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CHAPTER 5. COASTAL STRUCTURE MODELS
5.3.2
Sloping Impermeable Structure Scale Effects
Physical models of sloping impermeable structures have many of the same
laboratory effects as discussed in Chapter 4 in connection with short-wave,
fixed-bed hydrodynamic models. These include effects related to
1. Physical constraints of model boundaries on the flow
2. Unintentional nonlinear effects brought about by using mechanical means of wave and current generation
3. Simplification of prototype forcing conditions
The section entitled Short-Wave Model Lab and Scale Effects in Chapter 4
contains a more detailed discussion of laboratory effects.
The primary scale effect to be considered regarding when conducting a
physical model of a smooth, sloping, impermeable structure is the impact
loading caused by plunging waves breaking directly on the structure.
Führbôter (1986) conducted prototype-scale and mid-scale (1:10) tests
of plunging wave impact loads on a smooth impermeable 1:4 slope. He used
regular waves ranging in height from 0.1 m in the mid-scale flume up to
2.1 m in the Grofier Wellenkanal. The along-slope distribution of impact
pressure was measured using an array of sensors placed in the impermeable
slope.
Qualitatively, the time records of wave impact pressure were similar
between the two models, however, it was noted that more air was entrained
by plunging breakers in the larger model. Also, it was observed that the
forward lip of the plunging wave never impacted the dry slope, but instead
hit the downrush water from the previous wave. Impacting the downrush
water was likely related to the period and regularity of the generated waves,
and probably would not always be the case if irregular waves had been used.
Increased aeration of the downrush in the larger waves helped to absorb
the wave impact and decrease the pressure at the structure. Führbôter
concluded his analysis by stating
With increasing wave height towards prototype conditions a scale
effect exists in such a manner that in prototype the relative pressures are a little lower than those extrapolated from small scale
tests. This means that results obtained from small scale tests
lie on the safe side. The reason for this phenomenon can be
explained by increasing aeration effects in the case of prototype
tests. (Führbôter 1986).
Oumeraci (1984) presented results of Popov and Ryabich10 that showed
wave impact pressure scale effects existed for Reynolds numbers less than
Oumeraci (1984) referenced this 1971 Russian-language paper.
CHAPTER 5. COASTAL STRUCTURE MODELS
5.3.2
Sloping Impermeable Structure Scale Effects
Physical models of sloping impermeable structures have many of the same
laboratory effects as discussed in Chapter 4 in connection with short-wave,
fixed-bed hydrodynamic models. These include effects related to
1. Physical constraints of model boundaries on the flow
2. Unintentional nonlinear effects brought about by using mechanical means of wave and current generation
3. Simplification of prototype forcing conditions
The section entitled Short-Wave Model Lab and Scale Effects in Chapter 4
contains a more detailed discussion of laboratory effects.
The primary scale effect to be considered regarding when conducting a
physical model of a smooth, sloping, impermeable structure is the impact
loading caused by plunging waves breaking directly on the structure.
Führbôter (1986) conducted prototype-scale and mid-scale (1:10) tests
of plunging wave impact loads on a smooth impermeable 1:4 slope. He used
regular waves ranging in height from 0.1 m in the mid-scale flume up to
2.1 m in the Grofier Wellenkanal. The along-slope distribution of impact
pressure was measured using an array of sensors placed in the impermeable
slope.
Qualitatively, the time records of wave impact pressure were similar
between the two models, however, it was noted that more air was entrained
by plunging breakers in the larger model. Also, it was observed that the
forward lip of the plunging wave never impacted the dry slope, but instead
hit the downrush water from the previous wave. Impacting the downrush
water was likely related to the period and regularity of the generated waves,
and probably would not always be the case if irregular waves had been used.
Increased aeration of the downrush in the larger waves helped to absorb
the wave impact and decrease the pressure at the structure. Führbôter
concluded his analysis by stating
With increasing wave height towards prototype conditions a scale
effect exists in such a manner that in prototype the relative pressures are a little lower than those extrapolated from small scale
tests. This means that results obtained from small scale tests
lie on the safe side. The reason for this phenomenon can be
explained by increasing aeration effects in the case of prototype
tests. (Führbôter 1986).
Oumeraci (1984) presented results of Popov and Ryabich10 that showed
wave impact pressure scale effects existed for Reynolds numbers less than
Oumeraci (1984) referenced this 1971 Russian-language paper.