• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.385-392
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• 2018

This paper presents 2D numerical modeling to calculate ship-ice interactions that occur when an icebreaker advances into ice-covered water. The numerical model calculates repeated icebreaking of an ice plate and removal of small ice floes. The icebreaking of the ice plate is calculated using a ship-ice contact detection technique and fluid-structural interaction of ice plate bending behavior. The ship-ice interactions in small ice floes are calculated using a physically based modeling with 3DOF rigid body equations. The ice plate is broken in crushing, bending, and splitting mode. The ice floes drift by wind or current and by the force induced by the ship-ice interaction. The time history of ice force and ice floe distribution when an icebreaker advances into the ice-covered water are obtained numerically. Numerical results demonstrate that the time history of ice force and distribution of ice floes (ice channel width) depend on the ice floe size, ship motion and ice drifting by wind or current. It is shown that the numerical model of ship maneuvering in realistic ice conditions is necessary to obtain precise information about the ship in ice-covered water. The proposed numerical model can be useful to provide data of a ship operating in ice-covered water.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권4호
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• pp.491-498
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• 2018

The cost evaluation for voyage route planning in an ice-covered sea is one of the major topics among ship owners. Information of the ice properties, such as ice type, concentration of ice, ice thickness, strength of ice, and speed-power relation under ice conditions are important for determining the optimal route in ice and low operational cost perspective. To determine achievable speed at any designated pack ice condition, a model test of resistance, self-propulsion, and overload test in ice and ice-free water were carried out in a KRISO ice tank and towing tank. The available net thrust for ice and an estimation of the ice resistance under any pack ice condition were also performed by I-RES. The in-house code called 'I-RES', which is an ice resistance estimation tool that applies an empirical formula, was modified for the pack ice module in this study. Careful observations of underwater videos of the ice model test made it possible to understand the physical phenomena of underneath of the hull bottom surface and determine the coverage of buoyancy. The clearing resistance of ice can be calculated by subtracting the buoyance and open water resistance form the pre-sawn ice resistance. The model test results in pack ice were compared with the calculation results to obtain a correlation factor among the pack ice resistance, ice concentration, and ship speed. The resulting correlation factors were applied to the calculation results to determine the pack ice resistance under any pack ice condition. The pack ice resistance under the arbitrary pack ice condition could be estimated because software I-RES could control all the ice properties. The available net thrust in ice, which is the over thrust that overcomes the pack ice resistance, will change the speed of a ship according to the bollard pull test results and thruster characteristics (engine & propulsion combination). The attainable speed at a certain ice concentration of pack ice was determined using the interpolation method. This paper reports a procedure to determine the attainable speed in pack ice and the sample calculation using the Araon vessel was performed to confirm the entire process. A more detailed description of the determination of the attainable speed is described. The attainable speed in 1.0 m, 90% pack ice and 540 kPa strength was 13.3 knots.

• 대한조선학회논문집
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• 제48권5호
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• pp.390-395
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• 2011

The main purpose of ice model basin is to assess and evaluate the performance of the Arctic ships and offshore structures because the full-scale tests in ice covered sea are usually very expensive and difficult. There are various ice conditions, such as level ice, brash ice, pack ice and ice ridge, in the real sea. To estimate their capacities in ice tank accurately, an appropriate model ice sheet and prepared ice conditions copied from actual sea ice conditions are needed. Pack ice is a floating ice that has been driven together into a single mass and a mixture of ice fragments of varying size and age that are squeezed together and cover the sea surface with little or no open water. So Ice-class vessels and Icebreaker are usually operated in pack ice conditions for the long time of her voyage. The most ice model tests include the pack ice test with the change of pack ice concentration. In this paper, the effect of pack ice size and channel breadth in pack ice model test is conducted and analyzed. Also we presented some techniques for the calculation of pack ice concentration in the model test. Finally, we developed a new model test methodology of pack ice condition in square type ice tank.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.361-366
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• 2018

Ice crushing occurs in many situations that involve a sliding frictional component such as sports involving ice-contact, ice interaction with ship hulls, and ice-on-ice sliding/crushing within glaciers and between interacting sea ice floes. Ice crushing-friction tests were conducted in the lab at $-10^{\circ}C$ using a set of acrylic ice-crushing platens that included a flat smooth surface and a variety of high-roughness surfaces with regular arrays of small prominences. The experiments were part of Phase II tests of the Blade Runners technology for reducing ice-induced vibration. Ice was crushed against the platens where the ice movement had both a vertical and a horizontal component. High-speed imaging through the platens was used to observe the ice contact zone as it evolved during the tests. Vertical crushing rates were in the range 10-30 mm/s and the horizontal sliding rates were in the range 4.14-30 mm/s. Three types of freshwater ice were used. Friction coefficients were extraordinarily low and were proportional to the ratio of the tangential sliding rate and the normal crushing rate. For the rough surfaces all of the friction coefficient variation was determined by the fluid dynamics of a slurry that flowed through channels that developed between leeward-facing facets of the prominences and the moving ice. The slurry originated from a highly-lubricating self-generating squeeze film of ice particles and melt located between the encroaching intact ice and the surfaces.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.60-68
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• 2018

A series of tests in an ice tank was carried out using a model-scale ship to investigate the ice loading process. The ship model Uikku was mounted on a rigid carriage and towed through a level ice field in the ice tank of the Marine Technology Group at Aalto University. The carriage speed and ice thickness were varied. In this paper, ice loading process was described and the corresponding ice forces on the horizontal plane were analysed. A new method is proposed to decompose different ice force components from the total ice forces measured in the model tests. This analysis method is beneficial to understanding contributions of each force component and modelling of ice loading on hulls. The analysed experimental results could be used for comparison with further numerical simulations.

• 한국해양공학회지
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• 제28권1호
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• pp.28-33
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• 2014

The Korean icebreaking research vessel "Araon" performed four sea trials in the Arctic and Antarctic Seas. The ice properties, such as the ice thickness, floe size, ice strength, and power of the vessel were quite different in these trials. To compare the speeds of ship with the same ice strength and power, the AARC (Arker Arctic Research Center) method is used with a vessel power of 10 MW and an ice strength of 630 Pa in this paper. Based on the analysis results, the speed of the ship was 1.62 knots (0.83 m/s) with a 1.02-m ice thickness and 2.5-km floe size, 5.3 knots (2.73 m/s) with a 1.2-m ice thickness and 1.0-km floe size, and 13.8 knots (7.10 m/s) with a 1.1-m ice thickness and 200-m floe size. The analysis results showed that the ship speed and floe size have an inversely proportional relationship. Two reasonable reasons are given in this paper for the final result. One is an ice breaking phenomenon, and the other is the effect of the ice floe mass. For the breaking phenomenon, the ice breaking force is very small because the ice floe is not breaking but tearing when a ship is passing through a small ice floe. Regarding the effect of the ice floe mass, it is impossible for a ship to push and tear an ice floe if the mass of the ice floe is too large compared to the mass of the ship. The velocity of the ship decreases when the ice floe has a large mass and a large size because the ship has to break the ice floe to move forward.

• 대한조선학회논문집
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• 제45권5호
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• pp.562-568
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• 2008

In this study, the target FSICR class is 1A whose target thickness of the brash ice is 46 mm in model scale. Normally ice floes for brash ice do not exceed 2 m in full scale, so the model ice sheet was cut by about 10 cm by 10 cm using hand saws. Since the target thickness of brash ice is 46 mm, 46 mm ice sheet makes one layer brash ice. For 23 mm thickness ice sheet, two layers should be accumulated to reach 46mm brash ice thickness. For 15mm thickness ice sheet, three layers need to be accumulated as the same as those in 23 mm ice sheet. New methodology to produce a brash ice was proposed. The results showed that it would be important to use multi-layer rather than single layer possibly because of significant thrust deduction from the propeller-ice interaction in the present ice condition (FSICR 1A).

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 추계학술대회
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• pp.37-39
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• 2015

The ships transiting the Northern Sea Route (NSR) have been gradually increased so that the number of ship-ice collision accidents would be increased. The collision between ship and ice floe can lead to serious damage of hulls and decline of ship's maneuverability. In this study, collision tests that a model ship is forced to collide with disk-shaped synthetic ice floes are conducted in a towing tank. The synthetic ice floes made of polypropylene which has similar density with real ice are used. The ice load is measured by a load cell installed on the carriage rod. The ice floe's motion is measured by a motion sensor installed on the synthetic ice floe. The influences of contact conditions such as hull form and ship speed on the ship-ice collision response are investigated and discussed by measured peak force and ice floe's motion.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.414-427
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• 2020

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

• 한국기계기술학회지
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• 제13권4호
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• pp.109-115
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• 2011

The ice tank is important facility to check the performance of the ship and offshore in ice condition before the construction. MOERI(Maritime & Ocean Engineering Research Institute) constructed ice model basin on the end of 2010. The ice technology to know the phenomena of ice near the ship and to estimate power of the ship in model scale is the main characteristic of the ice model basin. To achieve this goal in one ice sheet, making of test plan and feasibility check of test possibility have to review in the beginning stage of the every test. This paper describes the number of maximum resistance and self propulsion test in a sheet of level ice and proposes the methodology to optimize pack ice, rubble ice, brash ice and ice ridge test in MOERI ice tank. The feasibility of free running test to know maneuvering performance in ice field and some specific idea to measuring ice thickness and ice ridge shape was proposed.