Acoustic cavitation noise caused by propeller is used in many underwater applications as one of the ships noise signatures. This paper reports characterization process done by measuring the cavitation noise generated by a propeller in a cavitation tunnel. The cavitation tunnel used for the measurement is of the K16B type belonging to the Indonesian Hydrodynamic Laboratory, Surabaya, Indonesia. The experiment is done using a B-series four-blade bronze propeller (diameter 23cm) using a hydrophone placed in the tunnel at window section (60x90)cm2 of the measurement section (400x85x85)cm3. Some of the solutions to get accurate and reliable measurement results include calibration measurement and minimizing acoustic noise system and environment. Preliminary process has been done to analyse the characteristics of the measurement results in the time-frequency domain, with the objective being to detect when and which type of cavitation noise occurs in any kind of condition. Measurement outcomes in the form of acoustic data signals are obtained in different conditions by varying the water pressure, flow velocity and propeller speed rotation.
Fuel consumption is most widely used in ship propulsion system, therefore, in ship propulsion system must be considered and designed as efficiently as possible. Propeller is one of the mechanical components on a ship, which can run ships from one place to another. The most important thing in a propeller is the mechanical properties or strength of the propeller in accepting the load to be able to run the ship. Another factor that affects mechanical propeller properties is the propeller design itself. In propeller design, one thing that can be considered is the rake angle of propeller. The rake angle is the slope angle between the propeller blade and the propeller center. The rake angle on the propeller is used to increase the amount of mass water used to produce thrust that needed by ship. Reducing the rake angle can increase the efficiency of the B-Series propeller slightly. Previous research has analyzed the effect of variations in rake angle to determine the relationship between thrust and fluid flow in the B-series propeller, but for the cavitation that occurs in the propeller has not been analyzed. In this research, variations ware made from the B-Series propeller rake angle to obtain propeller thrust and cavitation values. The analysis carried out in this study is to use the CFD (Computational Fluid Dynamic) method and the results obtained from the simulation with greatest thrust and efficiency, that is in the 5º rake angle variations of 2310,273 KN and 70% efficiency, while the smallest thrust value is variation of rake angle 25º for 1110,933 KN. Then for the largest cavitation level in the variation of the 25º rake angle and the smallest at the 15º original rake angle.
Propeller cavitation noise analysis is necessary since this noise is one of the components of the ship noise signature that would be different for each type of the ship. Therefore, the noise can be used for detection and identification process of a ship. This noise can be simulated by doing the experiment generating one component of the ship noise signature, i.e. the propeller cavitation noise. The experiment is done in the cavitation tunnel of the Indonesian Hydrodynamic Laboratory (IHL), Surabaya, Indonesia to generate this noise. Two techniques, i.e. the WignerVille distribution and the backpropagation neural network, are applied to analyse this noise. The results are compared to examine which technique shows better representation.
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