Time filter

Source Type

New Delhi, India

Das A.,Indian navy
Applied Acoustics | Year: 2011

Study and characterization of distant shipping component of ambient noise in shallow water aid in design of passive surveillance algorithms and effective signature analysis of marine vessels. This letter presents the work carried out on real ambient noise recording in very shallow water condition close to a commercial port with heavy shipping activity to study and characterize the distant shipping noise component for variations due to tide. Ambient noise recording was carried out by a bottom mounted sensor at 30 m depth at regular interval for a period of over one month and the spectrum in the band 10-1.6 kHz was characterized for its diurnal spectral variation. The study concluded that the distant shipping noise component due to heavy small vessel activity in the nearby port resulted in up to 35 dB variation in the shallow water ambient noise in coastal areas that may have serious implication on passive surveillance algorithms performance in the vicinity if adequately not addressed. This is the first such effort in ambient noise measurement and characterization in the extremely shallow water channel condition prevalent in the tropical waters off the west coast of India. © 2011 Elsevier Ltd. All rights reserved. Source

Srivastava S.,Indian navy | Chatterjee A.,Indian Institute of Technology Kanpur
International Journal of Mechanical Sciences | Year: 2014

Oscillations of solid bodies like boats interacting with liquids like water are commonly studied in the marine science community but less so in the broader mechanical sciences. This paper presents a clear and simple exposition of a basic problem in this field, for a general nonspecialist audience. A two dimensional analysis is developed from first principles of small free oscillations of a boat in inviscid water in a finite tank. The water motions obey the Laplace equation. The boat motions are not imposed, but rather found as a part of the overall solution using rigid body dynamics under time-varying pressures on the hull. The importance is clarified of the difference between nominal and displaced configurations of the boat. The equations for water, boat, and boundary conditions are assembled into an eigenvalue problem that determines the oscillation frequencies and mode shapes. The equations are discretized using a boundary element formulation, and the corresponding discrete version of the eigenvalue problem is constructed and solved. The mode shapes thus found include (i) a well defined roll-dominated oscillation, (ii) easily interpretible nearby equilibrium solutions ("rigid body" modes), and (iii) tank-scale sloshing-dominated modes. The roll frequency is found to vary negligibly with tank size, and goes to zero as the boat center of mass is moved to the metacenter. The net added inertia implied by the roll frequency is discussed. Finally, experiments conducted with two boat models, one round bottomed and one square, match roll frequencies predicted by the above calculations. © 2013 Elsevier Ltd. Source

Vanithakumari S.C.,Indira Gandhi Center for Atomic Research | Yadavalli P.,Indian navy | George R.P.,Indira Gandhi Center for Atomic Research | Mudali U.M.,Indira Gandhi Center for Atomic Research
Surface Innovations | Year: 2015

A close observation of natural lotus leaves provided the inspiration to develop superhydrophobic surfaces on marine steels to inhibit biofouling. Low-alloyed steel such as DMR 249A is chosen for the present study and modified using mechanical polishing, shot blasting, grit blasting, glass bead blasting and pickling, and coated with a low-surface energy material such as silane. The resultant samples are found to be superhydrophobic with apparent advancing water contact angles around 150° and tilting angles less than 5°. The surface morphology and surface roughness are analysed using scanning electron microscopy and surface proflometer. Depending on the surface treatment employed, the morphology and surface roughness vary widely and they are correlated to the wetting behaviour of the samples. The surface-modified marine steels are exposed to the bacterial cultures of Pseudomonas sp. to elucidate their antifouling behaviour. The exposure studies revealed less bacterial adhesion in surface-modifed samples as compared to the uncoated samples. The aim of this paper is to stress the unconventional use of superhydrophobic coatings based on silanes to inhibit biofouling on marine steels. © 2015, ICE Publishing. All rights reserved Source

Ray A.,Indian navy
RINA, Royal Institution of Naval Architects - Warship 2014: Naval Submarines and UUV's, Papers | Year: 2014

Prototypes for technology induction are rare for submarines. In the second half of the 20∗ century, several design prototypes were built in the USA and the erstwhile USSR as test platforms for radical new submarine technologies. These one-of-a-kind prototypes represented advances in hydrodynamics, propulsion, silencing, materials and payload that led to incorporation of new features in series production. In the present scenario of shrinking numbers of submarines in most navies, prototypes appear to be an unaffordable luxury. Their alternatives for new technology induction are discussed. Proposals are offered for fostering technological innovations, and for scheduling induction timelines for better management of the development process. © 2014 The Royal Institution of Naval Architects. Source

Waghmare R.G.,Dr iversity Lonere | Nalbalwar S.L.,Dr iversity Lonere | Das A.,Indian navy
Procedia Engineering | Year: 2012

In underwater passive surveillance systems, narrowband displays help in classifying tonal sounds but transient sounds are largely classified through audition. Over the years, the intensity of tonal has been reduced by ship/submarine constructors, and so their use for classifying underwater targets has become diminished. Transient sounds are harder to disguise and are becoming more useful for detecting targets. In the naval scenario, quick and accurate detection of transient signals offers an advantage of longer response time to thwart an enemy attack. Underwater transients from manmade objects and biologics are very rich in structure and detail, very diverse in terms of duration, highly non-stationary, and often mixed with multipath. The need is for automatic detection and classification of underwater transients, in order to assist the overburdened sonar operator. Recently, the work on wavelet transform for transient signal detection is carried out but the problem with these detectors is that these are computationally very expensive. We are presenting a new kind of detector which works on energy of the segments and the corresponding mean of the zero crossings of the signal. Source

Discover hidden collaborations