OPERATIVA MISIONAL
CRITERIOS DE DECISIÓN
The objectives of the tests were to derive a set of Gavia AUV propeller thrust and torque data under the four-quadrant conditions. A three-bladed Gavia AUV FPP, as shown in Figure 4.1, was selected for the tests. This propeller is made from aluminium alloy and particularly de- signed for the torpedo shaped underwater vehicle. An adapter was specifically designed and manufactured to fit the propeller into the driving shaft of the testing apparatus as shown in Figure 4.2. The fundamental specifications of the tested Gavia propeller are also listed in Table 4.2 below.
Figure 4.1. Gavia AUV propeller.
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Table 4.2. Fundamental specifications of tested propeller.
Symbol Description Value Unit
Scale 1:1 Z Number of blades 3 D Diameter 0.143
m
/ P D Pitch ratio 1.7 / E OA A Blade area ratio 0.4
O
A Disk area 0.0161 2
m
4.3.1 Open Water Test Setup
The open water tests are usually performed in the towing tank. The experiments in this study were conducted in the towing tank at AMC as shown in Figure 4.3. The primary dimensions of the AMC towing tank are listed in Table 4.3.
Table 4.3. Towing tank dimensions.
Length Width Depth Maximum speed
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Figure 4.3. The towing tank at AMC-UTAS.
The key equipment for the open water tests was the propeller open water dynamometer, shown in Figure 4.4. Further details of the propeller open water dynamometer can be found in (Liu et al., 2015; Liu et al., 2014), which was designed and built during the that project.
Figure 4.4. Propeller Open Water Dynamometer.
The thrust and torque of propeller were measured by a Cussons Propulsion Dynamometer R31. This R31 dynamometer was mounted in line with the shaft of the propeller, and the dynamom- eter static calibration was carried out before the test. The driving motor was the Dunkermotoren BG 75 attached behind the dynamometer. An encoder was used to measure propeller rotational speed (RPM) and the motor speed was controlled from the computer on the carriage by the encoder feedback signal. Both the dynamometer and the driven motor were located inside the Propeller Open Water Dynamometer as shown in Figure 4.5.
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Figure 4.5. Internal assembly of Propeller Open Water Dynamometer.
4.3.2 Data Acquisition and Post Processing
The measured data were acquired with the National Instruments BNC-2090 acquisition system and a LabVIEW software program was developed to ensure accurate data acquisition. The in- house developed program was able to control the propeller rotational speed at desired constant values and acquire the measured data via different channels. A sampling rate of 1000 Hz was selected with sampling time was 20s for the acquired signals. The low pass Kalman filter was also applied in order to reduce the high frequency noise of collected raw data. A schematic dia- gram and a photo of the experimental setup and data acquisition system are given in Figure 4.6.
Figure 4.6. The experimental setup of Propeller Open Water Test.
The four-quadrant tests were conducted by varying the carriage speed and direction, the pro- peller rotational speed and the direction of rotating propeller. The experiments were run at a
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wide range of advance ratio, especially at off design conditions on both ends of the range in order to evaluate the performance characteristics of the AUV equipped with this propeller dur- ing manoeuvring. In a conventional open water propeller test, for each quadrant condition, the propeller rotational speed is kept constant while the advance speed of the propeller varies, as recommended by procedures and guidelines of the International Towing Tank Conference (ITTC) (ITTC, 2008a). The carriage speed was set at different constant speed in the range from
0.5 m/s to 3 m/s during these tests. The tests with negative advance speed were conducted with reversely mounted propeller without changing motion direction of the carriage to avoid effect of the submerged testing apparatus on the propeller. From equation (4.9), the relationship between and J over the four quadrants is intensively described in Table 4.4 below:
Table 4.4. The relationship between
and J in the four quadrants.First quadrant Second quadrant
0 26 69 90 95 112 146 180J 0 1.1 5.7 -28 -5.5 -1.5 0
Third quadrant Forth quadrant
190 206 241 270 275 300 327 360J 0.4 1.1 3.9 -25 -3.7 -1.5 0
It can be seen from Table 4.4 that to cover the full range of
in each quadrant, the advance ratio J had to be adjusted progressively from 0 to very high values in the tests. This procedure was difficult to manage in practice due to the physical limitations of the facility. In addition, the high values of J refer to the off-design conditions in which the underwater vehicles would not ma- noeuvre in practical application as they are not realistic. Therefore in the presented tests, within61
the capability of models and instrumentations, the advance ratio J was controlled up to 1.5 in the first and third quadrant and to -1.5 in the second and forth quadrant. It should be noted that when
0 and
360 , or J0 the model was at the bollard pull conditions. Moreover, for the condition when
90 and 0270