Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, Jan-Mar 2011
advance ratio decreases, something that leads to increased thrust and torque.
Oblique inflow, gives rise to two flow components acting at the propeller plane. The first component is parallel to the shaft and the second is perpendicular to the shaft. In oblique inflow, due to the different sense of in-plane velocity component (perpendicular to the shaft) in the tangential direction to the propeller experienced by different parts of the propeller leads to a difference in the thrust
between different
hydrodynamic bending moment. In other words, in oblique
inflow the perpendicular velocity
sides causing a net component
presents an asymmetry when viewed in terms of propeller relative velocities, since on one side of the propeller disc the perpendicular velocity component is additive to the propeller rotational velocity whilst on the other side it is subtractive. This gives rise to a differential loading of the blades as they rotate around the propeller disc, which causes a thrust eccentricity and side force components. Therefore, it is worth mentioning that it is the tangential component of inflow velocity to the propeller caused by the overall in-plane velocity, which is important for the side forces and bending moments. Even though the radial component of inflow gets a similar contribution from the in-plane velocity it is believed to be of less importance for the side forces and bending moments.
0.02 0.04 0.06 0.08 0.1
-40-30 -20-10 0
-0.06 -0.04 -0.02 0
10 20 30 40 Heading angle
J=0.2-Hull J=0.6-Hull J=1-Hull J=0.2 J=0.6 J=1
Figure 5: Comparison of the vertical component of the side force coefficient between open water condition and behind the hull
Figure 5 and Figure 6 show the vertical component of the side force and bending moment for the thruster propeller in open water and behind conditions. The side forces and bending moments in negative heading angles are much higher for the open water condition than for the behind condition due to a smaller effective heading angle, similar to torque and thrust results. In positive heading angles, the differences are smaller, with the forces in the behind condition being slightly larger than in open water.
Figure 7 and Figure 8 show the comparison between open water tests results and results for the thruster in behind condition for the horizontal component of the side
©2011: The Royal Institution of Naval Architects force and bending moment. The horizontal force
increases with the increase in heading angle and advance coefficient. The larger horizontal force at a higher heading angle with the same advance coefficient is believed to be due to the stronger in-plane velocity component to the propeller disc compared to the lower heading angle. The increase in horizontal force with increasing advance coefficient is expected because the induced axial velocity is large compared to the incoming flow velocity at low advance coefficients, so the effective heading angle is significantly less than the geometric one.
0.06 0.04 0.02 0 -40-30 -20-10 -0.02 -0.04 Heading angle -0.06 Figure bending moment
6: Comparison of the vertical component of coefficient
between condition and behind the hull.
0.15 0.2
0.05 0.1
-40 -30 -20 -10 0
-0.05 0
-0.15 -0.1
Heading angle -0.2
Figure 7: Comparison of the horizontal component of the side force coefficient between open water condition and behind the hull
Again, the side force and bending moment components in the horizontal direction are higher for open water than in the behind condition for negative heading angles. The explanation is believed to be the same as for the vertical force and bending moment (see above).
oblique inflow, typically due to steering, without considering any wake from the thrusters’ body and ship
10 20 30 40
J=0.2-Hull J=0.6-Hull J=1-Hull J=0.2 J=0.6 J=1
open water 0 10 20 30
J=0.2-Hull J=0.6-Hull J=1-Hull J=0.2 J=0.6 J=1
40
In purely
A- 13
Vertical side force Kfz
Horizental side force Kfy
Vertical bending moment Kmz
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74