RPD Analysis Of A Jack-up Unit During Jacking Operation

Benefited from the movability, relatively low cost and good performance in storm, jack-up units are widely used in oil and gas industry for drilling. Although research about jack-up units are focused on stability during transit, spudcan-soil interaction and structural dynamic response in elevated and storm condition nowadays, structural behavior during installation is very important.For a jack-up unit, localized failure or structural collapse may happen if installation were taken in severe sea state or bad seafloor foundation, and the direct cause of above failure is buckling of brace members of leg between upper and lower guides. Rack phase difference (RPD) as an indicator of brace load is studied in this paper to assure the safety and avoid the tremendous loss for a jack-up unit in the design phase. The primary work included in this paper are:1) Introduce the background, definition, measurement, classification and cause of formation of RPD, and also a dissertation about state of art is given, such as sensitivity analysis of leg brace configuration with regard to RPD using 2D FEA model and time domain simulation of RPD during jacking operation, also conclusions are discussed in this paper.2) Establish the time-domain simulation program of RPD during jacking operation, including building principles of FEA model, method to simplify the jacking system as a function of vertical reaction force verse moving-up velocity, and also the way to control the model displacement using above function.3) Calculate environmental load and establish the way how the load be applied on FEA model in time domain; Define the boundary condition at seafloor point and how to consider it in the FEA model.4) Using L780 Modâ…¤as structural model, do sensitivity analysis of RPD during jacking operation with regard to wave load, wind load, and boundary condition at seafloor point.