海流作用下多立柱式Spar平臺繞流流場與渦激運動特性研究
發(fā)布時間：2018-07-22 20:32
【摘要】：油氣資源在未來幾十年中仍將占據能源結構的主體地位，而隨著我國經濟發(fā)展，能源需求也日益增大，開發(fā)南海深水區(qū)域的油氣資源能夠有效緩解我國能源緊張的壓力。Spar平臺作為典型的深水浮式平臺，由于其具有穩(wěn)性好，垂蕩小，不受水深限制以及良好的經濟性等優(yōu)點，能夠成為開發(fā)南海油氣資源的理想選擇。本文所研究的新型多立柱式Spar平臺概念應用而生，其硬艙為四根圓柱方形陣列布置加方形中心井的形式，比傳統(tǒng)的單立柱式Spar平臺更易施工建造。 Spar平臺有著諸多優(yōu)點的同時，也面臨著一種特殊的困擾——渦激運動問題。Spar平臺的主體為典型的鈍體結構，當遭遇一定速度的海流作用時，主體上將會產生流動分離和旋渦脫落，進而引發(fā)較大幅度的垂直流向的運動。渦激運動會使得系泊纜和立管上產生較大的張力，對系泊系統(tǒng)和立管系統(tǒng)造成疲勞損傷，使得平臺整體的疲勞壽命降低。由于多柱式Spar平臺的各柱間會產生復雜的相互干擾，不同于常規(guī)的單立柱Spar平臺或半潛式平臺，因此對其開展相應的繞流和渦激運動研究具有重要意義。 本文通過數(shù)值計算方法，對平臺整體的繞流特性進行了分析。研究發(fā)現(xiàn)：由于平臺主體形式的特殊性，在15°和30°來流角下，平臺不再關于流向對稱，，此時平臺所受升力的均值不再為零；除了升力和阻力作用外，平臺還受到一定的力矩作用；平臺各柱渦結構會在尾流側匯聚，脫渦形式為單渦街。 在研究平臺整體繞流特性的同時，還發(fā)現(xiàn)各柱之間存在著復雜的相互干擾。平臺的方柱部分尾渦發(fā)展受到下游側圓柱的抑制，且30°來流角時一側的流動分離規(guī)律不同于單方柱繞流。平臺四圓柱部分中下游側圓柱受到的升力波動幅值更大，上游側圓柱在來流角較低時受到的阻力比單圓柱繞流時大，而在來流角較高時阻力小于單圓柱情況。 采用拖曳水池模型試驗手段，研究了是不同來流角、不同流速下平臺的渦激運動特性。通過對橫蕩運動、縱蕩運動、水平面內運動軌跡、首搖運動、渦脫頻率和水動力系數(shù)的分析，可得：在折合速度約為6~8范圍內，平臺橫蕩運動存在明顯的“鎖定”現(xiàn)象（0°來流角無側板時“鎖定”范圍約為Ur：7~10）。在0°來流角下較高流速時，減渦側板對渦激運動有明顯的抑制效果。平臺的運動軌跡近似與平臺硬艙截面的對角線平行（0°來流角除外），這不同于常規(guī)的單立柱Spar平臺。此外，試驗中還觀察到較明顯的首搖運動。在“鎖定”區(qū)間范圍內，平臺的脫渦頻率不再隨著流速的增大而線性增大，而是近似保持水平。 通過數(shù)值模擬方法，從繞流流場角度，對平臺的渦激運動現(xiàn)象開展了進一步的研究。相較于平臺固定繞流情況，由于平臺約束變?yōu)榱藦椥约s束，會在渦激力作用下產生渦激運動，平臺的尾渦結構會偏向于運動的反方向。在較高來流角下，平臺各柱的流動分離特性也會發(fā)生改變，分離位置和尾渦結構形式與固定繞流時有較明顯的區(qū)別。
[Abstract]:Oil and gas resources will still occupy the main position of energy structure in the next few decades, and with the development of China's economy and the increasing demand for energy, the development of the oil and gas resources in the deep water area of the South China Sea can effectively alleviate the pressure of.Spar as a typical deep-water floating platform, because of its good stability, small drooping and unaffected. The limitations of water depth and good economy can be an ideal choice for the development of the South China Sea oil and gas resources. The new multi column Spar platform studied in this paper has been applied and its hard module is arranged with four square cylindrical arrays with square center well, which is more easily constructed than the traditional single column Spar platform.
While the Spar platform has many advantages, it is also faced with a special problem - the main body of the.Spar platform of vortex excited motion is a typical blunt body structure. When the current is encountered at a certain speed, the main body will generate flow separation and vortex shedding and lead to a larger vertical direction movement. Vortex induced motion will make it possible The tension of mooring and riser causes fatigue damage to the mooring system and the riser system, which reduces the fatigue life of the platform as a whole. Due to the complex mutual interference between the columns of the multi column Spar platform, different from the conventional single column Spar platform or the semi submersible platform, the corresponding flow and vortex excitation are carried out. Sports research is of great significance.
In this paper, the flow behavior of the whole platform is analyzed by numerical method. It is found that, due to the particularity of the platform body form, the platform is no longer about the flow symmetry at the 15 and 30 degree angle, and the lifting force is no longer zero. Besides the lift and resistance, the platform is also subjected to a certain moment. The vortex structure of each column will converge on the wake side, and the vortex shedding form is single vortex street.
At the same time, it is found that there is a complex interaction between the columns. The development of the part tail vortex of the square column of the platform is restrained by the downstream side cylinder, and the flow separation law on one side is different from the single square column when the 30 degree angle is coming. The lift fluctuation amplitude of the middle and lower reaches of the four cylinder part of the platform is even more. The resistance of the upstream cylinder is larger than that of a single cylinder when the angle of flow is low, and the resistance of the upstream cylinder is smaller than that of a single cylinder when the flow angle is high.
The characteristics of the vortex excited motion of the platform with different flow angles and different velocities are studied by a towed pool model test. Through the analysis of the sway motion, the longitudinal motion, the moving trajectory in the horizontal plane, the head rolling, the vortex removal frequency and the hydrodynamic coefficient, the motion of the platform is obvious in the range of about 6~8. The "locking" phenomenon is about Ur:7~10 at the time of 0 degrees without side plates. At the high flow rate at the 0 degree angle, the vortex side plate has an obvious suppression effect on the vortex excitation. The trajectory of the platform is parallel to the diagonal of the platform section of the platform (except for the 0 degree angle), which is different from the conventional single column Spar platform. In the "lock" range, the frequency of the platform is no longer linearly increased with the increase of velocity, but the approximate maintenance level.
Through the numerical simulation, the vortex induced motion of the platform is further studied from the angle of flow around the flow field. Compared to the stationary flow situation of the platform, the vortex induced motion will be produced under the action of vortex excitation because the platform constraints become elastic constraints. The tail vortex structure of the platform will be biased toward the reverse direction of the motion. The flow separation characteristics of each column will also change. The separation position and the wake vortex structure are obviously different from the fixed flow.
【學位授予單位】：上海交通大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：U674.38;U661.1
[Abstract]:Oil and gas resources will still occupy the main position of energy structure in the next few decades, and with the development of China's economy and the increasing demand for energy, the development of the oil and gas resources in the deep water area of the South China Sea can effectively alleviate the pressure of.Spar as a typical deep-water floating platform, because of its good stability, small drooping and unaffected. The limitations of water depth and good economy can be an ideal choice for the development of the South China Sea oil and gas resources. The new multi column Spar platform studied in this paper has been applied and its hard module is arranged with four square cylindrical arrays with square center well, which is more easily constructed than the traditional single column Spar platform.
While the Spar platform has many advantages, it is also faced with a special problem - the main body of the.Spar platform of vortex excited motion is a typical blunt body structure. When the current is encountered at a certain speed, the main body will generate flow separation and vortex shedding and lead to a larger vertical direction movement. Vortex induced motion will make it possible The tension of mooring and riser causes fatigue damage to the mooring system and the riser system, which reduces the fatigue life of the platform as a whole. Due to the complex mutual interference between the columns of the multi column Spar platform, different from the conventional single column Spar platform or the semi submersible platform, the corresponding flow and vortex excitation are carried out. Sports research is of great significance.
In this paper, the flow behavior of the whole platform is analyzed by numerical method. It is found that, due to the particularity of the platform body form, the platform is no longer about the flow symmetry at the 15 and 30 degree angle, and the lifting force is no longer zero. Besides the lift and resistance, the platform is also subjected to a certain moment. The vortex structure of each column will converge on the wake side, and the vortex shedding form is single vortex street.
At the same time, it is found that there is a complex interaction between the columns. The development of the part tail vortex of the square column of the platform is restrained by the downstream side cylinder, and the flow separation law on one side is different from the single square column when the 30 degree angle is coming. The lift fluctuation amplitude of the middle and lower reaches of the four cylinder part of the platform is even more. The resistance of the upstream cylinder is larger than that of a single cylinder when the angle of flow is low, and the resistance of the upstream cylinder is smaller than that of a single cylinder when the flow angle is high.
The characteristics of the vortex excited motion of the platform with different flow angles and different velocities are studied by a towed pool model test. Through the analysis of the sway motion, the longitudinal motion, the moving trajectory in the horizontal plane, the head rolling, the vortex removal frequency and the hydrodynamic coefficient, the motion of the platform is obvious in the range of about 6~8. The "locking" phenomenon is about Ur:7~10 at the time of 0 degrees without side plates. At the high flow rate at the 0 degree angle, the vortex side plate has an obvious suppression effect on the vortex excitation. The trajectory of the platform is parallel to the diagonal of the platform section of the platform (except for the 0 degree angle), which is different from the conventional single column Spar platform. In the "lock" range, the frequency of the platform is no longer linearly increased with the increase of velocity, but the approximate maintenance level.
Through the numerical simulation, the vortex induced motion of the platform is further studied from the angle of flow around the flow field. Compared to the stationary flow situation of the platform, the vortex induced motion will be produced under the action of vortex excitation because the platform constraints become elastic constraints. The tail vortex structure of the platform will be biased toward the reverse direction of the motion. The flow separation characteristics of each column will also change. The separation position and the wake vortex structure are obviously different from the fixed flow.
【學位授予單位】：上海交通大學
【學位級別】：碩士
【學位授予年份】：2014
【分類號】：U674.38;U661.1
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