Although the scope and use of flexible pipe systems in deepwater developments is expanding, the mechanical behavior for these environments is not fully understood. This is due to the complex response and interaction between multiple layers within the pipe system that introduces significant difficulties and constraints into the engineering analysis. As future developments look to extend the use of this technology to greater water depths and harsher operating conditions there is a need to develop advanced numerical tools that can evaluate the mechanical integrity of these complex hybrid pipe systems. Availability of increasingly advanced computational packages has enabled substantial improvements to be made in the complexity of simulation tools for combined loading, external pressure collapse and fretting. This study establishes a foundation for the development of advanced numerical modeling procedures to assess the collapse failure of composite flexible pipe systems for deepwater applications. Here, a continuum finite element model is constructed using the software package ABAQUS/Standard, and studied using non-linear (arc length) methods. The carcass, pressure armor and corresponding polymer layers are represented in detail and modeled with three dimensional solid brick elements in order to examine the interlayer relationships influencing collapse initiation. In many recent studies, an initial geometric imperfection in the form of general ovality is explored as the predominant bifurcation mode. A similar approach is adopted here, coupled with case studies chosen such as to facilitate validation against existing analytical and numerical data. The importance of element selection, contact mechanics, interface properties and initial imperfections on the system mechanical response and performance is presented and compared to the available literature.
The objective of this paper is to incorporate the outcomes of laboratory and physical testing carried out under the SIIBED program in order to develop, calibrate and validate a design tool for assessment of risk to subsea infrastructure due to ice keel interaction with pipelines, flexible flowlines, and electrical cables. This tool could then also be used to investigate load transfer to other subsea structures and facilities. A numerical modeling procedure is developed using the finite element analysis software Abaqus where the large deformation process of iceberg-pipe-soil interaction can be accommodated using the Coupled Eulerian Lagrangian (CEL) technique. The complexity of the ice-pipe-soil interaction is captured by appropriate and varied contact strategies in different areas of the model. Details of the model are discussed, including advancements of soil behavior and flexible flowline mechanical response, where it is desirable for the design tool to be optimized for computational efficiency while retaining reliable predictions of response. Case studies are presented for thick walled pipeline, flexible flowlines and electrical cables. Typically, the ice is modeled as a rigid body with unlimited strength. Limiting ice interaction forces, via pressure, is shown to have an effect on the displaced shape of the pipeline and flexible. Including radial compliance of the electrical cable is also shown to have an effect. With mesh refinement and retaining sufficient complexity in key areas, the complex model can be analyzed with a reasonable amount of computational cost. Advancements in the modeling of the ice feature strength limits are highlighted as well as application of large deformation modeling of electrical cables, which is atypical.
The move to reduce greenhouse gas emissions in the offshore hydrocarbons production industry has resulted in a growing interest in the possibility of using offshore wind to reduce on-platform power generation. While some offshore areas are progressing towards, or planning for, the use of offshore wind to electrify hydrocarbon producing platforms, they do not have some of the challenges associated with Newfoundland & Labrador's offshore environment. The authors are undertaking a study to investigate the feasibility of, and the benefits associated with the use of offshore floating wind to displace power generation for offshore hydrocarbon production platforms, thus reducing GHG emissions. The work is focusing on the applicability of potential concepts, services, supply chain, fabrication, facilities, and operations, and how these tie into various floating wind concepts and technologies that might be fabricated and assembled locally, and operated offshore Newfoundland & Labrador (NL). Electrification of offshore oil and gas production facilities through offshore wind could reduce the requirement for local power generation via turbine generators under normal operation. This paper examines the suitability of potential offshore floating wind concepts in the NL offshore, using wind energy to supply power to offshore facilities, reducing the need for fuel powered turbine generators, and thereby decreasing GHG emissions from power generation. The study looks at the full-field approach, from suitability of design to construction to operations and maintenance of offshore wind technology.
Accurate computation of tensile armor wire stresses remains a major challenge in flexible riser fatigue life predictions and integrity management. Accuracy of the results relies heavily on capturing the kinematics of the flexible’s helically contra-wound tensile armor layers and their interaction with the other metallic and thermo-plastic layers in a dynamic simulation. The standard industry practice to assess the fatigue life of flexibles is to use high fidelity 3D Finite Element Models (FEMs) to capture the complex kinematics and produce accurate stresses. However, direct simulation of flexible riser detailed FEMs is limited to regular wave analyses and computation of wire stress time-histories subjected to irregular waves have been computationally infeasible. This is due to the complexity of the nonlinear FEM and the long simulation time of the irregular wave environment coupled with large number of fatigue sea states. As a result, simplified approaches which do not directly simulate the local model and instead assume that wire stresses can be interpolated based on static stress versus curvature material curves within a pre-defined tension /pressure envelope have been utilized. This paper utilizes Nonlinear Dynamic Substructuring (NDS), a simulation-based approach that that extends the framework of dynamic substructuring to nonlinear problems. NDS enables the efficient nonlinear dynamic simulation of multiple pitch lengths of detailed flexible riser FEM subjected to irregular wave inputs and the computation of wire stress time-histories at any location on the local model. In this paper, a 14-inch diameter flexible riser under consideration by ExxonMobil is subjected to vessel motion and wave load in irregular wave environments and is modeled using a detailed 3D FEM and simulated via NDS. The flexible riser design features four tensile armor layers to mitigate localized lateral buckling of the wires near the touch down point. Tension and curvature time-histories of the riser near the hang-off, calculated from a conventional beam model global analysis, is used to drive a 5.1m long local model. Irregular wave wire stress time-histories extracted at the corners of the tensile armor wires are used to compute the fatigue life of the flexible. To demonstrate the inaccuracies associated with the regular wave approach, fatigue life is computed via the regular wave approach and compared against the irregular wave approach. It is shown that the NDS capability to efficiently compute irregular waves mitigates over- and under-predictions due to environment idealizations leading to a more accurate and reliable flexible riser life prediction and structural integrity assessment.
The nonlinear kinematic response of a damaged 2.5” flexible pipe under combined tensile and bending cyclic loads is simulated and compared to experimental results. High fidelity finite element model substructures are constructed for intact and broken outer and inner armor wire configurations and assembled in a nonlinear dynamic substructuring (NDS) framework to efficiently simulate the full-scale test configurations. Overall, 12 analysis configurations involving all intact wires, up to 4 broken outer wires, and 2 and 4 broken inner wires combined with 4 broken outer wires are constructed. Each analysis configuration is first preloaded axially and then subject to multiple cycles of (i) pure tension and (ii) combined tension and bending. For each case, tensile armor wire strains are extracted from the simulations and compared to strain measurements from the test. For all cases, numerical predictions and test measurements agree well accurately capturing the redistribution of strains into the adjacent intact wires which result in stress concentration factors. This comprehensive demonstration of accurate capture of flexible pipe damaged wire kinematics by high fidelity finite element models and nonlinear simulations has direct applications to flexible pipe integrity management and remnant life assessments. Given that the NDS framework allows highly efficient computation, it is now feasible to execute real-time irregular wave local fatigue simulations with finite element models that include damaged wire data from physical inspections to more accurately predict remnant life.
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