4.2. SHORT-WAVE HYDRODYNAMIC MODELS
117
cept by conducting small and large scale tests of regular and irregular breaking waves on an initially 1:40 plane sloping beach8. Tests were scaled according to the undistorted Froude criterion. He examined measured values
of wave heights, wave set-up, and the vertical profiles of maximum seaward
and shoreward and time-mean horizontal water velocities. Stive’s results
indicated that there was no significant departure from Froude scaling in
the wave height range of 0.1 m to 1.5 m with regard to the parameters
measured. This result implied that observed differences in air entrainment
between model and prototype have no significant dynamic influence.
The beach was sand in the large scale flume and concrete in the small scale tests.
In other wave-breaking-related processes, Le Méhauté (1990) reported
that systematic experiments have shown that the model wave height must
exceed 50 cm to prevent significant scale effects in the study of breaking waves on piles where air is entrained. Also, when waves break on
armor units in a physical model, the flow is turbulent so it is expected that
pressures produced in the model are in similitude with the prototype (Le
Méhauté 1976).
Other Scale Effects in Short-Wave Models. The scale effects discussed in the previous sections comprise the more common effects encountered in short-wave physical models. However, there are several others scale
effects that may become important in certain instances, and the modeler
should be aware of their potential effect.
Le Méhauté (1976) pointed out several scale effects that might occur in
coastal models. These are listed below.
• Scale model experiments usually are conducted using fresh
water. If the prototype condition is salt water, there is
about a 3% difference in density and this changes wave
forces accordingly. Le Méhauté (1976) estimates that this
effect could cause as much as 15% error in breakwater stability studies if no correction were made. (Chapter 5 provides a correction method for modeling coastal structure
stability for salt-water prototype conditions.)
• Because the compressibility of water is not scaled, shock
waves caused by underwater explosions will not be in similitude. Phenomena related to compressibility of solid materials, such as slamming and impact loading between two
solid bodies, are usually not in similitude because of the
difficulty in finding a model material that has both the
proper density and compressibility properties.
117
cept by conducting small and large scale tests of regular and irregular breaking waves on an initially 1:40 plane sloping beach8. Tests were scaled according to the undistorted Froude criterion. He examined measured values
of wave heights, wave set-up, and the vertical profiles of maximum seaward
and shoreward and time-mean horizontal water velocities. Stive’s results
indicated that there was no significant departure from Froude scaling in
the wave height range of 0.1 m to 1.5 m with regard to the parameters
measured. This result implied that observed differences in air entrainment
between model and prototype have no significant dynamic influence.
The beach was sand in the large scale flume and concrete in the small scale tests.
In other wave-breaking-related processes, Le Méhauté (1990) reported
that systematic experiments have shown that the model wave height must
exceed 50 cm to prevent significant scale effects in the study of breaking waves on piles where air is entrained. Also, when waves break on
armor units in a physical model, the flow is turbulent so it is expected that
pressures produced in the model are in similitude with the prototype (Le
Méhauté 1976).
Other Scale Effects in Short-Wave Models. The scale effects discussed in the previous sections comprise the more common effects encountered in short-wave physical models. However, there are several others scale
effects that may become important in certain instances, and the modeler
should be aware of their potential effect.
Le Méhauté (1976) pointed out several scale effects that might occur in
coastal models. These are listed below.
• Scale model experiments usually are conducted using fresh
water. If the prototype condition is salt water, there is
about a 3% difference in density and this changes wave
forces accordingly. Le Méhauté (1976) estimates that this
effect could cause as much as 15% error in breakwater stability studies if no correction were made. (Chapter 5 provides a correction method for modeling coastal structure
stability for salt-water prototype conditions.)
• Because the compressibility of water is not scaled, shock
waves caused by underwater explosions will not be in similitude. Phenomena related to compressibility of solid materials, such as slamming and impact loading between two
solid bodies, are usually not in similitude because of the
difficulty in finding a model material that has both the
proper density and compressibility properties.