波浪作用下直立圆柱结构高频响应现象的研究
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摘要
当较大波浪与结构物作用时会引起结构的高频响应,对结构安全构成极大威胁。该文通过物理模型实验,考虑了不同波浪参数和结构尺度,对极限规则波浪作用下直立圆柱结构的受力进行模拟,观测结构高频响应现象并分析其形成机理。实验中发现,当波陡超过一定临界值,波浪作用下结构受力会出现"secondaryloadcycle"现象,同时伴随高频响应现象发生。进一步针对"secondary load cycle"现象进行分析表明,"secondary load cycle"现象主要受波浪陡度影响,当波浪陡度(H/L)大于0.095tanh(kh)时,结构就会产生"secondary load cycle"现象;而且高频响应远高于波浪高阶成分,它并非由波浪与结构物非线性作用产生,而是结构的一种高频自振现象。该现象产生的机理是由于波浪经过结构产生较大涌高,涌高水体坠落对结构产生瞬时的挤压,进而造成了结构的高频振动。
When a large wave interacts with a structure, it will cause high-frequency response of the structure, posing a great threat to marine structures. In the present paper, wave force of vertical cylinders under extreme regular waves were measured by a physical experiment, considering various wave parameters and structure scales. The high-frequency response phenomenon was observed and its mechanism was analyzed. It was found that when the wave steepness exceeded critical values, a secondary load cycle phenomenon appeared in the time series of wave force of the structure under the action of waves, and a high frequency response accompanied this phenomenon. Further analysis showed that secondary load cycle strongly depended on wave steepness.When the wave steepness was larger than the value of 0.095 tanh(kh), the secondary load cycle occurred. Moreover, the high-frequency response was much higher than the high-order components of the wave, which was not caused by the non-linear interaction between the wave and the structure, but was a kind of resonant of the structure. The mechanism of this phenomenon was due to the large run-up on the cylinder while waves passed the structure, and the falling of the runup led to an instant impact on the structure, which in turn caused structural high-frequency vibration.
When a large wave interacts with a structure, it will cause high-frequency response of the structure, posing a great threat to marine structures. In the present paper, wave force of vertical cylinders under extreme regular waves were measured by a physical experiment, considering various wave parameters and structure scales. The high-frequency response phenomenon was observed and its mechanism was analyzed. It was found that when the wave steepness exceeded critical values, a secondary load cycle phenomenon appeared in the time series of wave force of the structure under the action of waves, and a high frequency response accompanied this phenomenon. Further analysis showed that secondary load cycle strongly depended on wave steepness.When the wave steepness was larger than the value of 0.095 tanh(kh), the secondary load cycle occurred. Moreover, the high-frequency response was much higher than the high-order components of the wave, which was not caused by the non-linear interaction between the wave and the structure, but was a kind of resonant of the structure. The mechanism of this phenomenon was due to the large run-up on the cylinder while waves passed the structure, and the falling of the runup led to an instant impact on the structure, which in turn caused structural high-frequency vibration.
引文
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[15]RAINEY R.Weak or strong nonlinearity:the vital issue[J].Journal of Engineering Mathematics,2007:1-27.
[2]NATVIG B J,TEIGEN P.Review of hydrodynamic challenges in TLP design[J].International Journal of Offshore and Polar Engineering.1993,3(4):243-249.
[3]JEFFERYS R.A slender body model of ringing[C].In International Workshop for Water Waves and Floating Bodies,IWWWFB,Institute for Marine Dynamics,St John’s,Newfoundland,Canada,1993.
[4]FALTISEN O M,NEWMAN J N,VINJE T.Nonlinear wave loads on a slender vertical cylinder[J].Journal of Fluid Mechanism,1995,289:179-198.
[5]MALENIEA S,MOLIN B.Third-Harmonic wave diffraction by a vertical cylinder[J].Journal of Fluid Mechanics.1995,302:203-229.
[6]KROKSTAD J R,STANSBERG C T,NESTEGAARDA,et al.A new non-slender ringing load approach verified against experiments[J].Trans.ASME:Journal of Offshore Mechanics and Arctic Engineering,1998,120:20-29.
[7]HUSEBY M,GRUE J.An experimental investigation of higher-harmonic wave forces on a vertical cylinder[J].Journal of Fluid Mechanics,2000,414:75-103.
[8]BOO S Y.Measurements of higher harmonic wave forces on a vertical truncated circular cylinder[J].Ocean Engineering,2006,33:219-233.
[9]周斌珍.开敞水域完全非线性数值波浪模型的建立及在平台Ringing现象中的应用[D].大连理工大学,大连,中国,2013.Zhou Bin-zhen.Fully nonlinear numerical wave model in open water and its application in Ringing phenomenon of platform[D].Dalian University of Technology,Dalian,China,2013.
[10]CHAPLIN J R,RAINEY R C T,YEMM R W.Ringing of a vertical cylinder in waves[J].Journal of Fluid Mechanics,1997,350:119-147.
[11]GRUE J,HUSEBY M.Higher-harmonic wave forces and ringing of vertical cylinders[J].Applied Ocean Research,2002,24:203-214.
[12]RAINEY R.Weak or strong nonlinearity:the vital issue[J].Journal of Engineering Mathematics,2007:1-27.
[13]PAULSEN B T,Bredmose H,Bingham,H B,et al.Forcing of a bottom-mounted circular cylinder by steep regular water waves at finite depth[J].Journal of Fluid Mechanics,2014,755:1-34.
[14]LI J,WANG Z,LIU S.Experimental study of interactions between multi-directional focused wave and vertical circular cylinder,part II:Wave force[J].Coastal Engineering,2014,83:233-242.
[15]RAINEY R.Weak or strong nonlinearity:the vital issue[J].Journal of Engineering Mathematics,2007:1-27.
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