Browsing by Author "Kumar, G. V. V. Pavan"

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Measurement of small vessel machinery vibration induced acoustic signature levels /
(Journal of Naval Architecture and Marine Engineering, 2019-12-26) Kumar, G. V. V. Pavan ; Nagesh, B. H.
Ship vibrations, airborne and underwater noise levels have always been a challenging topic from a performance point of view in ship design, building and operation. The measurement shall help in monitoring the self-noise and the technical state of their machinery mechanism. The vibration levels on the main engine and auxiliary Genset foundation, airborne noise levels of the engine room and underwater self-noise levels of a small mechanized fishing trawler was measured at the jetty in idling condition. The vibration levels on the foundation measured the average value of 0.207 mm/s for the main engine and 1.36 mm/s for auxiliary Genset. The airborne noise levels measured 99 dB (A) in the engine room. The peak underwater sound pressure levels measured 162 dB re 1µPa. The response spectra indicate the peak vibration and noise levels in the lower frequency region <1.2 kHz. The machinery excitation forces transferred to the hull surface as pressure fluctuations which generated the airborne and underwater noise levels. Though the measurement limited to jetty conditions, detailed analysis can be useful for detection, classification, and tracking of small vessels.
Underwater noise levels in Indian waters off the coast of Mormugao Port /
(Taylor & Francis, 2019-06-25) Kumar, G. V. V. Pavan; Ramesh, U. S.
Among various factors influencing the ocean noise levels, shipping traffic radiated underwater noise levels were identified as the major contributors. The increase in ambient noise levels due to natural and anthropogenic sources threatens the marine species communication. India has a coastline of 7,516.6 Km with 12 major and ∼187 minor ports. The hydrophone system measured for 39 days helped in investigating the distant shipping traffic lane noise levels and its influence on ambient noise levels of the region. The ocean noise levels measurement were ∼115 dB re 1 µPa for the prevailing environmental conditions. The noise exposure levels were ∼10 dB higher at <1 kHz due to ship passage to and from the port. The fish noise dominated the ambient sea noise mostly at high frequencies >1 kHz. The maximum and minimum range of shipping noise spectra for both the month’s data indicated peak sound pressure level in the lower frequency. Thus, the outcome of the measurements helped in understanding ocean noise levels off the coast of Mormugao Port and the influence of shipping traffic. A similar study for longer duration shall be useful to develop specific traffic lanes in the port entrance which is free from the mammal movements.
Underwater noise radiated by fishing vessels in visakhapatnam fishing harbor /
(Journal of Offshore Structure and Technology, 2019-04-24) Kumar, G. V. V. Pavan ; Ramesh, U. S.
The sound has always been a better measure to understand the oceans. Among the various sources of underwater noise, mainly physical, biological and anthropogenic, it is seen that through the increase in anthropogenic noise in the oceans, the ambient noise levels are rising. Fishing vessel radiated noise has been a major concern in the fisheries acoustic scientific community due to the possible effects on altering the natural activities of the target species. The fishing vessel noise signature shall be valuable in building a quiet vessel with effective combination of the machinery in opposing excessive noise levels. In the present paper, the measurements of the underwater noise levels within the Visakhapatnam fishing harbor (VFH) limits are detailed to understand the fishing vessel radiated noise levels. The VFH is a bay spreading over 22 ha next to the Visakhapatnam Port channel entrance. At VHF, there are around 700 fishing boats engaged in fishing activity within the coast of Andhra Pradesh. A vertical omni-directional hydrophone and TASCAM handheld linear PCM recorder was deployed at five different locations with deployment depth of 2 m within the VHF bay. Fast Fourier Transformation spectral analysis program is used to post-process the time domain signal to the frequency domain. The measured data helped to understand the ambient noise levels within the VFH limits being ~120 dB re 1 μPa and with a distant boat idling having peak amplitude 136.97 dB re 1 μPa at peak frequency of 425 Hz. The regular fishing vessel movement recorded peak amplitude 160.39 dB re 1 μPa at peak frequency of 425 Hz. The changes in the ambient noise levels due to the fishing vessel movement recorded a significant increase in sound pressure levels (SPL) by about 20 dB. The increase in SPL is mainly due to propeller and machinery radiated noise which is clearly identified in lower frequency range <500 Hz. The measurements also helped to understand the effect of each vessel type on the ambient levels due to vessel movements, mainly during entrance and exit within the VHF bay. However, the noise pollution due to vessel movement has similar effects on the local environment, i.e., the residential area close to VFH.