Constrained-layer Dampers for
Attenuation of Structural Vibration
N.R. Manoj*, S. Barman,
L. Chandrasekhar, and B.C. Chakraborty
Naval Materials Research Laboratory,
Ambernath-421 506
and
R. Ramesh and
R.M.R. Vishnubhatla
Naval Physical & Oceanographic
Laboratory, Kochi-682 021
ABSTRACT
In a constrained-layer damping system, a thin layer of a
viscoelastic material is applied over the vibrating substrate and covered with a
stiff constraining layer of a metal or a fibre-reinforced plastic. Several
viscoelastic materials based on elastomeric blends of copoly
(acrylonitrile-butadiene) and polyvinyl chloride were developed. These materials
were characterised for hardness, tensile properties, ozone resistance, and
electrical and dynamic mechanical properties. Two polymer compositions were used
to fabricate 1 mm sheets. The sheets were fixed on an aluminium substrate with a
rigid epoxy glue. A fibre-reinforced plastic sheet of 300 m was fixed on the
viscoelastic layer by a rigid epoxy glue. The experimental setup for the
measurement of vibration response has been elaborated. The study was carried out
with and without the constrained-layer damping system. The vibration attenuation
achieved was to a minimum of 5-7 dB at 200-500 Hz and to a maximum of 9-16 dB at
3000 - 4000 Hz for the selected constrained-layer damping system.
Keywords: Constrained-layer damping system, CLD system,
viscoelastic material, structural vibration, fibre-reinforced plastic, vibration
attenuation, epoxy glue, free-layer damping system
Advanced
Magnetostrictive Materials for Sonar Applications
Rajapan Dhilsha, P.M. Rajeshwari, and V.
Rajendran
National
Institute of Ocean Technology, Chennai–601 302
ABSTRACT
Piezoelectric or magnetostrictive materials can be utilised
as active materials for electro-acoustic underwater transducers. Piezoceramic
materials gained edge over the conventional magnetostrictive materials during
1940s due to their unique electro-acoustic properties. At present, inspite of
passive sonars there is a need of low-frequency high-power active sonars for the
Navy. This led to research for new active materials with competing
characteristics to that of the existing piezo transducers. The discovery of a
giant magnetostrictive material, commercially known as Terfenol-D, led to a
breakthrough in the development of a new generation of sonar transducers. Now,
the materials (including composites) as well as sensors are commercially
available. A new generation of transducers have emerged in ocean-related areas
like acoustic tomography, long-range underwater communication, geophysical
exploration, oil well exploration, etc.
Indian Institute of Technology
Madras, Chennai, has also developed the basic material technology a few years
back. At present, in India, National Institute of Ocean Technology, Chennai, is
developing underwater transducers utilising giant magnetostrictive materials as
well as piezoelectric materials for marine applications like sub-bottom
profiling (seafloor mapping) and long-range underwater communications. A
prototype of a portable, low-frequency medium power transmitter operating over a
wide-frequency range has been developed. The main advantage of this transducer
is its simplicity in design. In this paper, the recent developments in material
processes, importance of device-oriented material characterisation, and
transducer design aspects have been emphasised. Some results on the underwater
performance of a wide-band transducer have also been presented. These materials
also have ultrasonic applications, capable of revolutionising the processing
industry.
Keywords: New sonar materials, magnetostrictive sonars,
Terfenol-D sensors, actuators, magnetostrictive materials, piezoelectric
materials, sonar transducers, acoustic transducer, PZTs, underwater
transducers
Hydrodynamic Design of Integrated
Bulbous Bow/Sonar
Dome
for Naval Ships
R. Sharma and O.P.
Sha
Indian Institute
of Technology Kharagpur, Kharagpur–721 302
ABSTRACT
Recently, the idea of bulbous bow has been extended from
the commercial ships to the design of an integrated bow that houses a sonar dome
for naval ships. In the present study, a design method for a particular set of
requirements consisting of a narrow range of input parameters is presented. The
method uses an approximate linear theory with sheltering effect for resistance
estimation and pressure distribution, and correlation with statistical analysis
from the existing literature and the tank-test results available in the public
domain. Though the optimisation of design parameters has been done for the
design speed, but the resistance performance over the entire speed range has
been incorporated in the design. The bulb behaviour has been discussed using the
principle of minimisation of resistance and analysis of flow pattern over the
bulb and near the sonar dome. It also explores the possible benefits arising out
of new design from the production, acoustic, and hydrodynamic point of view. The
results of this study are presented in the form of design parameters (for the
bulbous bow) related to the main hull parameters for a set of input data in a
narrow range. Finally, the method has been used to design the bulbous bow for a
surface combatant vessel.
Keywords: Bulbous bow, hydrodynamic design, integrated bow,
sonar dome, sheltering effect, wave resistance, naval ship, bulb behaviour
Compliant Materials for Drag Reduction of
High-speed Submerged
Bodies
N. Banerjee and P.
Jayakumar
Naval
Science & Technological Laboratory, Visakhapatnam–530
027
ABSTRACT
This paper briefly discusses the possibility of employing
the compliant materials on underwater bodies for the drag reduction. Recent
studies in the area of hydrobionics all-over the world have drawn the attention
of hydrodynamicists for using the compliant materials on underwater body
surfaces, similar to that found in fast aquatic animals like dolphins, towards
achieving drag reduction and increased speeds of underwater vehicles and
weapons1. Some basic principles of hydrobionics in drag reduction have been
presented with special emphasis on the control of turbulent boundary layer
characteristics of flow over the compliant material surfaces and induce delay in
transition. Various researchers have estimated that the use of such compliant
material surfaces can lead to an overall drag reduction of the order of 10-12
per cent over drag of the rigid surface. This is a considerable drag reduction
and should arouse keen interest among the underwater weapon and vehicle
designers as the next stage of technological advancement in underwater
hydrodynamic technology.
Keywords: Compliant materials, drag reduction,
hydrobionics, turbulent boundary layer, skin friction drag, compliant walls,
underwater bodies, torpedoes, submarines, turbulence suppression mechanisms,
drag
Materials and
Coatings Damage Resulting from Environmental
Degradation Aboard Naval
Ships
Edward
Lemieux
Naval
Research Laboratory, P.O. Box 1739, Key West, Florida
33041-1739
and
Keith Lucas and Paul
Slebodnick
Naval
Research Laboratory, 4555 Overlook Avenue, S.W. Washington DC-20375
Abstract
Maintenance and preservation of seawater and fuel, ballast
tanks and voids resulting from the environmental degradation of coatings present
a unique and costly problem for the United States Naval Fleet. Present methods
of inspection require human entry into the tanks only after a series of
measurements have been taken to ensure safety. With the advent of remotely
operated vehicles and cameras having a high level of accuracy and functionality,
it has now become economically feasible to employ these instruments for the
inspection of tanks and voids of the United States Naval Fleet. This paper
presents two unique remotely operated inspections systems, which allow for
unmanned inspection of tanks and voids along with quantitative results of the
damaged coating areas.
Keywords: Coatings, environmental degradation, unmanned
inspection, tanks, voids, damage control, galvanic corrosion, corrosion
detection algorithm, remotely operated paint inspector, insertable stalk imaging
system, corrosion detection
Role
of Citrate Ions in the Phosphonate-based Inhibitor System
for Mild Steel in
Aqueous Chloride Media
G.
Gunasekaran, B.I. Dubey, and J. Rangarajan
Naval Materials Research Laboratory,
Ambernath–421 506
ABSTRACT
The corrosion inhibition efficiency of phosphonic acid and
its derivatives for the inhibition of corrosion of mild steel in neutral
chloride media is decided by its ability to form protective film over the
surface. In this context, the effect of addition of metal cations and certain
organic compounds, such as citrate in conjugation with phosphonic acid to impart
synergistic corrosion inhibition has been explored. The experiments were carried
out using various concentrations of trisodium citrate and zinc ions in an
aqueous solution of 2-carboxyethyl phosphonic acid (2CEPA) at 25 ppm. The
corrosion characteristics have been determined using electrochemical impedance
spectroscopy together with determination of corrosion rate by weight-loss
method. It has been observed that a combination of inhibitive ions, namely
citrate, 2CEPA, and zinc ions at 25 ppm gives 96 per cent inhibition efficiency
and this corrosion inhibition is due to the formation of a protective film. By
increasing the concentration of citrate beyond 25 ppm, the corrosion inhibition
efficiency decreases. This paper discusses the role of citrate and zinc ions in
imparting added corrosion inhibition ability using 2CEPA on the basis of
experimental results.
Keywords: Corrosion inhibition, phosphonic acid, surface
coating, corrosion inhibitors, trisodium citrate, electrochemical inhibition
spectroscopy, EIS, 2CEPA, weight-loss method, 2-carboxyethyl phosphonic acid
Synthesis of Corrosion-resistant Nanocrystalline Nickle-copper
Alloy
Coatings by Pulse-plating Technique
S.K. Ghosh, A.K. Grover, G.K. Dey, and A.K.
Suri
Bhabha Atomic
Research Centre, Mumbai–400 085
Abstract
Bright and smooth nanocrystalline Monel-type Ni-Cu alloy
gets deposited from complex citrate electrolyte by pulse electrolysis.
Transmission electron microscopy studies have revealed that the deposited Ni-Cu
alloy was nanocrystalline in nature and it comprised a two-phase (fcc+L1o)
mixture. The presence of twins could be seen in the nanocrystals. The Ni-Cu
alloys prepared by pulse electrolysis were finer grained (~ 2.5-28.5 nm) than
those deposited by direct current method. Nelson-Riley function has been used to
calculate the lattice parameters for both the pulse current-plated and direct
current-plated alloys from x-ray diffraction analysis. The microhardness values
for pulse current-plated alloys were higher than for the direct current-plated
alloys. The internal stresses of both the pulse current-deposited and the direct
current- deposited alloys have also been measured; the values were lower for
pulse current-plated alloys. Potentiodynamic polarisation studies were carried
out in aerated and deaerated neutral 3.0 Wt per cent NaCl solution and
instantaneous corrosion current density of the plated alloy was determined and
compared with the Monel-400 alloy. It was found that nanocrystalline pulse
current-Ni-35.8 Wt per cent copper alloy exhibited lower instantaneous value of
corrosion current density than that of specimens with direct current method and
Monel-400 alloy. The dissolution behaviour of the deposited nanocrystalline
material was found to be more like general corrosion rather than localised
corrosion as in the case of Monel-400 alloy.
Keywords: Monel-400 alloy, corrosion-resistant alloys,
nickel-copper alloys, pulse electrolysis, nanocrystalline alloys, nanocrystals,
pulse current-plating technique, corrosion current density, direct
current-plating technique
Fouling-release Coatings for Warships
Robert F. Brady
Naval Research Laboratory,
Washington DC–20375-5342
Abstract
The International Maritime Organisation, a unit of the
United Nations, has approved a resolution to phase out and eventually prohibit
the worldwide use of toxic organotin antifouling paints. Thus, there is a
compelling need to develop, test, and market eco-friendly hull coatings, which
effectively keep ships free of fouling. The replacement for tin coatings will
likely be low-toxicity copper-based paints, and various toxin-free
fouling-release coatings. This paper reviews the composition and mechanism of
action of these coatings and gives the strengths and weaknesses of each coating,
with the aim of clarifying the impact of these coatings on the operation of
warships.
Keywords: Antifouling paints, organotin antifouling paints,
antifouling biocides, copper-based paints, fouling-release coatings, tin-based
paints, hull coatings, toxin-free fouling-release coatings
Aluminium Alloy Cast Shell Development for Torpedoes
Vijaya Singh and A. A. Gokhale
Defence Metallurgical Research
Laboratory, Hyderabad–500 058
ABSTRACT
The sand-cast aluminium alloy cylindrical shells were
developed for the advanced experimental torpedo applications. The components had
intricate geometry, thin-walled sections, and stringent property requirements.
The casting defects, such as shrinkage, porosity, incomplete filling of thin
sections, cold shuts, inclusions and dimensional eccentricity, etc were found in
the initial castings trials. Improvements in casting quality were achieved
through modified methodology, selective chilling, risering, and by introducing
ceramic-foam filters in the gating system. The heat-treated and machined
components met radiographic class 1 grade C/E standards, mechanical properties
to BS1490 specifications, and leakage and hydraulic pressure test requirements
relevant for such applications.
Keywords: Aluminium alloy cast shells, torpedoes, advanced
experimental torpedo, shells, sand casting, chilling, risering, dross
defects
Thermomechanically-controlled Processing for Producing
Ship-building
Steels
B. Basu, S.M. Tripathi, and
V.V. Modak
Naval
Materials Research Laboratory, Ambernath– 421 506.
ABSTRACT
The thermomechanically-controlled processing of a newly
developed high-strength low-alloy steel has been designed in such a way that the
problems, normally faced in producing the quench and tempered steels, have been
mitigated and the final product (steel plates) are available in as rolled
condition rather than quench and tempered steels.
A low-carbon, low-alloy
steel having nickel, chromium, copper, niobium, boron, has been designed for
ease of welding, improved weldability over the conventional steels, and
responsive to the thermomechanically-controlled processing. A number of
laboratory-scale batches of the alloy were made with different combinations of
thermomechanically-controlled processing parameters. The different
thermomechanically-controlled processing parameters studied include (i)
slab-reheating temperature, (ii) deformation above recrystallisation
temperature, (iii) deformation below recrystallisation temperature, and (iv)
finish-rolling temperature. The thermomechanically-processed steel plates, under
certain combinations of thermomechanically-controlled processing parameters,
showed excellent combination of impact and tensile properties. In this paper,
the microstructure-property correlation has been made to throw light on the type
of microstructure required to obtain such superior package of mechanical
properties. Further, the optimised laboratory-scale
thermomechanically-controlled processing parameters, which were used to process
newer batches of the steel made through industrial route, have delivered
encouraging results.
Keywords: Thermomechanically-controlled processing, TMCP,
HSLA steels, high-strength low-alloy steels, steel plates, quench and tempered
steels, low-alloy steels, structural applications, ship-building steels, HICC,
hydrogen-induced cold cracking, ULCB steels, ultra-low carbon bainitic steels,
microalloyed steels