2.6.2 Ice index

Ice index is a parameter that quantitatively represents ice navigation difficulties with one value, which is introduced in order to run the simulation effciently. The purpose of　introducing ice index is to develop the chart showing the relation between ice index and the ship speed distribution. The chart is obtained based on the environmental data of WP2 and the code developed by WP6. The chart is put into the simulation code of WP8 as a lookup table. Ice index is a concept originally introduced in the CASPPR, however, it is different in the following points：considering not only ice type, ice thickness, and ice concentration, but also the influence of ice bending strength, compressive strength, ridge size, ridge distribution.

　

Components of ice index

Ice index： I consists of the three types of ice index： I_A, I_B, I_c as assumed in equation(2.6.14).These components are shown in the Figure 2.6.4.

　

Figure 2.6.4 Components of Ice Index

　

I_A

The calculation technique of I_A is almost the same as the Canadian ice numeral. The first year ice is categorized into four levels by ice thickness as shown in Table 2.6.2. Multipliers of multi-year ice and first year ice using ice class are assigned referring to Table 2.6.3. A part of ice multipliers given by the CASPPR is revised as Table 2.6.3. There is no difference between multi-year ice and second-year ice in the environmental data of WP2; therefore, the mean value of multi-year ice and second-year ice given in the CASPPR is used as an ice multiplier of MY.

　

Table 2.6.2 Type of first year ice

Table 2.6.3 Ice Multiplier

　

Finally, using the mean first-year ice concentration C_f, mean multi-year ice concentration C_m, and a multiplier that are given in Table 2.6.3, ice index I_A is calculated by the equation(2.6.15).

　

I_A=first-year ice conccntration multiplier x C_f + multi-year ice concentration multiplier x C_m

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