Ice Fragments Research Articles

Numerical simulation of heterogeneous ice sheet-structure interaction based on cohesive element method

The coupling process between sea ice and offshore structures is complex, which involves the influences of physical and mechanical properties of sea ice, structural dynamics, and fluid–structure interaction. In this work, a numerical model was established to simulate the ice-structure interactions, which is based on the cohesive element method combined with random field. The complicated spatial heterogeneity of ice sheet materials was considered, and the fracture energy, which is one of the material properties of the ice sheet model, was assumed to be a Gaussian random field. Numerical simulations of the ice sheet-vertical structures interactions were conducted with two mesh patterns, respectively. A more suitable element was adopted to build the heterogeneous ice field to investigate the effect of heterogeneity on the interactions. Moreover, the parametric sensitivity analysis of Gaussian random fields was performed. It has been found that the heterogeneity of ice sheet led to significant uncertainties in the numerical simulations. The location of ice sheet failure and the shape of ice fragments are associated with the distribution of the properties, and the cracks emerge and propagate in those weaker regions. Furthermore, the mean of ice load and the collision frequency show a decreasing trend with an increase in correlation length.

Simulation analysis for landing process of aviation tires with ice overlay

In general, amphibious aircraft is subjected to challenges with liquid water freezing to the tires or atmospheric air-cooled icing in low-temperature environments. A finite element modeling method for aviation tires was proposed in this study in accordance with LAGRANGE mesh coupling curtain and rubber to investigate and evaluate the tires' icing adaptability of amphibious aircraft and ensure landing safety. The accuracy of the model was verified through simulation calculation, and the shape dimension achieved the maximum error of less than 1.7%. The dynamic response of the vertical ground impact for ice-free and ice-overlaid tires and that of the ground impact of tires during grounded skidding were simulated and analyzed through explicit dynamic analysis. The results of the simulation analysis suggested that the size of ice fragments showed a positive correlation with the ice thickness, and residual broken ice in the tread groove led to local stress concentration in the tread. And the tread rubber stress of the ice-overlaid aircraft tire of this type was less than the tensile strength of 27.8 MPa in the landing process, thus conforming to the required standards. Moreover, a friction-time curve was plotted to examine the impact of tires on the friction force during landings.

Estimation of sea ice drift and concentration during melt season using C-band dual-polarimetric Sentinel-1 data

Characterizing sea ice changes over the Arctic can give proper insight into its extent in the current context of climate change. Sea ice motion's effect on ice area is influenced by seasonal conditions and the prevailing climate. However, the motion of thinner ice during the melt season can result in polynyas and cause significant ice loss that lasts the entire year. Sea ice drift and concentration during melt season are rarely discussed. The present study attempts to estimate sea ice drift during the melt season (July–August) using Differential Synthetic Aperture Radar Interferometry (DInSAR) with the usability of C-band Sentinel-1 data. The displacements/drifts were estimated using the phase shifts between two complex images with a temporal extent of 12 days. The study also proposed estimating sea ice concentration using polarimetric descriptors (power, purity, and randomness). The results revealed drifts of about 14–15 cm in the northeastern and southern parts followed by 45–50 cm in the middle parts and 20–25 cm along the coasts and open areas. Based on three polarimetric descriptors, thin ice and other ice fragments over open areas have shown less sea ice concentration as compared to the more concentrated pancake and pack ice with more compactness over the ice crystals. The study can be useful for computing drift in the melt season and carrying out spatiotemporal time-series analysis of seasonal sea ice drift/deformation studies. The algorithm and results can be used as a base study for the upcoming L- and S-band carrying NASA-ISRO Synthetic Aperture Radar (NISAR) mission.

Simulation of Sea Ice Fragmentation Based on an Improved Voronoi Diagram Algorithm in an Ice Zone Navigation Simulator

In order to reduce the cost of navigation training in the waters of ice zones and improve the effectiveness of the training process, a method for simulating sea ice fragmentation in an ice zone navigation simulator is proposed. The Voronoi diagram algorithm, which takes the ice thickness into account and affects the degree of fragmentation, was used to preprocess the sea ice model so that the number and sizes of the ice model fragmentations would be related to the ice thickness. According to the position of the preprocessed sub-blocks of the ice model, the collision bodies of the Mesh Collider and Sphere Collider were set up to realize the effect of the conduction of ice cracking as a result of the ship’s hull colliding with the ice surface. Based on the positional relationship between mesh triangle elements and the water surface, the volume of an ice floe that should have been underwater when it reached equilibrium was calculated to achieve the sea-floating effect of the broken ice floe. The quadtree method for the management of sea ice scenes was improved to improve the timeliness of the replacement of the ice model. The experiments show that this method improved the realism of simulations of sea ice breaking in ice zones and can be used for simulations in ice zone navigation simulators.

New six degree of freedom model for ice throw simulations

Icing and thus ice throw from wind turbines is currently unavoidable in cold climates. Therefore, the associated risk requires adequate quantification and assessment. In this study, a new six degree of freedom model with increased accuracy is introduced, which aims to overcome limitations of currently used approaches. This is achieved by taking into account translation and rotation of the thrown fragments and thus allowing to represent more complex trajectories. To limit the necessary numerical effort, look-up tables for forces and moments are pre-calculated with the help of CFD simulations. Validation of the model was achieved by comparison to real life experiments. For these, artificial ice fragments based on collected real fragments were produced and released from wind turbines under partially controlled conditions. This showed a significantly improved agreement between simulated and observed values when compared to the state-of-the-art model. Since the distribution patterns of the presented model differ significantly from those of the established model, these consequences must be taken into account in future risk assessments.

A Multi-Yield-Surface Plasticity State-Based Peridynamics Model and its Applications to Simulations of Ice-Structure Interactions

Due to complex mesoscopic and the distinct macroscopic evolution characteristics of ice, especially for its brittle-to-ductile transition in dynamic response, it is still a challenging task to build an accurate ice constitutive model to predict ice loads during ship-ice collision. To address this, we incorporate the conventional multi-yield-surface plasticity model with the state-based peridynamics to simulate the stress and crack formation of ice under impact. Additionally, we take into account of the effects of inhomogeneous temperature distribution, strain rate, and pressure sensitivity. By doing so, we can successfully predict material failure of isotropic freshwater ice,iceberg ice, and columnar saline ice. Particularly, the proposed ice constitutive model is validated through several benchmark tests, and proved its applicability to model ice fragmentation under impacts, including drop tower tests and ballistic problems. Our results show that the proposed approach provides good computational performance to simulate ship-ice collision.

Effects from Time Dependence of Ice Nucleus Activity for Contrasting Cloud Types

Abstract The role of time-dependent freezing of ice nucleating particles (INPs) is evaluated with the “Aerosol–Cloud” (AC) model in 1) deep convection observed over Oklahoma during the Midlatitude Continental Convective Cloud Experiment (MC3E), 2) orographic clouds observed over North California during the Atmospheric Radiation Measurement (ARM) Cloud Aerosol Precipitation Experiment (ACAPEX), and 3) supercooled, stratiform clouds over the United Kingdom, observed during the Aerosol Properties, Processes And Influences on the Earth’s climate (APPRAISE) campaign. AC uses the dynamical core of the WRF Model and has hybrid bin–bulk microphysics and a 3D mesoscale domain. AC is validated against coincident aircraft, ground-based, and satellite observations for all three cases. Filtered concentrations of ice (>0.1–0.2 mm) agree with those observed at all sampled levels. AC predicts the INP activity of various types of aerosol particles with an empirical parameterization (EP), which follows a singular approach (no time dependence). Here, the EP is modified to represent time-dependent INP activity by a purely empirical approach, using our published laboratory observations of time-dependent INP activity. In all simulated clouds, the inclusion of time dependence increases the predicted INP activity of mineral dust particles by 0.5–1 order of magnitude. However, there is little impact on the cloud glaciation because the total ice is mostly (80%–90%) from secondary ice production (SIP) at levels warmer than about −36°C. The Hallett–Mossop process and fragmentation in ice–ice collisions together initiate about 70% of the total ice, whereas fragmentation during both raindrop freezing and sublimation contributes <10%. Overall, total ice concentrations and SIP are unaffected by time-dependent INP activity. In the simulated APPRAISE case, the main causes of persistence of long-lived clouds and precipitation are predicted to be SIP in weak embedded convection and reactivation following recirculation of dust particles in supercooled layer cloud.

Scaling principles for model testing in old brash ice channel

Climate warming sets higher requirements for sustainability in ship industry, which fuels the introduction of stricter power restrictions and new types of ship hull design. The new designs invite us to reconsider the principles in model scale testing in ice, which is the state-of-the-art method to predict vessel's ice performance prior to its construction. Ice model testing principles were originally developed for the evaluation of performance in level ice at slow speed, but currently those principles are widely applied for ice model testing in other ice conditions as well.The forces forming the vessel resistance in a brash ice channel are different compared to forces forming the vessel resistance in level ice. In consequence, the current model scale testing principles are suboptimal when predicting vessel's performance in an old, frequently operated brash ice channel, as our earlier research indicates that the prediction is conservative especially for modern merchant ship bow shapes with high stem angles. An old brash ice channel is especially interesting, as it is the determining ice condition in Finnish-Swedish Ice Class Rules ice class granting process.This paper addresses the problem by introducing a new similitude number – a Channel number – to be applied alongside the currently applied Froude and Cauchy similitudes. The Channel number aims to realistically scale the dominating forces that form the resistance of the vessel in an old brash ice channel by developing further the modelling of the resistance component induced by displacing the ice fragments. This necessitates considering the brash ice fragment interaction and inertia forces. The new scaling principle, which supplements the currently applied Froude-Cauchy scaling principle by the Channel number, is considered more accurate for brash ice conditions. It is designed to predict fairly and uniformly the ship resistance for all bow shapes avoiding potential overpowering of the modern bow types with a high stem angle. This would contribute to providing a good harmonization of ships' expected ice performance with ice classes, and, further, improve the fleet schedule predictability that the logistic chains demand from the transportation.

Particle-based numerical simulation of continuous ice-breaking process by an icebreaker

The continuous ice-breaking capacity of an icebreaker is an important indicator of its efficiency. The ice resistance encountered by an icebreaker has a significant influence on its continuous ice-breaking capacity. In this study, we develop a numerical model based on the moving particle semi-implicit (MPS) method, which is a particle method based on continuum mechanics, for predicting the ice resistance encountered by icebreakers during continuous ice-breaking operations. Before fracture, the ice is assumed to be a linear elastic material, and the maximum tensile stress theory is used as the fracture criterion. A scalar function composed of the first principal stress gradient and the first eigenvector of the stress tensor is introduced to express the relative positions of the new crack and corresponding particle pair. As the hull is represented by polygons and the ice fragments are represented by particles, the collision points between the hull and the ice, i.e., between polygons and particles, is determined using a novel search algorithm that expands a cell linked-list algorithm. The collisions between individual ice fragments and between the hull and an ice fragment are considered using a particle-based model that is a modified form of the Hertz contact model. The proposed algorithm was verified using experimental data obtained from three-point bending tests on model and freshwater ice specimens that were performed by the Korea Research Institute of Ships and Ocean Engineering (KRISO) and Korea Maritime and Ocean University (KMOU), respectively. The verification process revealed that the closer the properties of the ice to the linear elastic properties assumed in the numerical model, the higher the accuracy of the proposed algorithm. The verified algorithm was used to predict the ice resistance encountered by a model icebreaker during a continuous ice-breaking process. A series of convergence and parametric tests were performed for the main parameters of the continuous ice-breaking simulation, and the experimental results obtained by KRISO were used for comparison. The maximum relative errors from experiment were approximately 12% and 30% under free (Fr) and semi-fixed (SF) side boundary conditions, respectively. The proposed numerical algorithm can successfully predict the ice resistance encountered by an icebreaker and the occurrence of near- and far-field fractures during a continuous ice-breaking process.

Rubber-ice friction

We study the friction when a rectangular tire tread rubber block is sliding on an ice surface at different temperatures ranging from −38 to −2 °C, and sliding speeds ranging from 3 µm/s to 1 cm/s. At low temperatures and low sliding speeds we propose that an important contribution to the friction force is due to slip between the ice surface and ice fragments attached to the rubber surface. At temperatures above −10 °C or for high enough sliding speeds, a thin premelted water film occurs on the ice surface and the contribution to the friction from shearing the area of real contact is small. In this case the dominant contribution to the friction force comes from viscoelastic deformations of the rubber by the ice asperities. We comment on the role of waxing on the friction between skis and snow (ice particles).

Dependencies of Four Mechanisms of Secondary Ice Production on Cloud-Top Temperature in a Continental Convective Storm

Abstract Various mechanisms of secondary ice production (SIP) cause multiplication of numbers of ice particle, after the onset of primary ice. A measure of SIP is the ice enhancement ratio (“IE ratio”) defined here as the ratio between number concentrations of total ice (excluding homogeneously nucleated ice) and active ice-nucleating particles (INPs). A convective line observed on 11 May 2011 over the Southern Great Plains in the Mesoscale Continental Convective Cloud Experiment (MC3E) campaign was simulated with the “Aerosol–Cloud” (AC) model. AC is validated against coincident MC3E observations by aircraft, ground-based instruments, and satellite. Four SIP mechanisms are represented in AC: the Hallett–Mossop (HM) process of rime splintering, and fragmentation during ice–ice collisions, raindrop freezing, and sublimation. The vertical profile of the IE ratio, averaged over the entire simulation, is almost uniform (102 to 103) because fragmentation in ice–ice collisions dominates at long time scales, driving the ice concentration toward a theoretical maximum. The IE ratio increases with both the updraft (HM process, fragmentation during raindrop freezing, and ice–ice collisions) and downdraft speed (fragmentation during ice–ice collisions and sublimation). As reported historically in aircraft sampling, IE ratios were predicted to peak near 103 for cloud-top temperatures close to the −12°C level, mostly due to the HM process in typically young clouds with their age less than 15 min. At higher altitudes with temperatures of −20° to −30°C, the predicted IE ratios were smaller, ranging from 10 to 102, and mainly resulted from fragmentation in ice–ice collisions.

Some Pertinent Issues for Interstellar Panspermia Raised after the Discovery of 1I/‘Oumuamua

The interstellar objects 1I/'Oumuamua and 2I/Borisov confirm the long-held expectation that bodies from one stellar system will be carried to another, allowing, in principle, interstellar panspermia. Life might be transferred between stellar systems, depending on the nature of the bodies and how they escaped their systems. 2I/Borisov appears to be a comet, with no more likelihood of carrying life than Solar System comets. In contrast, the nature of 1I/'Oumuamua has been difficult to determine. We review various hypotheses for its origin, including ejection of N2 ice from the surface of an exo-Pluto, formation in a molecular cloud by freezing of H2, and a derelict solar sail of alien construction. Of these, the N2 ice fragment hypothesis is uniquely falsifiable, plausible, and completely consistent with all observations. The possibility of interstellar panspermia would be made more probable if 'Oumuamua originated on a dwarf planet rather than a comet, although substantial challenges to transfer of life would remain. Of proposed mechanisms for interstellar panspermia, transfer of life via rocky meteoroids is perhaps less improbable.

Applying landscape fragmentation analysis to icescape environments: potential impacts for the Pacific walrus (Odobenus rosmarus divergens)

Sea-ice cover across the Arctic has declined rapidly over the past several decades owing to amplified climate warming. The Pacific walrus (Odobenus rosmarus divergens) relies on sea-ice floes in the St. Lawrence Island (SLI) and Wainwright regions of the Bering and Chukchi seas surrounding Alaska as a platform for rest, feeding and reproduction. Lower concentrations of thick ice floes are generally associated with earlier seasonal fragmentation and shorter annual persistence of sea-ice cover, potentially affecting the life history of the Pacific walrus. In this study, 24 Landsat satellite images were classified into thick ice, thin ice or open water to assess sea-ice fragmentation over the spring-summer breakup period. Geospatial fragmentation analyses traditionally used in terrestrial landscapes were newly implemented in this study to characterize the icescape environment. Fragmentation of sea ice was assessed based on the Percent of Landscape, Number of Patches, Mean Area, Shape Index, Euclidean Nearest Neighbor and Edge Density. Results show that lower sea-ice concentrations in both the SLI and Wainwright regions were associated with smaller sea-ice floes. In the Bering Sea, lower sea-ice concentrations were also associated with increases in the number of ice floes, floe isolation and edge density. By contrast, lower sea-ice concentrations in the Chukchi Sea were associated with ice floes that were more circular in shape. The continuation of sea-ice decline with shifting icescape characteristics may result in walruses having to swim longer distances in the northern Bering Sea and adapt to use less-preferred, rounder ice floes in the Chukchi Sea.

Особенности влияния формы кормовой оконечности современных крупнотоннажных судов на их ледовую ходкость при движении задним ходом

Object and purpose of research. Object of the study is the analysis of aft shape effect of modern heavy-tonnage ships on ice performance indices when moving astern. The purpose of the work is to identify additional specific factors that affect the performance of ice performance when moving stern first, which are usually not taken into account when considering moving ahead. Materials and methods. Material for the development are provided by the data from model experiments results, as well as previously published works devoted to the study of the ship's stern-first movement in ice. Main results. Models tests results of large capacity ice-going ships models moving stern first in an ice basin are analyzed. The phenomena of stern interaction with the ice cover in comparison with the mode of bow first movement are identified and discussed. Approximate estimates are done of the size of ice fragments formed when large capacity ships are moving astern. The obtained results create prerequisites for the development of a methodology for designing large capacity ships with increased ice-going capability. Conclusion. Analysis of heavy-tonnage vessel interaction with ice when sailing astern was carried out based on model tests in the ice basin. It was concluded that in order to develop the calculation procedure for ice resistance when the ship is sailing astern, it is necessary to elaborate new criteria for describing the main components of the ship hull lines and peculiarities of hull interaction with ice.

Icy molecule desorption in interstellar grain collisions

ABSTRACT Observations of gaseous complex organic molecules (COMs) in cold starless and prestellar cloud cores require efficient desorption of the COMs and their parent species from icy mantles on interstellar grains. With a simple astrochemical model, we investigate if mechanical removal of ice fragments in oblique collisions between grains in two size bins (0.01 and 0.1 µm) can substantially affect COM abundances. Two grain collision velocities were considered – 10 and 50 m s−1, corresponding to realistic grain relative speeds arising from ambipolar diffusion and turbulence, respectively. From the smaller grains, the collisions are assumed to remove a spherical cap with height equal to 1/3 and 1 ice mantle thickness, respectively. We find that the turbulence-induced desorption can elevate the gas-phase abundances of COMs by several orders of magnitude, reproducing observed COM abundances within an order of magnitude. Importantly, the high gaseous COM abundances are attained for long time-scales of up to 1 Myr and for a rather low methanol ice abundance, common for starless cores. The simple model, considering only two grain size bins and several assumptions, demonstrates a concept that must be tested with a more sophisticated approach.

Fatigue damage estimation of icebreaker ARAON colliding with level ice

This paper presents a methodology for precisely calculating the fatigue damage of an arctic vessel colliding with level ice. For accurate prediction of local ice loads acting on the external surface of the hull, focusing on the bow area, numerical simulation using the finite element method (FEM) was conducted first. The existing Drucker-Prager plastic model was combined with damage mechanics to simulate the icebreaking phenomenon. Furthermore, element erosion technology was considered to simulate crack formation and propagation through level ice that collides with a moving structure. Both dynamic drag and static buoyancy were applied to consider the dynamic behavior of submerged ice fragments. With this model, the ice resistance acting on rigid structures and a ship hull passing through level ice at multiple forward speeds were numerically calculated and compared with the test results. An additional simulation was performed in which ice fragments are removed immediately after being broken, with an attempt to decompose the total ice resistance into icebreaking resistance and the resistance of submerged ice fragments. Afterward, the spatial distribution of extreme values and frequencies of loads from the forefront to the vicinity of the hull shoulder area was derived. Finally, the ice load applied to the icebreaker ARAON at full scale under level ice conditions was calculated and then converted into stress at the target point using the influence coefficient method. Based on the converted stress information, the cumulative fatigue damage according to the speed was calculated, and the tendency of the cumulative fatigue damage was analyzed.

Investigation of vessel resistance in model scale brash ice channels and comparison to full scale tests

The ice class-based rules and restrictions aim to ensure the safety and efficiency of the winter navigation system in the Baltic Sea. The vessel resistance prediction in a brash ice channel is a mid-term step in Finnish-Swedish Ice Class Rules ice class granting process that can be based on model scale tests. However, there are some limitations in the current model scale test guidelines. To improve the test procedures and to provide a better real-world correlation for all ship shapes, this paper explores the relationship between the brash ice properties and vessel resistance utilizing channel resistances measurements in model scale and full scale. The results indicate that the model scale results can be scattered and conservative, especially for modern, open-water-optimized bow shapes when model ice with a scaled-down strength is utilized. Model scale tests in brash ice channels with unscaled ice strength provided good correlation with full scale resistance tests and small variation in repeated tests. The results suggest that the correct modeling of ice fragment interaction would improve the prediction quality for all hull shapes.

Peridynamic analysis of ice fragmentation under explosive loading on varied fracture toughness of ice with fully coupled thermomechanics

The computational investigation on the ice cover fragmentation under extreme loadings, such as a shock wave, is still a poorly understood research topic. In this process, the influence of the temperature change on the crack evolution, and the damage of the ice cover can be significant since the temperature is one of the critical factors affecting ice behaviour. Thus, it is necessary to analyse the coupled case of mechanics and thermotics. Based on ordinary state-based Peridynamic theory, a fully coupled model of mechanics and thermodynamics is employed to study the failure process and crack evolution of the ice sheet subjected to explosive loading in this paper. The load of the explosion, which is defined by the empirical formula, is non-uniformly distributed on the bottom surface (underwater side) of the ice layer. By comparing the damage modes to the observation from the existing field test, the present Peridynamic model is rigorously validated. The exponential decay constant, which is a coefficient that determines the distribution of shock waves acting on the bottom of the ice layer, is numerically examined. Since the fracture toughness (FT) of the ice contributes to the failure criterion and has no clear value, it is discussed according to the ice damage with various FT values. Finally, ice fragmentation with thermal effects is analysed and compared to uncoupled cases, and the crack propagation paths influenced by the thermal field are further investigated.

Ice ablation by pyroclast impact during subglacial fragmentation-dominated eruptions

Understanding magma-ice interaction processes is critical for mitigation of the hazards generated by subglacial explosive volcanism, including large flowrate meltwater floods and fine-grained volcanic ash. We propose and evaluate a subglacial eruption mechanism with potential for rapid ablation of the overlying ice that involves the impact of pyroclasts on the ice surfaces of depressurised, vapour dominated ice cavities that surround subglacial vents. Such impacts are likely to cause considerable fracturing and mechanical fragmentation of the ice and thus increase the heat transfer area available for ice-melt. This mechanism has not, to our knowledge, been explored previously in the literature, but we find that published experimental work on impact cratering of icy solar system bodies can be used to predict fragmentation damage by pyroclast impact. Our principal conclusions are as follows. (1) Ice ablation rates of order 100 m h−1 are predicted, for typical pyroclast velocities, provided that the mechanism is sustained. (2) The thermal energy of the eruption, together with the size of the ice fragments produced, is sufficient to prevent accumulation of fractured ice within the cavity. (3) Upward ablation of the ice cavity roof results in a progressive decrease in pyroclast impact velocity that is partly compensated by downward movement of the roof by ductile ice flow. (4) This ice ablation mechanism is likely common during subglacial eruptions on the relatively steep slopes of ice-covered stratovolcanoes, where steepness of slope and ice thickness are favourable for rapid drainage of meltwater by gravity and consequent depressurisation of the cavity.

Model-data comparison of sound propagation in a glacierized fjord with a simulated brash ice surface.

Glacier ice loss impacts sound propagation within Arctic fjords. Regular calving events contribute to a collection of floating ice fragments, known as brash ice, at the ocean surface that obstruct the natural and anthropogenic acoustic signals, yet are difficult to characterize. Transmission loss measurements using a maximum length sequence (m-sequence) signal were conducted in September 2017 near Hansbreen glacier in Hornsund Fjord, Svalbard with dense brash ice present at the water surface. An acoustic model of the brash ice surface was inferred through consideration of the experimental geometry, arrival amplitude, and travel time difference between the direct and surface reflected arrivals from the source to two receivers. The inferred surface was then incorporated into a forward simulation of the environment using sound speed profiles measured during the experiment. BELLHOP ([Porter and Bucker (1987). J. Acoust. Soc. Am. 82(4), 1349-1359],), a ray tracing code available in the Acoustics Toolbox (HLS Inc., San Diego, CA), was used to track the time difference of arrivals and amplitudes of the modeled direct and surface reflected rays. Comparisons between the measured and simulated results provide insight into the geometric shape and reflection characteristics of the brash ice surface within this and similar environments.