极浅水单点系泊FPSO低频响应分析
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摘要
对单点系泊FPSO在极浅水中波浪作用下的低频响应进行频域数值计算与模型试验研究,水深16.7m,入射波有义波高4.1m。计算结果与试验结果符合良好。试验中的波浪校验结果显示,在不规则波浪谱中出现明显的低频成分。由此产生了一阶低频波浪力,其能量谱是通常二阶波浪力谱的近百倍,导致FPSO在极浅水中所受低频波浪力大大增加,并引起极大幅度的共振纵荡运动响应。极浅水时,低频纵荡运动响应主要是一阶的,二阶成分几乎可以忽略,而且与深水相比,由于阻尼和二阶波浪力同时增加,二阶响应变化不大。低频浅水长波和一阶低频波浪力及其诱导大幅运动响应会给极浅水FPSO和系泊系统设计带来严重影响,在水动力性能预报时必须仔细予以考虑。
The low frequency(LF) response of a single point moored FPSO exposed to irregular waves in ultra-shallow water is investigated by conducting frequency domain computations and wave basin model tests.The water depth is 16.7m and the incident wave height is Hs=4.1m.It is shown that the agreement of results between calculation and experimentation is good.In terms of the measured wave spectrum by wave calibration in the wave basin,it can be seen that an obvious LF part appears.As a result,the first order LF wave force exists and is much larger than the second one.The difference of the spectrums is about one hundred times.The LF wave drift force increases enormously.Consequently,much larger resonant surge response is induced.The surge response is almost the same as the first order one and the second order one is almost negligible.The second order response changes indistinctively with the decrease of the water depth,since both the second order wave force and the damping increase.Therefore,in ultra-shallow water,LF part of incident waves should be taken into account carefully in the prediction of the hydrodynamic response of a single point moored FPSO due to the very serious wave induced LF response.
The low frequency(LF) response of a single point moored FPSO exposed to irregular waves in ultra-shallow water is investigated by conducting frequency domain computations and wave basin model tests.The water depth is 16.7m and the incident wave height is Hs=4.1m.It is shown that the agreement of results between calculation and experimentation is good.In terms of the measured wave spectrum by wave calibration in the wave basin,it can be seen that an obvious LF part appears.As a result,the first order LF wave force exists and is much larger than the second one.The difference of the spectrums is about one hundred times.The LF wave drift force increases enormously.Consequently,much larger resonant surge response is induced.The surge response is almost the same as the first order one and the second order one is almost negligible.The second order response changes indistinctively with the decrease of the water depth,since both the second order wave force and the damping increase.Therefore,in ultra-shallow water,LF part of incident waves should be taken into account carefully in the prediction of the hydrodynamic response of a single point moored FPSO due to the very serious wave induced LF response.
引文
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[2]肖龙飞,杨建民,范模,彭涛.160kDWT FPSO在极浅水中运动安全性研究[J].船舶力学,2006,10(1):7-14.
[3]王依群.减小海上浮式生产储油船与软刚臂系泊装置振动及相对运动措施的探讨[J].世界地震工程,1998,14(3):54-57.
[4]Li X,Yang J M,Xiao L F.Motion analysis on a large FPSO in shallow water[C]//Proc.of the 13th ISOPE Conf.Honolulu,Hawaii,USA:ISOPE,2003:235-239.
[5]肖龙飞,杨建民,王敏声等.浅水FPSO运动固有周期特性[J].上海交通大学学报,2005,39(5):686-690.
[6]余小川,谢永和,李润培等.水深对超大型FPSO运动响应与波浪载荷的影响[J].上海交通大学学报,2005,39(5):674-677.
[7]Naciri M,Buchner B,Bunnik T,et al.Low frequency motions of LNG carriers moored in shallow water[C]//Proc.of the23rd Int.Conf.on Offshore Mechanics and Arctic Engineering.Vancouver,BC,Canada,2004,3:995-1006.
[8]Aranha J A P.Formula for‘wave damping’in the drift of a floating body[J].Journal of Fluid Mechanics,1994,275:147-155.
[9]邹志利.水波理论及其应用[M].北京:科学出版社,2005.
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