COLD REGIONS TECHNICAL DIGEST NO. 96-1
12
mice ∆V 2
fi =
(6b)
2∆x L
The designer must determine the length over which this force is to
be distributed.
Forces from vessel
Large vessels navigating in winter can impose loads on an ice
passages
boom in a number of ways. First, a vessel may collide directly
with the boom. Second, waves produced by a vessel passage can
result in both vertical and lateral movement of an intact sheet ice
cover, transmitting forces to the boom. The hydrodynamics of
boom loading due to vessel-induced waves are quite complicated
and beyond the scope of this technical digest. Third, waves or
propeller wash from a vessel may push broken ice pieces or brash
ice into a boom. The most common vessel effect takes place when
ship traffic in the vicinity of the boom breaks shore ice free,
allowing it to act on the boom. If the shore ice breaks into rela-
tively small pieces, the increased ice load may be estimated by
increasing the ice area subject to water, wind and gravity forces
(eq 2, 3 and 4). If a large floe broken free by vessel passage moves
against the boom, it may be treated as an impact force and esti-
mated using eq 6a and 6b.
Typical ice boom
Ice booms have been built in many configurations. Some booms
configurations
cross the entire channel width, while others stabilize or retain ice
only at the channel sides. The boom in Figure 2 has an opening for
ship passage. Figure 4 illustrates a variety of boom configura-
tions. The upstream vee design shown in Figure 4e effectively
diverts arriving ice away from the highest velocity area at the
channel center and avoids the use of a midchannel anchor by
extending anchor cables to each shore. In more conventional con-
figurations such as Figure 4b, the spacing between anchor lines is
typically 100 to 400 ft (30120 m), depending on the loading and
the strength of the boom. Span lengths greater than 400 ft (Fig.
4c) are found in some debris boom applications, but are rare in
booms designed to retain ice.
In some applications, it may be advantageous to orient the
boom so that the region of maximum flow velocity does not
coincide with the area of maximum boom sag (Fig. 4e). In the
region of fastest current, the flow velocity component perpen-
dicular to the boom will therefore be lower and the ice capture
efficiency increased. This arrangement also tends to divert ice
from the faster areas to slower parts of the channel, making it
easier for the boom to retain ice. Often, the part of the river with
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