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Articles by Endang Widjiati
Total Records ( 2 ) for Endang Widjiati
  Endang Widjiati , Eko Budi Djatmiko , Wisnu Wardhana and Wirawan
  Analysing characteristics of propeller cavitation noise is necessary in relation with the identification of noise signature in conjunction with both surface ship and submarine operations. Since, the noise signature is determined by propeller, flow and machinery noise then any vessel that has certain propeller, hull shape and machines will have a peculiar signature. The propeller cavitation noise can be generated by means of experiment performed in a cavitation tunnel. This study reports some results of the noise characterization experiment conducted in the Cavitation Tunnel available at the Indonesian Hydrodynamic Laboratory, Surabaya, Indonesia. Two B-series propeller models, i.e., 4 and 7-blade were studied in the experiment. Time-Frequency distribution, namely Wigner-Ville Distribution (WVD) is applied to observe the characteristics of the cavitation noise. Results show that the WVD can differentiate whether the propeller cavitation noise is generated either by the 4 or 7-blade propeller. In this study, three different kinds of categories in the appearance of cavitation are distinguished, i.e., when the propeller does not experience cavitation, if only hub and tip vortex cavitation develop and when various cavitations occur simultaneously.
  Tri Budi Santoso , Endang Widjiati , Wirawan and Gamantyo Hendrantoro
  Understanding of channel propagation characteristics is a key to the optimal design of underwater acoustic communication. Generally, modelling of underwater acoustic channel is performed based on measurement result in certain site at certain times. Different sites might have different characteristics each of which can generally be described by a model obtained by averaging measurement results at multiple points in the same environment. This study describes a characterization of the underwater acoustic channel of tropical shallow water in a Mangrove estuary which has sediment up to 60 cm at the bottom. Such a channel model is beneficial for the design of communication system in an autonomous underwater vehicle for instance. The measurement result of delay spread parameter from three different points with the distance of 14~52 m has various values. The Root Mean Square (RMS) of delay spread ranges between 0.0621~0.264 msec and the maximum delay spread varies with the value of 0.187~1.0 msec. The PDF fitting shows that Rayleigh distribution describes the fading variation more accurately than Nakagami and Ricean.
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