Different kinds of offshore structures are designed and built to resist the scenarios of the arctic environment. This paper focuses on different ice load scenarios and the challenges for fixed offshore structures. Model test methods will be presented to assess the suitability of the design for the corresponding environmental scenarios. Measurement possibilities will be explained monitoring the design challenges as ice resistance, vibrations and encroachment of ice. The feasibility of different ice model test setups will be described and the main observations will be presented. The findings of the general phenomena of the resistance and encroachment will be discussed to assist the design process of offshore structures.

Approaches are presented in this paper for estimating the global mooring loads and response of a semi-submersible drilling rig, as a result of pack ice loading. The focus is on loading events from pack ice conditions relevant to the Grand Banks, where the pack ice typically consists of small floes and limited concentrations. The current practice for semi-submersible drilling operations on the Grand Banks is to avoid contact with pack ice by disconnecting and moving off-station in the event of an ice incursion. From a global loads perspective this may be unnecessary, given that the typical pack ice is of low severity and mooring loads may well be within acceptable limits. To be able to operate in pack ice while moored, operators need to demonstrate that the moored semi-submersible will have sufficient structural and mooring capacity to withstand the ice loads. Some existing semi-submersible hulls have ice strengthening in place as specified by a classification society, with associated allowable operating criteria in terms of ice conditions. These operating criteria are to ensure sufficient structural capacity given the ice conditions. No standardized approaches are currently available to quantify global pack ice loads and associated offsets for moored semi-submersibles, which are needed to assess the required mooring capacity. The objective of this paper is to address this gap and present approaches that can assist in specifying allowable operating criteria for station-keeping in pack ice.

The IMO's International Code for Ships Operating in Polar Waters (Polar Code) entered in to force on 1 January 2017 and provides, for the first time, an international regulatory framework for ships operating in Polar waters. In addition to technical regulations, the Polar Code requires that the Polar Ship Certificate should reference a methodology to assess operational capabilities and limitations in ice: essentially setting operational limitations for the specific ship navigating in Polar waters. The Polar Operational Limit Assessment Risk Indexing System (POLARIS) has been developed as an acceptable methodology for providing guidance on the operational limitations in ice of ships assigned different ice classes and has been directly referenced by the IMO in the Polar Code. The system was developed as a collaborative effort, drawing on operational and regulatory experience from industry and national administrations with experience in setting navigational limitations for ice covered waters. This paper presents the technical background behind the system and supporting information on its practical use both as a voyage planning tool and as real-time guidance on assessing ice regimes ahead of the ship. Validation of the system in the context of other existing regulatory requirements is discussed. The limitations of the system are explored and commentary and proposals are provided on recommended future enhancements.

Numerous field studies show that mature first-year (FY) ridges consist of a solid ice consolidated layer (CL) below which is a keel of ice rubble. The CL is generally thicker than the ambient level ice. With the decrease in multi-year ice in the Arctic, FY ridges may become the controlling ice feature at many Arctic locations. In sub-Arctic regions ridges are smaller but they also usually control design ice loads. For vertical structures, ISO 19906 (Standard on Arctic Offshore Structures) suggests calculating the load due to crushing of the CL and adding this to the load to fail the keel. In ISO a formula is provided for the load to fail the keel on a vertical-face which assumes that the keel material has Mohr-Coulomb properties. No specific algorithms are given in ISO for FY ridge loads on sloping structures. The work described in this paper addresses this gap. The study investigated three bounding methods and compared them with the measured loads due to FY ridges on Confederation Bridge (which has piers with upward breaking cones). The three bounding methods are: Model A; which assumes the CL breaks in bending and rides up as level ice and the keel load is calculated assuming a "dead wedge" is created on the slope which converts the slope into a vertical face against which the keel fails. This model can make use of the methods in ISO 19906 for calculating these two components and can be considered to be the implied "current ISO approach". Model B assumes that the CL layer fails in bending as "level ice" on an elastic foundation and rides up the slope with the accompaniment of additional ice rubble scooped-up from the sail and keel of the ridge. Model C assumes that the FY ridge can be idealized into an equivalent "solid ice" beam using composite beam theory. Then the beam on elastic foundation method, as used for solid ridges, is used to estimate breaking and clearing loads. These various approaches are reviewed and the derived loads are compared to failure modes and measured loads from Confederation Bridge for selected events involving FY ridges. Based on these comparisons a hybrid of Models B and C is recommended and the paper gives the details of how to apply this method. When used for example structures, the new model gives loads which are 40 – 50% lower than the current approach implied in ISO 19906. The method can be adapted to downward sloping structures.

The objective of this paper is to present an update of various research activities of a multi-year research and development project aiming at developing dynamic positioning (DP) system technologies specifically for ice-rich environments. Since the beginning of the project in 2014, significant progress has been made in various activities that aimed at achieving the primary project objective of improving the safety and efficiency of oil and gas operations in ice infested environments through the enhancement of existing DP system technologies for efficient operations and training of DP operators in simulated realistic ice environments by providing necessary exposure to DP operations in ice. Prototypes of multiple vessel models, ice force models, and other environmental force models have been developed and are being validated. A modularized simulation and validation platform has been developed for the integration, validation, testing of all these prototypes. The research team at the National Research Council's Ocean Coastal and River Engineering (NRC-OCRE) is on the verge of delivering the complete package of the simulation platform to the project lead, the Centre for Marine Simulation (CMS) at the Fisheries and Marine Institute (MI) of Memorial University of Newfoundland, for comprehensive checking and testing of the platform by the project commercial partner Kongsberg Digital Simulation (KDS) Ltd. In this article, an update on various activities regarding the physical model testing, numerical modeling and development of simulation platform is presented. Various modules of the prototype validation platform and their integration are discussed along with their current development status. A brief discussion on various components of the ice force modeling approach, the algorithms and implementation strategies is provided. Finally, the initial results of a number of DP in ice simulation cases and comparison with validation data is presented. A brief outline of the work remaining to be completed for achieving the project objectives, along with the associated limitations are also provided.

During July 2018, an expedition was carried out offshore northern Newfoundland to central Labrador to profile, track, and forecast the drift of icebergs. One of the central goals of the drift modelling work was to test potential improvements in iceberg drift forecast accuracy up to 24 hours when measured iceberg profiles are used as opposed to estimated iceberg draft and mass. During the expedition, 14 icebergs were profiled using a rapid iceberg profiling system which uses a multibeam for the underwater portion of the iceberg and a LiDAR for the freeboard. The 14 icebergs were tracked on the vessel marine radar, and their drift was forecast using a physical model which time integrates the momentum balance of the forces acting on the iceberg. The iceberg profiles were three-dimensional point clouds which provided a highly accurate representation of the iceberg dimensions and shape, and from which a volume and mass could be readily calculated. The point cloud was projected into a two-dimensional plane from 16 perspective angles and averaged into a single projection of iceberg keel and freeboard against which the currents and winds were forced in the drift model, respectively. Average results for the forecast iceberg position versus observed at 24 hours show approximately a nearly 3 km or 18% improvement when iceberg profiles are incorporated into the drift model as opposed to using estimated iceberg draft, shape, and mass. The drift model will become part of an integrated ice profiling, forecasting, and management system for oil and gas exploration and drilling operations on the Grand Banks offshore Newfoundland.

Design of offshore structures for arctic and subarctic regions requires consideration of wave, wind and ice actions. If individual actions are not mutually exclusive, then combined actions also need consideration. ISO 19906 recommends that, when possible, extreme level combined actions should be determined based on the joint probability distribution of the actions. As an alternative, ISO 19906 provides a framework where a user can determine principal and companion extreme actions independently, and sum these with calibrated combination factors applied. While the combination factors in ISO 19906 were calibrated over a range of conditions and platforms, site-specific information is not taken into account when applying the method. In this paper, a procedure is presented for determining extreme level combined actions for sea ice and waves based on site-specific sea ice and wave information, accounting for the joint probability distribution of the actions. The procedure is demonstrated for an example fixed structure on the Grand Banks off Canada's east coast. The results are compared with extreme actions determined using the ISO 19906 combination factors.

Ice-structure interaction (ISI) is a complex process, which requires a thorough understanding of the underlying physics to ensure safe operations in the ice-covered regions. Application of discrete element method (DEM) to compute ice loads on structures is a widely accepted approach, where the equations of rigid body motions are solved for all ice pieces in the computational domain. In most ISI simulations, the ice zone is assumed to be resting on a static water foundation omitting the hydrodynamic effects (added mass, water drag, wave damping) of the interacting bodies. This assumption can introduce erroneous results to simulations of the floating ice floes behavior, which in turn will incur uncertainties in planning ice management activities. In this paper, a smooth particle hydrodynamics (SPH) based computational fluid dynamics (CFD) code is coupled with a three-dimensional DEM model to take the hydrodynamic effects of the interacting bodies including the ice pieces into account. The ice zone is modeled as discrete elements, which allows computing interaction forces by considering contact laws. The water foundation is modeled using smooth particles, which are modelled with the Naiver-Stokes equations. Several applications of ship and offshore structures interacting with level ice and pack ice are simulated. A scenario of an offshore supply vessel operating in the marginal ice zone (MIZ) that is subject to wave forces is also simulated to show how this approach can be used for modelling complex real-world problems. This scenario is unique in a sense that it yields a multi-physics solution, where ice-structure-wave are all included in a single CFD simulation as a fully coupled analysis. The cost of the simulation is significantly reduced by running the computations on a Graphics Processing Unit (GPU) instead of a typical CPU workstation. Some of the initial results of ice-structure interactions are presented in this paper and a reasonable agreement with reduced scale model test results are found.

The presence of sea ice is the primary challenge for marine operations in the Arctic region. It is widely accepted that offshore structures running in the Arctic condition need station-keeping methods as well as ice management actions by icebreakers. Dynamic positioning (DP) is one of the station-keeping methods that can provide mobility and flexibility in marine operations. The presence of sea ice adds complex external forces and moments on the vessel which must be managed by the DP system. This paper presents an icevaning control algorithm of the Arctic DP system. To make the icevaning action of the Arctic offshore vessels without any measurements and estimation of the ice condition including ice drifting, a task space and a null space are defined in the vessel model, and the control law is formulated in the task space. A backstepping technique is utilized to handle the nonlinearity of the Arctic offshore vessel's dynamic model, and the Lyapunov stability theory is applied to guarantee the stability of the proposed icevaning control algorithm. A set of experimental tests are conducted in the ice tank of the Korea Research Institute of Ships and Ocean Engineering to examine the practical feasibility of the proposed icevaning control algorithm.

For oil and gas projects offshore Newfoundland, Canada, subsea structures are generally placed in excavated drill centres which lower the equipment below the natural mudline, protecting the equipment from damage due to iceberg impact. This paper introduces a concept of protecting this equipment by utilizing a concrete structure affixed to the seabed using hammer driven piles. Iceberg loads have been assessed utilizing a Monte Carlo iceberg contact model and a modified version of the Iceberg Load Software (ILS) developed for regions offshore eastern Canada. The Subsea Iceberg Protection Structure (SIPS) was designed using post-tensioned concrete construction. Preliminary concrete design in addition to pile capacity design is performed utilizing FE analysis. Using a hammer driven piled system, the maximum lateral resistance capacity can be determined in addition to the maximum impact energy absorption. The internal Subsea Production System (SPS) system has been designed to specifically fit inside the SIPS while maintaining full ROV access for operation, maintenance and future well intervention. The SIPS was designed as an L1 structure in accordance with ISO 19906. This includes impact from free floating and gouging icebergs. The design load for this impact event was calculated based on energy absorbed through ice crushing. The deformation and global movement of the SIPS was not considered as part of the energy absorption mechanism. The maximum ice crushing design load on the SIPS was determined for four locations on the Grand Banks offshore Eastern Canada. In addition to the structural design of the SIPS, the piling system was analysed to determine the maximum capacity. The total lateral resistance was determined using a combination of a continuum model and a structural beam model (P-y method). The global movement was less than the maximum allowable deformation of the structure. The structure is therefore considered fit for purpose. The projected construction and installation cost of this structure shows the potential for reduced costs compared to an excavated drill centre, thereby increasing the feasibility of potential tie-backs. Using updated knowledge regarding iceberg size and geometry, areal density and ice strength, the analysis and design presented in this paper suggests that it may be more economical to install protection structures rather than dredge excavated drill centres, for marginal fields. In addition, the advancement of the internal SPS system is such that the equipment footprint is compact, requiring limited space within the SIPS. This paper provides the necessary information to show that installing a structure to protect subsea equipment is technically achievable.

The hydrocarbon production facilities offshore eastern Canada must contend with icebergs. Subsea infrastructure is typically protected by placement in excavated drill centers (EDCs). EDCs are large excavations where subsea infrastructure is installed below the depth of potential iceberg penetration. However, EDCs are expensive for marginal field developments and therefore alternative concrete Subsea Ice Protection Structures (SIPS) are being evaluated. A concept 8 m high circular concrete SIPS of 45m and 25m outside and inside diameter, respectively, would be placed directly on the seabed. Global loads from contact with an iceberg are estimated to be less than 100 MN without ice management. Pipe piles are proposed to resist the lateral forces. Such large diameter pipe piles are commonly used on the Grand Banks to anchor mooring lines. Movement of the iceberg onto the SIPS may also generate greater vertical load onto the structure, increasing the sliding resistance. This paper presents an evaluation of the ultimate lateral load capacity of the piled foundation at large displacements. Centrifuge model tests were compared to numerical modelling results and to reduce the uncertainty with extrapolating the P-y method of pile analysis beyond its typical limits. The load sharing behavior between the piles and the SIPS foundation base was also evaluated.

Currently, iceberg risk mitigation at production facilities in shallower waters (80 to 120 m) on the Grand Banks off the coast of Newfoundland and Labrador is accomplished using iceberg surveillance, towing, water cannons and, in the case of floating facilities, disconnection. Future developments in deeper waters such as the Flemish Pass or the Orphan Basin may be able to utilize compliant mooring and riser systems to allow a floating facility to simply move out of the path of an approaching iceberg without disconnecting. The analysis described here shows that, using simple extrapolation of the observed iceberg trajectory, the risk mitigation provided by facility side-tracking is comparable to existing physical management techniques (iceberg towing and water cannons). Improved short-term iceberg drift forecasting would allow further risk mitigation.

A new type of ocean platforms is discussed in this paper. The uniqueness of this concept is that its hull is restrained such that any of the hull motions will be resisted by the axial stiffness of moorings. As a result, the platform is essentially motionless. Because of the superb motion characteristics, it can have many applications when a stationary platform is required, such as an oil producing platform in the partially ice-locked arctic environment or a host structure for wind turbines in deeper water.

Icebergs can pose risks to platforms in arctic and subarctic regions. These risks require careful consideration during design, and as well during operations. Platforms must be designed to withstand potential impacts from icebergs, or to disconnect and move offsite to avoid impacts. ISO 19906 allows use of ice management to mitigate iceberg and sea-ice actions. In the case of icebergs, management may include detection, monitoring, towing, disconnection and evacuation. Threat assessment is also a critical input to the iceberg management decision-making process. For example, given one or more detected icebergs and available information on the iceberg and environment characteristics, what is the probability of exceeding platform design ice actions? Based on the threat assessment, better decisions can be made regarding which iceberg to manage, whether more information should be acquired, and whether shut-down or evacuation is needed. This paper describes a new tool developed to estimate the distribution of iceberg impact actions from an encroaching iceberg given concurrent metocean conditions, conditional on impact. The tool can be used in a number of ways depending on the information available to the user. It can be used to assess the threat from a single iceberg or can be used to compare actions from multiple icebergs in the region, or for the same iceberg but with changing weather conditions. The iceberg load assessment tool is demonstrated for several example cases on the Grand Banks, showing the benefit of improved iceberg characterization obtained through rapid iceberg profiling.

When designing oil and gas platforms for offshore arctic and subarctic regions, operators may need to consider the influence of iceberg impacts on optimal structure configuration and ice strengthening requirements. Icebergs have complex and varied shapes, are mostly underwater and are usually moving in currents and waves. Previous iceberg profiles developed from sonar profiles and above water measurements have varying limitations in accuracy, necessitating approximations in modeling both the overall and local shape of the icebergs. A field program was conducted to obtain high resolution full three dimensional (3D) iceberg profiles that allow for detailed modeling of icebergs. Following the field program, a number of studies were conducted to utilize this data to develop improved tools both for calculating design iceberg impact loads for offshore structures and for improving ice management. One of these studies, described here, entails development of a full 3D timedomain simulation model for icebergs impacting fixed and floating platforms in 6 and 12 degrees of freedom (DOF) respectively. A key requirement of the model is that existing scale dependent models for global ice crushing failure pressure can be incorporated. The main objective in developing the model was to provide a tool for evaluating specific iceberg impact scenarios that considers 3D effects and requires fewer assumptions regarding interaction mechanics than previous methods. In this paper, the basic framework of the 3D time-domain model is described, and initial model results are presented for several example applications: icebergs impacting a cylindrical GBS, a stepped cylindrical GBS and a moored spar floating production unit (FPU), the probability of iceberg pinnacles impacting a platform topsides, and subsea interactions. For the cylindrical Gravity Base Structure (GBS), sensitivity analyses are presented for ice strength, friction, drag coefficient, damping coefficients, platform diameter and iceberg velocity.

This paper presents an overview of a five year research and development project aiming to develop dynamic positioning (DP) system technologies specifically for ice-rich environments. It has been initiated by the Centre for Marine Simulation (CMS) at the Fisheries and Marine Institute (MI) of Memorial University of Newfoundland, with its technical partner National Research Council’s Ocean Coastal and River Engineering (OCRE-NRC) and commercial partner Kongsberg Maritime Simulation Ltd. (KMS). The primary objective of the project is to develop solutions for some of the critical challenges related to safe Arctic offshore operations by dynamic positioning. More specifically, the objective is to improve the safety and efficiency of oil and gas operations in ice infested environments through the enhancement of existing DP system technologies and training of DP operators in simulated realistic ice environments for ship operations. The project is envisioned to achieve its objective through developing a modularized simulation platform for prototype integration, validation, testing and operational studies/training. Prototypes of a DP control system, a vessel model, an ice force model, and other environmental force models will be developed. The project commenced in 2013 and is set to complete in late 2018. In this first article of the project, a discussion on the contextual aspects and formation of the project, its planning and status to-date is presented. A synopsis of the scientific and engineering research performed to-date within the project scope, with a justification of their relevance to the safe DP operations in ice is given. The high level system design of the validation platform and the deployment strategies of its major components are presented. An introductory discussion on the novel ice force modeling approach is provided. Finally, an overview of the model test program of a fully DP controlled vessel in managed ice conditions, which was completed to provide a database for building and validating the ice force model, is also offered.

Global ice loads at different locations on a ship during rams into ice are a function of ship motions and added mass in addition to the failure mode and strength of the ice. In the literature, various analytical added mass models have been used for ship-ice interactions, which could lead to significant differences in the prediction of global ice loads on ships. In this work, an improved added mass model has been developed based on numerical results and existing analytical models. Added mass coefficients of three ice-going ships, CCGS Amundsen, CCGS Louis S. St-Laurent and MVArctic , were estimated using four analytical added mass models. It was found that the differences in added mass coefficients predicted by these models are significant and enhancements can be made. A body-exact numerical simulation tool based on the potential-flow theory, MAPS0, has been used to compute the added mass coefficients of the three vessels in the frequency domain and the results were used for the development of the improved added mass model. The improvement in the load predictions has been demonstrated by applying the new added mass model to the three vessels.

Ice infested shallow waters of the North Caspian Sea imposes challenging tasks like ice pile up, fatigue due to ice-induced vibrations and ice impact loads, which strongly affect the structural integrity of offshore installations. This paper explores the potential application of a Minimal Facilities Platform or is also known as a Conductor Supported Wellhead Platform (CSWP) in the North Caspian Sea region and specifically focuses on the design optimization of the substructure due to ice loads. The CSWP has not been used in the cold climate regions before. The intention of this research is to prove feasibility of CSWP to withstand loads in the ice infested shallow waters. The substructure design was optimized by application of an ice resistant conical structure with specific inclination angle at the ice-structure interface. Usually conical structures reduce ice loads and ice induced vibrations. However, a fatigue capacity may be reduced due to geometrical discontinuity with the increase of inclination angle. This was shown in the design analysis.

A Common Operational Picture (COP) can generally be described as a system of hardware and software that produces a shared display of information to facilitate situational awareness and decision making. A brief history of the development and use of COP technology in Arctic operations is provided. Experience and learnings from ExxonMobil's research into the use of COPs in ice management and Arctic floating drilling is described. Experience gained from simulations, desktop studies, and field observations is used to frame preliminary functional requirements for such technology needed for future Arctic floating drilling operations in high concentration ice. The COP must facilitate the planning and execution of complex and remote operations with many geographically distributed assets (e.g., drilling rig; icebreakers; shore base; manned or unmanned aviation) and stakeholders (e.g., icebreaker captains, drilling management, ice analysts, weather forecasters) at times communicating over limited bandwidth channels. The COP will serve to collect, store, communicate, and display the necessary data and information. The role of COP components (e.g., databases; communication network, displays) is described and functional requirements are outlined.

This paper describes a study conducted to develop new capabilities for offshore geomagnetic surveying. To conduct the research we equipped two (2) new generation autonomous marine vehicles (AMVs) with towed marine magnetometers. This paper describes the validation study of the measurement system offshore between 2013 and 2015 that compares a regular pattern with main, tie and perimeter lines. It was investigated whether the new AMV was suitable for use as a "base station" to monitor time variations of the disturbance field. The geomagnetic data measured by the vehicles from May 11 - 14, 2015 was analyzed and compared against data obtained from the USGS Honolulu Geomagnetic Observatory (HON). Highly sensitive sensors were used to establish the minimum required separation between the AMV and the magnetic sensor payload. Directional drilling requires accurate knowledge of the geomagnetic field direction and strength in the wellbore. To compute wellbore azimuth, the measurement while drilling (MWD) tool takes a measurement of the magnetic field and then the directional driller compares it with the geomagnetic field reference in order to position the wellbore in real-time while drilling. By utilizing the AMV we were able to accurately map the crustal field direction and strength in the area of interest where the drilling activity for oil and gas will take place. This study shows that the AMV is ideally suited to carry out geomagnetic surveys in offshore remote locations. Correction for the disturbance field is essential for crustal field mapping that requires a base station recording the variations of the disturbance field. A second AMV circulating at a fixed location provides a more accurate base station than a land-based station. This is due to two factors: The land- based station is further away from the measurement site and the disturbance fields are different on land than in the ocean, due to the different electrical conductivity of the subsurface. The new generation AMV offers distinct advantages for data collection in offshore environments. Their low cost compared to seaborne or airborne vehicle allow them to be deployed in tandem and collect data repeatedly over predefined areas yielding accurate measurements to determine the disturbance and crustal fields. It solves the problem of accurately mapping the geomagnetic reference field in offshore locations that previously unknown of.