First-year Ice Ridges Research Articles

A Framework for Structural Analysis of Icebreakers during Ramming of First-Year Ice Ridges

This paper presents a framework for structural analysis of icebreakers during ramming of first-year ice ridges. The framework links the ice-ridge load and the structural analysis based on the physical characteristics of ship–ice-ridge interactions. A ship–ice-ridge interaction study was conducted to demonstrate the feasibility of the proposed framework. A PC-2 icebreaker was chosen for the ship–ice interaction study, and the geometrical and physical properties of the ice ridge were determined based on empirical data. The ice ridge was modeled by solid elements equipped with the continuous surface cap model (CSCM). To validate the approach, the simulated ice resistance was computed using the Lindqvist solution and in situ tests of R/V Xuelong 2. First, the local ice-induced pressure on the hull shell was determined based on numerical simulations. Subsequently, the local ice pressure was applied to local deformable sub-structural models of the PC-2 icebreaker hull by means of triangular impulse loads. Finally, the structural response of sub-structural models with refined meshes was computed. This case study demonstrates that the proposed framework is suitable for structural analysis of ice-induced stresses in local hull components. The results show that the ice load and the structural response obtained based on the four first-year ice-ridge models show obvious differences. Furthermore, the ice load and corresponding structural response increases with the width of the ridge and with increasing ship speed.

Observations of preferential summer melt of Arctic sea-ice ridge keels from repeated multibeam sonar surveys

Abstract. Sea-ice ridges constitute a large fraction of the total Arctic sea-ice area (up to 40 %–50 %); nevertheless, they are the least studied part of the ice pack. Here we investigate sea-ice melt rates using rare, repeated underwater multibeam sonar surveys that cover a period of 1 month during the advanced stage of sea-ice melt. Bottom melt increases with ice draft for first- and second-year level ice and a first-year ice ridge, with an average of 0.46, 0.55, and 0.95 m of total snow and ice melt in the observation period, respectively. On average, the studied ridge had a 4.6 m keel bottom draft, was 42 m wide, and had 4 % macroporosity. While bottom melt rates of ridge keel were 3.8 times higher than first-year level ice, surface melt rates were almost identical but responsible for 40 % of ridge draft decrease. Average cross-sectional keel melt ranged from 0.2 to 2.6 m, with a maximum point ice loss of 6 m, showcasing its large spatial variability. We attribute 57 % of the ridge total (surface and bottom) melt variability to keel draft (36 %), slope (32 %), and width (27 %), with higher melt for ridges with a larger draft, a steeper slope, and a smaller width. The melt rate of the ridge keel flanks was proportional to the draft, with increased keel melt within 10 m of its bottom corners and the melt rates between these corners comparable to the melt rates of level ice.

Consolidated layer thickness in probabilistic simulation of first-year ice ridges

This research study focuses on resolving the issue of sparse data and information required for the probabilistic assessment of ice ridge loads in offshore structures in Arctic regions. The study introduces the consolidated layer thickness into the simulation of ice ridge loads. Through the analysis of seasonal development of level ice draft, ridge keel draft, and ridge frequency, conclusions were drawn on the timing of ridge creation. The data used for this analysis was obtained from ice profiling sonars located in the Beaufort Sea. An analytical approach was established to estimate the probability density function of ridge formation timing, which was then used to simulate ridge age, determine an analytical formulation for consolidated layer growth, and investigate its thickness properties. The study found a negative correlation between consolidated layer thickness and ridge keel draft, which contradicts the previously held assumption in the literature that these variables are not related. This research establishes a framework for probabilistic simulation of ice ridge systems characterized by certain parameters, such as ridge keel draft, level ice draft, ridge frequency, and consolidated layer thickness, which facilitates maintaining the correlations between the parameters in the simulation.

Snowmelt contribution to Arctic first-year ice ridge mass balance and rapid consolidation during summer melt

Sea ice ridges are one of the most under-sampled and poorly understood components of the Arctic sea ice system. Yet, ridges play a crucial role in the sea ice mass balance and have been identified as ecological hotspots for ice-associated flora and fauna in the Arctic. To better understand the mass balance of sea ice ridges, we drilled and sampled two different first-year ice (FYI) ridges in June–July 2020 during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). Ice cores were cut into 5 cm sections, melted, then analyzed for salinity and oxygen (δ18O) isotope composition. Combined with isotope data of snow samples, we used a mixing model to quantify the contribution of snow to the consolidated sea ice ridge mass. Our results demonstrate that snow meltwater is important for summer consolidation and overall ice mass balance of FYI ridges during the melt season, representing 6%–11% of total ridged ice mass or an ice thickness equivalent of 0.37–0.53 m. These findings demonstrate that snowmelt contributes to consolidation of FYI ridges and is a mechanism resulting in a relative increase of sea ice volume in summer. This mechanism can also affect the mechanical strength and survivability of ridges, but also contribute to reduction of the habitable space and light levels within FYI ridges. We proposed a combination of two pathways for the transport of snow meltwater and incorporation into ridge keels: percolation downward through the ridge and/or lateral transport from the under-ice meltwater layer. Whether only one pathway or a combination of both pathways is most likely remains unclear based on our observations, warranting further research on ridge morphology.

Morphometry of First-Year Ice Ridges with Greatest Thickness of the Consolidated Layer and Other Statistical Patterns

Morphometry of First-Year Ice Ridges with Greatest Thickness of the Consolidated Layer and Other Statistical Patterns

ТОРОСЫ ПРОЛИВА ШОКАЛЬСКОГО (АРХИПЕЛАГ СЕВЕРНАЯ ЗЕМЛЯ): ИССЛЕДОВАНИЯ 2019 Г

Morphological characteristics of three first-year ice ridges were investigated in the Shokalsky Strait in April and May 2019 by hot-water thermal drilling with the recording of penetration rate. Boreholes were drilled along the ice ridge cross-section with an interval of 0.25 m. The ice ridge cross-sectional profiles are presented. The sail height for the investigated ridges varied within 1.8-2.7 m, and the keel draft varied from 7.0 to 9.1 m. The ratio of the keel draft to the sail height was equal to 2.7-5.2, the thickness of the consolidated layer was 2.4-2.7 m. The mean porosity of the unconsolidated part of the keel in the ice ridges made up 28-36%. The porosity distributions for the unconsolidated part of the keel along the drilling profile are given for the analyzed ice ridges. The main feature of one of the ridges was an almost rectilinear slope of the keel, which laterally extended for 16 m.

Morphometry and unusual internal structure of ice ridge investigated at Barneo ice camp in April 2013

First-year ice ridge has been examined with respect to geometry and morphology at the Barneo ice camp in April 2013. Its characteristics are discussed in the paper. The sail height was 4.7 m, the keel depth was 8.6 m. The keel depth to sail height ratio was equal to 1.8. Structure of the keel of the examined ice ridge was too heterogeneous in its composition. Significant fragment in the keel of ice ridge is fully consolidated, its draft reaches to 5.8 m but the fragment's upper boundary is located at the sea level. This indicates the presence of hydrostatic unbalance. Away from the point of maximum keel draft on the cross-section, the average porosity of the unconsolidated part of the keel tends to increase, but again decreases at the periphery of the keel. The distribution of ice fraction in sea ice versus depth for the ice ridge is presented. Increased ice fraction corresponds to the consolidated layer. The depth of the lower boundary of consolidated layer is confirmed by distributions of ice temperature versus depth.

Trends in porosity сhanges of the unconsolidated part of ice ridge keel

An ice ridge is a special case of granular medium with a wide range of fractions. It represents a chaotic piling-up of blocks occurring under the action of gravity in the sail and due to the Archimedes force in the keel. An important characteristic of the internal structure of ice ridges is their porosity. Scientists from different countries have been dealing with this problem. First-year ice ridges are taken into consideration in Arctic and subarctic marine structural design, and the calculation of ice loads includes ridge porosity and strength, as well as other parameters. The aim of the present work is to discern the regularities of porosity distribution in the unconsolidated part of the keel with depth. Ice ridge porosity is identified by means of processing thermodrilling records. In this paper, porosity is interpreted as a step function equal to zero if there is ice at the point (x, y, z), and to one if there is no ice at the point (x, y, z). The author applies the model of compaction of the bulk medium under the influence of gravity, and, particularly for the keel, due to the Archimedes force. A zero depth corresponds to the lower surface of the keel, so each individual porosity distribution of the unconsolidated part of the keel at the drilling point must be shifted down until the maximum keel draft depth is reached in the region under consideration. After alignment, the step curves are averaged. The distance is measured up, starting from the depth of the maximum keel draft. The curve of the averaged porosity can be divided into segments reflecting the characteristic features of the distribution. According to the graphs, average porosity decreases exponentially. Ice ridges of several geographical regions are considered, and in each region is divided into groups by years of research. On the whole, 17 depth-wise distributions of the average porosity are obtained for seven regions. Each distribution was approximated according to the model, taking into account the average density of water and ice in the region. For each distribution, the values of compactibility and porosity at the zero depth, i. e. at the lower edge of the keel, were obtained; the second value only has mathematical sense. It is more convenient to consider the maximum value of the average porosity, which is taken as the initial porosity. With a probability of 90 %, the initial porosity is within the range of 0.450 ± 0.125. As the distance from the keel edge increases, the porosity curves converge to a fairly narrow range of values. At a distance of 12–14 m, this range is 0.07…0.12. The second parameter characterizing the porosity distribution in the unconsolidated part of the keel is compactibility. The steepness of the exponent approximating the average porosity curve depends on it, too. Compactibility is most affected by the strength of the ridged ice as well as the ice thickness. From the literature on the physical properties of ice it is known that as the temperature of ice increases, its strength decreases, and its plasticity increases. Thus, it can be concluded that compactibility is determined by the ice crystal structure as well the ice average temperature at the time of ridging — the warmer the ice, the higher the compactibility of the ice blocks in the keel.

О ПОРИСТОСТИ НЕКОНСОЛИДИРОВАННОЙ ЧАСТИ КИЛЯ ТОРОСОВ

The paper discusses the distribution of porosity of the unconsolidated part of the keel of ten first-year ice ridges investigated in the central Arctic basin and the Shokalsky Strait (Severnaya Zemlya) in 2012–2019. These studies were performed using thermal drilling with the computer (logger) recording of penetration rate. Boreholes were drilled along the cross-section of the ridge crest, mainly at 0.25-m intervals. The porosity values for the unconsolidated part of the keel are presented on the diagram as a point cloud. The horizontal position of the points is determined by the relative distance between the borehole and the point where the keel has the maximum draft. As moving away from this point, the average porosity of the unconsolidated part of the keel tends to increase. This feature is a consequence of the Archimedes force effect and agrees with the model of porosity changes from the theory of granular media.

On the results of studying ice ridges in the Shokal'skogo Strait, part III: New data

The paper presents information on the studies of the first-year ice ridges conducted by the AARI experts in April–May 2018 in the fast ice of the Shokal'skogo Strait (Severnaya Zemlya Archipelago) using hot water drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals mainly. One of the ice ridges had an unusual configuration: the sail crest was on the edge of the perpendicular extended keel crest. Cross-sectional profiles of ice ridges are illustrated. The records of thermodrilling rate revealed the presence of residual ice fragments in the keel of the ice ridges. The sail height varied from 2.9 up to 3.2 m, the keel depth varied from 8.5 up to 9.6 m. The average keel depth to sail height ratio varied from 2.8 to 3.3, and the thickness of the consolidated layer was 2.5–3.5 m. The porosity of the unconsolidated part of the keel was about 23–27%. The distributions of porosity versus depth for all ice ridges are presented and discussed.

Development of environmental contours for first-year ice ridge statistics

Ice ridges represent a major threat to ships and offshore structures in areas with sea ice but no icebergs, since they frequently determine and govern the structural design loads. This work focuses on the development of environmental contours for first-year sea ice ridge statistics, which are able to represent the key parameters that will influence the extreme loads that would be acting on ice-capable vessels sailing in Arctic regions. Based on the inverse first order reliability method (IFORM), the development of environmental contours to be applied for the reliability-based design of ice-capable vessels in Arctic regions is elaborated. The number of relevant parameters and hence the dimension of the space containing the environmental contour will depend on the particular ice-vessel interaction model that is to be applied. Furthermore, the influence from the degree of correlation between the environmental parameters as well as from the number of ship-ice ridge interaction during the voyage on the environmental contour shapes are studied.

On the results of studying ice ridges in the Shokal'skogo Strait, part I: Morphology and physical parameters in-situ

The paper presents information on the studies of the first-year ice ridges conducted by the AARI experts in April–May 2016 in the Shokal'skogo Strait (Severnaya Zemlya Archipelago) using hot water drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals mainly. The results of a detailed study of one of the ice ridges are presented. The sail height varied from 2.5 up to 3.4 m, the keel depth varied from 8.3 up to 10.3 m. The average thickness of the consolidated layer was 2.2–2.4 m. Cross-sectional profiles of the ice ridge are illustrated. Ratio of the mean CL thickness of ice ridge to the mean thickness of level ice was equal 1.7. The distribution of salinity in the upper part of the CL is Z-shaped, and on the scale of the entire ice column, C-shaped. The CL growth rate is approximately twice as high as the growth rate of level ice. It was detected that the ridged ice was slightly stronger than the level ice. The porosity of the ice ridges is investigated in Part II.

Ice ridges in landfast ice of Shokal'skogo Strait

Three first-year ice ridges have been examined with respect to geometry and morphology in landfast ice of Shokal'skogo Strait (Severnaya Zemlya Archipelago) in May 2018. Two of the studied ice ridges were located on the edge of the ridged field and were part of it, because their keels extended for a long distance deep into this field. Ice ridges characteristics are discussed in the paper. These studies were conducted using hot water thermal drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest at 0.25 m intervals. Cross-sectional profiles of ice ridges are illustrated. The maximal sail height varied from 2.9 up to 3.2 m, the maximal keel depth varied from 8.5 up to 9.6 m. The average keel depth to sail height ratio varied from 2.8 to 3.3, and the thickness of the consolidated layer was 2.5-3.5 m. The porosity of the non-consolidated part of the keel was about 23-27%. The distributions of porosity versus depth for all ice ridges are presented.

Properties of ice from first-year ridges in the Barents Sea and Fram Strait

First-year ice ridges are one of the main load scenarios that off-shore structures and vessels operating in ice-covered waters have to be designed for. For simulating such load scenarios, the knowledge gap on ice mechanical properties from the consolidated part of first-year ridges has to be filled. In total 410 small-scale uniaxial compression tests were conducted at different strain rates and ice temperatures on ice from the consolidated layer of 6 different first-year ridges in the sea around Svalbard. For the first time uniaxial tensile tests were performed on ice from first-year ridges using a new testing method. Ice strength was evaluated for different ice type, which are determined for each specimen based on a proposed ice classification system for ice from first-year ridges. 78% of all samples contained mixed ice with various compounds of brecciated columnar and granular ice. Ice strength of mixed ice showed isotropy, except for the samples containing mainly columnar ice crystals. For horizontal loading, mixed ice was stronger than columnar and granular ice. The residual strength of ductile ice depended on the strain rate. At 1.5% strain remained 70% of peak strength at 10−4 s−1 and 50% at 10−3 s−1. Ductile failure dominated for 75% of all mixed ice tests at 10−3 s−1 and − 10 °C. Ductile compressive strength was generally higher than brittle compressive strength for mixed ice. Brine volume was the main parameter influencing the tensile strength of the mixed ice which was between 0.14 MPa and 0.78 MPa measured at constant ice temperature of −10 °C.

On the results of studying ice ridges in the Shokal'skogo Strait, part II: Porosity

The paper describes the morphometric characteristics of three first-year ice ridges investigated in April and May 2016 in the Shokal'skogo Strait (Severnaya Zemlya Archipelago). These studies were conducted using hot water thermal drilling with computer recording of the penetration rate. Boreholes were drilled along the cross-section of the ridge crest mainly at 0.25 m intervals. The main results of the ice ridges studies are given in Part I. Cross-sectional profiles of ice ridges are illustrated. In each borehole, porosity of an ice ridge was calculated as the ratio of the length of all voids to total length of the borehole. Processing of the results showed that when studying ice ridges for obtaining the porosity values close to the true ones, the boreholes should be drilled with a spacing not exceeding two meters. Away from the point where the keel has the maximum draft, the average porosity of the unconsolidated part of the keel tends to increase. This feature is a consequence of the effect of the Archimedes force and agrees with the model of porosity changes from the theory of granular media.

Dem Simulation of First-Year Ice Ridge Interactions With Moored Structures

First-year ice ridges determine the design load of moored structures in many Arctic and sub-Arctic regions. Their interactions with moored structures were simulated with discrete element method (DEM), considering the complex ... | Find, read and cite all the research you need on Tech Science Press

An engineering method for simulating dynamic interaction of moored ship with first-year ice ridge

This paper aims to present a new tool to simulate dynamic ice ridge-structure interaction in 6 Dofs in time domain. The global forces caused by ice ridge as well as responses of the structure are simulated. The ice ridge loads are composed of loads due to sail, consolidated layer and unconsolidated keel. The sail load is neglected since it is small compared to the other two components. The consolidated layer could be taken as level ice. The related level ice force is simulated by integrating ice breaking force and ice accumulation force. Two ice failure modes, namely bending and crushing, are used when calculating the breaking force. A numerical model is used to calculating the ice accumulation force underwater by determining the relative horizontal positions and motions of ice rubble to the strip of the structure. The ice load due to the unconsolidated keel is calculated based on a modified theoretical model in probabilistic design. The motions of the moored ship are also applied to update the waterline of the hull at each time step to estimate precisely local contact areas between ice and hull. The simulation results are compared with model test data.

Morphology, internal structure and formation of ice ridges in the sea around Svalbard

The results from 3 years of comprehensive field investigations on first-year ice ridges in the Arctic are presented in this paper. The scopes of these investigations were to fill existing knowledge gaps on ice ridges, gain understanding on ridge characteristics and study internal properties of ice. The ability of developing reliable simulations and load predictions for ridge-structure interactions is the final principal purpose, but beyond the scope of this paper. The presented data comprise ridge geometry, ice block dimensions from ridge sails, ice structure in the ridge and values on the ridge porosity and the degree of consolidation. The total ridge thickness conformed to other ridges studied in the same regions. The consolidated layer thickness was on average 2–3 times the level ice thickness. Minimum 33% and in average 90% of the ridge keel area was consolidated. The distribution of ice block sizes and block shapes within a ridge appears to be predictable. A new approach for deriving a possible ridging scenario and ridge age is presented. Different steps of the ridge building process were identified, which are in good agreement with earlier simulated ridging events. After formation of very thin lead ice between two floes deformation occurs through rafting and ridging until closure of the lead. Subsequently the adjacent level ice floe fractures proceeding ridge formation until ridging forces exceed driving forces. A time span of 10 days could be assessed for a possible ridge formation date, estimating the ridge age of the studied ridge located east of Edgeøya at 78° N to be 7 to 8 weeks.

On the decay of first-year ice ridges: Measurements and evolution of rubble macroporosity, ridge drilling resistance and consolidated layer strength

In this study, four first-year ice ridges (R1, R2, R3 and R4) were measured during the transition from the “main” phase to the “decay” phase. The measurements were conducted on two ice floes in the Arctic Ocean northwest of Svalbard during May and June 2015. Ice ridge R1 was approximately 13 m thick and 200 m long, R2 was 5 m thick and 500 m long, R3 was 6 m thick and 75 m long, and R4 was 9 m thick and 150 m long. The objective of this study was to investigate the rubble macroporosity evolution, ridge drilling resistance and consolidated layer small-scale strength in the decaying ridges. The ice rubble macroporosity and ridge drilling resistance values were obtained through mechanical drilling. The drilling resistance was measured by the drill operator, which was defined as hard, medium or soft. The small-scale strength was measured in the field via uniaxial compression with a nominal strain rate of 10−3 s−1. The rubble macroporosities in R1, R2, R3 and R4 ranged from 10% to 27%, and the temporal macroporosity variation was the result of seasonal developments. The rubble macroporosity in R2 decreased from 25% (27 days old) to 16% (34 days old, 4 days before breakup). In R1, which was larger, colder and older than R2, the rubble macroporosity remained constant (11%–10%) over a ten-day period. Because ridges R3 (22% rubble macroporosity) and R4 (27% rubble macroporosity) were only mapped once, no temporal development was measured. We suggest that the ice rubble macroporosity in saline, first-year ridges continuously decreases over time and that this decrease accelerates during the decay phase. Furthermore, both the consolidated layer uniaxial compressive strength (measured in R1, R2 and R3) and the ridge drilling resistance (measured in R1, R2, R3 and R4) decreased during the transition from the main phase to the decay phase, due to an increase in ice temperatures. After the ridges reached an isothermal state, the drilling resistance and strength remained constant, and the brine volume (microporosity) increased. The ice cores collected from the decaying ice exhibited ductile failure modes when subjected to uniaxial compression.

Environmental contours based on inverse SORM

It is well known that the full long-term response analysis is recognized as the most accurate and reliable method for evaluation of the extreme response in the design of ships and marine structures. However, such a method is time consuming for large and complex systems. To improve efficiency, the environmental contour method (ECM) is frequently used to approximate the long-term extreme response. The ECM is based on an environmental contour, which is traditionally obtained by the inverse first order reliability method (IFORM) with the assumption that the failure surface in the U space is approximated as a tangent plane at the design point. However, such an approximation underestimates the true failure probability if the failure surface in the U space is a concave set, and then the corresponding environmental contour would not be conservative for possible designs. In this work, a more conservative ISORM (inverse second order reliability method) contour is proposed. In this method, a specific second-order surface is applied to approximate the failure surface at the design point, and then the failure domain in the U space would always be overestimated since the corresponding safe domain is approximated and underestimated as a sphere, regardless of the shapes of the failure surfaces. Therefore, the generated environmental contour can be always conservative for design purposes. The differences of the environmental contours generated by different methods, i.e., the traditional IFORM and the proposed ISORM, are illustrated by relevant examples, such as the wave statistics, wind wave statistics, and first-year ice ridge statistics.