Broken Ice Field Research Articles

Non-smooth discrete element method analysis of channel width's effect on ice resistance in broken ice field

A numerical model based on NDEM is used to investigate the effect of channel width on broken-ice resistance in the channel. The model incorporates a limited impulse method to simulate the ice crushing failure. The accuracy of the numerical model is benchmarked against experimental data from model tests conducted on the Araon icebreaker at KRISO. The simulations successfully capture the characteristic effects of channel width on broken-ice resistance observed in the experiment. Beyond benchmarking of the numerical model, this study analyses the force chain characteristics in the broken ice field, revealing the crucial role of force chains in the resistance increase caused by channel width constraints. Building upon the established numerical model, further sensitivity analyses are conducted to investigate the correlation between channel width effect and other relevant factors such as ice concentration, ship velocity and ice thickness. Among these factors, it is found that ice concentration emerges as the predominant determinant of the critical channel width. The increase in ice resistance attributable to the channel width is exacerbated under the condition of thicker ice floes and lower ship velocity, where the occurrence of ice floe rotation is less frequent and the corresponding force chains are stronger and more stable.

Development of a Numerical Ice Tank Based on DEM and Physical Model Testing: Methods, Validations and Applications

The determination of ice loads on polar vessels and offshore structures is important for ice-resistant design, safe operation, and management of structural integrity in ice-infested waters. Physical model testing carried out in an ice tank/basin is usually an important technical approach for evaluating the ice loads. However, the high cost and time consumption make it difficult to perform multiple repetitions or numerous trials. Recently, the rapid development of high-performance computation techniques provides a usable alternative where the numerical methods represented by the discrete element method (DEM) have made remarkable contributions to the ice load predictions. Based on DEM simulations validated by physical model tests, numerical ice tanks can be developed as an effective complement to their counterparts. In this paper, a numerical ice tank based on 3D spherical DEM was established with respect to the small ice model basin of China Ship Scientific Research Center (CSSRC-SIMB). Based on spherical DEM with parallel bond model, the model tests of typical structures (vertical cylinder and inclined plate) in level ice sheets were established in the numerical ice tank, and the ice–structure interaction process under the same initial conditions was simulated. The accuracy of the simulations is verified by comparing the simulated ice loads with the measured ice loads from the model tests in the CSSRC-SIMB. Furthermore, the application of the numerical ice tank was extended to simulate the navigation of a Wass bow in level ice and broken ice conditions. The value of the break resistance of the Wass bow in level ice was evaluated, and the numerical ice tank produced results that were found to be consistent with those obtained from Lindqvist’s formula. The statistical properties of the bow load for different broken ice fields with the same initial physical conditions are analyzed by performing a repeatability test on the broken ice fields.

Experimental and numerical study of ice loads on a four-legged semi-submersible

ABSTRACT In this study, the ice loads on a scaled four-legged semi-submersible in a broken ice field were measured in a wave tank. Artificial ice models made of paraffin were applied in the experiment. The influence of ice floe properties, type of platform, incident velocity, and incident angle on ice loads was investigated. Shelter effect were observed most effective at a 0° incident angle, followed by a 45° incident angle. A sensitive analysis showed that a square-shaped platform with a narrow column spacing resulted in reduced ice loads in the broken ice field. The shape of floe has limited influence on the ice load under low incident velocity. Additionally, based on the Kolmogorov–Smirnov test, the lognormal distribution model best fit the experimental data of the ice load peak values (at a 5% significance level). The numerical simulation based on Ice-MAS was validated with experimental results.

Fatigue damage calculation of ship hulls caused by ice loads in broken ice fields

ABSTRACT Fatigue damage induced by ice loads is a key concern as ships operates in broken ice fields where a sea route is normally developed. This paper proposes a method for calculating fatigue damage of a ship structure advancing in broken ice, on the basis of numerical simulations. A random broken ice domain with polygon-shaped ice floes is generated using Centroidal Voronoi Tessellation (CVT) algorithm. A discrete element method (DEM) is employed to imitate ice-ice and ice-structure interactions, and produce the required ice loads data for fatigue assessment. A Weibull model is used to describe the probability distribution of ice load peaks. The fatigue stress is determined using structural beam theory. Finally, the fatigue damage is estimated based on the Palmgren–Miner rule. An example of fatigue calculation is presented with hypothetical scenarios in broken ice fields, and comparisons of the proposed method are made against the ShipRight FDA ICE procedure.

A Review of Computational Simulation Methods for a Ship Advancing in Broken Ice

Apart from breaking level ice, polar ships can interact with broken ice in various scenarios. In recent years, computational simulation models have increasingly been used for the evaluation of ship operability under broken ice conditions, presenting some challenging issues. This paper reviews existing simulation methods used to estimate ship performance and ice loads for ships advancing continuously in broken ice fields. Models for different types of broken ice, including ice floes, ice ridges, brash ice, and sliding ice pieces, are reviewed separately. A ship’s response in broken ice is divided into two categories: resistance, which relates to the overall ship performance, and local loads, which relates to structural safety. This review shows that most existing models are proposed for unbreakable ice particles, which are only applicable to broken ice of small size; most models treat fluid flow with extensive simplification, which does not reflect the influence of a ship’s wake or bow waves, and most models are aimed at resistance estimation, adopting elastic or viscoelastic contact models which do not include ice crushing. As for future work, it is suggested that more effort should be assigned to simulating a ship’s interaction with ice ridges and sliding ice pieces, the modelling of breakable ice floes, and the coupling of the Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD). More attention to the local ice load estimation is also encouraged.

The MALINA oceanographic expedition: how do changes in ice cover, permafrost and UV radiation impact biodiversity and biogeochemical fluxes in the Arctic Ocean?

Abstract. The MALINA oceanographic campaign was conducted during summer 2009 to investigate the carbon stocks and the processes controlling the carbon fluxes in the Mackenzie River estuary and the Beaufort Sea. During the campaign, an extensive suite of physical, chemical and biological variables were measured across seven shelf–basin transects (south–north) to capture the meridional gradient between the estuary and the open ocean. Key variables such as temperature, absolute salinity, radiance, irradiance, nutrient concentrations, chlorophyll a concentration, bacteria, phytoplankton and zooplankton abundance and taxonomy, and carbon stocks and fluxes were routinely measured onboard the Canadian research icebreaker CCGS Amundsen and from a barge in shallow coastal areas or for sampling within broken ice fields. Here, we present the results of a joint effort to compile and standardize the collected data sets that will facilitate their reuse in further studies of the changing Arctic Ocean. The data set is available at https://doi.org/10.17882/75345 (Massicotte et al., 2020).

Development of the Analysis Procedure for the Ice-Induced Fatigue Damage of a Ship in Broken Ice Fields

AbstractA simplified analysis method was developed to evaluate the fatigue damage of an ice-going ship under broken ice conditions. The ice resistance, which is available in the early design stages of an ice-going vessel, and the hull form information were used to estimate the local ice load acting on the outer-shell of the ship. The local ice load was applied to a finite element analysis model, and the Weibull parameters of the local stress range at the target fatigue point were derived. Finally, the fatigue damage was evaluated by applying the S–N curve and Palmgren–Miner rule. To verify the proposed method, numerical analyses using the direct approach, which takes into account the detailed interaction model among the fluid, structure, and ice, were performed under the same conditions. Fatigue analyses of the Baltic Sea for actual ice conditions were performed to check the validity and applicability of the proposed method, and the resulting fatigue damage was compared with that obtained by the classification society’s recommended practice.

Numerical simulation of ice loads on a ship in broken ice fields using an elastic ice model

The finite element method is used to simulate the navigation of an ice-area bulk carrier in broken ice fields. The ice material is defined as elastic, and the simulations are accomplished at four model speeds and three ice concentrations. The movements of ice floes in the simulation are consistent with those in the model test, and the percentage deviation of the numerical ice resistance from the ice resistance in the model test can be controlled to be less than 15 %. The key characteristics of ice loads, including the average ice loads, extreme ice loads, and characteristic frequency, are analyzed thoroughly in a comprehensive manner. Moreover, the effects of sailing speed and ice concentration on the ice loads are analyzed. In particular, the stress distribution of ice floes is presented to help understand how model speed and concentration affect the ice loads. The “ice pressure” phenomenon is observed at 90 % ice concentration, and it is realistically reflected both in the time–and frequency–domain ice force curves.

A bonded discrete element method for modeling ship–ice interactions in broken and unbroken sea ice fields

This work investigates the failure patterns of ice cakes and floe-ice when loaded by a moving and sloping structure (ice-breaking ships and cones). In the paper, we introduce the most frequently encountered ice-infested scenarios, the main characteristics of ice-breaking ships and the predicted failure modes of floe-ice depending on the loading conditions, the structure type and the ice feature dimensions and thickness. For the simulations, a local bonded discrete element method (DEM) is used to model sea ice and its fractures. The packing of bonded spherical particles which reproduce the ice continuum can break due to ship–ice interactions and the failure modes are studied. A set of validation simulations are first carried out. A level ice sheet breaking against an installed ice-breaking cone with different slope angles is studied, and the results are compared with other DEM simulations. Then, a group of bonded DEM simulations are performed to predict the different failure modes produced when an ice-breaking ship bow contacts with ice cakes and floe-ice of different dimensions and thickness, typical in broken ice fields. Finally, the study of breaking a continuous level ice sheet is carried out by modeling with the bonded DEM an “infinite” large domain of sea ice and loaded by a single-degree-of-freedom model of an ice-breaking ship.

Numerical simulation of ice impacts on ship hulls in broken ice fields

Ice loads should be considered in the design stage of the ice-going ships. The loads will be determined by the ice features present given the location, the time of year and the environmental conditions. Normally, a ship follows a sea path covered with ice broken by an ice breaker. Therefore, it is important to estimate its performance in broken ice fields. In this study, a numerical simulation of an ice going ship navigating through broken ice field was carried out using the finite element method. Ice floes with random distributions of size, thickness and shape were modeled, and an efficient numerical simulation method for ice-sea, ice-structure, and ice-ice interactions was proposed for rapid computation. Important parameters, such as the drag force coefficient and the pressure-penetration relationship in interaction modeling were obtained based on the results of detailed analysis using the coupled Eulerian-Lagrangian method. The simulations were conducted under the same conditions as tests carried out in an ice model basin, and the results were compared.

유빙 하중을 받는 내빙 선박의 피로손상도 추정Part I - 직접 해석법

In this study, a fatigue damage estimation for an ice-going vessel navigating through broken ice fields was carried out. A numerical model to simulate the interaction between ice and structure developed using the finite element method was introduced. Time series of stresses calculated by the proposed model and the corresponding fatigue analysis results are presented. The numerical model enables the long time analysis through an efficient interaction model, the application of the periodic media analysis and the convolution integral, and it allows the stress time history to be extracted directly using the finite element method. To describe the probability distribution of stress amplitudes, the 2-parameter Weibull model was applied to the calculated stress time history, and the fatigue damage was calculated using the Palmgren-Miner rule. Finally, the fatigue damage considering the ice conditions of the Baltic Sea was calculated using the proposed method and LR method, and the results were compared to each other.

WITHDRAWN: Numerical simulation of ice impacts on ship hulls in broken ice fields

WITHDRAWN: Numerical simulation of ice impacts on ship hulls in broken ice fields

Numerical simulation on the ice-induced fatigue damage of ship structural members in broken ice fields

A fatigue damage assessment for an ice-going ship navigating through broken ice fields was carried out using a numerical model to simulate the interactions between ice floes and structure. The stress history was obtained by a numerical model and the corresponding fatigue analysis results are presented. The stress time series required for fatigue analysis could be extracted directly using an efficient interaction model, the application of a periodic media analysis method, and the convolution integral. A 2-parameter Weibull model was applied to describe the probability distribution of the stress amplitude, and the fatigue damage was obtained using the Palmgren-Miner rule. Finally, the fatigue damage considering the actual ice conditions of the Baltic Sea was calculated using the proposed method and LR method, and each result was compared.

The effect of ice floe shape on the load experienced by vertical-sided structures interacting with a broken ice field

In this study, numerical experiments are conducted to investigate the effect of ice floe shape on the load experienced by vertical-sided structures interacting with a broken ice field. We create numerical ice fields with different floe shapes and otherwise identical properties. These fields are used to simulate ice-structure interaction with vertical-sided structures. First, we investigate the effect of floe shape in ice-tank tests by comparing the numerical results to the ice tank test results. Then, we conduct a sensitivity study to investigate the correlation between the floe shape effect and other parameters. The primary finding is that the ice floe shape has a large influence on the mean and standard deviation of the ice load in interaction scenarios dominated by ice accumulation and clearance around the structure. In particular, square floes, which are often used in ice tank tests, result in higher mean loads and standard deviations than other floe shapes. The simulation results show that the greater length and higher stability of force chains is the primary mechanism causing the floe shape effect. The floe shape effect is exacerbated in confined conditions, where the force chains may cause bridging between the structure and a rigid boundary. The presence and length of ‘parallel opposite edges’ is an important factor influencing the floe shape effect. This result is novel compared to earlier studies, which only consider body ‘roundness’ or ‘angularity’ in assessing shape effects. We demonstrate the importance of using accurate floe shapes in ice tank tests and in discrete element method (DEM) modelling of broken ice-structure interaction scenarios.

Numerical Study of a Moored Structure in Moving Broken Ice Driven by Current and Wave

This paper presents a numerical model intended to simulate the mooring force and the dynamic response of a moored structure in drifting ice. The mooring lines were explicitly modeled by using a generic cable model with a set of constraint equations providing desired structural properties such as the axial, bending, and torsional stiffness. The six degrees-of-freedom (DOF) rigid body motions of the structure were simulated by considering its interactions with the mooring lines and the drifting ice. In this simulation, a fragmented ice field of broken ice pieces could be considered under the effects of current and wave. The ice–ice and ice–structure interaction forces were calculated based on a viscoelastic-plastic rheological model. The hydrodynamic forces acting on the floating structure, mooring line, and drifting ice were simplified and calculated appropriately. The present study, in general, demonstrates the potential of developing an integrated numerical model for the coupled analysis of a moored structure in a broken ice field with current and wave.

An implicit time-stepping scheme and an improved contact model for ice-structure interaction simulations

This paper presents a novel time-stepping scheme for the modelling of discrete ice-structure interaction. The scheme extends the non-smooth discrete element modelling (NDEM) technique to enable compliant continuous and discontinuous contacts. This increases the accuracy and expands the applicability range of the NDEM technique related to ice-structure interaction problems. We derive the parameters representing the compliant behaviour of contacts. The accuracy of the presented scheme for discontinuous contacts is compared to an existing, simpler scheme that limits the contact force based on a maximum force assumption. The comparison shows that the derived scheme results in more accurate contact forces, for the same time step size, as previously applied NDEM schemes in ice-structure interaction. An example simulation is compared against ice tank tests of a 4-legged, vertical-walled structure moving through a broken ice field.

Ice load on floating structure simulated with dilated polyhedral discrete element method in broken ice field

The discrete element method with dilated polyhedral elements is developed to simulate the interaction between ice floes and the floating structure. The 2D-Voronoi tessellation algorithm is adopted to generate polyhedral ice floes with a given ice thickness in broken ice field. According to the Minkowski sum theory, the dilated polyhedron is constructed via sweeping a sphere on the surface of a basic polyhedron. The Hertzian contact model and its simplified form are then adopted to determine the contact force between dilated elements due to the round profile of the element. Meanwhile, the buoyancy and buoyancy moment, the drag force and drag moment on ice floes are calculated by meshing every polyhedral element as tetrahedrons. The floating structure Kulluk, which operates in the Arctic, is modeled as a rigid body restricted by mooring lines with the linear stiffness. The structure motion is calculated with six degrees of freedom in terms of the ice contact force, the buoyancy, the drag force of current, and the mooring force. Under different ice thickness and concentration, the ice load on the floating structure is reasonably compared with the field data. General influences of different ice conditions are analyzed to provide operational principles in engineering.

Innovative Oil Spill Recovery Technology Developments

ABSTRACT (2017-404) Long-term challenges for the oil spill response industry include spills occurring in the open ocean or ice-infested waters, as well as spills of heavy oil. Historically, only a small percentage of the oil from major spills is ever recovered. For example, during the Deepwater Horizon incident, skimming operations only accounted for approximately 3% of the spilled oil. This low number was due to the delayed response of assets as well as the use of inefficient skimming systems and methods. Both government and private organizations seek effective response solutions that are capable of rapid deployment to existing platforms and infrastructure. Alion Science and Technology, under contract to the Bureau of Safety and Environmental Enforcement has developed two proof-of-concept technologies; both of which were successfully tested in 2016. Both of these research projects have been pushing the edge of the envelope for oil spill recovery operations with the use of existing technologies. The first of these concepts is the “ICEHORSE”, an oil-in-ice skimmer designed to recover surface oil pooled in broken ice fields. The system is designed to submerge and transit below the ice field where it may then be surfaced in a pocket of oil to begin skimming. This allows for remote skimming operations while the boat remains in safer waters and gives the skimmer the ability to position itself in the thickest areas of oil. The initial proof-of-concept system has seen further development with the goal being a commercially available product. The “Autonomous Oil Skimmer” is designed to be used with any vessel-based skimming system to improve the efficiency of recovery operations. Our proprietary control algorithm collects oil thickness data from a sensor and then directs and tracks the oil recovery operation autonomously. Collection data may be remotely accessed, allowing for centralized project oversight of multiple resources. Part of this effort included the evaluation of different oil sensors and the development of algorithms to incorporate the sensor data into the control system. This paper discusses some of the design challenges of each system as well as the results of testing, and plans for further development.

Out-of-plane failure of an ice floe: Radial-crack-initiation-controlled fracture

Out-of-plane failure of an ice floe has been studied extensively over the past several decades for different application purposes (e.g., an ice cover's bearing capacity for transportation; bending failure of level ice interacting with a sloping structure). Notably, most of the previous studies have idealised the considered ice floe as an infinite or semi-infinite thin plate resting on a Winkler-type elastic foundation. However, a typical ice field in the Arctic is far from continuous. Furthermore, recent Arctic offshore structures have usually been designed with support from ice management; i.e., these sloping structures are most often operating in a broken ice field and are interacting with ice floes of finite sizes. Bearing this loading environment in mind, this paper starts with the question ‘What are the physical processes behind the failure of a finite size ice floe interacting with a sloping structure, and what will the failure pattern look like?’ Based on an in-depth literature review in relation to out-of-plane failures of infinite and semi-infinite ice floes, depending on the floe sizes, we propose a conservative classification of an ice floe's out-of-plane failures under an edge load, i.e., 1) finite size ice floes that are broken at radial crack initiation and 2) a semi-infinite ice floe that is broken by sequentially forming radial and circumferential cracks. Between these two scenarios, we focused our study on ‘radial-crack-initiation-controlled fracture’ of a finite size ice floe. Specifically, we are trying to answer the following question: ‘how small/large should an ice floe be to be treated as a finite size/semi-infinite ice floe?’ Based on a series of assumptions, radial crack initiation and propagation within a square ice floe were theoretically formulated and numerically studied. The respective loads to initiate and propagate a radial crack have been extracted and compared to quantify the required size smaller than which an ice floe would fail at radial crack initiation. For typical ice material properties, it is theoretically illustrated that a nearly square shaped ice floe can fail at crack initiation if its physical size is smaller than approximately 27×(ice thickness)3/4. On the theoretical side, this paper contributes to the derivation of non-dimensional formulae to study radial crack initiation and propagation. Additionally, simplified yet effective numerical models to study radial crack initiation and propagation within an ice floe were proposed and validated. On the practical side, the research methodologies and conclusions presented herein shed light on the possibility of a more economic design for an Arctic offshore structure whose major operating environment is filled with finite size ice floes. In addition, because the ‘radial-crack-initiation-controlled fracture’ of an ice floe means a much smaller ice load (i.e., compared with continuous circumferential type bending failure within a level ice environment) on a sloping structure, it is recommended, from a mechanically preferred point of view, that floes with sizes smaller than 27×(ice thickness)3/4 should be produced in the downstream of an ice management operation.

Discrete element modeling of ice loads on ship hulls in broken ice fields

Ice loads on a ship hull affect the safety of the hull structure and the ship maneuvering performance in ice-covered regions. A discrete element method (DEM) is used to simulate the interaction between drifting ice floes and a moving ship. The pancake ice floes are modelled with three-dimensional (3-D) dilated disk elements considering the buoyancy, drag force and additional mass induced by the current. The ship hull is modelled with 3D disks with overlaps. Ice loads on the ship hull are determined through the contact detection between ice floe element and ship hull element and the contact force calculation. The influences of different ice conditions (current velocities and directions, ice thicknesses, concentrations and ice floe sizes) and ship speeds are also examined on the dynamic ice force. The simulated results are compared qualitatively well with the existing field data and other numerical results. This work can be helpful in the ship structure design and the navigation security in ice-covered fields.