了侧鳍减阻的流动机理。研究结果表明:侧鳍通过对上翘后体流动的疏导与整流作用显著减小了机身阻力。同时,给出了侧鳍几何参数的影响规律和设计原则。

翼吊发动机短舱对三维增升装置的影响及改善措施研究

运用数值模拟方法,结合风洞试验数据,研究了翼吊发动机短舱对于增升装置气动性能的影响以及在发动机短舱的不同位置安装涡流片进行流动控制的效果。结果表明:翼吊发动机短舱挂架与机翼前缘结合处的缝翼缺口及大迎角时绕过短舱的分离气流会对三维增升装置造成不利影响,其主要表现为在主翼上方形成一个很大范围的低速流动区。在发动机短舱适当位置安装涡流片能明显改善增升装置的气动性能。主要机理在于:涡流片在大迎角时产生的强漩涡能向低速区内注入能量,搅动该区域的流动,从而减小低速流动区的范围。但是涡流片的位置必须进行优化,在不适当的位置安装涡流片会进一步恶化增升装置的气动性能。

大迎角下鸭翼涡与边条涡的干扰特性

在风洞测力、水洞染色线和激光片光实验的基础上 ,对翼身组合体鸭翼边条翼布局大迎角涡系干扰机理进行了分析和探讨 ,揭示了该布局增升的机理。鸭翼涡位于机翼内侧 ,其与边条涡的相互诱导致使边条涡向外翼偏折 ,既改善了外翼的流态 ,又使机翼前缘涡量卷入边条涡 ,增强了边条涡的强度 ,从而延迟其破裂。两方面的共同作用 ,提高了主翼的涡升力 。

材质对超高压压裂泵泵头体自增强性能的影响研究

以某型号的超高压压裂泵泵头体为研究对象,在改变其材料屈服强度的情况下,对其进行弹性有限元分析,得出其屈服强度和弹性承载能力的内在关系。在此基础上对自增强处理过程进行弹塑性有限元分析,可知提高泵头体的自增强性能应从材料的屈服强度和自增强内压两方面入手。

边条翼和近距鸭翼布局模型动态气动特性分析

针对边条翼与近距鸭翼这两类典型战斗机布局模型，在中国空气动力研究与发展中心FL-24风洞进行了大振幅俯仰动态试验与模型自由摇滚试验，并对比分析了边条翼与近距鸭翼布局模型高速大迎角的动态气动特性。结果表明：边条翼模型纵向动态特性明显优于近距鸭翼模型，尤其是俯仰力矩迟滞效应更强；近距鸭翼模型在攻角26°～45°区间出现了较大的滚转力矩，容易诱发摇滚运动；最后，通过自由摇滚试验验证了俯仰动态试验分析结论，即近距鸭翼模型在迎角大于30°后出现了极限环摇滚现象。