Application of robotics in offshore oil and gas industry- A review Part II

Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent op...

/pdf/advanced-perception-navigation-and-planning-for-autonomous-2zpm735sky.pdf

Advanced perception, navigation and planning for autonomous in-water ship hull inspection

Magnetic flux leakage (MFL) detection is one of the most popular methods of pipeline inspection. It is a nondestructive testing technique which uses magnetic sensitive sensors to detect the magnetic leakage field of defects on both the internal and external surfaces of pipelines. This paper introduces the main principles, measurement and processing of MFL data. As the key point of a quantitative analysis of MFL detection, the identification of the leakage magnetic signal is also discussed. In addition, the advantages and disadvantages of different identification methods are analyzed. Then the paper briefly introduces the expert systems used. At the end of this paper, future developments in pipeline MFL detection are predicted.

https://www.mdpi.com/1424-8220/15/12/29845/pdf

Theory and Application of Magnetic Flux Leakage Pipeline Detection

This paper reports a real-time monocular visual simultaneous localization and mapping (SLAM) algorithm and results for its application in the area of autonomous underwater ship hull inspection. The proposed algorithm overcomes some of the specific challenges associated with underwater visual SLAM, namely, limited field of view imagery and feature-poor regions. It does so by exploiting our SLAM navigation prior within the image registration pipeline and by being selective about which imagery is considered informative in terms of our visual SLAM map. A novel online bag-of-words measure for intra and interimage saliency are introduced and are shown to be useful for image key-frame selection, information-gain-based link hypothesis, and novelty detection. Results from three real-world hull inspection experiments evaluate the overall approach, including one survey comprising a 3.4-h/2.7-km-long trajectory.

/pdf/real-time-visual-slam-for-autonomous-underwater-hull-47msc21576.pdf

Real-Time Visual SLAM for Autonomous Underwater Hull Inspection Using Visual Saliency

Note: Includes index + new features guide (1995) + quick reference Reference Record created on 2004-09-07, modified on 2016-08-08

Signal processing toolbox for use with MATLAB : ユーザーズガイド


 Mooring systems play an important role in the safety of floating production units and must comply with ultimate, accidental, and fatigue limit states criteria defined by design standards and classification societies. However, in the last few decades, many mooring lines failures have been reported in the literature. Most of these were related to fatigue and corrosion degradation in the top chain links, becoming a major concern. Since then, a great effort has been made to improve fatigue assessment methodologies of these elements and to model the effects that are not properly considered in the current design practice, such as the mean tension effect and the chain-link surface roughness due to localized corrosion.
 The design practice of mooring lines usually assumes a uniform corrosion model with a constant corrosion rate. That way, corrosion degradation is considered only by reducing the net area of the chain-link. As a consequence, effects of stress concentration due to localized pitting are not directly addressed, and this may lead to an unconservative design.
 The present work aims at assessing the stress concentration associated to chain links with pitting corrosion employing finite element analyses and by comparing the localized pitting against the uniform corrosion stresses conditions in the chain link hotspots. Results highlight that, even for small pits, fatigue damages are higher than considering a uniform area reduction, showing one feasible way of improving the current fatigue design methodologies.

The Effect of Pitting Corrosion on Fatigue Performance of Mooring Line Chain Links

Torpedo anchors have been used in various offshore applications especially due to its low cost installation and the ability to withstand high inclined loads. This anchor consists of a shaft in which flukes are welded in order to increase the soil-anchor contact region and, consequently, its holding capacity. Since this anchor presents a singular geometry, different from a regular cylindrical anchor/pile, the computation of the holding capacity of a torpedo anchor is not straightforward. In a previously presented work, the holding capacities of typical torpedo anchors were assessed with a finite element (FE) model in which both the anchor and the surrounding soil are represented with three-dimensional finite elements. However, this FE model demands a significant computational effort and, consequently, simpler approaches would be desirable in order to design these anchors. Relying on the FE model and a parametric study, this paper presents simple formulae to predict the holding capacities of torpedo anchors embedded into cohesive soils. These formulae are employed to predict the holding capacities of two different torpedo anchors, which are compared to those estimated with the FE model. Results agreed very well indicating that this simpler approach may be employed to quickly evaluate the holding capacities of these anchors.Copyright © 2013 by ASME

A Simple Approach for Determining the Holding Capacity of Torpedo Anchors Embedded in Cohesive Soils

The joint probabilistic models (JPM) of the environmental parameters of wave, wind and current are nowadays extremely needed in order to perform reliability analyses of offshore structures. These JPM are also essential steps for the design of offshore structures based on long-term statistics and to perform dynamic response analysis of floating units that are strongly dependent on the directionality of the environmental actions, such as turret-moored FPSOs. Recently, some JPM have been proposed in the literature to represent the joint statistics of a reduced number of environmental parameters. However, it is difficult to find a practical and fully operational model taking into account the complete statistical dependence among all the environmental parameters intensities and their correspondent directions. In this paper, it is presented a straightforward methodology, based on the Nataf transformation, to create a JPM of the environmental parameters taking into account the dependence between the intensity and direction of all variables. The proposed model considers the statistical dependence of ten short-term variables: the significant wave height, peak period and direction of the sea waves, the significant wave height, peak period and direction of the swell waves, the amplitude and direction of the 1-h wind velocity and, finally, the amplitude and direction of the surface current velocity. The statistical dependence between them is evaluated using concepts of linear-linear, linear-circular and circular-circular variables correlation. Some results of the proposed JPM methodology are presented based on simultaneous environmental data gathered in a location offshore Brazil.Copyright © 2008 by ASME

A Joint Probability Model for Environmental Parameters

This paper proposes a Load and Resistance Factors Design (LRFD) code format for structural components of offshore structures under multiple load effects. This code format accounts for the long-term variation of seastate and the actual correlation between dynamic load effects due to environmental actions. Ultimate limit states are formulated in terms of an Interaction Ratio (IR) random variable, such that the long-term extreme value of IR greater than unity means component failure. The long-term distribution of IR is obtained by combining the distribution of each short-term seastate. The short-term response of the generally nonlinear IR is determined by time domain simulation, taking into account partial load and resistance factors. The IR short-term distribution may be fitted, for instance, by using Rayleigh or Weibull distribution. The main advantages of the proposed code format are: • This code format accounts implicitly and correctly for the actual correlation among all dynamic environmental load processes. • Structural designers have used interaction ratios for a long time. Hence, it is straightforward to evolve from a deterministic stage of looking for IR < 1, as in old Working Stress Design codes, to a code format where the aim is to design structural components with long term IR extreme value < 1. The feasibility of the proposed code format is demonstrated by calibrating partial factors for beam-column cylindrical members based on components of a Floating Production System Semi-submersible hull.Copyright © 2002 by ASME

A LRFD Code Format for Accounting Long-Term Variation of Multiple Load Effects

This paper presents a Load and Resistance Factor Design (LRFD) criterion applied to the design of Tension Leg Platform (TLP) tendons in their intact condition. The design criterion considers the Ultimate Limit State (ULS) of any tendon section along its whole length taking into account both dynamic interactions of load effects and the statistics of its associated extreme response. The partial safety factors are calibrated through a long-term reliability-based methodology for the storm environmental conditions, like hurricanes and winter storms, in deep waters of the Campeche Bay, Mexico. In the reliability analysis, the uncertainties in the definition of load effects and analytic limit state models for calculation of tendon strength and randomness of material properties are included. The results show that the partial safety factors reflect both uncertainty content and the importance of the random variables in structural reliability analysis. When tendons are designed according to the developed LRFD criterion, a less scattered variation of reliability indexes is obtained for different tendon sections across a single or various TLP designs.Copyright © 2006 by ASME

Luis Volnei Sudati Sagrilo

Papers

The Effect of Pitting Corrosion on Fatigue Performance of Mooring Line Chain Links

A Simple Approach for Determining the Holding Capacity of Torpedo Anchors Embedded in Cohesive Soils

A Joint Probability Model for Environmental Parameters

A LRFD Code Format for Accounting Long-Term Variation of Multiple Load Effects

Reliability-Based Design Criterion for TLP Tendons