빙해선박의 선수 선형에 관한 연구

Numerical simulation on an icebreaking vessel with fixed drift angles in level ice

With the rapid decline of Arctic sea ice, the freshwater produced by melting of summer sea ice makes the depth of the halocline under ice become shallower. This has an impact on the drift of sea ice because internal waves may be generated at the interface of the halocline by disturbance from the draft of an ice floe or ridge keel. A laboratory experimental study was carried out to investigate the interactions between an ice ridge and stratifed fluid using the method of Particle Image Velocimetry (PIV). The drift velocity of an ice ridge ( U ) and the draft of the ridge keel ( D ) were altered in different experimental cases, and the velocity field in the stratifed fluid was then measured by PIV. The results reveal that an obvious vortex exists in the wake field of the ridge keel, and the center of the vortex moves away from the ice ridge with increasing D . Internal waves at the interface of the stratifed fluid were observed during the drift of the ice ridge, and the wave height shows a positive correlation with U and D . This study demonstrates that ice ridges could introduce internal waves at the interface of a stratifed fluid and thus affect the oceanic drag coeffcient and ice drift. It supports improved parameterization of the ice drag coeffcients. Citation: Tie W, Lu P, Li Z J, et al. PIV experimental study on the interactions between ice ridges and stratified fluids. Adv Polar Sci, 2016, 27: 107-116, doi:10.13679/j.advps.2016.2.00107

Wave interactions with circular ice ridge embedded in level ice

Numerous field studies show that mature first-year (FY) ridges consist of a solid ice consolidated layer (CL) below which is a keel of ice rubble. The CL is generally thicker than the ambient level ice. With the decrease in multi-year ice in the Arctic, FY ridges may become the controlling ice feature at many Arctic locations. In sub-Arctic regions ridges are smaller but they also usually control design ice loads. For vertical structures, ISO 19906 (Standard on Arctic Offshore Structures) suggests calculating the load due to crushing of the CL and adding this to the load to fail the keel. In ISO a formula is provided for the load to fail the keel on a vertical-face which assumes that the keel material has Mohr-Coulomb properties. No specific algorithms are given in ISO for FY ridge loads on sloping structures. The work described in this paper addresses this gap. The study investigated three bounding methods and compared them with the measured loads due to FY ridges on Confederation Bridge (which has piers with upward breaking cones). The three bounding methods are: Model A; which assumes the CL breaks in bending and rides up as level ice and the keel load is calculated assuming a "dead wedge" is created on the slope which converts the slope into a vertical face against which the keel fails. This model can make use of the methods in ISO 19906 for calculating these two components and can be considered to be the implied "current ISO approach". Model B assumes that the CL layer fails in bending as "level ice" on an elastic foundation and rides up the slope with the accompaniment of additional ice rubble scooped-up from the sail and keel of the ridge. Model C assumes that the FY ridge can be idealized into an equivalent "solid ice" beam using composite beam theory. Then the beam on elastic foundation method, as used for solid ridges, is used to estimate breaking and clearing loads. These various approaches are reviewed and the derived loads are compared to failure modes and measured loads from Confederation Bridge for selected events involving FY ridges. Based on these comparisons a hybrid of Models B and C is recommended and the paper gives the details of how to apply this method. When used for example structures, the new model gives loads which are 40 – 50% lower than the current approach implied in ISO 19906. The method can be adapted to downward sloping structures.

Propellers for ships can be distinguished into two main types: fixed pitch propeller and controllable pitch propeller (CPP). The CPP design is an alternative for improved efficiency, especially in the need of a wide range of thrust and load levels, while maintaining an optimum shaft speed, as in the case of diesel or gas turbines. A dynamic positioning ship presented a problem on its CPP system after 8 months of operation. By means of fractography, microstructural, microhardness, and chemical analyses, it was possible to determine that fatigue was the main responsible for the failure. Fatigue cracks were initiated at welded connections between the wire spacers and concentric pipes, positioned inside the hollow shaft of the propeller. The stress concentration caused by a sharp defects like lack of penetration and lack of fusion and the geometric restriction of this type of weld contributed to a shorter fatigue crack initiation phase and premature failure.

<p>During the melt season, sea ice melts from the surface and bottom. The melt rates substantially vary for sea ice ridges and undeformed first- and second-year ice. Ridges generally melt faster than undeformed ice, while the melt of ridge keels is often accompanied by further summer growth of their consolidated layer. This summer consolidation is related to refreezing of less saline meltwater, originating from snowmelt and ridge keel melt. We examine the spatial variability of ice melt for different types of ice from <em>in situ</em> drilling, coring, and from multibeam sonar scans of remotely operated underwater vehicle (ROV). Seven ROV scans, performed from 24 June 2020 to 28 July 2020 during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition were analyzed. The area investigated by the ROV (400 by 200 m) consisted of several ice ridges, surrounded by first- and second-year ice. Seven ice drilling transects were additionally performed to validate ROV measurements. The maximum keel depth of the ridge investigated by ice drilling was 6.5 m. We show a substantial difference in melt rates of first-year ice, second-year ice, and sea ice ridge keels. We also show how ridge keels decay depending on keel depth, width, steepness, and orientation relative to the ice drift direction. These results are important for quantifying ocean heat fluxes for different types of ice during advanced melt, and for estimation of the ridge contribution to the total ice mass and summer meltwater balances of the Arctic Ocean.</p>

This paper describes the development of three candidate hull forms for 190,000 DWT ore carrier for operation in ice covered water. It builds on Hyundai Heavy Industries expertise in ore carrier design, and discusses some of the changes required for operation in heavy ice conditions. The overall concept was to have a target speed of 6 knots in land fast ice 1.7m thick and 15 knots in open water. Three candidate bow shapes were designed and analyzed, based on a common stern arrangement. The development of the hull form included three methods of predicting the performance of the ships in ice. Empirical analysis was carried out for all three hulls, based on experience gained from model experiments on bulk carrier hull forms in ice. Numerical analysis was carried out on all three bow shapes using a computer program (based on the discrete element method) to simulate the interaction between the ship and the ice. Physical model experiments were carried out for resistance and propulsion in level ice, pack ice and ridges on the selected design. As a result of the model experiments, the selected bow shape was modified to reduce its resistance in ice. The improved performance of the modified hull was confirmed with additional numerical simulations.

Biogeochemical characteristics of brash sea ice and icebergs during summer and autumn in the Indian sector of the Southern Ocean

Polar sea ice is one of the Earth’s climate components that has been significantly affected by the recent trend of global warming. While the sea ice area in the Arctic has been decreasing at a rate of about 4 % per decade, the multi-year ice (MYI), also called perennial ice, is decreasing at a faster rate of 10 %–15 % per decade. On the other hand, the sea ice area in the Antarctic region was slowly increasing at a rate of about 1.5 % per decade until 2014 and since then it has fluctuated without a clear trend. However, no data about ice type areas are available from that region, particularly of MYI. Due to differences in physical and crystalline structural properties of sea ice and snow between the two polar regions, it has become difficult to identify ice types in the Antarctic. Until recently, no method has existed to monitor the distribution and temporal development of Antarctic ice types, particularly MYI throughout the freezing season and on decadal time scales. In this study, we have adapted a method for retrieving Arctic sea ice types and partial concentrations using microwave satellite observations to fit the Antarctic sea ice conditions. The first circumpolar, long-term time series of Antarctic sea ice types; MYI, first-year ice and young ice is being established, so far covering years 2013–2019. Qualitative comparison with synthetic aperture radar data, with charts of the development stage of the sea ice, and with Antarctic polynya distribution data show that the retrieved ice types, in particular the MYI, are reasonable. Although there are still some shortcomings, the new retrieval for the first time allows insight into the evolution and dynamics of Antarctic sea ice types. The current time series can in principle be extended backwards to start in the year 2002 and can be continued with current and future sensors.

PurposeThis paper aims to simulate a punch shear test of partly consolidated ice ridge keel by using a three-dimensional discrete element method. The authors model the contact forces between discrete ice blocks with Hertz–Mindlin contact model. For freeze bonds between the ice blocks, the authors apply classical linear cohesion model with few modifications. Based on punch shear test simulations, the authors are able to determine the main characteristics of an ice ridge from the material parameters of the ice and freeze bonds.Design/methodology/approachThe authors introduced a discrete model for ice that can be used for modelling of ice ridges. The authors started with short introduction to current status with ice ridge modelling. Then they introduced the model, which comprises Hertz–Mindlin contact model and freeze bond model with linear cohesion and softening. Finally, the authors presented the numerical results obtained using EDEM is commercial Discrete Element Modeling software (EDEM) and analysed the results.FindingsThe Hertz–Mindlin model with cohesive freeze bonds and linear softening is a reasonable model for ice rubble. It is trivial that the ice blocks within the ice ridge are not spherical particles, but according to results, the representation of ice blocks as spheres gave promising results. The simulation results provide information on how the properties of freeze bond affect the results of punch shear test. Thus, the simulation results can be used to approximate the freeze bonds properties within an ice ridge when experimental data are available.Research limitations/implicationsAs the exact properties of ice rubble are unknown, more research is required both in experimental and theoretical fields of ice rubble mechanics.Originality/valueBased on this numerical study, the authors are able to determine the main characteristics of an ice ridge from material parameters of ice and freeze bonds. Furthermore, the authors conclude that the model creates a promising basis for further development in other applications within ice mechanics.

Arctic sea ice type information is essential for various operational and scientific applications including the support of marine users and guiding ice thickness retrieval algorithms operating with SMOS and CryoSat-2 data for improved sea ice prediction. A sea ice type analysis system developed at Environment and Climate Change Canada’s (ECCC) generates pan-Arctic ice type analyses at 5 km resolution every 6 hours. The ice type analysis system assimilates ice type information provided by passive microwave (AMSR2, SSMIS) and scatterometer (ASCAT) data, but assimilation of these observations is not reliable in the areas near land and in the narrow channels of the Canadian Arctic Archipelago due to their low spatial resolution of ~20-50 km. Therefore, assimilation of high-resolution ice type observations from synthetic aperture radar (SAR) is highly desired.In this study, we extended our approach for automated detection of winter multi-year ice (MYI) and first-year ice (FYI) at 1.6 km scale from RADARSAT-2 to RCM data. To this end, we collected more than 2,000 RCM images and corresponding image analyses products that were manually generated by the Canadian Ice Service (CIS) ice experts for the period of time between July 1, 2020 and July 31, 2023. From these RCM images we extracted SAR information for more than 30,000 pure MYI and more than 619,000 pure FYI data samples under no melt conditions as identified by the CIS image analyses.We demonstrated that separability measures for MYI and FYI classes in the spaces of the two predictor parameters (HV/HH polarization ratio and standard deviation of HV signal) are consistent with those we previously observed for RADARSAT-2. Furthermore, we found that our RCM-based MYI/FYI detection approach allows us to classify 60% of the winter CIS ice data samples with the accuracy of 99.6%. Preliminary results of assimilating RCM-based MYI/FYI high-resolution retrievals in combination with passive microwave and scatterometer data in the ECCC ice type analysis system will be also presented.

Propellers is part movement propulsion system of the ships wich duty for pushing of the ship at forward movement and towing the body of ship at backward movement. As a part mechanical drive propeller consist of some blade attached to the boss and mounted on the propeller shaft of the axis relationships from the main engine of the ships. Propeller can drive of the ships both forward and backward with by rotating on its axis. To produce forward and backward movement of the ships can be done in two ways namely with use controllable pitch propellers and with use fixed pitch propellers.

Climate warming has enabled the Arctic region to achieve seasonal navigation, and sea ice concentration is an important factor affecting the navigation of the Arctic waterways. This article uses the Arctic sea ice concentration data of the three highest temperatures in 2016, 2019, and 2020, combined with the Arctic summer sea level pressure, wind field, temperature, temperature anomaly, ice age, and sea ice movement data to analyze the spatial and temporal variation of sea ice and connectivity in the Northeast Passage (NEP) of the Arctic in Summer in three hot years, and summarizes the causes of sea ice anomalies. The results show that: (1) the summer Arctic sea ice extent in 2016, 2019 and 2020 were all lower than the multi-year average sea ice extent, and the summer sea ice extent in 2020 had the largest change trend; (2) in October of these three years, the sea ice was all negative anomalies, extending the opening time of the NEP; (3) when the sea ice concentration was 30% as the threshold, the navigation period of the NEP in 2016 was from mid-August to late October, 2019 was from the beginning of August to mid-October, 2020 was from the end of July to the end of October, and 2020 was the longest year since the opening of the NEP; (4) when the sea ice concentration was 10% as the threshold, the navigation period of the NEP in 2016 was from the end of August to the end of October, 2019 was from early August to mid-October, and 2020 was from the beginning of August to the end of October; (5) the key navigable areas of the NEP in the past three years were the central waters of the East Siberian Sea, the New Siberian Islands and the Vilkitsky Strait; (6) the navigation period of the NEP in 2016, 2019 and 2020 was longer. The main reasons were that the temperature of the NEP in the past 3 years was relatively high, the wind was weak, the sea ice movement had little effect, and the sea ice age in the key navigable areas was first year ice, which was easy to melt, which greatly promoted the opening of the NEP.

Sea ice thickness and ice surface roughness profiles were collected over many tens of kilometers in the Gulf of St. Lawrence, Canada with a helicopter-borne electromagnetic (HEM) system containing a laser altimeter. The profiles are compared with RADARSAT ScanSAR Wide images, and digital video images captured in real-time using a downward-looking video camera mounted on the outside of the helicopter. A survey done in early March, 2001 sampled many different ice conditions, including heavily ridged coastal ice, large rough floes, rafted nilas, and brash ice near the ice edge. Near the north coast of PEI in 2001, there were large quantities of thick ice due to ridging of grey-white or thin first-year ice. However, high SAR backscatter was associated with floes that had a rough surface on scales of a few meters or less.

The polar bear (Ursus maritimus) is considered an indicator species of ecosystem health because of its longevity, life-history requirements, reliance on sea ice (i.e., sea ice obligate), and position in the Arctic food web. Polar bear distribution and habitat association should both be reliable signals for environmental perturbation, as the bears respond behaviorally to changes in sea ice extent, the timing and duration of ice formation, and ablation. Polar bears and sea ice conditions were monitored as part of the annual fall bowhead whale (Balaena mysticetus) aerial survey in the Alaskan Beaufort Sea between 1979 and 2005. Habitats associated with polar bear sightings changed during the study, with fewer bears associated with ice (irrespective of ice type and percent) and more bears associated with land and open water. Large-scale differences were documented for both ice type and percent ice cover, particularly in September. In general, the pattern in September (and to a lesser extent in October) included a reduction in old ice and a concomitant increase in open water. In addition, there was an eastward and landward shift in polar bear sightings. From 1979 to 1987, polar bears were observed primarily on ice along the shelf break near Barrow, whereas from 1997 to 2005, polar bears were observed on barrier islands or along the mainland coast near Kaktovik. The changes in polar bear distribution and habitat association appear to reflect a behavioral response by polar bears to changes in ice (type and percent cover) and in the timing of ice formation and ablation.