S-lay Installation Analysis for Deepwater Pipeline
|School||Harbin Engineering University|
|Course||Design and manufacture of ships and marine structures|
|Keywords||deepwater subsea pipeline s-lay pipe-laying ABAQUS finite element Matlab numerical iteration|
With the steady development of deepwater oil and gas exploitation, the subsea pipeline, as marine "lifeline", plays a more and more important role in this field. In different kinds of subsea pipeline projects, the construction design always proves to be a difficult point. Therefore, in order to keep abreast with the world’s deepwater oil and gas industry, the deepwater pipeline installation technology is indispensable for China’s offshore industry development. Although, for the time being, many domestic entrepreneurs and universities have performed widespread researches and studies, there are still many problems waiting to be solved due to the complexity of this technology itself.In our country, at the earlier stages of subsea pipeline installation, the towing methods are widely adopted; however, with the continual increase of water depth, many of the subsea pipelines are now installed by pipe-laying vessel method. In different kinds of pipe-laying methods, the S-lay method is greatly preferred. Especially with the birth of dynamic positioning S-lay vessel, this method can install subsea pipelines into deep areas with several kilometers water depth.First, this thesis, based on the widespread reading of relevant domestic and overseas s-lay references, has earnestly summarized the latest progress of domestic and overseas oil/gas exploitation and s-lay analysis. Then almost every kind of subsea pipeline installation method has been introduced in great detail, including their installation style, advantages arid disadvantages and scope of application. Besides, several deepwater s-lay numerical calculation methods have been detailedly presented.Second, this thesis has broken the over-dependence of OFFPIPE software for pipeline installation in industry and a case study of 600 meter subsea pipeline s-lay installation has been performed by the author for the first time, which includes the pipeline model creation, load steps definition, boundary conditions application and the concerned results extraction. In the case study, model creation and boundary conditions are realized by using ABAQUS/CAE, however, the current and wave loads should be applied in AQUA module by editing the.inp file. Moreover, by basing some reasonable model simplifications, this case study has derived almost all of the concerned results for static pipeline s-lay installation analysis, includes the pipeline s-shape configuration, the stress and strain distribution, the moment distribution and the tensioner tension etc., which are quite approximate the real s-lay configuration. The accuracy of these results is verified by another Matlab numerical iteration method in chapter four.Third, in order to verify the correctness of the case study results for the deepwater pipeline s-lay installation by ABAQUS, another novel Matlab numerical iteration model is adopted to perform the same case study. The originality of this method is comprehensively combine several previous s-lay theoretical research achievements to successfully finish the deepwater pipeline s-lay installation case study analysis, which include the theory of using the knowledge of material mechanics to calculate the moment, stress and strain in pipeline by assuming the overband pipe section to be an ideal circular arc, using the theoretical expressions proposed by Gu Yongning to calculation the curvature of the short pipeline section below the lift-off point, using the natural catenary method to approximately calculate the relationship between the tension and curvature in the sagband pipeline section, and using the elementary beam method to calculate the pipeline section from the touch-down point to the seabed part. The results derived from the Matlab numerical iteration method are quite close to that of by ABAQUS method, and the error of many key results are no more than 5%, which dramatically proves the accuracy of the calculating results by adopting the general finite element method.Finally, after the case study, some sensitivity analyses have been preformed with respect to the key parameters for deepwater s-lay method to obtain the loading characteristics and variation principles and to derive some meaningful conclusions for directing real projects. Finally, the development of domestic deepwater pipeline isntallation has been prospected in this thesis.