| As a deep sea oil platform, a Spar platform’s adaptation to water depth is from500m to3000m. In the ocean, the Spar platform affords a variety of environmentalloads, such as the wind, waves and current, the loads of waves and current give thegreatest impact on marine structures, thus, the paper uses AQWA software to researchthe motion stability of the Spar platform under wave and current. At the same time,the paper also researches the mooring system and the cable tension problem. Thespecific work and conclusions are as follows:The paper introduces the characteristics and the current research of the Sparplatform simply from the development process of the Spar platform, the overallperformance and the structural characteristics. The direction of the paper isdetermined by reviewing the study on the nonlinear dynamic responses of the Sparplatform under wave and current and the mooring system at home and abroad.The heave-pitch coupled motion equations of Spar platform is established byusing the rigid body dynamics theory, and it is also simplified in the paper. Thecalculation methods of the mooring force, the current force and the wave force aregiven in the paper.The first-order approximate solution is obtained by using the multiple scales tosolve the heave-pitch coupled equations which include the current force, the AQWAsoftware is used for simulation. The conclusion is when the current is added, thephenomenon of internal resonance is not changed, so as the resonance frequency ofthe Spar.The second-order slow drift force of surge is also studied when the current isadded, the conclusions are as follows: when the incident direction of the wave and current is same（180degree）, the current will increase the second-order slow driftforce of surge greatly in wave direction; when the wave-current angle is90degree,the current can be added without impact on the second-order slow drift force of surgein wave direction; when the wave and current reverse, the current will reduce thesecond-order slow drift force of surge in wave direction.The cable tension is studied by changing the wave-current angle, the layout ofthe mooring, and the initial pre-tension angle, at four groups of mooring lines, thecable tension, surge motion, heave motion and pitch motion are analyzed when acable is broken. The conclusions are as follows: In mooring system, the cable tensionat fairlead is the greatest in the whole mooring lines; under the action of the differentwave-current angles, when the wave and current are in the same direction (180degree),the cable tension in fairleads is the greatest in wave direction. Although the cabletension is the greatest, the security factor of cable is within the limits of thespecification, and will not in danger; however, at the junction of wire rope and chaincables, the security factor needs to be checked, because the breaking tension of thewire rope is small but its tension is large; with increasing of the wave-current angle,the cable tension in wave direction will decrease, but contrary to the wave direction,the cable tension will increase, to a certain extent, the change of the current angle willaffect the distribution of cable tension; when the environmental conditions and theparameters of the mooring lines are same, the maximum cable tension of four groupof mooring lines at fairlead in wave direction is greater than the cable tension of threegroup of mooring lines; when the initial pre-tension angle increases, the cable tensionwill increase greatly, it will have some effect on the security factor of cables; whenthe incident direction of wave and current are same (180degree), in wave direction,the cable tension near the breaking cable will increase greatly if one cable is broken,this may make the cables fracture; in addition, compared to the complete mooringsystems, when one cable is broken, the surge motion will increase strongly, but theeffect to the heave and pitch motions are small, in certain circumstances, the platformis still work properly as long as the other cables are complete. |
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