D.G. Hamilton, B.A. Ebersole r Coastal Engineering 42 (2001) 199218
204
neath the waveguide was used. At the downstream
is the wave period Zpeak spectral wave period, Tp ,
boundary, the bottom edge of the waveguide was set
for the irregular wave case., H is the wave height
at approximately the minimum wave trough eleva-
Zenergy-based significant wave height, Hmo , for the
irregular wave case., l is wavelength, d is still
tion. In addition to the waveguides, a matrix of
water depth, u is the angle of incidence relative to
0.1-m diameter rigid polyvinyl chloride pipe was
shore normal, and the subscripts A0B and A1B refer to
installed in each of the flow channels to absorb the
residual wave energy that entered beneath the wave-
values in deep water and at the wave generators,
guides, and to minimize wave reflection in the flow
respectively. Deepwater values were calculated using
channels. Svendsen Z1991. discussed similar con-
linear wave theory. For the irregular wave tests, Hmo
cepts. Additional information regarding the design
was selected so that the root-mean-square wave
and evaluation of the performance of the LSTF is
height, Hrms , was comparable to the average wave
documented in Hamilton et al. Z2000..
height, Havg , for the regular wave case. Therefore,
the total incident wave energy used for both regular
and irregular waves was similar. For the irregular
wave tests, a TMA spectrum was used to define the
4. Experimental program
spectral shape. The spectral width parameter was
3.3, a value representing typical wind sea conditions.
A number of preliminary experiments were con-
A random phase method was used to synthesize the
ducted to investigate: Za. long-term oscillations in
pseudo-random wave train used to drive the wave
pump discharge rates Zthey were found to be negligi-
generators. The length of the drive signal was 500 s,
ble., Zb. flow patterns created by pumping only Zi.e.,
a duration of 200 times the peak wave period Z2.5 s..
no wave forcing., Zc. flow patterns with waves only
The still water depth at the wave generators was held
Zi.e., no external current recirculation., and Zd. the
constant at 0.667 m during all experiments.
time required for the mean velocities in the wave
basin to reach steady state.
Once these preliminary experiments were com-
pleted, two comprehensive test series were con-
5. Measurement methodology
ducted, one using regular waves and the other using
irregular waves. A total of 20 experiments were
conducted, each with a different magnitude and
An automated instrumentation bridge was used to
cross-shore distribution of pumped flow rate. Fifteen
position the wave and current sensors at various
regular wave experiments were conducted in the
positions along the beach. Transect locations were
process of determining the proper magnitude and
selected every 4.0 m, from y s 15.0 to y s 39.0 m,
cross-shore distribution of the longshore current, and
as shown in Fig. 2. Transects are identified as Y15,
were identified as Test 2 Zwaves only. and Tests
Y19, Y23, Y27, Y31, Y35 and Y39, according to
6AN Zwaves and currents.. Five irregular wave
their longshore coordinate. During each experiment,
experiments were conducted and identified as Tests
measurements were made along at least three pri-
8AE.
mary transects to represent general hydrodynamic
The incident wave conditions adopted for Tests
conditions along the beach: Y19 Zcenter of the down-
6AN and Tests 8AE are given in Table 1 where T
stream half of the beach., Y27 Zcenter of the entire
Table 1
Summary of incident wave conditions
H1rl1 Z.
u1 Z8.
H0rl0 Z.
u 0 Z8.
T Zs.
H1 Zm.
d1 Zm.
H0 Zm.
Test
Wave type
Test 6AN
Regular
2.5
0.182
0.031
0.667
10.0
0.189
0.019
16.6
Test 8AE
Irregular
2.5
0.225
0.038
0.667
10.0
0.233
0.024
16.6
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