Low Cost Anchor System for Flexible Risers in Deep Waters
01 Jan 2002-
About: The article was published on 2002-01-01. It has received 89 citations till now.
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TL;DR: In this paper, an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water is presented, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seafloor; and submarine slides and their impact on infrastructure.
Abstract: The paper presents an overview of recent developments in geotechnical analysis and design associated with oil and gas developments in deep water. Typically the seabed in deep water comprises soft, lightly overconsolidated, fine grained sediments, which must support a variety of infrastructure placed on the seabed or anchored to it. A particular challenge is often the mobility of the infrastructure either during installation or during operation, and the consequent disturbance and healing of the seabed soil, leading to changes in seabed topography and strength. Novel aspects of geotechnical engineering for offshore facilities in these conditions are reviewed, including: new equipment and techniques to characterise the seabed; yield function approaches to evaluate the capacity of shallow skirted foundations; novel anchoring systems for moored floating facilities; pipeline and steel catenary riser interaction with the seabed; and submarine slides and their impact on infrastructure. Example results from sophisticated physical and numerical modelling are presented.
167 citations
Cites methods from "Low Cost Anchor System for Flexible..."
...Initial use of torpedo anchors took place in the Campos Basin (Medeiros, 2001, 2002)....
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TL;DR: In this paper, the authors explored the penetration response of dynamically installed anchors in normally consolidated clay and found that for anchors with no flukes, expected anchor tip embedment depths are two to three times the anchor length for impact velocities approaching 30 m/s, with a strong dependence on the net density of the anchor and smaller dependence on impact velocity.
Abstract: This paper utilises centrifuge data to explore the penetration response of dynamically installed anchors in normally consolidated clay. The data indicate that for anchors with no flukes, expected anchor tip embedment depths are two to three times the anchor length for impact velocities approaching 30 m/s, with a strong dependence on the net density of the anchor and smaller dependence on the impact velocity. Total energy, defined as the sum of the kinetic energy of the anchor at the mudline and the potential energy released as it penetrates the seabed, is shown to be a useful quantity for comparing the embedment depth of anchors with markedly different geometries and mass, impacting the soil at different velocities. The centrifuge data were used to calibrate an analytical embedment model, based on strain-rate-dependent shearing resistance and fluid mechanics drag resistance. The merit of the anchor embedment model has been demonstrated by predicting the final embedment depths for a series of offshore fiel...
95 citations
TL;DR: Torpedo anchors are used as foundations for mooring deep-water offshore facilities, including risers and floating structures as mentioned in this paper, and they are cone-tipped cylindrical steel pipes ballasted with concrete an...
Abstract: Torpedo anchors are used as foundations for mooring deep-water offshore facilities, including risers and floating structures. They are cone-tipped cylindrical steel pipes ballasted with concrete an...
65 citations
TL;DR: In this paper, the Lagrangian-Eulerian (ALE) method is used to analyze free-falling objects penetrating soil deposits, and the effect of the mechanical properties of the clay soil on the penetration characteristics is presented, and an approximate closed-form expression is derived for the dynamic penetration factor, Ndp.
Abstract: The finite-element analysis of free-falling objects penetrating soil deposits is one of the most sophisticated and challenging problems in geomechanics. A robust numerical method will be described here for dealing with such complex and difficult problems. The approach is based on the arbitrary Lagrangian–Eulerian (ALE) method of analysis, the main features and challenges of which are described briefly in the paper. The ALE method is then employed to perform a parametric study of a perfectly smooth penetrometer free-falling into a uniform layer of clay, which deforms under undrained conditions. The effect of the mechanical properties of the clay soil on the penetration characteristics is presented, and an approximate, closed-form expression is derived for the dynamic penetration factor, Ndp. Comparisons are made between the deduced values of Ndp and published values of the conventional cone factor, Nc, and comparisons are made with experimental data to validate the approach.
63 citations
Cites background from "Low Cost Anchor System for Flexible..."
...For instance, torpedoes used to anchor flexible risers are typically 12–15 m long, weigh 240– 950 kN in air, and are 762–1077 mm in diameter (Medeiros, 2002), and the STING penetrometer, developed by Canada’s Defence Research Establishment Atlantic to investigate the upper seabed, consists of a steel rod 1 m long and 19 mm in diameter, with an enlarged tip at its base with diameters of 25–70 mm (Mulhearn, 2002)....
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...For instance, torpedoes used to anchor flexible risers are typically 12–15 m long, weigh 240– 950 kN in air, and are 762–1077 mm in diameter (Medeiros, 2002), and the STING penetrometer, developed by Canada’s Defence Research Establishment Atlantic to investigate the upper seabed, consists of a…...
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TL;DR: In this paper, the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of torpedo anchors during dynamic installation in non-homogeneous clay were reported.
Abstract: This paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of torpedo anchors during dynamic installation in non-homogeneous clay. The large deformation finite element (LDFE) analyses were carried out using the coupled Eulerian–Lagrangian approach, modifying the simple elastic-perfectly plastic Tresca soil model to allow strain softening, and incorporate strain-rate dependency of the shear strength using the Herschel–Bulkley model. The results were validated against field data and centrifuge test data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of anchor shaft length and diameter; number, width and length of fins; impact velocity and soil strength. The anchor velocity profile during penetration in clay showed that the dynamic installation process consisted of two stages: (a) in Stage 1, the soil resistance was less than the submerged weight of the anchor and hence the anchor accelerated; (b) in Stage 2, at greater penetration, frictional and end bearing resistance dominated and the anchor decelerated. The corresponding soil failure patterns revealed two interesting aspects including (a) mobilization of an end bearing mechanism at the base of the anchor shaft and fins and (b) formation of a cavity above the shaft of the installing anchor and subsequent soil backflow into the cavity depending on the soil undrained shear strength. To predict the embedment depth in the field, an improved rational analytical embedment model, based on strain rate dependent shearing resistance and fluid mechanics drag resistance, was proposed, with the LDFE data used to calibrate the model.
62 citations