ERDC/CHL CHETN-III-67
September 2003
values for wavelength. These same dimensionless
Table 2
parameters are also used to characterize irregular
Common Dimensionless Wave
Parameters
wave trains by substituting wave heights, wave
periods, and wavelengths representative of irregu-
Parameter
Value
lar waves, such as those shown on Table 1.
h
h
;
; kh
Relative depth
gT 2
L
H
This CHETN describes a new wave parameter for
Relative wave height
h
depicting processes that occur when waves
H
H
H
;
;
Wave steepness
impinge on coastal structures. The new wave
gT 2
L
Lo
parameter has the following attributes:
Ho
Ho
;
Deepwater wave steepness
gT 2
Lo
a. The parameter is physically meaningful so
tan α
ξ=
Local Iribarren number
it can be incorporated into theoretical
H/L
models of specific physical processes in a
tan α
ξ=
Deepwater Iribarren number
Ho /Lo
rational way.
b. The parameter applies to both periodic waves and nonperiodic waves.
c. The parameter spans the range of relative depths from deep water to shallow water.
d. The parameter is stable and robust.
e. The parameter is easy to estimate so design guidance using the parameter can be pro-
grammed into computer spreadsheets or simple programs.
WAVE MOMENTUM FLUX PARAMETER: Surface waves possess momentum that is directed
parallel to the direction of wave propagation. When a wave encounters a solid object, momentum is
reversed, and the resulting force on the object is equal to the rate of change of momentum, also
known as the wave momentum flux. Thus, wave momentum flux is the property of progressive
waves most closely related to force loads on coastal structures or any other solid object placed in the
wave field. And for this reason wave momentum flux is a compelling wave property for
characterizing coastal structure response to wave loading.
The instantaneous flux of horizontal momentum (mf) across a unit area of a vertical plane oriented
parallel to the wave crests is given by
mf (x,z,t) = pd + ρ u2
(1)
where
= horizontal direction perpendicular to wave crests
x
= vertical direction, positive upward with z = 0 at still-water level (swl)
z
= time
t
= instantaneous wave dynamic pressure at a specified position
pd
ρ = water density
u = instantaneous horizontal water velocity at the same specified position
2
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