useful for ocean waves studies.

1. OceanWaves

2. Kinematic Viscosity of Sea
Water

3. Density of Fresh and Sea
Water

4. Distribution of Wind Speed

5. Wind Speed – Beaufort
Number

6. Wave Generation
 Of the momentum transformed from wind to
water 97% go to the surface layer producing
surface currents. The remaining energy is
transferred to water surface creating waves
 Gentle breeze creates ripples which provide
rough surface allowing wind to move water
 If the wind dies ripples disappear quickly
 If the wind continues, these are gradually
transformed to larger waves

7. Wave generation (contd.)
 Newly formed waves are generally short and
choppy providing a roughened water surface for
more energy to be transferred to water. These
waves are steep which slowly change to smooth
waves of larger length depending on steady wind
blowing over a long period over large body of
water.

8. Wave generation (contd.)
 The wave size depends on
Wind speed
wind direction
time that the wind blows
fetch (distance over which wind
blows in a constant direction)

9. Sea State

10. Wave generation (contd.)
 Waves break when height to length of wave ratio
reaches 1:7
 Ocean waves reach maximum size when these
can not accept more energy from wind. The sea
is then said to be fully developed (FDS) when it
can accept no more energy and thus waves
break. The energy supplied by the wind is equal to
the energy lost by breaking waves.

11. Wave generation (contd.)
 As sea develops wave length and speed increase
and slope reduces. Eventually waves travel out of
the wind area and these are called swells. Long
period swells travel long distances without loosing
energy (amplitude)

12. Waves in Shallow water
As deep water waves
move towards the coast
they come to shallow
water zone, become
shorter and slower and
steeper and ultimately
break. Deep water waves
move faster towards the
coast compared to the
waves in shallower
regions. This interaction
leads to the breaking
waves being parallel to
coastline irrespective of
wave direction in deep
water

13. Isobar (Surface Wave) elevation
(i) General
(ii) In deep water, h>>0 and z>= 0
(iii) In deep water on surface, z=0

14. Regular sine wave in
Deep water
   tkxtx a  ,

15. Regular Wave –
contours of equal pressure
   tkxetx
h
a  


 0
2
,

20.   ( )w
a
P H a f x dx

  

21.    iii
i
ai
i
i txktx   




cos,
11
 22
4
1
,
4
1
apak gEgE 
 2
2
1
2
a
pk
g
EE
E 











ii
i
ii
i
w
ai
w
ai ggE




 22
2
1
2
1
21
2
( )
i
i
ai
iS
 










22. 21
( )
2
i aiS d   

24. 0
( )n
nm S d   

 
0 2
0
0, ( ) (var )nFor n wehave m S d ianceof      

  
2 2
0
2, ( ) (var )nFor n wehave m S d ianceof  
    

  
4 2
0
4, ( ) (var )nFor n wehave m S d ianceof  
    

  

25. 010/1
031
0
1.5
0.4
5.2
mh
mh
mh


So,
Average Wave Height: ĥ
Significant Wave Height (Average
of highest 1/3 wave heights): h⅓
Average of highest 1/10 wave hts:
h1/10

27. Effects of waves on ship
operation
 Motions – discomfort
 Slamming
 Green sea on board
 Speed loss
 Mechanical failure
 Instantaneous loss of stability
 Structural stresses and vibration