Research On Vibration Characteristic Of Semi-submersible Tender Drilling Unit

With the rapid development of economy, the industry has a greater demand in oil. Energy crisis becomes a grand challenge of human beings. After decades’exploitation, the oil and gas fields onshore and offshore are exhausted. It is inevitable tend to exploit deepwater oil and gas. Semi-submersible platforms are more suitable for deep water and can bear large variable loads. What’s more, they are multifunctional. With the advantages, semi-submersible platforms become important equipments to exploit deepwater oil and gas. The structures and vibration characteristics of semi-submersible platforms are variable and complex. The operation of equipments can cause the vibration problem easily. It’s necessary to analyze the vibration characteristics, the response and the vibration reducing measure of semi-submersible platforms.In this paper, the research is based on a semi-submersible tender drilling unit. The research is carried out in these aspects:(1) Using software ANSYS to build up the finite element model of the platform. The method how to build the structure model is also studied.(2) The calculation and research of the natural vibration characteristics.(3) The calculation and research of vibration response which is caused by the equipments.(4) The calculation and research of vibration reduction measure. The research is described in detailed as follow:Firstly, the finite element model is built up by software ANSYS according to the structure characteristic. The main steel structure, equipments mass and the boundary conditions are included.Secondly, modal analysis method is introduced and the natural frequencies of local structures are calculated. Evaluation of decks’ natural frequencies is carried out according to "Guidance to Ship Vibration" published by CCS. The regularities of the characteristics of local structures are also summered.Thirdly, the calculation methods of excitation resource and damping are introduced.Fourthly, three calculation methods of vibration response are introduced. The vibration response analysis is calculated by finite element method. The results are evaluated according to ISO6954-2000E. The distribution of nodes with large response values is studied. Finally, vibration reduction measures of platforms are introduced. The vibration problems of target platform are summarized. The excitation equipments are isolated by elastic supports according to vibration isolation theory. And then, the vibration response calculation is carried out after the vibration isolation measure applied. The regularity of the vibration response reduction is summered.Equipments on semi-submersible platforms are variable and high-power. Excitation forces and moments of equipments are large. Large excitation forces can cause serious vibration problems. Vibration reduction measures can reduce the excitation forces transmitted to main structure and reduce the platform vibration response value.