앵커 충돌에 의한 해저케이블 보호구조물의 거동 특성

Abstract

For the protection of underwater lifeline such as submarine power cables, structures (so-called protectors) have been frequently used along with burying methods. The protector can experience several accidental loads such as anchor collision. Therefore, protectors are tested for stability assessment under anchor collision before the installation. The numerical analysis and verification test are performed. The accuracy of test result cannot be guaranteed without considering correct analysis conditions (collision velocity, material model, etc.). This study presents the behavior characteristics of the submarine power cable protectors under anchor collision. To achieve the objective, the following works are implemented. First, rock-berms and tunnel-type A-ducts were selected as the target structures. Anchor collision was selected as the hazardous activity. Second, the drag coefficients of the anchors were obtained using a computational fluid dynamics package ANSYS-CFX, to calculate the terminal velocities of the five anchors (stock anchor: 1, 2-ton, stockless anchor: 2, 4.89, 10.5-ton). Finally, the anchor collision of the target structures was performed by a general purpose finite element package ANSYS AUTODYN. The rock berm was modeled by the piecewise Drucker-Prager material model and analyzed by the smooth-particle hydrodynamics (SPH) method. In the analyses, to investigate the behavior characteristics, the following parameters are considered: type of anchor, ground condition, sizes of SPH particles (100, and 200mm), collision velocity and location. The A-duct was modeled by the RHT concrete model and analyzed by the Lagrange-based finite element method. For the analyses, type of anchor, ground condition, collision velocity and location were considered to investigate the response characteristics. From the analysis results, the following conclusions are made. First, the terminal velocities of each anchor are calculated. Second, in the cases of rock-berms, the rock-berm size (mainly the height) and type (mainly the weight) of anchor are important to the responses In overall, the height of rock-berm is critical to the safety of the rock-berm; hence, it is suggested to use higher rock-berm to increase the safety. Third, in the case of the A-ducts, the collision by the anchor gives severer damages. Because the anchor collision with the terminal velocity causes the perfect damage (D = 1.0), it is suggested to install the A-duct in the shallow water depth smaller than 23.819m.