During the end fitting (EF) mounting process, the tensile armor wires of flexible pipes are folded and then unfolded. This process usually leaves plastic deformations and generates sharp curvatures on these wires just at the EF entrance. Dissections performed in several flexible risers, which were in operation or subjected to qualification tests, revealed that this region is especially prone to fatigue failure thus affecting the overall performance of these structures. In this work, an analytical approach devoted to predict the stresses induced in the tensile armor wires at the EF entrance is combined with a previously presented methodology to compute the fatigue life of flexible risers in order to account for the EF mounting process. A parametric study is also conducted aiming at evaluating the effect of the folding radius, the stress level induced during pre-operational tests and the contact conditions between the epoxy resin and the tensile armor wires on the fatigue resistance of a free hanging flexible riser. These analyses indicate that the choice of the mean stress correction model, the folding radius and the stress level induced during the pre-operational tests significantly modify the fatigue resistance of the tensile armor wires. The contact conditions also influence the fatigue resistance, but their effect is less significant.
ResumoO procedimento mais realista para se efetuarem análises dinâmicas de risers flexíveis é o uso da análise no domínio do tempo. Análises no domínio do tempo conseguem levar em conta todas as não-linearidades inerentes ao sistema como a geométrica, a interação solo-estrutura, etc. Entretanto essas análises demandam um esforço computacional e um tempo de simulação muito grandes. Outros problemas associados às análises no domínio do tempo são: o sinal produzido pela simulação não é único e o comprimento do sinal deve ser grande o suficiente para garantir a estabilidade dos parâmetros estatísticos. Com o intuito de solucionar esses problemas, podem-se utilizar análises no domínio da freqüência ao invés de análises no tempo por serem muito mais rápidas e necessitarem menor esforço computacional. Uma das diferenças entre as duas metodologias é que, no domínio da freqüência, as não-linearidades inerentes ao sistema são linearizadas e os efeitos dessas alterações ainda não são bem conhecidos. Por essa razão, foi proposto um estudo comparativo entre análises no domínio do tempo e da freqüência de estruturas flexíveis, a fim de verificar a influência da não consideração de algumas não-linearidades e tentar determinar uma faixa de utilização para análises no domí-nio da freqüência. Palavras-chave:
When performing a direct vertical connection (DVC), the gooseneck may suffer severe damage due to the transfer of the load acting on the flexible pipe to the VCM (vertical Connection Module) when the bend restrictor is locked. On the other hand, the bend restrictor is necessary to guarantee that the minimum bend radius (MBR) of the flexible pipe is not violated during the installation. Nowadays there is no way to assess this information in real time, except visually, thus the operation is very dependent on the pipe-laying engineer experience. In critical situations, to mitigate risks, a team of specialists onshore is requested to carefully evaluate the situation, assessing the radius of curvature, running DVC simulations using as input the geometric properties of the line and the VCM. Those geometric properties are estimated from images acquired by a remotely operated vehicle (ROV). This process is exhausting and time consuming, reducing the overall efficiency and increasing operational costs. Furthermore, it is error-prone because it does not consider the perspective effects of the image projection and the distortion caused by wide-angle lenses. This paper describes a methodology to help the pipe-laying engineer carry out the DVC operations in a safe way. It is based on a computer vision system, SOIS, to estimate the curvature of flexible pipes during DVC operations, in order to increase the operational efficiency, through the use of stereo rig cameras and some markers along the pipe. It is faster and has a lesser margin of error than the simulated and manual assessment. This system relies on a stereo rig of lowlight cameras and on an interleaved pattern of black and white markers painted over the pipe. The 3D reconstruction process takes into account radial and perspective distortions of the images, resulting in a more accurate 3D geometry of the pipe. The system accomplishes its task through a sequence of three distinct phases: calibration, detection, and estimation of radius of curvature. The camera calibration process, conceived for the underwater scenario, allows us to remove the radial lens distortion and to identify the camera intrinsic parameters, necessary to map image coordinates into world coordinates. The proposed detection algorithm is robust to non-uniform illumination and occlusion effects caused by fishes and particles floating around. From the detected points in both cameras of the stereo rig, it is possible to reconstruct the 3D geometry of the pipe. The estimation of the radius of curvature is obtained by fitting a 3D version of a catenary curve through the reconstructed geometry of the pipe. Experiments demonstrated that the radius of curvature estimate is within a 3% margin of error at the 90% level of confidence. Field experiments showed that the pipe can be detected up to a distance of 15 meters. It is foreseen that the new methodology will significantly improve operational safety and shorten the average time of DVC operations, thus reducing its costs. Ongoing activities include improvements in the calibration phase to make it easier to be performed, and usability studies that are being conducted to improve the user experience with the system, especially for non-specialists in computer vision techniques.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.