Numerical And Experimental Study On Performance Of Truss Spar In The Process Of Wet Tow And Upending

As oil resource on the land and near the coast is going to be exhausted, oil exploration is extending to deepwater. As one of the most prospective floating structures for deepwater oil exploration , Spar platform has become one of the hottest topic in ocean engineering field. Wet tow and upending are the common processes for Spar transportation and installation, hence the performance of spar in these procedures is important for the structure design and project design. The thesis presents numerical and experimental research on the performance of Truss Spar in the process of wet tow and upending.Experimental and numerical study has been done on the hydrodynamic performance of Spar during wet tow. Through model test, including decay test, tow resistance test, RAO test and wave test, the natural period, damping coefficient, tow resistance curve, RAO, motion response, relative wave elevation on the heave plates and load were gained. At the meanwhile, based on the potential flow theory, numerical calculation in the frequency-domain and time-domain was done, calculation results are compared with model test results.Under DNV max condition for wet tow with Hs=5.0m, roll, pitch and heave response are acceptable at bow sea and bow quartering sea condition. In the irregular wave with Hs=3.0m,roll, pitch and heave response are small at all 5 different headings. The relative wave elevations on the heave plates at bow quartering sea condition are larger than that at other conditions. At the heading of 90o, 135oand 180o, relative wave elevation on the edge of the upper heave plate is the largest, while at the heading of 45o and 0o, relative wave elevation at the center of upper heave plate and lower heave plate are the larger than other places. The effect of wave and current on the roll, pitch and heave response is not significant, but it is importance to the drift force.Research on the upending experiment method has been done, such as model design, technique of measurement and upending simulation, flooding equipment design and so on. The process of upending has been successfully simulated in deepwater basin, based on which the performance of Spar during upending, including the motion response and global bending moment were obtained.Based on the ballast condition of Spar in the upending process, the floating condition and global bending moment at the connection section between hard tank and truss was calculated. The resulted indicates that the maximum response of sway, surge, heave and roll are 42m, 90m, 34m and 42o respectively. During upending, the global bending moment at the connection section between hard tank and truss increases dramatically first and then decrease gradually to zero, and the maximum value is 780MN.m, occurring at the moment of start pumping water to the hard tank.The results and conclusions presented and discussed in the paper has great meaning, which could provide valuable reference for further research and practice in real operations.