Numerical Simulations of Ice Loads on Fixed and Floating Offshore Structures using the Discrete Element Method

Abstract

AbstractExisting standards and codes do not comprehensively address and provide all necessary guidance and requirements for the design of Arctic offshore structures. Reliably assessing ice loads on offshore structures remains a challenge for industry, especially as "new" Arctic platform concepts are proposed for deployment in lighter ice operations, e.g. Arctic SEDU (Self- Elevating Drilling Units) and Arctic CSDU (Column-Stabilized Drilling Units). As a pragmatic solution, a comprehensive approach including relevant field measurements, physical model tests and numerical simulations is usually adopted in assessing the ice loads for a particular design. Field measurement results are limited in number and there is often uncertainty concerning actual ice conditions and load measurement techniques. Furthermore several data sets are constrained with proprietary restrictions. In particular no direct field data is available for the example "new" structures (SEDUs and CSDUs). Physical model tests always present challenges due to scale issues, ice property calibration, measurement uncertainties and high costs. Therefore, numerical simulations using the validated DEM tool based on the related field/model test data are anticipated to provide supplementary information for standards/rule-based designs.ABS has expended efforts to develop practical and advanced tools to assess the ice loads on offshore structures for several years. One promising numerical approach, a graphic processing unit (GPU) based Discrete Element Method (DEM) model, processes the computations in parallel and solves the DEM model with millions of particles for complicated ice-structure interaction problems, e.g. ice simultaneously loading on multiple legs and ice loading on a large CSDU. The paper presents details of the developing ABS GPU-DEM tool, status of the verification program, plans for the current and the future developments and applications. Included are brief descriptions of background technologies, an approach to derive the DEM model bonding strength inputs, and validation studies of ice breakage simulations based on the Bohai Bay Jacket ice data. The ice load simulations for fixed and floating structures, i.e. jack-up legs and the Kulluk floating drilling platform, are also shown to demonstrate the tool's capability and feasibility for Arctic offshore structure design. The interactions of ice and fixed/floating structures were analyzed, which provides useful references for future ice load modelling and offshore structure design.