Abstract Due to the effect of global warming, navigation on the Northern Sea Route (NSR) has become a more economical and reliable choice for international cargo transportation. In some ways, global warming has increased the opportunity of shipping activities in the Arctic region and hence the need for ice-capable vessels. NSR shipping provides benefits for international trade, but challenges still exist. Although conventional direct drive propulsion system connected to 2 stroke marine engine is normally considered the most efficient approach for long-range transport, for icebreaking operation which requires prime movers to work at partial load, conventional mechanical propulsion systems generally have poor fuel efficiency and high emissions. Moreover, the harmful gases produced by ships trading in NSR have a significant impact on the Arctic climate. Moreover, a traditional mechanical drive icebreaker with a diesel engine is required to operate at high torque, low rpm during icebreaking operation. Thus conventional diesel engine that isn’t optimised to operate at this point would be inefficient and would produce black carbon due to incomplete combustion, which has the potential to cause ice, snow, and cloud albedo out of proportion with normal pattern, thus lead to serious impacts on the Arctic environment and eco-system. Arctic ship propulsion systems have been developing since the 19 th century, with modifications such as the use of diesel electric propulsion systems and nuclear power propulsion systems which can ideally meet the requirements of ice breaking operation (low speed and high torque), however, drawbacks still exist in these systems, such as poor fuel efficiency at low speeds for diesel electric propulsion and for nuclear power, there are limitations such as high initial cost, management of nuclear waste and the fact that the required deep knowledge of nuclear technology is mastered by few countries. Hybrid propulsion is a new technology for ice-capable ships, which can address the partial loading efficiency problem in diesel-electric propulsion by charging and discharging a battery energy storage unit which can allow the ship to work in zero-emission mode in some sensitive areas. In this paper, detailed modelling, primary control strategies (voltage and frequency stability) and efficiency analysis of system components such as the motor, generator, battery and conversion devices etc. are and implemented in software, and then the whole power system is simulated with a secondary control strategy (load power sharing and battery aging concern) in both ice and open water load conditions. The results from the diesel electric system and hybrid system total fuel consumption within a target journey are compared to investigate the advantage of the hybrid system, which show up to a 40% fuel consumption reduction for hybrid propulsion arrangement. A tertiary control strategy for energy management is analysed and implemented in the system to further reduce system fuel consumption.

Abstract In order to simulate drifting and run-up ice floes driven by tsunamis, we developed a quasi-3D Discrete Element Method (DEM) in which phenomena unique to granular solids, such as the arch action, jam and pile up of such solids, can be simulated with a small computation load. The validity of the simulation method was verified by hydraulic experiments using synthetic ice. Some numerical simulations of drifting and run-up ice floes driven by a tsunami were performed to investigate the fundamental characteristics of ice run-up and the applicability to actual seas. It was confirmed that the simulation results could estimate risk areas where ice pile up and jam form as well as hazardous areas showing the degree of damage to buildings. Such calculation was expected to be useful for the compilation of hazard maps and the development of disaster mitigation plans in the future.

Abstract For offshore plants operating in the Arctic region, it is important to reflect the motion characteristics of the ice in the design stage. When the ice load is applied, the platform should rotate in the direction to reduce the tension acting on the mooring system using the DP system. However, it is very difficult to conduct the simulation by predicting the size and direction of the ice. This paper presents a heading control strategy to reduce the ice load acting on the arctic production platforms equipped with DP (Dynamic Positioning) Assisted Mooring System. In order to save computation time, grids are created in the operating area and the size of the tension acting on each grid is calculated considering the current position, the current tension, and the rate of change of tension. Based on the tension information, target heading angle is assigned and the platform is rotated with DP module. Developed process is validated through the simulation.

Abstract A model for the computation of failure probabilities for partly reshaping mass-armored berm breakwaters in the Arctic is presented. The model consists of a reliable tool for the design of port structures in the rapidly changing Arctic environment and considers the simultaneous effects of wave and ice forces. The applied probabilistic approach was based on Bayesian inference. Hydrodynamic and ice historical data from Prudhoe Bay, Alaska were collected and analyzed to supply the Bayesian network with a large pool of information for the analysis. The model performed real-time predictions based on historical data and the user’s prior knowledge and assigned relevant values to load and resistance parameters. The predictive skill of the Bayesian network was validated with log-likelihood tests. Furthermore, the main outputs were applied for a Level III (fully probabilistic) reliability assessment of the structure. The study shows that a well-formulated Bayesian network can be a powerful tool in the design process and for the purpose of reliability analysis of coastal structures in highly unpredictable environments, such as the Arctic. The model can represent the dependencies between wave and ice loads in relation to the characteristics of the breakwater, as well as, its response. The average deviation of computed probabilities of failure relative to the prior estimates was 58.7%.

Abstract Surface rust layers of corroded steel of coastal structures is removed by sea ice action in winter, leaving bare mild steel. This phenomenon is repeated every winter, promoting wear due to increasing corrosion. Serious damage to training levees comprising steel-sheet-pile seawalls on the Sea of Okhotsk, JAPAN occurred earlier than expected, since large wear rates were not considered in their design. This paper proposes a simple method for estimating wear amount (thickness) per year based on wear rate in a steady (mild) wear region obtained from sliding wear tests. This wear thickness can thus be taken as an additional thickness for the expected lifetime of a structure, as a rational countermeasure to corrosion as a sacrificial layer.

Abstract The eastern Canadian Arctic is an ice-prone environment that is a vital part of Canadian Arctic shipping lanes. A better understanding of the ice environment and ice characteristics in this region is essential for supporting safe and economical marine activities. This study presents a first analysis of the drift of ice islands that originated from the Petermann Glacier calving events in northwest Greenland between 2008 and 2012. These massive calving events generated numerous smaller ice islands and icebergs through subsequent deterioration and break-up events. Surviving ice features drifted further southward into the Baffin Bay and reached as far as offshore Newfoundland (∼47 °N) for the case of the 2010 calving event. The drift characteristics of Petermann ice islands are evaluated through the analysis of the recently developed Canadian Ice Island Drift, Deterioration and Detection (CI2D3) database. The average drift distance, speed, and directions of the ice islands that resulted from the 2008, 2010, and 2012 calving events were estimated using successive observations of the monitored ice islands in the CI2D3 database. This study also includes an assessment of fracture events, including the total number of ice island break-up events following each massive calving event and the average number of daughter ice islands resulting from each break-up event. A geographical analysis of the data was also performed to present the location of the fracture events, as well as the time series of latitude change of Petermann ice islands from their origin (northwest Greenland ice tongues) to where until they became too small (< 0.25 km 2 ) to be delineated in the CI2D3 database. This information is of particular interest to marine activities in the eastern Canadian Arctic, and oil and gas operations offshore Newfoundland and Labrador.

Abstract Countries around the world are increasingly interested in resource development in the Arctic due to global warming. Recently, Arctic coastal states (Russia, USA, Canada, etc.) are pursuing infrastructure construction projects for resource development in the Arctic region. Because the offshore structures in the Arctic are exposed to the sea ice, in order to ensure the safety of the structures, the calculation of the ice resistance is of paramount importance for offshore structures. In general, studies on the ice resistance have been carried out for the breaking and clearing performance of icebreakers. However, in the case of fpu (floating production unit) for resource development in the Arctic region, it is necessary to estimate the ice resistance in the oblique condition to ensure safety. Thus, despite estimation of the ice resistance in the oblique condition is significant, there has not been enough research until recently. In this paper, we suggest algorithms for estimating the ice resistance in the oblique condition. For the estimation process, an in-house code software program is used and an ice resistance estimation module is implemented for the oblique condition using empirical formula. This paper shows results of the ice resistance which was calculated in the oblique condition, and the change of the ice resistance is shown according to various oblique angles in pack ice. In addition, the results are compared to the model test result of a fpu in pack ice of 80% concentration.

Abstract Impact scenarios involving a typical drilling rig and glacial ice are studied. The goal is to better identify the important physical effects in modelling the dynamics of glacial ice in presence of waves and a floating platform, whilst improving simulation tools to capture the location and energy of possible collisions. A state-of-the-art numerical model of a typical semi-submersible is developed and calibrated with model tests to represent the drilling rig. A systematic incremental approach is adopted to model the dynamics of glacial ice. Long wave approximation, nonlinear excitation and restoring forces, interaction forces with the semi-submersible, and viscous forces due to flow separation are among the models which are considered step by step. The sensitivity of the resulted collision scenario to the modelling choices is investigated. The possibility of impact with columns, pontoons, and risers are particularly studied. Based on the obtained results, recommendations are made for modelling of glacial ice dynamics in presence of a floating platform.

Abstract As development of the Arctic grows in intensity, semi-submersible platforms are one of promising type of offshore structures used for arctic oil exploitation. Generally a good ice management is equipped by a moored floating platform to reduce ice loads to manageable levels, thus the most common scenario for a polar operating semi-submersible platform is pack ice conditions. The resistance test of a 4-columns structure is performed in a normal towing tank in China using synthetic non-refrigerated material with similar density to model sea ice. Three component load cells on top of each column and a batch of single component load cells embedded in the surface of the columns near the waterline are used to measure indirect and direct ice loads on the structures. The effects of a series of parameters such as column shapes, orientations, column spacing ratios, ice floe shapes, ice drift speeds and ice concentrations are analyzed.

Abstract Although the hull shapes of modern ice breaking vessels seem to be quite similar at a first glance, there are significant differences in their ice breaking performance. A significant amount of research effort was spent on investigations of the icebreaking process and the resulting forces. However, little information is available on the correlations between ice floe characteristics, hull shape parameters, ice properties and the ice resistance. Thus, systematic model tests in level ice and pre-sawn ice with four icebreaking ship models of one ship type have been conducted to gain new insight on these correlations. During the tests in level ice under water video records have been taken from below the ship model. Video frames have been analyzed by application of a dedicated image analysis procedure which is mainly based on a number of semiautomatic scripts applied in Matlab ® . Results of the analysis are presented and discussed within this paper.

Abstract The environment in cold regions undergoes significant changes that manifest in rising temperatures and melting ice caps. These processes allow access to new areas for shipping and the installation of structures. However, the occurring changes are not solely a reduction of ice, but also waves increasingly occur in cold regions contributing to ice break up in the Marginal Ice Zone (MIZ) and the transport of ice towards the open sea. Much work has been done to combine the single topic disciplines: wave-hydrodynamics, ice mechanics and structure mechanics to wave-structure (WSI) and ice-structure interaction (ISI). The changing environment in cold regions and the increased wave activity form a new combined discipline: wave-ice-structure interaction (WISI). This paper addresses existing knowledge gaps of the future loading scenario WISI that need to be addressed in engineering to ensure safety for future operations in Polar Regions. The knowledge gaps however, do not only refer to the discipline interfaces, i.e. challenges in combining them, but also to knowledge gaps within them. Wave statistics and the cross-effect between wave and ice are widely unknown which limits the definition of a design wave-scenario. Structures in such environments are exposed to subzero temperatures and neither their impact on properties nor on fatigue life is fully understood. While most phenomena of these two disciplines and their implementation into numerical models are established the ice mechanics appear as the weakest link. Ice is a complex material and not all aspects of its mechanical behaviour are understood and if – the implementation into (numerical) models has not been successful yet. Ice pieces that are energetically charged by waves and collide with structures at high velocities and for such high impact loads the governing ice mechanics are hardly covered by the state of the art or not at all.

Abstract Modulational instability of nonlinear waves in dispersive environments is known across a broad range of physical media, from nonlinear optics to waves in plasmas. Since it was discovered for the surface water waves in the early 60s, it was found responsible for, or able to contribute to the topics of breaking and rogue waves, swell, ice breakup, wave-current interactions and perhaps even spray production. Since the early days, however, the argument continues on whether the modulational instability, which is essentially a one-dimensional phenomenon, is active in directional wave fields (that is whether the realistic directional spectra are narrow enough to maintain such nonlinear behaviours). Here we discuss the distinct features of the evolution of nonlinear surface gravity waves, which should be attributed as signatures to this instability in oceanic wind-generated wave fields. These include: wave-breaking threshold in terms of average steepness; upshifting of the spectral energy prior to breaking; oscillations of wave asymmetry and skewness; energy loss from the carrier waves in the course of the breaking. We will also refer to the linear/nonlinear superposition of waves which is often considered a counterpart (or competing) mechanism responsible for breaking or rogue waves in the ocean. We argue that both mechanisms are physically possible and the question of in situ abnormal waves is a problem of their relative significance in specific circumstances.

Abstract One of the major challenges for a ship sailing in Arctic waters is ice aggregation. Atmospheric water or sea spray that comes into contact with the cold railing, equipment and superstructure deposits ice on the exposed surfaces. This ice can build up over time to such an extend, that the weight of the ice can severely impair the ships stability, even lead to capsizing. To prevent such accidents, the IMO Polar Code for ships operating in Arctic areas requires countermeasures against icing. Ulmatec Pyro has developed a “double pipe system” that makes use of waste heat, recovered from the ships propulsion and energy system. The main objective of this research project has been to investigate the behavior of anti-icing and de-icing for pipe structures to provide design rules and operational guidelines for such systems. Pipe systems have been studied using both numerical and experimental methods. First a simple 1D pipe system, simulating the steady heat transfer with a finite difference method, was implemented. The purpose of this model is was to be able to quickly study design variations. Next, a more advanced 3D axis-symmetric heat flow model was simulated, using a commercial transient finite element solver. The results of the advanced model was used to evaluate the simple model. Subsequently these simulation tools were used to support the design decisions for the experimental setup. To get the IMO approval for the double pipe system, the experiments were conducted at the site of the classification society. The experimental setup was used to validate the simulation model, and furthermore as a design verification lab for Ulmatec Pyro. A comparison of the results between both numerical simulation models and experiments show a good correlation. In addition, the experiments provide a valuable insight into the icing- and anti-icing processes. Specifically, a better understanding of the complex ice melting process.

Abstract The motions of ice floes in linear waves were simulated by coupling Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). The interactions between ice floes are investigated by DEM. The hydrodynamics of ice floes, mainly including the drag force and the buoyancy, are calculated by CFD. In the simulation, the ice floes are treated as discrete elements, and the contact forces between ice floes are determined by the Hertz-Mindlin (no-slip) contact model. The shape of ice floes is an approximate square composed of a number of spherical faces, which can reduce the computation cost. The waves are treated as First Order Airy wave, which is linear in nature and applied to small amplitude waves in shallow liquid depth ranges. The volume of fluid (VOF) method was adopted to capture the free surface. The simulation results are in agreement with the actual situation to a certain extent.

Abstract The Arctic region contains abundant oil and gas resources. Due to the harsh environment of extremely low temperature and strong wind, it has a great impact on drilling activities. Therefore, it is necessary to carry out insulation measures for drilling equipment such as drilling derricks. This paper analyzes the heat transfer mechanism of the derrick insulation wall of the drilling platform in the polar ice region. Based on the theory of computational fluid dynamics, the insulation materials of derrick on the polar drilling platform are investigated by numerical simulation. The number and position distribution of the heaters are selected, the effect of wind speed on insulation effect is explored, and the heating power of the derrick under the thermal insulation conditions is obtained. The simulated results are compared with those calculated by theoretical analysis. The results show that in the polar environment, polyurethane can be used as the insulation material for the derrick of polar drilling platform. Five heaters can be arranged in the derrick, wherein three heaters are arranged on the bottom layer, and two heaters are arranged on the second floor of the derrick. When the heating time is short, the external wind speed has a relatively large influence on the temperature of the air inside the derrick, but when the heating time is long, the influence of the external wind speed is small. Under the thermal insulation conditions, according to the heat transfer equation and the heat balance theory, the required heating power is similar to the heating power obtained by the fluent software simulation.

Abstract This paper investigates the fundamental question of nonlinear wave-ice interaction under level ice focusing on nonlinear wave propagation and dispersion of waves. Therefore, numerical investigations are performed to verify theoretically if nonlinearity takes place under level ice and if this can lead to intense wave events far away from the ice edge in order to provide an explanation for observed real-world ice break-ups. Therefore, nonlinear wave-ice interaction as well as the impact of the ice characteristics on this interaction will be investigated. The direct numerical simulations of the nonlinear wave propagation under solid ice are performed within the Nonlinear Schrödinger Equation (NLSE) framework. The Peregrine breather solution is applied to represent exact solutions of the NLSE for a nonlinear wave group. The application of such a nonlinear wave group is predestined for the verification of occurring nonlinear wave-wave interaction below the ice sheet. For the definition of wave and ice parameters in the simulation setup, the results of the presented parameter study are used. The parameters are analyzed regarding relevant characteristics of nonlinear wave-ice interaction and wave propagation. By assuming constraints with respect to physical consistency, the parameter range for the NLSE simulations can be narrowed. The scope of this investigation is to provide a better understanding of the ice conditions required to observe nonlinear wave effects under level ice.

Abstract This paper presents a numerical method for forecasting the ice resistance of polar ships navigating in floating ice region. The finite element method is adopted to analyze the interaction between ship and floating ice including the coupling effect between ice and water. Based on the comparison between the sea ice test data and the numerical simulation of the ice model, it is verified that the numerical method can successfully simulate the characteristics of sea ice materials. The accuracy of the numerical method is validated against ice tank model test. By using this method, the resistances of a polar ship navigating in floating ice region with different ice coverage rate (60%, 70%, 80% and 90%) at different speeds are calculated. The results show that the ice coverage rate has a great influence on the ice resistance, and the ice resistance varies with ship speeds.

Abstract The increasing activities in arctic sea areas over the last years have led to a rising demand for numerical tools to design and evaluate ice-going ships. Numerical simulation of ship-ice interaction can be a suitable method for engineers to evaluate ship designs in early development phases. We present an efficient method to evaluate local and global loads on ships in level ice at moderate computational effort. The objective of this contribution is the holistic simulation of the icebreaking process along with the hydrodynamic interplay of the broken ice cups with the surrounding level ice and the hull. For this purpose, a free surface flow solver based upon the Lattice Boltzmann method is coupled to an icebreaking model and a contact-dynamic physics engine. Overall, the approach seeks to compute both local loads, acting on the ship hull, as well as the total resistance in ice. The direct simulation approach makes it possible to consider the load contributions of icebreaking and displacement separately and to analyze their contribution to the total resistance more precisely. Simulation results for a tanker in various ice conditions show significant differences in load distribution and can provide valuable information for the designer of ice-going ships.

Abstract A floating platform in deep water East Canada is required to withstand iceberg loads and/or be disconnected and towed away in the event of very large approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and in most cases, provide large quantities of oil storage in the hull. Concepts considered for deep water application in the area include ship shaped self-propelled disconnectable FPSO and disconnectable and permanently connected deep draft floaters. This paper presents the details of Concrete Spar platforms that have been configured to satisfy all the above requirements. Several variations in the functionality and configurations of the platforms were studied to understand the impact on the overall cost and risks. The case variations primarily included: • Disconnectable options for hull, mooring and risers • Non-disconnectable option able to handle the full iceberg load • With and without crude oil storage in hull • Sacrificial or non-sacrificial mooring or risers • Steel riser configurations (freely hanging catenary, SCR vs. lazy wave, SLWR) • Hull with and without riser support Buoy • Location of mooring fairleads (on Upper hull or Buoy) • Riser support configuration (Pull Tubes or Flex Joints) The iceberg loads experienced by the hull depended on the disconnection philosophy. The Concrete Spar hull is a 6-cell structure with the risers located inside the open centerwell. The paper describes several key features of the hull, mooring and riser systems for each case that are specifically designed to withstand iceberg loads and other environment loads while maintaining the characteristic low motion response for all the options considered. Additionally, the system has been designed to minimize the disconnection and reconnection time for the disconnectable cases. The platform dimensions and weights have been compared for the various options considered. The cases without oil storage in the hull have significantly smaller and lighter hull relative to similar cases with oil storage. The cases without hull disconnection option had similar hull dimensions but marginally higher concrete weight relative to the hull disconnection option. However, the cost of Buoy, required for the disconnection option, compensates for the concrete cost difference. The SCRs work for the inplace extreme environment and iceberg load cases. Depending on the hull offset required to avoid icebergs for the non-disconnection cases or the risers lowering depth for disconnection cases, SLWR may be needed. Recommendations are made for the preferred option for field development.

Abstract In response to the UNCCC held in Paris in 2015 the need to reduce the global warming, due to CO 2 release in atmosphere, led to a new business for the capture and storage of CO 2 in dedicated deep water reservoir. In this sense the transport of the CO 2 at low temperature, necessary to condensate the gas, through offshore pipeline is a commercial and technical valid strategy. One of the issues related to the transport of a condensate gas is the thermal exchange between the transport system, in this case offshore pipelines, and the environment. The gas is usually carried by ships in a liquid phase at very low temperatures, for example −30 °C in case of CO 2 . The fluid is introduced into the pipeline at the same temperature to not further consume energy for warming up. The design of the offshore pipeline subject to these operating conditions, very cold fluid internally and a water temperature slightly over 0°C at external side, can be affected by the ice formation around the pipe. The ice thickness formation is primarily governed by the external convection coefficient. For the offshore pipelines located in deep waters where the sea currents are negligible, only the natural convection phenomena can occur on the external surface of the pipeline. Considering steady state scenario the heat transfer from the internal fluid to the external environmental is governed by the thermal resistance of each component of the system like fluid, steel, anticorrosion coating, thermal insulation if any and external convection due to the seawater. The low temperatures of both seawater and ice formation, approximately at −2°C, allow to be close to the maximum value of the seawater density: usually this occurs at a slightly colder temperatures depending on salinity and water depth (for the fresh water the maximum is at 4°C). The natural convection is driven by the buoyancy effect due to fluid density variation with temperature: the scenario described above lead to minimizes these effects and consequently the heat transfer due to the natural convection (increasing the thermal resistance). Most of the correlations in literature are related to different temperature ranges, far away from this particular situation: a numerical investigation using computational fluid dynamics technique has been performed. The analysis is executed by means of commercial CFD software FLUENT: the model is based on a two dimensional grid of a pipe submerged in water. In this paper: • The state-of-the-art about the natural convection coefficient estimate for submerged cylinders proposed by different authors through Nusselt number assessment; • A description of the proposed numerical approach is given highlighting the different approaches based on the boundary layer behavior; • A typical application is shown.