Extreme Ice Conditions Research Articles

A Study on the Ice Resistance Characteristics of Ships in Rafted Ice Based on the Circumferential Crack Method

In previous studies of ship–ice interactions, most studies focused on ship–level ice interactions, overlooking potential rafted ice conditions in extreme ice conditions. The purpose of this study is to develop a numerical model for predicting ship resistance in rafted ice regions. Numerical modeling of rafted ice was carried out using preset grid cells. By comparing the model test results, the accuracy and reliability of the numerical model are verified. On this basis, we undertook the analysis of the impacts of different ice thicknesses, ship speeds, bending strengths, and crushing strengths on the ice resistance of ships under level and rafted ice conditions. The results show that the ice resistance of ships is significantly higher than that of rafted ice under the condition of level ice; however, level ice and rafted ice have different effects on ship ice resistance. Compared with level ice, the ice resistance of ships navigating in rafted ice is more concentrated. The findings of the present research can serve as a technical reference for studies focused on predicting ship resistance in rafted ice regions.

Study of Ice Accretion on Horizontal Axis Wind Turbine Blade Using 2D and 3D Numerical Approach

In order to optimize the wind turbine operation in ice prone cold regions, it is important to better understand the ice accretion process and how it affects the wind turbine performance. In this paper, Computational Fluid Dynamics (CFD) based 2D and 3D numerical techniques are used to simulate the airflow/droplet behaviour and resultant ice accretion on a 300 kW wind turbine blade. The aim is to better understand the differences in the flow behaviour and resultant ice accretion between both approaches, as typically the study of ice accretion on the wind turbine blade is performed using simple 2D simulations, where the 3D effects of flow (air & droplet) are ignored, which may lead to errors in simulated ice accretion. For 2D simulations, nine sections along a 300 kW wind turbine blade are selected, whereas for 3D study, a full-scale blade is used. The obtained results show a significant difference in the ice accretion for both approaches. Higher ice growth is observed in 2D approach when compared with the full-scale 3D simulations. CFD simulations are carried out for three different icing conditions (typical, moderate and extreme), in order to estimate the extent of differences the different operating conditions can introduce on the ice accretion process in the 2D and the 3D simulations. Complex ice shapes are observed in case of extreme ice conditions, which affect the aerodynamic performance of the blade differently from typical and moderate ice conditions.

Инновационные разработки Крыловского государственного научного центра для повышения безопасности и надежности судов с винто-рулевыми колонками в экстремальных ледовых условиях

Инновационные разработки Крыловского государственного научного центра для повышения безопасности и надежности судов с винто-рулевыми колонками в экстремальных ледовых условиях

Movement and habitat use of juvenile Lake Sturgeon (Acipenser fulvescens, Rafinesque, 1817) in a large hydroelectric reservoir (Nelson River, Canada)

Summary Movement and habitat utilization of juvenile Lake Sturgeon (Acipenser fulvescens) were examined in Stephens Lake, a large hydroelectric reservoir on the Nelson River, Manitoba, Canada, between 21 June 2011, and 15 October 2012. Stephens Lake is defined by a sharp hydraulic gradient at the upstream end (Gull Rapids) and a pronounced reservoir transition zone (RTZ), characterized by a change in substrate composition from coarse to fine. Twenty juvenile Lake Sturgeon <600 mm fork length were captured in the RTZ, implanted with acoustic transmitters, and tracked using stationary receivers. Our primary hypothesis considered that, if foraging behaviour was contingent on sand substrate, these fish would spend the majority of the open-water season foraging in the relatively small area where hydraulic gradients dictate sand deposition. Data indicated that tracked individuals were highly bottom oriented, and utilized deeper thalweg habitats exclusively during the first open-water season. On average, juveniles spent only 22% of their open-water time in the RTZ (river kilometer [rkm] 4.5–7.0). Most fish spent more time upstream as opposed to downstream, but a few individuals did utilize backwatered thalweg areas, suggesting that silt-overlay habitats may be suitable for foraging. A seasonal spatial shift in distribution was also observed. Juveniles vacated the RTZ as winter progressed, moving further downstream and occasionally laterally into backwatered shallows, potentially avoiding extreme ice conditions and a large hanging ice dam that develops downstream of Gull Rapids. After ice break-up, most individuals with active tags returned to the upstream end of Stephens Lake. The results add to the growing body of evidence that suggests factors other than habitat suitability influence Lake Sturgeon movement and utilization patterns, raising questions about the mechanisms for core-area affinity in this species.

Atmospheric teleconnection patterns associated with severe and mild ice cover on the Great Lakes, 1963–2011

Atmospheric teleconnection circulation patterns associated with severe and mild ice cover over the Great Lakes are investigated using the composite analysis of lake ice data and National Center of Environmental Prediction (NCEP) reanalysis data for the period 1963–2011. The teleconnection pattern associated with the severe ice cover is the combination of a negative North Atlantic Oscillation (NAO) or Arctic Oscillation (AO) and negative phase of Pacific/North America (PNA) pattern, while the pattern associated with the mild ice cover is the combination of a positive PNA (or an El Niño) and a positive phase of the NAO/AO. These two extreme ice conditions are associated with the North American ridge–trough variations. The intensified ridge–trough system produces a strong northwest-to-southeast tilted ridge and trough and increases the anomalous northwesterly wind, advecting cold, dry Arctic air to the Great Lakes. The weakened ridge–trough system produces a flattened ridge and trough, and promotes a climatological westerly wind, advecting warm, dry air from western North America to the Great Lakes. Although ice cover for all the individual lakes responds roughly linearly and symmetrically to both phases of the NAO/AO, and roughly nonlinearly and asymmetrically to El Niño and La Niña events, the overall ice cover response to individual NAO/AO or Niño3.4 index is not statistically significant. The combined NAO/AO and Niño3.4 indices can be used to reliably project severe ice cover during the simultaneous –NAO/AO and La Niña events, and mild ice cover during the simultaneous +NAO/AO and El Niño events.

Lake Ladoga ice phenology: Mean condition and extremes during the last 65 years

AbstractWinter conditions play an important role for the largest lake in Europe—Lake Ladoga. The ice cover lasts for 171 ± 3 days on average from the early November until the mid‐May. We investigated the ice regime of Lake Ladoga using a constructed ice database of aircraft surveys and satellite images. More than 1250 surveys of the lake's ice cover from 1943 to 2010 were collected and analysed to determine mean and extreme ice conditions for winters of different types of severity. The time series of ice cover percentage over the lake was plotted. On average, 18 observational ice charts were made every winter. Individual ice phenology records show considerable year‐to‐year variation. For this reason, records typically have been combined and analysed as groups (categories). Extremely cold winters were determined as winters with complete ice cover that lasts more than three months which is approximately 90% quartiles from all winters with complete ice cover. The lake surface was completely covered with ice for more than three months during 5 seasons. Extremely warm winters when the maximum ice cover was less than 70% of the lake area occurred during 5 seasons as well. A basic relationship between the winter severity as winter maximum of accumulated freezing degree‐days (AFDD) and the earlier derived Relative Ice Cover Index (RICI) was established. We have used teleconnection indices such as North Atlantic Oscillations (NAO) and Arctic Oscillation (AO) for the period from October to May for estimation of different types of Lake Ladoga's ice conditions. The AO index in winter months and local winter maximum of AFDD explained much of the interannual variation in ice cover. Copyright © 2011 John Wiley &amp; Sons, Ltd.

Segmentation of the eastern North Greenland oblique-shear margin — Regional plate tectonic implications

Late Cenozoic opening of the Fram Strait led to formation of the NW–SE striking, eastern North Greenland oblique-shear margin at transition from the Norwegian–Greenland Sea to the SW Eurasia Basin. Onshore geology exposed on large peninsulas in front of the major Greenland Inland Ice reveals a highly complex, Paleozoic–early Cenozoic pre-opening setting. However, due to extreme ice conditions, very little is known about the offshore areas seawards of – and between – the peninsulas. Consequently, prevailing structural-tectonic models of the margin tend to be significantly oversimplified and inadequate. We present the first, combined onshore–offshore, model of the margin integrating onshore outcrops with potential field data, new offshore seismic reflection data and receiver-function analysis of seismic broad band data. The results reveal a margin which is far more complex than previously anticipated. In particular, we interpret strong margin segmentation along N/NE-striking fault structures. The structures are likely to have formed by Late Mesozoic–early Cenozoic strike-slip tectonics and have continued to be active during the late Cenozoic. A more than 8 km deep sedimentary basin is interpreted to underlie the central Wandel Sea, confined by these N/NE-striking structures. We suggest that similar margin segmentation affected the conjugate Yermak Plateau–North Svalbard margin as well as parts of the NE Greenland margin to the SE. Hence, the results have important implications for the general understanding of the Mesozoic–early Cenozoic development of the intra-continental De Geer Mega-shear Region between North Greenland and Eurasia.

The Relationships Between the North Atlantic Oscillation and Southern Baltic Coast Ice Conditions

This paper focuses on relationships between the North Atlantic Oscillation (NAO) Index in selected months and periods and the ice conditions along the southern coast of the Baltic Sea. The data on ice conditions, including the number of days with ice (L) and the length of ice season (counted in days; S), cover 25 observation regions located between Arkona in the West and Kaliningrad in the East for winters of the 1950/51–1989/90 period. The NAO Index, understood to be the difference between normalized values of atmospheric pressure in Gibraltar and Reykjavik, was applied.Correlation and regression analysis methods were applied to determine and study the relationships between NAO (independent variable) and the parameters of ice conditions L and S (dependent variables). The linear relationships recorded for sheltered basins (Szczecin Lagoon, Puck Bay Small, Vistula Lagoon) were stronger than those calculated for unsheltered ones (e.g., open Baltic Sea coast). The majority of relationships of ice conditions (L and S) to winter monthly NAO values, particularly for January (NAOII) and February (NAOII) in sheltered basins, are statistically significant, some of them even at the level of α = 0.01. The linear correlation coefficients, in most cases, were included within the range from −0.3 to −0.7. The strongest of them were calculated for January and February and encompassed the range from −0.5 to −0.7. The strength of these relationships tended to increase when particular months were connected into several-month periods of NAO Index, especially during the January–March and December–March periods. During these periods the correlation coefficients were usually in the −0.7 to −0.8 interval. In addition, the relationships of the NAO index with L were distinctly stronger than those with S. The strongest relationships, with linear correlation coefficients exceeding −0.80, were obtained for the number of days with ice (L) in protected areas, e.g., in Vistula Lagoon for a period of December–March (NAOXII–III) and in Puck Bay for January–March period (NAOI–III). These relationships are weaker in unsheltered areas, where the correlation coefficient does not exceed the value of −0.75. The strongest of them concern the estuarine regions of large rivers (Dziwnów, Świbno) and bays (Mie dzyzdroje), whereas the relationships between the NAO Index and L and S did not differ significantly from each other in unsheltered basins. However, for the NAO periods of December–March and January–March, they were stronger with S than with L.The correlation coefficients show a decreasing tendency eastward along the southern Baltic Sea coast from Pomeranian Bay to Gdańsk Bay (northward of the Hel Peninsula). They become stronger in the western part of the Gulf of Gdańsk and in the mouth of the Vistula and again decrease eastward.During some extremely severe or very mild winters, the extreme ice conditions do not always match the extreme NAO index values. During extremely severe winters, the ice cover could exist for a relatively long period, which is a result not only of the high inertia of thick ice covers but also of high cloudiness restricting the impact of insolation. However, during extremely mild winters, ice can disappear relatively quickly (thin covers, low cloudiness), comparable to the NAO index values.

The Design, Installation, and Performance of a Berm-Supported Exploration Structure in the Beaufort Sea

The design, installation, and performance of a berm-supported exploration structure in a dynamic ice environment is presented. Details are provided on design considerations which include horizontal ice loads, wave loads, seismic considerations, foundation characteristics and extreme temperatures. The development of specifications and installation techniques to account for these design concerns is presented. A case history is presented which includes a discussion of on-site modifications to the idealized placement technique, which were necessitated by extreme ice conditions. The success of this modified placement technique is confirmed through a review of the units performance during the drilling season, and the response of the structure to dynamic ice and drilling-related activity is examined.

THE METEOROLOGICAL ASPECTS OF ICE COVER ON THE GREAT LAKES*

Abstract The formation and break-up of ice on the Great Lakes as observed by regular ice reconnaissance flights conducted by the Meteorological Service of Canada is discussed in terms of the meteorological parameters involved. Ice cover on the individual lakes over the past four years is correlated with the winter temperature regime and an index of the heat stored in each lake using the concept of cumulative degree-days of freezing and thawing. Subjective consideration is also given to the effect of other meteorological factors. As a result of the study, graphs and regression equations have been developed as aids in the prediction of ice cover for the individual lakes. In addition, a comparison of the four years of observations with the 14-yr. period from 1949 to 1963 provides an indication of the average and extreme ice conditions that may be expected for each lake.