36 W and with turbine was 14.95 W which corresponds to a decrease of 27%. For T=2.5 s a significant reduction of about 37% was recorded. On the other hand, the reduction in the water power for T=3 s was 20% indicating that the turbine did not offer that much of flow resistance. Table 2 reveals an interesting observation, even though at T=2.5 s the wave power is higher than that at SP600125 3 s but the power available to the turbine (water power) is more at T=3 s. In simple words, higher the water power, higher will be the turbine output power. Table 3 shows the turbine

power while the turbine efficiency is given in Fig. 16 for the different wave periods and turbine speed respectively. The turbine power for a fixed turbine speed increases with increasing wave period. There is a significant increase check details in the turbine power at 2.5 s and a dramatic increase in the turbine power at wave period of 3 s. This is because of higher water power as highlighted

in Table 2 hence the turbine is able to extract more energy from the incoming and outgoing flow through the augmentation channel. The results indicate that for this device, higher power is produced from incoming waves with longer wavelengths. The efficiency increases with increasing rotational speed, reaches a maximum and decreases from here onwards as shown in Fig. 16. In the present study, the number of blades was fixed at 30. The only variables were the wave period and the turbine speed. Under these varying conditions, there has to be a point where the turbine has the highest efficiency. The flow is generally

constant at a given wave period and if the turbine is rotating too fast, looking at an instant, water passing through the turbine blade is unable to impart energy effectively because the time between two successive blades to come in contact with the fluid is very short. On the other hand if the turbine rotates too slowly, the water passes quickly through the blade passage and again imparts very little energy. So it is critical the to obtain the speed at which the turbine produces maximum power and has peak efficiency under a given wave condition. The peak in efficiency basically indicates that the interaction between the turbine and flow is maximized at this optimum rotational speed. At this speed maximum energy is extracted hence higher turbine power and efficiency. For T=2 s, highest efficiency of 44.73% is obtained at rotational speed of 35 rpm. At wave periods of 2.5 s and 3 s, the best efficiency point shifts from 35 rpm to 30 rpm. Maximum turbine power of 14 W which corresponds to an efficiency of 55% is obtained at a wave period of 3 s. It is interesting to see that, at speeds of 35 rpm and 40 rpm, the turbine efficiency is higher at T=2 s than at T=2.5 s. Flow in the augmentation channel with and without the turbine at T=3 s is shown in Fig. 17.