Dynamic behavior of blow out preventer (BOP)
Nowadays, the offshore is very extensive and of great economic value for gross development. Typically all kinds of offshore structure will experience storm loading and need to consider the influence of cyclic loading. When cyclic loading is applied, the soil failure mechanism and strength of soil should be changed, which means the cyclic analysis need to perform in the way different from static analysis. If designer ignore the effect of cyclic load, the failure or large plastic deformation will occur with increasing the number of cyclic loading.
I have studied the lateral displacement of conductor under influence of cyclic loading, and the numble of cyclic loading is 10, 100, 1000 and 10000 in the calculation, respectively. Moreover the soil modulus will be calculated from Matlab with the elastic pile theory (Lars Grande, Phd thesis 1976). During the cyclic loading, the soil degradation should be considered, therefore, the modified P-y curve for influence of cyclic loading is included which describes the change of soil. In terms of calculation, there are two types of BOP, 450 tons and 250 tons, meanwhile the horizontal cyclic loading equal to 2000 kN which is performed on BOP.
Then the natural frequency analysis is performed in last chapter. The natural frequencies of the conductor, BOP, wellhead and soil system have a significant influence on the system stability. The frequencies that correspond to the maxima magnification factor M which means the vibration could be magnified. Without the damping impact, when a frequency of cyclic loads equal to the natural frequencies of the system, the magnification factor will be infinite, while the damping is included, the factor will also meet a peak value when the two kinds of frequencies meet each other. Consequently the analysis will be operated for both two types BOP in this calculation. And The multiple-degree-of freedom model is operated in this case, therefore, the conductor is considered as an elastic pile which is divided into several elements and that conductor only connect soil with springs is included in this chapter.
Further work in connection to soil plasticity theory, can be developing more accuracy deflection calculation. When cyclic loading is considered, the plastic zone is developing around conductor, therefore the new soil model need to use for practical project.
Place, publisher, year, edition, pages
Institutt for bygg, anlegg og transport , 2012. , 87 p.
ntnudaim:7459, MSGEOTECH Geotechnics and Geohazards
IdentifiersURN: urn:nbn:no:ntnu:diva-18683Local ID: ntnudaim:7459OAI: oai:DiVA.org:ntnu-18683DiVA: diva2:566183
Grande, Lars Olav, ProfessorHolme, Jan