分层流体中内波与半潜平台相互作用的模型试验

EXPERIMENTS ON INTERACTION OF INTERNAL WAVES WITH SEMI-SUBMERSIBLE PLATFORM IN A STRATIFIED FLUID

对密度分层流体中内波与半潜平台的相互作用问题进行了模型试验研究.采用摇板方法进行了内波造波试验,对内波波长、周期和波高进行了测量分析,获得了内波波高和波长与周期之间的相关关系.利用激光和倾角仪方法对半潜平台的纵荡和纵摇运动响应进行了测量分析,获得了平台纵荡运动及纵摇角幅值与内波周期之间的相关关系.结果表明,在半潜平台的设计与应用中,内波对其运动响应的影响是不可忽视的.特别地,发现了在内波周期的某个范围内,半潜平台的纵荡和纵摇都会出现倍频周期运动响应的现象.

In ocean engineering hydrodynamics,the fluid is mostly assumed with constant density.However, the density does change in oceans owing to variations in salinity and temperature in the vertical direction through the water.Internal waves are abundant in stratified oceans.Such waves are known to produce significant effects on hydrodynamic characteristics of offshore structures.The aim of this paper is to present the experimental results on the interaction of internal waves in a stratified fluid with a semi-submersible platform.The wavelength, the waveheight as well as the wave period of the internal wave generated by the rocker-flap wave maker are measured;the relations on both the wavelength and the wave height with the wave period are obtained.Both the laser and the clinometer are applied to measure the surge and pitch responses of the semi-submersible platform due to the internal waves,and the relations on the amplitudes of the surge and pitch motions for the platform with the wave periods of internal waves are obtained.Results show that the influence of internal waves on the motion responses of the semi-submersible platforms can not be neglected in their designs and applications.In particular,the sum-frequency effect of the motion response of the semi-submersible platform due to internal waves is found over a wide range of wave periods.