Research On Strength Assessment Of Self-elevating Drilling Units

The surroundings where the Jack-up is placed are very complicated. Jack-up is suffering from not only loads induced by winds, waves and current but also the sophisticated interaction with the bottom condition of the sea. These loads acting on the Jack-up shows obvious nonlinearity as well as dynamicity and randomicity. This paper is to discuss several problems in the strength assessment technology for self-elevating drilling units based on the practical demand of engineering, and the main contents are as follows:1. Research has been carried out on the calculation method of environmental loads for self-elevating drilling units. Loads induced by wind, wave, and current are calculated according to the related specifications. The morison force calculation program for Jack-up is modified and improved, including the module of coefficient selecting, the coordinate transformation of spatial bar system, the stretching of wave free-surface, the addition of current effect, the creation of random waves and its inversion program to the ocean wave spectrum, and also the random wave loads calculation program.2. The direct calculation method of self-elevating drilling units at specified location is explored, including the modeling technology of 3-D finite element model, the interface technology of MSC patran and the Morison force calculation program to perform the automatic application of wave loads, disposal of constraint and the connection method between the platform and the legs.3. The selection method of environmental parameter for self-elevating drilling units is discussed. A finite element analysis is platformed after the determination of load condition with the consideration of P-DELTA effect. The key failure mode of the Jack-up structure is found through the yielding and buckling assessment.4. The interface program between Nastran and the dynamic loads is developed, and the dynamic analysis procedure under the circumstance of regular waves and irregular waves is studied, Dynamic amplify effects and the extreme value of dynamic response is obtained via the simulation results.5. The interaction between spun can and soil is discussed. Taking advantage of the superiority of ABAQUS in the field of material nonlinear analysis, huge displacement analysis and contact analysis, the interaction between spud can and soil is preliminarily studied through numerical simulation method.6 The strength assessment method of the Jack-up in the transit condition is studied. Firstly, short-term prediction of Jack-up's motion is carried out, and then the results are compared with the values in the rules. Therefore the loads acting on the Jack-up can be obtained, and at last the strength assessment of the Jack-up in the transit condition is carried out.