Ice Tank
Encyclopedia
An ice tank is a ship model basin
whose purpose is to provide a physical modeling environment for the interaction of ship, structures, or sea floor with both ice and water. Ice tanks may take the form of either a towing tank or maneuvering basin
.
Many un-refrigerated ship model basins use ice simulants such as paraffin wax, plaster, and mixtures of foam or plastic beads. The clean up and handling of such simulants often proves cumbersome. What differentiates an ice tank from other ship model basins is that an ice tank has purpose built provisions into its structure for handling such material conveniently. Use of a refrigerated basin containing mostly water allows freezing and melting to be a convenient method of model ice preparation and clean up.
Many factors and properties are of interest when simulating ice. The actual environment that will be simulated is of prime concern. For example, ice pieces flowing then jamming a spring river would be modeled very differently than a ship model traversing a simulated arctic ice sheet. Different again would be a ship traversing an area of loose broken ice pieces or pack ice.
If one was to use pure-water ice, the problem lies in the fact that pure-water ice does not soften.
Many ice tanks simulate ice using a mixture consisting mostly of water and chemical additives called dopants. Dopants are chemicals which reduce the melting temperature of pure water ice. Common dopants used are salt, ethanol
, ethylene glycol
, or urea
.
By using a sufficiently cold temperature, both water and dopant are frozen in solution together forming an ice sheet. This impure ice sheet is inherently softer than pure-water ice but may be much harder than the scale strength desired. Once a desired thickness is achieved, the air temperature is raised to a tempering temperature. As the temperature of the ice rises the dopants come out of frozen solution and form liquid brine pockets. These brine pockets slowly drain out of the ice sheet thus weakening it. Provided the ice-sheet isn't allowed to refreeze, the strength of the ice continues to decrease approaching an asymptotic value. Choosing a correct ice scale then becomes a question of when to conduct the test. This softening is often referred to as tempering.
Different ice simulants model ice differently. For example most icebreaker
s break ice by riding upward unto the ice and breaking downward by the weight of the vessel. In this case, correctly modeling ice's downward flexural strength
is most important. In the case of bridges or offshore structure, compressive strength
and/or upward flexural strength may be of more interest. The effects of ice on ship propulsion often requires model ice density to be reduced by adding controlled amounts of gas or air during the freezing process.
One of the first ice tanks to attempt to scale ice on a tow tank basin scale was the Krylov Institute using high concentrations of salt as a dopant to soften the ice.
Ship model basin
A ship model basin may be defined as one of two separate yet related entities, namely:* a physical basin or tank used to carry out hydrodynamic tests with ship models, for the purpose of designing a new ship, or refining the design of a ship to improve the ship's performance at sea;* the...
whose purpose is to provide a physical modeling environment for the interaction of ship, structures, or sea floor with both ice and water. Ice tanks may take the form of either a towing tank or maneuvering basin
Ship model basin
A ship model basin may be defined as one of two separate yet related entities, namely:* a physical basin or tank used to carry out hydrodynamic tests with ship models, for the purpose of designing a new ship, or refining the design of a ship to improve the ship's performance at sea;* the...
.
Many un-refrigerated ship model basins use ice simulants such as paraffin wax, plaster, and mixtures of foam or plastic beads. The clean up and handling of such simulants often proves cumbersome. What differentiates an ice tank from other ship model basins is that an ice tank has purpose built provisions into its structure for handling such material conveniently. Use of a refrigerated basin containing mostly water allows freezing and melting to be a convenient method of model ice preparation and clean up.
Ice scaling
Ship model basins often simulate full-scale processes in miniature. Ships/structures are reduced linearly in size, and cubic in mass, displacement, and volume. The challenge in ice modeling is correctly reducing the ice properties of interest to provide an accurate simulation.Many factors and properties are of interest when simulating ice. The actual environment that will be simulated is of prime concern. For example, ice pieces flowing then jamming a spring river would be modeled very differently than a ship model traversing a simulated arctic ice sheet. Different again would be a ship traversing an area of loose broken ice pieces or pack ice.
Weakened ice method
One important factor in icebreaker model testing is the effect of changing ice strengths and thickness. For example: if a 1 to 30 scale is chosen, then the ship model is 1/30th the size. The ice used must also be 1/30th the thickness and 1/30th the strength.If one was to use pure-water ice, the problem lies in the fact that pure-water ice does not soften.
Many ice tanks simulate ice using a mixture consisting mostly of water and chemical additives called dopants. Dopants are chemicals which reduce the melting temperature of pure water ice. Common dopants used are salt, ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
, ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
, or urea
Urea
Urea or carbamide is an organic compound with the chemical formula CO2. The molecule has two —NH2 groups joined by a carbonyl functional group....
.
By using a sufficiently cold temperature, both water and dopant are frozen in solution together forming an ice sheet. This impure ice sheet is inherently softer than pure-water ice but may be much harder than the scale strength desired. Once a desired thickness is achieved, the air temperature is raised to a tempering temperature. As the temperature of the ice rises the dopants come out of frozen solution and form liquid brine pockets. These brine pockets slowly drain out of the ice sheet thus weakening it. Provided the ice-sheet isn't allowed to refreeze, the strength of the ice continues to decrease approaching an asymptotic value. Choosing a correct ice scale then becomes a question of when to conduct the test. This softening is often referred to as tempering.
Different ice simulants model ice differently. For example most icebreaker
Icebreaker
An icebreaker is a special-purpose ship or boat designed to move and navigate through ice-covered waters. Although the term usually refers to ice-breaking ships, it may also refer to smaller vessels .For a ship to be considered an icebreaker, it requires three traits most...
s break ice by riding upward unto the ice and breaking downward by the weight of the vessel. In this case, correctly modeling ice's downward flexural strength
Flexural strength
Flexural strength, also known as modulus of rupture, bend strength, or fracture strength, a mechanical parameter for brittle material, is defined as a material's ability to resist deformation under load...
is most important. In the case of bridges or offshore structure, compressive strength
Compressive strength
Compressive strength is the capacity of a material or structure to withstand axially directed pushing forces. When the limit of compressive strength is reached, materials are crushed. Concrete can be made to have high compressive strength, e.g...
and/or upward flexural strength may be of more interest. The effects of ice on ship propulsion often requires model ice density to be reduced by adding controlled amounts of gas or air during the freezing process.
One of the first ice tanks to attempt to scale ice on a tow tank basin scale was the Krylov Institute using high concentrations of salt as a dopant to soften the ice.
Some of the world's ice tanks
Some ice tanks ranked by volume. Dimensions are given in meters.| Facility | Dimensions (m) | Location | Country |
|---|---|---|---|
| http://www.tkk.fi/Units/Ship/General Helsinki University of Technology Helsinki University of Technology Aalto University School of Science and Technology , was the temporary name for Helsinki University of Technology during the process of forming the Aalto University... |
40 x 40 x 2.8 | Espoo | Finland |
| http://www.moeri.re.kr/eng/study/institution08.aspx Maritime & Ocean Engineering Research Institute MOERI | 42 x 32 x 2.5 | Daejeon, Hoseo | South Korea |
| http://iot-ito.nrc-cnrc.gc.ca/facilities/it_e.html National Research Council of Canada National Research Council of Canada The National Research Council is an agency of the Government of Canada which conducts scientific research and development.- History :... NRCC-IOT |
90 x 12 x 3.0 | St. John's, Newfoundland | Canada |
| http://www.hsva.de HSVA, Large Ice Model Basin | 78 x 10 x 2.5 | Hamburg | Germany |
| http://www.akerarctic.fi/modeltesting.htm Aker Arctic Technology Inc. (formerly Kvaerner Masa-Yards) | 77.3 x 6.5 x 2.3 | Helsinki | Finland |
| http://www.crrel.usace.army.milhttp://www.crrel.usace.army.mil/ierd/testbasin.htm CRREL | 37 x 9 x 2.4 | Hanover, New Hampshire | United States of America |
| http://www.nmri.go.jp/main/overview/facilities/facilities_e.html NMRI | 35 X 6 X 1.8 | Mitaka, Tokyo | Japan |
| http://www.ksri.ru/eng1/exp/hydro/ice.htm Krylov Institute | 35 X 6 X 1.5 | St.Petersburg | Russia |
| http://www.hsva.de HSVA, Environmental Test Basin | 30 x 6 x 1.2 | Hamburg | Germany |
| http://chc.nrc-cnrc.gc.ca/English/Cold%20Regions/Facilities/CRTools_LabStudies_e.html National Research Council of Canada National Research Council of Canada The National Research Council is an agency of the Government of Canada which conducts scientific research and development.- History :... NRCC-CHC |
21 X 7 X 1.1 | Ottawa, Ontario | Canada |
| http://www.dspi-aari.ru Arctic and Antarctic Research Institute Arctic and Antarctic Research Institute The Arctic and Antarctic Research Institute, or AARI is the oldest and largest Russian research institute in the field of comprehensive studies of Arctic and Antarctica... |
35 X 5 X 1.8 | St.Petersburg | Russia |