A literature survey of broken ice-structure interaction modelling methods for ships and offshore platforms

Highlights

• An extensive survey of models to predict stationkeeping structures’ interactions with broken ice-fields is presented.

• The modelling techniques are categorized into groups: Analytical, Empirical-Statistical, Numerical, and Hybrid Methods.

• Not all the methods surveyed can model ice-structure interaction with the relevant reliability and accuracy.

• Researchers have made recognizable progress; however, more validations are needed to have confidence in the models.

Abstract

Numerical modelling present an alternative to the more industry-accepted full-scale trials and physical model tests for predicting ice actions on ships and offshore platforms in a broken ice-field. Before a method is developed or adopted, it is essential to survey the existing methods that modelled relevant aspects of ice-ship interaction processes. This work presents an extensive literature survey of various existing ice-structure interaction models, primarily in the context of their applications to the simulations of stationkeeping and dynamic positioning (DP) of ships and offshore platforms in broken and managed ice-fields. A brief discussion is presented on various modelling methods, highlights of their capabilities, limitations, and applicability for real-time or fast simulations. Most of the computational methods such as finite element method (FEM), discrete element method (DEM), particle in cell (PIC) method, smoothed particle hydrodynamics (SPH) method, and other conventional computational fluid dynamics (CFD) methods require high computation resources. They often take a long calculation time, which is unsuitable for real-time simulations. The suitable methods for such simulations are perhaps the non-smooth DEM (NDEM), 2-D DEM, empirical, and some hybrid methods. Regardless of the methods adopted, validations with quality measurements and observations are paramount to the success of the models.

Introduction

The interest in future oil and gas exploration in deep water arctic regions is expected to demand customized stationkeeping systems. Of particular interest are dynamic positioning (DP) capabilities for drill-ships, offshore supply ships, floating production, storage and offloading (FPSOs), and icebreakers, allowing them to operate under challenging sea ice drift conditions. One of the greatest threats to the DP systems of ships and offshore installations is the multi-directionality of drifting sea ice with a wide variety of types and forms, ranging from isolated first-year floes to compacted multi-year ridges (Metrikin, 2015). This issue is further complicated by the ice-ship interaction process that depends on many complex and interconnected parameters and characteristics related to the ice-field, the ship, and the surrounding environment (Metrikin, 2014). Analytical and numerical models and their validations using measurements are essential and a key to understanding the problem and designing both the floating and stationkeeping systems.

The operators have gained limited experience in real-world stationkeeping in broken ice-fields (managed and unmanaged) over the last few decades. Early experiences include the Canmare/Dome drillship operations (Jolles et al., 1989), the Kulluk drilling campaigns (Wright, 1999) and the Sakhalin 2 phase 1 oil production operations that were using the floating storage and offloading tanker Okha (Keinonen et al., 2000, 2006a, 2006b). For the first time in history, dynamic positioning operations in ice were performed in the offshore Sakhalin, May–June 1999 (Keinonen et al., 2000). In support of compression diving, the CSO constructor performed the dynamic positioning operation in ice of a type B ice-class ship with support from two icebreakers acting as an ice management team. Ice management has been an integral part of exploration and production activities in the Arctic, where stationkeeping is required. Rohlén (2009) discussed the relationship between ice management and stationkeeping in ice with specific references for some full-scale efforts. Based on the experience in the Arctic Core Expedition (ACEX2004) and KANUMAS 2008 operations, the author stressed the importance and relevance of ice management in stationkeeping of floating structures during oil and gas related activities in the arctic region. Impacts from unmanaged ice floes and changes in the ice drift direction were hazardous to the stationkeeping systems during the pioneering operations of the CSO Constructor (Keinonen et al., 2000) and the Vidar Viking (Keinonen et al., 2006a). Recently, a DP operation was performed by the icebreaking rescue and emergency ship Baltika equipped with the Navis Nav DP4000 (DP System) and the Navis AP4000 Heading control system (autopilot) in the Kara Sea (Navis Engineering, 2015). A majority of the researchers and operators above identified the need for developing prediction capabilities, simulation technologies and training facilities for DP operations in heavy managed and unmanaged dynamic ice conditions. Before developing these technologies, the current knowledge gap in understanding the magnitude and nature of ice actions encountered by the DP-controlled drilling and production systems operating in broken ice-fields need to be addressed.

Several Research and Development projects were initiated worldwide to improve the understanding of ice-structure interactions and enhance the capabilities of the existing stationkeeping systems. HSVA in Germany led a 3-year (2010–2012) R & D project titled “Dynamic Positioning in Ice-covered Waters (DYPIC)” primarily aiming at developing and improving its numerical modelling and physical model testing capabilities of DP ships (Jenssen et al., 2012; Kerkeni et al., 2014). Norwegian University of Science and Technology (NTNU) led a five year (2010–2014) R & D project titled “Arctic DP – Safe and Green Dynamic Positioning Operations of Offshore Ships in an Arctic Environment,” primarily aiming at developing DP control system technologies for proper DP operations in the Arctic environment (Skjetne et al., 2014). The Centre for Marine Simulation at the Marine Institute (CMS-MI), the NRC-OCRE and Kongsberg Digital Simulation (KDS) Ltd., has completed a 5 year R & D project and developed a statistically reliable numerical model to predict in real-time the ice actions encountered by stationkeeping ships due to the complex and dynamic ice-ship interactions in different managed ice environments. These projects resulted in multiple numerical tools for modelling the broken ice and floating structure interactions and contributed to the advancement of knowledge and understanding of the intricate ice-structure interactions (Islam et al., 2016a, Islam et al., 2016b, 2018). Besides the above endeavour, several other methods have been developed for modelling the global ice loads on stationary and moving ships. Documentation on various numerical methods and their capabilities and limitations is expected to benefit the current and new researchers. This encourages an effort to accumulate all existing research to better understand the effect of various ice-field parameters on the performance of a stationkeeping structure and the ice-structure interactions modelling endeavours.

This paper presents a comprehensive literature survey of publicly available ice-structure interaction prediction models and research. Section 2 presented a summary of the detailed literature survey on various existing ice-structure interaction models. In the survey, all methods are conveniently grouped into four categories. A brief discussion is presented for each method, highlighting their capabilities, limitations, and applicability for practical and real-time simulations. After this, the authors present a summary of the methods in the context of several modelling aspects for practical and real-time simulations of DP ships and broken ice interactions. Finally, the authors present a few concluding remarks and a comprehensive list of references.