5.2 Experimental Design
5.2.1 Bollard pull test
5.2.1.1 Effect of Collective Pitch Angle Settings
Figure 5.5 shows the thrust coefficient KT and the torque coefficient KQ as functions of the col-
lective pitch angle
col for different propeller rotational speeds ranging from 100 RPM to 500 RPM.As can be seen in the first graph for KT curve, the thrust magnitude increases gradually to the
maximum positive and negative values as
col expands from 0 to 100% and from 0 to -100% respectively. The KT absolute values for the positive
col is slightly higher than that of the neg- ative
col which means that the CCPP produce more thrust in forward direction than in the re- verse direction. There is also a difference in the torque coefficient KQ as
col varied from -100%80
flow recirculation resulted from the hull interaction. Moreover, as previously noted, the rake angle makes the CCPP asymmetrical in the rotational plane which causes the lower reverse thrust.
Figure 5.5. Effect of Collective Pitch Angle Settings to KT and KQ.
In addition, it can be seen that at a particular
col,KT increases as rotational speed n decreases.For the fixed pitch propeller (FPP), changing the rotational speed is the only way to adjust the thrust magnitude. On the other hand, for the CCPP, the thrust magnitude and direction could be changed by controlling the combination of the rotational speed and the collective pitch angles. This mechanism is found to be similar to the CPP, which offers significant advantages such as the capability to gain high efficiency at different cruising speed, high thrust rate of change, flex- ibility in straight-line motion with both forward and reverse direction, stability in the power generation by not changing the rotor shaft speed continuously.
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5.2.1.2 Effect of horizontal cyclic pitch angle settingsIn Figure 5.6, the horizontal force coefficient KY is plotted against the cyclic pitch angle cyc,
which are presented in percentage for a range of different rotational speeds.
Figure 5.6. Effect of horizontal cyclic pitch angle settings.
The results show that the KY absolute value increases as cyc ranging from -100% to 100% the
limitation at both ends. The positive cyc settings would result in a horizontal force to starboard
with positive KY. On the contrary, the negative cyc would result in a horizontal force to the
port. This trend is observed at every rotational speed setting.
In addition,KY increases with the decrease of rotational speed. However, at the high rotational
speeds, above 300 RPM, KY appears to be independent of rotational speed to within the exper- imental errors in this data.
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5.2.1.3 Effect of vertical cyclic pitch angle settingsFigure 5.7 illustrates the relationship between the vertical force coefficient KZ and the cyclic pitch angle cyc presented in percentage for a range of propeller rotational speeds.
Figure 5.7. Effect of Vertical Cyclic Pitch Angle Settings.
It can be seen that the results show the similar trend in the CCPP side force performance, which has been observed in the previous case. The positive cyc settings would result in a vertical force
upwards with positive KZ. On the contrary, the negative cyc would result in a vertical force
downwards.
In the cases of pure cyclic pitch angle settings, it could be concluded that CCPP are able to gen- erate a significant side forces, which are observed with steady trend. Nevertheless, increasing the rotational speed would result in the dramatic decrease in the side forces, horizontal force and vertical force.
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5.2.1.4 Effect of collective and horizontal cyclic pitch angle settings
Considering the effect of both collective and horizontal cyclic pitch angle setting to the CCPP horizontal force and thrust, Figure 5.8 shows the relationship between the horizontal force co- efficient KY and cyclic pitch angle at various collective pitch angles.
Figure 5.8. Effect of collective and horizontal cyclic pitch angle settings.
From the figure it can be seen that at the positive
col, in the range of cyc from -100% to 100%, the CCPP has the horizontal force performance in the same fashion as in the pure cyclic settings discussed in previous section. However, at the negative
col, the horizontal force direction changes in the opposite manner. The positive cyc settings would result in a horizontal force tothe port with negative KY. On the contrary, the negative cyc would result in a horizontal force
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It also noted that the cycdoes not have dramatic influence on thrust at different
colsettings.This means that the underwater vehicles equipped with CCPP would be able to make a turning manoeuvre without loss in thrust.
5.2.1.5 Effect of collective and vertical cyclic pitch angle settings
Similarly to the previous case, the relationship between the vertical force coefficient KZand cy- clic pitch angle at various collective pitch angles is presented in Figure 5.9.
Figure 5.9. Effect of collective and vertical cyclic pitch angle settings.
Similar to the horizontal force coefficient, the vertical force coefficient is affected by the change of cyc at different
col.At the positive
col,the CCPP has the vertical force performance in thesame way to the pure cyclic settings. At the negative
col,the positive cyc settings would result in a vertical force downwards with negative KZ. On the contrary, the negative cyc would result85
In both cases of horizontal force and vertical force performance from the effect of the cyclic pitch angle, it could be concluded that the CCPP is able to generate effective side forces with and without the presence of thrust. In contrast to the FPP, CPP and vectored thrusters, these propul- sors only produce thrust effectively in one direction. This feature enable the manoeuvrability of underwater vehicle at various operational conditions, low speed and cruising speed.