ABSTRACT

Dynamically installed anchors have been identified as the most cost-effective anchoring solution for mooring floating facilities because of its simple installation (free-fall) procedure. For numerical simulation of free-fall installation, the coupled Eulerian-Lagrangian (CEL) technique is broadly used. However, to date, the challenge is to adopt an appropriate algorithm to capture the frictional resistance between the anchor and the adjacent soil. This paper introduces an advanced frictional resistance algorithm to improve (i) the accuracy of capturing frictional resistance, and (ii) computational efficiency. Main feature of the new frictional resistance algorithm is to automatically capture the contacted anchor shaft area at the advancing anchor nodes, which is conducted by an external FORTRAN code. Benchmark tests were carried out using published field installation data and numerical analysis results for a finless torpedo anchor. The comparisons showed that the advanced algorithm is able to (i) increase the accuracy of capturing frictional resistance profile along the penetration depth and hence the final tip embedment depth significantly, and (ii) reduce the computational expense.

INTRODUCTION

Dynamically installed anchors are the most recent generation of anchoring solution for tethering floating facilities. Anchors are installed by releasing from a designed height above the seabed and free fall in the water column by its self-weight. The anchor then impacts the seabed with a high kinetic energy and penetrates the soil (Fig. 1). Owing to this quick and external energy free installation process, compared to conventional piles and suction caisson anchors, cost saving has been calculated at $14 million per spread on fabrication cost alone (O'Loughlin et al., 2015) and total at 30∼70% (Medeiros, 2002). Dynamically installed anchors can be used to moor oil and gas drilling platforms (accordingly anchors may need to scale up), floating wind turbines, wave energy converters, floating plastic collection barriers, aquaculture cages, and other marine renewable energy devices and floating facilities regardless of water depth so long vertical free-fall from a targeted drop height can be ensured during dynamic installation.

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