EXAMPLE PROBLEM II-1-4

FIND:

The height of the wave *H *assuming that linear theory applies and the average frequency corresponds to the

average wave amplitude.

GIVEN:

An average maximum pressure *p *= 124 kilonewtons per square meter is measured by a subsurface

pressure gauge located in salt water 0.6 meter (1.97 ft) above the bed in depth *d *= 12 m (39 ft). The average

frequency *f *= 0.06666 cycles per second (Hertz).

SOLUTION:

1

1

. 15 *s*

'

(0.0666)

12

. 0.0342

'

351

From Figure II-1-5, entering with *d/L*0,

' 0.07651

hence,

12

' 156.8 *m *(515 *ft*)

(0.07651)

and

2π*d*

' 1.1178

cosh

Therefore, from Equation II-1-43

2 π (*z *% *d*)

2 π(&11.4 % 12)

cosh

cosh

156.8

' 0.8949

'

1.1178

2π*d*

cosh

Since η = *a *= H/2 when the pressure is maximum (under the wave crest), and *N *= 1.0 since linear theory is

assumed valid,

1.0 [124 % (10.06) (&11.4)]

' 1.04 *m *(3.44 *ft*)

'

'

2

ρ*gK*z

(10.06) (0.8949)

Therefore,

Note that the value of *K *in Figure II-1-5 or SPM (1984) could not be used since the pressure was not measured

at the bottom.

II-1-24

Water Wave Mechanics

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