Penetration Depth Of Anchor Research Articles

Formulation of Anchor and Chain Specifications for Establishing Subsea Cable Burial Depth

The penetration of ship anchor, which is a very important factor considered in the design stage of subsea cable burial, is highly dependent on the geometrical specifications and shapes of the anchor and chain. In order to facilitate predicting the anchor penetration depth by an arbitrary ship, formulations of the correlation between the ship mass and the existing anchor and chain specifications were attempted. In particular, for small ships with an equipment number of 40 (corresponding to DWT 90) or less, which were not covered by the existing classification data, a method for estimating the anchor mass, chain diameter, and mass per unit length was proposed.

Numerical Analysis for Estimating Penetration Depth by Ship-dragged Fluke Anchor

Anchor penetration by ship anchoring is emerging as a major risk factor for submarine cable. A numerical analysis method was established to predict the anchor penetration depth by ship-dragged fluke anchor in relation to setting the optimal burial depth of submarine cable. The soil resisting forces (bearing force, friction force) generated during the anchor penetration process were calculated for each of the fluke, shank and mooring chain of the anchor. The results of the numerical analysis were compared with the existing chart values of Vryhof (2015). It was found that it is desirable to use the force coefficients of strip foundation for the fluke and shank, and the force coefficients of a single vertical pile for mooring chain. The numerical analysis well reproduced the penetration trajectory in which the inclination angle of the lower surface of fluke gradually converged to zero.

Dynamic installation of torpedo anchors in slightly overconsolidated clay-overlaying-sand deposit

Torpedo anchor installation involves uncertain design and construction parameters, especially in layered soil deposits. Large deformation finite element and coupled Eulerian–Lagrangian (LDFE/CEL) analyses are performed in this study to elucidate the dynamic installation of torpedo anchors in an over consolidated clay-overlaying-sand deposit. The parametric analysis is conducted after model verification to explore the effect of upper clay layer thickness, anchor impact velocity, anchor submerged weight, soil properties and anchor geometric dimensions. The soil failure patterns and dynamic installation behaviour in the clay-overlaying-sand soil deposit are found to differ substantially from those in single-layer clay and sand deposits, which exhibit a squeezing flow pattern at the clay-sand soil layer interface. As the demarcation of the two velocity phases during the anchor penetration process (acceleration and deceleration phases) falls below the interface of two soil layers, the contribution of the internal friction angle of sand to the anchor final penetration depth exceeds that of the clay undrained shear strength. Based on intensive modelling data, an empirical method for predicting the anchor penetration depth in single and layered soil deposits is derived for engineering applications.

Study on Buried Depth Protection Index of Submarine Cable Based on Physical and Numerical Modeling

The buried depth of submarine cables is very important to avoid damage on the cable from dropping and dragging anchors. This study focused on the actual engineering needs of submarine power cable protection and laying construction. In order to investigate the buried depth protection index of submarine cable, physical model tests, theory analysis, and numerical simulations were conducted in this study. The effects of the bottoming velocity, dropping energy, and anchor mass on the anchor penetration depth were analyzed and investigated. The analytical model based on the impact and drag mechanism is presented to analyze the forces and energy on the anchor. The accuracy and reliable of the model test results are verified by the theory analysis and numerical simulation, indicating that the buried depth protection index of the submarine cable in the research area is recommended to be 3 m. The research results can provide guidance for operation of the submarine cable laying machine and submarine cable protection.

Anchor penetration depth in sandy soils and its implications for cable burial

Modern society is dependent on offshore cables and consequently cable faults lead to major disruption and economic loss. The most effective way to protect offshore cables from anchor damage is to bury them in the seabed, but current guidance is ambiguous. This paper attempts to produce more rational design guidance for anchor penetration in sand based on centrifuge modelling, allowing suitable burial depths for cables to be calculated based on the more useful metrics of anchor or ship size.A miniature anchor was dragged through sand of different densities within a centrifuge with maximum anchor penetration being measured. The most significant factor that influences anchor penetration depth is the size of the anchor, investigated by completing centrifuge tests at different g-levels. A linear relationship was recorded between anchor size and penetration depth which was used to develop new guidelines for cable burial. The new chart is clear and easy to use, with the cable burial depths given in relation to anchor size, anchor mass and ship mass. Use of this chart will enable the safe and economic burial of cables, and lead to a decrease in the impact of anchor damage to offshore cables.

Evaluation of Anchor Penetration Depth based on Numerical Analysis for Burial Protection Method of Submarine Cables

Submarine cables are installed and operated for the stable power supply of island regions, and feature protective measures to counter marine hazard factors. With regard to the protection techniques to prevent damage to submarine cables, the method of digging and embedding the submarine ground is applied the most. However, since there are no design criteria and techniques for such protection facilities, the burial depth of the submarine ground has been calculated only qualitatively and empirically after an ocean survey is conducted. Such an imperfect method has led to assorted damages to submarine cables. Therefore, in this study, to ensure the safety of submarine cables from marine hazard factors, the three-dimensional dynamic interaction analysis model was established for the ship anchor and ground, and the penetration depth of this anchor was calculated through numerical analysis for the burial protection method. These results were compared and evaluated with the results of the full scale test for anchoring and dragging anchor. As a result, the error rate(average) of the anchor penetration depth through the numerical analysis and test was 12.2% in the ground conditions of sand, clay and multi(clay/sand) layers. This error rate was analyzed to be caused by various uncertainties in the test, such as the dynamic impact of the anchor and ground conditions, and the numerical analysis was evaluated to ensure sufficient reliability. The results of this study are expected to be useful in the burial depth calculation of the burial protection method to ensure the safety of submarine cables.

Research on the characteristics and physical model test method of penetration depth for ship emergency anchoring

Based on the whole process theory, the characteristics of penetration depth for ship emergency anchoring are summarized. Combined with the actual project, the physical model test was carried out, and the scale ratio was set for the soil and anchor. Different working conditions are designed for water flow, vertical height and horizontal velocity Angle, and the model test of anchor penetration depth was carried out. The experimental results show that whether there is water flow or not and the variation of water flow conditions have certain effects on the penetration depth of anchor; when the anchor only has vertical velocity, the faster the anchor hits the bottom, the deeper the anchor penetrates into the soil; when the anchors have horizontal velocity synchronously, the penetration depth of the anchors increases slightly. Compared with the traditional model, the results obtained by this method are closer to reality and provide ideas and references for penetration depth for ship emergency anchoring.

An innovative booster for dynamic installation of OMNI-Max anchors in clay: Physical modelling

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 1g 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).

An innovative concept of booster for OMNI-Max anchor

OMNI-Max anchors are newly developed dynamically installed anchors for deep water mooring systems. However, the final penetration depth of the anchor after its dynamic installation can be limited, especially in a strong soil seabed with high strength gradient, due to its limited release height in water and large contact areas between the anchor flukes and the adjacent soil. To increase the anchor final penetration depth in seabed, an innovative concept of anchor booster is proposed in this paper. The booster, comprised of a cylindrical shaft with three rear fins, is attached to the anchor tail during its dynamic installation and then is retrieved after installation for reuse. The boosters with three different sizes, hence different masses, are designed and tested. Three dimensional computational fluid dynamics (CFD) simulations were conducted to investigate the working efficiency of a booster on the final penetration depth of the OMNI-Max anchor in a strong soil seabed. Moreover, the entire process of the dynamic installation of the hybrid anchors (an OMNI-Max anchor with a booster) from water to seabed is predicted by a theoretical model. The results demonstrate that the booster is beneficial both in improving the directional stability and impact velocity for the OMNI-Max anchor during its free fall in water. Relative to the OMNI-Max anchor, the final penetration depth of a hybrid anchor increases significantly (from 23% to 115%) due to the addition of the booster, which helps the anchor to gain higher holding capacity. This preliminary study is only to prove effectiveness of the booster concept without a complete investigation of the booster. More detailed studies are planned in the pipeline.

考虑浅埋破坏的拖曳锚在黏土中安装运动特性分析

The drag anchor is widely used in offshore engineering as a foundation for the mooring system due to high capacity and low cost. The prediction of kinematic behavior and trajectory is still challenging due to the complex interaction of the anchor fluke with soil. The existing plastic yield envelope method is generally used for the kinematic analysis, where the deep anchor failure is assumed to occur during the whole dragging process. In reality, the penetration is a process of anchor fluke being dragged into seabed soil continuously from shallow to deep depths. Obviously, the existing yield envelope method could not capture the effect of shallow anchor failure, which may lead to inaccurate prediction of the anchor trajectory. Finite element analyses were conducted firstly to obtain the influences of the anchor embedment depth and angle of the fluke on the drag anchor behaviors under unidirectional and combined loadings. The yield envelope for the shallow anchor failure was determined accordingly, with which the shallow failure effect can be taken into account for the yield envelop method. The effects of the fluke angle, the bearing capacity factor and the shallow zone size were investigated. The predicted trajectories with and without the shallow failure effect were compared. It is shown that the fluke angle and the shallow failure zone size influence significantly the kinematic behaviors and the trajectory of the drag anchor. The consideration of shallow failure results in a shallower predicted anchor embedment depth and a smaller anchor line force before the anchor penetration depth stabilizes, but hardly changes the ultimate embedment depth.

Design of Rock-berm by Anchor Dragging Simulation using CEL Method

In this study, an anchor dragging simulation was performed using the CEL method to design a rock-berm, which is a protection method for submarine cables. In order to simulate an anchor drag, preliminary simulations were first performed to determine the initial anchor penetration depth, anchor drag velocity, drag angle, and distance between the anchor and rock-berm. Based on the preceding simulation results, a safe rock-berm design for protecting the submarine cables was simulated to calculate the anchor penetration depth by the anchor dragging. As a result, the penetration depth of the anchor was found to be shallower in a hard seabed, and the penetration depth was deeper in a soft seabed. , the height of the rock-berm was determined according to the physical properties of the seabed.

Dynamic installation of a torpedo anchor in two-layered clays

The behaviour of a torpedo anchor during dynamic installation in two-layered nonhomogeneous clay sediments was investigated through large-deformation finite-element (LDFE) analyses. Parametric analyses were undertaken varying the top layer thickness and strength ratio between two layers. Results show that the location of the demarcation point between the acceleration and deceleration phases of the anchor in the soil relative to the layer interface is the key factor directing the anchor behaviour in layered soils including the final embedment depth. Broadly speaking, the anchor behaviour in soft-over-stiff clay deposits is somewhat similar to that in single layer clay with strength increasing with depth. In stiff-over-soft clay deposits, the anchor penetrates deeper where the anchor deceleration phase (or the demarcation point) falls within the soft layer. Where the demarcation point lies within the top stiff layer, the anchor penetration depth decreases with increasing strength ratio, and the anchor penetration is terminated between the two layers for strength ratios ≥15. For assessing the anchor embedment depth in two-layered fine-grained ocean sediments in the field, an extended total energy–based method, along with a design expression, is proposed.

Penetration depth of torpedo anchor in cohesive soil by free fall

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.

A prediction method for anchor penetration depth in clays

Anchoring is one of the main causes of subsea pipeline damage, which makes anchor penetration depth one of the most important references for the design of subsea pipeline burial depth. The anchor penetration process is analysed experimentally, numerically and theoretically. First, a series of model tests of dropping anchors are conducted to study the influences of anchor weight, dropping height on the penetration depth. Second, taking the effects of strain and strain rate into account, a finite element method (FEM) model of anchor penetration is set up with Coupled Eulerian–Lagrangian (CEL) method. The soil deformation and effects of strain and strain rate are analysed with the CEL model, and the model is validated against the test results. Then the effects of touch-down velocity and soil properties on penetration depth are analysed with the numerical model. Third, the anchor penetration process is analysed with classical bearing capacity theory. The average bearing coefficient during anchor penetration is back-analysed with experimental and numerical results. And a prediction method for the average bearing coefficient, which takes into account the effect of touch-down velocity, is proposed. Finally, the prediction process for the penetration depth of dropped anchor is proposed. The proposed method is of great significance for predicting anchor penetration depth and subsea pipeline burial depth.