| Energy is an essential condition for the development of human society. In order to find new oil resource, oceans became the next choice. As a result, the development speed of Jack-up platform become faster which is used as the equipment for the exploitation of oil and gas. however, the environments which the Jack-up platform serviced in often subject to the earthquakes, waves, wind and ice.All of these may cause the vibration of the Jack-up. while the vibration of Jack-up platform become stronger, it may cause a variety of negative influence,such as: broke the equipment on the jack-up platform, affect the mental and physical health of the staff, even cause the platform damage. So, the study of jack-up platform vibration characteristics became very important. In this paper, a jack-up platform in the bohai sea was selected as the research object. The vibration characteristic and similar model experiment of this jack-up platform has be made. The major aspects of the research of this paper are shown as follows.1) Refer to Morison equation,the maximal horizontal wave force and maximal horizontal wave force torque of the jack-up platform is calculated, and the relationship function of them was drawn. The maximal horizontal wave force is 2.33 MN while the phase Angle theta is 40 °and the maximal horizontal wave force torque is 55.892 MN?m while the phase Angle theta is 40°.2) A CAD model based on the design parameters of the jack-up platform was build, and a test model with suitable water depth and condition was designed. The total height of the model is 500 mm. The size of the main hull is 100 x 150 x 50(mm),and the size of the counterweight block is 50 * 50 * 50(mm).The pile legs is replace by a pipe replacement which size is 6 mm.3)With the wave load which is calculate by the Morison equation, executed the statics analysis in the condition of the jack-up platform suffered to the wave load with different phase Angle theta. The result is when the jack-up platform suffered the maximum horizontal wave force torque and maximum horizontal wave force, in other words, when the phase Angle theta is 40 °,the hull will engender the maximal displacement which is 4.747 cm.When the phase Angle theta is 60 ° the pile will engender the maximal stress which is 15.216 Mpa. Moreover, as its height increased, the displacement of the jack-up platform also increase gradually, and show the trend to inclined to Y axis direction with the effect of wind load and wave load.4)Through using the finite element analysis software, the dynamics analysis analysis was carried out on the jack-up platform,which includes modal analysis, seismic response spectrum analysis and the fluid-structure interaction analysis. Through the modal analysis,the first three order natural frequency of the Jack-up platform is calculated which is 6.10 Hz, 6.12 Hz and 14.73 Hz, the first order vibration mode of the platform is vibrating along the X axis, the second is vibrating along the Y axis and the third order vibration mode is revere vibration around the Z axis. In the seismic response spectrum analysis, the displacement of the Jack-up platform under the seismic wave was done.The result shows that the peak displacement of the Jack-up platform under the action of EI- Centro NS seismic wave and Taft EW seismic wave is 0.2462 m and 0.2745 m.In the fluid-structure interaction analysis, the result of the fluid-structure interaction analysis is similar to the modal analysis.the first three order natural frequency is calculated which is 5.85 Hz,5.86 Hz and 14.56 Hz which is lower than the result in the modal analysis.5)The vibration modal experiment of the jack-up platform was planned and conducted,which included the hammering modal experiment and the seismic response experiment two parts. In the hammer modal experiment, the vibration mode of the platform is similar to the finite element analysis result.However the first three order natural frequency is calculated which is7.8Hz,97.05 Hz,136.17 Hz,which is quite different from the result of finite element analysis.In the seismic response experiment, the first order natural frequency is 4.43 Hz along the X axis, and the second order is 5.06 Hz along the Y axis.This Proved the accuracy of the finite element analysis and the correctness of the vibration table experiment. The hammering modal experiment was failed as the counterweight block absorb the hammer force.In addition, the peak displacement of the jack-up platform in the seismic response experiment is 0.188 m under EL-Centro NS and 0.2049 m under Taft EW, which is similar to the result of the seismic response spectrum analysis.In a word,this paper use the wave load theory, finite element analysis and experiment research to study the vibration characteristics of jack-up platform which laid foundation for applying the TMD device to the experiment model and studying its effect of vibration control. |
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