Research On Jacket Lauch Based On Field Measurement

With the development of offshore oil and gas in our country, the jacketplatform becomes more and more popular and the dimension of it increases.Therefore, jacket launch has become the most wildly used way for jacketinstallation. This paper presents the field measurement of a mega jacket launch.Model test and numerical simulation are also conducted in order to study thedifferences between these3methods.The field measurement is designed to record the trajectory of both thejacket and the launch barge. Both Inertial Navigation System (INS) and GlobalPositioning System (GPS) are used to ensure the accuracy of the fieldmeasurement. The GPS is used to measure the velocities of the jacket abovewater. When the jacket completely goes into water, the INS is used to measurethe accelerations of the launched jacket for GPS can’t work under water. Themotion time series of both the jacket and the barge are calculated. Accordingthe load distribution on barge rockers during launch, several FBG strain gaugeswere installed into the selected points which may have large strain.The motion results obtained in the field measurement show that the wholeprocess of jacket launch lasts about80seconds, which contains3main stagespurely sliding stage, sliding and rotating stage, up-righting stage. Themaximum depth the jacket can reach is about80~90m, and the maximum pitchangle of the jacket is about25°. The largest load on a single barge rocker isabout6000~7000t, which occurs in the moment when the COG of the jacket isright above the rocker arm shaft.In the model test, different initial trim angle of the barge were chosen tostudy the launch process. The results show that different initial trim angle haslittle effect on the jacket’s motion. But for the barge, large initial trim angle will result in a large pitch motion. A comparison between the field measurementand model test were conducted, whose results show that the key time pointscan’t match well in these two methods. This paper argues that this is becausethe difference of Reynolds number between model test and the actual situation.In the numerical simulation, different friction between the jacket andlaunch way were chosen to study the launch process. Results show that thefriction will have a large influence to the launch process, especially to the keytime point. With the same initial trim angle, draft and friction coefficient, thejacket’s motion obtained by numerical simulation is a little larger than that infield measurement. This may because the numerical simulation underestimatethe added mass and viscous damping of the jacket.