내부흐름을 고려한 해양생산라이저의 거동 분석에 관한 실험연구

Abstract

Ocean Production Riser is the slender structure to get the oil. It is classified into three types such as Top Tensioned Riser(TTR), Steel Catenary Riser(SCR) and flexible riser. TTR can be deployed for production at the fixed platforms or platforms with very reduced heave motion like the Tension Leg Platforms and Spar platforms. To analyze the TTR, many kinds of loads are considered. Especially floating structure's excitation induced by wave and internal flow are considered as the important factor.

To conduct the experiment, the oscillator is needed to make the motion of floating structure by the wave. At the model riser test, the motion can be measured by the video cameras. The waterproof housings are needed to put the camera in the water. The animation data can be gained by the cameras is analyzed into 2-D image analysis program. And this graph is calibrated by Matlab program.

Law of similarity is necessary to gain the reliable data from the experiment. In this study, geometry similarity and dynamic similarity is also considered. The physical data of model riser comes from the law of similarity. The velocity of internal flow and excitation period of oscillator is considered by Reynold's similarity and Froude similarity, respectively.

In this study, the experiments are conducted as two part. The first experiments are about the wave induced vibration. The second are about the resonance frequency.

At the first experiments, the behavior of the ocean production riser is analyzed in the four cases. The first is the motion analysis in the forcing excitation. The second is combined excitation. That is net force by forcing and parametric excitation. And the third is the motion analysis effected by forcing excitation and internal flow. The last is the case that combined excitation and internal flow work together. And at the second experiment, the excitation type is classified by two cases. The first case is focus on the resonance frequency. And the second case is the amplitude of excitation.

When the riser is effected by the wave excitation with internal flow, the riser motion is expressed into the correlation between the inertia force induced by motion of riser and the viscosity force by the internal flow.

And mode analysis is very important about a slender structure like riser. The riser motion become smaller toward higher mode about in-line direction. Also the motion is larger at the mode 3 and mode 6 about cross-line direction. It means that resonance periods of cross-line motion are around 1.5 seconds.