Trans RINA, Vol 157, Part A3, Intl J Maritime Eng, Jul-Sep 2015
tunnel has a working section with length of 1000 mm, width of 600 mm and a usable depth of 200 mm. The T- Foil model tests needed to be conducted in an open working section so that the free surface was at atmospheric pressure. When operated with an open working section,
the water
velocity was achieved in the flow by Bell et al [6] using a flow constriction flap (Figure 5). A maximum flow velocity of 2.7 m/s was achieved by changing the angle of the constriction flap as well as water depth.
Figure 5 shows the set-up of the T-Foil and the load cell in the water tunnel. Using a LabVIEW program, the load cell output signals were acquired by a National Instruments (NI) PCI- 6221 DAQ card through an AMTI amplifier.
achieved velocities above 1.2 m/s with an acceptable flow quality [6]. However, a significant
tunnel had not previously increase of
Figure 5: T-Foil and load cell set-up in the circulating water tunnel (flow is left to right).
Figure 3: University of Tasmania water tunnel (from Barton [17]).
A stepper-motor was used to activate the T-Foil and a potentiometer was used to measure the angular position of the T-Foil control surface. A National Instruments (NI) 9174- USB compact DAQ (cDAQ) chassis with two NI modules, NI 9263 Analogue Output (AO) and NI 9201 Analogue Input (AI), was used whilst running LabVIEW for both static and dynamic tests. The T-Foil angle of attack was demanded through the NI 9263 AO module and the NI 9201 AI module was used to acquire the potentiometer voltage in order to measure the actual instantaneous T-Foil angle of attack. The channel related to the potentiometer voltage in the NI 9201 AI module was directly connected to an AI channel of the NI PCI-6221 DAQ card in order to measure the true T-Foil angle of attack during force measurements.
3. CALIBRATION
Calibrations of the stepper-motor and the potentiometer were carried out in order to find a relationship between demand voltage for the stepper-motor and T-Foil angle of attack as well as a relationship between output voltage from the potentiometer and T-Foil angle of attack. The T-Foil
angle of attack was measured by a
digital
inclinometer with a resolution of 0.05º. The digital inclinometer was calibrated and oriented relative to the apparatus as the T-Foil chord line was parallel to the water surface at 0º. Figure 6 shows the calibration graphs for potentiometer and stepper-motor. The system has good linearity. Equations 1 and 2 show these relationships respectively:
Figure 4: Load cell set-up on top of the T-Foil vertical strut.
T-foil lift and drag force measurements were carried out using an AMTI 6 Degree of Freedom (DOF) load cell. The load cell was assembled on top of the T-Foil as shown in Figure 4.
57.46 Vout 156.93 80.00 Vin 244.00
(1) (2)
©2015: The Royals Institution of Naval Architects
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