• Smart Structures and Systems
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• v.15 no.2
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• pp.299-314
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• 2015

Submersed rock-berm structures are frequently used for protection of underwater lifelines such as pipelines and power cables. During the service life, the rock-berm structure can experience several accidental loads such as anchor collision. The consequences can be severe with a certain level of frequency; hence, the structural responses should be carefully understood for implementing a proper structural health monitoring method. However, no study has been made to quantify the structural responses because it is hard to deal with the individual behavior of each rock. Therefore, this study presents a collision analysis of the submersed rock-berm structure using a finite element software package by facilitating the smoothed-particle hydrodynamics (SPH) method. The analysis results were compared with those obtained from the Lagrange method. Moreover, two types of anchors (stock anchor and stockless anchor), three collision points and two different drop velocities (terminal velocity of each anchor and 5 m/s) were selected to investigate the changes in the responses. Finally, the effect of these parameters (analysis method, anchor type, collision point and drop velocity) on the analysis results was studied. Accordingly, the effectiveness of the SPH method is verified, a safe rock-berm height (over 1 m) is proposed, and a gauge point (0.5 m above the seabed) is suggested for a structural health monitoring implementation.

• Journal of Ocean Engineering and Technology
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• v.30 no.2
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• pp.109-116
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• 2016

A flexible concrete mattress (FCM) is a structural system for protecting submarine power or communication cables under various load types. To evaluate its of protection performance, a numerical analysis of an FCM under an anchor collision was performed. The explicit dynamics of the finite element analysis program ANSYS were used for the collision analysis. The influences of the steel reinforcement modeling and collision angle of the anchor on the collision behavior of the FCM were estimated. The FCM damage was evaluated based on the results of the numerical analysis considering the numerical modeling and collision environment.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.81-87
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• 2010

This study presents the results of collision and lift analyses of a cylinders-connected protector under stock anchor colliding and dragging. For the analyses, the terminal velocity of the stock anchor was obtained first, and, then, the velocity was used to calculate the falling distance of the stock anchor in air. In addition, two other falling distances were considered for purposes of comparison. From the finite element analyses, using ANSYS, the maximum responses obtained from the stock anchor colliding and dragging were obtained and compared for different collision distances (3, 5, and 8.83 m) and dragging angles (0, 30, 60, $90^{\circ}$). Then, the maximum displacements and stresses were discussed, along with the strength and dimensions of the protector. Finally, conclusions were made for the maximum responses.

• Journal of Ocean Engineering and Technology
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• v.29 no.1
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• pp.70-77
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• 2015

The purpose of this study was to provide fundamental data for an anchor collision simulation of an FCM (flexible concrete mattress). Numerical material models (elastic-perfectly plastic model, Drucker-Prager model, and RHT concrete model) were compared. ANSYS Explicit Dynamics was used for collision analyses. An FE model was used for the anchor, FCM, andreinforcement bars. The results showed that the behavior of the FCM was verydifferent that those ofthe material models. In particular, the effect of the pressure dependent strength was most noticeable among the properties of concrete.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.24 no.6
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• pp.609-616
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• 2011

In the study, we analyzed the collision characteristics of a so-called arch-type submarine cable protector by considering the changes in drop heights of a stock anchor and material models for concrete and steel reinforcing bars. We considered plastic kinematics model and Johnson-Holmquist Concrete model for the concrete and linear elastic model and plastic kinematics model for the reinforcing bars. The drop heights of 2-ton stock anchor were selected as 3, 5, and 8.83m, respectively. ANSYS, a finite element analysis program, was used for the collision analysis. To save computational time, we converted those drop heights into initial velocities by the principle of energy conservation. From the sensitivity of the material models on the drop height changes, it is shown that the collision response of the reinforcing bars is sensitive firstly on the steel models and secondly on the concrete models, while the collision response of the concrete is sensitive only on the concrete models.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.2
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• pp.59-65
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• 2017

When an anchor is dropped into the sea, there exists a danger of collision on the pipeline and subsea cables in the seabed. This collision could cause huge environmental disasters and serious economic losses. In order to secure the safety of subsea structures such as pipelines and subsea cables from the external impact, it is necessary to estimate the exact external force through the anchor's terminal velocity on the water. FLUENT, a computational fluid dynamic program, was used to acquire the terminal velocity and drag coefficient computation. A half-symmetry condition was used in order to reduce the computational time and a moving deforming mesh technique also adapted to present hydrostatic pressure. The results were examined with the equation based on Newton's Second Law to check the error rate. In this study, three example cases were calculated by stockless anchors of 5.25 ton, 10.5 ton, and 15.4 ton, and for the onshore experiment dropped height was back calculated with the anchor's terminal velocity in the water.

• Journal of the Korean Society of Marine Environment & Safety
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• v.8 no.2
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• pp.9-15
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• 2002

Ship operators use anchor dredging for the collision avoidance or safety of ship handling in a harbour or narrow channel. This paper clarifies the technique of the anchor dredging known as a common sense for. the seafarers A mathematical model at low speed range is established for the estimation of ship motion under the assumed environment, simulate the advance speed , and turning ability under the anchor dredging or not. The results shows good agreement with the conventional seamanship and their experiences as follows. Ahead speed used the anchor dredging is slower(speed reduction ratio:40%) than the normal ahead speed and the stopping distance is shorter (distance reduction ratio:40%)than the normal ahead distance without the anchor dredging.. Turning speed used anchor dredging is slower(speed reduction ratio:72%)than the normal ahead speed and the tactical diameter is shorter(distance reduction ratio:24%)than the diameter by the normal turning without the anchor dredging.

• Proceedings of KOSOMES biannual meeting
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• 2002.10a
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• pp.127-134
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• 2002

Ship operators are used to dredge anchor for the collision avoidance or safety of ship handling in a harbour or narrow channel. This paper clarifies the technique using tile anchor dredging known as a common sense for the seafarers. A mathematical model at low speed range has been established for the estimation of ship motion under the assumed environment , simulate the advance speed , and turning ability under the anchor dredging or not. The results shows good agreement with the conventional seamanship and their experiences as follows. Ahead speed used the anchor dredging is slower(speed reduction ratio:40%) than the normal ahead speed and the stopping distance is shorter (distance reduction ratio:40%)than the normal ahead distance without the anchor dredging. Turning speed used anchor dredging is slower(speed reduction ratio:72%)than the normal ahead speed and the tactical diameter is shorter(distance reduction ratio:24%)than the diameter by the normal turning without the anchor dredging.

• Journal of the Korean Institute of Navigation
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• v.23 no.4
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• pp.21-28
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• 1999

In some cases a towing vessel and her tow, a fishing boat, and a vessel at anchor have a priority against a general power-driven vessel underway in the application of collision rule. This article aims at suggesting a practical guide for the construction of the meaning of a vessel engaging in fishing, a vessel engaged in towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course and a vessel at anchor, which are permitted to have the above priority. The construction of the application of the collision rule on the above vessels is supported by the decisions of MAIA and the judgment of civil courts.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.96-103
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• 2009

In 2006, Jeju Island in South Korea experienced a crisis, no electricity for three hours anywhere in the entire island. This incident was caused by a domino effect that occurred after one of the submarine power cables connecting the island to Haenam, a coastal city on the mainland, was damaged by an external load, probably from a ship anchor or a steel pile being used in marine farming. This study presents a collision analysis of a new submarine power cable protector called arch type reinforced concrete. For the analysis, a dynamic finite element program, ANSYS AUTODYN, was used to examine the displacement and stress of the submarine power cable protector using different material models (RHT concrete model, Mohr.Coulomb concrete model). In addition, two reinforcing bar spacings, 75 mm and 150 mm, were considered. From the analyses, the effects of the parameters (concrete model and spacing) on the results (displacement and stress) were analyzed, and the relations between the damage and parameters were found.