Figure 3: Relationship between the momentum of the ice at the collision and the time until the maximum impact ice force.
Figure 4: Relationship between the amount of apparent deformation at the time of the maximum impact ice force and the momentum
Figure 5: Strain of the ice floes at the time of the maximum impact ice force
Figure 6: Strain rate of the ice floes
with half the area in contact; this shows that the time until the maximum impact force tended to be constant within 1 msec to 3 msec as the momentum increased. Since tmax is about 6.5 msec at its maximum when the momentum is small, a group of ice floes in motion due to waves rarely generate impact forces simultaneously. The typical ice floes along the Okhotsk Sea coast are generally square with sides of about 4 m. Therefore, it is appropriately conservative for design purposes to consider that the impact ice force acts on a structure at points approximately every 4 meters of its length.
Figure 4 shows the relationship between V tamx, i.e. the product of V (the velocity immediately before the collision) and tmax (the time up to the maximum impact ice force), and M (the momentum). The expression V･tmax shows the apparent amount of deformation of the ice plate at the time of the maximum impact ice force, assuming the velocity remains constant after the collision. Since in practice the falling velocity of ice plates decreases after the collision, the actual amount of deformation when the maximum impact ice force takes place should be slightly smaller than the apparent amount. In most cases, the apparent amount of deformation (V･tmax) was within 3 cm. The strain (ε (= V･tmax/1)) at the time of the maximum impact force was computed by dividing the V･tmax by the length of each ice plate (1). Figure 5 shows the relationship between the strain ( ε ) and the momentum, and Figure 6 shows the relationship between the strain rate ( ε (= v/l)) and the momentum. Although the strain rate was great in the figure, many of the values of the strain at the time of the maximum impact ice force were a little smaller than 0.01, almost equal to the values of the strain at the time of the destruction in the unconfined compressive strength test of ice.
