Study On General Performance Of Jack-Up Under Elevated Condition Based On Quasi-Static Method

With the development of the oil engineering, the jack-up, as an important equipment of oil exploitation, has been widely used. Under the elevating condition, the jack-up suffers the tough environment loads besides self-weight, and it's very important to evaluate the global performance in order to check the safety of the jack-up. Especially, when the water depth is increasing, the length of legs and the flexibility of the jack-up are increasing and the environment becomes more and more harsh. All of these become the challenge of the traditional research method.In this thesis, considering the dynamic effects, a "quasi-static" method is used to evaluate the general performance of a jack-up under elevating condition using the FEM software ANSYS. The equivalent model and detail model of the jack-up are built with different calculation requires. The equivalent model is proved to be effective and is used in the time domain analysis of the jack-up and the calculation efficiency is increased greatly. The large displacement method and the geometric stiffness method are used to calculate the p-A effects of the jack-up. According to the results, it can be found that in the static analysis, the accuracy of the two methods is very close. In the dynamic analysis, the accuracy of the geometric stiffness method is lower. For the large displacement method, iteration is needed in the procedure which is time consuming, and the geometric stiffness method is a simplified method, so it would be better to choose a suitable method under the actual situation.For the "quasi-static" method, the key point is to get the dynamic amplification factor DAF which is also the emphasis of this thesis. The regular wave theory and random wave theory is separately used in the time domain analysis of jack-up, and DAF is computed using the structural responses. According to the comparison with the result of the single freedom method, it can be known that with the increasing of water depth, the traditional single freedom method could not meet the requirements, and it's necessary to use the time domain method to get the DAF. Comparing with the random wave analysis, the regular wave analysis is a more effective method to calculate DAF. At last, considering various kinds of environment factors, a comparatively complete method is formed to compute the general performance of jack-up and is applied to a 350 feet jack-up. The results have been approved by ABS and CCS. The method in this paper can evaluate the general performance of the jack-up with high accuracy and efficiency. At the same time, it can provide good advice for the designer and user of the jack-up.