Research On The Key Mechanical Problems In Stinger Basic Design For Deep Water S-Lay

In the deep-water offshore oil and gas development, the laying of submarine pipelines faces enormous challenges. Using the classic S-lay technology, pipeline in the overbend section with large diameter will generate large bending deformation. To figure out this issue, J-lay is presented. But due to the low efficiency of the J-lay method, recently, deep sea S-lay technology made breakthroughs, and the design of the stinger is one of the key factors. However, it still exists great risks using S-lay technology in deep-water, such as the stinger design, which has many uncertain factors, especially in its basic design.Stinger comprises a main structure and aided devices. As the main study object, stinger structure is designed with sufficient length and rigidity simultaneously, to provide the overbend section with geometric boundary conditions. Particularly, it could be simplified as curved beam, and its curvature, length and rigidity are key factors in basic design.Stinger design loads are roller loads and inertia loads caused by hull motions. For deep sea S-lay, stinger sustains large pipe pressure, which is hard to be obtained under vessel motions. Meanwhile, the basic parameters of stinger is not only about tension, but it is all about pipeline. However, the relationship of these parameters is not described clearly, and this leads to lack of appropriate analysis and design theory for stinger design.To overcome these problems in stinger basic design, parameters relationship of stinger and pipeline is firstly researched. By analyzing the sagbend section, the departure angle and tension at the top of the pipe are obtained, based on which we discuss the overbend section, the relationship of stinger basic parameters and pipeline is studied, and the design model of stinger geometric parameters is finally gained, which include the curvature and length of stinger, the length and spacing of rollers, and also the static forces acting on rollers. Additionally, by condensing stinger structure stiffness to the points gotten in the geometric parameter design of stinger, and introducing the GAP element, a model for stinger stiffness design verification was proposed. Eventually, the relationship between pipeline, geometric parameters and stiffness of stinger is acquired. Meanwhile, for dynamic contact problems caused by pipelaying vessel motions in deep water S-lay, a substructure test model is presented. In this approach, the overbend section and stinger are treated as a substructure, the pipelaying vessel and the sagbend are simplified as equivalent excitation and lumped mass respectively. So, a large-scale of the stinger and the overbend section of the pipeline can be used, and there are no inherent limits to the scale of the laying system model, which is important for a deep water S-lay test model. The dynamic roller loads influenced by stinger stiffness and vessel movement are discussed based on the substructure test model. To resolve the dynamic roller load, the amplification factor is defined, and the envelope of the factors is received. This is a useful reference work for stinger design loads. Based on the test model, the measurement data are then used to carry out stinger fatigue life analyzes, the accumulative fatigue damage at hot spots during the stinger design life is finally evaluated using a CDM-based fatigue damage evolution model. And based on the conclusion of pipeline and stinger design analysis, a real-time pipelaying monitoring scheme based on the numerical model is proposed, this program can collect real-time data during laying to estimate the safe state of pipe and stinger, and protect both of them.Through numerical analysis and model tests, mechanical problems in stinger basic design process are solved, such as the relationship of the pipelay parameters, the roller loads, and the stinger design process is formulated, at the same time, a real-time safety monitoring and early warning scheme program for pipelaying is proposed, all of which provide technical support for deepwater S-lay and stinger design.