Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
-16.0 -8.0 0.0 8.0 16.0
2.40
Potentiometer Stepper-Motor
Figures 7 and 8 show the calibration graphs for lift and drag
respectively. These both show good linearity.
Equations 3 and 4 show these relationships respectively: Fz 0.025503 0.000255 Fy 0.024268 0.000871
4. EXPERIMENTAL TESTS AND RESULTS 2.60 2.80 Voltage (V)
Figure 6: Relationship between T-Foil angle of attack and output voltage from the potentiometer as well as input voltage to the stepper-motor.
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00 2.00 4.00 6.00 Applied lift force, L (N)
Figure 7: Relationship between lift force and load-cell output voltage measuring force in the vertical z-axis direction, Fz .
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00 2.00 4.00 6.00 Applied drag force, D (N)
Figure 8: Relationship between drag force and load-cell output voltage measuring force in the horizontal y-axis direction, Fy .
Calibration of the load cell was conducted by applying a static load in the vertical (z-axis) direction of the load cell to find a relationship between lift and output voltage from the channel
related to the force in the z-axis
direction, FZ. Similar tests were carried out by applying static loads in the y-axis direction of the load cell to find a relationship between drag and output voltage from the channel related to the force in the horizontal y-axis direction, FY.
A-178 8.00 10.00
In addition to the static tests, dynamic tests were carried out on the T-Foil. The dynamic tests were carried out in the water tunnel at the three water flow velocities as mentioned above. Three ranges of angle of attack consisting ±5º, ±10º and ±15º were tested for each flow velocity. All these tests were done at 18 different frequencies ranging from 0.5 Hz to 9 Hz in 0.5 Hz increments. The aim of these dynamic tests was to measure the dynamic forces on the T-Foil to compare with static forces as well as to define the T-Foil frequency response. Figure 11 shows a sample of measured dynamic forces at a flow velocity of 1.82 m/s, a frequency of 1.5 Hz and a demand T-Foil incidence (α) range of ±15º.
-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0
Figure 9: Lift
V=1.82 m/s V=2.30 m/s V=2.70 m/s
8.00 10.00 3.00 3.20
After installation of the T-Foil and the load cell in the water tunnel, the static tests were carried out at three different water flow velocities consisting of a low speed of 1.82 m/s, a medium speed of 2.30 m/s and a high speed of 2.70 m/s. The flow velocities were selected on the basis of the forward test speeds required for the 2.5 m catamaran model for future testing of motion control response in head-seas. For each water flow velocity, the T-Foil angle of attack was fixed at 10 different angles ranging from -15º to +15º in 3º increments and the magnitude of both lift and drag was measured. The magnitudes of force are shown in Figures 9 and 10 for lift and drag respectively based on a sign convention where the T-Foil angle of attack (α) from port side is positive clockwise with a left to right generated lift
flow and the force is positive upwards. These
dimensional results can be compared directly with the lift results for stern tabs [6] in assessing the combined performance of a T-foil and stern tabs.
(3) (4)
-15 -12 -9 -6 -3 0 3 6 9 12 15 T-Foil angle of attack, α (º)
force measured on the T-Foil at fixed
angles of attack for static tests undertaken at different water flow velocities.
©2015: The Royals Institution of Naval Architects
Measured horizontal force, Fy (V)
Measured vertical force, FZ (V)
T-Foil angle of attack, α (º)
Lift force, L (N)
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