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The pull-out capacity of plate anchor is significantly impacted by the embedment loss during keying, necessitating its prior estimation. The soil surrounding the anchor undergoes considerable disturbance during keying, but the soil softening induced by accumulated shear strains was neglected in almost all the existing numerical studies. In this paper, an elastic-perfectly plastic model with strain-softening was combined with the integral-type nonlocal method to overcome the mesh dependency in large deformation finite element simulations. The biaxial compression tests were simulated firstly and the keying process of strip anchors were reproduced by varying anchor width, thickness, loading eccentricity, undrained shear strength and sensitivity. It was observed that the ultimate embedment loss increased nearly linearly with soil sensitivity, a trend that was especially pronounced at lower loading eccentricity ratio. The generalized equations for evaluating the ultimate embedment loss were proposed and their reliabilities were verified by the existing centrifuge tests. • An empirical equation to evaluate the embedment loss of plate anchor in strain-softening clay is proposed. • Soil model is regulized via an integral-type nonlocal method to overcome the mesh dependency in FE. • Roughness of the anchor-soil interface is accounted for to re-visit the keying of anchor. [ABSTRACT FROM AUTHOR]

The pile response of taut mooring systems considering chain-soil interactions remains unclear. In this study, model tests on the performance of anchor piles and the surrounding soil displacement field were conducted using transparent sand. Cyclic motion was imposed at the top end of the chain. The effects of pad eye location (z), motion velocity (v), motion amplitude (A), and amplitude increment (A i) are discussed. In the constant-amplitude tests, the soil displacement caused by chain motion was apparent near the dip-down point, and the soil displacement increased with z and A. The maximum chain tension decreased owing to chain-soil interactions. The maximum tension with z = 0.55 L and 0.67 L (where L is the pile length) increased 9% and 15%, respectively, compared with that with z = 0.40 L , and the maximum tensions at A = 80 and 120 mm decreased 15% and 29%, respectively, of that at A = 40 mm. In the incremental-amplitude tests, soil displacement was evident around the dip-down point and pile. The maximum tension during each cycle increased almost linearly with the number of cycles before pile failure, and the maximum tension during the entire test increased with z and v. • Model tests using transparent sand are conducted to study the anchor pile performance considering chain-soil interactions. • The effects of pad eye position, motion velocity, motion amplitude, and amplitude increment are analyzed. • Advices on practical anchor pile design considering chain-soil interactions are given. [ABSTRACT FROM AUTHOR]

Dynamic installation of anchors is now commonly simulated using the coupled Eulerian-Lagrangian (CEL) approach in ABAQUS/Explicit. However, capturing anchor (Lagrange)-soil (Eulerian) interface frictional resistance during continuous penetration remains a challenge. This paper introduces an advanced frictional resistance algorithm called the Integrated Nodal Friction Algorithm (INFA) to improve the accuracy of capturing frictional resistance, and to increase computational efficiency. The innovative features of the method include automatic capturing of the anchor nodes in contact with the adjacent soil, estimating local shear strength of the contacted soil nodes, and calculating frictional resistance for the identified contacted areas based on the estimated local shear strengths. The algorithm was validated against centrifuge test data for a free-fall piezocone penetrometer, with good agreement obtained in terms of measured frictional resistance and end bearing profiles with penetration depth, and final tip embedment depth. Parametric analyses were then conducted for optimising mesh sizes and output frequency. Performance of the INFA method was compared with the existing two methods, demonstrating that the proposed algorithm is capable of improving the accuracy of capturing anchor-soil interface frictional resistance profile along the penetration depth. • The novel algorithm shows good potential for automatically identifying anchor surface areas in contact with the adjacent soil, ultimately of capturing mobilised interface friction resistance. • Eliminating the need for a prior analysis saves half of the analysis time. • Assumptions of embedded anchor bodies in full contact with the adjacent soil may not always be valid. [ABSTRACT FROM AUTHOR]

Subsea flowlines are flexible or rigid pipelines that are used in oil and gas fields commonly for transporting production fluids from wells. The majority of the flowlines operating in basins across the world (including e.g. Australia's 1700 km infield flowlines) are approaching the end of their productive life, and will need to be decommissioned over the next 5 decades. This paper, for the first time, investigates the potential of repurposing decommissioned flowlines to dynamically installed anchors for mooring floating facilities. Five shapes of anchor have been developed using segments of flowline. Two series of tests were subsequently carried out on models of those shapes. The first series of tests involved releasing the models in still water to assess free-fall trajectory (i.e. verticality), terminal velocity, and anchor drag coefficient. The second series of tests were carried out at 50 g in clay to investigate the performance of the anchors in terms of tip embedment depth during dynamic installation and capacity under vertical loading. The results confirmed performance similar to conventional dynamically installed anchors, suggesting that there is potential to fabricate offshore anchors using segments of flowline. • Decommissioned flowlines. • Repurposing decommissioned flowlines to dynamically installed anchors. • Verticality, terminal velocity, and drag coefficient in water. • Tip embedment depth during dynamic installation in clay. • Capacity under monotonic vertical loading in clay. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced polymer (CFRP) cable anchors, possessing exceptional mechanical properties and corrosion resistance, are increasingly serving as alternatives to traditional steel strands in coastal excavation support engineering. This study draws upon in-situ tests of deep excavation near the sea to examine the stress characteristics of CFRP cable anchors throughout their service period at various positions within the excavation plane. Moreover, the parameters of these cable anchors are optimized and analyzed through numerical simulations. The study revealed that the planar position, backfilling of the excavation and the time effect significantly affected the service performance of the CFRP cable anchors. As the days increase, the overall axial force and shear stress in the CFRP cable anchors undergo five stages of changes. Compared to steel strands, CFRP cable anchors demonstrated superior supporting effects on the adjacent soil. Given similar engineering geological conditions, the advisable range for inclination angle for CFRP cable anchors ranges between 20° and 30°, and cable anchor lengths is 10% shorter than the test length up to the test length itself. Within the scope of this study, the optimal support strategy recommends a 30° inclination angle and a length that is 10% shorter than that of the test length. • The application of Carbon Fiber Reinforced Polymer (CFRP) material in coastal excavation support engineering has been proposed. • Based on the in-situ test, the stress characteristics of CFRP cable anchors have been revealed throughout their service period. • Through numerical simulations, an analysis and optimization of the parameters of CFRP cable anchors have been conducted. [ABSTRACT FROM AUTHOR]

Torpedo anchors are increasingly popular for tethering of offshore structures. Using fins improves their directional stability during penetration, however, fins' shape affects both penetration depth and pullout capacity. Experiments were carried out to investigate the effect of the width of fins on the behavior of torpedo anchors during penetration and extraction. Four torpedo models having the same weight were made, one without fins and three with four fins. A transparent soil was used to simulate soft marine clay, thus permitting visualizing torpedo soil interaction. Particle trajectories showed that soil movements in the vicinity of the torpedo were downward as the torpedo approached a given depth, and that movements reversed to upwards once the torpedo passed that depth. Measurements of soil displacements suggest that the pullout capacity of finless torpedoes depends on the friction with the shank, and for torpedoes with fins it depends mainly on the reverse end bearing. • Effects of fins width on penetration and pullout was investigated. • Soil torpedo interaction visualized in a transparent clay simulant. • Zone of influence during penetration depends on fin configuration. • Use of fins decreases penetration depth but increases pull out capacity. • Use of fins improves verticality. [ABSTRACT FROM AUTHOR]

This paper demonstrates a series of 1 g model tests and numerical modelling in order to investigate the pushout extraction process of suction anchors in sand. The suction anchor models used in this study have aspect ratios of 1 and 2, and the pumping rate and soil permeability are varied to reveal their influence on the extraction process. It is shown that changes in the pumping rate and soil permeability rarely alter the overpressure during the extraction process but can affect the displacement rate and final extracted length of the suction anchor. The ratio of the final extracted length over the total length of the suction anchor is also found to be different for suction anchors with different aspect ratios in the 1 g model tests. Eventually, a calculation method for this pushout extraction process is proposed and validated to determine the peak overpressure with some basic parameters of the suction anchor and sands. The relationship between the pumping rate and the displacement rate of the suction anchor is also revealed in the calculation method. • Pumping rate and soil permeability barely affect the overpressure during extraction. • The final extracted length is dependent on the pumping rate and anchor geometry. • The initial displacement rate has a linear relationship with the pumping rate. • The overpressure can be obtained with basic parameters using the proposed method. [ABSTRACT FROM AUTHOR]

In a marine environment, a submerged compound suction anchor foundation has non-uniform structure dimensions, which affect the local scour to varying degrees. Based on a series of laboratory flume experiments, the local scour of the submerged compound suction anchor foundation under the combination of waves and a current was examined in this study, taking into account the respective effects of the superstructure dimension h 0 / D 1 and the substructure dimension h 1 / D 2. The experimental results indicated that under all flow regimes, the non-dimensional equilibrium scour depths S e / D 1 and S e / D 2 increased with the increase in h 0 / D 1 and h 1 / D 2. At the same time, the non-dimensional time-scale T * decreased, while the relative scour rate increased. Prediction equations of S e / D 1 and S e / D 2 for the compound suction anchor foundation considering the effects of h 0 / D 1 and h 1 / D 2 are proposed under waves alone, a current alone, and a combination of waves and a current. The development processes of the scour depth on the upstream and downstream sides of the foundation had different sensitivities to changes in the excess pore water pressure. When there was a small accumulated excess pore water pressure on the downstream side of the foundation, a larger scour depth could still be formed. • Scour around a compound suction anchor foundation is studied under waves and current. • Scour patterns of different foundation dimensions under different flows are analyzed. • Upstream and downstream scour depths had different pore pressure sensitivities. • Factors such as the superstructure and substructure dimensions are discussed. • A new scour prediction method for compound suction anchor foundation is proposed. [ABSTRACT FROM AUTHOR]

A shared multiline anchor system may reduce material and installation costs for floating offshore wind farms, but the concept also expands the physical space over which the analysis of the system must be considered. The multiline anchor force is a combination of forces that originate from different floating offshore wind turbine (FOWT) platforms, and this interconnectivity mandates investigation of spatial coherence of waves over the area of the connected turbines. The goal of this work is to determine if anchor force characteristics are sensitive to spatial coherence of the wave field, or if an assumption of independent wave fields at different FOWT locations provides sufficiently accurate anchor load characterizations. Spatially coherent irregular wave fields are generated and applied to FOWT systems in 3-line and 6-line anchor systems, revealing negligible sensitivity of multiline anchor force to wave spatial coherence. These results are continued with a parametric study showing how wave characteristics affect correlation lengths of spatially coherent waves. A review of installed offshore wind turbine spacings is presented as a context for these results. In each section, regular waves are first used to examine the dynamics in a simple context, then irregular waves are used to more realistically simulate ocean conditions. • Multiline anchor forces in floating wind farms are not a function of wave coherence. • Independent waves at turbines provide adequate modeling of multiline anchor forces. • 1-D wave elevation correlation is negligible at distances greater than 300 m. • Many installed offshore wind farms employ turbine spacings of 4–8 rotor diameters. [ABSTRACT FROM AUTHOR]

This paper aims to optimise the dimensions of Suction Embedded Anchors (SEAs) by investigating the opening mechanism through numerical large deformation finite element (LDFE) modelling. Consisting of two hinged half-cylindrical flukes, an SEA anchor uses a tactical design to allow the flukes to open under preloading to achieve more bearing area and, thus, a higher holding capacity. However, the applicability and practicability of this anchor depends on the opening process, where a critical dimension is the ratio of the anchor height relative to the diameter. A longer anchor increases both the forces prompting the opening process and the forces resisting it. The initial prompting force is the friction along the flukes and pressure on the wall annulus, while the initial resisting force is the soil pressure on the fluke faces. The LDFE results of this study demonstrate that these two components are in different orders of magnitude. Therefore, increasing the anchor height does not necessarily always increase the holding capacity but can have a detrimental effect on the holding capacity. The optimal anchor height is found to be ∼0.75 times the diameter. The detailed opening process and mechanism are demonstrated in the systematic LDFE analyses presented in this paper. • This paper investigates the practicability of a type of expandable anchor, i.e. Suction Embedded Anchor (SEA). • This paper employs LDFE modelling to rigorously explore the opening process of the expandable anchor SEA. • This paper demonstrates that the optimal SEA anchor height is ~0.75 times the diameter. [ABSTRACT FROM AUTHOR]

Challenges associated with dynamically installed anchors (DIAs) include prediction of anchor embedment depth and subsequent pullout performance under chain loading. Numerical analyses on the behaviour of DIAs require advanced modelling methods that can deal with a) hydrodynamic aspects during the free-fall in water; b) large soil deformations with high strain rate effects during the dynamic penetration; c) post-installation consolidation; d) pullout performances considering installation and anchor chain effect. This paper divides the behaviour of DIAs into three stages, including anchor free-fall in water (Stage 1), anchor dynamic penetration in soil (Stage 2), and anchor pullout under operational loadings (Stage 3), and gives an overview of numerical advancements on the analysis of DIAs at each stage. By illustrating typical numerical results and comparisons between various methods, the advantages and limitations of the numerical modelling methods are highlighted. The advantage of the finite volume method (FVM) based on computational fluid dynamics is its capability in the full simulation of an anchor dynamic installation in water followed by in soil (Stages 1 and 2). However, the stress-induced anisotropy of the soil cannot be captured by the FVM. The finite element (FE) method, especially the large deformation finite element (LDFE) method, is preferable to analyse Stages 2 and 3. The effects of soil properties on the performance of DIAs can be quantified by the LDFE method, in terms of strain rate, strain softening, pore pressure and drag force. • Review of numerical modelling methods and soil constitutive models. • Dynamically installed anchors. • Dynamic installation in water. • Dynamic installation and loading in clay. • Comparative advantages and limitations of numerical modelling methods. [ABSTRACT FROM AUTHOR]

Abstract Plate anchors are commonly used in mooring systems of offshore facilities for gas and oil production in deep and ultra-deep water. They may encounter hydrate-bearing sediments widespread in marine continental margins. The pullout capacity of square anchors embedded shallowly in a hydrate-bearing sand is investigated with small-scale model tests using tetrahydrofuran (THF) hydrate as the substitute of gas hydrate. The results show that the pullout capacity of the anchors increases with the increase of the anchor width and the burial depth. The pullout capacity of the anchors can be estimated by a dimensionless breakout factor. This factor increases with the increase of the burial depth ratio (defined as the ratio of the burial depth to the width of a plate anchor), exhibiting a trend similar to that obtained numerically and experimentally from plate anchors shallowly-embedded in undrained clays. Hydrate dissociation brings detrimental effects on the pullout capacity of the anchors. The pullout capacity of the anchors drops to 0.3% of the initial value after the hydrates dissociate. This pronounced reduction highlights the need for further investigation on the effect of oceanic hydrate dissociation on engineering performance of offshore facilities as a result of natural or anthropologic perturbation. Highlights • Newly-developed apparatus for physical model tests of anchors in hydrate-bearing soil. • A breakout factor experimentally correlating to the embedment ratio of anchors. • Extreme reduction in pullout capacity of anchors attributed to hydrate dissociation. [ABSTRACT FROM AUTHOR]

Abstract An innovative booster concept is proposed to increase both the kinetic and potential energies and hence to increase the penetration depth of the OMNI-Max anchor within the clayey soil with high strength gradient. This paper carried out 1 g model tests to investigate the working efficiency of the booster on the anchor penetration depth both in normally consolidated (NC) and lightly over-consolidated (LOC) soils. The similarity relationships of the anchor dynamic penetration within the soil were first deduced, and then a series of dynamic penetration tests were performed to investigate the parameters that influence the anchor penetration depth. The parameters include the soil strength characterisation, impact velocity, booster weight, inclined impacting angle, and water drag and entrainment effects. The anchor dynamic penetration process within the soil was measured by a micro-electromechanical systems (MEMS) accelerometer, through which the soil strain-rate effect and the hydrodynamic aspects including the water drag force and potential water entrainment along the anchor-soil interface were analysed. Finally, energy-based and force-based prediction models were put forward to estimate the penetration depths of OMNI-Max anchors and hybrid anchors (i.e. an OMNI-Max anchor with a booster). Highlights • The working efficiency of the booster on the penetration depth of the OMNI-Max anchor is investigated using physical modelling. • The similarity relationships of geotechnical dynamic problems in clay are induced. • The effect of the inclined impacting angle on the anchor penetration depth is investigated. • Energy-based models are put forward to predict the anchor penetration depth. [ABSTRACT FROM AUTHOR]

Abstract Floating structures are often secured in position with a taut mooring system and suction caissons. Large seabed trenches have been observed adjacent to some suction caisson anchors with taut-line mooring systems. The trenches may jeopardise the geotechnical capacity of the caissons and in turn the stationkeeping of the floating structures. Finite-element method is employed to examine the geotechnical capacity of suction caissons in a trenching seabed. The results show that the reduction in the geotechnical capacity becomes more significant with increasing trench width due to the loss of soil support and a change in failure mechanism as the caisson rotates into the trench. For a given trench width, the reduction in capacity becomes more significant as the load inclination angle to the horizontal decreases. However, the shape of the normalised failure envelopes for combined vertical and horizontal load is insensitive to trench width. A strategy to design for inevitable trenching by moving the padeye shallower to reduce the depth of trench formation is not straightforward. The gain from a shallower trench may often be outweighed by the reduction in capacity from rotation of the caisson at failure for loading angles typical of taut moorings. Highlights • Geotechnical capacity of the suction caisson anchors exposed to large seabed trenches. • Governing soil flow failure mechanisms around suction caisson anchors in trenching seabed. • The effects of trench configurations, caisson-soil interface conditions and loading paths are examined. • Design for inevitable trenching by moving the padeye to a shallower depth is not straightforward. • A strategy to overcome the challenge of seabed trenching is presented based on a case study. [ABSTRACT FROM AUTHOR]

Abstract The OMNI-Max anchor, a newly developed gravity installed anchor, offers a cost effective anchoring solution with improved reliability for deep-water mooring facilities. However, the anchor final penetration depth is relatively shallow in the soil with high strength gradient. A booster, which can be attached at the tail of the OMNI-Max anchor, is designed with the aim to improve both the anchor directional stability and terminal velocity, such that the anchor can penetrate deeper into the seabed and consequently gain higher holding capacity. The objective of this paper is to investigate the directional stability and terminal velocity of the OMNI-Max anchor and hybrid anchor (i.e. an OMNI-Max anchor with a booster) based on the computational fluid dynamics (CFD) approach. The numerical simulation results demonstrated that the booster is beneficial in moving the position of the hydrodynamic centre towards the anchor rear, hence the directional stability of the hybrid anchor is improved. Moreover, the anchor terminal velocity was increased from 22.44 m/s to 32.01 m/s by the aid of a booster. Finally, an optimised design on the booster geometry was performed to ensure that the hybrid anchor can obtain high terminal velocity and maintain directional stability at the same time. Highlights • The hydrodynamic characteristics of OMNI-Max anchor are investigated. • The booster structure was optimised to improve both the terminal velocity and directional stability of hybrid anchors. • The efficiency of the booster on the terminal velocity of OMNI-Max anchor was investigated. [ABSTRACT FROM AUTHOR]

The suction anchor base has been widely used in marine engineering as an innovative and efficient foundation for marine structures. However, prior research endeavors have neglected to account for the influence of hydrate dissociation within the seabed sediments on suction anchors' negative pressure installation process. This paper elucidates the intricate coupling mechanism of hydrate dissociation, seepage, and heat transfer within marine sedimentary layers, all of which are induced by installing suction anchors. Employing a multi-physical field coupling methodology, numerical simulations were conducted to analyze the influencing factors and spatiotemporal evolution of hydrate dissociation and the impact of hydrate dissociation on seepage and pressure fields. The results indicate that the increases in negative installation pressure, penetration depth, and stratigraphic sensible heat promote hydrate dissociation. The hydrate dissociation enhances seepage, reduces the pressure gradient in the anchor, and decreases the suction anchor sinking force. Consequently, this research holds practical implications for guiding suction anchor installation within seabed characterized by buried hydrate. • The innovation is that this study examines an engineering reality of installing suction anchors in the seabed where hydrates are buried. • The study elucidates the complex coupling mechanism of suction anchor installation, hydrate dissociation, seepage, and heat transfer. • The effects of installation negative pressure, penetration depth, and temperature on hydrate dissociation are analyzed. • This study analyzes the hydrate dissociation rules and the effects of hydrate dissociation on the seepage and pressure fields around the anchor. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation of torpedo anchors penetrating into sand-overlying-nonhomogeneous clay deposit, with the main objective of predicting the anchor embeddment depth after it penetrates through the top sand layer. The behavior of the torpedo anchor and soil failure mechanisms during the installation process are analyzed using large deformation finite element (LDFE) methods. To validate the numerical models, comparisons are made with data from existing centrifuge and field tests. An extensive parametric study is then conducted, exploring a wide range of soil properties, soil layer thickness, anchor velocities, and parameters related to torpedo anchor geometry. Two intriguing findings emerge from the analysis. Firstly, there is an evolving soil failure, with the strain-softening region expanding in the clay near the boundary between the two soil layers. Secondly, the velocity profile during both the acceleration and deceleration stages varies with different sand layer thicknesses, displaying a nonlinear relationship with the anchor's final embedment depth. Based on the findings, a simple design procedure is developed to account for the influencing factors on the anchor installation depth. This procedure is expected to be valuable for engineers seeking to estimate the behavior of torpedo anchor installations in sand-overlying-nonhomogeneous clay soil deposits. • The installation of torpedo anchors in sand-overlying-nonhomogeneous clay is explored through the CEL analyses. • The installation depth, velocity profiles and failure patterns of the anchor are studied through parametric analyses. • A design procedure is proposed for predicting the anchor penetration depth in sand-overlying-nonhomogeneous clay deposit. [ABSTRACT FROM AUTHOR]

Methods for calculating the uplift capacity of horizontal anchor plates have the problem of artificially distinguishing shallow and deep buried types in advance, but the classification standards differ greatly. Based on the application of digital photographic measurement technology in experiment, this paper focuses on a theoretical method for calculating the uplift capacity of horizontal anchor plate in sand at arbitrary depth without distinguishing shallow and deep burial types. The results show that the sliding surface in the soil extends to ground surface in approximately a straight oblique line at shallow burial depths, then gradually confined within the soil as a balloon shape as the burial depth increases, and further shrinks toward the anchor plate. This change of sliding surface has no absolute boundary but undergoes continuous evolution, and can be described by a morphological function of logarithmic spiral line, which is used to develop a unified mechanical model, and a theoretical method for calculating uplift capacity is deduced and established. The new mechanical model well reflects the continuous variation of the sliding surface, and comparison with other four methods on 8 experimental cases show that the new calculation method has good adaptability for different types of burial depths. • The continuous evolution process of sliding surface with depth ratio was revealed by experiments. • A morphological function is proposed to characterize the continuous evolution of sliding surfaces. • The unified mechanical model of anchor plate uplifting is established. • The unified calculation method of uplift bearing capacity is deduced and verified. [ABSTRACT FROM AUTHOR]

Three-dimensional finite element analysis offers a more realistic representation of the geometry of the helix plate anchor. For the helical anchor with a single helix plate or multiple helix plates whose spacing distance is large between each plate, each helix plate behaves independently during uplifting. Although numerous studies have estimated the uplift capacity factor of independent circular plate anchors in uniform clay, rare research comprehensively considers the effects of helix pitch, anchor shaft, and soil rigidity on estimating the uplift capacity factor for independent helix plate anchors. In this paper, three-dimensional finite element analyses were conducted to investigate the impacts of helix pitch, anchor shaft, and soil rigidity on estimating the uplift capacity factor of independent helix plate anchors with shafts in uniform clay. Analysis results demonstrated that the increasing helix pitch and anchor shaft diameter could significantly decrease the uplift capacity factor. The change in the soil rigidity also influenced uplift capacity factor estimation. Therefore, determining the uplift capacity factor should comprehensively account for the effects of embedment depth, helix pitch, anchor shaft, soil rigidity, and overburden pressure. In this study, a procedure was suggested for creating design guidelines to estimate uplift capacity factors for independent helix plate anchors. • Three-dimensional finite element analysis on uplifting helix plate anchor. • Effect of helix pitch on the uplift capacity factor of helix plate anchor. • Effect of shaft diameter on the critical embedment depth of helix plate. • Design procedure for the uplifting capacity factor of helix plate anchor anchor [ABSTRACT FROM AUTHOR]

To study the feasibility of deploying a novel type of anchor with variable buoyancy for mooring floating offshore wind turbines, a set of detailed modelling studies was performed in the state of-the-art Marine Simulator at the National Decommissioning Centre. The aim of the multiphysics simulations is to assess fully a proposed craneless deployment method that involves towing the anchor from the harbour to the installation site, pumping liquid ballast to overcome anchor's buoyancy and lowering it to the seabed using only a winch, thereby simplifying the process, and reducing installation costs. As a test case, a novel shape of the floating anchor is considered, to establish the feasibility of its deployment in conjunction with the variable buoyancy technology and installation sequence. The analysis is divided into three sections: characterisation of the anchor buoyancy, positioning the anchor under the stern of the vessel and the controlled descent of the anchor to the seabed, under varying weather and operational conditions (e.g significant wave height, current, winch velocity, liquid ballast mass, ballast pump rate). The analysis allows assessment of the importance of the different factors affecting the proposed deployment scenario of variable buoyancy anchors, such as the winch velocity, the ballast mass and the pump rate. • Feasibility of deploying variable buoyancy anchors for floating wind applications. • Virtual prototyping of anchor deployment scenarios. • Parametric studies of the effect of environmental and operational conditions. • Unveiling complexities of deploying variable buoyancy anchors using simple techniques. • Reducing cost and risk for future offshore deployment of variable buoyancy anchors. [ABSTRACT FROM AUTHOR]

Unburied subsea pipelines under cyclic thermal loading are often prone to axial walking. The axial movements accumulate over operational cycles, which can lead to potential failure at the mid-line or end connections. Anchoring is a commonly adopted method to -control pipeline walking, however, it requires accurate estimation of anchor force for efficient pipeline design. In view of this, the present study proposes a calculation method for anchor force of full mobilized lengths for different anchoring positions. Furthermore, the anchoring mechanism for partial mobilized lengths is analyzed. The anchor force is then determined using a strain diagram method for partial mobilized lengths. Finally, an analytical solution for anchor force based on the strain diagram method is derived and validated against finite element results. The results show that the mobilized length ratio of pipeline anchor force increases with the loading temperature and seabed slope but decreases with the pipeline length. The proposed analytical solution for anchor force which has advantages over traditional analytical solutions can comprehensively consider the effects of pipeline parameters, load parameters, and contact parameters. • A new analytical solution of the anchor force considering the anchoring position is derived. • The factors affecting the mobilized length of anchor force are studied. • The strain diagram method is proposed to analyze the anchor force mechanism for partial mobilized length. • A new analytical solution which can determine the mobilized length of the anchor force is proposed. [ABSTRACT FROM AUTHOR]

Dynamically installed anchor is an innovative and cost-effective technology in marine foundation engineering. However, most of the existing researches on the hydrodynamic characteristics of dynamically installed anchors are limited to their free-fall installation performance in water without considering the action of marine environmental loads such as current. Therefore, this study aims to investigate the hydrodynamic performance of dynamically installed anchors subjected to current in a systematical manner. A complete three-dimensional CFD model is firstly established using "dynamic model analysis" method. Then, the effects of anchor geometric characteristics on the installation efficiency (i.e., penetration velocity and drag coefficient) and installation positioning accuracy (i.e., lateral velocity and displacement, and inclination angle) of the anchors subjected to current are systematically studied using the established CFD model. The influences of current velocity, current direction and geometric characteristics including anchor shaft geometry and anchor fin geometry on the hydrodynamic characteristics of anchor are discussed. Based on the obtained findings, some practical design recommendations are given, and a simple semi-empirical method for estimating the falling velocity and inclination angle of dynamically installed anchor subjected to current considering anchor geometric effects is finally proposed, which may benefit the engineering design of dynamically installed anchors. • Effects of anchor geometry characteristics on hydrodynamic performance of DIAs under current action were investigated. • Practical significance of geometric design and recommended configuration of DIAs under current action were provided. • A semi-empirical method for estimating the falling velocity and inclination angle of DIAs under current action was proposed. [ABSTRACT FROM AUTHOR]

This paper reports the results from three-dimensional dynamic finite element analysis undertaken to provide insight into the behaviour of a novel dynamically installed anchor (DIA), termed as fish DIA, during dynamic installation and monotonic pullout in non-homogeneous clay and calcareous silt. The fish DIA has an elliptic-shaped shaft, which reduces hydrodynamic drag resistance. The shaft is shaped to be thicker near the head to lower the mass centroid, and increase its diving potential with a specialised padeye position. A series of large deformation finite element analyses have been carried out considering the relevant range of parameters in terms of soil undrained shear strength; impact velocity, padeye offset ratio and pullout angle. Considering the difference in soil undrained shear strength, and DIA dimensions and mass; overall anchor tip embedment depths of the fish DIA lied in the range of that of the OMNI-Max DIA. The tracked anchor trajectory confirmed that, compared to the OMNI-Max DIA, the fish DIA dove deeper and earlier for a wide range of padeye offset ratio. These are more critical and beneficial for calcareous silt where the achieved embedment depths are generally lower compared to those in clay. [ABSTRACT FROM AUTHOR]

Torpedo anchors are regarded as one of the most efficient mooring solutions for taut mooring systems and can withstand vertical loads. The estimation of the undrained pullout capacity of the anchors is vital for the design of offshore floating facilities. There have been some achievements obtained for the calculation of the holding capacity of a torpedo anchor via field tests, conventional model tests under one gravity, centrifuge tests with a high value of gravity acceleration and numerical tests. However, a simple and reliable formula is still required to calculate the holding capacity of a torpedo anchor. In this study, 240 sets of laboratory tests were performed, and 11 differently shaped model anchors, vertically embedded in a soft sedimentary bed, were pulled out vertically from different types of cohesive soils and different embedment depths. The characteristics of the loading curves were analyzed, and the relationship between the pullout capacities and properties of the anchors and types of soils were investigated. Based on force analysis and the laboratory data, a formula was proposed for the calculation of the undrained monotonic holding capacity of a torpedo anchor, which mainly depends on the embedded depth of the anchor, net weight, geometry, and in situ soil properties. The calculated vertical holding capacities were consistent with the laboratory and field data obtained by the authors and other scientists. [ABSTRACT FROM AUTHOR]

Based on rigid block collapse mechanism and employing the upper bound theorem of limit analysis, the ultimate vertical uplift resistance of rectangular plate anchors embedded horizontally in two layered sand has been determined. Closed form analytical expressions were derived for computing the vertical uplift resistance in terms of dimensionless uplift factors F γ and F q , due to the components of soil unit weight ( γ ) and surcharge pressure ( q ) acting on the ground surface, respectively. For given embedment ratios of the anchor, the effect of relative position and thickness of sand layer with higher angle of internal friction ( φ h ) and unit weight ( γ h ), and sand layer with lower angle of internal friction ( φ l ) and unit weight ( γ l ), on the magnitude of F γ and F q was studied for different length to width ratio of anchor varying from unity to infinity (square to strip). The solutions obtained from the present theory compare reasonably well with the available data from literature. [ABSTRACT FROM AUTHOR]

The emergence of commercial offshore floating renewable energy devices that are expected to be deployed in large integrated arrays in relatively shallow water requires anchor types that are suited to sandy seabeds. This paper considers centrifuge test data that quantify the capacity of a novel dynamically installed plate anchor in sand under drained monotonic and cyclic loading. The monotonic tests investigated the role of the eccentricity of the load attachment point from the plate, the mooring line load inclination at the seabed and the plate embedment depth, whereas the cyclic tests examined the capacity mobilisation due to both regular and irregular drained cyclic loading for a fixed embedment depth and seabed load inclination. The test data indicate that an optimal anchor design would employ a load attachment point that is eccentric from the plate by at least 0.6 times the plate height, and that the anchor provides higher capacity when the seabed load inclination is horizontal (catenary mooring) than when it is vertical (vertical taut mooring). The centrifuge data show that drained cyclic loading does not degrade anchor capacity, and may be beneficial provided the cyclic loading involves a history of lower level cyclic loading that densifies the sand. [ABSTRACT FROM AUTHOR]

A novel gravity installed anchor with ring fins (RGIA) is proposed in the present work, which combines features of the conventional gravity installed anchor (GIA) and the drag embedment plate anchor, with two soft shanks attached to the anchor body. A systematic study on the performance of the RGIA in clay is performed by large deformation finite element analyses using the coupled Eulerian-Lagrangian technique (CEL), with emphasis on the initial penetration, the behaviors of keying, diving and pulling out, the optimization of the shackle point, and the effect of loading rates on the maximum embedment loss (MEL). The initial penetration of the anchor is simulated under various impact velocities, from which the maximum initial embedment depth in the seabed is acquired. Two factors of the shackle point, e n and e h , are defined and the detailed criteria for optimizing the shackle point are put forward. A series of analytical cases are designed to thoroughly explore the effects of the shackle point on the performance of the RGIA in clay, focusing on the keying and diving behaviors and the pullout capacity. The formulas for calculating the diving angle and the MEL are then constructed with high precision, by taking into account the effect of the shackle point, and can be utilized to optimize the position of the shackle point. Comprehensive drag effects under multiple factors, especially the high loading rate, on the performance of the RGIA in clay are quantitatively investigated by performing six groups of cases, from which the effects of drag velocity, initial embedment depth, gradient of shear strength of clay, and cable parameters can be known. The formula for calculating the MEL of the RGIA in clay is also constructed with high precision by taking into account comprehensive drag effects. The numerical study demonstrates that, compared with the OMNI-Max anchor, the RGIA achieves deeper initial penetration depth during installation, requires shallower initial penetration depth that ensures subsequent keying and diving, and possesses stronger ability of resisting dynamic loading with high loading rates. • Systematic techniques of simulating comprehensive behaviors of the RGIA in clay. • Innovative technique of simulating soft shanks of the anchor. • Method of determining the optimum shackle point for the RGIA. • Formulas of calculating the maximum embedment loss under different loading rates. • Enhanced anchor performance of the RGIA in clay compared with the OMNI-Max anchor. [ABSTRACT FROM AUTHOR]

Suction anchor is a widely used anchorage foundation in taut or catenary mooring systems to fix floating structures. This paper aims to investigate the pull-out capacity and failure mechanism of suction anchors in sand using the finite element method which models the attached mooring line on the anchor padeye. The advanced critical state elastoplastic constitutive model SIMSAND is utilized which can well simulate the state-dependent peak strength and stress-dilatancy behavior of sand, and its accuracy and effectiveness are validated with centrifuge test results. A series of systematical parametric studies are then carried out to explore the effects of the mooring line, aspect ratio, padeye position and loading angle on the pull-out capacity and failure mechanism of the suction anchor. Based on the numerical results and those obtained in other researchers' work, the optimal padeye position and the normalized V – H envelopes are explicitly discussed. Finally, a calculation framework is put forward for predicting the inclined pull-out capacity of suction anchor in sand considering the mooring line effect. • The effects of mooring line on the pull-out capacity and failure mechanism of suction anchors in sand are clarified. • The optimal padeye depth and normalized V – H failure envelopes are discovered. • A calculation framework is put forward for predicting the inclined pull-out capacity considering mooring line effect. [ABSTRACT FROM AUTHOR]

A rapid expansion of the anchor market is required to meet the increasing demand for floating offshore wind. This paper, which is aimed at a broad readership within and beyond geotechnical engineering, summarises the current state-of-the-art and discusses future developments of anchor types and geotechnical design methods. Current anchor technologies are presented via comparative analytical assessments of performance across a range of practical scales and seabed conditions. This analysis demonstrates the relative merits and performance of different anchor types, using simplified cost-performance indicators for each anchor technology. An example outcome is the large differences in anchor efficiency (capacity per unit weight), that are linked to the different ways anchors achieve their holding capacity. Potential improvements in the performance-cost response for each anchor type, through future enhancements, are then explored. These enhancements are categorised as (1) unlocking higher anchor performance through improved design methods with a better understanding of the geotechnical response, (2) upscaling or (3) commoditising of the anchor type, by making larger versions or enabling more efficient mass production and installation, or (4) invention of new anchor technologies. Finally, findings of the different sections are summarised within a single table to enable a quick selection of anchoring solutions. • The resistance of several anchor technologies was systematically compared. • Plate type anchors and screw anchors were shown to be the most efficient. • Advanced design methods to deal with complex ground or loading were summarised. • 4 Innovation axes were described: unlocking, upscaling, commoditising, inventing. [ABSTRACT FROM AUTHOR]

This research introduces an alternative recent technique, bladed pile anchor, which aims to increase the surface area under the soil during uplift. This provides more shear resistance acting along the failure surface and increases the dead weight of the surrounding sand within the failure zone to resist the uplift force. As a result, the uplift capacities are increased. In this experimental study, the effect of many parameters, such as blade length ratio, blade width ratio, and sand relative density, on the ultimate uplift capacity of bladed pile anchors is investigated. The uplift capacities of bladed pile anchors embedded in sand increase with the increase of the blade surface area by increasing the blade length ratio and the blade width ratio. At blade length ratio of 3 and blade width ratio of π/2, the percentage increase in the uplift capacity reaches (275%, 233%, and 230%) at relative densities of (30%, 50%, and 80%), respectively, compared with regular pile. The existence of blades created an ideal anchorage system due to the increased surface area beneath the soil, resulting in increased uplift capacity. This pile modification is valid and suitable for marine structures, and it is easy to install for this application. • This research introduces an alternative recent technique, bladed pile anchor, which aims to increases the surface area under the soil during uplift, and this provides more shear resistance acting along the failure surface and increases the dead weight of the surrounding sand within the failure zone to resist the uplift force. • An experimental laboratory study was used to investigate the behavior of bladed pile anchor subjected to uplift load for different parameters. • Pre-displacement to open the blades. • Load factor, Break-out factor, Unit shaft resistance, lateral earth pressure, and Diameter of equivalent regular pile. • This pile modification is valid and suitable for marine and offshore structures to resist uplift load and is easy to install for this application. [ABSTRACT FROM AUTHOR]

It is worth deliberating on torpedo anchors, a development that emerged in the offshore exploration field in recent times. The demand for ocean renewable energy exploration and this interest required developing a new sort of mooring and anchoring systems for offshore platforms. Though a vast type of anchors has been developed, the literature lacks a critical review of torpedo anchors. This critique summarizes a state-of-the-art discussion on torpedo anchors. It aims to review the developments of deep-water torpedo anchors that occurred during the last few decades. The level of growth achieved in this field is significant, economical, and reliable, making it simple and easing the anchor installation operation. This paper recapped the detailed survey of theoretical, experimental (laboratory and field-test) and numerical analysis and design of torpedo anchors and reviewed their performance. And a complete discussion of the torpedo anchor's primary factors (pullout capacity and embedment depth) influencing characteristic features is explained. In addition, it describes the soil failure process of the anchors during penetration and pullout of the anchor. A wide range of features for the application of torpedo anchors is readily enabled. In conclusion, the current challenges encountered in this field are mentioned. • This critique summarizes a state-of-the-art discussion on the torpedo anchors and aims to review the recent developments. • This paper recapped the theoretical, experimental and numerical method of analysis and design of torpedo anchors. • This paper also reviewed various characteristic features influencing torpedo anchor's performance. • A wide range of features for the application of torpedo anchors are readily enabled from this study. [ABSTRACT FROM AUTHOR]

Dynamically installed anchors (DIA) provide a time-efficient and cost-effective anchoring solution for offshore floating moorings. The dynamic installation and capacity mobilisation of the DIA in clayey seabed have been systematically investigated. However, the performance of the DIA in sand and silt is rarely studied. This study aims at investigating the performance of a newly proposed light-weight gravity installed plate anchor in sand and silt by conducting large deformation finite element (LDFE) analyses. Parametric studies were conducted to investigate the effects of varied factors on the final penetration depth of the anchor. By combining the present numerical results and previous experimental results, a comprehensive theoretical model was proposed for predicting the final penetration depth of the anchor in sand, silt and clay. Then the anchor-chain-soil interaction was simulated to investigate the keying behaviour of the anchor in silt, such that the motion trajectory and capacity mobilisation of the anchor could be derived. The conditions ensuring the anchor diving have been recommended. • The performance of a newly proposed light-weight gravity installed plate anchor in sand and silt is investigated. • A comprehensive theoretical model was proposed to predict the final penetration depth of the anchor in sand, silt and clay. • The motion trajectory and capacity of the anchor are investigated and the conditions for anchor diving are recommended. [ABSTRACT FROM AUTHOR]

Accurate prediction of the final embedment depth and installation-induced excess pore pressure of dynamically installed anchors (DIAs) are prerequisites for the design of subsequent anchor set-up during a waiting period and capacity under operational loadings. This paper presents a dynamic large deformation finite element approach within the effective stress framework and investigates the installation behaviour of DIAs in clay. An elasto-viscoplastic model is adopted to capture strain rate dependency of the undrained shear strength. Development of excess pore pressure for various impact velocities, anchor geometries, viscosity parameters are quantified. An expression is proposed for estimating the final embedment depth of DIAs in clay. • A dynamic LDFE approach within the effective stress framework is developed, incorporating a strain rate-dependent model. • The excess pore pressures caused by rapid penetration of a dynamically installed anchor can be captured. • A simple equation is proposed to predict the final embedment depth of anchor. [ABSTRACT FROM AUTHOR]

Considerable efforts are being made worldwide to develop offshore wind energy, both in shallow and deep waters, where bottom fixed solutions are still dominating. Development and successful implementation of offshore floating wind will depend on reducing costs in all areas including design, manufacturing, installation, and operation. Two important cost drivers are manufacturing and installation of the anchoring system. This paper discusses the application of dynamically installed anchors for floating offshore wind turbines. Based on experience from field and model tests, a detailed description of the different aspects of anchor design is presented. At the example of a recently installed floating offshore wind farm, the advantages of the proposed concept are demonstrated. Further cost reduction is achieved by the presented and discussed shared anchoring system. • Dynamically installed anchors for use in floating offshore wind farms. • Anchor sharing using gravity-installed anchors in floating offshore wind farms. • Dynamically installed anchors can reduce the costs of floating offshore wind farms. [ABSTRACT FROM AUTHOR]

The reliability of mooring systems is a critical issue for deepwater floating structures. Gravity installed anchors (GIAs) have been effectively employed in a significant number of mooring systems, whose embedment loss and kinematic behaviors under the cable loading conditions also attract attention to the reliability of the anchors during service. Particularly, the embedment loss of the anchor may result in the failure of the anchor. The present work focuses on systematically investigating the failure state of anchors in clay induced by embedment loss under various complex conditions. A theoretical model for analyzing the comprehensive behaviors of the anchor is constructed, which is validated by previous centrifuge tests and 1g model tests. A rational criterion for determining the state of failure induced by embedment loss is proposed and applied to the analytical results of the theoretical model. The factors that have a substantial impact on embedment loss of the anchors, including the anchor embedment depth, anchor orientation, cable loading angle at the seafloor, soil adhesion factor, soil strength, and cable properties are investigated in the analytical cases. OMNI-Max anchors, being one of the most remarkable GIAs and having complex kinematic behaviors, are selected to reveal the influences of these factors on the failure state of the anchors. Based on the results of numerous analytical cases, the failure surfaces in the three-dimensional spatial data field are presented, which reveal the critical state of the anchor under different conditions. Furthermore, these failure surfaces are stated using a surface function. The function can be used as a simple judgment condition for the state of failure owing to anchor embedment loss. The findings of earlier investigations support the applicability of the surface function. In addition, the promising application of the surface function in practice is highlighted. • Systematical investigation of the failure induced by embedment loss of GIAs. • An efficient theoretical model for analyzing comprehensive behaviors of GIAs. • A rational criterion for determining the failure status of GIAs induced by embedment loss. • Failure surfaces of GIAs based on numerous analytical data. • A convenient failure surface function for different scenarios in engineering practice. [ABSTRACT FROM AUTHOR]

Anchoring steel pipes to bare and hard rock under deep water is a challenging and labor-intensive task, traditionally requiring a socket hole the full diameter of the steel pipe pile. We propose and analyze a novel anchoring method using three tendons, requiring three holes totaling a small fraction of the pile's cross-sectional area. This study presents a numerical analysis of the proposed anchoring construct, a steel pile with a concrete core and three tendons. The results indicate that the load-displacement response of the proposed pile system can be generally divided into three regions by two characteristic points: tendon-rock interface debonding, and tendon yielding. The pile stiffness declines significantly beyond these characteristic points. Analysis reveals that the diameter of the steel bar and interaction between tendons and rock are key links that control the load transfer efficiency. The parametric studies indicate that the length of the concrete core, the length of tendon, and the diameter of steel bar are the more important factors influencing the load-displacement responses. There are thresholds for the lengths of the concrete core and of the tendons, beyond which increases in the parameters have no further ameliorative effect on the performance of the steel pipe pile. •A novel anchoring method for steel pipe pile in bare and hard rock under deep water is proposed. •The load transfer mechanism for the proposed steel pipe pile is analyzed. •A parametric study is conducted systematically. [ABSTRACT FROM AUTHOR]

Floating offshore wind turbines are characterised by complex coupled dynamics between the floating structure and turbine. These are subjected to a combination of aerodynamic, hydrodynamic and servo-dynamic loads which must be quantified when considering the requirements of a mooring and anchoring system. If suitably engineered, shared anchors enable reduced hardware and installation costs for floating wind turbines. This paper presents the results of coupled dynamic simulations, evaluating single and shared anchor loads for different mooring configurations considering the IEA 15 MW turbine and VolturnUS-S reference platform subjected to environmental loads representative of the Celtic Sea. Simulations highlight that increasing the mooring footprint in shallow waters can reduce loads by up to 56% and through anchor sharing, peak loads can be reduced by 67%. The advent of anchor sharing, however, significantly alters the directionality of the applied loads. Misalignment of wind and wave conditions is also shown to have a considerable impact on anchor loads highlighting the importance of considering operational and parked design load cases, with wind and waves propagating from a range of directions, to adequately design and optimise a mooring and anchoring system. This paper will inform mooring and anchor design optimisation for large-scale floating wind turbines. • Mooring and anchoring analysis undertaken for floating IEA 15 MW turbine in single and array configurations. • Shallow water (70 m depth) site representative for farm deployments considered in the Celtic Sea. • Misalignment between turbine, wind, and waves found to have impacts on loads. • Shared anchor systems can reduce loads on anchor, but alter directionality. • Presented results inform mooring optimisation and anchor design. [ABSTRACT FROM AUTHOR]

Submarine cables are important equipment in many power engineering and communication engineering projects. However, power transmission and signal transmission is threatened by anchors hitting submarine cables. Due to the nature of the helical structure of the cable, different angles of impact have different effects on submarine cable damage. In this paper, a three-dimensional dynamic response analysis model, "ship anchor – three-core composite submarine cable – soil", is developed based on ABAQUS to study how the impact angle of ship anchors influences the damage to submarine cables. It explores the damage to cables struck by anchors of different weights and at different speeds. The longitudinal compression rates of conductors and the optical fibre units of submarine cables at different burial depths are obtained and advice for the protection of cables is provided. The results show that anchor speed has a greater impact on cable damage than anchor mass. The impact angle on cable conductors and the optical fibre units decreases as the depth of burial increases. A burial depth greater than 1.9 times the cable diameter provides a protective effect on the submarine cable. • ABAQUS establishes the anchor-three-core composite submarine cable-soil three-dimensional dynamic response analysis model. • Study the damage of submarine cables to anchor impacts in different states. • Considering the impact angle of the anchor. • Summarizing the protection method of the submarine cable. [ABSTRACT FROM AUTHOR]

Mooring line responses have been widely analyzed in the past three decades. Most of these studies have assumed that the anchor point is fixed at the seabed. However, with the increasingly employment of the taut mooring system, the suction anchors are more and more often used. To achieve an appropriate hold capacity, the anchor points are embedded several meters beneath the seabed, making part of the mooring lines embedded, whereby complex soil-chain interaction occurs. The soil-chain interaction has not been incorporated in previous mooring dynamic analyses. In this study, a dynamic method using the lumped mass model was used to consider the soil-chain interaction for the embedded anchor chain. Validation has been conducted against both analytical results and those from the commercial code. To clarify the influence of the embedded chain, case studies were conducted to compare the line's dynamic response at the anchor point, touchdown point and fairlead in three different configurations. Recommendations have been given on two frequently-used in simplifying the mooring dynamic calculation. [ABSTRACT FROM AUTHOR]

Developing deep sea technologies, many marine novel facilities have been introduced; and mooring systems, however, have become more expensive, complex, and hard cooperative in deep-water marine industry. The torpedo anchor is regarded as a modern technology benefits from easy installation, cost efficiency, and high level of anchor force. In this study, the penetration depth of a free falling torpedo anchor into cohesive soil has been laboratory investigated. 128 Sets of tests have been conducted with nine different torpedo anchors not only in shape, but also in size. Three anchor aspect ratios and three different types of muds were tested while mud rheological properties such as the yield stress and flow curves were also measured. Finally, a formula calculating the penetration depth of the anchor, regardless of soil separation has been proposed based on energy conservation principle and experimental measurements. Results indicate that the predicted penetration depth has a good conformity with the measured penetration depths in laboratory and field tests. Static undrained shear strength values should be reduced in formula when the impact velocity exceeds a critical value. Soil separation occurs depending on the anchor nose angle and surface roughness, and also soil properties. Nevertheless, the critical impact velocity resulting into soil separation and its degree require further study in the future. [ABSTRACT FROM AUTHOR]

Gravity installed anchors (GIAs) are designed to dive into deeper seabed under cable loading to seek higher capacity, typically for OMNI-Max anchors. This feature makes the anchors more likely to penetrate through different soil layers, leading to more complicated behaviors than in single-layered soil. Furthermore, the behavior of anchor lines in multi-layered soils becomes more complicated and significantly affects the anchor behaviors. All of these bring challenges to the trajectory prediction of GIAs in the multi-layered seabed. The present work introduces theoretical and numerical approaches to predict the comprehensive behaviors of GIAs by dealing with the coupled effect of anchor lines in multi-layered clays. The theoretical and numerical models are verified by comparing with the published data of centrifuge tests and numerical simulations. The comparative study indicates that both the models have the ability to explore the effects of different factors, such as the embedment depth, the soil strength, the thickness of layers and the distribution of multi-layered soil. The complexity and variety of anchor behaviors in multi-layered clays are revealed by typical application cases, further confirming the ability and potential of the developed models. • A theoretical model for three-dimensional GIAs in multi-layered clays. • LDFE analyses on the trajectory of OMNI-Max anchors in multi-layered clays. • Anchor line behavior in multi-layered clays coupled in theoretical and numerical analyses. • Complicated behaviors of the OMNI-Max anchor in multi-layered clays. • High efficiency of the theoretical model for analyzing GIAs in multi-layered clays. [ABSTRACT FROM AUTHOR]

Single point mooring system anchored by piles has been widely used to support floating offshore platforms. However, the failure mechanism and soil displacement of the anchor pile subjected to oblique pullout loads are still unclear. Based on transparent sand and PIV technique, a visual centrifuge test system for anchor piles of single point moorings was established. A series of centrifuge model tests were performed on the pile under oblique pullout loads, and the measured soil displacement field results were compared with the finite element simulation, indicating that the centrifuge modeling using transparent sand are suitable for studying the anchor pile behaviors and soil deformation. A modified semi-empirical method was also proposed, which can predict the bearing capacity of piles under difference loading angle and loading position in sand. It shows that with the increasing loading angle and pad eye depth, the pile horizontal translation and soil horizontal deformation become more obvious, and the pullout bearing capacity increases. The proportion of the soil horizontal displacement for θ = 75° is nearly 4.1 times of that for θ = 37°, and the horizontal displacement proportion for z = 0.75 L increases approximately 25% of that for z = 0.67 L. • Based on transparent sand and PIV technique, a visual centrifuge test system for anchor piles is established. • Centrifuge model tests are performed on the behavior of anchor piles and soil displacement field under oblique pullout load. • A semi-empirical equation considering loading position and loading angle is proposed to predict the pullout bearing capacity. [ABSTRACT FROM AUTHOR]

This paper assesses the performance of the fish anchor in silty sand deposits with the aim being potentially using the anchor in supporting floating wind turbines in shallow water sandy seabed. A total of seven tests were undertaken in a beam centrifuge. The model fish anchors were dropped from a height of 36.75–57.72 m above ground level. The achieved impact velocities were 17.15–27.42 m/s. The anchor with a dry weight of 1175–1338 kN embedded into the soil deposit to a depth of 0.81–1.18 times the length. The normalized tip embedment depths were plotted in a total energy framework, and explained by a shear resistance method. The embedded anchor was loaded monotonically up to the failure. The peak capacity at failure was found to reduce with increasing the loading (mooring) angle at the mudline to the horizontal. For vertical or 90° loading, the capacity was around 2 times the weight of the anchor submerged in water. The capacity increased to 7.13 times the weight as the loading angle reduced to 0° (horizontal). The strong resistance of sandy soil and higher load inclination at the padeye prevented the diving potential of the anchor. • Performance of the dynamically installed fish anchor in silty sand. • Centrifuge model tests simulated dynamic installation and loading tests. • Fish successfully embedded into silty sand by 0.81–1.4 times the anchor length. • Holding capacity of fish anchor was 3–7.13 times its submerged weight. [ABSTRACT FROM AUTHOR]

The penetration behavior of drag anchors in the seabed is directly controlled by the anchor handling vessel (AHV) and the installation line. However, the drag effects produced by the AHV and the installation line are difficult to investigate by either theoretical or experimental methods. In the present work, a large deformation numerical analysis employing the coupled Eulerian–Lagrangian technique is performed to investigate the effects of the drag velocity of AHV, the uplift angle of installation line, the diameter of installation line, and the length of installation line. It is demonstrated that the movement direction and the drag angle at the shackle of the anchor are not influenced by drag effects, while the drag effects on the anchor trajectory and the drag force are significant. Findings of the present study also yield a relation between drag velocity and drag force and the knowledge of the ultimate embedment depth of anchor and the critical length of installation line, which are beneficial to fully understanding the drag embedment problems and to enhancing the installation techniques for drag anchors. [ABSTRACT FROM AUTHOR]

This study investigates the performance of group suction anchors installed in silty sand and subjected to horizontal pullout loading. The group anchors in this study consist of two or three unit suction anchors rigidly connected to each other in parallel array to improve the pullout resistance. The performance of these group anchors was studied extensively using centrifuge model tests and numerical simulations. The pullout resistances of the group anchors were compared with that of a single anchor. To quantify the improvement, the efficiency of a group anchor was defined as the ratio of the pullout resistance of a group anchor to that of a single anchor multiplied by the number of the unit anchors, and the improvements are discussed. Additional parametric studies were performed using numerical models to study the effect of the physical conditions of the group anchor. The parameters include the L / D ratio of a unit suction anchor, and the spacing between unit suction anchors. [ABSTRACT FROM AUTHOR]

A procedure for obtaining the dynamic characteristics of rock berms in the event of an anchor collision is developed, a safety analysis is performed, and associated recommendations are made. The drag coefficients of five target anchors were obtained through finite element flow analysis, and their terminal velocities calculated to maximise colliding kinetic energy. The dynamic behaviours of the rock berms were modelled by smoothed particle hydrodynamics (SPH). Six parameters were considered in the collision analysis: anchor type, collision velocity, SPH particle size, ground state, rock berm size, and collision point. The results were verified by an existing field test and a safety analysis was carried out with respect to parameter variation; the associated recommendations are discussed. It was found that rock berm height is the most critical factor in ensuring the safety of power cables. Rock size and installation depth are important to satisfy the safety criteria established in this study. [ABSTRACT FROM AUTHOR]

A multi-plate vertical anchor is a structural member designed to resist the horizontal pullout forces to provide stability to retaining structures inland and onshore. The tensile load of a structure is resisted by the multi-plate anchors using a number of plates connected axially along the central shaft. For a given embedment depth and placement ratio considered, the multi-plate vertical anchors generate higher pullout capacity than the single-plate vertical anchors. This paper presents a detailed experimental study to estimate the ultimate pullout capacity of circular multi-plate vertical anchors embedded in the sand. The plate anchors are placed at varying horizontal distances from the sidewall of the test tank. The pullout capacity of the single-plate vertical anchors was compared with the existing studies. The dimensionless breakout factors show that the multi-plate anchor can efficiently replace the existing single-plate anchors. The paper briefly discusses the scale effect, the effect of spacing, and the effect of anchors' placement ratio on pullout capacity. Results show an increase in pullout capacity of double-plate and triple-plate vertical anchors with an increase in embedment ratio and placement ratio. The results also show an increase in the breakout factor of multi-plate anchors with increased spacing between the plates. • Archaic usage of single-plate anchors occupying a stretch of land area; their replacement with a newer technology. • Laboratory studies on multi-plate vertical anchors of circular shape. • Development of passive mobilization of soil, a study on its interference with the side-wall of test chambers. • Effect of multiple plates on the development of heave, and its monitoring in the field. • Reduction of area of land use with the contribution of an effectively faster construction practice. [ABSTRACT FROM AUTHOR]

Natural gas hydrate (NGH) is a potentially green energy resource for the future. Five trial production experiments of marine NGH have been carried out worldwide. However, the currently widely used drilling method has poor economic applicability, and there are still many critical technical problems that need to be solved. Based on the characteristics of marine NGH reservoir and the exploration principle, a novel self-entry exploration device (SEED) according to the penetration mechanism of torpedo anchor was proposed, and the working principle was described in detail. The SEED could significantly reduce the cost of NGH exploitation because it eliminates the need for deepwater drilling rigs. Moreover, unlike traditional cement wellbore, the SEED is an artificial rigid structure that withstands greater depressurization to increase efficiency. The penetration laws and gas production characteristics of the SEED were studied through numerical simulation. The research results show that the penetration depth into the seabed can reach more than 300 m, which can cover most of the NGH reservoirs' depth. The gas production efficiency is significantly improved compared to the traditional wellbore. The SEED has specific potential for exploring marine NGH, providing a new idea for commercial exploitation. • A self-entry exploration device (SEED) was proposed to enhance gas recovery from natural gas hydrate reservoirs. • The new device penetrates into the reservoir by impact and then performs depressurization exploitation. • The penetration depth of the device can cover the buried depth of most natural gas hydrate reservoirs. • The device consists of a steel structure, allowing for greater pressure drop and expanding contact area with hydrates. • New method eliminates the need to drill wells and is reusable, promising a significant reduction in production costs. [ABSTRACT FROM AUTHOR]

Abstract: Suction embedded plate anchors, as used in practice, include a hinged keying flap aligned with the main anchor plate (fluke). The flap was designed to rotate away from the shank during keying of the anchor, to minimise loss of anchor embedment and the associated reduction in pull-out resistance. However, it has been observed experimentally that the flap is activated only once keying is nearly completed, and thus does not assist in reducing embedment loss. In this paper, the performance of the keying flap is investigated using a large deformation finite element approach based on frequent mesh regeneration. The moment acting at the flap hinges, determined from the soil pressures and shear forces on the keying flap, is quantified. The moment controlling the flap activation depends mainly on the net soil pressure on the front or back face of the flap, and this prevents activation of the flap while the anchor is rotating significantly. The flap is only activated once the anchor motion becomes dominated by forward translation, normal to the plate. Various factors affecting flap activation and embedment loss are explored, including flap height, eccentricity of the padeye, soil strength profile, initial anchor depth and load inclination. [Copyright &y& Elsevier]