PSI - Issue 14

V Kiran Govind et al. / Procedia Structural Integrity 14 (2019) 435–441 Author name / Structural Integrity Procedia 00 (2018) 000–000

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1. Introduction A typical towed array sensor system consists of an electro optic-mechanical Heavy Cable (HC), a Towed Body (TB), a Light Tow Cable (LC) and the towed array modules followed by a tail rope at the aft-end. The configuration is shown in Fig 1. An active cum passive towed sensor array system uses negatively buoyant Heavy Cable of length varying from 100 m to 500 m, a neutrally buoyant Light Cable of length 100 m to ~ 600 m, several sensor array modules each of length 20 m to 30 m, followed by a tail rope of length 1 m to ~ 30 m. The diameter of tow cables is ~ 33 mm and that of array is ~ 80 mm.

Fig. 1. Typical towed array sensor system

The sensor array and cables are designed to withstand harsh marine environment and hydrodynamic forces experienced due to waves and currents during operation. Nevertheless, tow cable and array are vulnerable to failure due to dynamic loading during deployment & retrieval operations, see Chapman (1984). Then the sensor array being negatively buoyant, will sink to sea-bottom and is irretrievable, see Dowling (1988). During a series of towed array trials, sever flattening and failure of a few number of optical lines was observed in indigenously developed Heavy Cable after initial cycles of deployment and retrieval of the system. To verify the suspected cause of these issues, cyclic test was conducted on the cable in the factory under different test conditions simulating the deployment-retrieval scenario in ship. An imported HTC was also subjected to same tests to understand and compare the performance of both cables. This report discusses the details of cyclic tests, their results and final recommendations. 2. Tow Cable Specifications The Heavy Cable and Light Cable used in a towed array sonar system provide the optical, electrical and mechanical connection of the towed body and array with on-board processors, see Bowers (1973). The tow cables used in the marine environment transmit power to the underwater equipment and carry signals for underwater communications. In addition these cables are capable of withstanding the hydrodynamic forces experienced in the ocean environment due to waves, currents or towing loads, see Triantafyllou (1991). The HC is metallic armoured & negatively buoyant and plays an important role in depth keeping of towed body and rest of the array. The LC is fiber armoured & nearly neutrally buoyant cable which ensures sufficient trail or standoff distance of the linear array from the ship to keep self-noise of the platform away from the array and also helps the array modules to be in the same depth as towed body. The key technical specifications of Heavy Cable are provided in Table 1.