Simulation Study On Static And Dynamic Mechanical Characteristics Of Marine Tower

With the massive exploition of deep-sea petroleum and natural gas resources, offshore floating platform, used to deep-sea petroleum exploration and development, will be paid more and more attention. As the key parts of floating platform of drilling rig hoisting system, offshore derrick is not only bearing the conventional static load, but suffering the effect of dynamic load from wind, wave, current and etc. Its stress condition is very complex. In our country the research and design of offshore derrick is still at groping stage. In order to ensure reasonable, safe and reliable of this structure, it is great significance for carrying out the research about static and dynamic mechanical properties of offshore derrick.The paper takes the tower derrick as the research object which is widely used on offshore drilling platform at present, the finite element model of the offshore tower derrick was established through the simplification and assumptions of the structure. A certain scale model derrick was designed and constructed, and to verify the correctness of the finite element model, the comparative study of the test and the simulation was launched, and then extended to the finite element model of the offshore tower derrick to analyze the static and dynamic mechanical properties of it. The concrete research contents are as follows:(1) According to the structural parameters of the actual derrick and through reasonable simplification and hypothesis, the tower derrick geometric model was built using Pro/Engineer software, and input it into ANSYS, and after setting the unit material parameters and sizes sections of the bars, meshing, the finite element model of the offshore tower derrick was finished.(2) According to the structure parameters of the offshore tower derrick, the model derrick is designed and bulit with the scaling factor14, and the static and modal test of the model derrick were done. According to the structure parameters of the model derrick, the modeling method is applied which is the same as the offshore tower derrick’s, and finite element model of the model derrick is bulit. Meanwhile the corresponding static and modal tests were done. To promote the finite element model of offshore tower derrick, the results of test and simulation were compared, and the correctness of the finite element model is verified.(3) The static and stability was analyzed of the offshore tower derrick. The load of the derrick under constant load conditions, the maximum weight of drill string conditions, maximum hook load and the combination of three conditions with wind load were calculated, and the static analysis of all conditions was simulated and the static strength safety evaluation of offshore derrick was carried out. The stability of the derrick was analyzed to predict the theoretical buckling strength of the derrick, and the buckling critical load was obtained.(4) Studying on dynamic mechanical properties of the offshore tower derrick, the modal analysis, the analysis of dynamic response of tripping moment, harmonic response of periodic heave load and spectrum response of indirection ocean wave were done.Through the comparison of test of model derrick and its finite element model simulation the correctness of the finite element model of the offshore tower derrick was verified indirectly. Using the finite element model, the simulation research of the offshore derrick static and dynamic mechanical properties was completed, and the static and dynamic response characteristics of the derrick were found, which lay the theoretical foundation for offshore derrick safety assessment and structure optimization design.