to model ice, although the bond strength between
pieces may be insufficiently scaled. One means to
simulate, at least approximately, consolidation
using other materials as model ice is to mix or
add some sticky liquid that glues the pieces to-
gether. Garbrecht et al. (1981), for example, used
polypropylene blocks with a distribution of sizes,
shapes, and thicknesses to model a jam on the
Elbe River. They consolidated their model ice us-
ing a liquid paraffin wax.
Interparticle bonding is a characteristic feature
of accumulations of the smallest of ice pieces,
snow. Moisture and electrostatic forces between
snow flakes cause them to move as particulate
agglomerations and enable snow to accrete on di-
verse structures and snowdrift accumulations to
Figure 6. Roughness attached to flume side walls
stand with leeward slopes steeper than those of,
traps ice material and correctly models the ice-on-ice
say, fine sands. The agglomerative, or cohesive,
shear zone.
behavior of snow is handled customarily (e.g.,
during model calibration.
Haehnel et al. 1993) using either activated clay or
CRREL's experience with particulate model ice
fine-diameter glass beads. The latter material is
preferred because the particle size (∼3 microns) of
materials includes the use of so-called Iowa
beads, CRREL beads, and NYPA ice, a fractured
activated clay, a powder of refined bentonite clay,
polypropylene material (Fig. 7). Several other
makes it hazardous as a potential promoter of sil-
materials have been tested in very small quanti-
icosis or lung cancer. These days the use of acti-
ties to determine their suitability for model stud-
vated clay has been replaced largely by the use of
ies. Figure 8 gives a close-up view of NYPA ice,
glass beads with diameters in the range of 40 to
about 100 m and specific gravity of 2.44. Thus,
CRREL beads, and Iowa beads. Table 2 describes
the general physical characteristics of these three
as the specific gravity of dry snow is about 0.7,
model ice materials. The values given in Table 2
snowdrift modeling relies on densimetric Froude
for k1, k0, ξ, and are calculated by eq 20 through
number similitude.
23 and, as can be seen from the NYPA ice values,
Material handling is fairly easy for small or
are probably overestimated. Equations 2022 are
particulate model ice pieces, because most partic-
based on dry angular materials and may not hold
ulate sizes pass through pumps. The handling
for wetted plastics. Experimental measurements
difficulty is eased also because particulate model
of the values of these coefficients are currently
ice can be added to the water inflow at the up-
lacking for both prototype and model particulate
stream end of a model with little surface distur-
ice materials.
bance.
During ice jamming or ice runs there is typical-
Breakable ice
ly a zone along the shoreline where ice is either
Of primary importance in the consideration of
frozen to or grounded on the banks. This results
sheets of model ice that are used for investigating
in a shear zone with frictional resistance to move-
ship or structure impact with ice sheets is the
ment along the banks dependent on the interpar-
dynamic similitude of ice buoyancy, friction, and
ticle friction characteristics of the ice material. It is
ice failure mode(s). Real ice with weakening
important to maintain similitude of friction forc-
additives may serve as a breakable model ice
es. Model boundaries should be sufficiently
when modeling in a refrigerated environment.
rough so that, as may occur for many rivers, mod-
Alternately, when modeling in a nonrefrigerated
el ice material grounds along the banks and pro-
environment, several nonaqueous materials may
vides a true iceice shear zone (Fig. 6). Excess sur-
serve as a breakable model ice. Modeling practice
face tension forces between particles can result in
favors the use of real ice with weakening addi-
an overreduction of ice velocity. Zufelt et al.
tives and requires the use of refrigerated labora-
(1994) used an air bubbler along one portion of a
tories and ice-towing tanks.
scale physical model boundary to counter surface
There has been a major investment in research-
tension forces and increase model ice velocities
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