Ice Tank

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 Manovering 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.

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 comprised 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 icebreakers 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.

ome of the Worlds Ice Tanks

Some Ice Tanks ranked by volume. Dimensions are given in meters.

References