| As the demand of oil and gas for human increasing, and the storage land oil and gas falling sharply year by year, more and more people focus their attention on the development of Marine oil and gas. The Semi-submersible (SEMI), with its large deck space, good ability of motion and positioning performance, and large enough variable load, gradually become the mainstream exploration equipment for ocean engineering. The research object of this article is a novel SEMI platform, which has a lot of innovation on structural design. This new type of SEMI, with two non-symmetrical pontoons and without horizontal connection braces, is used as an accommodation/crane unit. A comprehensive research of the hydrodynamic characteristics, the motion response and the global strength has conducted in the present paper.First of all, it establishes the hydrodynamic models of the novels SEMI and other two conventional SEMIs, i.e., a twin symmetric pontoon SEMI with horizontal braces and a twin symmetric pontoon SEMI without horizontal braces. Then, the hydrodynamic performance of the novel SEMI is studied and compared with that of other two models in frequency domain. Numerical results demonstrate that there exist significant heave-roll/heave-pitch coupling effects for the novel SEMI due to the non-symmetrical pontoon shapes, requiring more attention to long wave whose period is close to the heave resonance period. And for the two pontoons SEMI, if the size and shape of two pontoons or the bow and stern of each pontoon have larger difference, the heave-roll/heave-pitch coupling effects would be more notable. And when the incident wave degree is 0°, the first order wave loads of the novel SEMI in surge, pitch and heave are generally the same with that of other two conventional SEMIs. But in sway, roll and yaw, the first order wave loads of the novel SEMI is largger than that of other two models.Secondly, the novel SEMI, Explorer Lifter, which is a lifting installation and accommodation facility, has a very strict requirement for motion response. Since working as a crane vessel, preventing capsizing is crucially important. Therefore the excursion of pitch and roll motion should be taken more attention, especially the roll motion response. Therefore, based on the hydrodynamic results, the motion response research of the new type of SEMI is conducted in the time domain under the joint action of wind, wave and current. It mainly analyzes the motion response characteristics of the novel SEMI under different wave direction and different wave period, respectively. The response results show that except the heave motion, other five motions are sensitive to wave direction; Heave-roll coupling effect influences the roll motion obviously, but the heave-pitch coupling effect has a little influence pitch motion.Finally, the unique structure form of the novel SEMI platform makes its global strength characteristics different from that of the traditional SEMI platform. Based on the design wave method, the global strength analysis of this novel SEMI is conducted. It studies the global strength characteristics of the novel SEMI, and compares it with that of a control SEMI model. The results show that the large column and the transverse deck connection areas, the columns and pontoons connection areas are mainly regions where the maximum Von Mises stress happens; and the large fillet radius shape for the joint area, where columns and deck connect with each other, is a effective design to improve the novel SEMI’s global strength. |
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